High transmission from 2D periodic plasmonic finite arrays with sub-20 nm gaps realized with Ga focused ion beam milling.

Fabricating plasmonic nanostructures with good optical performances often requires lengthy and challenging patterning processes that can hardly be transferred to unconventional substrates, such as optical fiber tips or curved surfaces. Here we investigate the use of a single Ga focused ion beam process to fabricate 2D arrays of gold nanoplatelets for nanophotonic applications. While observing that focused ion beam milling of crossing tapered grooves inherently produces gaps below 20 nm, we provide experimental and theoretical evidence for the spectral features of grooves terminating with a sharp air gap. We show that transmission near 10% can be obtained via two-dimensional nano-focusing in a finite subset of 2D arrays of gold nanoplatelets. This enables the application of our nanostructure to detect variations in the refractive index of thin films using either reflected or transmitted light when a small number of elements are engaged.

Biomimetic, Multiresponsive, and Self-Healing Lactose-Modified Chitosan (CTL)-Based Gels Formed via Competitor-Assisted Mechanism.

The present paper describes an original method to form under physiological conditions homogeneous lactose-modified chitosan (CTL) gels avoiding syneresis. Specifically, combination of boric acid-i.e., the cross-linker-and mannitol-i.e., a polyol competitor for boron binding-were exploited to reduce the very fast kinetics of CTL/boron self-assembly. Resulting gels were homogeneous as proved by scattering analyses. An in-depth rheological characterization was undertaken to identify the correct mannitol-to-boron ratio at which gels showed homogeneity without weakening. Stress sweep and frequency sweep tests were performed to investigate the viscoelastic properties of these dynamic networks, highlighting a marked strain-hardening behavior, which is pivotal in native tissues. Notably, herein we report for the first time that CTL-boric acid gels are multiresponsive systems, whose mechanics can be tailored by different stimuli such as the presence of small molecules like glucose. Moreover, we demonstrate that these networks spontaneously self-heal after breakage. The biocompatibility of such gels was studied under 2D and 3D conditions toward three different cell models, namely, pig primary chondrocytes, human Dental Pulp Stem Cells (hDPSCs), and mouse fibroblasts. Giving the peculiar mechanical performance of selected systems and considering the well-known bioactivity of the chitosan derivative, CTL-boric acid networks are promising candidates as multiresponsive gels to be used in the field of tissue engineering, especially for articular cartilage regeneration.

Concepts for Developing Physical Gels of Chitosan and of Chitosan Derivatives.

Chitosan macro- and micro/nano-gels have gained increasing attention in recent years, especially in the biomedical field, given the well-documented low toxicity, degradability, and non-immunogenicity of this unique biopolymer. In this review we aim at recapitulating the recent gelling concepts for developing chitosan-based physical gels. Specifically, we describe how nowadays it is relatively simple to prepare networks endowed with different sizes and shapes simply by exploiting physical interactions, namely (i) hydrophobic effects and hydrogen bonds-mostly governed by chitosan chemical composition-and (ii) electrostatic interactions, mainly ensured by physical/chemical chitosan features, such as the degree of acetylation and molecular weight, and external parameters, such as pH and ionic strength. Particular emphasis is dedicated to potential applications of this set of materials, especially in tissue engineering and drug delivery sectors. Lastly, we report on chitosan derivatives and their ability to form gels. Additionally, we discuss the recent findings on a lactose-modified chitosan named Chitlac, which has proved to form attractive gels both at the macro- and at the nano-scale.