A Novel Cryogenic Approach to 3D Printing Cytocompatible, Conductive, Hydrogel-Based Inks.

In the field of tissue engineering and regenerative medicine, developing cytocompatible 3D conductive scaffolds that mimic the native extracellular matrix is crucial for the engineering of excitable cells and tissues. In this study, a custom cryogenic extrusion 3D printer was developed, which afforded control over both the ink and printing surface temperatures. Using this approach, aqueous inks were printed into well-defined layers with high precision. A conductive hydrogel ink was developed from chitosan (CS) and edge-functionalised expanded graphene (EFXG). Different EFXG:CS ratios (between 60:40 and 80:20) were evaluated to determine both conductivity and printability. Using the novel customized cryogenic 3D printer, conductive structures of between 2 and 20 layers were produced, with feature sizes as small as 200 µm. The printed structures are mechanically robust and are electrically conducting. The highest Young's modulus and conductivity in a hydrated state were 2.6 MPa and ∼45 S/m, respectively. Cytocompatibility experiments reveal that the developed material supports NSC-34 mouse motor neuron-like cells in terms of viability, attachment, and proliferation. The distinctive mechanical and electrical properties of the 3D-printed structures would make them good candidates for the engineering of 3D-structured excitable cells. Moreover, this novel printing setup can be used to print other hydrogel-based inks with high precision and resolution.

Toward Three-Dimensional Printed Thermal Conductive Polymeric Composites Using a Binary-Composite Hybrid Based on Boron Nitride Nanoparticles and Micro-Diamonds.

Thermally conductive polymeric composites are promising for heat management in microelectronic devices. This work presents a binary-hybrid composite of boron nitride (BN) nanoparticles and micro-diamond (D) fillers in an elastomeric polyurethane (PU) matrix which can be three- dimensionally printed to produce a highly flexible and self-supporting structure. The research shows that a combination of 16.7 wt% BN and 16.7 wt% D results in a robust network within the polymer matrix to improve the tensile modulus more than nine times with respect to neat PU. Significantly, the hybrid matrix enhances the thermal conductivity by more than two times when compared to neat PU. The enhancement in mechanical, and thermal features make this three-dimensional printable multiscale hybrid composite suitable for flexible and stretchable microelectronic applications.

Polyethylene Oxide (PEO) Provides Bridges to Silica Nanoparticles to Form a Shear Thickening Electrolyte for High Performance Impact Resistant Lithium-ion Batteries.

The development of shear thickening electrolytes is proving to be pivotal in the quest for impact resistant lithium-ion batteries (LIBs). However, the high viscosity and poor stability associated with the need for high filler content has to date impeded progress. Here, this work reports a new type of polymer-bridged shear thickening electrolyte that overcomes these shortcomings, by utilizing the interaction between polymer chains and silica nanoparticles. The incorporation of polyethylene oxide (PEO) facilitates hydrocluster formation providing impact resistance with a filler content as low as 2.2 wt%. This low viscosity electrolyte has a high ionic conductivity of ≈5.1 mS cm-1 with excellent long-term stability, over 30 days. The effectiveness of this electrolyte in LIBs is demonstrated by excellent electrochemical performance and high impact resistance.

Tuning the electrophoretic separations on a surface-accessible and flexible fibre-based microfluidic devices.

Electrophoresis on textile fiber substrates provides a unique surface-accessible platform for the movement, separation and concentration of charged analytes. The method employs the inherently inbuilt capillary channels existing within textile structures, which can support electroosmotic and electrophoretic transport processes upon applying an electric field. Unlike confined microchannels in classical chip-based electrofluidic devices, the capillaries formed by the roughly oriented fibers within textile substrates can impact the reproducibility of the separation process. Here, we report an approach for precise experimental conditions affecting the electrophoretic separation of two tracer solutes, fluorescein (FL) and rhodamine B (Rh-B) on textile-based substrates. A Box-Behnken response surface design methodology has been used to optimise the experimental conditions and predict the separation resolution of a solute mixture using polyester braided structures. The magnitude of the electric field, sample concentration and sample volume are of primary importance to the separation performance of the electrophoretic devices. Here, we use a statistical approach to optimise these parameters to achieve rapid and efficient separation. While a higher potential was shown to be required to separate solute mixtures of increasing concentration and sample volume, this was counteracted by a reduced separation efficiency due to joule heating, which caused electrolyte evaporation on the unenclosed textile structure at electric fields above 175 V cm-1. Using the approach presented here, optimal experimental conditions can be predicted to limit joule heating and attain effective separation resolution without compromising the analysis time on simple and low-cost textile substrates.

Optimizing the composition of gelatin methacryloyl and hyaluronic acid methacryloyl hydrogels to maximize mechanical and transport properties using response surface methodology.

Hydrogel materials are promising candidates in cartilage tissue engineering as they provide a 3D porous environment for cell proliferation and the development of new cartilage tissue. Both the mechanical and transport properties of hydrogel scaffolds influence the ability of encapsulated cells to produce neocartilage. In photocrosslinkable hydrogels, both of these material properties can be tuned by changing the crosslinking density. However, the interdependent nature of the structural, physical and biological properties of photocrosslinkable hydrogels means that optimizing composition is typically a complicated process, involving sequential and/or iterative steps of physiochemical and biological characterization. The combinational nature of the variables indicates that an exhaustive analysis of all reasonable concentration ranges would be impractical. Herein, response surface methodology (RSM) was used to efficiently optimize the composition of a hybrid of gelatin-methacryloyl (GelMA) and hyaluronic acid methacryloyl (HAMA) with respect to both mechanical and transport properties. RSM was employed to investigate the effect of GelMA, HAMA, and photoinitiator concentration on the shear modulus and diffusion coefficient of the hydrogel membrane. Two mathematical models were fitted to the experimental data and used to predict the optimum hydrogel composition. Finally, the optimal composition was tested and compared with the predicted values.

Topical application of an irreversible small molecule inhibitor of lysyl oxidases ameliorates skin scarring and fibrosis.

Scarring is a lifelong consequence of skin injury, with scar stiffness and poor appearance presenting physical and psychological barriers to a return to normal life. Lysyl oxidases are a family of enzymes that play a critical role in scar formation and maintenance. Lysyl oxidases stabilize the main component of scar tissue, collagen, and drive scar stiffness and appearance. Here we describe the development and characterisation of an irreversible lysyl oxidase inhibitor, PXS-6302. PXS-6302 is ideally suited for skin treatment, readily penetrating the skin when applied as a cream and abolishing lysyl oxidase activity. In murine models of injury and fibrosis, topical application reduces collagen deposition and cross-linking. Topical application of PXS-6302 after injury also significantly improves scar appearance without reducing tissue strength in porcine injury models. PXS-6302 therefore represents a promising therapeutic to ameliorate scar formation, with potentially broader applications in other fibrotic diseases.

Development of an In Situ Printing System With Human Platelet Lysate-Based Bio-Adhesive to Treat Corneal Perforations.

Purpose: Corneal perforation is a clinical emergency that can result in blindness. Currently corneal perforations are treated either by cyanoacrylate glue which is toxic to corneal cells, or by using commercial fibrin glue for small perforations. Both methods use manual delivery which lead to uncontrolled application of the glues to the corneal surface. Therefore, there is a need to develop a safe and effective alternative to artificial adhesives. Methods: Previously, our group developed a transparent human platelet lysate (hPL)-based biomaterial that accelerated corneal epithelial cells healing in vitro. This biomaterial was further characterized in this study using rheometry and adhesive test, and a two-component delivery system was developed for its application. An animal trial (5 New Zealand white rabbits) to compare impact of the biomaterial and cyanoacrylate glue (control group) on a 2 mm perforation was conducted to evaluate safety and efficacy. Results: The hPL-based biomaterial showed higher adhesiveness compared to commercial fibrin glue. Treatment rabbits had lower pain scores and faster recovery, despite generating similar scar-forming structure compared to controls. No secondary corneal ulcer was generated in rabbits treated with the bio-adhesive. Conclusions: This study reports an in situ printing system capable of delivering a hPL-based, transparent bio-adhesive and successfully treating small corneal perforations. The bio-adhesive-treated rabbits recovered faster and required no additional analgesia. Translational Relevance: The developed in situ hPL bio-adhesives treatment represents a new format of treating corneal perforation that is easy to use, allows for accurate application, and can be a potentially effective and pain relief treatment.

Effect of Graphene Addition on Polycaprolactone Scaffolds Fabricated Using Melt-Electrowriting.

Melt-electrowriting (MEW) is an emerging method that combines electrospinning and extrusion printing, allowing the fabrication of micron-scale structures suitable for tissue engineering. Compared to other additive fabrication methods, melt-electro written structures can offer more appropriate substrates for cell culture due to filament size and mechanical characteristics of the fabricated scaffolds. In this study, polycaprolactone (PCL)/graphene composites were investigated for fabrication of micron-size scaffolds through MEW. It was demonstrated that the addition of graphene can considerably improve the processability of PCL to fabricate micron-scale scaffolds with enhanced resolution. The tensile strength of the scaffold prepared from PCL/graphene composite (with only 0.5 wt.% graphene) was proved significantly (by more than 270%), better than that of the pristine PCL scaffold. Furthermore, graphene was demonstrated to be a suitable material for tailoring the degradation process to avoid undesirable bulk degradation, rapid mass loss and damage to the internal matrix of the polymer. The findings of this study offer a promising route for the fabrication of high-resolution scaffolds with micron-scale resolution for tissue engineering.

Wireless bipolar electrode-based textile electrofluidics: towards novel micro-total-analysis systems.

Point of care testing using micro-total-analysis systems (µTAS) is critical to emergent healthcare devices with rapid and robust responses. However, two major barriers to the success of this approach are the prohibitive cost of microchip fabrication and poor sensitivity due to small sample volumes in a microfluidic format. Here, we aimed to replace the complex microchip format with a low-cost textile substrate with inherently built microchannels using the fibers' spaces. Secondly, by integrating this textile-based microfluidics with electrophoresis and wireless bipolar electrochemistry, we can significantly improve solute detection by focusing and concentrating the analytes of interest. Herein, we demonstrated that an in situ metal electrode simply inserted inside the textile-based electrophoretic system can act as a wireless bipolar electrode (BPE) that generates localized electric field and pH gradients adjacent to the BPE and extended along the length of the textile construct. As a result, charged analytes were not only separated electrophoretically but also focused where their electrophoretic migration and counter flow (EOF) balances due to redox reactions proceeding at the BPE edges. The developed wireless redox focusing technique on textile constructs was shown to achieve a 242-fold enrichment of anionically charged solute over an extended time of 3000 s. These findings suggest a simple route that achieves separation and analyte focusing on low-cost surface-accessible inverted substrates, which is far simpler than the more complex ITP on conventional closed and inaccessible capillary channels.