PubMed · 4762189
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J A Hersey, J E Rees, E T Cole. 1973. Density changes in lactose tablets.. https://doi.org/10.1002/jps.2600621243
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This study was performed to provide insight into the functioning of a selection of materials used in the fabrication of orthoses. A series of mechanical and physical tests was performed on five materials, under strict laboratory conditions. The results demonstrate that the polyurethane foams are the most promising material in the design of foot orthoses. The results also suggest that an agglomeration of properties, not just one specific property, can influence the behavior of materials.
The objective was to examine possible reasons for delamination observed in tibial inserts of the porous-coated anatomic (PCA) knee replacement. To date, 33 PCA inserts have been forwarded to the authors' labs. Of these 33, 52% showed severe delamination within four years of implantation. Visual, structural, and mechanical analyses were conducted and data compared on the heat-pressed PCA type and the common machined inserts. Twenty inserts of the two different types were examined. Visual data using polarized light microscopy showed the presence of a surface layer separated from the middle region of the heat-pressed inserts by a line of demarcation 250-580 microns beneath the articulating surface. This anomaly was not observed in machined inserts. Structural analysis showed the new heat-pressed inserts had increased crystallinity in the surface layer when compared to new machined inserts. The retrieved heat-pressed inserts showed increased crystallinity in the surface and middle regions. There was a slight increase in surface crystallinity in the retrieved machined inserts. Microhardness data showed that there was an increased hardness associated with the crystallinity seen on the heat-pressed inserts. Orthopedic surgeons should be aware of early delamination and surface failure in heat-pressed inserts.
Substrate cracking occurred during film coating of a bilayered tablet. The cause was traced to differences in the expansion characteristics of the two layers upon exposure to heat. Thermal mechanical analysis was used to determine the coefficients of thermal expansion of the respective layers.