p(HEMA) composite as allografting material during therapy of periodontal disease: three case reports.

The p(HEMA) composite is shown to be a possibly effective allografting material for therapy of periodontal disease. Three cases from a clinical pilot study are presented in this report. The p(HEMA) composite may be used alone or as a part of more complex biomaterial, together with tricalcium phosphate ceramics. Further scientific and clinical work is needed for definitive judgement on the use of the p(HEMA) composite in periodontology.

Preliminary report on use of a p(HEMA)-collagen composite in maxillo-facial surgery.

After being thoroughly tested on animals, a composite polymer material based on poly(2-hydroxyethyl methacrylate) and calf skin collagen has been allowed in a limited clinical trial in the Czech Republic. Up to now, the medical use of the biomaterial comprises implants for maxillo-facial surgery, i.e. augmentation of soft tissues (seven cases); reparation of fractured eye sockets (12 cases) and in special indications (two cases). The clinical results obtained so far are presented here as case reports. These preliminary results are very encouraging for a broader utilization of this type of biomaterial in the surgical fields of human medicine.

Irritation effects of residual products derived from poly(2-hydroxyethyl methacrylate) gels. I. Testing of some model compounds.

2-Hydroxyethyl methacrylate (HEMA) monomer and sodium benzoate, diluted with saline in the range 0-20%, were tested for intradermal irritation in rats. Radioactive indicator (113mIn) was used to quantify this biological response. At low concentrations (up to 1%) only a little irritation was recorded, while at higher levels (5% or more) a significant adverse reaction developed. The degree of irritation was dose dependent. In the concentration range 0-10%, the response was exponential. Model decomposition products derived from three different polymerization initiators were also tested. How the results obtained with the model irritants relate to real polymerization systems is discussed.

Poly(2-hydroxyethyl methacrylate)--collagen composites which promote muscle cell differentiation in vitro.

A new simple method has been developed which allows the mixing of poly(2-hydroxyethyl methacrylate)--polyHEMA--and fibrillar collagen in any desired ratio. PolyHEMA alone was shown to be an unsuitable cultivation substrate for primary cultures of chicken embryonic skeletal muscle cells. Composites containing polyHEMA and 50% (w/w) or more collagen supported myogenesis. Such layers, firmly adhered to the bottom of plastic Petri dishes, were mechanically stable and biologically active, thus favourably combining properties of both the original materials. It is suggested that polyHEMA-collagen composite layers may be used for cultivation of differentiating cells in vitro.

Structural alterations of p(HEMA)--collagen implants.

Samples of linear (additionally crosslinked) p(HEMA) with different amounts of fibrillar collagen were implanted into the popliteal region of rats. After 3 month, the implanted materials were harvested and examined by SEM. The implants underwent marked structural or morphological changes. While the fibrillar collagen was readily resorbed by invading cells, the synthetic constituent persisted to biodegradation. The p(HEMA) residues were shaped into spherical particles, approx. 1-15 microns in diameter. The possible fate of these microparticles in the host organism is discussed.

Calcification of poly(2-hydroxyethyl methacrylate)-collagen composites implanted in rats.

Samples of the polyHEMA-collagen composites with varying collagen content have been implanted into the popliteal region of rats. Three, six and twelve months after the implantation, calcification of the implanted material was determined using a radioactive indicator. At the same time, the implants and surrounding tissue were examined histologically. The degree of calcification of the implants was dependent on the collagen content; it was more pronounced with a higher amount of collagen. The composites with 30% (w/w) or more collagen were biodegraded during the long-term implantation. It is suggested that the composites containing less than 20% (w/w) of fibrillar collagen are used for biomedical applications and that those with a higher collagen content for the in vitro studies.

Irritation effects of residual products derived from p(HEMA) gels. II. Compounds extracted from hydrogels.

Samples of poly(2-hydroxyethyl methacrylate) p(HEMA) hydrogels were prepared using three different polymerization initiators. The gels were washed in water under standard conditions. The extracts were then examined for intradermal irritation in rats using a radioactive indicator (113mIn). The irritation effects were dependent on the concentrations of the irritating substances and also on the gel type. Solid discs made of the gels, washed to varying degrees of purity, were also implanted into rats. Tissue irritation, as well as some other biological responses, were followed in situ using the radioindicator and common histological techniques. The irritation effects were very mild (even with the unextracted gel material). A possible explanation for the events taking place at the site of implantation is presented.

Influence of carboxylate ions containing polymers on calcification: in vitro study.

Calcification of implant or surrounding tissues represents an important complication of its function. The role of the molecular structure of a model hydrogel on the calcification is studied here in a simple in vitro, cell free system. The results show that-COO- containing polymers have an inhibitory effect on Ca2+ crystal formation. This process seems to be unspecific, because the polymers of different structure and origin have an inhibitory effect. However, its efficiency is related to a different extent of Ca2+ binding capacity of distinct polymers.

Implantation of p(HEMA)-collagen composite into bone.

The replacement of bone defects is very important in clinical practice. This study compares biological properties of poly(2-hydroxyethyl methacrylate)-collagen composite with those exhibited by pure p(HEMA), an insoluble fraction of calf skin collagen (ISC-40) and demineralized bone matrix after implantation into pig or dog femurs. The levels of biodegradation or destruction of implants and healing of bone defects were studied using X-ray photography, histology and enzyme histochemistry. The results indicated a significant effect of collagen on biological destruction of the p(HEMA)-composite implants; even a minute amount of collagen influences this process dramatically. A stimulatory action of collagen on new bone formation may be of importance in bone defect healing.

Electrostatic interaction influences cell adhesion?

The effect of electrostatic forces on the adhesion of LEP-19 diploid embryonal fibroblasts, Hep-2 laryngeal carcinoma cells, Raji lymphoblastoma cells and Sp 2/0 myeloma cells was examined in vitro. Adhesivity of all tested cell lines was higher on the cationized glass than on untreated or anionized glass. The negatively charged sialic acids on the cell surface play a role in cell adhesion. The participation of electrostatic interaction is independent of the energy metabolism in serum-free conditions.

The effect of different collagens and of proteoglycan on the retraction of collagen lattice.

The effect of various collagens and proteoglycan on the formation and retraction of collagen lattices was tested. The most rapid aggregation of collagen molecules was observed by the use of the least cross-linked collagen fractions (ie pepsin-digested calf skin collagen type I). Lattices formed with more cross-linked collagens (acid soluble collagen-ASC, type III) contracted slowly and less intensively. Unpurified pepsinized cartilage extract containing collagen types II, IX and XI, some glycoproteins and proteoglycans formed lattices rather well. On the contrary, purified collagen type II as well as polymeric collagen (solubilized by denaturing conditions) did not form lattices at all. The lattice formation and retraction was intensified by addition of proteoglycan into the culture medium. The authors suggest that the kinetics of the lattice formation and retraction depends on the amount of collagen cross-links and the concentration of proteoglycan in the culture medium.

Artificial mineralization in vitro--a model of tissue mineralization.

Calcium chloride and sodium hydrogen phosphate form precipitation zones in gelatin gel, gel supplemented with cartilaginous extract, articular cartilage slices, and in demineralized bone. The cartilaginous extract exerts a marked inhibitory effect on the crystal quantity and clustering. The pretreatment of cartilage slices with hyaluronidase increases the crystal frequency. The morphology of crystals formed in gelatin and in cartilage was similar but quite different from the precipitation pattern found in demineralized bone.

Changes in vascular pattern of chicken chorioallantois after cartilaginous extract, chondroitin sulfate and dextran sulfate treatment.

Cartilaginous extract, chondroitin sulfate C as well as dextran sulfate in gelatin pellets have an inhibitory effect on the development of fine capillaries, in contrast to pure gelatin pellets or pellets with sucrose. These results suggest an unspecific inhibitory effect of anionic saccharidic polymers on the development of chorioallantoic membrane vessels, because the chemical structure of dextran sulfate is (except anionic groups) different from chondroitin sulfate in the pure form or in the form of proteoglycans (in cartilaginous extract).

Comparison of the influence of gelatine and collagen substrates on growth of chondrocytes.

The effect of culture substrates on adhesion and growth of chondrocytes and the influence of varying amounts of foetal calf serum on cell proliferation are compared. Skin and cartilage gelatines and type II collagen were used as substrates. The cells used in the experiments were the primary cultures of chondrocytes, frozen primary cultures of chondrocytes and chondrocytes after the 1st subculture. Cartilage gelatine had a more marked influence on cell proliferation than skin gelatine, especially in primary cultures. The differences were off in cells after the 1st subculture. Differences in the number of cells are evident also after decreasing the serum concentration in culture medium.

Preparation of poly(2-hydroxyethyl methacrylate)-collagen composites.

Linear and three-dimensional polymer composites were prepared on the basis of poly(2-hydroxyethyl methacrylate)--pHEMA--and collagen. Their biological properties were tested by in vitro as well as in vivo methods. The composite material (unlike pure pHEMA) supported myoblast adhesion as well as their fusion into multinuclear myotubes in vitro. The three-dimensional polymer composites stimulated a new bone formation after their intraosseal implantation in dogs and pigs. The biomaterial itself was degraded in the host organism, in contrast to stable pHEMA.

[Prosthesis of ligament by specially treated collagenous tissue.]. / Náhrada vazu pomocí speciálne upravené kolagenní tkáne.

Artificial prostheses of ligaments are associated with many problems. At first they take over the function of the ligament, later however their strength declines. Therefore at present collagen autotransplants are prefered. Prosthesis made from processed seem however promising, after their breakdown they should be replaced by the patient's connective tissue with an orientation of fibres resembling the original ligament. The poor results reported in the literature are probably due to inadequate treatment of these ligaments. The authors mention their own method of treatment of collagen and its use as a prosthesis of ligaments in experiments on dogs. These ligaments were investigated by histological methods after an interval of 3 and 6 months following operation. The reported results are promising. Histological examination revealed incorporation of connective tissue into the artificial collagen and the connective tissue fibres were oriented parallel with the implanted ligament. Further investigation call for long-term implantation, but even the present investigation confirms that treatment of collagen in the described manner is a suitable method. Key words: xenograph, arteficial ligament replacement, tendon prosthesis.

[Collagen as a biomaterial]. / Kolagen jako biomateriál.

The authors discuss the characteristics of different types of collagen, their incidence, structure, chemical composition and physical properties with regard to their use as biomaterial. They also mention the antigenicity, effect on platelet aggregation, cytodifferentiation and cellular proliferation. The authors discuss different biomedical applications of collagen and methods of its sterilization.

[Replacement of the trachea with a prosthesis--an unsolvable problem?]. / Náhrada prudusnice protézou--neresitelný problém?

Reconstruction of the trachea by means of a segmental prosthesis is a complicated problem, which has not been completely resolved so far. The authors present a brief historical review of attempts to bridge the gap by different types of prostheses Evon Neville's silicone prostheses are not well tolerated on a long-term basis and its is thus important to look for other materials for the manufacture of an "ideal" tracheal prosthesis. (ur synthetic prosthesis made from poly/ARMA/is very well tolerated, similarly as silicone prostheses. Despite this the authors produced in 1993 a new type of prosthesis, based on antigenicity-deprived heterologous pig tissue. Trials with this prosthesis will be evaluated in a subsequent paper.

[A tracheal prosthesis made from P(AEMA)--a further step toward tracheal replacement]. / Tracheální protéza z P(AEMA)--dalsí krok k náhrade prudusnice.

In animal experiments (5 dogs) the authors tested a material for the construction of tracheal prostheses so far not used in other countries. P(AEMA), the polymer 2-acetoxy-ethylmethacrylate is well tolerated, it did not produce a rejection reaction. The inner wall of the prosthesis was throughout the experiment patent, smooth and secretion did not adhere to it. Macroscopic examination did not reveal cumulation of mucus and signs of infection. The self-cleansing capacity was not impaired and the dog was able to expectorate mucus over a 5 cm length of the prosthesis. The solid ends of the prosthesis, however, caused mechanical irritation of the site of anastomosis and after cca 4 weeks of the experiment granulation tissue began to form. The experiments were terminated on account of complete occlusion of the lumen of the airways by granulation tissue 4-6 weeks after operation. The authors' efforts to design a suitable tracheal prosthesis led to a change of strategy of subsequent research. They started experiments with a heterologous portion of the pig trachea devoid of antigenicity; this will be the subject of a subsequent paper.

[Tracheal replacement with a swine prosthesis]. / Substituce trachey protézou z vepre.

In 12 experimental operations the authors tested the biocompatibility of a xenologous trachea from a pig which was used to replace a 5 cm defect of the trachea in a dog. After special preparation eliminating the antigenicity of the pig trachea the thus prepared graft was sutured into the thoracic portion of the dog trachea. The experiment could not be evaluated in two instances because the dog died on the operating table. In the remaining ten cases it was found that all anastomoses healed perfectly. The fibrous tissues of the tunica propria of the graft was replaced by granulation tissue. Across the anastomoses newly formed capillaries penetrated into the trachea where they caused chondrolysis. This led to a breakdown of the central portion of the prosthesis and stenosis in the airways with terminal respiratory failure. The mucosa of the graft was at some sites covered by metaplastically altered epithelium. Even a reinforcing vascular prosthesis did not prevent the breakdown of the wall of the xenologous graft. An asset for future work is the finding of a well healed suture between the graft and the trachea and evidence that newly formed blood vessels penetrated into the prosthesis.