U.S. patent application number 11/131891 was filed with the patent office on 2005-12-08 for tetracalcium phosphate (ttcp) having calcium phosphate whisker on surface.
This patent application is currently assigned to Calcitec, Inc.. Invention is credited to Chen, Wen-Cheng, Ju, Chien-Ping, Lin, Jiin-Huey Chern.
Application Number | 20050268820 11/131891 |
Document ID | / |
Family ID | 33313093 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050268820 |
Kind Code |
A1 |
Lin, Jiin-Huey Chern ; et
al. |
December 8, 2005 |
Tetracalcium phosphate (TTCP) having calcium phosphate whisker on
surface
Abstract
A tetracalcium phosphate (TTCP) particle for use in preparing a
fast-setting, bioresorbable calcium phosphate cement is disclosed.
The TTCP particle has a basic calcium phosphate whiskers or fine
crystals on a surface thereof, the basic calcium phosphate whiskers
or fine crystals having a Ca/P molar ratio greater than 1.33, and
having a length up to about 5000 nm and a width up to about 500
nm.
Inventors: |
Lin, Jiin-Huey Chern;
(Winnetka, IL) ; Ju, Chien-Ping; (Carbondale,
IL) ; Chen, Wen-Cheng; (Tainan Hsien, TW) |
Correspondence
Address: |
MEYERTONS, HOOD, KIVLIN, KOWERT & GOETZEL, P.C.
P.O. BOX 398
AUSTIN
TX
78767-0398
US
|
Assignee: |
Calcitec, Inc.
|
Family ID: |
33313093 |
Appl. No.: |
11/131891 |
Filed: |
May 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11131891 |
May 18, 2005 |
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10607023 |
Jun 27, 2003 |
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10607023 |
Jun 27, 2003 |
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10414582 |
Apr 16, 2003 |
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10414582 |
Apr 16, 2003 |
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09615384 |
Jul 13, 2000 |
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Current U.S.
Class: |
106/690 |
Current CPC
Class: |
A61L 27/12 20130101;
C04B 2111/00836 20130101; C04B 28/344 20130101; C04B 28/344
20130101; A61L 24/02 20130101; C04B 2111/00086 20130101; C04B
28/344 20130101; Y10T 428/2991 20150115; C04B 12/02 20130101; A61L
27/50 20130101; C30B 29/62 20130101; C04B 2111/0025 20130101; Y10T
428/2993 20150115; A61L 24/001 20130101; C30B 7/00 20130101; C04B
28/346 20130101; C04B 28/344 20130101; C04B 2111/00206 20130101;
C30B 29/14 20130101; C04B 28/344 20130101; C04B 12/025 20130101;
C04B 14/383 20130101; C04B 20/008 20130101; C04B 22/064 20130101;
C04B 40/0259 20130101; C04B 12/025 20130101; C04B 22/064 20130101;
C04B 40/0082 20130101; C04B 22/126 20130101 |
Class at
Publication: |
106/690 |
International
Class: |
C04B 028/34; C04B
012/02 |
Claims
1-3. (canceled)
4. A method of making a calcium phosphate cement article
comprising: forming a paste by contacting tetracalcium phosphate
(TTCP) particles with a setting solution, wherein at least a
portion of the tetracalcium phosphate particles have whiskers or
crystals comprising basic calcium phosphate crystals on the surface
of the particles; placing the paste in a form; and allowing the
paste to at least partially harden in the form.
5. The method of claim 4, wherein the compressive strength of the
hardened calcium phosphate article is from about 18.6 MPa to about
48.8 MPa.
6. The method of claim 4, further comprising forming whiskers or
crystals comprising basic calcium phosphate crystals on the surface
of least a portion of the tetracalcium phosphate particles by
contacting the tetracalcium phosphate particles with a
whisker-inducing solution.
7. The method of claim 6, wherein the whisker-inducing solution
comprises an acid.
8. The method of claim 6, wherein the whisker-inducing solution
comprises a base.
9. The method of claim 6, wherein the whisker-inducing solution
comprises an organic solvent.
10. The method of claim 6, wherein the whisker-inducing solution
comprises substantially pure water.
11. The method of claim 6, wherein forming whiskers or crystals on
the surface of TTCP particles comprises heating the TTCP particles
to at least about 50.degree. C. after contacing the TTCP particles
with the whisker-inducing solution.
12. The method of claim 4, wherein the ratio of TTCP particles to
setting liquid is at least about 2.8 g/ml.
13. The method of claim 4, wherein the Ca/P molar ratio of the
calcium phosphate crystals on the surface of the particles is at
least about 1.33.
14. The method of claim 4, wherein the dimensions of the whiskers
or fine crystals are up to about 5000 nm long and up to about 500
nm wide.
15. The method of claim 4, further comprising removing the at least
partially hardened paste from the form and contacting the at least
partially hardened paste with an aqueous solution.
16. The method of claim 15, wherein the at least partially hardened
paste is contacted with the aqueous solution for a period of time
ranging from about 20 minutes to about 24 hours.
17. The method of claim 15, wherein the aqueous solution is Hank's
solution.
18. The method of claim 4, wherein the setting solution comprises a
basic solution.
19. The method of claim 4, wherein the setting solution comprises
phosphate ions.
20. The method of claim 4, wherein the setting solution comprises
(NH.sub.4).sub.2HPO.sub.4.
21. The method of claim 4, wherein the XRD profile of the hardened
calcium phosphate cement articles substantially resembles that
shown in FIG. 2c.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation-in-part
application of U.S. patent application Ser. No. 10/414,582, filed
Apr. 16, 2003, which is a continuation-in-part application of U.S.
patent application Ser. No. 09/615,384, filed Jul. 13, 2000, now
abandoned, which is a continuation-in-part application of U.S.
patent application Ser. No. 09/351,912, filed Jul. 14, 1999, now
U.S. Pat. No. 6,379,453B1. The above-listed applications are
commonly assigned with the present invention and the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a tetracalcium phosphate
(TTCP) for producing fast-setting, bioresorbable calcium phosphate
cements (CPC), and in particular, to a tetracalcium phosphate
having whiskers or fine crystals on the surface thereof for
producing fast-setting, bioresorbable CPC having a high initial
strength.
[0004] 2. Description of the Related Art
[0005] U.S. Pat. No. 6,379,453B1 which is commonly assigned with
the present invention discloses a process for producing a
fast-setting, bioresorbable calcium phosphate cement comprising the
following steps: obtaining a powder mixture from at least one
calcium phosphate selected from the group consisting of
Ca.sub.4(PO.sub.4).sub.2O, Ca(HPO.sub.4).sub.2H.sub.2O,
CaHPO.sub.4, Ca.sub.8H.sub.2(PO.sub.4).sub.6- .5H.sub.2O,
.alpha.--Ca.sub.3(PO4).sub.2, .beta.--Ca.sub.3(PO.sub.4).sub.2- ,
Ca.sub.2P.sub.2O.sub.7, Ca.sub.2H.sub.2P.sub.2O.sub.8, wherein the
molar ratio of Ca to P in the mixture is roughly between 1 and 2;
mixing the powder mixture in a phosphate-containing solution to
obtain a powder/solution mixture having a concentration of less
than 4 g powder mixture per ml solution; immediately heating the
powder/solution mixture to a temperature of roughly 50.degree.
C.-350.degree. C. to obtain a powder containing uniformly
distributed submicron-sized apatite crystals; and mixing the
apatite crystal-containing powder in a phosphate ion-containing
solution to obtain a fast-setting, bioresorbable calcium phosphate
cement.
SUMMARY OF THE INVENTION
[0006] An extensive study on the preparation of the fast-setting,
bioresorbable calcium phosphate cement disclosed in U.S. Pat. No.
6,379,453 B1 has been conducted by the same inventors and their
co-workers, and found that a fast-setting, bioresorbable CPC having
a high initial strength can be prepared from a unique calcium
phosphate, tetracalcium phosphate (Ca.sub.4(PO.sub.4).sub.2O, TTCP)
particle having basic whiskers or fine crystals on the surface
thereof, wherein said basic whiskers or fine crystals have a Ca/P
ratio greater than 1.33. Therefore an object of the invention is to
provide such a unique TTCP particle. Another object of the present
invention is to provide a process for preparing said unique TTCP
particle. A further object of the present invention is to provide a
fast-setting, bioresorbable CPC calcium phosphate cement prepared
from said unique TTCP particle.
[0007] The invention accomplishes the above object by providing a
tetracalcium phosphate (Ca.sub.4(PO.sub.4).sub.2O, TTCP) particle
having basic whiskers or fine crystals on the surface, basic
whiskers or fine crystals having a Ca/P ratio greater than 1.3, and
preferably greater than 1.35 and less than 4.0. Said whiskers or
fine crystals have a length up to about 5000 nm and a width up to
about 500 nm, and preferably, a length from about 1 nm to about
2000 nm and a width from about 1 nm to about 200 nm. Said basic
whiskers or fine crystals comprises TTCP as a major portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1a to 1c are related to microstructure and diffraction
pattern of calcium phosphate whiskers grown on TTCP surface
according to the present invention, wherein (a) bright field image
of whiskers; (b) electron diffraction pattern of whiskers; and (c)
interpretation of the diffraction pattern.
[0009] FIG. 2 shows XRD patterns, wherein (a) TTCP without whisker
treatment; (b) TTCP with whisker treatment in
(NH.sub.4).sub.2HPO.sub.4 for 5 minutes; and (c) CPC prepared from
whisker-treated TTCP powder immersed in Hanks' solution for 24
hours.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] A suitable method for preparing tetracalcium phosphate
(TTCP) particles having a basic calcium phosphate whiskers or fine
crystals on the surfaces of said TTCP particles of the present
invention, said basic calcium phosphate whiskers or fine crystals
having a Ca/P molar ratio greater than 1.33, comprises the
following steps:
[0011] (a) obtaining TTCP particles;
[0012] (b) mixing said TTCP particles with a whisker-inducing
solution, allowing basic calcium phosphate whiskers or fine
crystals having a Ca/P molar ratio greater than 1.33 to grow on the
surfaces of said TTCP particles; and
[0013] (c) drying the whisker/fine crystal-grown particles.
[0014] Optionally, at least one additive selected from the group
consisting of sodium phosphate (Na.sub.3PO.sub.4), disodium
hydrogen phosphate (Na.sub.2HPO.sub.4), sodium dihydrogen phosphate
(NaH.sub.2PO.sub.4), disodium hydrogen phosphate dodecahydrate
(Na.sub.2HPO.sub.4.12H.sub.2O), disodium hydrogen phosphate
heptahydrate (Na.sub.2HPO.sub.40.7H.sub.2O), sodium phosphate
dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), orthophosphoric acid
(H.sub.3PO.sub.4), calcium sulfate (CaSO.sub.4),
Ca.sub.4(PO.sub.4).sub.2O, CaHPO.sub.40.2H.sub.2O, CaHPO.sub.4,
Ca.sub.8H.sub.2(PO.sub.4).sub.6.5H.s- ub.2O,
.alpha.--Ca.sub.3(PO.sub.4).sub.2,
.beta.--Ca.sub.3(PO.sub.4).sub.2- , Ca.sub.2P.sub.2O.sub.7, and
Ca.sub.2H.sub.2P.sub.2O.sub.8, (NH.sub.4).sub.3PO.sub.4,
(NH.sub.4).sub.2HPO.sub.4, and (NH.sub.4)H.sub.2PO.sub.4 together
with said TTCP particles are mixed with the whisker-inducing
solution in step (b).
[0015] Optionally, step (c) comprises separating the
whisker-inducing solution and the TTCP particles, and heating the
separated TTCP particles to a temperature up to about 1000.degree.
C., preferably about 50 to 500.degree. C., to allow the basic
calcium phosphate whiskers or fine crystals to grow to a length up
to about 5000 nm and a width up to about 500 nm on the surfaces of
said TTCP particles.
[0016] The heating includes (but not limited to) the conventional
oven/furnace heating, resistance heating, infrared heating,
microwave heating, electron beam heating, ion beam heating, laser
beam heating and plasma heating. Preferably said heating is
conducted in vacuum, inert atmosphere or air atmosphere.
[0017] The whisker-inducing solution in step (b) may be an acidic
aqueous solution, a basic aqueous solution, an organic solvent or a
substantially pure water. The acidic aqueous solution may contain
at least one Ca or P source, or is free from Ca and P. The acidic
aqueous solution can be selected from the group consisting of
nitric acid (HNO.sub.3), hydrochloric acid (HCl), phosphoric acid
(H.sub.3PO.sub.4), carbonic acid (H.sub.2CO.sub.3), sodium
dihydrogen phosphate (NaH.sub.2PO.sub.4), sodium dihydrogen
phosphate monohydrate, sodium dihydrogen phosphate dihydrate,
potassium dihydrogen phosphate (KH.sub.2PO.sub.4), ammonium
dihydrogen phosphate (NH.sub.4H.sub.2PO.sub.4), malic acid, acetic
acid, lactic acid, citric acid, malonic acid, succinic acid,
glutaric acid, tartaric acid, oxalic acid and their mixture.
[0018] The basic aqueous solution for use as the whisker-inducing
solution in the method of the present invention may contain at
least one Ca or P source, or is substantially free from Ca and P.
The basic aqueous solution may be selected from the group
consisting of ammonia, ammonium hydroxide, alkali metal hydroxide,
alkali earth hydroxide, disodium hydrogen phosphate
(Na.sub.2HPO.sub.4), disodium hydrogen phosphate dodecahydrate,
disodium hydrogen phosphate heptahydrate, sodium phosphate
dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), dipotassium hydrogen
phosphate (K.sub.2HPO.sub.4), potassium phosphate tribasic
(K.sub.3PO.sub.4), diammonium hydrogen phosphate
((NH.sub.4).sub.2HPO.sub- .4), ammonium phosphate trihydrate
((NH.sub.4).sub.3PO.sub.4.3H.sub.2O), sodium bicarbonate
(NaHCO.sub.3), and their mixture.
[0019] The present invention also discloses a calcium phosphate
cement (CPC) powder comprising the TTCP particles of the present
invention.
[0020] The following examples are intended to demonstrate the
invention more fully without acting as a limitation upon its scope,
since numerous modifications and variations will be apparent to
those skilled in this art.
[0021] TTCP Preparation
[0022] The TTCP powder was fabricated in-house from the reaction of
dicalcium pyrophosphate (Ca.sub.2P.sub.2O.sub.7) (Sigma Chem. Co.,
St. Louis, Mo., USA) and calcium carbonate (CaCO.sub.3) (Katayama
Chem. Co., Tokyo, Japan) using the method suggested by Brown and
Epstein [Journal of Research of the National Bureau of Standards--A
Physics and Chemistry 6 (1965) 69A 12].
[0023] TEM Examination
[0024] A Hitachi Model-HF2000 200 kV field emission transmission
electron microscope (TEM) equipped with a Noran Vayager Model 1000
energy dispersive spectroscopy (EDS) system was used for the study.
The aperture size for microchemical analysis (Ca/P ratio) is 15
nm.
[0025] [NOTE: All "average" Ca/P ratios are averages of 10
measurements]
EXAMPLE 1
[0026] Whisker-Inducing Treatment of TTCP Particles Treated in
Phosphate-Containing Basic Solution
[0027] Ca.sub.4(PO.sub.4).sub.2O (TTCP) powder as synthesized was
sieved with a #325 mesh. The sieved powder has an average particle
size of about 10 .mu.m. An aqueous solution of diammonium hydrogen
phosphate was prepared by dissolving 20 mg of diammonium hydrogen
phosphate, (NH.sub.4).sub.2HPO.sub.4, in 40 ml deionized water. The
resulting solution had a pH value of 8.02. To the TTCP powder the
basic aqueous solution of diammonium hydrogen phosphate was added
according to the ratio of 1 gm TTCP/13 ml solution. The TTCP powder
was immersed in the basic aqueous solution for various periods of
time of 1, 5 and 10 minutes, filtered rapidly and washed with
deionized water, and filtered rapidly with a vacuum pump again. The
resulting powder cake was dried in an oven at 50.degree. C. The
dried powder was dispersed in ethanol with supersonication. A drop
of the dispersion was dripped on a single-side carbon sieve of #325
mesh having a diameter of 3 mm, and left dry to obtain a specimen
coated with a thin carbon film for electrical conductivity for TEM
examination.
[0028] Results:
[0029] (a) treated for 1 min: Whiskers grown on TTCP surface are
acidic (Ca/P<1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.0 and 1.3 with an average Ca/P ratio of
about 1.2. Majority of whiskers have lengths <200 nm and widths
<100 nm.
[0030] (b) treated for 5 min: Whiskers grown on TTCP surface are
basic (Ca/P>1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.4 and 1.9 with an average Ca/P ratio of
about 1.6. Majority of whiskers have lengths <200 nm and widths
<100 nm.
[0031] (c) treated for 10 min: Whiskers grown on TTCP surface are
basic (Ca/P>1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.4 and 3.8 with an average Ca/P ratio of
about 2.1. Majority of whiskers have lengths <300 nm and widths
<100 nm.
[0032] FIG. 1 represents a typical microstructure of the calcium
phosphate whiskers grown on TTCP surface under such condition. FIG.
1(a) is a bright-field image showing the whiskers are substantially
radial-oriented and the majority of which have lengths <300 nm
and widths <100 nm; FIG. 1(b) is a typical electron diffraction
pattern of such whiskers. The dotted-ring pattern is a direct
result of the diffraction of numerous nano-sized whiskers; FIG.
1(c) is the indexing/interpretation of the diffraction pattern,
which clearly shows that every ring matches a certain
crystallographic plane of TTCP phase, indicating the whiskers have
a TTCP crystal structure. The absence of HA (100) ring (d=0.817 nm)
in the diffraction pattern excludes the possibility for the
whiskers to have an apatite crystal structure under this whisker
treatment conditions.
[0033] The results show that Ca/P ratio is sensitive to the process
condition (in this case, treating time).
EXAMPLE 2
[0034] Whisker-Inducing Treatment of TTCP Particles Treated in
Phosphate-Containing Acidic Solution
[0035] The procedures of Example 1 were repeated except that the
basic aqueous solution was changed to IM phosphorus acid aqueous
solution having a pH of 0.8 and the immersion time was changed to
30 seconds.
[0036] Results:
[0037] Whiskers grown on TTCP surface are basic (Ca/P>1.33) in
nature. The EDS-determined Ca/P molar ratios are between about 1.4
and about 3.7 with an average Ca/P ratio of about 2.0. Majority of
whiskers have lengths <1000 nm and widths <200 nm.
EXAMPLE 3
[0038] Whisker-Inducing Treatment of TTCP Particles Treated in
Phosphate-Free Basic Solution
[0039] The procedures of Example 1 were repeated except that the
basic aqueous solution was changed to a basic aqueous NaOH solution
having a pH of 10.66 and the immersion time was changed to 30
seconds and 24 hours.
[0040] Results:
[0041] (a) treated for 30 sec: No whisker was observed on TTCP
surface.
[0042] (b) treated for 24 h: Whiskers grown on TTCP surface are
basic (Ca/P>1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.5 and about 3.4 with an average Ca/P
ratio of about 2.0. Majority of whiskers have lengths <1000 nm
and widths <300 nm.
EXAMPLE 4
[0043] Whisker-Inducing Treatment of TTCP Particles Treated in
Phosphate-Free Acidic Solution
[0044] The procedures of Example 1 were repeated except that the
basic aqueous solution was changed to 0.16M HCl aqueous solution
having a pH of 0.8 and the immersion time was changed to 30
seconds, 10 minutes, one hour and 24 hours.
[0045] Results:
[0046] (a) treated for 30 sec: No whisker was observed on TTCP
surface.
[0047] (b) treated for 10 min: Whiskers grown on TTCP surface are
basic (Ca/P>1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.4 and about 1.9 with an average Ca/P
ratio of about 1.6. Majority of whiskers have lengths <200 nm
and widths <100 nm.
[0048] (c) treated for 1 h: Whiskers grown on TTCP surface are
basic (Ca/P>1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.4 and about 1.9 with an average Ca/P
ratio of about 1.6. Majority of whiskers have lengths <300 nm
and widths <100 nm.
[0049] (d) treated for 24 h: Whiskers grown on TTCP surface are
basic (Ca/P>1.33) in nature. The EDS-determined Ca/P molar
ratios are between about 1.5 and about 2.7 with an average Ca/P
ratio of about 1.8. Majority of whiskers have lengths <1000 nm
and widths <300 nm. The diffraction patterns indicate these
whiskers have a TTCP crystal structure.
EXAMPLE 5
[0050] Compressive Strength of CPC Prepared from the Whisker-Grown
TTCP Particles
[0051] Ca.sub.4(PO.sub.4).sub.2O (TTCP) powder as synthesized was
sieved with a #325 mesh and has an average particle size of about
10 .mu.m. To the sieved TTCP powder a HCl aqueous solution having a
pH of 0.8 was added according to the ratio of 1 gm TTCP/13 ml
solution. The sieved TTCP powder was immersed in the HCl solution
for 12 hours, filtered rapidly and washed with deionized water, and
filtered rapidly with a vacuum pump again. The resulting powder
cake was dried in an oven at 50.degree. C. The dried powder was
divided into halves, ground for 20 minutes and 120 minutes
separately, and combined. A setting solution of diammonium hydrogen
phosphate was prepared by dissolving 20 mg of diammonium hydrogen
phosphate, (NH.sub.4).sub.2HPO.sub.4, in 40 ml deionized water. 100
g of the mixed ground powder and 35 ml of the setting solution were
well mixed to form a paste, which was then filled in molds to form
specimens for compression test. The specimens were removed from the
molds 15 minutes after the mixing, and soaked in a Hanks' solution.
The soaked specimens were removed from the Hanks' solution at
various periods of soaking time, and were immediately subjected to
the compression test without drying. The compression test was
conducted according to a method commonly used in the literature.
The cylindrical samples have a diameter of 6 mm and a length of 12
mm.
[0052] Results: compressive strength is 27.4 MPa for the soaking
time of 20 minutes, and 48 MPa for one-day soaking time.
EXAMPLE 6
[0053] Compressive Strength of CPC Prepared from the Whisker-Grown
TTCP Particles
[0054] Ca.sub.4(PO.sub.4).sub.2O (TTCP) powder as synthesized was
sieved with a #325 mesh and has an average particle size of about
10 .mu.m. To the sieved TTCP powder the aqueous
(NH.sub.4).sub.2HPO.sub.4 solution prepared in Example 1 was added
according to the ratio of 1 gm TTCP/13 ml solution. The sieved TTCP
powder was immersed in the (NH.sub.4).sub.2HPO.sub.4 solution for 5
minutes, filtered rapidly and washed with deionized water, and
filtered rapidly with a vacuum pump again. The resulting powder
cake was dried in an oven at 50.degree. C. The dried powder was
ground 120 minutes to obtain a powder A. The procedures in Example
5 were repeated to obtain a powder B except that the dried powder
was ground only for a period of 300 minutes. A mixed powder of A
and B in a ratio of 1:1 ratio was subjected to the compression
tests following the procedures recited in Example 5.
[0055] Results: compressive strength is 26 MPa for the soaking time
of 20 minutes, and 42.8 MPa for one-day soaking time.
EXAMPLE 7
[0056] Compressive Strength of CPC Prepared from the Whisker-Grown
TTCP Particles
[0057] The procedures in Example 5 were repeated except that the
HCl solution was changed to the aqueous (NH.sub.4).sub.2HPO.sub.4
solution prepared in Example 1 and the soaking time was changed to
5 minutes.
[0058] Results: compressive strength is 18.6 MPa for the soaking
time of 20 minutes, and 48.8 MPa for one-day soaking time.
EXAMPLE 8
[0059] Compressive Strength of CPC Prepared from the Whisker-Grown
TTCP Particles
[0060] Ca.sub.4(PO.sub.4).sub.2O (TTCP) powder as synthesized was
sieved with a #325 mesh and ground for two hours. To the ground
TTCP powder the powder B prepared in Example 5 was added and mixed
in a ratio of 1:1. The resulting mixed powder was subjected to the
compression tests following the procedures recited in Example
5.
[0061] Results: compressive strength is 19.7 MPa for the soaking
time of 20 minutes, and 43.6 MPa for one-day soaking time.
EXAMPLE 9
[0062] X-Ray Diffraction of Whisker-Treated TTCP Powder and
Immersed CPC Prepared from such TTCP
[0063] A TTCP powder was whisker-treated for 5 minutes according to
the process described in Example 1. X-ray diffraction (XRD) was
performed using an X-ray diffractometer (Rigaku D-max IIIV, Tokyo,
Japan) with Ni-filtered CuK .alpha. radiation operated at 30 kV and
20 mA at a scanning speed of 1 degree/min. The phases were
identified by matching each characteristic XRD peak with that
compiled in JCPDS files.
[0064] Results: As indicated in FIG. 2, the XRD pattern of the
whisker-treated TTCP powder (b) is substantially identical to that
of TTCP as synthesized (a). The perfect match of every XRD peak
position (diffraction angle) with the JCPDS data indicates that
there is no additional phase formed during the whisker treatment.
0.7 g whisker-treated TTCP powder with 0.25 ml setting solution to
form a CPC paste. The setting solution was prepared by dissolving
20 g (NH.sub.4).sub.2HPO.sub.4 in 40 ml deionized water. The CPC
paste was filled in a cylindrical mold (12 mm in height and 6 mm in
diameter), allowing hardening of the paste to occur within the
mold. After 15 minutes the hardened CPC sample was removed from the
mold and immersed in a 37.degree. C. Hanks' solution for 24 hours.
After removing from the Hanks' solution and drying, the CPC sample
was ready for XRD analysis. After immersion in Hanks' solution for
24 hours, the XRD pattern (c) of the CPC shows a large amount of HA
phase which has replaced TTCP as the dominant phase. At this time
only a small amount of TTCP remains. The result suggests that the
CPC prepared from the whisker-treated TTCP powder of the invention
can quickly transform into HA (the major component of human bone),
once implanted.
[0065] Although a "basic" whisker can be grown on TTCP surface by
immersion in a variety of solutions, the process should be
carefully controlled. For example, when the solution contains a P
source in the absence of Ca, the immersion time should be long
enough to grow a basic whisker (an "acidic" whisker is grown at the
early stage due to the excess P ions in the solution). Yet the
immersion time should not be too long either to avoid the basic
whisker's growing too large (should be within our claimed range),
that can largely deteriorate the CPC properties.
[0066] On the other hand, when the solution does not contain P
(e.g., HCl), acidic whisker is never grown on the surface of TTCP
particles. All the observed whiskers on TTCP particles at all
stages are basic in nature.
[0067] In addition to Ca/P ratio, the growth rate of a basic
whisker is also sensitive to such process parameters as the type,
pH, temperature and ion concentrations of the solution, to name a
few.
[0068] Although the present invention has been described with
reference to specific details of certain embodiments thereof, it is
not intended that such details should be regarded as limitations
upon the scope of the invention except as and to the extent that
they are included in the accompanying claims. Many modifications
and variations are possible in light of the above disclosure.
* * * * *