Effects of ultrasound settings on temperature changes in NiTi implants.

BACKGROUND: Shape memory alloys (SMAs) are well-known for their unique ability to undergo a shape change in response to a thermal stimulus. A frequently-used SMA for biomedical devices is NiTi, although its superelastic features tend to be emphasized more than the ability to change shape. Minimally invasive NiTi implants which can reconfigure or adjust their shape across several temperature points could provide desirable surgical outcomes. For decades, therapeutic ultrasound has been used medically as a non-invasive method for tissue thermal therapy. Ultrasound's ability to quickly raise temperatures, and transcutaneously activate shape changes in NiTi implants is a novel approach for eliciting the martensitic thermoelastic transformation. METHODS: The purpose of this study was to investigate the features of therapeutic ultrasound that correspond with temperature changes in different NiTi specimens. For this purpose, ultrasound was applied to two NiTi specimens for two minutes each at varying low- and high-frequency and power settings using a Sonicator 740 and a Dynatron 150. FINDINGS: The baseline temperature for all 32 trials was room temperature (23.0 ± 1.7°C). This study successfully increased the specimen temperature with the application of Sonicator 740 and Dynatron 150 therapeutic ultrasound machines (2.2 ± 2.4°C and 1.5 ± 1.15°C, respectively). From the statistical analyses of the experimental data, it was clear that there is a significant difference between low- and high-power settings on mean temperature change using the Dynatron 150 (ANCOVA; p = 0.013). Interpretation Of clinical relevance, NiTi implants can quickly and easily increase in temperature when applying therapeutic ultrasound. Ultrasound power causes temperature changes and should be accounted for when designing orthopedic implants for applications where dimensional changes are desirable.

Review: Inelastic Constitutive Modeling: Polycrystalline Materials.

This article provides a literature review that details the development of inelastic constitutive modeling as it relates to polycrystalline materials. This review distinguishes between inelastic constitutive models that account for nonlinear behavior at the microstructural level, time-independent classic plasticity models, and time-dependent unified models. Particular emphasis is placed on understanding the underlying theoretical framework for unified viscoplasticity models where creep and classical plasticity behavior are considered the result of applied boundary conditions instead of separable rates representing distinct physical mechanisms. This article establishes a clear understanding of the advantages of the unified approach to improve material modeling. This review also discusses recent topics in constitutive modeling that offer new techniques that bridge the gap between the microstructure and the continuum.

Assessing the biomechanical properties of nitinol staples in normal, osteopenic and osteoporotic bone models: A finite element analysis.

OBJECTIVE: Bone staples are internal fixation devices that are frequently used in the foot, ankle, and hand to provide stabilization. Fixation stability is vital after fusion or fracture surgeries to ensure proper bone healing. Patients undergoing surgeries that require fixation to keep bones aligned and stable may present with diminishing bone mechanical properties, and this may compromise the ability of the fixation hardware to maintain a stable construct. The purpose of this study was to investigate the mechanical performance of shape memory and superelastic nitinol bone staples with different bridge geometries in normal, osteopenic, and osteoporotic bone models. Contact forces and maximum principal stress and strain in the bone were recorded. METHODS: Finite element simulations of a bone staple fixation procedure were performed to examine the initial and post-surgery contact force, as well as the maximum principal stress and strain of 15 mm bridge and 20 mm bridge staple-bone constructs. RESULTS: Shape memory nitinol staples exhibited higher contact forces compared to superelastic nitinol staples. Nitinol bone staples with 20 mm bridge lengths displayed higher contact forces and lower stresses in all bone types, as well as lower strains in osteoporotic bone models compared to nitinol staples with a 15 mm bridge length. CONCLUSION: Nitinol bone staple constructs with 20 mm bridge length staples provide higher contact forces and display lower stresses in the bone than 15 mm bridge staple-bone constructs, which may be beneficial in bone with diminishing mechanical properties. Both superelastic and shape memory effect nitinol staples provide adequate compression and stress relief. However, if osteopenia is present, shape memory effect nitinol staples with a 20 mm bridge length may provide more stress relief and compression, if the bone anatomy allows.

Reduced Bacterial Counts from a Sewage Treatment Plant but Increased Counts and Antibiotic Resistance in the Recipient Stream in Accra, Ghana-A Cross-Sectional Study.

Wastewater treatment plants receive sewage containing high concentrations of bacteria and antibiotics. We assessed bacterial counts and their antibiotic resistance patterns in water from (a) influents and effluents of the Legon sewage treatment plant (STP) in Accra, Ghana and (b) upstream, outfall, and downstream in the recipient Onyasia stream. We conducted a cross-sectional study of quality-controlled water testing (January-June 2018). In STP effluents, mean bacterial counts (colony-forming units/100 mL) had reduced E. coli (99.9% reduction; 102,266,667 to 710), A. hydrophila (98.8%; 376,333 to 9603), and P. aeruginosa (99.5%; 5,666,667 to 1550). Antibiotic resistance was significantly reduced for tetracycline, ciprofloxacin, cefuroxime, and ceftazidime and increased for gentamicin, amoxicillin/clavulanate, and imipenem. The highest levels were for amoxicillin/clavulanate (50-97%) and aztreonam (33%). Bacterial counts increased by 98.8% downstream compared to the sewage outfall and were predominated by E. coli, implying intense fecal contamination from other sources. There was a progressive increase in antibiotic resistance from upstream, to outfall, to downstream. The highest resistance was for amoxicillin/clavulanate (80-83%), cefuroxime (47-73%), aztreonam (53%), and ciprofloxacin (40%). The STP is efficient in reducing bacterial counts and thus reducing environmental contamination. The recipient stream is contaminated with antibiotic-resistant bacteria listed as critically important for human use, which needs addressing.