In this work, we describe the fabrication and working of a modular microsystem that recapitulates the functions of the "Neurovascular Unit". The microdevice comprised a vertical stack of a poly(dimethylsiloxane) (PDMS) neural parenchymal chamber separated by a vascular channel via a microporous polycarbonate (PC) membrane. The neural chamber housed a mixture of neurons (~4%), astrocytes (~95%), and microglia (~1%). The vascular channel was lined with a layer of rat brain microvascular endothelial cell line (RBE4). Cellular components in the neural chamber and vascular channel showed viability (>90%). The neural cells fired inhibitory as well as excitatory potentials following 10 days of culture. The endothelial cells showed diluted-acetylated low density lipoprotein (dil-a-LDL) uptake, expressed von Willebrand factor (vWF) and zonula occludens (ZO-1) tight junctions, and showed decreased Alexafluor™-conjugated dextran leakage across their barriers significantly compared with controls (p < 0.05). When the vascular layer was stimulated with TNF-α for 6 h, about 75% of resident microglia and astrocytes on the neural side were activated significantly (p < 0.05 compared to controls) recapitulating tissue-mimetic responses resembling neuroinflammation. The impact of this microsystem lies in the fact that this biomimetic neurovascular platform might not only be harnessed for obtaining mechanistic insights for neurodegenerative disorders, but could also serve as a potential screening tool for central nervous system (CNS) therapeutics in toxicology and neuroinfectious diseases.

Due to the limited regenerative ability of neural tissue, a diverse set of biochemical and biophysical cues for increasing nerve growth has been investigated, including neurotrophic factors, topography, and electrical stimulation. In this report, we explore optogenetic control of neurite growth as a cell-specific alternative to electrical stimulation. By investigating a broad range of optical stimulation parameters on dorsal root ganglia (DRGs) expressing channelrhodopsin 2 (ChR2), we identified conditions that enhance neurite outgrowth by three-fold as compared to unstimulated or wild-type (WT) controls. Furthermore, optogenetic stimulation of ChR2 expressing DRGs induces directional outgrowth in WT DRGs co-cultured within a 10 mm vicinity of the optically sensitive ganglia. This observed enhancement and polarization of neurite growth was accompanied by an increased expression of neural growth and brain derived neurotrophic factors (NGF, BDNF). This work highlights the potential for implementing optogenetics to drive nerve growth in specific cell populations.

Poly (trivinyl-trimethyl-cyclotrisiloxane) or polyV3D3 is a promising insulating thin film known for its potential application in neural probe fabrication. However, its time-consuming synthesis rate renders it impractical for manufacturing standards. Previously, the growth mechanism of polyV3D3 was shown to be affected by significant steric barriers. This article describes the synthesis of a copolymer of polyV3D3 via initiated chemical vapor deposition (iCVD) using V3D3 as the monomer, hexavinyl disiloxane (HVDS) as a spacer, and tert-butyl peroxide (TBP) as the initiator to obtain nearly a 4-fold increase in deposition rate. The film formation kinetics is limited by the adsorption of the reactive species on the surface of the substrate with an activation energy of −41.5 kJ/mol with respect to substrate temperature. The films deposited are insoluble in polar and non polar solvents due to their extremely crosslinked structure. They have excellent adhesion to silicon substrates and their adhesion properties are retained after soaking in a variety of solvents. Spectroscopic evidence shows that the films do not vary in structure after boiling in DI water for 1 hour, illustrating hydrolytic stability. PolyV3D3-HVDS has a bulk resistivity of 5.6 (±1) × 1014 Ω-cm, which is comparable to that of parylene-C; the insulating thin film currently used in neuroprosthetic devices.

Immobilized extracellular matrix proteins and neurotrophins have been extensively studied to enhance neuronal adhesion and proliferation on surfaces for applications in nerve tissue engineering and neuroprosthetic devices. This article describes how the coimmobilization of laminin, an extracellular matrix protein and nerve growth factor (NGF), a neurotrophin can enhance neurite outgrowth observed separately with each type of molecule. In the absence of immobilized NGF, PC12 neurite outgrowth is influenced strongly by the presence of NGF in solution and unaffected by significant increases in laminin surface density (18.7-93.5 ng/mm(2)). However, when both laminin and NGF are immobilized together, the surface density of laminin is an important factor in determining whether or not the neurite outgrowth-promoting effect of NGF can be obtained. PC12 neurite outgrowth on surfaces with coimmobilized laminin and NGF with surface densities of 27.6 ng/mm(2) and 1.4 ng/mm(2), respectively, are similar to that observed on surfaces with immobilized laminin and dissolved NGF.