Biomedical subjects

C E Holy

Publications and source records attributed to C E Holy.

4 recordsLinked to original sources

PubMed2001

Optimizing the sterilization of PLGA scaffolds for use in tissue engineering.

There are few suitable techniques available to sterilize biodegradable polyester three-dimensional tissue engineering scaffolds because they are susceptible to degradation and/or morphological degeneration by high temperature and pressure. We used a novel polyllactide-co-glycolide) scaffold (Osteofoam) to determine the optimal sterilization procedure--i.e. a sterile product with minimal degradation and deformation. Initial studies, found that an argon plasma created at 100W for 4min was optimal for sterilizing Osteofoam scaffolds without affecting their morphology. The RFGD plasma sterilization method was compared to two well-established techniques--ethylene oxide (ETO) and gamma-irradiation (gamma)--which were in turn compared to disinfection in 70% ethanol. Disinfection in 70% ethanol serves as a useful control because it affects neither the morphology nor the molecular weight of the polymer: yet, ethanol is unsuitable as a sterilization method because it does not adequately eliminate hydrophilic viruses and bacterial spores. The three sterilization techniques, ETO, gamma and RFGD plasma, were compared in terms of their immediate and long-term effects on the dimensions, morphology, molecular weight and degradation profile of the scaffolds. Scaffolds shrank to 60% of their initial volume after ETO sterilization whereas their molecular weight (Mw) decreased by approximately 50% after gamma-irradiation. Thus, both ETO and gamma-irradiation posed immediate problems as sterilization techniques for 3-D biodegradable polyester scaffolds. During the in vitro degradation study, all sterilized samples showed advanced morphological and volume changes over time relative to ethanol (EtOH) disinfected samples, with the greatest changes observed for gamma-irradiated samples. ETO, RFGD plasma sterilized and EtOH disinfected samples showed similar changes in Mw and mass over the 8-week time frame. Overall, of the three sterilization techniques studied, RFGD plasma was the best.

Absorbable Implants↗

PubMed2000

Engineering three-dimensional bone tissue in vitro using biodegradable scaffolds: investigating initial cell-seeding density and culture period.

New three-dimensional (3D) scaffolds for bone tissue engineering have been developed throughout which bone cells grow, differentiate, and produce mineralized matrix. In this study, the percentage of cells anchoring to our polymer scaffolds as a function of initial cell seeding density was established; we then investigated bone tissue formation throughout our scaffolds as a function of initial cell seeding density and time in culture. Initial cell seeding densities ranging from 0.5 to 10 x 10(6) cells/cm(3) were seeded onto 3D scaffolds. After 1 h in culture, we determined that 25% of initial seeded cells had adhered to the scaffolds in static culture conditions. The cell-seeded scaffolds remained in culture for 3 and 6 weeks, to investigate the effect of initial cell seeding density on bone tissue formation in vitro. Further cultures using 1 x 10(6) cells/cm(3) were maintained for 1 h and 1, 2, 4, and 6 weeks to study bone tissue formation as a function of culture period. After 3 and 6 weeks in culture, scaffolds seeded with 1 x 10(6) cells/cm(3) showed similar tissue formation as those seeded with higher initial cell seeding densities. When initial cell seeding densities of 1 x 10(6) cells/cm(3) were used, osteocalcin immunolabeling indicative of osteoblast differentiation was seen throughout the scaffolds after only 2 weeks of culture. Von Kossa and tetracycline labeling, indicative of mineralization, occurred after 3 weeks. These results demonstrated that differentiated bone tissue was formed throughout 3D scaffolds after 2 weeks in culture using an optimized initial cell density, whereas mineralization of the tissue only occurred after 3 weeks. Furthermore, after 6 weeks in culture, newly formed bone tissue had replaced degrading polymer.

Animals↗

PubMed2000

Processing cell-seeded polyester scaffolds for histology.

Biodegradable 3-dimensional scaffolds of various morphologies are currently being developed for tissue engineering. Poly(lactide-co-glycolide)s (PLGAs) of various lactide to glycolide ratios are frequently used for such applications. Tissue engineering involves an in vitro stage during which cells are seeded onto scaffolds and allowed to settle and/or grow for various time periods. To assess cell distribution and/or tissue formation throughout the scaffolds during this in vitro stage, techniques such as confocal microscopy and magnetic resonance imaging have been applied. However, such cultured scaffolds have been refractory to histological evaluation because of numerous technical difficulties. We describe a method to prepare histological sections of cell cultured PLGA scaffolds for tissue engineering. The technique involves in situ labeling of cultured scaffolds, infiltration of the scaffolds with a 10% poly(vinyl alcohol) solution under a low vacuum, and cryosectioning of samples onto acid-treated glass coverslips. Sections obtained with this technique show cell distribution and cell-tissue morphology on the pore wall structures of entire centimeter-thick scaffolds. This rapid and easy technique allows for fast evaluation of tissues grown on biodegradable scaffolds.

Animals↗

PubMed1999

In vitro degradation of a novel poly(lactide-co-glycolide) 75/25 foam.

Macroporous poly(lactide-co-glycolide) PLGA 75/25 foams were prepared for application in bone tissue engineering. Their in vitro degradation behaviour was followed over a 30 week period at 37 degrees C and at one of three pHs: (1) pH 5.0, which mimics the acidic environment produced by activated macrophages, (2) pH 7.4, which reproduces normal physiological conditions and (3) an intermediate pH 6.4. The degradation of the PLGA 75/25 foams was studied by measuring changes in mass, molecular weight and morphology. The degradation profile of foams maintained at pH 5.0, 6.4 and 7.4 was similar until week 16, after which foams maintained at pH 6.4 and 7.4 had comparable degradation patterns whereas foams maintained at pH 5.0 degraded faster. For example, mass loss was less than 3% for foams maintained at all three pHs until week 16; however, by week 30, foams maintained at pH 6.4 and 7.4 had lost 30% of their mass whereas foams maintained at pH 5.0 had lost 90% of their mass. Foams maintained at pH 6.4 and 7.4 showed a similar constant decrease in molecular weight over the entire degradation study. Foams maintained at pH 5.0 had a similar rate of molecular weight loss as those maintained at pH 6.4 and 7.4 until week 16, after which the rate of molecular weight loss of foams maintained at pH 5.0 was accelerated. The morphology of the foams maintained at pH 6.4 and 7.4 was unchanged for 25 weeks. Foams maintained at pH 5.0 collapsed after week 18. Thus the PLGA 75/25 foams, described herein, maintained their 3-D morphology at physiological pH for over 6 months, which is an important feature for tissue engineering applications.

Bone Substitutes↗