Microneedles are small-scale devices that may be used for drug delivery and biosensing. In this study, the forces required for mechanical failure, the modes of mechanical failure, as well as the mechanisms for microneedle penetration into porcine skin were examined. Microneedles produced from the acrylate-based polymer e-Shell 200 using an indirect rapid prototyping approach involving two-photon polymerization and poly(dimethylsiloxane) micromolding were found to possess sufficient strength for penetration of porcine skin. The failure forces were an order of magnitude greater than the forces necessary for full insertion into the skin. Bending was the most common form of failure; an increasing aspect ratio and a decreasing tip diameter were associated with lower failure forces. Video captured during skin penetration revealed that microneedle penetration into the skin occurred by means of a series of insertions and not by means of a single insertion event. Images obtained during and after skin penetration confirmed microneedle penetration of skin as well as transdermal delivery of lucifer yellow dye. These findings shed insight into the mechanisms of microneedle penetration and failure, facilitating design improvements for polymer microneedles.

This study evaluates the bond strength and related properties of photo-polymerizable, remineralizing amorphous calcium phosphate (ACP) polymeric composite-adhesive systems to dentin after various periods of aqueous aging at 37 °C. An experimental ACP base and lining composite was made from a photo-activated resin comprising 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and zirconyl dimethacrylate (ZrDMA); designated BTHZ. An experimental orthodontic composite was formulated from a photo-activated resin comprising ethoxylated bisphenol A dimethacrylate (EBPADMA), TEGDMA, HEMA and methacryloxyethyl phthalate (MEP); designated ETHM. In both composite series three fillers were compared: 1) freshly precipitated zirconium-modified ACP freshly precipitated (as-prepared Zr-ACP), 2) milled Zr-ACP and 3) an ion-leachable fluoride glass. In addition to the shear bond strength (SBS), work to fracture and failure modes of the orthodontic composites were determined. The SBS of the base and lining ACP composites appeared unaffected by filler type or immersion time. In the orthodontic ACP composite series, milled ACP composites showed initial mechanical advantages over as-prepared ACP composites, and produced higher incidence of a failure mode consistent with stronger adhesion. After six months of aqueous exposure, 80 % of specimens failed at the dentin-primer interface, with a 42 % overall reduction in bond strength. BTHZ and ETHM based ACP composites are potentially effective anti-demineralizing-remineralizing agents with possible clinical utility as protective base-liners and orthodontic cements, respectively. The analysis of the bond strength and failure modalities suggests that milled ACP composites may offer greater potential in clinical applications.

We have investigated the influence of micrometer- and sub-micrometer-scale surface heterogeneities in patterned octadecyltrichlorosilane (OTS) films on human serum albumin (HSA) adsorption and its spatial distribution. 5-μm-wide OTS patterns were created on glass substrates by micro-contact printing and in some instances subsequent annealing was used to alter OTS molecule distribution within the patterns. Scanning force microscopy (SFM), advancing water contact angles and water vapor condensation figures were used to characterize the OTS films and to assess the nature of the heterogeneities within the various surface areas. High-resolution fluorescence microscopy was used to record images of fluorescently labeled albumin on OTS patterned films and fluorescence intensity was quantified and converted into the adsorbed amount. Adsorbed albumin was also characterized through SFM measurements. Combined SFM topography and lateral force microscopy (LFM) imaging revealed that micro-contact printing of OTS onto glass both replicated the stamp pattern and created small islands within the non-stamped regions between the patterns. The OTS coverage within stamped regions was not fully continuous but improved with subsequent annealing. Annealing also resulted in OTS island growth within the non-stamped regions and decreased average wettability on both the stamped and non-stamped areas. The extent of albumin adsorption was not proportional to OTS coverage, but correlated with the sub-μm distribution of OTS chains. We inferred that the surface distribution of ligands such as OTS on a sub-μm length scale determines the nature of albumin adsorption and its kinetics.