Stiffness-Changing of Polymer Nanocomposites with Cellulose Nanocrystals and Polymeric Dispersant.

Bio-inspired, water-responsive, mechanically adaptive nanocomposites are reported based on cellulose nanocrystals (CNCs), poly(ethylene oxide-co-epichlorohydrin) (EO-EPI), and a small amount of poly(vinyl alcohol) (PVA), which is added to aid the dispersion of the CNCs. In the dry state, the CNCs form a reinforcing network within the polymer matrix, and the substantial stiffness increase relative to the neat polymer is thought to be the result of hydrogen-bonding interactions between the nanocrystals. Exposure to water, however, causes a large stiffness reduction, due to competitive hydrogen bonding of water molecules and the CNCs. It is shown here that the addition of PVA to the EO-EPI/CNC nanocomposite increases the modulus difference between the dry and the wet state by a factor of up to four compared to the nanocomposites without the PVA. The main reason is that the PVA leads to a substantial increase of the stiffness in the dry state; for example, the storage modulus E ' increased from 2.7 MPa (neat EO-EPI) to 50 MPa upon introduction of 10% CNCs, and to 200 MPa when additionally 5% of PVA was added. By contrast, the incorporation of PVA only led to moderate increases of the equilibrium water swelling and the E ' in the wet state.

Influence of resveratrol release on the tissue response to mechanically adaptive cortical implants.

The stability and longevity of recordings obtained from intracortical microelectrodes continues to remain an area of concern for neural interfacing applications. The limited longevity of microelectrode performance has been associated with the integrity of the blood brain barrier (BBB) and the neuroinflammatory response to the microelectrode. Here, we report the investigation of an additive approach that targets both mechanical and chemical factors believed to contribute to chronic BBB instability and the neuroinflammatory response associated with implanted intracortical microelectrodes. The implants investigated were based on a mechanically adaptive, compliant nanocomposite (NC), which reduces the tissue response and tissue strain. This material was doped with various concentrations of the antioxidant resveratrol with the objective of local and rapid delivery. In vitro analysis of resveratrol release, antioxidant activity, and cytotoxicity suggested that a resveratrol content of 0.01% was optimal for in vivo assessment. Thus, probes made from the neat NC reference and probes containing resveratrol (NC Res) were implanted into the cortical tissue of rats for up to sixteen weeks. Histochemical analysis suggested that at three days post-implantation, neither materials nor therapeutic approaches (independently or in combination) could alter the initial wound healing response. However, at two weeks post-implantation, the NC Res implant showed a reduction in activated microglia/macrophages and improvement in neuron density at the tissue-implant interface when compared to the neat NC reference. However, sixteen weeks post-implantation, when the antioxidant was exhausted, NC Res and the neat NC reference exhibited similar tissue responses. The data show that NC Res provides short-term, short-lived benefits due to the antioxidant release, and a long-term reduction in neuroinflammation on account of is mechanical adaptive, compliant nature. Together, these results demonstrate that local delivery of resveratrol can provide an additive advantage by providing a consistent reduction in the tissue response.