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Many inner ear disorders cannot be adequately treated by systemic drug delivery. A blood-cochlear barrier exists, similar physiologically to the blood-brain barrier, which limits the concentration and size of molecules able to leave the circulation and gain access to the cells of the inner ear. However, research in novel therapeutics and delivery systems has led to significant progress in the development of local methods of drug delivery to the inner ear. Intratympanic approaches, which deliver therapeutics to the middle ear, rely on permeation through tissue for access to the structures of the inner ear, whereas intracochlear methods are able to directly insert drugs into the inner ear. Innovative drug delivery systems to treat various inner ear ailments such as ototoxicity, sudden sensorineural hearing loss, autoimmune inner ear disease, and for preserving neurons and regenerating sensory cells are being explored.

Without bioadhesive delivery devices, complex compounds are typically degraded or cleared from mucosal tissues by the mucus layer. 1-3 While some chemically-modified, micro-structured surfaces have been studied in aqueous environments, 4,5 adhesion due to geometry alone has not been investigated. Silicon nanowire-coated beads show significantly better adhesion than those with targeting agents under shear, and can increase the lift-off force 100-fold. We have shown that nanowire coatings, paired with epithelial physiology, significantly increase adhesion in mucosal conditions. KeywordsNanowire; nano-structure; bioadhesion; mucoadhesion; gecko-inspired; drug delivery; mucosa Because of their easy accessibility, large surface area, and rich blood supply, mucous membranes (mucosae), such as intestinal, nasal, ocular, vaginal, and buccal tissues, are frequently targeted for therapeutic drug delivery. 1,6 However, the mucosae present significant barriers to permeation, including a 1-450 μm motile mucous gel layer, tight junctions, and in some tissues, harsh enzymes and low pH. 7 Delivery devices have been able to protect compounds from chemical degradation, but without adhesion to the underlying epithelium, the *Additional contact information for Tejal A. Desai: -Tejal. Desai@ucsf.edu, phone -415-514-9695, fax -415-476-2414 Under nanoadhesive conditions, as the number of adhesive elements per surface area increases (ie: diameter of individual elements decreases), the surface area to volume ratio increases and van der Waals adhesion is predicted to increase 24,25 . Furthermore, because mucosal epithelia exhibit nano-structured microvilli, available surface area contact is considerably increased on the cell surface [26][27][28][29] . Thus, by decreasing the diameter of the elements on the device surface to the nano-scale and targeting a microvilliated surface, it may be possible to generate strong bioadhesive forces due to geometric features alone.To test the interaction of microvilli and nano-structures, a prototype device was created to couple the adhesive characteristics of nanowires with the drug delivery capacity of beads. A standard vapor liquid solid method for synthesizing silicon nanowires on flat wafer surfaces was modified to achieve growth of size-specific nanowires on the surface of 30-50 micron diameter glass beads (Figure 1). 30A Caco-2 cell monolayer was used as an in vitro model of the intestinal mucosa because the cells display a microvilliated structure which closely corresponds to that found in vivo 31 . From scanning electron microscopy ( Figure 1b), significant interdigitation of the nanowires and microvilli was visible at the cell-nano-structure interface, showing significant areas of contact between the cells and nanowires.In order to characterize the effects of geometric and chemical modifications of the nanowires, three nanowire test geometries and a control group with no nanowires (See Table 1 in Supporting Information) were fabricated. A subset of the long nanowire group and the contr...

Diseases that cause photoreceptor cell degeneration afflict millions of people, yet no restorative treatment exists for these blinding disorders. Replacement of photoreceptors using retinal progenitor cells (RPCs) represents a promising therapy for the treatment of retinal degeneration. Previous studies have demonstrated the ability of polymer scaffolds to increase significantly both the survival and differentiation of RPCs. We report the microfabrication of a poly(glycerol-sebacate) scaffold with superior mechanical properties for the delivery of RPCs to the subretinal space. Using a replica molding technique, a porous poly(glycerol-sebacate) scaffold with a thickness of 45 microm was fabricated. Evaluation of the mechanical properties of this scaffold showed that the Young's modulus is about 5-fold lower and the maximum elongation at failure is about 10-fold higher than the previously reported RPC scaffolds. RPCs strongly adhered to the poly(glycerol-sebacate) scaffold, and endogenous fluorescence nearly doubled over a 2-day period before leveling off after 3 days. Immunohistochemistry revealed that cells grown on the scaffold for 7 days expressed a mixture of immature and mature markers, suggesting a tendency towards differentiation. We conclude that microfabricated poly(glycerol-sebacate) exhibits a number of novel properties for use as a scaffold for RPC delivery.

Stem and progenitor cells can be combined with polymer substrates to generate tissue equivalents in culture. The replacement of retinal tissue lost to disease or trauma using retinal progenitor cells (RPCs) delivered on polymer scaffolds and transplanted into the sub-retinal space of the damaged retina is a promising therapeutic strategy. Micromachining-based, ultra-thin PMMA poly(methyl methacrylate) scaffolds may provide a suitable cytoarchitectural environment for tissue engineering and transplantation to the diseased eye. Here, adhesion of RPCs to polymer, as well as migration and differentiation in the host retina were compared for PMMA scaffolds (6 microm thickness) with either smooth or porous (11 microm diameter) surface topography. RPCs were cultured under identical conditions on smooth or porous laminin-coated polymer scaffolds and transplanted into the subretinal space of C57BL/6 mice. RPCs could be cultured on both scaffolds with similar results, although transplantation with non-porous scaffolds showed limited RPC retention. Porous scaffolds demonstrated enhanced RPC adherence during transplantation and allowed for greater process outgrowth and cell migration into the host retinal layers. Integrated cells expressed the mature neuronal marker neurofilament-200 (nf-200), the glial marker glial fibrillary acidic protein (GFAP) and the retinal-specific marker recoverin. No host foreign body response was seen. In conclusion, ultra-thin film PMMA scaffolds micromachined to contain through pores retain adherent RPCs to a considerably greater extent than unmachined versions during the transplantation process and can serve as a biocompatible substrate for cell delivery in vivo.

Retinal progenitor cells (RPCs) can be combined with nanostructured polymer scaffolds to generate composite grafts in culture. One strategy for repair of diseased retinal tissue involves implantation of composite grafts of this type in the subretinal space. In the present study, mouse retinal progenitor cells (RPCs) were cultured on laminin-coated novel nanowire poly(e-caprolactone)(PCL) scaffolds, and the survival, differentiation, and migration of these cells into the retina of C57bl/6 and rhodospsin −/− mouse retinal explants and transplant recipients were analyzed. RPCs were cultured on smooth PCL and both short (2.5 μm) and long (27 μm) nanowire PCL scaffolds. Scaffolds with adherent mRPCs were then either co-cultured with, or transplanted to, wild-type and rhodopsin −/− mouse retina. Robust RPC proliferation on each type of PCL scaffold was observed. Immunohistochemistry revealed that RPCs cultured on nanowire scaffolds increased expression of mature bipolar and photoreceptor markers. Reverse transcription polymerase chain reaction revealed down-regulation of several early progenitor markers. PCL-delivered RPCs migrated into the retina of both wild-type and rhodopsin knockout mice. The results provide evidence that RPCs proliferate and express mature retinal proteins in response to interactions with nanowire scaffolds. These composite grafts allow for the migration and differentiation of new cells into normal and degenerated retina.

We demonstrate that the technically simple, low-cost, and rapid method of template synthesis can be used to create arrays of nanowires and nanofibers from the biocompatible, biodegradable polymer poly(epsilon-caprolactone) (PCL). PCL substrates introduced into a standard laboratory oven at temperatures as low as 65 degrees C are able to form nanostructures. Nanostructure morphology can be controlled, and complex patterning can be achieved. Solvent-free and low-temperature fabrications also allow for the encapsulation of therapeutics for sustained release.

Nanostructured materials are ubiquitous in tissue engineering, drug delivery, and biosensing applications. Nonetheless, little is known about the inflammatory response of materials differing in surface nanoarchitecture. Here we report human monocyte viability and morphology, in addition to inflammatory cytokines (IL-1alpha and B, IL-6, IL-10, IFN-alpha and gamma, TNF-alpha, IL-12, MIP-1alpha and beta), and reactive oxygen species production on several nanostructured surfaces, compared to flat surfaces of the same material. The surfaces studied were titiania nanotubes, short and long silicon oxide, and polycaprolactone nanowires. The results indicate that inflammation on titanium, polycaprolactone, and silicon oxide materials can be reduced by restructuring the surface with nanoarchitecture. Nanostructured surfaces display a reduced inflammation response compared to a respective flat control, with significant differences between titanium and nanotubular titanium. Little difference is observed in the inflammatory response between short and long nanowires of PCL and silicon oxide. All surfaces are significantly less inflammatory than the positive control, lipopolysaccharide. Additionally, we show that flat titanium is more inflammatory than silicon oxide and polycaprolactone. This study shows that nanoarchitecture can be used to reduce the inflammatory response of human monocytes in vitro.