Effects of sterilization on implant mechanical property and biocompatibility.

This article concisely reviews the effects of sterilization on the mechanical properties and surface chemistries of implantable biomaterials. This article also summarizes the biological effects of the sterilization-related changes in the implant. Because there are so many different types of implant materials currently in use (including metals, polymers, and diverse biological materials), the response of tissue to these different materials varies dramatically. This review further discusses the effects of sterilization on in vivo and in vitro tissue response specifically to implantable metals and polyethylene, with the possibility of future biocompatibility testing of the implants sterilized with supercritical phase carbon dioxide sterilization.

Overload arthrosis: strain patterns in the equine metacarpal condyle.

An overload arthrosis occurs consistently in the palmar region of the metacarpal condyle of the equine fetlock (metacarpophalangeal) joint characterized by subchondral bone sclerosis, devitalization and mechanical failure leading to collapse of the overlying articular cartilage. Samples were selected of joints with mild, moderate, and severe subchondral sclerosis, in which cartilage collapse had not yet occurred. An additional group that had severe sclerosis with focal rarefaction suggesting impending collapse was also studied (n=5/group). Parasagittal slices were milled to 2.0 mm thickness and subjected to palmar forces 50 to 200% of those applied by the sesamoid bone at angles corresponding to early, mid and late stance support phases of the gait cycle. From contact radiographs in the loaded and unloaded samples, strains were determined by recognizing displacements in the trabecular patterns using texture correlation analysis. Failure did not occur in any of the samples. Strains were generally proportional to the forces applied and greatest at midstance. Strain patterns varied between samples and with the different loading positions. With increased subchondral bone sclerosis there was greater shear strain in overlying trabeculae. Strain patterns were not consistently different within the sclerotic bone at the site of failure. Focally higher strains at the surface were sometimes related to the edge of the platen which was molded to mimic the sesamoid bone in vivo. These results indicate that sclerotic thickening of subchondral bone transmits stresses to overlying trabeculae. No consistent strain pattern was recognized where devitalization and mechanical failure occurs. Focally higher strains related to the edge of the opposing sesamoid bone may play a role.

The effect of boundary conditions on experimentally measured trabecular strain in the thoracic spine.

Vertebral bodies are the primary structural entities of the spine, and trabecular bone is the dominant material from which vertebral bodies are composed. Understanding the mechanical characteristics of vertebral trabecular bone, therefore, is of critical importance in the many clinical conditions that affect the spine. Numerous studies have loaded vertebral bodies to investigate the influence of trabecular bone characteristics on deformation and failure patterns, but the methods of load application have been inconsistent. These differences in the method of load application are a potential confounding factor in the interpretation of the experimental results. We investigated this problem by measuring the distribution of minimum principal strain and maximum shear strain magnitude within 6.35 mm thick samples cut from thoracic spine segments (T8-T10) and loaded to simulate three common experimental configurations. Measurements were made using the texture correlation technique, which extracts deformation patterns from digitized contact radiographs of samples under load. The three loading configurations examined were a three-body construct, a single vertebral body loaded through sectioned intervertebral discs, and polymethylmethacrylate molded directly to the endplates. Results indicate that from both probability and spatial distribution standpoints the best simulation of in vivo loading generates the least uniform strains. Loading through disc remnants or through plastic molded to the endplates causes increasing degrees of strain homogenization. This result has implications not only for the design of experiments involving spinal loading, but also for theories concerning the adaptation of trabecular bone to functional loads.

Lipid uptake by silicone enteral access feeding devices.

BACKGROUND/PURPOSE: Deterioration of long-term enteral access devices remains a significant patient care and financial problem. Because it is known that lipids, particularly medium-chain triglycerides oil (MCT oil), can soften and break certain types of polymeric materials, the authors evaluated the effect of liquid enteral feeding formulas containing different amounts of MCT oil on silicone feeding tubes. METHODS: Commercially available and widely used gastrostomy silicone catheters of two sizes (20F and 15F) were sectioned in 5-cm-long samples and cleaned. Five groups of five pieces were immersed for 8 weeks in pure MCT oil and in four commercial formulas having similar protein, carbohydrate, and fat contents. These formulas were chosen because they contained similar percentages of fat (37% to 45%), although they contained differing amounts of MCT oil. Sodium azide 0.05% was added as a bactericide. Samples were maintained at 37 degrees C in an incubator-shaker. After incubation, specimens were rinsed, dried, and weighed. Selected samples were extracted with a chloroform-methanol solution (2:1). Super-critical fluid chromatography (SFC) and infrared (IR) spectroscopy were performed. A tensile tester was used to generate force-elongation curves for the remaining samples. A statistical analysis (ANOVA, alpha = .05) was conducted to compare data from test groups with results from 20 samples of control silicone material. RESULTS: Data demonstrate that silicone is significantly affected by liquid formulas and pure MCT oil. SFC and IR findings indicated that fractions of MCT oil, corn oil, and canola oil were absorbed by the material. The most dramatic weight gain (3.7%) was observed for specimens immersed in pure MCT oil. An average increase (9.6%) of silicone compliance was measured along with oil migration in the tubing. CONCLUSIONS: Lipid uptake contributes significantly to deterioration of the silicone tested, leading to device failure. Surface damage can create a potential nidus for microorganisms, particularly fungi. Lipid type and rate of administration should be taken into account when long-term enteral feedings are given. These data contribute to the understanding of the causes of the physico-chemical deterioration of long-term enteral feeding devices and provide helpful information for the design and manufacture of improved products.

Anatomical reconstruction of the anterior cruciate ligament in goats.

A surgical procedure was developed for the implantation of an anatomical, two-banded anterior cruciate ligament (ACL) prosthesis. Prostheses were fabricated of braided long-chain polyethylene fibers. The left ACL of adult male goats was surgically excised and replaced with either an anatomical reconstruction (5 goats) or a conventional reconstruction (5 goats). The anatomical reconstruction required drilling four bone tunnels, two each in the femur and tibia. Each band of the prosthesis was placed through one tunnel in the femur and the corresponding tunnel in the tibia, recreating the anteromedial and posterolateral bands. The two bands were tensioned independently and stapled in place. In the conventional procedure, the prosthesis was doubled and placed through two larger tunnels, one in the femur and one in the tibia, tensioned and stapled together. All animals were terminated 3 months after surgery. Clinical evaluation of passive range of motion, antero-posterior laxity and the appearance of the joint space showed little or no difference between the reconstruction methods. The ultimate failure load for the natural (unoperated) ACL was 1691 +/- 210 N, while the anatomical and conventional reconstruction groups had mean ultimate failure loads of 1233 +/- 732 and 1012 +/- 220 N, respectively. The elongation to failure of all groups was similar: the natural ACL group = 7.1 +/- 2.8 mm, the anatomical group = 7.2 +/- 2.9 mm, and the conventional group = 7.7 +/- 3.9 mm. The slope of the load-deformation curve, or stiffness, was significantly higher for the natural ACL (4.53 +/- 1.24 x 10(5) N/m) than for either of the reconstruction methods (2.75 +/- 1.59 x 10(5) N/m for the anatomical and 2.34 +/- 0.60 x 10(5) N/m for the conventional). The energy to failure, or area under the load-deformation curve, showed no significant difference between groups. In conclusion, both types of reconstructions were less strong, stiff, and tough than the natural ACL. There was no significant difference observed between the anatomical and conventional reconstruction methods over the 3-month implantation time in either clinical evaluation or mechanical testing. Therefore, at 3 months postsurgery, the anatomical reconstruction technique was considered no better and no worse than the conventional reconstruction technique.

A chemical and engineering analysis of dust in textile mills.

Proximate chemical analysis was conducted on the carding, spinning and weave rooms of textile mills. The dust was found to be composed of inorganic, cellulosic and noncellulosic organics in carding and spinning. The percentage of noncellulosic organic (the component of cotton dust considered to be responsible for byssinosis in cotton textile workers) in ring spinning was found to be one-half the percentage composition of the card room dust. The cellulosic percentage of spinning room dust is elevated above that found in card rooms. In weave rooms the composition of dust is a function of the fabric being produced, environmental control systems, and machinery. In all weave rooms where dust levels were sufficiently above background, all components of the dust were accounted for by the proximate chemical analysis without the presence of a noncellulosic organic component. The card room, spinning room and weave room produce dusts that are very different in composition, to the extent that the proximate chemical analysis could identify the area of origin of dust samples from a textile mill.