U.S. patent application number 10/483545 was filed with the patent office on 2004-11-25 for medical products comprising a haemocompatible coating, production and use thereof.
Invention is credited to Di Biase, Donato, Faust, Volker, Hoffmann, Erika, Hoffmann, Michael, Horres, Roland, Linssen, Marita Katarina.
Application Number | 20040234575 10/483545 |
Document ID | / |
Family ID | 29421502 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040234575 |
Kind Code |
A1 |
Horres, Roland ; et
al. |
November 25, 2004 |
Medical products comprising a haemocompatible coating, production
and use thereof
Abstract
The invention relates to the use of polysaccharides, that
comprise the sugar building unit N-acylglucosamine, for the
preparation of hemocompatible surfaces as well as methods for the
hemocompatible coating of surfaces with these polysaccharides,
which are classified to be the common biosynthetic precursor
substances of heparin and heparansulphates. Described are medical
devices coated according to invention, especially stents, which
comprise paclitaxel as antiproliferative active agent as well as
the use of these stents for the prevention of restenosis.
Inventors: |
Horres, Roland; (Stolberg,
DE) ; Linssen, Marita Katarina; (Aachen, DE) ;
Hoffmann, Michael; (Eschweiler, DE) ; Hoffmann,
Erika; (Eschweiler, DE) ; Di Biase, Donato;
(Aachen, DE) ; Faust, Volker; (Aachen,
DE) |
Correspondence
Address: |
Gregory Turocy
Amin & Turocy
National City Center 24th Floor
1900 East Ninth Street
Cleveland
OH
44114
US
|
Family ID: |
29421502 |
Appl. No.: |
10/483545 |
Filed: |
May 24, 2004 |
PCT Filed: |
April 15, 2003 |
PCT NO: |
PCT/DE03/01254 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10483545 |
May 24, 2004 |
|
|
|
60378676 |
May 9, 2002 |
|
|
|
Current U.S.
Class: |
424/426 ;
623/1.42; 623/1.46 |
Current CPC
Class: |
A61P 35/00 20180101;
A61L 31/16 20130101; A61K 31/045 20130101; Y02A 50/475 20180101;
A61K 31/28 20130101; C08L 5/10 20130101; A61K 31/12 20130101; A61K
31/727 20130101; A61L 33/08 20130101; A61K 31/075 20130101; A61K
31/095 20130101; A61L 31/10 20130101; A61K 31/722 20130101; A61K
31/11 20130101; A61P 37/06 20180101; A61P 19/06 20180101; A61P 3/06
20180101; A61K 31/13 20130101; C08B 37/0075 20130101; Y02A 50/30
20180101; A61P 29/00 20180101; A61K 31/33 20130101; A61K 31/21
20130101; C09D 105/08 20130101; A61P 7/02 20180101; A61L 33/08
20130101; C08L 5/10 20130101; A61L 31/10 20130101; C08L 5/10
20130101 |
Class at
Publication: |
424/426 ;
623/001.42; 623/001.46 |
International
Class: |
A61F 002/02; A61F
002/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2002 |
DE |
102 21 055.1 |
Claims
1. Medical device, wherein at least one part of the surface of the
medical device is coated directly or via at least one interjacent
biostable and/or biodegradable layer with a hemocompatible layer
comprising at least one compound of the formula 1 3wherein n
represents an integer between 4 and 1050, Y represents a residue
--CHO, --COCH.sub.3, --COC.sub.2H.sub.5, --COC.sub.3H.sub.7,
--COC.sub.4H.sub.9, --COC.sub.5H.sub.11, --COCH(CH.sub.3).sub.2,
--COCH.sub.2CH(CH.sub.3).sub- .2; --COC H(CH.sub.3)C.sub.2H.sub.5,
--COC(CH.sub.3).sub.3, --CH.sub.2COO--, --C.sub.2H.sub.4COO.sup.-,
--C.sub.3H.sub.6COO--, --C.sub.4H.sub.8COO--, as well as salts of
these compounds, and on, in and/or under the hemocompatible layer
the active agent paclitaxel is present.
2. Medical device according to claim 1, wherein Y represents the
residue --CHO, --COCH.sub.3, --COC.sub.2H.sub.5,
--COC.sub.3H.sub.7, as well as salts of these compounds.
3. Medical device according to claim 2, wherein Y is
--COCH.sub.3.
4. Medical device according to claim 1, wherein the hemocompatible
layer is directly placed on the surface of the medical device and
onto said hemocompatible layer paclitaxel as well as mixtures of
these active agents are deposited.
5. Medical device according to claim 1, wherein under the
hemocompatible layer or between two hemocompatible layers at least
one biostable and/or biodegradable layer is present.
6. Medical device according to claim 1, wherein the hemocompatible
layer is coated completely or/and incompletely with at least one
additional, above lying biostable and/or biodegradable layer.
7. Medical device according to claim 1, in which at least one
active agent layer of paclitaxel is present between the biostable
and the hemocompatible layer.
8. Medical device according to claim 1, in which paclitaxel is
bound covalently and/or adhesively in and/or on the hemocompatible
layer and/or the biostable and/or the biodegradable layer.
9. Medical device according to claim 1, characterised in, that as
biodegradable substances for the biodegradable layer
polyvalerolactones, poly-.epsilon.-decalactones, polylactonic acid,
polyglycolic acid, polylactides, polyglycolides, copolymers of the
polylactides and polyglycolides, poly-.epsilon.-caprolactone,
polyhydroxybutanoic acid, polyhydroxybutyrates,
polyhydroxyvalerates, polyhydroxybutyrate-co-valera- tes,
poly(1,4-dioxane-2,3-diones), poly(1,3-dioxane-2-one),
poly-para-dioxanones, polyanhydrides as polymaleic anhydrides,
polyhydroxymethacrylates, fibrin, polycyanoacrylates,
polycaprolactonedimethylacrylates, poly-b-maleic acid,
polycaprolactonebutyl-acrylates, multiblock polymers as e.g. from
oligocaprolactonedioles and oligodioxanonedioles, polyetherester
multiblock polymers as e.g. PEG and poly(butyleneterephtalates),
polypivotolactones, polyglycolic acid trimethyl-carbonates,
polycaprolactone-glycolides, poly(g-ethylglutamate),
poly(DTH-iminocarbonate), poly(DTE-co-DT-carbonate),
poly(bisphenol-A-iminocarbonate), polyorthoesters, polyglycolic
acid trimethyl-carbonates, polytrimethylcarbonates,
polyiminocarbonates, poly(N-vinyl)-pyrrolidone, polyvinylalcoholes,
polyesteramides, glycolated polyesters, polyphosphoesters,
polyphosphazenes, poly[p-carboxyphenoxy)propane],
polyhydroxypentane acid, polyanhydrides,
polyethyleneoxide-propyleneoxide, soft polyurethanes, polyurethanes
with amino acid rests in the backbone, polyetheresters as
polyethyleneoxide, polyalkeneoxalates, polyorthoesters as well as
their copolymers, lipids, carrageenans, fibrinogen, starch,
collagen, protein based polymers, polyamino acids, synthetic
polyamino acids, zein, modified zein, polyhydroxyalkanoates, pectic
acid, actinic acid, modified and non modified fibrin and casein,
carboxymethylsulphate, albumin, moreover hyaluronic acid, chitosane
and its derivatives, heparansulphates and its derivatives, heparin,
chondroitinsulphate, dextran, b-cyclodextrins, copolymers with PEG
and polypropyleneglycol, gummi arabicum, guar, gelatine, collagen,
collagen-N-Hydroxysuccinimide, lipids, phospholipids, modifications
and copolymers and/or mixtures of afore mentioned substances are
used.
10. Medical device according to claim 1, characterised in, that as
biostable substances for the biostable layer polyacrylic acid and
polyacrylates as polymethylmethacrylate, polybutylmethacrylate,
polyacrylamide, polyacrylonitriles, polyamides, polyetheramides,
polyethylenamine, polyimides, polycarbonates, polycarbourethanes,
polyvinylketones, polyvinylhalogenides, polyvinylidenhalogenides,
polyvinylethers, polyisobutylenes, polyvinylaromates,
polyvinylesters, polyvinylpyrollidones, polyoxymethylenes,
polytetramethyleneoxide, polyethylene, polypropylene,
polytetrafluoroethylene, polyurethanes, polyetherurethanes,
silicone-polyetherurethanes, silicone-polyurethanes,
silicone-polycarbonate-urethanes, polyolefine elastomeres,
polyisobutylenes, EPDM gums, fluorosilicones,
carboxymethylchitosanes, polyaryletheretherketones,
polyetheretherketones, polyethylenterephthalat- e, polyvalerates,
carboxymethylcellulose, cellulose, rayon, rayontriacetates,
cellulosenitrates, celluloseacetates, hydroxyethylcellulose,
cellulosebutyrates, celluloseacetatebutyrates, ethylvinylacetate
copolymers, polysulphones, epoxy resins, ABS resins, EPDM gums,
silicones as polysiloxanes, polydimethylsiloxanes,
polyvinylhalogenes and copolymers, celluloseethers,
cellulosetriacetates, chitosanes and copolymers and/or mixtures of
these substances are used.
11. Medical device according to claim 1, whereas instead of the
active agent paclitaxel one of the following active agents is used:
simvastatin, 2-methylthiazolidine-2,4-dicarboxylic acid and the
correspondent sodium salt, macrocyclic suboxide (MCS), derivatives
of MCS, activated protein C (aPC), PETN, trapidil, .beta.-estradiol
as well as mixtures of these active agents or mixtures of one of
these active agents with paclitaxel.
12. Medical device according to claim 1, characterised in, that the
medical device comprises prostheses, organs, vessels, aortas, heart
valves, tubes, organ spareparts, implants, fibers, hollow fibers,
stents, hollow needles, syringes, membranes, tinned goods, blood
containers, titrimetric plates, pacemakers, adsorbing media,
chromatography media, chromatography columns, dialyzers, connexion
parts, sensors, valves, centrifugal chambers, recuperators,
endoscopes, filters, pump chambers.
13. Medical device according to claim 12, characterised in, that
the medical device is a stent.
14. Stents according to claim 13, wherein the polymer is deposited
in amounts between 0.01 mg to 3 mg/layer, preferred between 0.20 mg
to 1 mg and especially preferred between 0.2 mg to 0.5
mg/layer.
15. Stent according to claim 13, characterised in, that the active
agent is used in a pharmaceutically active concentration of
0.001-10 mg per cm.sup.2 stent surface and per layer.
16. Use of the stent according to claim 13 for the prevention or
reduction of restenosis.
17. Use of the stent according to claim 13 for continuous release
of paclitaxel, simvastatin, 2-methylthiazolidine-2,4-dicarboxylic
sodium salt, macrocyclic suboxide (MCS), derivatives of MCS,
activated protein C (aPC), PETN, trapidil and/or
.beta.-estradiol.
18. Use of the medical device according to claim 1 for the direct
contact with blood.
19. Use of the medical device according to claim 1 for prevention
or reduction of the unspecific adhesion and/or deposition of
proteins on the coated surfaces of the medical devices.
20. Use according to claim 18, characterised in, that the
hemocompatibly coated surface of the medical device is a surface of
micro-titer plates or other carrier media for detection
processes.
21. Use according to claim 18, characterised in, that the
hemocompatibly coated surface of the medical device is the surface
of adsorber media or chromatography media.
22. Method for the hemocompatible coating of biological and/or
artificial surfaces of medical devices comprising the following
steps: a) providing a surface of a medical device and b) deposition
of at least one compound of the general formula 1 according to
claim 1 as hemocompatible layer on this surface and/or b')
deposition of a biostable and/or biodegradable layer on the surface
of the medical device or the hemocompatible layer.
23. Method according to claim 22, wherein the hemocompatible layer
or the biostable and/or biodegradable layer is coated via dipping
or spraying method with at least one biodegradable and/or
biostabile layer which conspires paclitaxel covalently and/or
adhesively bound.
24. Method according to claim 22 comprising the further step c): c.
deposition of paclitaxel in and/or on the hemocompatible layer or
the biostable and/or biodegradable layer.
25. Method according to claim 24, wherein paclitaxel is implemented
and/or deposited via dipping or spraying methods on and/or in the
hemocompatible layer or the biostable and/or biodegredable layer
and/or is bound via covalent and/or adhesive coupling to the
hemocompatible layer or the biostable and/or biodegradable
layer.
26. Method according to claim 22, comprising the further step d) or
d'): d. deposition of at least one biodegradable layer and/or at
least one biostable and/or biodegradable layer on the
hemocompatible layer or the layer of paclitaxel respectively, or
d') deposition of at least one compound of the general formula 1
according to claim 1 as hemocompatible layer on the biostable
and/or biodegradable layer or the layer of paclitaxel.
27. Method according to claim 22, comprising the further step e.):
e. deposition of paclitaxel in and/or on the at least one
biodegradable and/or biostable layer or the hemocompatible
layer.
28. Method according to claim 27, wherein paclitaxel is deposited
and/or implemented via dipping or spraying methods on and/or in the
at least one biodegradable and/or biostable layer or the
hemocompatible layer and/or is bound via covalent and/or adhesive
coupling to the at least one biodegradable and/or biostable layer
or the hemocompatible layer.
29. Method according to claim 22, wherein the biostable and/or
biodegradable layer is covalently and/or adhesively bound on the
surface of the medical device and the hemocompatible layer is
covalently bound to the biostable and/or biodegradable layer and
covers it completely or incompletely.
30. Method according to claim 22, characterised in, that the
hemocompatible layer comprises heparin of native origin of
regioselectively synthesised derivatives of different sulphation
coefficients and acylation coefficients in the molecular weight
range of the pentasaccharide, which is responsible for the
antithrombotic activity, up to the standard molecular weight of the
purchasable heparin of 13 kD, heparansulphate and its derivatives,
oligo- and polysaccharides of the erythrocytic glycocalix,
desulphated and N-reacetylated heparin, N-carboxymethylated and/or
partially N-acetylated chitosan as well as mixtures of these
substances.
31. Method according to claim 22, characterised in, that as
biodegradable substances for the biodegradable layer
polyvalerolactones, poly-e-decalactones, polylactonic acid,
polyglycolic acid, polylactides, polyglycolides, copolymers of the
polylactides and polyglycolides, poly-.epsilon.-caprolactone,
polyhydroxybutanoic acid, polyhydroxybutyrates,
polyhydroxyvalerates, polyhydroxybutyrate-co-valera- tes,
poly(1,4-dioxane-2,3-diones), poly(1,3-dioxane-2-one), poly-para-d
ioxanones, polyanhydrides as polymaleic anhyd rides,
polyhydroxymethacrylates, fibrin, polycyanoacrylates,
polycaprolactonedimethylacrylates, poly-b-maleic acid,
polycaprolactonebutyl-acrylates, multiblock polymers as e.g. from
oligocaprolactonedioles and oligodioxanonedioles, polyetherester
multiblock polymers as .e.g. PEG and poly(butyleneterephtalates),
polypivotolactones, polyglycolic acid trimethyl-carbonates,
polycaprolactone-glycolides, poly(g-ethylglutamate),
poly(DTH-iminocarbonate), poly(DTE-co-DT-carbonate),
poly(bisphenol-A-iminocarbonate), polyorthoesters, polyglycolic
acid trimethyl-carbonates, polytrimethylcarbonates,
polyiminocarbonates, poly(N-vinyl)-pyrrolidone, polyvinylalcoholes,
polyesteramides, glycolated polyesters, polyphosphoesters,
polyphosphazenes, poly[p-carboxyphenoxy)propane],
polyhydroxypentane acid, polyanhydrides,
polyethyleneoxide-propyleneoxide, soft polyurethanes, polyurethanes
with amino acid rests in the backbone, polyetheresters as
polyethyleneoxide, polyalkeneoxalates, polyorthoesters as well as
their copolymers, lipides, carrageenanes, fibrinogen, starch,
collagen, protein based polymers, polyamino acids, synthetic
polyamino acids, zein, modified zein, polyhydroxyalkanoates, pectic
acid, actinic acid, modified and non modified fibrin and casein,
carboxymethylsulphate, albumin, moreover hyaluronic acid, chitosane
and its derivatives, heparansulphates and its derivatives, heparin,
chondroitinsulphate, dextran, .beta.-cyclodextrins, copolymers with
PEG and polypropyleneglycol, gummi arabicum, guar, gelatine,
collagen, collagen-N-Hydroxysuccinimide, lipids, phospholipids,
modifications and copolymers and/or mixtures of afore mentioned
substances are used.
32. Method according to claim 22, characterised in, that as
biostable substances for the biostable layer polyacrylic acid and
polyacrylates as polymethylmethacrylate, polybutylmethacrylate,
polyacrylamide, polyacrylonitriles, polyamides, polyetheramides,
polyethylenamine, polyimides, polycarbonates, polycarbourethanes,
polyvinylketones, polyvinylhalogenides, polyvinylidenhalogenides,
polyvinylethers, polyisobutylenes, polyvinylaromates,
polyvinylesters, polyvinylpyrollidones, polyoxymethylenes,
polytetramethyleneoxide, polyethylene, polypropylene,
polytetrafluoroethylene, polyurethanes, polyetherurethanes,
silicone-polyetherurethanes, silicone-polyurethanes,
silicone-polycarbonate-urethanes, polyolefine elastomeres,
polyisobutylenes, EPDM gums, fluorosilicones,
carboxymethylchitosanes, polyaryletheretherketones,
polyetheretherketones, polyethylenterephthalat- e, polyvalerates,
carboxymethylcellulose, cellulose, rayon, rayontriacetates,
cellulosenitrates, celluloseacetates, hydroxyethylcellulose,
cellulosebutyrates, celluloseacetatebutyrates, ethylvinylacetate
copolymers, polysulphones, epoxy resins, ABS resins, EPDM gums,
silicones as polysiloxanes, polydimethylsiloxanes,
polyvinylhalogenes and copolymers, celluloseethers,
cellulosetriacetates, chitosanes and copolymers and/or mixtures of
these substances are used.
33. Method according to claim 22, characterised in, that the
deposition of the polysaccharides of the formula 1 according to
claim 1 is achieved via hydrophobic interactions, van der Waals
forces, electrostatic interactions, hydrogen bonds, ionic
interactions, cross-linking and/or covalent bonding.
34. Method according to claim 22, wherein instead of the active
agent paclitaxel one of the following active agents is used:
simvastatin, 2-methylthiazolidine-2,4-dicarboxylic sodium salt,
macrocyclic suboxide (MCS), derivatives of MCS, activated protein C
(aPC), PETN, trapidil, .beta.-estradiol as well as mixtures of
these active agents or mixtures of one of these active agents with
paclitaxel.
35. Medical device available by the method according to claim 22.
Description
[0001] The invention concerns the utilisation of polysaccharides
containing the sugar building block N-acylglucosamine for the
preparation of hemocompatible surfaces of medical devices, methods
for the hemocompatible coating of surfaces with said
polysaccharides as well as medical devices with these
hemocompatible surfaces.
[0002] In the human body the blood gets only in cases of injuries
in contact with surfaces other than the inside of natural blood
vessels. Consequently the blood coagulation system gets always
activated to reduce the bleeding and to prevent a life-threatening
loss of blood, if blood gets in contact with foreign surfaces. Due
to the fact that an implant also represents a foreign surface, all
patients, who receive an implant, which is in permanent contact
with blood, are treated for the duration of the blood contact with
drugs, so called anticoagulants, that suppress the blood
coagulation, so that considerable side effects have to be taken in
account.
[0003] Whilst the usage of vessel supports, so-called stents, the
described risk of thrombosis also occurs as one of the risk factors
in blood bearing vessels. In cases of vessel strictures and
sealings due to e.g. arteriosclerotic changes especially of the
coronary arteries the stent is used for the expansion of the vessel
walls. It fixes lime fragments in the vessels and improves the flow
properties of the blood inside the vessel as it smoothens the
surface of the interior space of the vessel. Additionally a stent
leads to a resistance against elastic restoring forces of the
expanded vessel part. The utilised material is mostly medicinal
stainless steel.
[0004] The stent thrombosis occurs in less than one percent of the
cases already in the cardio catheter laboratory as early thrombosis
or in two to five percent of the cases during the hospital
recreation. In about five percent of the cases vessel injuries due
to the intervention are caused because of the arterial lock and the
possibility of causing pseudo-aneurysms by the expansion of vessels
exists, too. Additionally the continuous application of heparin as
anticoagulant increases the risk of bleeding.
[0005] An additional and very often occuring complication is
restenosis, the resealing of the vessel. Although stents minimise
the risk of a renewed sealing of the vessel they are until now not
totally capable of hindering the restenosis. The rate of resealing
(restenosis) after implantation of a stent is with up to 30% one of
the main reasons of a repeated hospital visit for the patients.
[0006] An exact conceptual description of the restenosis does not
exist in the professional literature. The mostly used morphologic
definition of the restenosis is that after a successful PTA
(percutaneous transluminal angioplasty) the restenosis is defined
as a reduction of the vessel diameter to less than 50% of the
normal one. This is an empirically defined value of which the
hemodynamic relevance and its relation to clinical symptomatics
lacks of a massive scientific basis. In praxis the clinical
aggravation of the patient is often viewed as a sign for a
restenosis of the formerly treated vessel part.
[0007] The vessel injuries caused during the implantation of the
stents arise inflammation reactions, which play an important role
for the healing process during the first seven days. The herein
concurrent processes are among others connected with the release of
growth factors, which initiate an increased proliferation of the
smooth muscle cells and lead with this to a rapid restenosis, a
renewed sealing of the vessel because of uncontrolled growth. Even
after a couple of weeks, when the stent is grown into the tissue of
the blood vessel and totally surrounded by smooth muscle cells,
cicatrisations can be too distinctive (neointima hyperplasia) and
lead to not only a coverage of the stent surface but to the sealing
of the total interior space of the stent.
[0008] It was tried vainly to solve the problem of restenosis by
the coating of the stents with heparin (J. Whorle et al., European
Heart Journal (2001) 22, 1808-1816). Heparin addresses as
anticoagulant only the first mentioned cause and is moreover able
to unfold its total effect only in solution. This first problem is
meanwhile almost totally avoidable medicamentously by application
of anticoagulants. The further problem is intended to be solved now
by inhibiting the growth of the smooth muscle cells locally on the
stent. This is carried out by e.g. radioactive stents or stents,
which contain pharmaceutical active agents.
[0009] Consequently there is a demand on non-thrombogeneous,
hemocompatible materials, which are not detected as foreign surface
and in case of blood contact does not activate the coagulation
system and lead to the coagulation of the blood, with which an
important factor for the restenosis stimulating processes is
eliminated. Support is supposed to be guaranteed by addition of
active agents which shall suppress the inflammation reactions or
which shall control the healing process accompanying cell
division.
[0010] The undertakings are enormous on this area of producing a
stent which can reduce the restenosis in this manner or eliminate
totally. Herein different possibilities of realisation are examined
in numerous studies. The most common construction type consists of
a stent, which is coated with a suitable matrix, usually a
biostable polymer. The matrix includes an antiproliferative or
antiphlogistic agent, which is released in temporally controlled
steps and shall suppress the inflammation reactions and the
excessive cell division.
[0011] U.S. Pat. No. 5,891,108 reveals for example a hollow moulded
stent, which can contain pharmaceutical active agents in its
interior, that can be released throughout a various number of
outlets in the stent. Whereas EP-A-1 127 582 describes a stent that
shows on its surface ditches of 0.1-1 mm depth and 7-15 mm length,
which are suitable for the implementation of an active agent. These
active agent reservoirs release, similarly to the outlets in the
hollow stent, the contained pharmaceutical active agent in a
punctually high concentration and over a relatively long period of
time, which leads to the fact, that the smooth muscle cells are not
anymore or only very delayed capable of enclosing the stent. As a
consequence the stent is much longer exposed to the blood, what
leads again to increased vessel sealings by thrombosis (Liistro F.,
Colombo A., Late acute thrombosis after paclitaxel eluting stent
implantation. Heart (2001) 86 262-4).
[0012] One approach to this problem is represented by the
phosphorylcholine coating of Biocompatibles (WO 0101957), as here
phosphorylcholine, a component of the erythrocytic cell membrane,
shall create a non thrombogeneous surface as ingredient of the
coated non biodegredable polymer layer on the stent. Dependent of
its molecular weight the active agent is absorbed by the polymer
containing phosphorylcholine layer or adsorbed on the surface.
[0013] Object of the present invention is to provide hemocompatibly
coated medical devices as well as methods of hemocompatible coating
and the use of hemocompatibly coated medical devices, especially
stents, to prevent or reduce undesired reactions as for example
restenosis.
[0014] Especially object of the present invention is to provide
stents which permit a continuous controlled ingrowth of the
stent--on the one side by suppression of the cellular reactions in
the primal days and weeks after implantation by the support of the
selected agents and agent combinations and on the other side by
providing an athrombogeneous resp. inert resp. biocompatible
surface, which guarantees that with the decrease of the agent's
influence no reactions to the existing foreign surface take place
which also can lead to complications in a long term.
[0015] The intentions of creating a nearly perfect simulation of
the native athrombogeneous conditions of that part of a blood
vessel that is allocated on the blood side are enormous. EP-B-0 333
730 describes a process to produce hemocompatible substrates by
recess, adhesion and/or modification and anchorage of non
thrombogeneous endothelic cell surface polysaccharide (HS I). The
immobilisation of this specific endothelic cell surface
proteoheparane sulphate HS I on biological or artificial surfaces
effects that suchlike coated surfaces get blood compatible and
suitable for the permanent blood contact. A disadvantage whereas
is, that this process for the preparation of HS I premises the
cultivation of endothelic cells, so that the economical suitability
of this process is strongly limited, because the cultivation of
endothelic cells is time taking and greater amounts of cultivated
endothelic cells are only obtainable with immense expenditure.
[0016] The present invention solves the object by providing medical
devices that show properties of a surface coating of determined
polysaccharides and paclitaxel. Instead of or together with
paclitaxel determined other antiphlogistic as well as
anti-inflammatory drugs resp. agent combinations of simvastatine,
2-methylthiazolidine-2,4-dicarboxylic acid and the correspondent
sodium salt), macrocyclic suboxide (MCS) and its derivatives,
tyrphostines, D24851, thymosin a-1, interleucine-1.beta.
inhibitors, activated protein C (aPC), MSH, fumaric acid and
fumaric acid ester, PETN (pentaerythritol tetranitrate), PI88,
dermicidin, baccatin and its derivatives, docetaxel and further
derivatives of paclitaxel, tacrolimus, pimecrolimus, trapidil, a-
and .beta.-estradiol, sirolimus, colchicin, and
melanocyte-stimulating hormone (.alpha.-MSH) can be used. Methods
for the production of these hemocompatible surfaces are given in
the claims 20-31. Preferred embodiments can be found in the
dependent claims, the examples as well as the figures.
[0017] The subject matter of the present invention are medical
devices the surface of which is at least partially covered with a
hemocompatible layer, wherein the hemocompatible layer comprises at
least one compound of the formula 1: 1
[0018] wherein
[0019] n is an integer between 4 and 1050 and
[0020] Y represents the residues --CHO, --COCH.sub.3,
--COC.sub.2H.sub.5, --COC.sub.3H.sub.7, --COC.sub.4H.sub.9,
--COC.sub.5H.sub.11, --COCH(CH.sub.3).sub.2,
--COCH.sub.2CH(CH.sub.3).sub.2, --COCH(CH.sub.3)C.sub.2H.sub.5,
--COC(CH.sub.3).sub.3, --CH.sub.2COO.sup.-,
--C.sub.2H.sub.4COO.sup.-, --C.sub.3H.sub.6COO.sup.-- ,
--C.sub.4H.sub.8COO.sup.-.
[0021] It is also possible to use any salts of the compounds of
formula 1. The hemocompatible layer can be added directly onto the
surface of a preferably non hemocompatible medical device or
deposited onto other biostable and/or biodegradable layers. Further
on additional biostable and/or biodegradable and/or hemocompatible
layers can be localised on the hemocompatible layer. In addition to
this the active agent paclitaxel is present on, in and/or under the
hemocompatible layer or the hemocompatible layers, respectively.
The active agent (paclitaxel) can form herein an own active agent
layer on or under the hemocompatible layer and/or can be
incorporated in at least one of the biostable, biodegradable and/or
hemocompatible layers. Preferably the compounds of the general
formula 1 are used, wherein Y is one of the following groups:
--CHO, --COCH.sub.3, --COC.sub.2H.sub.5 or --COC.sub.3H.sub.7.
Further on preferred are the groups --CHO, --COCH.sub.3,
--COC.sub.2H.sub.5 and especially preferred is the group
--COCH.sub.3.
[0022] The compounds of the general formula 1 contain only a small
amount of free amino groups. Because of the fact that with the
ninhydrine reaction free amino groups could not be detected
anymore, due to the sensitivity of this test it can be implied that
less than 2%, preferred less than 1% and especially preferred less
than 0.5% of all --NH--Y groups are present as free amino groups,
i.e. within this low percentage of the --NH--Y groups Y represents
hydrogen.
[0023] Because polysaccharides of the general formula 1 contain
carboxylate groups and amino groups, the general formula covers
alkali as well as alkaline earth metal salts of the corresponding
polysaccharides. Alkali metal salts like the sodium salt, the
potassium salt, the lithium salt or alkaline earth metal salts like
the magnesium salt or the calcium salt can be mentioned. Further on
with ammonia, primary, secondary, tertiary and quaternary amines,
pyridine and pyridine derivatives ammonium salts, preferably
alkylammonium salts and pyridinium salts can be formed. Among the
bases, which form salts with the polysaccharides, are inorganic and
organic bases as for example NaOH, KOH, LiOH, CaCO.sub.3,
Fe(OH).sub.3, NH.sub.4OH, tetraalkylammonium hydroxide and similar
compounds.
[0024] The polysaccharides according to formula 1 possess molecular
weights from 2 kD to 15 kD, preferred from 4 kD to 13 kD, more
preferred from 6 kD to 12 kD and especially preferred from 8 kD to
11 kD. The variable n is an integer in the range of 4 to 1050.
Preferred n is an integer from 9 to 400, more preferred an integer
from 14 to 260 and especially preferred an integer between 19 and
210.
[0025] The general formula 1 shows a disaccharide, which has to be
viewed as the basic module for the used polysaccharides and that
formes the polysaccharide by the n-fold (multiple) sequencing of
the basic module. This basic module which is built of two sugar
molecules shall not be interpreted in the manner, that the general
formula 1 only includes polysaccharides with an even number of
sugar molecules. The formula implements of course also
polysaccharides with an odd number of sugar building units. The end
groups of the polysaccharides are represented by hydroxyl
groups.
[0026] Especially preferred are medical devices which contain
immediately on the surface of the medical device a hemocompatible
layer consisting of the compounds according to formula 1 and above
it a layer of paclitaxel. The paclitaxel layer can diffuse
partially into the hemocompatible layer or get taken up totally by
the hemocompatible layer.
[0027] It is further preferred, if at least one biostable layer is
present under the hemocompatible layer. In addition the
hemocompatible layer can be coated totally and/or partially with at
least one more, above lying biostable and/or biodegradable layer.
Preferred is an external biodegradable or hemocompatible layer.
[0028] A further preferred embodiment contains a layer of
paclitaxel under the hemocompatible layer or between the biostable
and the hemocompatible layer, so that paclitaxel is released slowly
through the hemocompatible layer. Paclitaxel can be bound
covalently and/or adhesively in and/or on the hemocompatible layer
and/or the biostable and/or the biodegradable layer, in which the
adhesive bonding is preferred.
[0029] As biodegradable substances for the biodegradable layer(s)
can be used: polyvalerolactones, poly-.epsilon.-decalactones,
polylactonic acid, polyglycolic acid, polylactides, polyglycolides,
copolymers of the polylactides and polyglycolides,
poly-.epsilon.-caprolactone, polyhydroxybutanoic acid,
polyhydroxybutyrates, polyhydroxyvalerates,
polyhydroxybutyrate-co-valerates, poly(1,4-dioxane-2,3-diones),
poly(1,3-dioxane-2-one), poly-para-dioxanones, polyanhydrides such
as polymaleic anhydrides, polyhydroxymethacrylates, fibrin,
polycyanoacrylates, polycaprolactonedimethylacrylates,
poly-b-maleic acid, polycaprolactonebutyl-acrylates, multiblock
polymers such as e.g. from oligocaprolactonedioles and
oligodioxanonedioles, polyether ester multiblock polymers such as
e.g. PEG and poly(butyleneterephtalates), polypivotolactones,
polyglycolic acid trimethyl-carbonates,
polycaprolactone-glycolides, poly(g-ethylglutamate),
poly(DTH-iminocarbonate), poly(DTE-co-DT-carbonate),
poly(bisphenol-A-iminocarbonate), polyorthoesters, polyglycolic
acid trimethyl-carbonates, polytrimethylcarbonates,
polyiminocarbonates, poly(N-vinyl)-pyrrolidone, polyvinylalcoholes,
polyesteramides, glycolated polyesters, polyphosphoesters,
polyphosphazenes, poly[p-carboxyphenoxy)propane],
polyhydroxypentanoic acid, polyanhydrides,
polyethyleneoxide-propyleneoxide, soft polyurethanes, polyurethanes
with amino acid residues in the backbone, polyether esters such as
polyethyleneoxide, polyalkeneoxalates, polyorthoesters as well as
their copolymers, lipides, carrageenans, fibrinogen, starch,
collagen, protein based polymers, polyamino acids, synthetic
polyamino acids, zein, modified zein, polyhydroxyalkanoates, pectic
acid, actinic acid, modified and non modified fibrin and casein,
carboxymethylsulphate, albumin, moreover hyaluronic acid, chitosan
and its derivatives, heparansulphates and its derivatives,
heparins, chondroitinsulphate, dextran, b-cyclodextrins, copolymers
with PEG and polypropyleneglycol, gummi arabicum, guar, gelatine,
collagen, collagen-N-hydroxysuccinimide, lipids, phospholipids,
modifications and copolymers and/or mixtures of the afore mentioned
substances.
[0030] As biostable substances for the biostable layer(s) can be
used: polyacrylic acid and polyacrylates as polymethylmethacrylate,
polybutylmethacrylate, polyacrylamide, polyacrylonitriles,
polyamides, polyetheramides, polyethylenamine, polyimides,
polycarbonates, polycarbourethanes, polyvinylketones,
polyvinylhalogenides, polyvinylidenhalogenides, polyvinylethers,
polyisobutylenes, polyvinylaromates, polyvinylesters,
polyvinylpyrollidones, polyoxymethylenes, polytetramethyleneoxide,
polyethylene, polypropylene, polytetrafluoroethylene,
polyurethanes, polyetherurethanes, silicone-polyetherurethanes,
silicone-polyurethanes, silicone-polycarbonate-urethanes,
polyolefine elastomeres, polyisobutylenes, EPDM gums,
fluorosilicones, carboxymethylchitosanes,
polyaryletheretherketones, polyetheretherketones,
polyethylenterephthalat- e, polyvalerates, carboxymethylcellulose,
cellulose, rayon, rayontriacetates, cellulosenitrates,
celluloseacetates, hydroxyethylcellulose, cellulosebutyrates,
celluloseacetatebutyrates, ethylvinylacetate copolymers,
polysulphones, epoxy resins, ABS resins, EPDM gums, silicones as
polysiloxanes, polydimethylsiloxanes, polyvinylhalogenes and
copolymers, celluloseethers, cellulosetriacetates, chitosanes and
copolymers and/or mixtures of these substances.
[0031] It is possible to furnish any medical devices with the
herein disclosed hemocompatible surfaces, especially those, which
shall be suitable for the short- or the longterm contact with blood
or blood products. Such medical devices are for example prostheses,
organs, vessels, aortas, heart valves, tubes, organ spareparts,
implants, fibers, hollow fibers, stents, hollow needles, syringes,
membranes, tinned goods, blood containers, titrimetric plates,
pacemakers, adsorbing media, chromatography media, chromatography
columns, dialyzers, connexion parts, sensors, valves, centrifugal
chambers, recuperators, endoscopes, filters, pump chambers. The
present invention is especially related to stents.
[0032] The polysaccharides of formula 1 can be formed from heparin
and/or heparansulphates. These materials are in structurally view
quite similar compounds. Heparansulphates occur ubiquitously on
cell surfaces of mammals. In dependence from the cell type they
differ strongly in molecular weight, degree of acetylation and
degree of sulphation. Heparansulphate from liver shows for example
an acetylation coefficient of about 50%, whereas the
heparansulphate of the glycocalix from endothelic cells can exhibit
an acetylation coefficient from about 90% and higher. Heparin shows
only a quite low degree of acetylation from about up to 5%. The
sulphation coefficient of the heparansulphate from liver and of
heparin is .about.2 per disaccharide unit, in case of
heparansulphate from endothelial cells close to 0 and in
heparansulphates from other cell types between 0 and 2 per
disaccharide unit.
[0033] The compounds of the general formula 1 are characterized by
an amount of sulphate groups per disaccharide unit of less than
0.05. Further on the amount of free amino groups in these compounds
is less than 1% based on all --NH--Y groups.
[0034] The following image shows a tetrasaccharide unit of a
heparin or a heparansulphate with random orientation of the
sulphate groups and with a sulphation coefficient of 2 per
disaccharide unit as it is typical for heparin: 2
[0035] All heparansulphates have with heparin a common sequence in
biosynthesis. First of all the core protein with the
xylose-containing bonding region is formed. It consists of the
xylose and two galactose residues connected to it. To the last of
the two galactose units a glucuronic acid and a galactosamine is
connected alternately until the adequate chain length is reached.
Finally, a several step enzymatic modification of this common
polysaccharide precursor of all heparansulphates and of heparin
follows by means of sulphotransferases and epimerases which
generate by their varying completeness of transformation the broad
spectra of different heparansulphates up to heparin.
[0036] Heparin is alternately build of D-glucosamine and
D-glucuronic acid resp. L-iduronic acid, in which the amount of
L-iduronic acid is up to 75%. D-glucosamine and D-glucuronic acid
are connected in a .beta.-1,4-glycosidic resp. L-iduronic acid in
an a-1,4-glycosidic bonding to the disaccharide, that forms the
heparin subunits. These subunits are again connected to each other
in a .beta.-1,4-glycosidic way and lead to heparin. The position of
the sulphonyl groups is variable. In average one tetrasaccharide
unit contains 4 to 5 sulphuric acid groups. Heparansulphate, also
named as heparitinsulphate, contains with exception of the
heparansulphate from liver less N- and O-bound sulphonyl goups as
heparin but in exchange more N-acetyl goups. The amount of
L-iduronic acid compared to heparin is also lower.
[0037] As it is evident from FIG. 1 the compounds of the general
formula (cf. FIG. 1b as example) are structurally similar to the
natural heparansulphate of endothelial cells, but avoid the
initially mentioned disadvantages by the use of endothelial cell
heparan sulphates.
[0038] For the antithrombotic activity a special pentasaccharide
unit is made responsible, which can be found in commercial heparin
preparatives in about every 3.sup.rd molecule. Heparin preparations
of different antithrombotic activity can be produced by special
separation techniques. In highly active, for example by
antithrombin-III-affinitychromatography obtained preparations
("High-affinity"-heparin) this active sequence is found in every
heparin molecule, while in "No-affinity"-preparations no
characteristical pentasaccharide sequences and thus no active
inhibition of coagulation can be detected. Via interaction with
this pentasaccharide the activity of antithrombin III, an inhibitor
of the coagulation key factor thrombin, is essentially
exponentiated (bonding affinity increase up to the factor
2.times.10.sup.3) [Stiekema J. C. J.; Clin Nephrology 26, Suppl. Nr
1, S3-S8, (1986)].
[0039] The amino groups of the heparin are mostly N-sulphated or
N-acetylated. The most important O-sulphation positions are the C2
in the iduronic acid as well as the C6 and the C3 in the
glucosamine. For the activity of the pentasaccharide onto the
plasmatic coagulation basically the sulphate group on C6 is made
responsible, in smaller proportion also the other functional
groups.
[0040] Surfaces of medicinal implants coated with heparin or
heparansulphates are and remain only conditionally hemocompatible
by the coating. The heparin or heparansulphate which is added onto
the artificial surface loses partially in a drastic measure its
antithrombotic activity which is related to a restricted
interaction due to steric hindrence of the mentioned
pentasaccharide units with antithrombin III. Because of the
immobilisation of these polyanionic substances a strong adsorption
of plasma protein on the heparinated surface is observed in all
cases what eliminates on the one hand the coagulation suppressing
effect of heparin resp. of heparansulphates and initialises on the
other hand specific coagulation processes by adherent and hereby
tertiary structure changing plasma proteins (e.g. albumin,
fibrinogen, thrombin) and hereon adherent platelets.
[0041] Thus a correlation exists on the one hand between the
limited interaction of the pentasaccharide units with antithrombin
III by immobilisation on the other hand depositions of plasma
proteins on the heparin-resp. heparansulphate layer on the
medicinal implant take place, which leads to the loss(es) of the
antithrombotic properties of the coating and which can even turn
into the opposite, because the plasma protein adsorption, that
occurs during a couple of seconds leads to the loss of the
anticoagulational surface and the adhesive plasma proteins change
their tertiary structure, whereby the antithrombogenity of the
surface turns vice versa and a thrombogenous surface arises.
Surprisingly it could be detected, that the compounds of the
general formula 1, despite of the structural differences to the
heparin resp. heparansulphate, still show the hemocompatible
properties of heparin and additionally after the immobilisation of
the compounds no noteworthy depositions of plasma proteins, which
represent an initial step in the activation of the coagulation
cascade, could be observed. The hemocopatible properties of the
compounds according to invention still remain also after their
immobilisation on artificial surfaces.
[0042] Further on it is supposed that the sulphate groups of the
heparin resp. the heparansulphates are necessary for the
interaction with antithrombin III and impart thereby the heparin
resp. the heparansulphate the anticoagulatory effect. The inventive
compounds are not actively coagulation suppressive, i.e.
anticoagulative, due to an almost complete desulphation the
sulphate groups of the compounds are removed up to a low amount of
below 0.2 sulphate groups per disaccharide unit.
[0043] The inventive compounds of the general formula 1 can be
generated from heparin or heparansulphates by first substantially
complete desulphation of the polysaccharide and subsequently
substantially complete N-acylation. The term "substantially
completely desulphated" refers to a desulphation degree of above
90%, preferred above 95% und especially preferred above 98%. The
desulphation coefficient can be determined according to the
so-called ninhydrin test which indicates free amino groups. The
desulphation takes place in the way as with DMMB (dimethylmethylene
blue) no colour reaction is obtained. This colour test is suitable
for the indication of sulphated polysaccharides but its detection
limit is not known in technical literature. The desulphation can be
carried out for example by pyrolysis of the pyridinium salt in a
solvent mixture. Especially a mixture of DMSO, 1,4-dioxane and
methanol has proven of value.
[0044] Heparansulphates as well as heparin were desulphated via
total hydrolysis and subsequently reacylated. Thereafter the number
of sulphate groups per disaccharide unit (S/D) was determined by
.sup.13C-NMR. The following table 1 shows these results on the
example of heparin and desulphated, reacetylated heparin
(Ac-heparin).
1TABLE 1 Distribution of functional groups per disaccharide unit on
the example of heparin and Ac-heparin as determined by
.sup.13C-NMR-measurements. 2-S 6-S 3-S NS N--Ac NH.sub.2 S/D
Heparin 0.63 0.88 0.05 0.90 0.08 0.02 2.47 Ac-heparin 0.03 0 0 0
1.00 -- 0.03 2-S, 3-S, 6-S: sulphate groups in position 2, 3, 6
respectively NS: sulphate groups on the amino groups N--Ac: acetyl
groups on the amino groups NH.sub.2: free amino groups S/D:
sulphate groups per disaccharide unit
[0045] A sulphate content of about 0.03 sulphate
groups/disaccharide unit (S/D) in case of Ac-heparin in comparison
with about 2.5 sulphate groups/disaccharide unit in case of heparin
was reproducibly obtained.
[0046] As described above the difference in the sulphate contents
of heparin resp. heparansulphates has a considerable influence on
the activity adverse to antithrombin III and the coagulatory
effects of these compounds. These compounds have a content of
sulphate groups per disaccharide unit of less than 0.2, preferred
less than 0.07, more preferred less than 0.05 and especially
preferred less than 0.03 sulphate groups per disaccharide unit.
[0047] By the removal of the sulphate groups of heparin, to which
the active coagulation suppressive working mechanism is accredited
to, one receives for a surface refinement suitable hemocompatible,
coagulation inert oligo-resp. polysaccharide which on the one hand
has no active role in the coagulation process and which on the
other hand is not detected by the coagulation system as foreign
surface. Accordingly this coating imitates successfully the nature
given highest standard of hemocompatibility and passivity against
the coagulation active components of the blood. The examples 3 and
4 clarify, that surfaces, which are coated with the compounds
according to invention, especially are coated covalently, result in
a passivative, athrombogeneous and hemocompatible coating. This is
definitely proven by the example of Ac-heparins.
[0048] Substantially completely N-acylated refers to a degree of
N-acylation of above 94%, preferred above 97% and especially
preferred above 98%. The acylation runs in such a way completely
that with the ninhydrin reaction for detection of free amino groups
no colour reaction is obtained anymore. As acylation agents are
preferably used carboxylic acid chlorides, -bromides or
-anhydrides. Acetic anhydride, propionic anhydride, butyric
anhydride, acetic acid chloride, propionic acid chloride or butyric
acid chloride are for example suitable for the synthesis of the
compounds according to invention. Especially suitable are
carboxylic anhydrides as acylation agents.
[0049] As solvent especially for carboxylic acid anhydrides
deionised water is used, especially together with a cosolvent which
is added in an amount from 10 to 30 volume percent. As cosolvents
are suitable methanol, ethanol, DMSO, DMF, acetone, dioxane, THF,
ethyl acetate and other polar solvents. In case of the use of
carboxylic acid halogenides preferably polar water free solvents
such as DMSO or DMF are used.
[0050] The inventive compounds of the general formula comprise in
the half of the sugar molecules a carboxylate group and in the
other half a N-acyl group.
[0051] The present invention describes the use of the compounds
with the general formula 1 as well as salts of these compounds for
the coating, especially a hemocompatible coating of natural and/or
artificial surfaces. Under "hemocompatible" the characteristic of
the compounds according to invention is meant, not to interact with
the compounds of the blood coagulation system or the platelets and
so not to initiate the blood coagulation cascade.
[0052] In addition the invention reveals polysaccharides for the
hemocompatible coating of surfaces. Preferred are polysaccharides
in the range of the above mentioned molecular weight limits. The
used polysaccharides are characterised in that they contain the
sugar building unit N-acylglucosamine in a great amount. This means
that 40 to 60% of the sugar building units are N-acylglucosamine
and substantially the remaining sugar building units bear each a
carboxyl group. The polysaccharides consist generally in more than
95%, preferred in more than 98%, of only two sugar building units,
whereas one sugar building unit bears a carboxyl group and the
other one a N-acyl group.
[0053] One sugar building unit of the polysaccharides is
N-acylglucosamine preferred N-acetylglucosamine and in case of the
other one it is the uronic acids glucuronic acid and iduronic acid.
Preferred are polysaccharides, which conspire substantially the
sugar glucosamine, whereas substantially the half of the sugar
building units bears a N-acyl group, preferred a N-acetyl group,
and the other half of the glucosamine building units bears one
carboxyl group which is bond directly by the amino group or by one
or more methylenyl groups. In the case of these carboxylic acid
groups bound to the amino group it is concerned to be preferred the
carboxymethyl- or carboxyethyl groups. Furthermore, polysaccharides
are preferred which substantially conspire in one half of
N-acylglucosamine, preferred of N-acetylglucosamine and
substantially conspire in the other half of the uronic acids
glucuronic acid and iduronic acid. Especially preferred are the
polysaccharides, that show a substantially alternating sequence of
N-acylglucosamine and one of the both uronic acids.
[0054] Surprisingly it was shown, that for the applications
according to invention especially desulphated and substantially
N-acylated heparin is especially suitable. Especially N-acetylated
heparin is suitable for the hemocompatible coating.
[0055] The term "substantially" shall make clear, that statistical
variations are to be taken into account. One substantially
alternating sequence of the sugar building units implies, that
generally no two equal sugar building units are bound to each other
but does not exclude totally such a defect connection. In
accordance "substantially the half" means almost 50% but allows
small variations, because especially in the case of
biosynthetically synthesised macromolecules the ideal case is never
reached and some variations are always to be taken into account,
because enzymes do not work perfectly and in catalysis always some
error rate has to be anticipated. Whereas in case of natural
heparin a strongly alternating sequence of N-acetylglucosamine and
the uronic acid units is existing.
[0056] Furthermore, methods for hemocompatible coating of surfaces
are disclosed which are especially destined for the direct blood
contact. In case of these methods a natural and/or artificial
surface is provided and the above described polysaccharides are
immobilised on this surface.
[0057] The immobilisation of the polysaccharides on these surfaces
can be achieved via hydrophobic interactions, van der Waals forces,
electrostatic interactions, hydrogen bonds, ionic interactions,
cross-linking of the polysaccharides and/or by covalent bonding
onto the surface. Preferred is the covalent linkage of the
polysaccharides (side-on bonding), more preferred the covalent
single-point linkage (side-on bonding) and especially preferred the
covalent end-point linkage (end-on bonding).
[0058] In the following the coating methods according to invention
are described.
[0059] Biological and/or artificial surfaces of medical devices can
be provided with a hemocompatible coating by means of the following
method:
[0060] a) providing a surface of a medical device and
[0061] b) deposition of at least one compound of the general
formula 1 according to claim 1 as hemocompatible layer onto this
surface and/or
[0062] b') deposition of a biostable and/or biodegradable layer
onto the surface of the medical device or the hemocompatible
layer.
[0063] "Deposition" shall refer to at least partial coating of a
surface with the adequate compounds, wherein the compounds are
positioned and/or immobilised or anyhow anchored on and/or in the
subjacent surface.
[0064] Under "substantially the remaining sugar building units" is
to be understood that 93% of the remaining sugar building units,
preferred 96% and especially preferred 98% of the remaining 60%-40%
of the sugar building units bear a carboxyl group.
[0065] An uncoated and/or non hemocompatible surface is preferably
provided. "Non hemocompatible" surfaces shall refer to such
surfaces that can activate the blood coagulatory system, thus are
more or less thrombogeneous.
[0066] An alternative embodiment comprises the steps:
[0067] a) providing surface of a medical device and
[0068] b) deposition of at least one inventive polysaccharide
according to formula 1,
[0069] b') deposition of a biostable layer onto the surface of the
medical device and
[0070] d') deposition of a further hemocompatible layer of at least
one inventive polysaccharide according to formula 1.
[0071] The last-mentioned embodiment makes sure, even in the case
of e.g. mechanical damage of the polymeric layer and therewith also
of the exterior hemocompatible layer, that the surface coating does
not lose its characteristic of being blood compatible.
[0072] Under "biological or artificial" surface is the combination
of an artificial medical device with an artificial part to be
understood, e.g. pork heart with an artificial heart valve.
[0073] The single layers are deposited preferably by dipping or
spraying methods, whereas one can deposit also paclitaxel at the
same time with the deposition of one layer onto the medical device
surface, which is then implemented in the respective layer
covalently and/or adhesively bound. In this way it is possible at
the same time with the deposition of a hemocompatible layer onto
the medical device to deposit the active agent paclitaxel. The
substances for the biostable or biodegradable layers were itemised
already above.
[0074] Onto this first biostable and/or biodegradable or
hemocompatible layer it is then possible in an additional non
compulsory step c) to deposit an agent layer of paclitaxel. In a
preferred embodiment paclitaxel is bound covalently on the
subjacent layer. Also paclitaxel is preferably deposited by dipping
or spraying methods on and/or in the hemocompatible layer or the
biostable layer.
[0075] After the step b) or the step c) an additional step d) can
follow which implements the deposition of at least one
biodegradable layer and/or at least one biostable layer onto the
hemocompatible layer resp. the layer of paclitaxel.
[0076] According to the alternative embodiments after step b') or
step c) a step d') can follow which implements the deposition of at
least one compound of the general formula 1 as hemocompatible layer
onto the biostable and/or biodegradable layer resp. the layer of
paclitaxel. Preferably after step b') the step d') follows.
[0077] After step d) resp. d') the deposition of paclitaxel can
take place into and/or onto the at least one biodegradable and/or
biostable layer or the hemocompatible layer.
[0078] The single layers as well as paclitaxel are preferably
deposited and/or implemented by dipping or spraying methods onto
and/or into the subjacent layer.
[0079] According to a preferred embodiment the biostable layer is
deposited on the surface of the medical device and completely or
incompletely covered with a hemocompatible layer which (preferably
covalently) is bound to the biostable layer.
[0080] Preferably the hemocompatible layer comprises heparin of
native origin of regioselectively synthesised derivatives of
different sulphation coefficients (sulphation degrees) and
acylation coefficients (acylation degrees) in the molecular weight
range of the pentasaccharide, which is responsible for the
antithrombotic activity, up to the standard molecular weight of the
purchasable heparin of 13 kD, heparansulphate and its derivatives,
oligo- and polysaccharides of the erythrocytic glycocalix,
desulphated and N-reacetylated heparin, N-carboxymethylated and/or
partially N-acetylated chitosan as well as mixtures of these
substances.
[0081] Subject of the invention are also medical devices which are
hemocompatibly coated according to one of the herein mentioned
methods. In the case of the medical devices it is preferably a
matter of stents.
[0082] The conventional stents, which can be coated according to
the inventive methods, consist of stainless steel, nitinol or other
metals and alloys or of synthetic polymers.
[0083] The stents according to invention are coated with an
according to the general formula 1 preferred covalently bound
hemocompatible layer. A second layer covers this first
hemocompatible layer completely or also incompletely. This second
layer conspires preferably paclitaxel. The hemocompatible coating
of a stent provides on the one hand the necessary blood
compatibility and reduces so the risk of thrombosis and also the
containment of inflammation reactions due to the intrusion and the
absence of a non-endogenous surface, and paclitaxel, which is
preferred to be distributed homogeneously over the total surface of
the stent provides that the covering of the stent surface with
cells, especially smooth muscle and endothelial cells, takes place
in a controlled way, so that the interplay of thrombosis reactions
and inflammation reactions, the release of growth factors,
proliferation and migration of cells during the recovery process
provides the generation of a novel "repaired" cell layer, which is
referred to as neointima.
[0084] Thus, the use of paclitaxel, covalently or/and adhesively
bound to the subjacent layer or/and covalently or/and adhesively
implemented in at least one layer, ensures, that this active agent
is set free continuously and in small doses, so that the population
of the stent surface by cells is not inhibited, however an
excessive population and the ingrowth of cells into the vessel
lumen is prevented. This combination of both effects awards the
ability to the stent according to invention, to grow rapidly into
the vessel wall and reduces both the risk of restenosis and the
risk of thrombosis. The release of paclitaxel spans about a period
from 1 to 12 months, preferably 1 to 3 months after
implantation.
[0085] Paclitaxel is preferred contained in a pharmaceutical active
concentration from 0.001-10 mg per cm.sup.2 stent surface,
preferred 0.01-5 mg and especially preferred 0.1-1.0 mg per
cm.sup.2 stent surface. Additional active agents can be contained
in similar concentration in the same or in the hemocompatible
layer.
[0086] The applied amounts of polymer are per layer between 0.01 mg
to 3 mg, preferred 0.20 mg to 1 mg and especially preferred between
0.2 mg to 0.5 mg. Suchlike coated stents release the active agent
paclitaxel controlled and continuously and hence are excellently
suitable for the prevention and reduction of restenosis.
[0087] These stents with a hemocompatible coating are generated, as
one provides stents and deposits preferred covalently one
hemocompatible layer according to the general formula, which masks
the surface of the implantate permanently after the release of the
active agent and so after the decay of the active agent
influence.
[0088] The preferred embodiment of the stents according to
invention shows a coating, which consists of at least two layers.
Thereby named as second layer is that layer, which is deposited on
the first layer. According to the two-layer design the first layer
conspires the hemocompatible layer, which is substantially
completely covered by a second layer, which consists of paclitaxel,
that is covalently and/or adhesively bound to the first layer.
[0089] The paclitaxel layer is dissolved slowly, so that the active
agent is released according to the velocity of the solution
process. The first hemocompatible layer guarantees the necessary
blood compatibility of the stent in the degree as the active agent
is removed. By the release of the active agent the adhesion of
cells is strongly reduced only for a certain period of time and an
aimed controlled adhesion is enabled, where the external layer had
been already widely degradated. Finally the hemocompatible layer
remains as athrombogeneous surface and masks the foreign surface in
such a way, that no life-threatening reaction can occur
anymore.
[0090] Suchlike stents can be generated by a method of the
hemocompatible coating of stents, to which the following principle
underlies:
[0091] a. providing of a stent
[0092] b. deposition of a preferred covalently bound hemocompatible
layer
[0093] c. Substantially complete covering of the hemocompatible
layer by a dipping or spraying method with the antiproliferative
active agent paclitaxel.
[0094] The stents according to invention solve both the problem of
acute thrombosis and the problem of neointima hyperplasia after a
stent implantation. In addition the inventive stents are especially
well suited, because of their coating for the continuous release of
one or more antiproliferative, immuno-suppressive active agents.
Due to this capability of the aimed continuous active agent release
in a required amount the inventively coated stents prevent the
danger of restenosis almost completely.
[0095] The natural and/or artificial surfaces which had been coated
according to the above described method with a hemocompatible layer
of aforesaid polysaccharides, are suitable especially as implants
resp. organ replacement parts, that are in direct contact with the
blood circuit and blood, preferably in the form of stents in
combination with an antiproliferative active agent, preferably
paclitaxel, for the prevention of restenosis.
[0096] The inventively coated medical devices are suited especially
but not only for the direct and permanent blood contact, but show
surprisingly also the characteristic to reduce or even to prevent
the adhesion of proteins onto suchlike coated surfaces. The
adhesion of plasma proteins on foreign surfaces which come in
contact with blood is an essential and initial step for the further
events concerning the recognition and the implementing action of
the blood system.
[0097] This is for example important in the in vitro diagnostics
from body fluids. Thus the deposition of the inventive coating
prevents or at least reduces for example the unspecific adhesion of
proteins on micro-titer plates or other support mediums which are
used for diagnostic detection methods, that disturb the generally
sensitive test reactions and can lead to a falsification of the
analysis result.
[0098] By use of the coating according to invention on adsorption
media or chromatography media the unspecific adhesion of proteins
is also prevented or reduced, whereby better separations can be
achieved and products of greater purity can be generated.
DESCRIPTION OF FIGURES
[0099] FIG. 1 shows a tetrasaccharide unit of a heparin or
heparansulphate with statistic distribution of the sulphate groups
and a sulphation coefficient of 2 per disaccharide unit as it is
typical for heparin (FIG. 1a). For comparison of the structural
similarities FIG. 1b shows an example of a compound according to
the general formula in the description.
[0100] FIG. 2 shows the influence of an into a PVC-tube expanded,
surface modified stainless steel coronary stent on the platelet
loss (PLT-loss).
[0101] An uncoated stainless steel coronary stent was measured as
reference. As zero value the level of the platelet loss in case of
the PVC-tube without stainless steel coronary stent was set.
[0102] Thereby SH1 is a with heparin covalently coated stent, SH2
is a with chondroitinsulphate coated stent; SH3 is a stent coated
with polysaccharides gained from the erythrocytic glycocalix and
SH4 is a with Ac-heparin covalently coated stainless steel coronary
stent.
[0103] FIG. 3 shows a schematic presentation of the restenosis rate
of with completely desulphated and N-reacetylated heparin
(Ac-heparin) covalently coated stents and with oligo- and
polysaccharides of the erythrocytic glycocalix (polysacch. of
erythro. glycoc.) coated stents in comparison to the uncoated stent
and with polyacrylic acid (PAS) coated stents after 4 weeks of
implantation time in pork.
[0104] FIG. 4 quantitative coronary angiography:
[0105] Images of the cross sections through the stent containing
vessel-segment of one with Ac-heparin coated stent (a.) and as
comparison of one uncoated (unco. or bare) stent (b.). After four
weeks in the animal experiment (pork) a clear difference in the
thicknesses of the formed neointimas can be observed.
[0106] FIG. 5 elution plot of paclitaxel from the stent (without
support medium).
EXAMPLES
Example 1
[0107] Synthesis of Desulphated Reacetylated Heparin:
[0108] 100 ml amberlite IR-122 cation exchange resin were added
into a column of 2 cm diameter, with 400 ml 3M HCl in the
H.sup.+-form converted and rinsed with distilled water, until the
eluate was free of chloride and pH neutral. 1 g sodium-heparin was
dissolved in 10 ml water, added onto the cation exchange column and
eluted with 400 ml of water. The eluate was added dropvise into a
receiver with 0.7 g pyridine and afterwards titrated with pyridine
to pH 6 and freeze-dried.
[0109] 0.9 g heparin-pyridinium-salt were added in a round flask
with a reflux condenser with 90 ml of a 6/3/1 mixture of
DMSO/1,4-dioxan/methano- l (v/v/v) and heated for 24 hours to
90.degree. C. Then 823 mg pyridinium chloride were added and heated
additional 70 hours to 90.degree. C. Afterwards it was diluted with
100 ml of water and titrated with dilute sodium hyrdoxide to pH 9.
The desulphated heparin was dialyzed contra water and
freeze-dried.
[0110] 100 mg of the desulphated heparin were solved in 10 ml of
water, cooled to 0.degree. C. and added with 1.5 ml methanol under
stirring. To this solution were added 4 ml dowex 1.times.4 anion
exchange resin in the OH.sup.--form and afterwards 150 .mu.l of
acetic anhydride and stirred for 2 hours at 4.degree. C. Then the
resin was removed by filtration and the solution was dialyzed
contra water and freeze-dried.
Example 2
[0111] Synthesis of Desulphated N-Propionylated Heparin:
[0112] 100 ml amberlite IR-122 cation exchange resin were added
into a column of 2 cm diameter, with 400 ml 3M HCl in the
H.sup.+-form converted and rinsed with distilled water, until the
eluate was free of chloride and pH neutral. 1 g sodium-heparin was
dissolved in 10 ml water, added onto the cation exchange column and
eluted with 400 ml of water. The eluate was added dropvise into a
receiver with 0.7 g pyridine and afterwards titrated with pyridine
to pH 6 and freeze-dried.
[0113] 0.9 g heparin-pyridinium-salt were added in a round flask
with a reflux condenser with 90 ml of a 6/3/1 mixture of
DMSO/1,4-dioxan/methano- l (v/v/v) and heated for 24 hours to
90.degree. C. Then 823 mg pyridiniumchloride were added and heated
additional 70 hours to 90.degree. C. Afterwards it was diluted with
100 ml of water and titrated with dilute sodium hydroxide to pH 9.
The desulphated heparin was dialyzed contra water and
freeze-dried.
[0114] 100 mg of the desulphated heparin were solved in 10 ml of
water, cooled to 0.degree. C. and added with 1.5 ml methanol under
stirring. To this solution were added 4 ml dowex 1.times.4 anion
exchange resin in the OH.sup.--form and afterwards 192 .mu.l of
propionic anhydride and stirred for 2 hours at 4.degree. C. Then
the resin was removed by filtration and the solution was dialyzed
contra water and freeze-dried.
Example 3
[0115] Hemocompatibility Measurements of Compounds According to the
General Formula 1 by ISO 10933-4 (In Vitro Measurements):
[0116] For the measurement of the hemocompatibility of the
compounds according to formula 1 cellulose membranes, silicon tubes
and stainless steel stents were covalently coated with a compound
according to formula 1 and tested contra heparin as well as contra
the corresponding, in the single tests utilised uncoated material
surfaces.
[0117] 3.1. Cellulose Membranes (Cuprophan) Coated with
Desulphated, Reacetylated Heparin (Ac-Heparin)
[0118] For the examination of the coagulatory physiologic
interactions between citrated whole blood and the Ac-heparin-resp.
heparin-coated cuprophan membranes the open perfusion system of the
Sakariassen-modified Baumgartner-chamber is used [Sakariassen K. S.
et al.; J. Lab. Clin. Med. 102: 522-535 (1983)]. The chamber is
composed of four building parts plus conical nipples and threaded
joints and is manufactured of polymethylmethacrylate and allows the
parallel investigation of two modified membranes, so that in every
run a statistic coverage is included. The construction of this
chamber permits quasi-laminar perfusion conditions.
[0119] After 5 minutes of perfusion at 37.degree. C. the membranes
are extracted and after fixation of the adherent platelets the
platelet occupancy is measured. The respective results are set into
relation to the highly thrombogeneous subendothelial matrix as
negative standard with a 100% platelet occupancy. The adhesion of
the platelets takes place secondary before the formation of the
plasma protein layer on the foreign material. The plasma protein
fibrinogen acts as cofactor of the platelet aggregation. The such
induced activation of the platelets results in the bonding of
several coagulation associated plasma proteins, as e.g.
vitronectin, fibronectin and von Willebrand-factor on the platelet
surface. By their influence finally the irreversible aggregation of
the platelets occurs.
[0120] The platelet occupancy presents because of the described
interactions an accepted quantum for the thrombogenity of surfaces
in case of the foreign surface contact of blood. From this fact the
consequence arises: the lower the platelet occupancy is on the
perfunded surface the higher is the hemocompatibility of the
examined surface to be judged.
[0121] The results of the examined heparin-coated and
Ac-heparin-coated membranes show clearly the improvement of the
hemocompatibility of the foreign surface through the coating with
Ac-heparin. Heparin-coated membranes show a 45-65% platelet
occupancy, whilst Ac-heparin-coated surfaces show values from 0-5%
(reference to subendothelial matrix with 100% platelet
occupancy).
[0122] The adhesion of the platelets on the Ac-heparinated surface
is extremely aggravated due to the absent, for the activation of
platelets essential plasma proteins. Unlike to this the
heparin-coated surface with the immediately incipient plasma
protein adsorption offers optimal preconditions for activation,
deposition and aggregation of platelets, and ultimately the blood
reacts with the corresponding defense mechanisms to the inserted
foreign surface. Ac-heparin fulfills by far superior than heparin
the requirements to the hemocompatibility of the foreign
surface.
[0123] The interaction of plasma protein adsorption and platelet
occupancy as direct quantum for the thrombogenity of a surface, in
dependence of the to the blood offered coating, is made clear
especially well by this in-vitro test. Thus the utilisation of
covalently bound heparin as antithrombotic operant surface is only
strongly limited or not possible at all. The interactions of
immobilised heparin with blood revert themselves here into the
undesired opposite--the heparin-coated surface gets
thrombogeneous.
[0124] Obviously the outstanding importance of heparin as an
antithrombotic is not transferable to covalently immobilised
heparin. In the systemic application in dissolved form it can fully
unfold its properties. But if heparin is not covalently
immobilised, its antithrombotic properties, if at all, is only
short-lived. Different is the Ac-heparin ("No-affinity"-heparin),
that due to the desulphation and N-reacetylation in fact totally
loses the active antithrombotic properties of the initial molecule,
but acquires in return distinctive athrombogeneous properties, that
are demonstrably founded in the passivity versus antithrombin III
and the missing affinity towards coagulation initiating processes
and remain after covalent bonding.
[0125] Thereby Ac-heparin and thus the compounds of the general
formula 1 in total are optimally suitable for the camouflage of
foreign surfaces in contact with the coagulation system.
[0126] 3.2. Immobilisation on Silicone
[0127] Through a 1 m long silicon tube with 3 mm inside diameter
100 ml of a mixture of ethanol/water 1/1 (v/v) was pumped in a
circular motion for 30 minutes at 40.degree. C. Then 2 ml
3-(triethoxysilyl)-propylamine were added and pumped in a circular
motion for additional 15 hours at 40.degree. C. Afterwards it was
rinsed in each case for 2 hours with 100 ml ethanol/water and 100
ml water.
[0128] 3 mg of the deacetylated and reacetylated heparin
(Ac-heparin) were dissolved at 4.degree. C. in 30 ml 0.1 M
MES-buffer pH 4.75 and mixed with 30 mg CME-CDI
(N-cyclohexyl-N'-(2-morpholinoethyl)carbod
iimidemethyl-p-toluenesulphonate). This solution was pumped in a
circular motion for 15 hours at 4.degree. C. through the tube.
Afterwards it was rinsed with water, 4 M NaCl solution and water in
each case for 2 hours.
[0129] 3.3 Determination of the Platelet Number (EN30993-4)
[0130] In a 1 m long silicone tube with 3 mm inside diameter two 2
cm long formfitting glass tubes were placed. Then the tube was
closed with a shrinkable tubing to a circle and filled under
exclusion of air via syringes with a 0.154 M NaCl solution. In
doing so one syringe was used to fill in the solution and the other
syringe was used to remove the air. The solution was exchanged
under exclusion of air (bleb-free) with the two syringes against
citrated whole blood of a healthy test person. Then the recess
holes of the syringes were closed by pushing the glass tubes over
them and the tube was clamped taut into a dialysis pump. The blood
was pumped for 10 minutes with a flow rate of 150 ml/min. The
platelet content of the blood was measured before and after the
perfusion with a coulter counter. For uncoated silicone tubes the
platelet loss was of 10%. In contrast to it the loss was in silicon
tubes, which were coated according to example 5.2, in average at 0%
(number of experiments: n=3).
[0131] Also in this dynamic test system it is shown, that the
activation of platelets on an Ac-heparin coated surface is reduced.
Simultaneously it can be recorded, that the immobilisation of
heparin executes a negative effect on the hemocompatibility of the
utilised surface. Against it Ac-heparin shows, in accordance to its
passive nature, no effects in contact with the platelets.
[0132] 3.4 Whole Blood Experiments on 316 LVM Stainless Steel
Coronary Stents
[0133] In line with the biocompatibility experiments 31 mm long 316
LVM stainless steel stents were covalently coated with Ac-heparin.
In case of a total surface of 2 cm.sup.2 and a occupancy
coefficient of about 20 pm/cm.sup.2 stent surface the charging of
such a stent is about 0.35 .mu.g Ac-heparin. As comparison: in case
of thrombosis prophylaxis the usual daily application rate of
heparin is in contrast 20-30 mg and thus would correspond to the at
least 60.000 times the value.
[0134] These experiments were carried out with the established
hemodynamic Chandler loop-system [A. Henseler, B. Oedekoven, C.
Andersson, K. Mottaghy; KARDIOTECHNIK 3 (1999)]. Coated and
uncoated stents were expanded and tested in PVC tubes (medical
grade PVC) with 600 mm length and 4 mm inside diameter. The results
of these experiments confirm the according to the silicone tubes
discussed experiments. The initially to the stent attributed
platelet loss in the perfusate of 50% is reduced by the refinement
of the stent surface with Ac-heparin by more than 80%.
[0135] The influence of in the tube expanded, surface modified
coronary stents to the platelet loss is evaluated in further
Chandler tests during a 45 minute whole blood perfusion. For this
primarily the stent-free PVC tube is analysed, the outcome of this
is the zero value. The empty tube shows an average platelet loss of
27.4% regarding to the donor blood at a standard aberration of
solely 3.6%. This base value underlied different surface modified
stents are expanded in the PVC tubes and are analysed under
analogous conditions on the by them caused platelet loss. It occurs
also in this case, that the stent covered surface, which solely
accounts for about 0.84% of the total test surface, causes a
significant and reproducable effect on the platelet content.
According to the empty tube (base value) the analysis of the
polished, chemically not surface coated stent yields an additional
average platelet loss of 22.7%. Therewith causes this compared to
the PVC empty tube less than 1% measurable foreign surface an
approximately comparable platelet loss. A direct result is that the
medicinal stainless steel 316 LVM used as stent material induces an
about 100 times stronger platelet damage compared to a medical
grade PVC surface, although this test surface only accounts for
0.84% of the total surface.
[0136] The analysed surface coatings on the stainless steel
coronary stents show to be able to reduce very clearly the enormous
dimension of the stent induced platelet damage (see FIG. 2). As
most effective proved with 81.5% the Ac-heparin (SH4).
[0137] If the effects of the Ac-heparin-coated stents on the
platelet loss are considered, then good congruent values result.
The correlation of the platelet loss in the perfusate resp. the
adhesion of the platelets to the offered surfaces show the
reliability of the measurements.
[0138] 3.4.1 Covalent Hemocompatible Coating of Stents
[0139] Not expanded stents of medicinal stainless steel LVM 316
were degreased in the ultrasonic bath for 15 minutes with acetone
and ethanol and dried at 100.degree. C. in the drying closet. Then
they were dipped for 5 minutes into a 2% solution of
3-aminopropyltriethoxysilane in a mixture of ethanol/water (50/50:
(v/v)) and then dried for 5 minutes at 100.degree. C. Afterwards
the stents were washed with demineralised water over night.
[0140] 3 mg desulphated and reacetylated heparin were dissolved at
4.degree. C. in 30 ml 0.1 M MES-buffer
(2-(N-morpholino)ethanesulphonic acid) pH 4.75 and mixed with 30 mg
N-cyclohexyl-N'-(2-morpholinoethyl)car-
bodiimide-methyl-p-toluenesulphonate. In this solution 10 stents
were stirred for 15 hours at 4.degree. C. Then they were rinsed
with water, 4 M NaCl solution and water in each case for 2
hours.
[0141] 3.4.2 Determination of the Glucosamine Content of the Coated
Stents by HPLC
[0142] Hydrolysis: the coated stents are given in small hydrolysis
tubes and are abandoned with 3 ml 3 M HCl for exactly one minute at
room temperature. The metal probes are removed and the tubes are
incubated after sealing for 16 hours in the drying closet at
100.degree. C. Then they are allowed to cool down, evaporated three
times until dryness and taken up in 1 ml de-gased and filtered
water and measured contra an also hydrolysated standard in the
HPLC:
2 desulphat. + desulphat. + desulphat. + sample reacet. heparin
area reacet. heparin reacet. heparin stent area [g/sample]
[cm.sup.2] [g/cm.sup.2] [pmol/cm.sup.2] 1 129.021 2.70647E - 07
0.74 3.65739E - 07 41.92 2 125.615 2.63502E - 07 0.74 3.56084E - 07
40.82 3 98.244 1.93072E - 07 0.74 2.60908E - 07 29.91 4 105.455
2.07243E - 07 0.74 2.80058E - 07 32.10 5 119.061 2.33982E - 07 0.74
3.16192E - 07 36.24 6 129.202 2.53911E - 07 0.74 3.43124E - 07
39.33 7 125.766 2.53957E - 07 0.74 3.43185E - 07 39.34
Example 4
[0143] In Vivo Examination of Coated Coronary Stents (FIG. 5)
[0144] 4.1. In Vivo Examinations of Coronary Stents Coated with
Ac-Heparin
[0145] Due to the data on hemocompatibility, which Ac-heparin
yielded in the in-vitro experiments, the suitability of the
Ac-heparin surface as athrombogeneous coating of metal stents was
discussed in vivo (animal experiment).
[0146] The target of the experiments was primarily to evaluate the
influence of the Ac-heparin coating on the stent induced vessel
reaction. Besides the registration of possible thrombotic events
the relevant parameters for restenotic processes like neointima
area, vessel lumen and stenosis degree were recorded. For the
examinations 6-9 month old domestic porks were used, one for the
validation of stents for a long time established and approved
animal model.
[0147] As expected in these experiments neither acute, subacute nor
late acute thrombotic events were registered, what may be assessed
as proof for the athrombogeneous properties of Ac-heparin.
[0148] After four weeks the animals were dispatched (euthanized),
the stented coronary artery segments extracted and
histomorphometrically analysed. Indications to a possible acute or
subchronic toxicity, allergisation reactions or ulterior
irritations as consequence of the implantation of Ac-heparin coated
stents are not observed during the complete experimental phase,
especially in the histologic examination. During the stent
implantation as well as the follow-up coronary-angiographic data
sets were ascertained, which permit an interpretation with regard
to the vessel reaction to the stent implantation.
[0149] The difference between the uncoated control stent and the
Ac-heparin coated stent is unambiguous. The generation of a
distinct neointima layer is in case of the uncoated control stent
very well observable. Already after four weeks the proliferation
promotional effect of the uncoated stent surface on the surrounding
tissue occurs in such a degree, that ultimately the danger of the
vessel occlusion in the stent area is given.
[0150] Contrary in case of the Ac-heparin coated stents a clearly
thinner neointima layer is observed, which argues for a well
modulated ingrowth of the stent under maintenance of a wide, free
vessel lumen.
[0151] The detailed histomorphometric and coronary angiographic
data substantiate this conclusion, as it can be observed
congruently, that via the Ac-heparin coating (SH4) the neointima
hyperplasia ("restenosis") was repressed by about 17-20% in
comparison to the uncoated control stent. This result is unexpected
and remarkably at the same time. Surely it is not demanded of an
athrombogeneous surface to have an influence also on processes that
lead to a neointima hyperplasia, i.e. to prevent restenoses, in
addition to the preposition of hemocompatible characteristics.
[0152] On the one hand with a dense, permanent occupancy of the
stent surface with Ac-heparin a direct cell contact to the metal
surface is prevented. As in technical literature the emission of
certain metal ions into the implant close tissue is discussed as
one probable reason of restenosis, an anti-restenoic potency could
be founded by one of the coating caused prevention of a direct
metal contact.
[0153] On the other hand such a positive side effect is plausible,
because on a passive, athrombogenenous stent surface with the
absence of a platelet aggregation also the proliferative effects of
the thereby released growth factors are to be missed. Thus an
important, starting from the lumen side, stimulus of the neointimal
proliferation is omitted.
Example 5
[0154] Coating of the Stents with Taxol by the Spraying Method
[0155] The via example 1 and example 2 prepared not expanded stents
are balanced and horizontally hung onto a thin metal bar (d=0.2
mm), which is stuck on the rotation axis of the rotation and feed
equipment and rotates with 28 r/min. The stents are fixed in that
way, that the inside of the stents does not touch the bar. At a
feeding amplitude of 2.2 cm and a feeding velocity of 4 cm/s and a
distance of 6 cm between stent and spray valve the stent is sprayed
with the particular spray solution. After the drying (about 15
minutes) at room temperature and proximate in the fume hood over
night it is balanced again.
[0156] Fabrication of the spray solution: 44 mg taxol are dissolved
in 6 g chloroform.
3 stent no. before coating after coating coating mass 1 0.0194 g
0.0197 g 0.30 m
Example 6
[0157] Determination of the Elution Behaviour in PBS-Buffer
[0158] Per stent in a sufficient small flask 2 ml PBS-buffer is
added, sealed with para-film and incubated in the drying closet at
37.degree. C. After expiry of the chosen time intervals in each
case the excess solution is depipetted and its UV absorption at 306
nm is measured.
* * * * *