Significance: Skin exhibits direction-dependent biomechanical behavior, influenced by the structural orientation of its collagen-rich fibrous network and its viscous ground-substance matrix. Injury can affect the skin's structure and composition, thereby greatly influencing the biomechanics and directionality of the resulting scar tissue. Recent Advances: A combination of stress-relaxation and tensile failure testing identifies both the tissue's physiologically relevant viscoelastic behavior and resistance to rupture. When studied in mutually orthogonal directions in the plane of the tissue, these measures give insight into the directional properties of healthy tissue, and how they change with injury. By controlling the biomechanics of the wound environment, a new force-modulating dressing has demonstrated the ability to improve healing and reduce scar formation. Critical Issues: Skin and scar biomechanics are typically characterized by using tensile failure, which identifies the tissue's resistance to rupture but offers limited insight into its normal daily function. Characterizing physiologically relevant biomechanics of skin, and how they change with injury, is critical to understand the tissue's ability to resist elongation, bear load, and dissipate energy via viscous means. Future Directions: Compared with uninjured skin, scar tissue demonstrates similar high-load stiffness, greatly reduced resistance to failure, reduced low-load compliance, and altered material directionality. These findings, identified through combined stress relaxation and failure testing, suggest morphological changes with injury that are consistent with the viscoelastic and directional changes observed biomechanically. A more complete understanding of the directional, physiologically relevant skin biomechanics can guide the design and critical functional assessment of wound treatments, scaffolds, and tissue-engineered skin replacements.

Laser direct-writing provides a method to pattern living cells in vitro, to study various cell–cell interactions, and to build cellular constructs. However, the materials typically used may limit its long-term application. By utilizing gelatin coatings on the print ribbon and growth surface, we developed a new approach for laser cell printing that overcomes the limitations of Matrigel™. Gelatin is free of growth factors and extraneous matrix components that may interfere with cellular processes under investigation. Gelatin-based laser direct-write was able to successfully pattern human dermal fibroblasts with high post-transfer viability (91% ± 3%) and no observed double-strand DNA damage. As seen with atomic force microscopy, gelatin offers a unique benefit in that it is present temporarily to allow cell transfer, but melts and is removed with incubation to reveal the desired application-specific growth surface. This provides unobstructed cellular growth after printing. Monitoring cell location after transfer, we show that melting and removal of gelatin does not affect cellular placement; cells maintained registry within 5.6 ± 2.5 μm to the initial pattern. This study demonstrates the effectiveness of gelatin in laser direct-writing to create spatially precise cell patterns with the potential for applications in tissue engineering, stem cell, and cancer research.

Future biosensing applications will require high performance, including real-time monitoring of physiological events, incorporation of biosensors into feedback-based devices, detection of toxins, and advanced diagnostics. Such functionality will necessitate biosensors with increased sensitivity, specificity, and throughput, as well as the ability to simultaneously detect multiple analytes. While these demands have yet to be fully realized, recent advances in biofabrication may allow sensors to achieve the high spatial sensitivity required, and bring us closer to achieving devices with these capabilities. To this end, we review recent advances in biofabrication techniques that may enable cutting-edge biosensors. In particular, we focus on bioprinting techniques (e.g., microcontact printing, inkjet printing, and laser direct-write) that may prove pivotal to biosensor fabrication and scaling. Recent biosensors have employed these fabrication techniques with success, and further development may enable higher performance, including multiplexing multiple analytes or cell types within a single biosensor. We also review recent advances in 3D bioprinting, and explore their potential to create biosensors with live cells encapsulated in 3D microenvironments. Such advances in biofabrication will expand biosensor utility and availability, with impact realized in many interdisciplinary fields, as well as in the clinic.