CS255682B1 - Ossification's biological processes stimulating polymer composition and method of its preparation - Google Patents

Abstract

The solution relates to a polymeric composition stimulating biological processes of ossification a method of its preparation. Polymer composition based on a three-dimensionally crosslinked hydrogel poly (2-hydroxyethyl methacrylate) polyHEMA and soluble type I collagen has the ability when implanted in a human or animal organisms to induce biological processes osteoplasia or ossification. This property it can be successfully used in those fields medicine where new formation is required bone tissue, for example in bone surgery, orthopedics, maxillofacial surgery and endodontics. The essence of the preparation method of the polymer composition consists in preparing a polymerization mixture, which contains an aqueous solution of type 1 collagen, monomeric HEMA, suitable acid and components the so-called redox system, which is able to initiate radical polymerization of the monomer present at room temperature and this mixture then, in a short time, it becomes insoluble gel. Starting liquid polymerization mixture may, where appropriate, include other substances for example a filler, an X-ray contrast agent, antibiotics or other biologically active substances a alike. These excipients are possible up to 35 wt per total polymerization mixture.

Description

The present invention relates to a polymer composition stimulating biological processes of ossification and to a process for its preparation. It has been known for many years that a sponge hydrogel based on (2-hydroxyethyl methacrylate) -HEMA poles after its implantation in an animal or human organism is prone to calcification. Obviously, massive deposits of insoluble calcium salts are extremely undesirable in most cases of use of this prosthetic material. This is especially true for soft tissue replacement, such as mamma prostheses. Otherwise, this alloplastic material produces virtually no inflammatory reaction. *

Over time, the implant is usually surrounded by a thin fibrous sheath.

However, findings have been reported where the same material, implanted in the subcutis of experimental pigs, has produced biological processes that normally give rise to hard bone tissue. This species-dependent metaplastic ossification, induced by the presence of a macroporous polyHEMA implant, has not yet been fully explained. It is assumed that _E play an important role deposits of insoluble calcium salts, particularly in the form of hydroxyapatite.

It has now surprisingly been found that soluble type I collagen, present in polyHEMA hydrophel, is capable of stimulating osteoblast migration and subsequent osteoplasia processes at the implant site. Although two other types of polyHEMA-based and collagen-based composite materials are currently known, prepared according to U.S. Pat. No. 146,130 and U.S. Pat. No. 216,992, none of which has been shown to stimulate ossification processes. Both composite materials contain a mixture of type I and III collagen, generally in their insoluble form.

By analyzing this problem, we have come to the conclusion that the presence of a soluble form of collagen type I in the polyHEMA hydrogel is a guarantee of successful stimulation of these biological processes. The ability to calcify the polyHEMA hydrogel matrix itself also plays an important role.

It is known that normal bone cells produce exclusively type I macromolecules. These polarized cells are also responsible for the processes of nucleation of hydroxyapatite crystals and calcification of collagen fibrils in the extracellular matrix. In this respect, the histological finding in the implantation of a new composite material into the subcutaneous tissue of rats, where metabolically active bone cells - osteoblasts and over time also mature cells - osteocytes, occur between invading cells. These cells are apparently responsible for the formation of osteoid tissue with mineralization deposits within the implanted material.

SUMMARY OF THE INVENTION The present invention provides a polymer composition based on polyHEMA and a soluble form of type X collagen and a process for the preparation thereof, wherein the collagen of said properties, in an amount of 0.025 to 2.5% by weight, is dissolved in an aqueous mixture containing 15 to 50% by weight. . % HEMA monomer, further 0.01 to 1 wt. % suitable acids, for example acetic or hydrochloric acid, and at most 1 wt. a redox system which is capable of initiating the free-radical polymerization of the monomer present at normal room temperature, wherein the liquid mixture will soon become an insoluble gel.

The starting liquid polymerization mixture may optionally contain other substances, for example a filler or X-ray contrast agent, antibiotics or other biologically active substances and the like. These auxiliaries may be used in amounts of up to 35% by weight, based on the total polymerization mixture.

The monomeric HEMA must be of purity for biomedical applications ”and should not contain more than 1% by weight. of an appropriate sulfur diester, i.e. ethylene dimethacrylate.

Collagen isolated by known methods, i.e. extraction of animal tissues rich in type I collagen proteins, such as those _f blackbird, tendons and skin of vertebrates.

The extraction is carried out using acidic agents whose pH is optimally in the range of 2.5 to 3.5, for example 0.5 M acetic acid or 0.05 citrate buffer. Soluble fractions of type I collagen are further processed in a conventional manner and preferably stored in a lyophilized state.

All other chemicals must be of guaranteed purity, ie purity or for analysis. The water used must also be of high purity and pyrogen-free.

The starting liquid mixture with monomeric HEMA is autosterile in the stated concentration range, i.e. suppresses the growth of microorganisms, including pathogenic germs. This greatly simplifies and favors its use for said biomedical applications. This property, together with a demonstrable harmless effect on living tissues, predetermines this novel alloplastic material for its direct application, i.e. in situ polymerization. Thus, the liquid polymerization mixture can be applied directly where we want to deliberately induce osteoplasia or ossification processes. We can also use a conventional syringe.

However, the polymer composition of the present invention can be prepared in advance in any amount and shape, i.e., by polymerizing the starting liquid composition in a suitable form. Thus, a foil or gag or other shaped molding can be prepared which can be sterile stored for its instant use in surgery. It is also possible to adapt the implant by cutting or slicing, depending on the operating situation and using conventional surgical instruments. This allows the softness and elasticity of the new prosthetic material.

Sterilization of the composite material is possible, but due to the collagen protein content, a radiation technique such as beta- or gamma-ray sterilization is more suitable here.

Accordingly, conventional sterilization techniques, such as autoclaving or boiling in water, are not applicable herein. The use of other sterilizing agents, such as ethylene oxide or formaldehyde vapors, may also be recommended because of the toxic effects of residues or adducts and their possible diffusion into the interior of the implant. However, the latter property of the gel composite material can be used to form depots of suitable antibiotics or other biologically active substances. An aqueous solution of these substances readily diffuses into the mass of the gel composition and, over time, uniformly permeates the entire volume of implant material.

This property of a hydrophilic polyHEMA gel has been previously described and tested in some medical fields. The depot can be used for targeted therapy, i.e. at the implant site.

The composite material prepared by the process of the present invention may find practical application in those medical fields where it is desirable to stimulate bone formation, such as in bone surgery, orthopedics, maxillofacial surgery, and endodontics.

The following are examples to illustrate the invention, but in no way limit the number of possible combinations and uses of the individual components of the composition, both in terms of quality and quantity.

Example 1

Type I collagen was isolated from calf skin by extraction with 0.5 M acetic acid; for methodology see S. Bažin and A. Delaunay: Preparation of acid and citrate soluble collagen, in: The Methodology of Connective Tissue Research, Ed. D. A. Halí, Chapter 3, Joynson Bruvers Ltd., Oxford, 1976.

In 29.5 ml of a 0.5% w / w aqueous acetic acid solution. 0.5 g of the lyophilized collagen preparation was dissolved under stirring at +4 [deg.] C. and then 15 g of pure HEMA monomer containing 0.28 wt. sulfuric diester.

In a polyethylene tube containing 5 ml and dimensions: 9 x 80 mm, 2.7 ml of the above mixture was dispensed and 0.15 ml of an aqueous solution of ammonium persulfate and sodium pyrosulphite was added.

both at a concentration of 10 wt. The polymerization mixture was briefly homogenized with a glass rod and then left to stand at room temperature. The initially liquid mixture solidified to a flexible gel within 3-4 minutes. The gel glove was removed from the tube, then washed thoroughly in excess distilled water and finally in sterile saline 0.9% sodium chloride. Washing was carried out cold at +4 ° C. The washed gag was placed in a double polyethylene bag that was sealed and subjected to radiation sterilization using a cobalt gamma-emitter, with a total dose of 1.8 Mrad. Sterile implant material is stored refrigerated and ready for immediate surgical use.

Example 2

Example 1 was used to prepare the polymerization mixture.

The homogenized mixture was aspirated into a sterile plastic syringe and injected subcutaneously into Wistar rats. Each of the three animals was injected bilaterally with 0.5 ml of polymerization mixture in the dorsal region, which was then polymerized in situ in a short time. The presence of gel in the subcutaneous tissue was detected by palpation examination.

Within 4 to 6 weeks, extensive calcification of the implanted material and, after 3 to 4 months, also metaplasia of osteoid tissue could be demonstrated histologically.

Example 3

The procedure of Examples 1 and 2; the polymerization mixture consisted of 0.9 ml of an aqueous mixture of the above composition and 0.05 ml of both components of the redox initiation system.

Beagle dogs under pentoberbital anesthesia performed vital dental pulp exstirpation, root canal enlargement, tip trepanation, and after the bleeding stopped, the prepared channels were filled with the liquid polymerization mixture. Each dog was six lower premolars, ie a total of 12 root canals were filled, with a portion of the polymerization mixture being forced into the periapical region. The root canal was covered with phosphate cement and amalgam.

Histological findings showed a relatively abundant cellular fibroproduction as early as two months after implantation of the aqueous gel in the periapical region. In many cases, the penetration of fibroplasts into the interior of the gel mass has been found and no inflammatory reaction has been observed.

At 4 to 6 months post-implantation, apical cement neoplasia was observed, which in some cases closed the shaked apex of the dental roots. Tight root canal closure is considered an ideal repair process in current endodontics.

Example 4

Following Examples 1 to 3, however, the teeth were previously devitalized and the root canals were allowed free access to the oral cavity environment for six weeks. After this time, X-ray control showed chronic apical periodontitis.

Application of the polymerization mixture and treatment of the devitalized teeth were carried out as described in Example 3.

Here, too, good results have been achieved in the targeted formation of osteoid tissue, which is produced even in the environment of suppressed chronic inflammation.

Example 5

Following the procedure of Example 4, said polymerization mixture contained 30 wt. fine precipitated barium sulphate - for medical purposes.

This achieved good X-ray contrast in the resulting implant material and made it possible to control all phases of the experiment in vivo.

Example 6

Following the procedure of Example 1, the non-washed gel was placed under sterile conditions in a glass container with a well-sealed lid containing 1 liter of 0.9% saline. % sodium chloride and 0.1 wt. chlorhexidine (1: 6-di-4'-chlorophenyldiquanidohexane) as an antiseptic. The material thus treated will be sterile for many months and is ready for immediate surgical use.

OBJECT OF THE INVENTION

Claims (4)

OBJECT OF THE INVENTION Polymer composition for stimulating biological ossification processes, for medicine or biology, characterized in that it consists of a three-dimensionally crosslinked hydrogel based on poly (2-hydroxyethyl methacrylate) and soluble type I collagen and excipients, for example X-ray contrast agents or medicaments, in up to 35% by weight of the total mixture. 2. A process for the preparation of a polymer composition as claimed in claim 1 or claim 2, wherein the collagen of said properties, in an amount of 0.025 to 2.5% by weight, is dissolved in an aqueous mixture containing 15 to 15% by weight. 50 wt. % HEMA monomer, further 0.01 to 1 wt. % suitable acids, for example acetic or hydrochloric acid, optionally up to 35 wt. other additives, for example an X-ray contrast agent or drug, and at most 1 wt. a redox system which is capable of initiating the free-radical polymerization of the monomer present at normal room temperature, wherein the liquid mixture will shortly become an insoluble hydrogel. 3. A process according to claim 3, characterized in that the polymerization of said mixture is carried out in a suitable form, thereby obtaining a casting of the desired shape, for example a foil or gag, which is further sterile stored. 4. The method of claim 3, wherein the polymerization of the sterile mixture is carried out directly in the human or animal body in situ, wherein the application of the polymerization mixture is preferably carried out by syringe.