On the Mechanism of Self-Assembly by a Hydrogel-Forming Peptide.

Self-assembling peptide-based hydrogels are a class of tunable soft materials that have been shown to be highly useful for a number of biomedical applications. The dynamic formation of the supramolecular fibrils that compose these materials has heretofore remained poorly characterized. A better understanding of this process would provide important insights into the behavior of these systems and could aid in the rational design of new peptide hydrogels. Here, we report the determination of the microscopic steps that underpin the self-assembly of a hydrogel-forming peptide, SgI37-49. Using theoretical models of linear polymerization to analyze the kinetic self-assembly data, we show that SgI37-49 fibril formation is driven by fibril-catalyzed secondary nucleation and that all the microscopic processes involved in SgI37-49 self-assembly display an enzyme-like saturation behavior. Moreover, this analysis allows us to quantify the rates of the underlying processes at different peptide concentrations and to calculate the time evolution of these reaction rates over the time course of self-assembly. We demonstrate here a new mechanistic approach for the study of self-assembling hydrogel-forming peptides, which is complementary to commonly used materials science characterization techniques.

Elevated Intra-Articular Cobalt and Chromium Levels in Mechanically Assisted Crevice Corrosion in Metal-on-Polyethylene Total Hip Arthroplasty.

BACKGROUND: Failed total hip arthroplasty (THA) caused by mechanically assisted crevice corrosion (MACC) has serious consequences such as adverse local tissue reaction (ALTR). Serum cobalt (Co) and chromium (Cr) ion levels have been used to diagnose taper corrosion, but have not been shown to be an accurate measure of the severity of MACC or associated ALTRs. Additionally, elevated serum ions are not specific in patients with multiple artificial joints. METHODS: We examined the relationship between serum and intra-articular (IA) Co and Cr levels in a cohort of 20 patients undergoing revision THA, 16 who had symptomatic MACC. IA Co and Cr levels in MACC patients were compared with demographic, pre-operative, and operative findings. RESULTS: Serum and IA metal levels were found to be relatively low in THA patients undergoing revision surgery for isolated instability, aseptic loosening, or infection (average serum Co 0.03 ppb [parts per billion], IA Co 1.4 ppb, serum Cr 0.32 ppb, IA Cr 3.3 ppb). In patients with MACC, average IA Co (940 ppb) was significantly higher than serum Co (5.1 ppb) (P = .0003) and IA Cr (491 ppb) was significantly higher than serum Cr (1.3 ppb) (P = .0003). IA Co level was associated with shorter time of hip symptoms to revision surgery (P = .0043). CONCLUSION: Serum levels of Co and Cr correlated with joint levels in the entire cohort, but IA levels of MACC patients were 100 times greater than serum levels. IA Co and Cr levels may be useful in confirming MACC in a specific joint and the striking elevation may explain symptoms and ALTR with relatively low serum values.