Laryngeal Implant

Abstract

This invention relates to an implant for surgical purposes and which is especially useful for the operative treatment of afflicted vocal cords, as well as to the method for its production. The implant is made from water-swellable and physiologically inert material, such as a synthetic cross-linked hydrophilic gel, and has in a dry state, when it is ready for use in an operation, the shape of a straight or bent stick provided with a sharp, pointed tip. The implant body except the tip may contain physiologically inert plasticizers.

Description

BACKGROUND OF THE INVENTION

Vocal cords afficted with atropy or with a unilateral disorder of motion such as paralysis of the recurrent nerve cannot be used to any normal extent when treated by known methods. To improve the voice and reduce the subjective difficulties, such as hoarseness, injections of paraffin, polytetrafluorethylene or silicone polymer particles emulsified in glycerol, or of the cartilage of the nasal septum, which was surgically removed, crushed and emulsified in the physiologic saline, have been employed. All these method have a distinct disadvantage that is it is impossible to determine by the injection precisely in which direction the injected material shall penetrate the vocal cords. The aforementioned materials, such as paraffin and the others move inside the vocal cords over a period of time and eventually escape into the space below the glottis. The crushed cartilage, on the other hand, is absorbed in the course of time, so that the success of all the aforesaid operations is only temporary and the shape of the vocal cords after the operation cannot be determined in advance.

In the treatment of paralysis of the recurrent nerve bleeding is sometimes used as an operative procedure, necessitating an incision and subsequent scar on the throat. The larynx is opened from outside in this operation, as a rule by a cut between the thyroid cartilages, and a part of the cartilage of the nasal septum or of a plastic, respectively, is implanted in the paralysed cord.

The operations performed up until now have been of necessity carried out by indirect laryngoscopy and by one hand only.

SUMMARY OF THE INVENTION

The implant according to the invention overcomes all above mentioned disadvantages comprises a physiologically inert material which swells in water and has in the dry state, as prepared for the operation, the shape of a straight or bent elongated body, such as a stick provided with a sharp, pointed tip.

Hydrophilic material with a linear swelling capacity from 10 to 45 percent may be used as an inert material swelling in water. The copolymers of glycol methacrylate (or acrylate, respectively) which contain up to 2 weight percent of glycol dimethacrylate (or diacrylate, respectively) and up to 3 weight percent of methacrylic acid (or acrylic acid, respectively) are preferably used. This material can be substituted by other hydrophilic materials of similar properties which are based, for example, on acrylamide, N-substituted or N,N-disubstituted acrylamides and their copolymers. The implant may contain dyestuffs, pigments or contrast substances. The implant according to the invention has preferably the same length in a dry state as after equilibrium swelling in water. Its modulus of elasticity may be decreased, except with respect to the tip, by adding water or another physiologically inert plasticizer. Glycol as employed in the expression "glycol methacrylate" (or "glycol acrylate", respectively) to include not only simple ethyleneglycol, but also diethyleneglycol, triethyleneglycol, propyleneglycol, butyleneglycol and the like, that is, an arbitrary hydrophilic aliphatic diol. Glycerol monomethacrylate or acrylate may be also used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To prepare the implant according to this invention, the elongated body such as a stick is prepared in the dry state from the physiologically inert material swelling in water, preferably from a synthetic cross-linked hydrophilic gel, and this stick is provided with a sharp, pointed tip before or after drying. The stick is advantageously made from a material which contains a physiologically inert plasticizer or is impregnated with the plasticizer, and wherein the tip or the part used for making the tip is freed from the plasticizer by extraction. The stick can be also swollen in water, the clamped in such a way to be unable to shrink lengthwise, dried and provided with the tip, or the dried stick can be heated above the glass transition temperature, stretched in this state, cooled and provided with the tip.

The implant according to the invention may be prepared also in any manner such that the body has an uneven or combined shape made from a physiologically inert polymer swelling in water, which is dried and then shaped at a temperature above the glass transition point into a straight or bent rod, which is provided with a pointed tip. In this case the implant returns into the original uneven or combined shape after being swollen, due to its shape memory.

The characteristic glassy hard state of hydrophilic polymers in their dry condition is necessary only in the region of the stabbing tip for introduction of the implant into tissue. The remaining part of the implant need not to be in the glassy hard state. However, the body of the implant has to be sufficiently rigid to enable its introduction into tissue by overcoming the resistance of the opening tissue. The modulus of elasticity of the implant body is generally sufficiently high when above about 100 kg/cm.sup.2. However, a modulus about 1,000 kg/cm.sup.2 is especially advantageous. In general the hydrophilic materials show considerable decrease of brittleness when their modulus of elasticity in the dry state is reduced from the usual value of 20,000 - 50,000 kg/cm.sup.2 to 5,000 kg/cm.sup.2. The required reduction of modulus and thus also the high toughness of the implant body can be achieved by introduction of a small amount of a convenient plasticizer into the three-dimensional network of the hydrophillic polymer. This can even be water, in the simpliest case, which may be absorbed for instance from aqueous solutions of sodium chloride. The amount of water in the gel decreases with the increase of the concentration of the salt in water, since it is in equilibrium with this solution. For instance, sparingly cross-linked glycol methacrylate gel softens by long soaking in a 15 percent solution of salt in such a way that its elasticity modulus is then about 500 kg/cm.sup.2. Under these circumstances the tip is also softened. Therefore, it is necessary to dry the sharp end of the implant before application and to preserve the absorbed water in the residual material of the implant, for instance, by wrapping the implant in an aluminium foil and drying of the uncovered tip only.

If a non-volatile and physiologically inert plasticizer is used instead of water, the implant can be made so that it has a different hardness in its individual parts so that it has relatively long-term stability. For example, larger or smaller amounts of glycerol may be absorbed by the gel along with water from dilute solutions of glycerol at elevated temperature, and will remain in the gel permanently after drying. Subsequently, all of the glycerol may be extracted from the tip by dipping the tip into water so that it leashes out from the tip leaving the presence of glycerol limited to the remaining parts of the implant. The required effect is obtained at low concentrations of glycerol, such as at 0.2 - 2%. The glycerol remains localized in the implant, in the slightly swollen state, for a long time and its migration into the non-plasticized tip does not take place. The implant can be prepared in this condition in a sterilized package, ready for instant use without any special preparation before use by the consumer. Besides glycerol, several other substances may be used as plasticizers which are absorbed by the gel and are physiologically unobjectionable in small amounts, such as diacetin, triethyleneglycol, butanediol-1,3,urethane acetoin, diethyl tartrate, N,N'-dilactyl urea, lactamide and the like. These compounds may be introduced into the gel either from aqueous solutions or from solutions in other volatile solvents which heavily swell the gel and thus open the gel structure for the rapid diffusion of plasticizers. The same solvents are convenient for the reverse washing of plasticizers from the tip of the implant. However, the procedure can be also employed, where the tip is protected from the softening action of the solutions by coating, e.g. with paraffin, or where only other parts of the implant are dipped into the solutions.

The operation, employing the implant according to the invention, comprises insertion of the implant into the predetermined place of the vocal cord by direct laryngoscopy methods using a multiple magnifying surgical microscope, preferably after a very small incision in the mucous membrane at the upper surface of vocal cord is made. The implant is used in a dry state and is of almost glassy hardness. The implant swells in the tissue for several minutes, increases its volume as it has been predeterminedly designed to do and thus increases the mass of the atrophied vocal cord, shifting its edge more to the center and thereby contracting, or liquidating the slot between cords occuring hitherto at voice formation. This improves the voice in the objectively evident way and removes hoarseness and subjective difficulties, mainly the voice tiredness.

The implant can be employed in similar way for the treatment of paralysis of the recurrent nerve, when the afficted vocal cord is slack and excavated and the opposite vocal cord is unable to compensate for the disturbance formed by drawing across middle line. In this case the purpose of the implant is similar as in the case of atrophy of the vocal cords and it has to level the excavation by taking up the slack vocal cord, to improve the closure of glottis and to improve the voice and subjective difficulties of the patient. The application of the implant according to the invention has the distinct advantage in that the patient can speak within several minutes at the operation, while with other methods total vocal inactivity is required usually for from 3 to 7 days.

Analogously as with atrophied vocal cords, the implant can be used for surgical treatment in other regions which are afflicted with atrophy, such as with atrophy of nasal mucous membrane and the like.

The following examples will further illustrate the invention. It is to be understood that the examples are illustrative only and not limitative. In the example all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1

A mixture consisting of 70 parts of hydroxyethyl methacrylate containing 0.2 % of ethylene dimethacrylate, 15 parts of 0.25 % aqueous solution of ammonium persulfate and 15 parts of 0.25 % aqueous solution of sodium disulfite is charged by a pipette into a plurality of thin-walled 30 cm long glass capillary tubes having a inner diameter 0.8 to 2.5 mm which are placed horizontally. Polymeriz mixture is sucked into the whole length of the tubes by capillarity. The polymerization takes place at ambient temperature and is completed within 8 hours. The several gel sticks are then isolated either by breaking the capillary tubes and careful separation of the crushed glass, or, in more convenient way, by dissolving the glass in cold 20 % hydrofluoric acid. The sticks are thoroughly washed in water and then the ends cut off to remove any portions not perfectly polymerized due to diffusing oxygen. Thereafter, one end of each stick, preferably in semi-dry state, is cut with a sharp knife in a fairly oblique angle to form a shape similar to the tip of an injection needle. As a rule, the stick deforms in the course of further drying but the original shape was recovered and release of internal stress obtained by heating the stick above the softening point, i.e., to 120.degree. - 140.degree. C. The sticks were thereafter either laid loose on stretched knitted fabric made from terylene monofilament or suspended in boiling xylene. Fine files and abrasive paper are used for forming the finish and sterilization is carried out in an ethylene oxide atmosphere.

In like manner other water-swelling gels can be prepared from other neutral monomers, such as from N-methyl methacrylamide, acrylamide or vinylpyrrolidone in the presence of suitable cross-linking agents, such as methylene-bis-acrylamide. Also monomers containing ionizable groups in their molecule can be employed (such as methacrylic acid) which, present in slightly cross-linked gels, when employed in the amount of up to several percent substantial increase of swelling capacity in neutral aqueous solutions. With gels based on glycol methacrylate a substantial increase of swelling may also be achieved by esterification of hydroxy groups with sulfuric acid.

EXAMPLE 2

The monomer mixture as described in Example 1 is charged into a 3 m long thin-walled silicone rubber tube having an inner diameter of 1.2 mm. The opposite end of the tube is sealed and 1ml more mixture is pressed into the tube by a syringe so that the tube expands and is able to compensate precisely for the polymerization contraction. Then the other end is sealed, the tube is inserted into a wider glass tube, which is freed from all oxygen by a stream of nitrogen and sealed. After polymerization is completed, the silicone tube is split by two lengthwise cuts and the casted rod is released. It is quite regular, intact and free of contraction bubbles. The rod may be, after cutting to pieces and washing in water, impregnated with plasticizers, such as by heating in a 3 % aqueous solution of glycerol. If a rod is dried in the lengthwise fixed position, it is obtained in stretched state and by swelling under physiological condition only gets wider but not longer. To finish the implant, the tip is formed, freed from the plasticizer by dipping in water, and, after final drying, is sharpened with fine emery.

EXAMPLE 3

A mixture consisting of 30 parts of acrylonitrile, 70 parts of nitric acid (density 1.5) and 0.1 parts of ammonium persulfate was charged into similar capillary tubes, as those which are described in Example 1. The capillary tubes were inerted into a pressure vessel, air was replaced by nitrogen and the pressure of nitrogen was increased to 3 atm. After five days the capillary tubes were removed from the pressure vessel and heated for 10 hours to 45.degree. C. Further working was analogous to Example 1. The volume swelling capacity was about 60 %.

The foregoing fully reveals the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of the prior art, fairly constitute esential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims

We claim:

1. A larynreal implant for surgical purposes, for use in the surgical treatment of vocal cords comprising a body of hydrophilic polymeric crosslinked gel material having the form of a rod-like needle with a sharp, pointed tip in the dry state in which it is applied, said implant being swellable after implantation in the vocal cord to help improve closure of glottis.

2. An implant in accordance with claim 1 wherein the hydrophilic polymeric crosslinked material is an insoluble, hydrophilic gel having a linear swelling capacity in the region from 10 to 45 percent.

3. The implant according to claim 1 wherein said tip is glassy hard.

4. The implant according to claim 1 wherein the hydrophilic material is a copolymer selected from the group of glycol methecrylate and acrylate containing up to 2 weight percent of a material selected from the group consisting of glycol dimethacrylate and diacrylate and up to 3 weight percent of material selected from the group consisting of methacrylic acid or acrylic acid.

5. The implant according to claim 1 wherein a physiologically inert plasticizer is added to said material along the length of the body except at its tip to provide said rod with a lower modulus of elasticity.

6. The implant according to claim 1 wherein said material contains an additive selected from the group consisting of dyes, pigments and contrast substances.

7. The implant according to claim 1 which has approximately the same length in a dry state as after equilibrium swelling in water.