(261e) Biodegradable and Implantable Platform for Wireless Electrical Stimulation of Neural Stem Cells

Central nervous system (CNS) problems affected nearly 100 million Americans as of 2011 causing high mortality/morbidity rate, lifelong disabilities, social and economic burdens (total annual cost was estimated as $789 billion in 2014, which is expected to further increase by 2050).^1,2 There have been innovative approaches relying on regrowth of disrupted neuronal axons, replacement of lost neural cells, and recovery of lost neural function to address CNS problems. Among them, physiological stimulation of endogenous, self-renewing and multipotent neural stem cells (NSC) is considered as a promising strategy.^3-7 Particularly, electrical stimulation (ES) has demonstrated recovery potential in the pre-clinical studiesand the clinic. However, currently available ES strategies mostly rely on wired metal electrodes that are inherently planar, non-biodegradable and require expensive lithographic patterning techniques.

The inadequate availability of endogenous NSC in the CNS and lack of in-depth understanding of cellular mechanisms also limits the outcomes.Alternatively, exogeneous NSC, which can be derived from other stem cell types (i.e. human induced pluripotent stem cells, hiPSC), are able to differentiate into major cell types of CNS (i.e. neurons, astrocytes, and oligodendrocytes), and can be transplanted to enhance regeneration, repair and recovery of CNS.^8-12 However, our current knowledge regarding the mechanisms of NSC differentiation and fate commitment is still limited. Moreover, transplanted NSC demonstrated limited viability, proliferation and migration behavior, which create additional challenges and require further investigation to unravel the mechanisms.

The development of an implantable and biodegradable flexible electronic platform possessing 3D microstructure that can enable precise/accurate, local, and spatial wireless electrical stimulation (WES) to control NSC differentiation and fate commitment can be an advancement over traditionally used ES materials and approaches. Therefore, in this study, we developed a conductive graphene antenna integrated flexible PLLA/PLGA substrate as biodegradable and implantable platform to control NSC behavior using WES.

The fabrication of the wireless platform was conducted by using a novel approach based on our published and patented work.^13-14 This room temperature operated approach involves formation of graphene circuits on pre-patterned molds using microfluidics followed by subsequent circuit transfer by simple polymer casting. We apply finite element analysis using COMSOL to design the antenna and simulate frequency characteristics. The structure and integrity of the wireless platform was assessed via scanning electron microscopy. The conductivity/sheet resistance of the graphene antennas were evaluated via 4-point probe measurement. The functionality of the array was tested using a light-emitting diode electrically connected to the wireless array as a visual indicator in PBS (pH 7.4 at 37 °C) mimicking cell culture using a waveform/function generator, oscilloscope, and network analyzer. The frequency characteristics and selective driving of each individual multi-turn coils in the array will be assessed via the network analyzer. The degradation behavior of the wireless platform was also observed in PBS (pH 7.4 at 37 °C) over time.

The NSC were seeded on the wireless platforms and attachment, growth and cell viability were evaluated via immunocytochemical (ICC) staining and live/dead cell assays. Following the cell seeding, different WES parameters (i.e., voltage and frequency) was applied to evaluate the differentiation profile under different WES conditions.The NSC differentiation was investigated via ICC, ELISA, RT-PCR and Western Blot (WB) using specific markers, antibodies and primers such as Nestin, Sox1, Tuj1, MAP2, neurofilaments markers, SYP, TUBB3 and GAP43 antibodies and primers.

Our results indicated that application of different WES conditions via biodegradable wireless platforms influenced the expression of markers associated with neuronal, astrocyte and oligodendrocyte phenotypes, suggesting that WES can be used to control NSC differentiation and fate commitment. In conclusion, successfully developed biodegradable and implantable wireless platform has the potential to be used to control implanted NSC behavior using localized WES. However, in depth mechanistic approach is needed for future applications.

References:

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