Surface Functionalization of 3D-Printed Scaffolds with Seed-Assisted Hydrothermally Grown ZnO Nanoarrays for Bone Tissue Engineering.

Bioactive metal-based nanostructures, particularly zinc oxide (ZnO), are promising materials for bone tissue engineering. However, integrating them into 3D-printed polymers using traditional blending methods reduces the cell performance. Alternative surface deposition techniques often require extreme conditions that are unsuitable for polymers. To address these issues, we propose a metal-assisted hydrothermal synthesis method to modify 3D printed polycaprolactone (PCL) scaffolds with ZnO nanoparticles (NPs), facilitating the growth of ZnO nanoarrays (NAs) at a low-temperature (55 °C). Physicochemical characterizations revealed that the ZnO NPs form both physical and chemical bonds with the PCL surface; chemical bonding occurs between the carboxylate groups of PCL and Zn(OH)2 during seed deposition and hydrothermal synthesis. The ZnO NPs and NAs grown for a longer time (18 h) on the surface of PCL scaffolds exhibit significant proliferation and early differentiation of osteoblast-like cells. The proposed method is suitable for the surface modification of thermally degradable polymers, opening up new possibilities for the deposition of diverse metals.

3D nanomolding for lab-on-a-chip applications.

The ability to decorate microfluidic channel walls with additional micro/nanostructures becomes important as a means to modify the flow behavior, such as mixing and pressure drop, as well as to enhance the reactivity of bio-reactions to the surface in lab-on-a-chip applications. Despite the ability of mass production at low cost, conventional micro and nanomolding techniques are limited to the patterning of planar or slightly curved polymer substrates. Here we show a two-step molding technique, named 3D nanomolding, which allows the patterning of arbitrarily hierarchical multiscale structures, even nanostructures formed on the vertical sidewalls of microfluidic channels. In the first molding step, an ultra-thin intermediate polydimethyl siloxane (PDMS) stamp is produced by spin-coating and curing PDMS prepolymer on a pre-nanopatterned poly(methyl methacrylate) (PMMA) substrate, which is followed by the second molding step using the primary PDMS stamp containing microstructures. Various hierarchical micro and nanostructures are demonstrated, which include a biomimetic superhydrophobic structure in a lotus leaf surface to modify the surface wetting property and microfluidic channels where the walls are patterned with nanostructures. Despite the presence of nanostructures on the top surface, 3D nanomolded microchannels could be sealed well with a nanopatterned PMMA cover plate using solvent bonding to form enclosed microfluidic devices. The results indicate that the 3D nanomolding technique is suitable for decorating microchannel walls for lab-on-a-chip applications.

Highly sensitive biosensing using arrays of plasmonic Au nanodisks realized by nanoimprint lithography.

We describe the fabrication of elliptical Au nanodisk arrays as a localized surface plasmon resonance (LSPR) sensing substrate for clinical immunoassay via thermal nanoimprint lithography (NIL) and enhancement in the sensitivity of the detection of the prostate-specific antigen (PSA) using the precipitation of 5-bromo-4-chloro-3-indolyl phosphate p-toluidine/nitro blue tetrazolium (BCIP/NBT), catalyzed by alkaline phosphatase. Au nanodisks were fabricated on glass through an unconventional tilted evaporation, which could preserve the thickness of imprinted resists and create an undercut beneficial to the subsequent lift-off process without any damage to pattern dimension and the glass while removing the residual polymers. To investigate the optically anisotropic property of the LSPR sensors, a probe light with linear polarization parallel to and perpendicular to the long axis of the elliptical nanodisk array was utilized, and their sensitivity to the bulk refractive index (RI) was measured as 327 and 167 nm/RIU, respectively. To our knowledge, this is the first application of enzyme-substrate reaction to sandwich immunoassay-based LSPR biosensors that previously suffered from a low sensitivity due to the short penetration depth of the plasmon field, especially when large-sized antibodies were used as bioreceptors. As a result, a large change in local refractive index because of the precipitation on the Au nanodisks amplified the wavelength shift of the LSPR peak in the vis-NIR spectrum, resulting in femtomolar detection limits, which was ∼10(5)-fold lower than the label-free detection without the enzyme precipitation. This method can be extended easily to the other clinical diagnostics with a high sensitivity.