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Biomedical subjects

K Jamshidi

Publications and source records attributed to K Jamshidi.

11 recordsLinked to original sources
PubMed1997

Synthesis of polylactides with different molecular weights.

The synthesis of poly(lactic acid) through polycondensation of the lactic acid monomer gave weight average molecular weights (Mw) lower than 1.6 x 10(4), whereas ring-opening polymerization of lactides in bulk at 130 degrees C for 72 h using stannous octoate as catalyst in the concentration range from 0.003 to 0.8 wt% produced polylactides with viscosity average molecular weight (Mv) ranging from 2 x 10(4) to 6.8 x 10(5). The monomer conversion and Mv showed a maximum at a catalyst concentration around 0.05 wt%. The monomer conversion and Mv increased almost linearly with polymerization time up to a monomer conversion of 80%, but both the conversion and Mv decreased after passing through a maximum, when the polymerization reaction was allowed to proceed for longer periods of time. This time dependence was pronounced at higher polymerization temperatures. The decrease in Mv at prolonged polymerization and higher polymerization temperatures was attributed to thermal depolymerization of resultant polylactides, but no significant optical rotation of poly(L-lactide) was noticed.

Biocompatible Materials↗
PubMed1989

Bioabsorption of polylactides with different molecular properties.

In order to study the effects of factors governing the bioabsorption rate of polylactides, implantation tests were carried out in rabbits using various samples (20 x 10 x 2 mm3) differing in their chemical composition, residual monomer content, and molecular orientation. Copolymer samples with a higher lactic acid content showed a lower rate of absorption, whereas those with a higher unreacted monomer content were absorbed faster and showed a more drastic decrease in molecular weight. In contrast, degradation of the purified polymers was slow; the purified poly-L-lactide showed no weight change and a 50% reduction in molecular weight after 6 months of implantation. Scanning electron microscopy of the samples containing monomers showed a microporous structure extending from the surface to the inner region a few days after implantation, whereas the purified poly-L-lactide did not exhibit a microporous structural change even after 10 months of implantation.

Animals↗
PubMed1986

Polymer-hydroxyapatite composites for biodegradable bone fillers.

A number of composites made from biodegradable polymers and hydroxyapatite were studied in vivo and in vitro in an attempt to develop biodegradable artificial bone fillers. Histological observation in rats revealed that polylactic acid, of low molecular weight (PLAoligomer), was rapidly resorbed and replaced by newly formed bone tissue when incorporated with hydroxyapatite and this suggested that the incorporated hydroxyapatite seemed to play an active role in the new bone formation. In vitro testing revealed that the solubility of hydroxyapatite was markedly enhanced when mixed with PLAoligomer.

Animals↗
PubMedDate not supplied

Resorbable structured porous materials in the healing process of hard tissue defects.

The long-term goal of this research is to assist the resurfacing of damaged articular cartilage. Coralline hydroxyapatite (HA) was coated with a thin film of polylactide (PLa), maintaining pore structural characteristics. Cylindrical plugs (3 x 7 mm) implanted in non-load-bearing femoral and tibial diaphyses of the rabbit indicated substantial bone ingrowth at 3 weeks, with no significant difference between coated and uncoated HA in the amount and distribution of new bone. PLa-epsilon caprolactone polymeric negative replicas of coral Goniopora (G), inserted into the rabbit femur for 4 wks, showed newly formed bone grown deeply into the pores. Tight attachment of new bone to the implant and minimal inflammatory response suggested an osteocompatible reaction. In order to maintain the desirable pore structure of G while introducing controllable degradation rate and mechanical properties, a novel technique was employed to replicate G with PLa and its co-polymers. An intermediary negative replica of G was prepared with aspirin. A co-polymer positive replica of G was then prepared by solution or melt infusion into the negative replica; the aspirin was removed by methanol. A macro- (300-500 microns) and microporous (5-15 microns) structure was prepared by freeze-drying. This replica received appreciable bone ingrowth when implanted in the rabbit tibia for 3 wks. Our results demonstrate the feasibility of creating devices with interconnected pore structures and controlled porosity, elasticity, and mechanical strength sufficient for articular cartilage application, osteocompatibility, and controlled degradation rate.

Animals↗
PubMedDate not supplied

Mechanical evaluation of resorbable copolymers for end use as vascular grafts.

Nonwoven, nonporous, completely resorbable vascular grafts of selected polymeric composition (3 mm ID) were prepared and evaluated for similarity of mechanical properties to arterial blood vessels. Copolymers of L-lactide, D,L-lactide, and epsilon-caprolactone were selected for diversity of mechanical properties and degradation rates. Two homogeneous grafts were tested: a 50% L-lactide and 50% epsilon-caprolactone copolymer (L-epsilon), and a 70/30 solution blend of L-epsilon copolymer and its corresponding D,L-lactide copolymer (D,L-epsilon). Composite grafts also were tested: 1) a two-layer graft, 2) an alternating layers graft, and 3) a D,L-epsilon graft reinforced with circumferentially wound poly-L-lactide fibers. The resorbable grafts windowed the physiologic range for circumferential Young's modulus and tensile strength, and were kink resistant. The arterial compliance was greater than that of all solid wall resorbable grafts. Incorporation of porosity into the grafts, which is necessary for tissue ingrowth, is expected to lessen this difference.

Biodegradation, Environmental↗