Biomaterials, medical devices, and artificial organs最新文献

The properties of collagen films crosslinked by physical and chemical techniques were compared to the properties of films crosslinked with glutaraldehyde (GTA). Physical techniques studied include exposure to short wave (254 nm) u.v. irradiation and severe dehydration. Chemical techniques studied include immersion of collagen films in aqueous solutions of cyanamide or GTA. Collagen films exposed to combinations of aqueous solutions of cyanamide and severe dehydration had moduli of elasticity, swelling ratios and resistance to bacterial collagenase similar to films crosslinked with GTA. Theoretical calculations based on amino acid composition indicate that approximately seven times as many amino acid residues are capable of forming crosslinks using cyanamide or severe dehydration procedures as compared to GTA crosslinking. In addition, using severe dehydration or cyanamide forms crosslinks involving both amino and carboxyl residues which may allow these procedures to act synergistically. Based on our studies this two-step procedure effectively crosslinks collagen-based biomaterials while the only by-product of this reaction is water-soluble urea. Preliminary biocompatibility studies suggest that this crosslinking procedure may allow for pronounced tissue ingrowth.

In this work, attempts to reduce the levels of porosity in acrylic bone cements were studied. Specimens were cured with additional external pressures or were ejected from commercially available bone cement ejection systems. Density measurements were used to calculate levels of porosity in the specimens. Decreases in porosity were observed when specimens of Zimmer Low Viscosity Cement and Simplex-P bone cements were cured at increased pressures in a stainless steel die. Tensile strengths were increased in those specimens which demonstrated decreases in porosity. Specimens ejected from the cement guns demonstrated significant levels of porosity, but showed improved mechanical properties when ejected from cement guns with narrow orifices. Increased strengths were apparently due to a redistribution of the pores, as was demonstrated by SEM. Continued improvements in mixing and placement of bone cement which would help eliminate porosity are highly recommended.

Many different methods have been used to compare polymethylmethacrylate bone cements. In this paper the three currently available cements were compared in regard to dough and set times, heat of polymerization, compressive, tensile, 3 and 4 point bending strengths, fracture toughness, flexural modulus, void density distribution, and viscosity. Methods used were ASTM designated for bone cement or plastics in general whenever possible. Significant differences in set and dough times and heat of polymerization were noted. All cements were equal in compressive, tensile, and fracture toughness testing; Zimmer Regular Cement was significantly weaker (p less than 0.001) in flexural testing and had a significantly (p less than 0.001) decreased modulus of elasticity when compared to LVC and Simplex Cements. Void density distributions were not significantly different. Viscosity was shown to vary between these cements as well. This data was analysed both to determine differences between various brands of cement and to assess the relevance to clinical use and failure modes in vivo of these different means of testing.

The mouse peritoneal cavity was evaluated as a possible model for the preliminary screening of polymeric implant materials. The phagocytic cells of the cavity were stimulated prior to implant insertion by intraperitoneal injection of thioglycollate, glycogen, or sodium caseinate. Small, cylindrical polymeric implants of polyethylene, polychlorotrifluoroethylene, silicone, nylon-12, ethylene-chlorotrifluoroethylene copolymer, and polyethylene-silicone blend, were inserted and then retrieved at 1, 2, and 3 week intervals. The implants with attached cells were subsequently stained and evaluated as to the amount and type of cellular adherence. Results indicate that cell adherence varies according to the type of material used and therefore the mouse peritoneal cavity is a rapid and inexpensive method to evaluate cellular response to polymeric implant materials.

Biomaterials used as implants and in various devices must exhibit long-term (years) compatibility with the physiological environment, including blood, and additionally must also remain stable to perform mechanical functions, excepting applications where biodegradation is required. This paper focuses on problems and challenges of polymeric materials in contact with blood in the following categories: (1) artificial heart valves, (2) cardiovascular assist devices and artificial hearts, (3) vascular prostheses, and (4) the biological evaluation of materials prior to their human use, especially with respect to species related hematological differences of experimental animals. Besides thrombosis (which is the most obvious consequence of incompatibility), the calcification of chemically treated tissue prostheses as well as synthetic elastomers used in many cardiovascular devices is discussed in terms of biochemical and physico-chemical parameters together with its significance in long-term (years) implant applications. Complement activation brought about by contact of blood with foreign surfaces has received less than deserved attention in the evaluation of biomaterials and devices, despite the potentially serious problems. Relative ignorance in selecting appropriate animals for the biological evaluation of biomaterials whose hematological profiles and behavior of platelets, red and white cells to trauma and response to foreign surfaces differ decisively from those of humans, often leads to less than meaningful predictions for eventual clinical uses. The state-of-art realities are examined in conjunction with medical, societal, ethical, and economic boundaries.

The volumetric heating response of soft tissues to electrosurgical cutting and coagulation was studied. A series of experiments was conducted with thermistor probes embedded in a surrogate medium during controlled application of the electrosurgery current. A series of temperature profiles was obtained for various thermistor probe locations. These temperature profiles were found to be linear, exponential, or double exponential, depending upon the probe-incision distance. Temperatures next to the site of tissue destruction approached 70 degrees C, within 2 seconds of application of power. Temperature changes due to lateral heating were an order of magnitude greater than temperature changes directly under the incision. Anisotropic heat conduction was observed for muscle fibers oriented in different directions.

The rabbit tibia was used as a model to study the effects of metal sensitivity reactions on the healing of fractures. Animals were injected with nickel chloride in Freund's complete adjuvant to cause sensitivity, and fractures were stabilized with 316L stainless steel intramedullary rods and followed for 16 weeks. A control group received no injections. The response was evaluated biomechanically with torsional testing at sacrifice, radiologically by examining the roentgenograms for evidence of loosening, and histologically. The results demonstrated a slight decrease in strength, a moderate increase in resorption and a significant decrease in cellularity and new bone formation in the sensitive animals as compared to control. These results are consistent with a reaction of comparatively short duration.

A study is presented which describes the adsorption in vitro of albumin and fibrinogen onto a mini-shunt oxygenation unit. The unit is characterized by flow through 10 etched microchannel conduits with a microporous membrane and conduits are pretreated with a uniform layer of ULTI carbon and evaluated for the steady-state and time varying kinetics of protein adsorption. Corresponding results for oxygenator components not pretreated with ULTI carbon are also included.