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Biomedical subjects

C M Agrawal

Publications and source records attributed to C M Agrawal.

47 records · Page 3Linked to original sources
PubMed1995

Protein release kinetics of a biodegradable implant for fracture non-unions.

Non-union of long bone fractures is often a serious complication of fracture healing. It is estimated that 100 000 non-unions occur in the united States annually and result in the loss of function of the involved limb. The present study was performed to develop a microporous polylactic acid-polyglycolic acid (PLA-PGA) implant for the delivery of bone morphogenetic protein (BMP) to sites of fracture non-unions, and to characterize the protein release kinetics of such an implant in vitro. A 50:50 copolymer of PLA-PGA was used to fabricate the implants using a gel formation technique. The implants were subjected to hydrolytic degradation in phosphate-buffered saline at 37 degrees C for up to 72 d. The protein release and the polymer degradation were monitored during this time period. The release kinetics of these implants were studied using a model protein, soybean trypsin inhibitor (TI), as well as BMP. The results indicate that there is a burst release of the proteins in the initial 48 h followed by a lower elution rate. The release of both the proteins followed similar trends. The molecular weight of the polymer decreased at a faster rate compared to its mass.

Animals↗
PubMed1995

Applications of biodegradable lactides and glycolides in podiatry.

A comprehensive review of the clinical applications and the properties of biodegradable lactide and glycolides is presented. Specific podiatric and other orthopaedic applications of polylactic acid, polyglycolic acid, and their copolymers are reviewed also. The authors then discuss numerous biocompatibility studies, basic manufacturing techniques, sterilizations/storage of the polymers, and the development of biodegradable polymers.

Animals↗
PubMed1995

In vitro degradation and release characteristics of biodegradable implants containing trypsin inhibitor.

The use of a biodegradable implant system that provides a steady, controlled release of drugs or bioactive factors can be an attractive delivery vehicle of substances that can enhance repair processes in the musculoskeletal system. The present in vitro study examined the degradative characteristics and release kinetics of a 50 to 50 polylactic acid/polyglycolic acid implant, used as a carrier of trypsin inhibitor, during a 10-week period. Morphological and scanning electron microscopic examinations demonstrated that the implant degraded in a gradual, extended fashion such that by 10 weeks the implant was completely dissolved. It also was shown that the protein was released from the implant in a sigmoidal fashion with increased release between 3 and 7 weeks. More than 95% of the trypsin inhibitor originally incorporated in the implants was released during the 10-week test period. To describe further the degradation process of the implant, temporal changes in its molecular weight and surface axial strain were determined also. It was shown that in the initial 4 weeks, there was a marked decrease in molecular weight of the implants. Axial strain decreased and then increased over time, suggesting an initial period of stiffening followed by a period of degradative softening.

Biodegradation, Environmental↗
PubMed1994

Use of a compact sandwich specimen to evaluate fracture toughness and interfacial bonding of bone.

The objective of the present study was to develop a reliable and statistically valid test to measure the fracture toughness of small specimens of bone, and by extension, prosthetic materials, using a compact sandwich specimen. Samples of bone were sandwiched between holders of a different material and using this specimen configuration a new technique was developed to test the fracture toughness of the bone interlayer. The effects of different specimens sizes and holder materials were investigated empirically. Using finite element analysis a correction factor was determined to account for the finite thickness of the interlayer and the analytical solutions governing the test specimen were accordingly modified. Bulk compact tension specimens of bone were tested for comparison. Both wet and dry bone were evaluated and the fracture surface morphology characterized using scanning electron microscopy. The results indicate no statistically significant differences between the fracture toughness values obtained from the compact tension and sandwich specimens. The application of this technique to the testing of interfacial bonding between bone and biomaterials is discussed.

Aluminum↗
PubMed1994

The effects of ultrasound irradiation on a biodegradable 50-50% copolymer of polylactic and polyglycolic acids.

The aim of this study was to investigate the effects of ultrasound irradiation on a biodegradable drug delivery system. Microporous, disk-shaped specimens of a 50-50% copolymer of polylactic and polyglycolic acids were gel cast from an acetone solution. A protein was incorporated in these specimens, which were then immersed in phosphate buffered saline and subjected to ultrasound irradiation every second day. The investigation was performed in two phases: in the first, a study was performed for 58 days to determine if ultrasonic irradiation affected the kinetics of protein release from the specimens. In the second phase, effects of frequency and duration of the ultrasound signal on the degradation of the implant were studied for 40 days. The results indicate that ultrasound irradiation resulted in almost a threefold increase in protein elution from the specimens. Both the ultrasound frequency and signal duration affected the molecular weight loss and mass loss, and changed the overall degradation kinetics of the polymer.

Biocompatible Materials↗
PubMed1992

Evaluation of poly(L-lactic acid) as a material for intravascular polymeric stents.

Poly(L-lactic acid) (PLLA) monofilaments were evaluated for use as intravascular polymeric stents. The PLLA monofilaments were extruded and drawn to different draw ratios. They were then subjected to different thermal treatments and their mechanical properties characterized. Stents constructed with similar monofilaments were tested under hydrostatic pressure, and the results correlated with the properties of the monofilaments. Stent collapse pressure was a decreasing function of stent diameter and filament draw ratio.

Biocompatible Materials↗
PubMed1992

Deformation characteristics of a bioabsorbable intravascular stent.

RATIONALE AND OBJECTIVES: Biodegradable polymeric stents offer an alternative to metallic stents, which have a significant compliance mismatch with blood vessels and have the potential for long-term complications. In the current study, the deformation characteristics of polymeric stents have been investigated. METHODS: Stents were subjected to radial compressive pressure by inserting them in a wrap-around collar, one end of which was loaded in tension using dead-weights. The resulting decrease in stent diameter was measured under an optical microscope. Deformation curves for the stents were plotted, and an effective stiffness, E', was determined for each. RESULTS: The deformation curves exhibited two different regions: an initial linear region, followed by a steep nonlinear region. The transition from the linear region occurred at a fractional decrease in stent diameter of approximately 0.5. CONCLUSION: E' decreases with increasing stent diameter and filament draw-ratio. The relationship between E' and the initial stent diameter is not linear. The deformation curves can be used for choosing the appropriate stents for specific applications.

Biodegradation, Environmental↗
PubMed1991

Analysis of 2-DG autoradiograms using image-averaging and image-differencing procedures for systems-level description of neurobehavioral function.

Computer assisted 2-deoxyglucose (2-DG) autoradiography has been used to provide functional maps of areas of altered neural activity related to changes in an animal's behavior or state. The standard procedure for comparison of autoradiograms between different treatment groups has been to take measurement samples from predefined neuroanatomical regions and to average these across brains to attain statistical sensitivity for detecting treatment effects. Unfortunately, when sampling is restricted to predefined areas, important topographic information is lost along with the ability to reveal an unexpected change in neural activity. To preserve the rich topographical detail of metabolic information and to enhance the capacity to uncover novel areas of altered metabolic activity, we have developed a system for averaging entire images from 2-DG autoradiograms and for comparing the average images from two experimental groups by creating an image of differences. This procedure does not rely on sampling only preselected regions, but still allows statistical comparisons between experimental groups. The procedures we describe can be readily and inexpensively adapted for use in individual laboratories and are based on modifications of preexisting image analysis software. We show that, when average and difference images are created using standardized protocols for sectioning brain tissue and editing section images, they are impressively resolved and realistic and can serve as effective topographic descriptions of group differences in neural activity of functional and behavioral relevance.

Animals↗
PubMedDate not supplied

The effects of diabetes mellitus on the material properties of human metatarsal bones.

While some investigations have focused on the effect of diabetes on the material properties of connective tissue in both the human and animal model, no study to date has investigated the effects of the disease process on human metatarsal bones. This investigation compared the material properties of human metatarsal bones from young diabetic donors (51.3 +/- 8 years) and older nondiabetic donors (72.3 +/- 10 years). The results demonstrated no significant differences between the two groups. This would seem to suggest that the effects of aging are comparable to the effects of diabetes on the structural integrity of human metatarsal bones.

Adult↗