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Biomedical subjects

S Gogolewski

Publications and source records attributed to S Gogolewski.

At least 37 records · Page 2Linked to original sources
PubMed1997

The significance of angiogenesis in guided bone regeneration. A case report of a rabbit experiment.

A dome-shaped bioresorbable membrane was fixed to the wounded rabbit calvaria and filled with a bioresorbable fibre conglomerate. After 4 weeks, the histologic preparation revealed an intimate spatial and temporal correlation between newly formed blood vessels and de novo extraskeletal bone formation. These observations emphasize the significance of angiogenesis in guided bone generation.

Animals↗
PubMed1997

Regeneration of diaphyseal bone defects using resorbable poly(L/DL-lactide) and poly(D-lactide) membranes in the Yucatan pig model.

OBJECTIVES: To determine the effects of tubular resorbable polymer membranes on the healing of a segmental diaphyseal bone defect. DESIGN: A randomized prospective study using the minipig model. Animals were evaluated with in vivo roentgenograms on a biweekly basis until explanted at twelve weeks. SETTING: After surgery, animals were allowed unrestricted activity and weight bearing between twenty-four and forty-eight hours. ANIMALS: Fifteen yearling Yucatan minipigs. INTERVENTION: A 2.5- to 3.0-centimeter mid-diaphyseal defect was created in the middle third of the radius. Animals were assigned in groups of three to receive the following implants: (a) poly(L/DL-lactide), (b) poly(L/DL-lactide)-CaCO3, (c) poly(D-lactide), (d) poly(D-lactide)-CaCO3, and (e) an untreated defect. No adjunctive internal or external fixation was used as the ulna was left intact. MAIN OUTCOME MEASURES: The limbs were studied with in vivo anterior-posterior and lateral radiographs at biweekly intervals for the presence and pattern of bone formation. All limbs were explanted at twelve weeks postimplantation for methyl-methacrylate embedding and histologic and microradiographic study. RESULTS: The bone defects covered with membranes were completely reconstituted by six to eight weeks. Untreated defects healed with less bone formation and in a more disorganized pattern. Histologic evaluation of the implants demonstrated that the entire lumen of the implant was filled with bone, with some periosteal bone formation occurring on the outer surface of the membrane. There was direct apposition of bone onto the membrane surface or minimal fibrous tissue interposition between membrane and new bone. There was no foreign body or adverse reaction to the membrane. Untreated defects showed woven bone formation with clefts and irregularly shaped margins occupied by fibrous tissues or surrounding muscle tissues. CONCLUSIONS: This study supports the concept that a membrane enhances bone defect healing by excluding nonosseous tissues from a defect and providing structural scaffolding for periosteal and endosteal bone regeneration.

Absorption↗
PubMed1996

Enhancement of the mechanical properties of polylactides by solid-state extrusion. II. Poly(L-lactide), poly(L/D-lactide), and poly(L/DL-lactide.

Polylactides with various degrees of chain regularity-crystalline poly(L-lactide); amorphous poly(L/D-lactide), and amorphous poly(L/DL-lactide)-were processed into high-strength, high-modulus resorable rods using solid-state extrusion through a conical die. The rods with a highly fibrillated structure had flexural strengths at a yield of up to 215 MPa and flexural modulus of up to 13.7 GPa. The initially amorphous poly(L/DL-lactide) developed approximately 25% of crystallinity after solid-state extrusion. Poly(L/D-lactide) remained amorphous independently of the treatment procedure applied. The shear strengths, flexural strengths, and flexural moduli of the solid-state extruded rods increased with increasing draw ratio. For the semicrystalline materials, solid-state extrusion enhanced the crystallinity. The achievable draw ratios during solid-state extrusion, and in consequence the final mechanical properties, were lower for poly(L/D-lactide) and poly(L/DL-lactide) than for poly(L-lactide).

Calorimetry, Differential Scanning↗
PubMed1996

Bone regeneration with resorbable polymeric membranes. III. Effect of poly(L-lactide) membrane pore size on the bone healing process in large defects.

Poly(L-lactide) membranes of various pore sizes: microporous, medium pore size (10-20 microns), and large pore size (20-200 microns) were implanted in 15 mature New Zealand female rabbits to cover a 10-mm diaphyseal defect created in the radius. Five rabbits were implanted with each membrane. No internal fixation was used, as it was assumed that the intact ulna splints the radius adequately. Postoperative radiographs revealed the formation of hematoma within the bone defect. At the 2nd week after surgery, the hematoma was resorbed and the formation of new bone was noted radiologically either at the ends of the bone fragments or as osteophytes on the proximal and distal edges of the membrane. At 4 weeks, the newly formed bone was growing centripetally from the fragment ends. The bone regeneration took place in the majority of the cases under investigation, regardless of the pore size of the polymeric membranes used. There were, however, some differences in the intensity of the bone regeneration process. Although at 2 weeks after surgery bone formation was seen radiographically in all animals, at 6 months five rabbits of five, four rabbits of five, and three rabbits of five implanted respectively with microporous membrane, medium pore-size membrane, and large pore-size membrane showed complete regeneration of bone within the defects. It is suggested that the primary function of the membrane used to cover bone defects is to preserve the osteogenic components present in the space under the membrane from escaping and support the growth of cells within the "medullary cavity" formed by the tubular implant.

Animals↗
PubMed1996

Sterility, mechanical properties, and molecular stability of polylactide internal-fixation devices treated with low-temperature plasmas.

The effect of low-temperature plasma on sterility, molecular, mechanical, and crystalline properties of poly (L-lactide), poly (L/D-lactide) and poly (L/DL-lactide) was investigated. Polymers were treated for 15 and 30 min at 100 W with nitrogen, argon, oxygen, and carbon dioxide plasma. All polymers treated with oxygen or carbon dioxide plasma were rendered sterile after 15 min of treatment. Only 70% of the samples treated under similar conditions with nitrogen or argon plasma were sterile. Extension of the exposure time to 30 min and increasing power to 200 W did not improve sterilization efficiency. Plasma sterilization, under the conditions used, caused no significant decrease or increase in overall molecular weight or polydispersity of the polylactides used. In most instances the effect of plasma sterilization was to slightly increase the overall molecular weight of the polymers studied. Treatment with argon plasma led to a more consistent increase in molecular weight than did treatment with nitrogen, oxygen, or carbon dioxide. Analysis of the surface (skin) of a poly(L-lactide) injection-molded rod following plasma sterilization indicated an increase in molecular weight as related to the interior (core) of the rod. Comparison of Mark-Houwink plots for the surface and interior of poly(L-lactide) injection-molded rods following plasma sterilization indicated an increase in chain branching for the surface relative to the interior of the rod. Generally the highly crystalline poly(L-lactide) was less susceptible to change upon plasma treatment than was the less crystalline poly(L/D-lactide) and poly(L/DL-lactide). The mechanical properties (shear strength, bending strength, and moduli) of the polylactides were not affected by plasma treatment. The overall melting temperature and the heat of melting of polylactides studied were not affected by plasma treatment. The melting temperature of the skin of the samples was about 1 degree C higher than the melting temperature of the core due to the chain orientation upon injection-molding. Plasma treatment of the polylactides reduced the melting temperature of the skin by 3 degrees C to 5 degrees C due to the crosslinking or branching at the surface layer.

Analysis of Variance↗
PubMed1996

The effect of thermal treatment on sterility, molecular and mechanical properties of various polylactides. I. Poly(L-lactide).

Resorbable pins for the treatment of osteochondral defects produced by injection-moulding from poly(L-lactide) were subjected to the action of heat at 105-150 degrees C under a low moisture and low oxygen atmosphere for a predetermined time. Standard procedures were used to evaluate the sterility, mechanical properties, molecular weight, polydisperity and crystallinity of the heat-treated samples. All of the heat-treated samples were sterile after 2 h of exposure to heat. There was an 10% increase in the shearing strength of the samples treated thermally for up to 10 h. This was attributed to the increase in overall crystallinity and crystal dimensions in the samples which enhanced the propagation of cracks formed upon testing through areas of high ductility. There was, however, a 20-35% drop in flexural strength which might result from the decreased concentration of the amorphous regions in the heat-treated implants. A 20% increase in molecular weight of the heat-treated implants was assigned to the transesterification process between the -OH and -COOH groups present initially in the polymer and/or formed due to chain scission upon exposure of the material to heat.

Biocompatible Materials↗
PubMed1996

Enhancement of the mechanical properties of polylactides by solid-state extrusion. I. Poly(D-lactide).

Resorbable rods with circular cross-section were produced from poly(D-lactide) with Mv = 160,000 by solid-state extrusion through a conical die. The effects of extrusion temperature and the draw ratio/rate in the solid state on the final mechanical properties and morphology of the rods were evaluated. While the rods produced from polylactides by routine injection-moulding have bending strengths in the range of 40-140 MPa and bending moduli in the range of 2-5 GPa, the solid-state extrusion under the conditions applied led to rods with bending strengths at yield of up to 200 MPa and bending moduli of up to 9 GPa. Typically, for the highly oriented polymeric materials, the pins produced by the solid-state extrusion had highly fibrillated morphology.

Biocompatible Materials↗
PubMed1996

Bone regeneration with resorbable polymeric membranes: treatment of diaphyseal bone defects in the rabbit radius with poly(L-lactide) membrane. A pilot study.

Tubular poly(L-lactide) membranes with a pore size of 5-15 microns and a molecular weight of 70,000 Daltons were implanted into 24 New Zealand skeletally mature rabbits to cover 10-mm mid-diaphyseal defects of the radius of the forelimb. An identical defect on the contralateral limb was not treated with the membrane and served as a control. The animals were killed at 1, 2, 4, 8, 12, 24, 36, and 64 weeks after implantation, and radiographic and microscopic studies were conducted. The canals of the polymeric tubes were initially filled with blood. At 2 weeks, there was direct woven bone formation within the polymeric tube in continuity with the fragment cortices and its medullary canal. The formation of woven bone across the defect progressed until reconstruction of the defect had occurred at 6-8 weeks. The bone continued to remodel throughout the observation period of 64 weeks. By 12 weeks, bone within the lumen of the implant consisted of cancellous bone and cortical bone lining the membrane walls. At 24, 36, and 64 weeks, the implants were filled with cancellous bone and cortical bone in direct apposition to the polymer membrane. For one implant, the newly formed woven bone had only incompletely filled the defect at 8 weeks. This resulted in a nonunion with a residual gap of 0.5 mm and the appearance of mature bone. There was extensive bone formation along the intraosseous membrane in both control and implanted defects, although the untreated defects were rapidly filled with overlying muscle and soft tissues. The osseous activity of the untreated defects appeared confined to the bone ends by the interposed muscle and fibrous soft-tissue margins. The untreated defects resulted in radial-ulnar synostosis along the intraosseous membrane with cortical bone caps at the bone ends. The poly(L-lactide) membrane remained intact throughout the 64-week period without evidence of significant degradation. The membranes were encapsulated in a thin fibrous tissue. There was no histological evidence of acute or chronic inflammation associated with the implants.

Animals↗
PubMed1996

[Digestive involvement in dystrophic bullous epidermolysis. Presentation of 2 cases and review of the literature].

Congenital epidermolysis bullosa is an inherited disorder characterized by an anomaly of joint structures between epidermis and dermis. This anomaly involves different malpighian epithelium and particularly in the digestive chorioepithelial junction. Digestive and oropharyngeal manifestations include bullae, erosions and ulcerations that heal by fibrosis, leading to retraction and stenosis. We report two cases of esophageal stenosis, the first one in a young patient with a congenital epidermolysis bullosa of Hallopeau-Siemens and the second one, in a young woman with a Pasini variant. In the first case, the esophageal stenosis was treated by careful dilation. In the second case, the endoscopy induced hemorragic bullae and septicemia, which were treated with antibiotics and total parenteral nutrition.

Adolescent↗
PubMed1993

Tissue response and in vivo degradation of selected polyhydroxyacids: polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA).

The tissue response and in vivo molecular stability of injection-molded polyhydroxyacids--polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA, 5-22% VA content)--were studied. Polymers were implanted subcutaneously in mice and extirpated at 1, 3, and 6 months in order to study tissue response and polymer degradation. All polymers were well tolerated by the tissue. No acute inflammation, abscess formation, or tissue necrosis was observed in tissues adjacent to the implanted materials. Furthermore, no tissue reactivity or cellular mobilization was evident remote from the implant site. Mononuclear macrophages, proliferating fibroblasts, and mature vascularized fibrous capsules were typical of the tissue response. Degradation of the polymers was accompanied by an increase in collagen deposition. For the polylactide series, the inflammatory response after 1 month of implantation was less for materials containing the D-unit in the polymer chain, whereas in the case of the polyhydroxybutyrate/valerates, the number of inflammatory cells increased with increasing content of the valerate unit in the polymer chain. Between 1-3 months, there was slightly more tissue response to the PHB and PHB/VA polymers than to PLA. This response is attributed to the presence of leachable impurities and a low molecular weight soluble component in the polyhydroxybutyrate/valerates. At 6 months, the extent of tissue reaction was similar for both types of polymers. All polylactides degraded significantly (56-99%) by 6 months. For a poly(L-lactide) series, degradation rate in vivo decreased with increasing initial molecular weight of the injection-molded polymer. Several samples showed pronounced bimodal molecular weight distributions (MWD), which may be due to differences in degradation rate, resulting from variability in distribution of crystalline and amorphous regions within the samples. This may also be the result of two different mechanisms, i.e., nonenzymatic and enzymatic, which are involved in the degradation process, the latter being more extensive at the later stage of partially hydrolyzed polymer. The PHB and PHB/VA polymers degraded less (15-43%) than the polylactides following 6 months of implantation. Generally, the polymer with higher valerate content (19%, 22%) degraded most. The decrease in molecular weight was accompanied by a narrowing of the MWD for PHB and copolymers; there was no evidence of a bimodal MWD, possibly indicating that the critical molecular weight that would permit enzyme/polymer interaction had not been reached. Weight loss during implantation ranged from 0-50% for the polylactides, whereas for the PHB polymers weight loss ranged from 0-1.6%.

Absorption↗
PubMed1992

Resorbable polymers for internal fixation.

Bone fractures are usually fixed with metallic internal and/or external fixation devices. Such devices have to be removed from the implantation site, once the bone fracture is healed. Metallic devices may also corrode in vivo releasing ions into the tissues. An ideal internal fixation device should allow adequate fracture fixation, immediate recovery of mobility of the limb, and be produced from a material which can be safely left at the implantation site when the fracture healing is completed. Resorbable polymers are candidates for construction of such devices.

Animals↗
PubMed1992

Guided tissue regeneration using biodegradable membranes of polylactic acid or polyurethane.

The purpose of the present investigation was to evaluate the use of biodegradable membranes of polylactic acid or polyurethane for obtaining regeneration following treatment of circumferential periodontal defects in monkeys with the "guided tissue regeneration" procedure. Orthodontic elastic bands were placed around selected test and control teeth in 4 monkeys in order to induce breakdown of the periodontal tissues. When the destruction of the supporting tissues had progressed to a level corresponding to approximately half the length of the roots, the elastic bands were removed. After 1 to 8 months, full thickness flaps were raised on the buccal and lingual aspects of both test and control teeth. The exposed root surfaces were scaled and a notch was prepared in the root surface at the level of the reduced bone crest. Membranes of polylactic acid or polyurethane were placed circumferentially around the test teeth, while no membranes were placed around the control teeth. The tissue flaps were then sutured in a coronally displaced position. The surgical procedures and sacrifice of the animals were scheduled to provide observation times of 1, 4 and 8 months. During the healing period, various complications such as recession of the flap margins and exposure or exfoliation of the membranes were noticed. The histological analysis showed that the amount of new connective tissue attachment on test and control teeth did not differ and was restricted to the most apical part of the lesions. The bio-degradable membranes could be identified in a few specimens, and they were always surrounded by an epithelial layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Biodegradable guide for bone regeneration. Polyurethane membranes tested in rabbit radius defects.

Segmental, 1-cm osteoperiosteal defects were produced in both radii of 10 rabbits. One defect was covered with a biodegradable polyurethane membrane formed as a tube. The contralateral defect served as an untreated control. Healing was analyzed by radiographic and histologic studies after 5 weeks. Nine out of 10 control defects displayed nonunion, whereas membrane-treated defects consistently healed by forming callus external to the membrane fusing the bone fragments. Loose connective tissue was predominant in the bone gap underneath the membrane. Presumably, the membrane has served as a scaffold for regenerating periosteum.

Animals↗
PubMed1989

Long-term patency of regenerated neoaortic wall following the implant of a fully biodegradable polyurethane prosthesis: experimental lipid diet model in pigs.

The degradation of a polyurethane vascular prosthesis, the time course and characteristics of tissue ingrowth and prosthesis replacement, and the incidence of thrombosis have been investigated in 50 young pigs. A 6-7 cm long cone-shaped prosthesis was implanted in the infrarenal aorta of 50 young growing pigs which were sacrificed at intervals from 60 to 365 days. Ten animals were controls, 25 were given aspirin 10 mg/kg of body weight/day, and 15 were fed with cod liver oil. Aortography, done at 30, 60, and 90 days, showed 100% of implants were thrombosed in the surviving controls, 55% of the aspirin group had patent grafts, and 100% of animals in the lipid diet group had patent grafts. At final graft retrieval, the aspirin group showed only three patencies, while in the lipid diet group seven out of nine animals were patent. The laboratory and morphological studies indicated that all patent prostheses were lined with tissue that resembled the intima of native aorta with a layer of smooth muscle cells which appeared complete at 180 days. From these data we conclude that the biodegradable polyurethane vascular prosthesis is reliable for experimental implants in a pig model. The lipid-rich diet of polyunsaturated fatty acids potentiates long-term patency, perhaps by preventing platelet aggregation and thrombosis, and allowing the growth of a neoendothelium and neomedia within the lumen of the prosthesis, which slowly degrade towards fatty tissue and form neoadventitia.

Animals↗
PubMed1989

Prevention of platelet aggregation by dietary polyunsaturated fatty acids in the biodegradable polyurethane vascular prosthesis: an experimental model in pigs.

A 6-7 cm long degradable polyurethane vascular prosthesis was implanted in the infrarenal aorta of 25 young growing pigs, sacrificed from day 30 to 365 to study the processes of degradation and tissue growth, the characteristics of prosthetic substitutes and the incidence of thrombosis. Ten animals were used as controls and 15 were fed with cod liver oil (25 ml twice daily). Aortography performed at day 30, 60 and 90 showed 100% thrombosed implants in the controls, while in the lipid diet fed animals there was 100% patency. At graft retrieval, there were 7 patent grafts out of 9 in the cod liver oil fed animals. Laboratory tests indicated that the lipid diet rich in n-3 polyunsaturated fatty acids induces significant modifications of lipid metabolism preventing platelet aggregation. These data correlate well with findings of the morphological studies showing that all patent prostheses are lined with tissues similar to the endothelium of the native aorta with a mid layer made of circular and longitudinal smooth muscle cells well differentiated at day 180. These data show that the essential polyunsaturated fatty acid rich diet is able to prevent thrombosis of the biodegradable polyurethane vascular prosthesis. The combination of a synthetic material and the lipid diet experimental model, makes it possible to assess the long-term tissue-synthetic material interaction and the process of tissue growth.

Animals↗
PubMed1983

Development of a neo-artery induced by a biodegradable polymeric vascular prosthesis.

A microporous, compliant and biodegradable vascular prosthesis prepared from a polyurethane-poly-L-lactic-acid (PU-PLLA) mixture, induces fast growth of a neo-artery after implantation as an arterial substitute. The prostheses used in this study resulted in 100% patency. Mechanical functionality of the neo-arteries is suggested by the regeneration of elastic laminae throughout the subintimal tissue. The fact that elastogenesis occurs in our biodegradable PU-PLLA graft may be a step forward in solving the problem of how to maintain a natural compliance in vascular prostheses.

Animals↗