A high frequency, high resolution ultrasonic echo technique is presented for determining the thickness of human skin. An experimental series is described in which the accuracy of this new technique is demonstrated by comparison with a radiological method of proven accuracy. The "ultrasonic biometric ruler" is shown to provide an accurate, simple, noninvasive method for measuring full-thickness human skin. In addition to the determination of skin thickness, it is demonstrated that the underlying subcutaneous fat and muscle can also be noninvasively "explored" with the possibility of identifying a variety of skin and underlying tissue lesions.

This study focuses on examining the biological response of intramedullary bone to poly‐L‐lactic acid (PLLA), particularly during the PLLA degradation phase. To study the influence of spherical crystals (spherulites) of PLLA on intramedullary bone response, two different types of PLLA coupon, with and without spherulites but with the same molecular weight, were used. Chambers containing PLLA coupons were implanted into the right femur of eight dogs, four with and four without spherulites; chambers containing stainless steel (SS) coupons (as a control) were implanted in the left femurs of all eight. Two dogs, one with and one without spherulites, were sacrificed at 3, 6, 12, and 24 weeks postoperatively. Histomorphometric evaluation and histophathological assessment were used to compare the response to PLLA and SS. Scanning electron micrographs showed that there were minimal changes in the surface of PLLA coupons at 3 and 6 weeks. But at 12 and 24 weeks, there were many cracks and holes on the surfaces of the coupons, and some parts of the surface were scaling off. The cross‐sectional area of PLLA coupons showed no change at 3 and 6 weeks, but started to decrease by 12 weeks. The amount of ingrown bone between PLLA coupons was significantly greater than that between SS coupons at 3 and 6 weeks, but had decreased dramatically by 12 weeks. Extensive bone resorption around PLLA coupons occurred by 12 weeks accompanied by infiltration of inflammatory cells. An abundance of histiocytes, giant cells, and leucocytes were seen, along with a few histiocytes that had phagocytized PLLA particles of less than 2 μm. By contrast, no inflammatory reaction was seen in SS samples at any period up to and including 24 weeks. PLLA demonstrated excellent biocompatibility with intramedullary bone for the first 6 weeks in this model. Once degradation commenced, however, biocompatibility decreased dramatically. Our study detected no difference between coupons with and without spherulites. It thus appears that the existence of relatively large PLLA particles did not influence the response of intramedullary bone to PLLA, but rather that it was the smaller particles (< 2 μm) released from the PLLA that induced foreign‐body inflammatory reactions and bone resorption. It is also possible that a local decrease in pH occurred around PLLA coupons, which could have influenced vital kinetics. © 1993 John Wiley & Sons, Inc.

Orthopedic implants often loosen due to the invasion of fibrous tissue. The aim of this study was to devise a novel implant surface that would speed healing adjacent to the surface, and create a stable interface for bone integration, by using a chemoattractant for bone precursor cells, and by controlling tissue migration at implant surfaces via specific surface microgeometry design. Experimental surfaces were tested in a canine implantable chamber that simulates the intramedullary bone response around total joint implants. Titanium and alloy surfaces were prepared with specific microgeometries, designed to optimize tissue attachment and control fibrous encapsulation. TGF beta, a mitogen and chemoattractant (Hunziker EB, Rosenberg LC. J Bone Joint Surg Am 1996;78:721-733) for osteoprogenitor cells, was used to recruit progenitor cells to the implant surface and to enhance their proliferation. Calcium sulfate hemihydrate (CS) was the delivery vehicle for TGF beta; CS resorbs rapidly and appears to be osteoconductive. Animals were sacrificed at 6 and 12 weeks postoperatively. Results indicated that TGFbeta can be reliably released in an active form from a calcium sulfate carrier in vivo. The growth factor had a significant effect on bone ingrowth into implant channels at an early time period, although this effect was not seen with higher doses at later periods. Adjustment of dosage should render TGF beta more potent at later time periods. Calcium sulfate treatment without TGF beta resulted in a significant increase in bone ingrowth throughout the 12-week time period studied. Bone response to the microgrooved surfaces was dramatic, causing greater ingrowth in 9 of the 12 experimental conditions. Microgrooves also enhanced the mechanical strength of CS-coated specimens. The grooved surface was able to control the direction of ingrowth. This surface treatment may result in a clinically valuable implant design to induce rapid ingrowth and a strong bone-implant interface, contributing to implant longevity.

No abstract

Surface microgeometry plays a role in tissue-implant surface interactions, but our understanding of its effects is incomplete. Substrate microgrooves strongly influence cells in vitro, as evidenced by contact guidance and cell alignment. We studied "dot" colonies of primary fibroblasts and bone marrow cells that were grown on titanium-coated, microgrooved polystyrene surfaces that we designed and produced. Rat tendon fibroblast and rat bone marrow colony growth and migration varied (p < 0.01) by microgroove dimension and slightly by cell type. We observed profoundly altered morphologies, reduced growth rates, and directional growth in colonies grown on microgrooved substrates, when compared with colonies grown on flat, control surfaces (p < 0.01). The cells in our colonies grown on microgrooved surfaces were well aligned and elongated in the direction parallel to the grooves and colonies. Our "dot" colony is an easily reproduced, easily measured and artificial explant model of tissue-implant interactions that better approximates in vivo implant responses than culturing isolated cells on biomaterials. Our results correlate well with in vivo studies of titanium dioxide-coated polystyrene, titanium, and titanium alloy implants with controlled microgeometries. Microgrooves and other surface features appear to directionally or spatially organize cells and matrix molecules in ways that contribute to improved stabilization and osseointegration of implants.

No abstract

Calcium phosphate fibers designed for reinforcement of bioabsorbable fracture fixation devices were evaluated for their properties upon annealing. The composition of these fibers were 54% PO4, 27% Ca, 12% ZnO, 2.5% NaPO3, and 4.5% Fe2O3, and they were either not annealed, annealed at 250 degrees C, or annealed at 420 degrees C. Chemical degradation, mass loss, and morphology upon degradation were studied. Chemical degradation was performed in Tris-buffered HCl, while mass loss and morphologic studies were performed in both physiologic and nonphysiologic solutions. The results showed that degradation rates for fibers were inversely proportional to the annealing temperature. Mass loss analysis of fibers immersed in the two physiologic solutions (calf serum and simulated body fluid) revealed little change in fiber diameter up to 60 days. Morphologic examination revealed little change in fibers immersed in the two physiologic solutions until 60 days, after which thin shells were found to be peeling off the outer coating of the fiber. Samples in tris-buffered HCl revealed a dramatic difference in mode of degradation among the three fibers. Fibers not annealed and those annealed at lower temperatures underwent a delaminating type of degradation that appeared to destroy the overall integrity of the fiber, whereas fibers annealed at 420 degrees C underwent crater-like deterioration in which the overall alignment of the fiber remained intact. It is therefore concluded that annealing fibers at higher temperatures also undergo a mode of degradation that allows them to maintain their structural integrity. Although annealing fibers close to glass transition temperature may produce an initially weaker fiber, chemical and physical degradation occur much slower, making these fibers most suitable for reinforcement of biodegradable implants.

No abstract