Biomaterials, medical devices, and artificial organs最新文献

Guinea pigs fed an ascorbic acid-deficient diet develop scurvy because of the absence of the enzyme L-gulonolactone oxidase. In theory if this enzyme is provided and its substrate L-gulonolactone is present at adequate concentrations ascorbic acid will be synthesized and the development of scurvy prevented. Using this model we tested whether a viable segment of intestine could be used to contain the administered enzyme and act as an artificial organ for the production of ascorbic acid. A surgical procedure was developed to prepare an externalized pouch of intestine with its circulation left intact. When enzyme is inserted in this intestinal bag it is not toxic and not antigenic in some animals, whereas, enzyme injected intraperitoneally is clearly antigenic. Synthesis of ascorbic acid by this artificial organ could not, however, be detected by elevation of plasma concentrations of the vitamin.

The biocompatibility of a silicon neuroelectric interface for chronic use in mammalian peripheral nerves was investigated. New Zealand white rabbits were used as the animal model. The implant was made of (110) silicon coated with one micron of silicon dioxide. An anisotropic etch was used to form a grid of ten silicon bars each 40 microns wide and spaced 160 microns apart. A Silastic nerve cuff was molded onto each side of the grid. Using microsurgical techniques, the nerve was transected and sutured into the implant cuff. One implanted rabbit was completely analyzed and is reported here. By 32 days post operatively, the EMG of the affected muscles had partially recovered. The EMG of the affected muscles was indistinguishable from the contralateral control muscles after 150 days. At 332 days, the conduction properties of the implanted nerve confirmed that the nerve was capable of conduction through the silicon grid. Histological observations were consistent with normal peripheral nerve regeneration following microsurgical neurrorhaphy. Seven additional rabbits have been implanted and will be fully analyzed in the future. It was concluded that the silicon peripheral nerve implant described here should be pursued as a substrate for a chronic neuroelectric interface.

Following reports of the successful use of chemically processed human umbilical veins as medium and small diameter arterial substitutes, the development of new and improved techniques for the preparation, fixation and storage of these bioprostheses has been attempted. A series of physical and "in vitro" tests was undertaken to predict the "in vivo" performance of these devices. The results indicate that the new techniques are not only technically feasible but may provide a more convenient, versatile and effective surgical product.

The increasing number of reported femoral neck fractures following surface replacement indicates a potentially serious problem in this procedure. A comparison of the stress levels in the proximal femur before and after hip surface replacement was made using the finite element technique. A proposed surgical bone graft procedure utilizing a strut of cortical bone placed through the femoral head into the neck to help support the surface replacement was also studied as an adjunct for use in avascular necrosis. The findings indicate that stress magnitudes and distributions in the proximal femur are markedly altered after surface replacement when compared to a femur without a prosthesis. Stress levels in the femoral head with surface replacement were found to be significantly lowered suggesting future problems with stress shielding. Lateral neck stresses were found to be equal to or greater than stress levels in the femur without a prosthesis. Stress orientation in the femoral neck is also markedly altered. Surface replacement design and recommended surgical positioning were important variables in determining stress levels. Femoral neck stresses were found to be significantly lowered for all designs of surface replacement when the bone graft modification was utilized. The results of this study explain the major mechanisms of failure of the femoral component. The proposed bone graft modification is demonstrated by the finite element model to decrease the possibility of femoral neck fracture.

A synthetically prepared proteolipid complex was inserted into experimentally produced osseous wounds in the tibias of rats. Similar control wounds were made in the humeri and no proteolipid was inserted. At 7-day intervals for 28 days, rats were sacrificed and both the control and experimental sites were evaluated by gross inspection after the overlying soft tissues had been surgically removed. Specimens were then processed for histologic evaluation employing a Zeiss Videoplan Image Analysis System with Osteoplan for quantitative bone morphometrics. At the 7 and 14 day levels, the rate of osseous wound healing at the experimental sites greatly exceeded the rate at the control sites (p less than 0.0005). By 21 days the experimental areas still showed an accelerated healing response compared with the controls (p less than 0.005). By 28 days the experimental and the control wounds demonstrated almost complete osseous healing.

The development and properties of a novel adsorbent system consisting of polyacrolein microspheres encapsulated in agarose is described. In the model system, the microspheres contain covalently bound bovine serum albumin. In practice any protein or ligands with primary amino groups may be covalently bound. Circulating antibovine serum albumin antibodies were adsorbed from whole blood or serum of rabbits or goats onto the microspheres. The capacity of this batch is 10 mg antibody adsorbed/gm wet weight beads. When the column is operated at less than capacity, 50%, 70%, 90% and 95% of the anti BSA is adsorbed in 30, 60, 120 and 180 min, respectively. Thus, relatively short periods of hemoperfusion may be used. The beads are biocompatible. There are negligible decreases of RBC; up to a 10% decrease of WBC and up to a 20% decrease of platelets in 3 hrs. The beads are stable; neither breakdown nor leakage was observed over a period of 3 months. High flow rates were readily obtained. The mean diameter of the microspheres is 0.2 mu; the mean diameter of the agarose polyacrolein microspheres beads (APAMB) is 1.0 mm. We can produce monodisperse beads of any given diameter ranging from 200 mu to 1 cm.

Bone remodeling and strain distribution in the femur was studied after implantation of LTI pyrolytic carbon, bioglass coated Co-Cr-Mo alloy, and carbon coated porous Co-Cr-Mo alloy intramedullary plugs. Mechanical testing and finite element analysis has shown that the intramedullary stems significantly alter the strain pattern in the femur. However, no statistically significant differences were observed among the implant groups. The analytical and experimental results were found to be in good agreement. Radiographically, differences were observed in the bone remodeling around the carbon implant compared to either of the Co-Cr-Mo based implants. Both internal and external bone remodeling takes place when an intramedullary implant is present.

The interface characteristics of porous rooted cobalt-chromium-molybdenum alloy (Co-Cr-Mo) dental implants which had been in free standing function in canine mandibles for a period of two years were investigated. The displacement of the implants and of points on the adjacent mandibular cortex were determined by mechanical testing. Bone ingrowth was quantified, and the structure of the bone-implant interface and mandibular cortex were characterized using histologic and microradiographic analyses. Displacement characteristics were correlated with determinations of the tissue structure adjacent to and growth within the implant to provide information about the biological attachment. A correlation was found between the thickness of the buccal and lingual cortical plates and implant displacements; implants having the greatest displacement response were in mandibles with the thinnest cortical plates. A relationship could not be established between the implant displacement response and the quantitative tissue structure data. Differences observed in the displacement response of the implant by mechanical testing were not observed by clinical measurements of mobility. It was concluded that implant retention mechanical behavior results from both interfacial displacement and deflection of the adjacent mandibular structures.

An electronic laryngeal prosthesis, fully-implantable in the neck, is a desirable source of artificial voice. Emitted sound energy in a frequency range suitable for adult males and females must be of the correct period and intensity and rich in powerful harmonics. Any such device places severe demands on a bioencapsulant used to enclose the transducer. Location of the devices within the central neck demands a prosthesis-coating combination capable of passing sound energy at central body temperature. This study reports on four identical prostheses, coated with a polyvinylidene chloride, a copolyether polyurethane, a semi-rigid epoxy, or uncoated. Units were tested at room (72 degrees F) and body (100 degrees F) temperature in a sound-isolated chamber. Results indicated that performance of the uncoated unit was altered due to temperature effects. The presence of the polymer encapsulants did not have any differential effect on sound spectrum due to temperature differences.

A feasibility study on developing an implantable, biodegradable insulin delivery system was carried out. Insulin-albumin microbeads (50-1,000 microns diameter) were implanted in diabetic rats. After a single subcutaneous implant of the glutaraldehyde crosslinked microbeads, elevated blood-insulin levels were detected in the diabetic animals for longer than two months. While the blood-insulin levels of the treated animals were sustained between 10 and 67 microU/ml during the initial two month post-implantation period, complete in-vivo biodegradation of the microbeads took longer than five months. The diabetic animals, with the insulin-albumin microbead implants, gained weight. In contrast, untreated diabetic controls lost weight. Fibrous capsules were found to have surrounded the microbeads when the implants were recovered at one and two months post-implantation. The results suggest that the fibrous capsules played a role in retarding insulin release from the albumin microbead system. Cross-linked serum albumin microbeads have the clinical potential of providing long-term in-vivo drug release. This system has the additional advantage of being biodegradable and also provides more options for the method and site of implantation.