Biomaterials, medical devices, and artificial organs最新文献

Three mechanisms of direct biological attachment of implants to bone were examined using femoral intramedullary implants. The implant systems studied were; low temperature isotropic (LTI) pyrolytic carbon, carbon coated porous Co-Cr-Mo alloy and 45S5 bioglass coated Co-Cr-Mo alloy. A detailed radiographic examination revealed that all three implant systems caused significant remodeling of the femurs resulting in an hour-glass appearance. The implants were also associated with a densification of cancellous bone proximal and distal to the ends of the implant. Histologically, all three implant systems exhibited a direct bone-implant bond at the majority of the interfaces. The LTI pyrolytic carbon implants were associated with a higher incidence of fibrous tissue encasement in the proximal cancellous bone region. Active bone remodeling was observed within the pores of the porous Co-Cr-Mo alloy implants even after 8 months in situ.

Amino groups were added on to the surfaces of Celgard-2400 membranes by exposing them to an ammonia plasma. The presence of amino groups on the surfaces was detected by an attenuated total reflection Fourier Transform infrared spectrometer and by the Auger electron spectrometer. Through these amino groups, albumin was attached to the membranes. In some experiments, the attached albumin was further stabilized by cross-linking with glutaraldehyde. The effect of washing the albuminated membranes with saline and with plasma was investigated. It was observed that after the initial wash-out of albumin, the concentration of attached albumin tends to level off. The amount of albumin retained on the membranes varied between 275 to 357 micrograms/cm2.

In this preliminary study, the feasibility of fixing fractured bones was explored using the ethyl and isobutyl 2-cyano-acrylates, prepolymerized barnacle cement, and fibrin glue. Adequate cohesive strength cannot be obtained when lipids are present on the surface to be joined by alkyl 2-cyanoacrylates. Oxidized regenerated cellulose gauze soaked in a highly concentrated fibrinogen solution was inserted into the partially hollowed fracture ends to arrest the flow of oozing blood from the medullary canal. Anhydrous ether was used to sponge off any residual lipid from the bone surfaces. The displaced fracture ends were aligned and narrow strips of bone were secured around the fracture line resulting in a barrel stave arrangement. Roentgenograms indicated successful reduction of transverse (midshaft) fractures in eight rat (femur) and seven rabbit (tibia) models. In some cases, casts were used as supplementary fixation. Using the ethyl and isobutyl 2-cyanoacrylates, reduced fractures were maintained in a stable position for up to five and six days, respectively. Further study of the 2-cyanoacrylates is recommended. By using a standardized surgical method for testing the usefulness of future adhesives in vivo, consistent interpretation of results will be facilitated.

Data on the rate of dissolution (including fluoride ion release) of silicate and glass ionomer cement samples of variable surface area:volume ratios are examined in conjunction with dye penetration experiments and a simultaneous EDX analysis of the five elements F, Si, P, Al, Ca., as obtained by a series of point analyses taken at 10 micron intervals over a length of 7mm on a cement sample exposed to two months continuous immersion. Adding to this unpublished information on the surface area (from BET) and porosity (mercury porosimetry) it is shown that, in their behaviour, these cements behave as controlled release systems of the porous granular monolith type and that application of homogeneous monolith equations is inappropriate.

Using three-dimensional gait data, a mathematical model of the proximal femur was developed that will predict the loading conditions in the child's hip joint during walking. The model is based on knowledge of rim coordinates of the acetabulum, and consists of rotating unit vectors emanating from the center of the epiphysis. The results will be used in a variety of three-dimensional stress analyses of the femoral head in Legg-Perthes disease (a disorder of femoral head collapse).

Surface chemical analysis by x-ray photoelectron spectroscopy (XPS) was undertaken on 316 LVM stainless steel in the attempt to better understand corrosion occurring in vivo. Samples were dipped in saline or in blood serum, corroded in serum or saline by the application of a 5 volt anodic potential, or corroded by fretting. The products produced by fretting corrosion were also examined. XPS analysis revealed rapid protein coating of the stainless steel surfaces exposed to serum, changes in the oxidation state of the surfaces, and changes in the chlorine on the surface. In addition it was demonstrated that the corrosion products generated by fretting in saline had an oxidation state similar to that of chronic chloride whereas the corrosion products generated in serum had an oxidation state similar to that of potassium dichromate. These findings may have important implications since the chromium in dichromate is more biologically active than that in chronic chloride.

Retrieved stainless steel (Type 316L) T-28 femoral stems occasionally exhibit cracks on the medial surface. Since this region is loaded in compression during gait, a simple fatigue fracture explanation is not sufficient to account for these cracks. It has been suggested that they are related to residual stress. It is known that residual stress can contribute a large part of the strain energy near a crack tip. Four failed T-28 femoral stems have been analyzed after surgical retrieval. All of them had multiple visible cracks on the medial side in the region 2-5 cm distal to the calcar collar. All had failed by transverse fractures connecting with a crack on the medial side. These stems have been examined for residual stress by x-ray diffraction methods; significant levels of residual stress were found to be present in the sections tested. Stresses in the transverse direction (medial to lateral) were found to be strongly tensile near the lateral edge and changed to compressive near the medial edge. The area in the center of the sections was found to have nearly zero residual stress.

Both the homogeneous and heterogeneous hydrolysis of five new acrylic polymers having aspirin-moieties, i.e. polymers of beta-(acetylsalicylyloxy)ethyl methacrylate, beta-(acetylsalicylyloxy) propyl methacrylate,beta-(acetylsalicylyloxy) ethyl acrylate, beta-hydroxy-gamma-(acetylsalicylyloxy) propyl methacrylate, beta-hydroxy-gamma-(acetylsalicylyloxy) propyl acrylate were investigated in acidic or alkaline medium at 30 degrees C or 60 degrees C, respectively. It was observed that the chief hydrolyzed product is always aspirin with minor amount of salicylic acid.

Fretting corrosion, a mechanical-chemical phenomenon, most often occurs at screwhead-plate countersink junctions of internal fixation devices. An apparatus was constructed which would simulate the conditions of fretting corrosion in vivo. Fretting corrosion was studied as a function of the number of cycles and the solution in which the fretting occurred. The solutions studied were 0.9% physiological saline and a saline plus 0.5% albumin solution. The implant materials tested were Co-Cr-Mo alloy, 316L stainless steel, and Ti-6A1-4V alloy. The results demonstrated that weight loss increased with the number of fretting cycles but reached a plateau where further weight loss was negligible. Co-Cr-Mo alloy showed less weight loss than 316L stainless steel at any number of cycles. Weight loss for Ti-6A1-4V alloy was similar to Co-Cr-Mo alloy although marked abrasion was noted. All of the materials showed a marked decrease in weight loss when tested in the saline plus albumin solution as compared to the saline only solution.