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PubMed2002

New tubular bioabsorbable knitted airway stent: biocompatibility and mechanical strength.

OBJECTIVE: This study examines the biocompatibility and suitability of a new tubular bioabsorbable knitted stent made of poly-L -lactic acid in normal rabbit airways and examines the mechanical strength of this stent in vitro. METHODS: A tubular knitted airway stent (group B, n = 15) made of poly-L -lactic acid wire was implanted operatively in New Zealand White rabbits intratracheally; silicone stents served as controls (group A, n = 8). The cervical trachea was exposed, and the stent was implanted. Up to 40 weeks after stent implantation, the rabbits were killed, at which time bronchoscopy, histologic examination, and scanning electron microscopic study was done. We tested poly-L -lactic acid stents and silicone stents for their mechanical strength in vitro. We subjected stents to area loads and measured their mechanical strengths. RESULTS: In group A, which received silicone stents, 3 (37.5%) rabbits died within 4 weeks of stent implantation as a result of airway obstruction by secretions inside the stent lumen. In group B, poly-L -lactic acid stents, 1 (6.7%) rabbit died 3 weeks after implantation because of weakness caused by anorexia. In the remaining animals, except for 1 animal with stent trouble, the bronchial lumen was fully open until the 40th week after implantation. After 40 weeks of follow-up, the stents disappeared, except for nonabsorbable suture in the bronchial wall. None of the animals in group B died of airway complication. Histologic examination and scanning electron microscopic examination of the group A silicone stents showed marked regression of ciliated cells under the stent. In group B the ciliated epithelium was preserved, and there were numerous capillary blood vessels in the submucosa. In scanning electron microscopy of the group B poly-L -lactic acid stents, the ciliated cells were preserved between the mesh holes of the stent. For diameters between 4 and 6 mm, the mechanical strength of silicone stents was greater than that of poly-L -lactic acid stents. However, the mechanical strength of poly-L -lactic acid stents increased as a function of their diameter. CONCLUSION: A new tubular bioabsorbable stent made of poly-L -lactic acid is biocompatible in normal rabbit airways, indicating that poly-L -lactic acid is a promising material for airway stents for clinical use.

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PubMed2005

Evaluation of the adjunctive benefits of platelet-rich plasma in subantral sinus augmentation.

Subantral sinus augmentation is often necessary to permit placement of endosseous implants. Recent efforts to improve wound healing have focused on autogenous sources of bioactive mediators, such as platelet-rich plasma (PRP), which offer the potential to enhance the biological activity of bone replacement grafts. The purpose of this randomized, single-blinded, controlled study was to compare bone formation after subantral maxillary sinus augmentation with freeze-dried bone allograft (FDBA) plus PRP versus FDBA plus resorbable membrane. Ten patients underwent bilateral maxillary subantral sinus augmentation, with sites within subjects randomized to receive FDBA plus PRP or FDBA plus membrane. Core biopsy specimens were obtained 4.5 to 6 months after the grafting procedure at time of implant placement. Histomorphometric analysis revealed a significantly higher percentage of vital tissue in sinuses after treatment with FDBA and PRP (78.8 +/- 8.3) than with FDBA and membrane (63.0 +/- 15.7). Moreover, the percentage of bone formation in sinuses augmented with the combination of FDBA plus PRP (33.3 +/- 11.3) was nonsignificantly (P </= 0.10) higher than in sinuses grafted with FDBA plus membrane (26.5 +/- 6.8). Residual graft particles constituted a significantly higher percentage of the regenerate in sinuses treated with FDBA plus membrane than in sinuses augmented with FDBA plus PRP (37.0 +/- 15.7) versus (21.2 +/- 8.3, respectively). When comparing the relative proportion of vital bone to residual graft particles, a significant difference also was observed between sinuses treated with FDBA and membrane compared with sinuses augmented with FDBA and PRP (0.98 +/- 0.77 versus 1.82 +/- 0.88, respectively). The results of this study suggest that the combination of FDBA and PRP enhances the rate of formation of bone compared with FDBA and membrane, when used in subantral sinus augmentation. Future research is needed to determine the clinical significance and the cost- and risk-benefit considerations of the approach.

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PubMed2003

The importance of angiogenesis in the interaction between polymeric biomaterials and surrounding tissue.

The uncomplicated outcome of surgical interventions after biomedical application of biomaterials depends on successful wound healing. Wound healing is a highly complex process compossed of a number of overlapping phases, including inflammation, epithelialization, angiogenesis and matrix deposition. Inadequate angiogenesis limits the transport between the microvasculature and implanted biomaterials. The regulation of angiogenesis is based on numerous growth factors, proteolytic enzymes, extracellular matrix components, cell adhesion molecules, and vasoactive factors. Capillary endothelial cells were grown for different time periods (day 1, 3, 6, 9 and 12) on the surface of a recently developed biodegradable polymeric biomaterial. As control the cells were seeded on the gelatine coated polystyrene surface of commercially available cell cultures dishes. Endothelial cells became adherent and showed confluent cells layers during increasing time period on both surfaces. The total cell number of cells grown on the gelatine coated polystyrene surface was higher in comparison to the polymer surface. The chorioallantois membrane (CAM) assay was used as a sensitive assay to investigate the influence of angiogenesis in vivo. After 48 hours of exposure of the CAM to polymer samples no avascular zones, free of capillaries and/or thrombosis or hemorrhage were detectable. Considering the biofunctionality of our recently developed polymer in these experiments different surface modifications of the polymer are the topic of current investigation to support the biomaterial-microvasculature interactions in vivo.

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PubMed2005

A tissue-engineered artificial bile duct grown to resemble the native bile duct.

The aim of this study was to fabricate an artificial bile duct for the development of a new treatment for biliary diseases. Eighteen hybrid pigs were implanted with a bile duct organoid unit (BDOU) made of a bioabsorbable polymer. Twelve of the transplanted BDOUs had been seeded with autologous bone marrow cells (BMCs) in advance. Six animals, the controls, were grafted with the scaffold alone with no BMCs seeded. The common bile duct was cut, the hepatic cut end of the native common bile duct was anastomosed to the BDOU and the other end was anastomosed to the duodenum. The controls underwent a similar operation. The neo-bile duct was removed at pre-determined time points and investigated histologically. All 18 recipient pigs survived until their sacrifice at 6 weeks, 10 weeks or 6 months. Histological examination revealed incomplete epithelialization of the neo-bile duct at 6 weeks and 10 weeks after transplantation. At 6 months, the organoid exhibited a morphology almost identical to that of the native common bile duct. No differences were found between the controls and BMC-seeded pigs. These results show that the artificial bile duct thus fabricated can serve as a substitute for the native bile duct.

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PubMed2006

Maxillary sinus augmentation using an engineered porous hydroxyapatite: a clinical, histological, and transmission electron microscopy study in man.

Porous hydroxyapatite (HA) is a calcium-phosphate-based material that is biocompatible, nonimmunological, and osteoconductive, and has a macroporosity of about 200 to 800 microm. The pores seem to be able to induce migration, adhesion, and proliferation of osteoblasts inside the pore network and to promote angiogenesis inside the pore system. The aim of this study was to evaluate the clinical behavior and the histological and ultrastructural aspects of porous HA in maxillary sinus augmentation procedures. Twenty-four patients (19 men, 5 women; average age 53.4 years) in good general physical and mental health and with partially or completely edentulous maxillae were selected for this study. Six months after sinus floor elevation, at the time of dental implant placement, biopsies were carried out under local anesthesia. These bone cores were cut in half and were processed for light and transmission electron microscopy. After a mean 3 years after implantation, all implants are clinically in function and no surgical or prosthetic complications have occurred. Under light microscopy, newly formed bone was 38.5% +/- 4.5%, whereas the residual biomaterial represented 12% +/- 2.3% and the marrow spaces represented 44.6% +/- 4.2%. In addition, in the majority of cases, the biomaterial particles were in close contact with the bone, which appeared compact with the characteristic features of well-organized lamellar bone. A cement-like line was slightly visible at the bone-biomaterial interface, but there were no gaps or interposed connective tissue in between. A high quantity (about 40%) of newly formed bone was present. Bone was closely apposed to the biomaterials particles as shown in light microscopy and transmission electron microscopy. Moreover, no signs of inflammatory cell infiltrate or foreign body reaction were present. Also, most of the biomaterial was resorbed and only a small quantity (a little more than 10%) was still present. The results of our study show that porous HA can be a suitable synthetic material for bone regeneration in maxillary sinus augmentation procedures.

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PubMed2000

The foreign body reaction to a biodegradable biomaterial differs between rats and mice.

Before a biomaterial can be applied in the clinic, biocompatibility must be tested in in vivo models, by monitoring the foreign body reaction. In this study, we compared the foreign body reaction (FBR) to the biodegradable biomaterial hexamethylenediisocyanate crosslinked dermal sheep collagen (HDSC) between several strains of rats and mice. HDSC disks were implanted subcutaneously on the backs of AO, BN, F344, LEW, and PVG rats and on the backs of 129 SVEV, BALB/c, and C57BL/6 mice. Materials were explanted after 7, 14, 21, and 28 days and processed for (immuno) light and transmission electron microscopic evaluation. In all rat strains, giant cell formation and phagocytosis of HDSC bundles were comparable. In addition, in the PVG rat, many plasma cells infiltrated the HDSC disks. Only a few T cells were present in AO and PVG rats, whereas, in F344 and LEW rats, the presence of T cells was more pronounced. BN rats showed an intermediate T-cell infiltration. In mice, the FBR to HDSC was comparable between the different strains. Compared with rats, giant cell formation was limited, whereas stroma formation was more abundant. Phagocytosis of HDSC bundles rarely occurred in mice, whereas calcification was observed more often. It is concluded that the FBR to HDSC clearly differs between rats and mice. This has consequences for assessment studies on biocompatibility and also on fundamental biomaterial research.

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PubMed2006

Hyaluronan biodegradable scaffold for small-caliber artery grafting: preliminary results in an animal model.

OBJECTIVE: To evaluate a new Hyaluronan-based graft. MATERIAL AND METHODS: Hyaluronan-based grafts (HYAFF 11trade mark tube, diameter 2 mm, length 1.5 cm) were implanted in an end-to-end fashion in the abdominal aorta of 15 rats. Histology, immunohistochemistry and electron microscopy were used to evaluate the results at 7, 21, and 90 days. RESULTS: At day 7, new tissue was observed in the graft coming from both the proximal and distal ends of the aorta. The luminal surface of the regenerating tissue was covered by endothelial cells (CD34(+), VEGFR-2(+), vWF(+)). At day 21, regenerating tissue joined at the centre of the tube. The neo-vessel was formed by smooth muscle cells (Myosin Light Chain Kinase) as well as elastic, and collagen fibres. At day 90 a stable artery segment was formed and the biomaterial was almost completely degraded. Infiltration of neutrophils and lymphocytes was not observed. All animals survived the observation period and there were no signs of stenoses or aneurysms. CONCLUSION: The hyaluronan-based graft allowed complete regeneration of a newly formed vascular tube in which all the cellular and extracellular components are present and organized in a well defined architecture similar to native artery.

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PubMed2005

Load-shift--numerical evaluation of a new design philosophy for uncemented hip prostheses.

All hip replacement prostheses alter the load transfer from the hip joint into the femur by changing the mechanical loading of the proximal femur from an externally to an internally loaded system. This alteration of the load transfer causes stress shielding and might lead to severe bone loss, especially with uncemented prostheses. To minimize these effects, load transfer to the femur should occur as proximal as possible. In order to support sufficient primary stability, however, directly post operative (PO) distal stabilization is reasonable. Consequently, the prostheses have to alter its mechanical characteristics after implantation. This concept is referred to as load-shift concept. Primary stability during the early PO state is provided by a prosthesis shaft, which is widened at the tip by a biodegradable pin. After resorption of the pin load transfer occurs no longer distally. The objective of this study was the numerical evaluation of the load-shift concept. The analysis was performed with a finite element model. Three-dimensional non-linear dynamic gait analyses data were used to evaluate whether the load transfer during walking can be altered effectively by insertion and resorption of a distal pin. Directly PO 38% of the transverse load is transferred through the prosthesis shaft and micromotion of the proximal prostheses tip is below 55 microm. After resorption of the pin, no transverse loads are transferred through the prosthesis shaft. Therefore, the loading of the proximal bone tissue is far more pronounced than in the case of a standard prosthesis, demonstrating the feasibility of the load-shift concept. A balanced degradation of the pin simultaneously with the ingrowth of the prosthesis is expected to reduce hip replacement complications.

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PubMed2004

In vitro and in vivo correlation of buserelin release from biodegradable implants using statistical moment analysis.

Here we investigated the possibility to develop different levels of correlation between in vitro drug release profiles and in vivo pharmacokinetic parameters for three Buserelin implant formulations. The in vitro and in vivo data were analyzed using model-independent and model-dependent methods. Since diffusion, dissolution and erosion effects influence drug release in most cases a simple kinetic model is unlikely to explain the overall in vivo release behavior. Thus the in vitro drug release curves were analyzed according to the theoretical models of Higuchi and Korsmeyer-Peppas. For the formulation with predominant diffusion controlled release level A IVIVC could be established (R2=0.986). Independent on drug release mechanism, a level B correlation between the mean in vitro dissolution time (MDT) and mean in vivo residence time (MRT) was obtained with a correlation coefficient of 0.983. Finally, level C correlation were observed when single in vitro parameters, e.g. T50% (time required to release 50% of drug in vitro) where compared with single in vivo parameters like AUC. This study suggests that a level B correlation could be achieved even when drug release occurs by a combination of diffusion and erosion processes. More sophisticated in vitro models mimicking drug release under in vivo conditions are clearly desirable for parenteral depot formulations.

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PubMed2003

Bone augmentation osteogenesis using hydroxyapatite and beta-tricalcium phosphate blocks.

PURPOSE: In this study, we investigated the differences in osteogenesis and resorption between hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) implanted on the parietal bone of rats. MATERIALS AND METHODS: HA and beta-TCP were used in blocks with macropores and micropores. They were implanted between the parietal bone and the cranial periosteum in rats. Osteogenesis around the implanted materials was investigated histopathologically and histomorphometrically at 1, 2, 4, 8, and 24 weeks after surgery. RESULTS: At 2 weeks, osteogenesis from the parietal bone was observed around both materials, and new bone had attached directly to the surfaces of both materials. New bone grew into the pores of the upper regions of both materials with time. The beta-TCP block had a characteristic basophilic reticular structure in which the dissolution of the materials was observed close to the new bone. The HA blocks were stable for 24 weeks, whereas parts of the beta-TCP blocks were fractured and resorbed at 24 weeks. Histomorphometrically, the volume of new bone around HA was larger than that around beta-TCP. There was no remarkable change in the amount of remaining HA, but that of beta-TCP was decreased. CONCLUSION: HA blocks in this model are suitable for onlay grafts because of its stability and osteogenesis, beta-TCP is not stable. Therefore, when beta-TCP blocks are used for onlay grafts, the mechanical stress on the recipient site should be taken into consideration because of resorption and fracture.

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PubMed2001

Histology of human alveolar bone regeneration with a porous tricalcium phosphate. A report of two cases.

Porous beta-phase tricalcium phosphate particles (pTCP) (Cerasorb) were used in two patients to restore or augment alveolar bone prior to the placement of dental implants. In one patient, pTCP was used to fill a large alveolar defect in the posterior mandible after the removal of a residual cyst, and in another patient to augment the sinus floor. Biopsies were taken at the time of implant placement, 9.5 and 8 months after grafting, respectively, and processed for hard tissue histology. Goldner-stained histological sections showed considerable replacement of the bone substitute by bone and bone marrow. In the 9.5 months biopsy of the mandible, 34% of the biopsy consisted of mineralised bone tissue and 29% of remaining pTCP, while the biopsy at 8 months after sinus floor augmentation consisted of 20% mineralised bone and 44% remaining pTCP. Bone and osteoid were lying in close contact with the remaining pTCP and were also seen within the micropores of the grafted particles. Tartrate resistant-acid phosphatase (TRAP) multinuclear cells, presumably osteoclasts, were found surrounding, within and in close contact with the pTCP particles, suggesting active resorption of the bone substitute. Remodelling of immature woven bone into mature lamellar bone was also found. No histological signs of inflammation were detected. The limited data presented from these two cases suggest that this graft material, possibly by virtue of its porosity and chemical nature, may be a suitable bone substitute that can biodegrade and be replaced by new mineralising bone tissue.

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PubMed2004

Periodontal repair in dogs: evaluation of a bioresorbable calcium phosphate cement (Ceredex) as a carrier for rhBMP-2.

BACKGROUND: Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to induce clinically relevant bone formation for orthopedic, craniofacial, and oral indications. It appears critical, in particular for onlay indications, that the associated carrier technology exhibits structural integrity to offset compressive forces in support of rhBMP-2-induced bone formation. The objective of this study was to evaluate a calcium phosphate (CP) cement, Ceredex, as a candidate carrier for rhBMP-2 in a defect model with limited osteogenic potential. MATERIALS: Bilateral, critical size, 6-mm, supra-alveolar, periodontal defects were created in six, adult, male, Hound Labrador mongrels. Three animals received rhBMP-2/Ceredex (rhBMP-2 at 0.20 and 0.40 mg/ml) in contralateral defect sites (implant volume/defect approximately 1 ml). One defect site in each of the three remaining animals received Ceredex without rhBMP-2 (control). The animals were euthanized at 12 weeks postsurgery for histologic and histometric analysis. RESULTS: Mean induced bone height exceeded 80% of the defect height for supra-alveolar periodontal defects receiving rhBMP-2/Ceredex without major differences between rhBMP-2 concentrations compared with approximately 40% for the control. The newly formed bone, a mixture of lamellar and woven bone in fibrovascular tissue, circumscribed relatively large portions of the residual Ceredex biomaterial. Inflammatory lesions were associated with limited bone formation in some sites. From a periodontal perspective, sites receiving rhBMP-2/Ceredex exhibited increased cementum formation compared with control, but without a functionally oriented periodontal ligament, and increased ankylosis and root resorption. Control sites exhibited early wound failure and exposure, loss of the Ceredex biomaterial, and limited bone formation. CONCLUSIONS: The Ceredex CP cement appears a potentially promising carrier technology for rhBMP-2 onlay indications. However, a slow resorption rate may prevent its wider use. This study does not support use of the rhBMP-2/Ceredex combination for periodontal indications.

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PubMed2003

Changes in alveolar bone height and width following post-extraction ridge augmentation using a fixed bioabsorbable membrane and demineralized freeze-dried bone osteoinductive graft.

BACKGROUND: It has been shown that the amount of healed bone following guided bone regeneration (GBR) with demineralized freeze-dried bone allograft (DFDBA) and a bioabsorbable membrane is significantly less than the initial quantity. A study was designed to determine if the amount of GBR would be affected by using an osteoinductive DFDBA and bioabsorbable membrane and membrane stabilization. METHODS: Eleven extraction sites (10 patients) were treated with DFDBA and bioabsorbable membrane before placing endosseous implants. Standardized alveolar height and width measurements were taken after extraction, GBR, and 4 months postoperatively, at predetermined measurement points (sites midpoint and 3 mm mesial and distal from the midpoint) and classified as augmented (<1 mm increase of GBR height or width) or grafted (>1 mm increase). Five membranes were stabilized. RESULTS: Three mm from the crest, augmented points exhibited a complete loss of augmented width. There was also some loss of pre-GBR bone width (ranging from 4.7% to 20%) at augmented and grafted points. Five mm from the crest, augmented points lost 83.3% to 92.3% of augmented width and grafted points lost 12.9% to 18% of pre-GBR width. Loss of augmented height ranged from 93.5% to 100%. Augmented (except distal) and grafted measurement points lost 2.1% to 12% of pre-GBR height. Comparing tacked and non-tacked sites, the former manifested less loss of augmented bone width, the latter augmented bone height. CONCLUSIONS: Results indicate a complete loss of augmented width 3 mm from the crest and almost complete loss in height and width 5 mm from the crest. Membrane stabilization appeared beneficial.

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PubMed2003

Distribution patterns of the membrane glycoprotein CD44 during the foreign-body reaction to a degradable biomaterial in rats and mice.

Although biomaterials have been used in the clinical setting for a long time, little is known of the molecular mechanisms underlying the foreign-body reaction (FBR). A good understanding of these mechanisms is requisite for the controlled regulation of the FBR needed to prevent adverse tissue reactions and thus to improve the function of the biomaterial. Macrophages are essential in the inflammatory reaction in, as well as around, the implants, and they also are believed to initiate most of the adverse responses. Typically, during the FBR macrophages become activated and fuse into multinucleated giant cells (MnGCs). CD44, an integral membrane glycoprotein expressed on a broad spectrum of cell types, is involved in MnGC formation in vitro and in inflammation processes in general. In vivo it is not known whether CD44 is part of a specific protein machinery that enables macrophage fusion or whether it has additional functions in the FBR. In the present in vivo study, CD44 expression patterns were followed in rats and mice during the FBR to a degradable collagen type I biomaterial. We found that CD44 is upregulated on all migrating cells and on newly formed blood vessels at the onset of the FBR and that MnGCs, up to week 15 postimplantation, expressed CD44. Although no evidence was found that CD44 participates in macrophage fusion leading to multinucleation, it nevertheless may be an interesting target molecule for modulating the FBR in vivo, possibly by affecting cell activation, cell migration towards the biomaterial, vascularization, and MnGC formation.

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PubMed2004

Resorbability of bone substitute biomaterials by human osteoclasts.

Third generation biomaterials are being designed with the aim that once implanted they will help the body to heal itself. One desirable characteristic of these materials in bone is their ability to be remodeled, i.e. that osteoclasts resorb the material and it is subsequently replaced by newly formed bone through osteoblastic activity. So far the only way to test this biological property of bone substitutes are animal experiments with all their limitations like ethics, costs and limited transferability to man. The present study was designed, to develop a human in vitro assay, allowing to generate human osteoclasts directly on the biomaterial. The assay was validated using calcium phosphate cement and PMMA as biomaterials. Quantification was performed by raster electron microscopy and computer assisted image analysis. Dentin was used as internal standard. Our assay shows iso-bone resorbability of calcium phosphate cement in comparison to unresorbable PMMA cement. Both current clinical orthopedic practice and future skeletal engineering may profit from the availability and use of a test system for the assessment of resorption quality. The assay presented here allows to address this question of resorbability and to select the best materials for the use as bone substitutes in specific patients.

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PubMed2005

Fixation of syndesmotic ruptures in 38 patients with a malleolar fracture: a randomized study comparing a metallic and a bioabsorbable screw.

OBJECTIVES: To compare the performance of a metallic and a biodegradable screw in the fixation of tibia-fibula syndesmotic ruptures. DESIGN: A randomized, prospective, and blinded study. SETTING: Central hospital, Department of Surgery. PATIENTS: Forty consecutive patients with a clinically verified syndesmotic rupture in association with a malleolar fracture, of whom 38 completed the study. INTERVENTION: After syndesmosis rupture was diagnosed, implant selection was performed intraoperatively by a strict randomization with sealed envelopes. Eighteen patients were treated with a metallic screw, and 20 with a bioabsorbable polylevolactic acid screw. The metallic screws were removed in a second operation at 8 weeks postoperatively. All patients had a treatment-blinded clinical and radiographic control after a mean follow-up of 35 (range 17-51) months. MAIN OUTCOME MEASURES: Return to previous physical activity level, evaluation of ankle stability, range of motion, circumference of the ankle, and a radiographic evaluation of both ankles including a measure of the talocrural, medial joint, and syndesmotic space widths. RESULTS: More patients with a polylevolactic acid screw returned to their previous activity level, and there was less swelling in the ankles of these patients, but joint motion was similar between the groups. The mean values of syndesmotic and medial joint spaces were significantly higher in the radiographs of the operated ankles when compared to the uninjured ankle, but there was not a correlation to the type of screw used. CONCLUSIONS: Polylevolactic acid screws worked as well, or slightly better than, metallic ones in syndesmosis fixation in patients with an ankle fracture.

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PubMed2004

Characteristics of tissue-engineered cartilage from human auricular chondrocytes.

This study was done to define the mechanical and histological properties of tissue-engineered cartilage (TEC) derived from human chondrocytes and to compare these findings with those of native cartilage. Chondrocytes were obtained from 10 human auricular cartilages and seeded onto a biodegradable template of polyglycolic acid and poly L-lactic acid. Each template was shaped into a 1 cm x 2 cm rectangle. The templates were implanted in athymic mice for 8 weeks. Eight human auricular cartilages were used for comparison. Mechanical analysis with a tensile testing device provided values of ultimate tensile strength (UTS), stiffness, and resilience. Statistical analysis was performed with the Student's t-test. Histological assessment was done with hematoxylin-eosin staining along with other special stains. The TEC had UTS of 2.07 MPa, stiffness of 3.7 MPa, and resilience of 0.37 J/m3. The control specimens had UTS of 2.18 MPa, stiffness of 5.11 MPa, and resilience of 0.42 J/m3. No statistical difference was found between the experimental and control groups for each of the three parameters. Histological analysis showed mature cartilage with characteristic collagen, glycosaminoglycans, and elastin in the TEC. The neo-cartilage showed slightly smaller size and more irregular distribution of chondrocytes and unique fibrous capsule formation with peripheral infiltration of fibrous tissue. This study showed that the mechanical qualities of TEC from human chondrocytes are similar to those of native auricular cartilage. It suggests that the engineered cartilage from human chondrocytes may have sufficient strength and durability for clinical uses. The histological findings revealed some differences with neo-cartilage.

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PubMed2006

The effect of high temperature intraoperative molding on bioabsorbable PLLA-PGA craniofacial fixation.

Bioabsorbable internal fixation has become an established part of the surgeons' armamentarium. There are several unique aspects of bioabsorbable polymers that can enhance their versatility. One of these is the application of heat to adapt the implant. Hot-tip cautery has been used for years to cut and otherwise customize bioabsorbable implants intraoperatively. As the tips of these devices can reach temperatures of over 1,000 degrees C, there is the potential that such practice can modify the degradation properties of these polymers. This study was performed to better understand the extent to which this potential exists. Screw heads of an 82:18 poly-L-lactic acid and poly-glycolic acid copolymer were modified by repeated passage of a hot-tip cautery wire, deforming the hex geometry to that of a ball. There was no significant difference between the glass transition temperature (approximately 59 degrees C) and inherent viscosity (approximately 1.45 dL/g) of treated and untreated screw heads, indicating no overall change in these properties throughout the mass of the screw head. Additionally, these properties were measured and comparisons made between the treated screw heads and untreated plates made of the same polymer during 28-day exposure to an in vitro bath (pH 7.4, 37 degrees C). The glass transition temperature and inherent viscosity exhibited declines during this period, with no significant differences between the two groups. Collectively, these results suggest that hot-tip cautery results in no substantial changes in the degradation characteristics of this polymer.

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