Cross-linking to improve THR wear performance.

Polyethylene wear and associated osteolysis can limit the longevity of total hip replacement. In recent years, many improvements have been made in the consolidation, manufacture, and sterilization of polyethylene acetabular components. These improvements provided reduced polyethylene wear and prolonged usefulness of total hip replacement. Recent advances in extensively cross-linking polyethylene offer the possibility to substantially further reduce wear in total hip replacement. Hip simulator wear testing demonstrates an order of magnitude reduction in wear resulting from cross-linking GUR 1050 polyethylene by exposure to 100 kGy of electron beam radiation followed by annealing to encourage cross-linking and to reduce residual free radicals. Clinical investigation will be required to validate the wear advantage of these materials in vivo. (Hip International 2002; 2: 103-7).

The allergenic properties of fresh and preserved Hevea brasiliensis latex protein preparations.

The allergenic properties of the proteins of two lyophilized fractions of fresh natural rubber latex obtained by ultracentrifugation, the C serum and the sedimented bottom or lutoid fraction, have been compared with those of the serum proteins of two samples of high ammonia latex (HAL) [A]HALS obtained from HAL stored for more than 1 year, and [M]HALS derived from HAL stored for 6 weeks before ultracentrifugation and lyophilization. The most potent source of allergenic polypeptides both for skin prick testing of latex-sensitive patients and for immunoblots of their blood serum was the lutoid fraction of fresh latex. Skin prick tests and immunoblots of patients' sera showed that the allergenicity of the ammoniated latex decreased during storage. Skin prick tests using fractions of [A]HALS, C serum and lutoid proteins obtained after passage through a Sephacryl S300 column showed that the components of all three preparations which eluted in the largest volumes were almost equally effective in provoking the largest number of responses. Immunoblots of the sera of 43 latex-sensitive individuals showed that the majority (66%) of sera of the adult allergic patients reacted with a polypeptide of 19 kD. No characteristic pattern of binding latex polypeptides could be recognized in the sera from patients who were also asthmatic or from those who had an anaphylactic response to latex proteins.

Micromechanisms of fatigue crack initiation and propagation in bone cements.

The micromechanisms of fatigue fracture in bone cements were explored and characterized in this investigation. Fatigue crack initiation sites were identified and the microscopic features responsible for crack initiation are illustrated. Differences in the fracture morphology of PMMA beads, in early crack growth and rapid crack growth stages, are brought out. Based on the fractographic features, a micromechanism of PMMA bead fracture is proposed.