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L-3,4-dihydroxyphenylalanine (L-DOPA) is a naturally occurring catechol that is known to increase the adhesive strength of various materials used for tissue repair. With the aim of fortifying a porous and erodible chitosan-based adhesive film, L-DOPA was incorporated in its fabrication for stronger photochemical tissue bonding (PTB), a repair technique that uses light and a photosensitiser to promote tissue adhesion. The results showed that L-DOPA did indeed increase the tissue bonding strength of the films when photoactivated by a green LED, with a maximum strength recorded of approximately 30 kPa, 1.4 times higher than in its absence. The addition of L-DOPA also did not appreciably change the swelling, mechanical and erodible properties of the film. This study showed that strong, porous and erodible adhesive films for PTB made from biocompatible materials can be obtained through a simple inclusion of a natural additive such as L-DOPA, which was simply mixed with chitosan without any chemical modifications. In vitro studies using human fibroblasts showed no negative effect on cell proliferation indicating that these films are biocompatible. The films are convenient for various surgical applications as they can provide strong tissue support and a microporous environment for cellular infusion without the use of sutures. Statement of significance Tissue adhesives are not as strong as sutures on wounds under stress. Our group has previously demonstrated that strong sutureless tissue repair can be realised with chitosan-based adhesive films that photochemically bond to tissue when irradiated with green light. The advantage of this technique is that films are easier to handle than glues and sutures, and their crosslinking reactions can be controlled with light. However, these films are not optimal for high-tension tissue regenerative applications because of their non-porous structure, which cannot facilitate cell and nutrient exchange at the wound site. The present study resolves this issue, as we obtained a strong and porous photoactivated chitosan-based adhesive film, by simply using freeze drying and adding L-DOPA.

Photochemical tissue bonding with chitosan-based adhesive films is an experimental surgical technique that avoids the risk of thermal tissue injuries and the use of sutures to maintain strong tissue connection. This technique is advantageous over other tissue repair methods as it is minimally invasive and does not require mixing of multiple components before or during application. To expand the capability of the film to beyond just a tissue bonding device and promote tissue regeneration, in this study, we designed bioadhesive films that could also support stem cells. The films were modified with oligomeric chitosan to tune their erodibility and made porous through freeze-drying for better tissue integration. Of note, porous adhesive films (pore diameter ∼110 μm), with 10% of the chitosan being oligomeric, could retain similar tissue bonding strengths (13-15 kPa) to that of the nonporous chitosan-based adhesives used in previous studies when photoactivated. When tested in vitro, these films exhibited a mass loss of ∼20% after 7 days, swelling ratios of ∼270-300%, a percentage elongation of ∼90%, and both a tensile strength and Young's modulus of ∼1 MPa. The physical properties of the films were suitable for maintaining the viability and multipotency of bone-marrow-derived human mesenchymal stem cells over the duration of culture. Thus, these biocompatible, photoactivated porous, and erodible adhesive films show promise for applications in controlled cell delivery and regenerative medicine.

LiFePO 4 /Carbon nanocomposite was synthesised by two-step procedure hydrothermal synthesis in the presence of ascorbic acid followed by mixing of the product with citric acid and heating at 600 °C under a reducing atmosphere. During the first-step, slab or cuboid-shaped LiFePO 4 particles were formed with sizes of ∼100–150 nm in width and ∼300–600 nm in length. The second-step produced deformed slab or cuboid-like LiFePO 4 /Carbon nanocomposite with shapes somewhat resembling that of the precursor. The electrochemical properties were examined by electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT) at a series of equilibrium potentials within the voltage range 2.7–4.2 V. From the PITT measurements of cathodes with two thicknesses, the LiFePO 4 /Carbon nanocomposite exhibits a specific discharge capacity of 150.3 mAh/g and 164.3 mAh/g, for 9.4 μm and 6.9 μm thickness, respectively. The current relaxation measurements also showed that the kinetics of Li-ion transfer depends strongly on the phase composition; in the solid-solution regions the Li-ion kinetics is dominated by diffusion whereas in the two-phase region it is by phase transformation.

In this work, nanocrystalline Ti/Cu multilayer thin films were fabricated using direct current magnetron sputtering with different layer thicknesses, namely 250, 100, 50, 25 and 5 nm. Additionally, a group of the film specimens were prepared with various modulation ratios where each bilayer was set to 100 nm. The size-dependent deformation behavior of the films was studied using the nano-indentation and nano-scratching techniques. The results showed that the flow strength of the films tended to increase as the layer thickness decreased. Moreover, the strength and scratch resistance of the films can be further enhanced by tailoring the thicknesses of two adjacent layers, while keeping the thickness of each bilayer unchanged. Finally, the size-dependent strengthening mechanism was discussed by recourse to microscopic examination.