Design of a Novel Two-Directional Piezoelectric Energy Harvester With Permanent Magnets and Multistage Force Amplifier.

This article presents the design and testing of a novel two-directional (2-D) piezoelectric stack-based energy harvester for capturing the mechanical energy from the human footstep. The uniqueness of the harvester lies in the fact that the energy of 2-D excitation is scavenged by a single piezoelectric stack transducer, which can reduce the loss of harvestable energy. The harvester is constructed by the integration of permanent magnets, position protection plates, and multistage force amplification frame. The input force and input displacement are restricted to guarantee the device's safety. The reported multistage force amplification frame with leverage mechanism and bridge-type amplifier enlarges the force acting on the piezoelectric stack, which further improves the power output. A linear guiding mechanism based on leaf flexure is applied to minimize the impact of input forces in other than moving directions. Through analytical modeling, the main architectural parameters of the device are determined. Simulation study with finite-element analysis is conducted to optimize the device parameters for achieving the largest force amplification ratio with a high safety factor. A prototype harvester is fabricated for experimental study. Results demonstrate the feasibility of the developed 2-D piezoelectric stack-based energy harvester.

Dual-functional core-shell electrospun mats with precisely controlled release of anti-inflammatory and anti-bacterial agents.

Acute wounds are worldwide problems affecting millions of people and causing heavy economic burden to national healthcare systems. Herein, we describe novel wound dressing materials relying on core/shell electrospun mats incorporated with flurbiprofen and vancomycin for achieving programmable release of anti-inflammatory and anti-bacterial agents. The shell matrix of nanofibers consisted of polyethylene oxide while the core matrix was made from a blend of silk and collagen. Several optimal mat architectures were engineered with distinct configurations, of which release profiles displayed an exponential trend, which indicates a first-order process following Fickian diffusion behavior. The flurbiprofen release lasted from 2 to 6 days, which was much faster compared to the one of vancomycin prolonged up to about 20 days. Mechanical data indicated tensile modulus, tensile strength, elongation before break of core/shell electrospun mats became enhanced or comparable to those for human skin after methanol vapor treatment. Desirable release kinetics and mechanical characteristics achieved by novel core/shell electrospun mats were attributable to induced enrichment of ß-sheet phase in silk via methanol vapor treatment as well as water annealing process with time and judicious selections for matrix materials and mat configurations. The design principles considered in this study successfully addressed a range of inflammation and infection requirements in wound healing, potentially guiding construction of other biomedical coatings and devices.

Distinctive Stress-Stiffening Responses of Regenerated Silk Fibroin Protein Polymers under Nanoscale Gap Geometries: Effect of Shear on Silk Fibroin-Based Materials.

Interfacial dynamics, assembly processes, and changes in nanostructures and mechanical properties of Bombyx mori silk fibroin (SF) proteins under varying degrees of nanoconfinement without and with lateral shear are investigated. When only compressive confinement forces were applied, SF proteins adsorbed on the surfaces experienced conformational changes following the Alexander-de Gennes theory of polymer brushes. By contrast, when SF proteins were exposed to a simultaneous nanoconfinement and shear, remarkable changes in interaction forces were observed, displaying the second order phase transitions, which are attributed to the formation of SF micelles and globular superstructural aggregates via hierarchical assembly processes. The resultant nanostructured SF aggregates show several folds greater elastic moduli than those of SF films prepared by drop-casting and compression-only and even degummed SF fibers. Such a striking improvement in mechanical strength is ascribed to a directional organization of ß-sheet nanocrystals, effectively driven by nanoconfinement and shear stress-induced stiffing and ordering mechanisms.

A survey on financial support and research achievement of medical education research units in China.

AIM: To investigate the current situation of financial support and research achievement of medical education research units in China. METHODS: A total of 46 individuals in 46 medical schools completed a questionnaire including information about affiliation of the unit, financial support, published articles and achievement awards of the units. RESULT: Of the 46 schools, 24 had independent medical education research units, 36 had financial support, and 30 had research funding. The mean number of published articles was 2.53 per staff. The mean number of achievement awards was 3.80 per unit. There was a significant difference in funding and published articles between independent medical education research units and other types of units; and in published articles and achievement awards between the units with funding and without funding. CONCLUSION: The financial support from the school was the main source of medical education research units in China. More attention should be paid to the development of medical education research units, to their ability to produce high quality research and support the improvement of medical care in China.