A moisturizing chitosan-silk fibroin dressing with silver nanoparticles-adsorbed exosomes for repairing infected wounds

Refractory wounds caused by microbial infection impede wound healing, vascular regeneration, nerve system repair and the regeneration of other skin appendages. In addition, large-area infected wounds cause the appearance of multidrug-resistant (MDR) bacterial strains, which pose a major challenge both in clinical and scientific research. Although many stem cell-derived exosomes have been demonstrated to promote skin repair and regeneration, exosomes are seldom applied in the treatment of infective wounds due to the lack of antimicrobial function. In this study, we fabricated an asymmetric wettable dressing with a composite of exosomes and silver nanoparticles (CTS-SF/SA/Ag-Exo dressing) for promoting angiogenesis, nerve repair and infected wound healing. The CTS-SF/SA/Ag-Exo dressing possesses multifunctional properties including broad-spectrum antimicrobial activity, promoting wound healing, retaining moisture and maintaining electrolyte balance. It can effectively inhibit the growth of bacterial and promote the proliferation of human fibroblasts in vitro. Moreover, the in vivo results show that the CTS-SF/SA/Ag-Exo dressing enhanced wound healing by accelerating collagen deposition, angiogenesis and nerve repair in a P. aeruginosa infected mouse skin wound defect model. We hope that this dressing will provide a solution for the repair of infected wounds for treatments in the clinic.

High-Aspect-Ratio Nanostructured Surfaces as Biological Metamaterials

Materials patterned with high-aspect-ratio nanostructures have features on similar length scales to cellular components. These surfaces are an extreme topography on the cellular level and have become useful tools for perturbing and sensing the cellular environment. Motivation comes from the ability of high-aspect-ratio nanostructures to deliver cargoes into cells and tissues, access the intracellular environment, and control cell behavior. These structures directly perturb cells' ability to sense and respond to external forces, influencing cell fate, and enabling new mechanistic studies. Through careful design of their nanoscale structure, these systems act as biological metamaterials, eliciting unusual biological responses. While predominantly used to interface eukaryotic cells, there is growing interest in nonanimal and prokaryotic cell interfacing. Both experimental and theoretical studies have attempted to develop a mechanistic understanding for the observed behaviors, predominantly focusing on the cell-nanostructure interface. This review considers how high-aspect-ratio nanostructured surfaces are used to both stimulate and sense biological systems.

Defect-Rich Adhesive Nanozymes as Efficient Antibiotics for Enhanced Bacterial Inhibition

Nanozymes have emerged as a new generation of antibiotics with exciting broad-spectrum antimicrobial properties and negligible biotoxicities. However, their antibacterial efficacies are unsatisfactory due to their inability to trap bacteria and their low catalytic activity. Herein, we report nanozymes with rough surfaces and defect-rich active edges. The rough surface increases bacterial adhesion and the defect-rich edges exhibit higher intrinsic peroxidase-like activity compared to pristine nanozymes due to their lower adsorption energies of H₂ O₂ and desorption energy of OH*, as well as the larger exothermic process for the whole reaction. This was demonstrated using drug-resistant Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus in vitro and in vivo. This strategy can be used to engineer nanozymes with enhanced antibacterial function and will pave a new way for the development of alternative antibiotics.

Preparation of Au@Ag core-shell nanoparticle decorated silicon nanowires for bacterial capture and sensing combined with laser induced breakdown spectroscopy and surface-enhanced Raman spectroscopy

Three-dimensional nano-biointerfaces, emerging as significant cell-guiding platforms, have attracted great attention. Nevertheless, complicated chemical modifications and instability of bio-ligands limit their widespread application. In this study, a novel biointerface, based on silicon nanowires (SiNWs) array, was prepared for bacterial capture and sensing. Vertically aligned SiNWs were fabricated via metal assisted chemical etching and decorated with uniform Au@Ag core-shell nanoparticles (Au@Ag NPs). These deposited Au@Ag NPs formed multi-scale topographic structures with nanowires, which provided effective attachment sites for bacterial adhesins. In addition, the Au cores of Au@Ag NPs enhanced the activity of the surface silver atoms and promoted the binding of Au@Ag NPs to bacteria. Thus, the Au@Ag NPs decorated SiNWs (SiNWs-Au@Ag) substrate exhibited high capture capacity for bacteria in drinking water (8.6 and 5.5 × 106 cells per cm2 for E. coli and S. aureus in 40 min, respectively) via physical and chemical effects. Bacteria in drinking water can be sensitively detected by using a combination of laser induced breakdown spectroscopy (LIBS) and label based surface-enhanced Raman spectroscopy (SERS) techniques. Due to the antibacterial activity of Au@Ag NPs and the physical stress exerted on SiNWs, the prepared biointerface also showed high antibacterial rates towards both Gram-positive and Gram-negative bacteria strains. With these excellent properties, the flexible sensing platform might open a new avenue for the prevention and control of microbial hazards in water.

A Smart Antibacterial Surface for the On-Demand Killing and Releasing of Bacteria

For various human healthcare and industrial applications, endowing surfaces with the capability to not only efficiently kill bacteria but also release dead bacteria in a rapid and repeatable fashion is a promising but challenging effort. In this work, the synergistic effects of combining stimuli-responsive polymers and nanomaterials with unique topographies to achieve smart antibacterial surfaces with on-demand switchable functionalities are explored. Silicon nanowire arrays are modified with a pH-responsive polymer, poly(methacrylic acid), which serves as both a dynamic reservoir for the controllable loading and release of a natural antimicrobial lysozyme and a self-cleaning platform for the release of dead bacteria and the reloading of new lysozyme for repeatable applications. The functionality of the surface can be simply switched via step-wise modification of the environmental pH and can be effectively maintained after several kill-release cycles. These results offer a new methodology for the engineering of surfaces with switchable functionalities for a variety of practical applications in the biomedical and biotechnology fields.

Vertical SiNWAs for biomedical and biotechnology applications

Vertical silicon nanowire arrays (SiNWAs) are considered as one of the most promising nanomaterials.