Bone defect and nonunion are complex diseases which are difficult to treat due to insufficient bone regeneration. Electrical stimulation has attracted attention as a promising strategy to induce and enhance bone regeneration. Self-powered and biocompatible materials have been widely explored and used in biomedical devices, owing to their ability to produce electrical stimulation without an external power source. We aimed to prepare a piezoelectric polydimethylsiloxane (PDMS)/aluminum nitride (AlN) film with excellent biocompatibility and osteoconductive ability for the growth of murine calvarial preosteoblast MC3T3-E1 cells. By applying vibration to stimulate body movement, the PDMS/ AlN film demonstrated a current density of 2−6 μA cm −2 , and the generated continuous alternating current (AC) effectively promoted MC3T3-E1 cell growth, viability, and osteoblastic related gene expression (genes runt-related transcription factor 2 [RUNX2], osteocalcin [OCN], alkaline phosphatase [ALP]) and exhibited higher mineralization. Compared to blank plates and nonvibrated PDMS/AlN films, the vibrated PDMS/AlN film showed rapid and superior osteogenic differentiation. The design of the biocompatible and flexible piezoelectric PDMS/AlN film overcame the poor processability, brittleness, and instability of electrical stimulation of traditional electroactive materials, demonstrating great potential in the application of electrical stimulation for bone tissue engineering.
Reliable and long-term operation of thin film bulk acoustic resonators (FBARs) under high power relies on the optimization of thermal resistance. In this work, thermal design strategies for high power FBARs are explored theoretically. For accurate estimation of the thermal characteristics of FBARs, the thermal conductivity of the AlN epilayer with temperature and thickness dependence is included in the finite element simulation model, of which AlN thermal conductivity is calculated through normal-process, Umklapp, and boundary scattering. To further reduce thermal resistance and improve power capacity, the effects of aspect ratio, AlN thickness, the number of resonators, and pitch distance on thermal resistance are investigated. Compared with FBARs with a square electrode, the thermal resistance of the FBAR-on-diamond device is decreased by 43% at an aspect ratio of three. Meanwhile, the optimal AlN thickness is 2 µm, which maintains the balance between thermal resistance and electric performance. The power capacity is increased by 1.93 dB by substituting six resonators for four resonators. The improvement in power handling ability is attributed to the reduced thermal spreading resistance and lower power density. Our study can provide detailed thermal design strategies for high power FBARs toward high throughput data transmission.
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