Electrical Interconnects Fabricated From Biodegradable Conductive Polymer Composites.

This study presents the development and characterization of biodegradable electrical interconnects for transient implantable medical devices. The interconnects comprised micropatterned biodegradable conductive polymer composites, which were developed using iron (Fe) microparticles as the conductive filler and polycaprolactone (PCL) as the insulating matrix. The electrical properties of the composites were investigated under various degradation conditions. Electrical percolation was observed at 17% iron volume fraction, but higher volume fractions exhibited more stable electrical resistivity throughout the time course of physiological degradation. The electrical resistivity of 40%vf Fe-PCL composites increased tenfold in an emulated packaged environment under degradation. Biodegradable electrical interconnects based on 40%vf Fe-PCL composites were successfully micropatterned in daisy chain structures, illustrating the process compatibility of Fe-PCL composites for interconnect applications. The electrical resistance of the packaged daisy chain structures exhibited a reasonable increase under degradation. An electrical lifetime of over 5 days was also achieved. System integration with a commercial humidity sensor and analytical calculations supporting other application scenarios confirmed the feasibility of micropatterned Fe-PCL interconnects for use in implantable electrical systems.

Biodegradable batteries with immobilized electrolyte for transient MEMS.

Biodegradable batteries play an important role in fully degradable biomedical or environmental systems. The development of biodegradable batteries faces many challenges including power content, device compactness, performance stability, shelf and functional lifetime. In particular, a key driver in the lifetime and overall size of microfabricated biodegradable batteries is the liquid electrolyte volume. Harnessing liquid from the environment to serve as the battery electrolyte may, therefore, be desirable; however, for stable operation, maintaining a constant electrochemical environment inside the cell is required even in the presence of changing body or environmental conditions. We report a biodegradable battery featuring a solid electrolyte of sodium chloride and polycaprolactone. This approach harnesses the body fluid that diffuses into the cell as an element of the electrolyte; however, the large excess of sodium chloride suspended in the polycaprolactone holds intracell ionic conditions constant. A constant discharge profile can then be achieved even in the presence of varying external aqueous conditions, enabling compact, stable-performing cells. This design also features easy integration and automatic activation, providing a simplified strategy to fabricate batteries with long shelf life and desirable functional life span. In addition, the polymeric skeleton of the solid electrolyte system acts as an insulating layer between electrodes, preventing the metallic structure from short-circuit during discharge.

Implantable Sensors for Regenerative Medicine.

The translation of many tissue engineering/regenerative medicine (TE/RM) therapies that demonstrate promise in vitro are delayed or abandoned due to reduced and inconsistent efficacy when implemented in more complex and clinically relevant preclinical in vivo models. Determining mechanistic reasons for impaired treatment efficacy is challenging after a regenerative therapy is implanted due to technical limitations in longitudinally measuring the progression of key environmental cues in vivo. The ability to acquire real-time measurements of environmental parameters of interest including strain, pressure, pH, temperature, oxygen tension, and specific biomarkers within the regenerative niche in situ would significantly enhance the information available to tissue engineers to monitor and evaluate mechanisms of functional healing or lack thereof. Continued advancements in material and fabrication technologies utilized by microelectromechanical systems (MEMSs) and the unique physical characteristics of passive magnetoelastic sensor platforms have created an opportunity to implant small, flexible, low-power sensors into preclinical in vivo models, and quantitatively measure environmental cues throughout healing. In this perspective article, we discuss the need for longitudinal measurements in TE/RM research, technical progress in MEMS and magnetoelastic approaches to implantable sensors, the potential application of implantable sensors to benefit preclinical TE/RM research, and the future directions of collaborative efforts at the intersection of these two important fields.

Biodegradable resistive switching memory based on magnesium difluoride.

This study presents a new type of resistive switching memory device that can be used in biodegradable electronic applications. The biodegradable device features magnesium difluoride as the active layer and iron and magnesium as the corresponding electrodes. This is the first report on magnesium difluoride as a resistive switching layer. With on-off ratios larger than one hundred, the device on silicon switches at voltages less than one volt and requires only sub-mA programming current. AC endurance of 10(3) cycles is demonstrated with ±1 V voltage pulses. The switching mechanism is attributed to the formation and rupture of conductive filaments comprising fluoride vacancies in magnesium difluoride. Devices fabricated on a flexible polyethylene terephthalate substrate are tested for functionality, and degradation is subsequently demonstrated in de-ionized water. An additional layer of magnesium difluoride is used to hinder the degradation and extend the lifetime of the device.

Effects of increasing carbon nanofiber density in polyurethane composites for inhibiting bladder cancer cell functions.

Polyurethane (PU) is a versatile elastomer that is commonly used in biomedical applications. In turn, materials derived from nanotechnology, specifically carbon nanofibers (CNFs), have received increasing attention for their potential use in biomedical applications. Recent studies have shown that the dispersion of CNFs in PU significantly enhances composite nanoscale surface roughness, tensile properties, and thermal stability. Although there have been studies concerning normal primary cell functions on such nanocomposites, there have been few studies detailing cancer cell responses. Since many patients who require bladder transplants have suffered from bladder cancer, the ideal bladder prosthetic material should not only promote normal primary human urothelial cell (HUC) function, but also inhibit the return of bladder cancerous cell activity. This study examined the correlation between transitional (UMUC) and squamous (or SCaBER) urothelial carcinoma cells and HUC on PU:CNF nanocomposites of varying PU and CNF weight ratios (from pure PU to 4:1 [PU:CNF volume ratios], 2:1, 1:1, 1:2, and 1:4 composites to pure CNF). Composites were characterized for mechanical properties, wettability, surface roughness, and chemical composition by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and goniometry. The adhesion and proliferation of UMUC and SCaBER cancer cells were assessed by MTS assays. Cellular responses were further quantified by measuring the amounts of nuclear mitotic protein 22 (NMP-22), vascular endothelial growth factor (VEGF), and tumor necrosis factor alpha. Results demonstrated that both UMUC and SCaBER cell proliferation rates decreased over time on substrates with increased CNF in PU. In addition, with the exception of VEGF from UMUC (which was the same across all materials), composites containing the most CNF activated cancer cells (UMUC and SCaBER) the least, as shown by their decreased expression of NMP-22, tumor necrosis factor alpha, and VEGF. Moreover, the adhesion of HUC increased on composites containing more CNF than PU. Overall levels of NMP-22 were significantly lower in HUC than in cancerous UMUC and SCaBER cells on PU:CNF composites. Thus, this study provided a novel nanocomposite consisting of CNF and PU that should be further studied for inhibiting the return of cancerous bladder tissue and for promoting normal non-cancerous bladder tissue formation.