A Hand-Held Digital Printer for On-Site Fabrication of Micro/Nano Composite Dressings

Timely management of skin defects requires simultaneous filling of deep tissue defects with a scaffold and coverage of the surface to support tissue repair and barrier protection. However, conventional dressings and dermal substitutes often rely on in vitro prefabrication and secondary application, which are time-consuming and results in suboptimal interfacial integration. In situ printing enables point-of-care fabrication of dressings for early wound care; however, existing hand-held in situ printers typically employ a single fabrication modality, making it difficult to rapidly construct micro-nano composite dressings with combined scaffold-barrier functions at the bedside. To address these limitations, we developed a hand-held, digital, multiprocess in situ printing system for point-of-care fabrication of micro-nano composite dressings. The system integrates in situ photo-cross-linking extrusion printing, air-assisted spraying, and electrospinning, and incorporates an adaptive temperature-control module to stabilize the gelation of thermoresponsive hydrogels. In addition, wireless smartphone connectivity enables mobile configuration of key process parameters and precise material dispensing, thereby ensuring stable mode switching and continuous fabrication. The results show that the extrusion module enables stable printing of multiple hydrogels and supports in situ photo-cross-linking of cell-laden constructs with cell viability above 90%, indicating a cell-friendly fabrication process. The spraying mode allows rapid deposition of hydrogel precursors and achieves sustained drug release. The electrospinning mode enables the fabrication of nanofibrous membranes from different materials. Among them, cell-laden electrospinning with PEO achieved a cell viability of over 92%, while the PVB fibrous layer fabricated in this mode exhibited a porosity of 73.2%, providing both protection and gas exchange capability. Through multiprocess integration, a nanofibrous barrier layer can be rapidly constructed on the hydrogel surface, yielding a micro-nano composite dressing featuring a microscale hydrogel scaffold and a nanoscale fibrous barrier within a short time. The platform enables integrated fabrication of micro-nano composite dressings in rat and porcine wound models. This "arrive-on-site to scaffold-barrier dressing formation" capability demonstrates the technical feasibility of using a hand-held multiprocess printer for rapid, parametrically controlled wound coverage and provides a device platform for future studies on emergency wound management and personalized dressing fabrication.