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Biomedical subjects

P Mainil-Varlet

Publications and source records attributed to P Mainil-Varlet.

At least 19 recordsLinked to original sources
PubMed2006

Cartilage tissue engineering by expanded goat articular chondrocytes.

In this study we investigated whether expanded goat chondrocytes have the capacity to generate cartilaginous tissues with biochemical and biomechanical properties improving with time in culture. Goat chondrocytes were expanded in monolayer with or without combinations of FGF-2, TGF-beta1, and PDGFbb, and the postexpansion chondrogenic capacity assessed in pellet cultures. Expanded chondrocytes were also cultured for up to 6 weeks in HYAFF-M nonwoven meshes or Polyactive foams, and the resulting cartilaginous tissues were assessed histologically, biochemically, and biomechanically. Supplementation of the expansion medium with FGF-2 increased the proliferation rate of goat chondrocytes and enhanced their postexpansion chondrogenic capacity. FGF-2-expanded chondrocytes seeded in HYAFF-M or Polyactive scaffolds formed cartilaginous tissues with wet weight, glycosaminoglycan, and collagen content, increasing from 2 days to 6 weeks culture (up to respectively 2-, 8-, and 41-fold). Equilibrium and dynamic stiffness measured in HYAFF M-based constructs also increased with time, up to, respectively, 1.3- and 16-fold. This study demonstrates the feasibility to engineer goat cartilaginous tissues at different stages of development by varying culture time, and thus opens the possibility to test the effect of maturation stage of engineered cartilage on the outcome of cartilage repair in orthotopic goat models.

Animals↗
PubMed2005

Impact loading of articular cartilage during transplantation of osteochondral autograft.

Surgical reconstruction of articular surfaces by transplantation of osteochondral autografts has shown considerable promise in the treatment of focal articular lesions. During mosaicplasty, each cylindrical osteochondral graft is centred over the recipient hole and delivered by impacting the articular surface. Impact loading of articular cartilage has been associated with structural damage, loss of the viability of chondrocytes and subsequent degeneration of the articular cartilage. We have examined the relationship between single-impact loading and chondrocyte death for the specific confined-compression boundary conditions of mosaicplasty and the effect of repetitive impact loading which occurs during implantation of the graft on the resulting viability of the chondrocytes. Fresh bovine and porcine femoral condyles were used in this experiment. The percentage of chondrocyte death was found to vary logarithmically with single-impact energy and was predicted more strongly by the mean force of the impact rather than by the number of impacts required during placement of the graft. The significance of these results in regard to the surgical technique and design features of instruments for osteochondral transplantation is discussed.

Animals↗
PubMed2003

Short-term load bearing capacity of osteochondral autografts implanted by the mosaicplasty technique: an in vitro porcine model.

Articular surface congruency and graft stability are considered essential factors in the success of osteochondral grafting; however, quantitative measures of short-term load bearing capacity of grafts implanted by the mosaicplasty technique have not been reported. The purpose of this study was to develop a live tissue in vitro model to examine short-term fixation strength of mosaicplasty autografts immediately after and 1 week following graft implantation. Cylindrical osteochondral autografts were implanted in vitro by the mosaicplasty technique on five pairs of porcine femoral condyles within one and a half hours of animal sacrifice. Immediately following the surgical procedure, graft push-in and pull-out strength tests as well as indentation tests to determine modulus of the surrounding cancellous bone were performed on half of the specimens from the distal femurs of each animal. The remaining specimens, matched for location in the contralateral leg, were incubated in culture medium for 7 days prior to performing the same set of mechanical tests. Averaged push-in and pull-out graft fixation strength decreased 44% from 135.7 to 75.5N over the 7-day period, while no change in modulus was detected in the surrounding cancellous bone. These in vitro results demonstrate a substantial deterioration of short-term fixation strength of mosaicplasty grafts from the immediate post-operative state. Such a reduction in short-term graft load bearing capacity may pose a threat to the surgically established articular surface congruency and blood vessels formed during the early stages of the healing response.

Animals↗
PubMed2003

A static, closed and scaffold-free bioreactor system that permits chondrogenesis in vitro.

OBJECTIVE: To characterise in vitro engineered cartilaginous constructs made employing a novel static, scaffold-free and closed chamber system. DESIGN: Chondrocytes derived from slaughter age pigs (3-6 months) were seeded at high density (20 x 10(6)) into cylindrical chambers (1.0 x 0.5cm) and were maintained between an upper and a lower membrane (100 kDa) for 21 days and subsequently cultured in open culture for 7 additional days. RESULTS: Viable constructs produced were approximately 10 mmx2mm in size and were stable enough to be handled by surgical pincers. Histology and electron microscopy evaluations revealed a neo-cartilage structure of high cell density with a comprehensive extracellular matrix. Predominately collagen type II and negligible amounts of collagen types I and X were detected using RT-PCR and SDS-PAGE analyses. CONCLUSIONS: In this study, we provide evidence of a scaffold-free system that can produce immature hyaline-like cartilaginous constructs suitable for in vivo implantation, or that may be useful for in vitro studies of events related to the process of chondrogenesis.

Animals↗
PubMed2003

Early osteoarthritic changes of human femoral head cartilage subsequent to femoro-acetabular impingement.

OBJECTIVE: To use the surgical samples of patients with femoro-acetabular impingement due to a nonspherical head to analyze tissue morphology and early cartilage changes in a mechanical model of hip osteoarthritis (OA). DESIGN: An aberrant nonspherical shape of the femoral head has been assumed to cause an abutment conflict (impingement mechanism) of the hip with subsequent cartilage lesions of the acetabular rim and surface alterations of the nonspherical portion of the head. In this study, 22 samples of the nonspherical portions of the head have been obtained during hip surgery from young adults (mean 30.4 years, range 19-45 years) with an impingement conflict. The samples were first compared with tissue from the same area obtained from six age-matched deceased persons (control group) with normal hip morphology and second with cartilage from 14 older patients with advanced OA. All samples were characterized histologically and hyaline cartilage was graded according to the Mankin criteria. They were further subjected to examination on a molecular basis by immunohistology for cartilage oligomeric matrix protein (COMP), tenascin-C and a collagenase cleavage product (COL2-3/4C(long)) and by in situ hybridization for collagen type I and collagen type II. RESULTS: All samples from the patient group revealed hyaline cartilage with degenerative signs. According to the Mankin criteria, the cartilage alterations were significantly different when compared with the control group (p=0.007) but were less distinct when compared with cartilage from patients with advanced OA (p=0.014). Positive staining and distribution pattern for COMP, tenascin-C and COL2-3/4C(long) showed similarities between the samples from the impingement group and osteoarthritic cartilage but they were distinctly different when compared with healthy cartilage. Levels of collagen I and II transcripts were upregulated in 6 and 10, respectively, of the 14 samples with OA and in 9 and 12, respectively, of the 22 samples from the impingement group. None of the samples from the control group showed upregulation of Collagen I and II mRNA. CONCLUSIONS: The aberrant nonspherical portion of the femoral head in young patients with an impingement conflict consists of hyaline cartilage which shows clear degenerative signs similar to the findings in osteoarthritic cartilage. The tissue alterations are distinctly different when compared with a control group, which substantiates an impingement conflict as an early mechanism for degeneration at the hip joint periphery.

Adult↗
PubMed2001

Polylactide implants and bacterial contamination: an animal study.

Although bioresorbable aliphatic polyesters derived from lactic acid are now used clinically as sutures, bone-fracture fixation devices and sustained-release drug-delivery systems, very little is known about their behavior in the infected environment. The aim of the present study was to compare the resistance to infection of two polylactide implants with different degradation characteristics, and to evaluate the influence of a bacterial challenge on their mechanical and physicochemical properties. Various quantities of a beta-haemolyzing strain of Staphylococus aureus (V 8189-94) were inoculated into the medullary cavity of rabbit tibiae, and an extruded polylactide rod composed of either P(L)LA (Poly(L-Lactide)) or P(L/DL)LA (Poly(L/DL-Lactide)) was then inserted. Animals were sacrificed four weeks after surgery. The tibiae and implants were removed under sterile conditions and evaluated microbiologically by culturing. The severity of infection was graded according to positive colony-forming units in the bone. The mechanical properties of the retrieved implants were assessed by 4-point bending and shear tests, performed in compliance with the ASTM D790 standard and their physicochemical characteristics also were characterized. P(L)LA and P(L/DL)LA implants were equally resistant to local infection, their mechanical and physicochemical properties being unaffected by bacterial challenge. Hence, once an infection has become established, the release of bactericidal/bacteriostatic by-products during implant degradation does not appear to affect its natural course. The release of bactericidal/bacteriostatic degradation products at the implantation site is unlikely to affect the natural course of an established infection.

Animals↗
PubMed2001

Laser solder welding of articular cartilage: tensile strength and chondrocyte viability.

BACKGROUND AND OBJECTIVE: The surgical treatment of full-thickness cartilage defects in the knee joint remains a therapeutic challenge. Recently, new techniques for articular cartilage transplantation, such as mosaicplasty, have become available for cartilage repair. The long-term success of these techniques, however, depends not only on the chondrocyte viability but also on a lateral integration of the implant. The goal of this study was to evaluate the feasibility of cartilage welding by using albumin solder that was dye-enhanced to allow coagulation with 808-nm laser diode irradiation. STUDY DESIGN/MATERIALS AND METHODS: Conventional histology of light microscopy was compared with a viability staining to precisely determine the extent of thermal damage after laser welding. Indocyanine green (ICG) enhanced albumin solder (25% albumin, 0.5% HA, 0.1% ICG) was used for articular cartilage welding. For coagulation, the solder was irradiated through the cartilage implant by 808-nm laser light and the tensile strength of the weld was measured. RESULTS: Viability staining revealed a thermal damage of typically 500 m in depth at an irradiance of approximately 10 W/cm(2) for 8 seconds, whereas conventional histologies showed only half of the extent found by the viability test. Heat-bath investigations revealed a threshold temperature of minimum 54 degrees C for thermal damage of chondrocytes. Efficient cartilage bonding was obtained by using bovine albumin solder as adhesive. Maximum tensile strength of more than 10 N/cm(2) was achieved. CONCLUSIONS: Viability tests revealed that the thermal damage is much greater (up to twice) than expected after light microscopic characterization. This study shows the feasibility to strongly laser weld cartilage on cartilage by use of a dye-enhanced albumin solder. Possibilities to reduce the range of damage are suggested.

Animals↗
PubMed2001

In situ compressive stiffness, biochemical composition, and structural integrity of articular cartilage of the human knee joint.

OBJECTIVE: Reduction of compressive stiffness of articular cartilage has been reported as one of the first signs of cartilage degeneration. For the measurement of in situ compressive stiffness, a hand-held indentation probe has recently been developed and baseline data for macroscopically normal knee joint cartilage were provided. However, the histological stage of degeneration of the measured cartilage was not known. The purpose of this study was to investigate whether there is a relationship between the in situ measured compressive stiffness, the histological stage of degeneration, and the biochemical composition of articular cartilage. DESIGN: Instantaneous compressive stiffness was measured for the articular cartilage of 24 human cadaver knees. Additionally, biochemical composition (total proteoglycan and collagen content) and histological appearance (according to the Mankin score) were assessed for each measurement location. RESULTS: Despite visually normal surfaces, various histological signs of degeneration were present. A high correlation between Mankin score and cartilage stiffness was observed for the lateral patellar groove (R(2)=0.81), the medial (R(2)=0.83) and the lateral femoral condyle (R(2)=0.71), whereas a moderate correlation was found for the medial patellar groove (R(2)=0.44). No correlation was observed between biochemical composition and cartilage compressive stiffness. CONCLUSIONS: Our results are in agreement with others and show that the instantaneous compressive stiffness is primarily dependent on the integrity of the extracellular matrix, and not on the content of the major cartilage constituents. The high correlation between stiffness and Mankin score in mild osteoarthrosis suggests that the stage of cartilage degeneration can be assessed quantitatively with the hand-held indentation probe. Moderate and severe case of osteoarthrosis remains to be investigated.

Adult↗
PubMed2001

Articular cartilage repair using a tissue-engineered cartilage-like implant: an animal study.

OBJECTIVE: Because articular cartilage has limited ability to repair itself, treatment of (osteo)chondral lesions remains a clinical challenge. We aimed to evaluate how well a tissue-engineered cartilage-like implant, derived from chondrocytes cultured in a novel patented, scaffold-free bioreactor system, would perform in minipig knees with chondral, superficial osteochondral, and full-thickness articular defects. DESIGN: For in vitro implant preparation, we used full-thickness porcine articular cartilage and digested chondrocytes. Bioreactors were seeded with 20x10(6) cells and incubated for 3 weeks. Subsequent to culture, tissue cartilage-like implants were divided for assessment of viability, formaldehyde-fixed and processed by standard histological methods. Some samples were also prepared for electron microscopy (TEM). Proteoglycans and collagens were identified and quantified by SDS-PAGE gels. For in vivo studies in adult minipigs, medial parapatellar arthrotomy was performed unilaterally. Three types of defects were created mechanically in the patellar groove of the femoral condyle. Tissue-engineered cartilage-like implants were placed using press-fit fixation, without supplementary fixation devices. Control defects were not grafted. Animals could bear full weight with an unlimited range of motion. At 4 and 24 weeks postsurgery, explanted knees were assessed using the modified ICRS classification for cartilage repair. RESULTS: After 3-4 weeks of bioreactor incubation, cultured chondrocytes developed a 700-microm- to 1-mm-thick cartilage-like tissue. Cell density was similar to that of fetal cartilage, and cells stained strongly for Alcian blue and safranin O. The percentage of viable cells remained nearly constant (approximately 90%). Collagen content was similar to that of articular cartilage, as shown by SDS-PAGE. At explantation, the gross morphological appearance of grafted defects appeared like normal cartilage, whereas controls showed irregular fibrous tissue covering the defect. Improved histologic appearance was maintained for 6 months postoperatively. Although defects were not always perfectly level upon implantation at explanation the implant level matched native cartilage levels with no tissue hypertrophy. Once in place, implants remodelled to tissues with decreased cell density and a columnar organization. CONCLUSIONS: Repair of cartilage defects with a tissue-engineered implant yielded a consistent gross cartilage repair with a matrix predominantly composed of type II collagen up to 6 months after implantation. This initial result holds promise for the use of this unique bioreactor/tissue-engineered implant in humans.

Animals↗
PubMed2001

Quantification of laser-induced cartilage injury by confocal microscopy in an ex vivo model.

BACKGROUND: The application of lasers in orthopaedic surgery is increasing. However, some investigators have reported that osteonecrosis may occur after laser meniscectomy. The objective of the present study was to evaluate the effect of laser wavelength and energy on cartilage injury in an ex vivo model. METHODS: Fresh bovine articular cartilage was exposed to either holmium:yttrium-aluminum-garnet (Ho:YAG) or erbium:YAG-laser (Er:YAG) irradiation. Both lasers were operated in a free-running mode and at a pulse-repetition rate of 8 Hz. The effect of laser treatment at several energy levels (Er:YAG at 100 and 150 mJ and Ho:YAG at 500 and 800 mJ) was examined. For each light source and energy level, ten cartilage samples were assessed by conventional histological analysis and by confocal microscopy. Thermal damage was assessed by determining cell viability. RESULTS: The extent of thermal damage demonstrated by confocal microscopy was much greater than that demonstrated by histological analysis. The extent of thermal injury after Ho:YAG-laser irradiation was much greater than that after Er:YAG-laser irradiation, which was associated with almost no damage. In addition, the ablation depth was greater after treatment with the Er:YAG laser than after treatment with the Ho:YAG laser. CONCLUSIONS: In the present study, histological analysis underestimated thermal damage after laser irradiation. In addition, our findings highlighted problems associated with use of high-power settings of Ho:YAG lasers during arthroscopic surgery.

Animals↗
PubMed2001

Tissue engineering in space.

The purpose of this paper is to present the status of that part of the [Microgravity Application Program] project related to the study of cartilage formation from pig chondrocytes. The work carried out so far followed two lines: (i) chondrocytes were incubated for up to three weeks in the RPM; (ii) a module developed for in-vitro cartilage formation will be tested in a sounding rocket flight (MASER 9, November 2001).

Animals↗
PubMed1997

Effect of in vivo and in vitro degradation on molecular and mechanical properties of various low-molecular-weight polylactides.

The in vivo and in vitro degradation of low-molecular-weight poly(L-lactide), poly(L/D-lactide), and poly (L/DL-lactide) rods was investigated. The low-molecular-weight fast-degrading materials were used to accelerate the degradation process and make the test conditions more critical. In the in vivo study the rods were implanted in the soft tissue of sheep and explanted at 1, 3, 6, and 12 months. In the in vitro experiments the samples were subjected to aging at 37 degrees C in the phosphate buffer using two different modes. In the so-called pseudodynamic mode the aging buffer was regularly replaced if the pH dropped more than 0.5. In the static mode the buffer was not changed over the whole testing period of 52 weeks. The mechanical, molecular, and crystalline properties of the rods were measured and their appearance in the course of aging was evaluated using scanning electron microscopy. It was found that the changes in the mechanical properties of poly(L-lactide), poly(L/D-lactide), and poly(L/DL-lactide) samples subjected to in vitro degradation tests in both the static and pseudodynamic modes are in good approximation with data obtained from the in vivo study. The pH of the buffer solution had no evident effect on the mechanical properties or the rate of degradation as estimated from the drop in molecular weight of the aged samples. The replacement of the aging buffer to maintain a constant pH at 7.4 does not seem to be critical for the degradation of the polylactides. In vitro degradation tests can be used as a relevant procedure for predicting the in vivo functionality of implants from the polylactides used if the criteria for assessing such a functionality are the changes in mechanical properties and molecular weight.

Animals↗
PubMed1997

Positional stability of polylactide pins with various surface textures in sheep tibia.

Resorbable pins with a smooth or textured surface were produced from poly(L-lactide) P(L)LA poly(L/D-lactide) 95/5% P(L/D)LA, and poly(L/DL-lactide) 95/5% P(L/DL)LA by injection molding. The pins were implanted in sheep tibiae to establish whether the pin surface geometry and the polymer composition used for the pin preparation affect their positional stability in bone; i.e., can the pin design and its ability to swell in body fluids protect against loosening. Three of the 32 P(L)LA pins with a smooth surface loosened but none of the P(L/D)LA and P(L/DL)LA pins with a smooth surface did. This may indicate that expansion of the pin upon swelling protects against loosening, even if the pin's surface geometry is not optimal. None of the pins with a textured surface were loose, independent of the polymer used for the pin preparation. The textured surface of these pins allowed the ongrowth of new bone and hence, implant anchoring, secured the positional stability of the implant in the bone.

Animals↗
PubMed1997

The use of a resorbable augmentation device to secure plating of osteoporotic bones. An in vitro study.

Osteotomies in porotic human cadaveric humeri were fixed with metallic plates and screws in 3 experimental groups. In group I, osteotomies of the 3 arbitrarily chosen humeri were plated without reinforcement. The osteotomies of the contralateral 3 humeri were plated after reinforcement with a poly(L-lactide) augmentation device. In group II, osteotomies on one side were plated without reinforcement, but those of the contralateral humeri were plated after reinforcement with methylmethacrylate. In group III, the osteotomies of 3 humeri were plated and reinforced with poly(L-lactide) and in the 3 contralateral humeri were plated after reinforcement with methylmethacrylate. The pullout strength for screws from bones augmented with poly(L-lactide) was identical to those where methylmethacrylate had been used. The bones with poly(L-lactide) augmentation had a higher torsional stiffness than those with methylmethacrylate cement and those which were not reinforced. Resorbable polymeric medullary augmentation devices can be used to enhance plating of osteoporotic bones.

Bone Cements↗
PubMed1997

Long-term in vivo degradation and bone reaction to various polylactides. 1. One-year results.

Injection-moulded pins from poly(L-lactide), poly(L/DL-lactide) (95/5%) were implanted in the cortex of the tibiae of sheep. The bone-implant interface was evaluated to observe whether there is any bone resorption caused by the implants. The molecular weight and crystallinity changes upon implantation were also measured. There was no net bone loss around the implants or sterile cyst formation in any of the animals implanted with polylactides up to 1 year. The new bone formed around the poly(L-lactide) and poly(L/D-lactide) pins was separated from the implants with a thin layer of connective tissue. For the implants from poly(L/DL-lactide), there was direct apposition of bone on the polymeric material. At 1 year of implantation, the implants were not completely resorbed, although the molecular weight of polylactides was reduced from 40,000-50,000 to 500-300. The crystallinity at 1 year was about 45% for poly(L/DL-lactide) and poly(L/DL-lactide) and 65% for poly(L-lactide), respectively, indicating the presence in the degraded material of thermodynamically stable crystals.

Animals↗
PubMed1997

Effect of thermal treatment on sterility, molecular and mechanical properties of various polylactides. 2. Poly(L/D-lactide) and poly(L/DL-lactide).

Pins for orthopaedic applications injection-moulded from as-supplied poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5%, raw as-supplied polymers or raw methanol-extracted polymers were heat-treated for a predetermined time at 135 degrees C under moisture-free argon. The sterility, molecular weight, polydispersity, mechanical properties, and crystallinity of the heat-treated samples were evaluated. All the samples heat treated under argon were sterile after 2 h exposure to heat. The heat-treated pins and raw as-supplied polymers showed a continuous decrease in molecular weight over the entire 50 h of heating, the decrease being more substantial for poly(L/D-lactide) than poly(L/DL-lactide). Raw methanol-extracted polymers showed an increase of molecular weight after 2 h of heat treatment, followed by a gradual decrease of molecular weight up to 50 h. A drop in the bending strength, an increase in the bending moduli, and no change in the shear strength was observed for polylactide pins during the first 5 h of thermal treatment. For both the polymers, there was a progressive increase in crystallinity over time of thermal treatment, and practically no change in the melting temperature.

Bone Nails↗