Biomaterials, medical devices, and artificial organs最新文献

Phenolic compounds derived from the amino acid tyrosine are endogenous toxins, which are believed to be involved in the pathogenesis of hepatic coma. There are also xenobiotic phenolic substances, such as p-hydroxy-acetanilide (paracetamol or acetaminophen), which can lead to serious complications if taken in an overdose. In both cases, a drastic therapeutic measure such as haemoperfusion may be indicated to eliminate the toxin from the blood. In the present work, human serum has been dosed with the phenolic compounds of immediate relevance in exogenous and endogenous intoxication, and the effectiveness of various adsorbent materials for the elimination of the toxins from the serum has been investigated. Resins and charcoal in the native state have been compared with those encapsulated into large agarose beads, a process which improves the haemocompatibility and thus the practicability of the adsorbents. A certain degree of specificity has been observed. Whereas phenolic acids are adsorbed quite effectively onto the strongly basic ion exchange resins of the Dowex 1X type, particularly 1X8 or 2X8, phenol or paracetamol are less effectively eliminated. In contrast to many other classes of toxin, the Amberlite XAD-type resins are ineffective for all the phenolic substances investigated. Charcoal is the most effective adsorber in most cases, particularly when encapsulated in powder form into agarose beads.

In the last decade a number of chemically fixed, soft tissue based bioprostheses have become commercially available. Chemical fixation of these materials changes a number of their physical and chemical properties. Quantitation of these effects has been difficult because of: anisotropy of the biopolymers, variable composition of the materials, and sample size and configuration limitations. Collagen tape, made from reconstituted collagen, has been chosen as a model material because it alleviates many of the aforementioned problems. Its constituent fibers are homogeneous and unidirectional. The cross-sectional area is constant. Thus, the resultant uniaxial tensile stress-strain relationship is reproducible to allow for systematic parametric studies. Results are presented for the change in tensile properties of the collagen tape as a function of exposure time to glutaraldehyde fixative. These properties are described by the equation: sigma = A (eB epsilon-1) The tensile properties of fresh and fixed pericardial tissue were also tested and corroborative results were found.

In vitro experiments were conducted in which the fretting corrosion rate of stainless steel plates and screws in 0.9% saline was compared with the rate in solutions of 10% calf serum in saline. The results demonstrated a ten-fold decrease in the fretting corrosion rate with the addition of serum to saline. However, it also demonstrated that the lower concentration of nickel in the serum solutions was more biologically active than the higher concentration in saline when the solutions were used to skin test rabbits made allergic to nickel by injection.

The widespread acceptance of silicone rubber in a multitude of biomedical devices is a well-known fact. The proper compounding of the rubber to achieve the desired physical properties is of the utmost importance. The catalyst, 2, 4-dichloro benzoyl peroxide, used in the thermal crosslinking of the uncured silicone polymer, plays an important role in the ultimate properties of the polymer. Different post curing steps have been tried and the resultant effects on the hemocompatibility of the polymer is the subject of this work.

The strength characteristics of the interface between bone and a bone/porous metal composite were analyzed. The metal was 316L stainless steel. The average tensile strength of bone spicules ingrown to the porous metal was 46.5 MPa. This compares to a control bone sample strength of 89.7 MPa. The difference could be due to bone location and bone immaturity. The overall intefacial tensile strength (9.59 MPa) is necessarily lower since the spicules cover only a fraction of the interfacial cross-section. The overall interfacial strength had a wide range of scatter (s = +/- 4.11 MPa). This was probably due to inherent variations in bone strength with location. A population of samples using porous metal with average pore diameters under 100 micrometers exhibited measurably lower tensile strengths.

The rheological properties of setting acrylic bone cements were examined with a rotational cone and plate viscometer. The cements were tested over two orders of magnitude of shear rate to determine the nature of any non-Newtonian flow behavior. All three cements behaved with moderate pseudoplasticity (i.e., shear thinning) during setting, suggesting the use of higher pressures during administration for better flow and penetration. The low viscosity brand was found to be nearly one-half as viscous as the conventional cements during the working time (i.e., 2-5 minutes). A series of sieving experiments were performed to determine the particle size distributions of the powder components. Statistical analysis (chi square) showed the cements to have different distributions, with the low viscosity brand containing a larger proportion of smaller polymer particles. This difference is thought to contribute to the lower viscosity of this cement.

The essential considerations to be taken for the design of a composite elasto-dynamic intervertebral disc prosthesis (IDP) are discussed, and a disc implant, supposedly satisfying the demands for surgical and biomechanical applicability and biocompatibility, are outlined. The suggested IDP implant is composed of an elastic kernel, covered in a two-components telescoping shell, situated in a polymer slit-tube fundament, after preparation fixed to the respective vertebral bodies of the respective motion segment with bone cement. The approach to a lumbar motion segment is suggested to be by way of an abdominal and retroperitoneal incision and exploration.

A subminiature airflow sensor is described, which can discriminate between exhalation and inhalation, has good linearity and stability, and is small enough to fit inside the stoma button of a laryngectomee. The system employs two fast-response self-heated thermistors placed on opposing sides of an aerodynamic obstacle inside a tube; flow polarity discrimination is based on differences between the heat exchange patterns under laminar vs. turbulent flow. An output proportional to airflow is achieved by the connection of a circuit with a piecewise-linear transfer characteristic in cascade with the thermistors. Developed in-house, this circuit may be adjusted to create an arbitrary range of input-output characteristics. Applications are suggested for an input device for various handicapped aids, for medical diagnostics and in industrial control.

The research described herein is concerned with the development of a "restricted" three-dimensional finite element model of the femoral head that permits the mechanical behavior of the hip joint in Legg-Perthes' disease to be simulated and studied. This "restricted" finite element model allows the femoral head to be treated as a non-axisymmetrically loaded axisymmetric solid of revolution. In order to minimize computer costs, and in recognition of the several uncertainties present in the mechanical description of the system, a number of simplifying assumptions are introduced. These assumptions include an axisymmetric geometry, axisymmetric and linear-elastic material properties, small deformation and displacement, and an approximate load distribution on the femoral head. The computer analyses reveal the relation between the magnitude and the distribution of the stresses in the femoral head and such parameters as (1) the position in the gait cycle, (2) the thickness of the articular cartilage, (3) the extent of the necrotic bone, and (4) the type of corrective osteotomy. A sampling of the preliminary results is presented and some conclusions are drawn with respect to the implications of the study.