While tattooable nanotechnology for in-skin sensing and communication has been a popular concept in science fiction since the 1990s, the first tattooable intradermal nanosensors have only emerged in the past few years, and none have been demonstrated in human skin. We developed a photochromic tattoo that serves as an intradermal ultraviolet (UV) radiometer that provides naked-eye feedback about UV exposure in real time. These small tattoos, or “solar freckles”, comprise dermally implanted colorimetric UV sensors in the form of nanoencapsulated leuco dyes that become more blue in color with increasing UV irradiance. We demonstrate the tattoos’ functionality for both quantitative and naked-eye UV sensing in porcine skin ex vivo, as well as in human skin in vivo. Solar freckles offer an alternative and complementary approach to self-monitoring UV exposure for the sake of skin cancer prevention. Activated solar freckles provide a visual reminder to protect the skin, and their color disappears rapidly upon removal of UV exposure or application of topical sunscreen. The sensors are implanted in a minimally invasive procedure that lasts only a few seconds, yet remain functional for months to years. These semipermanent tattoos provide an early proof-of-concept for long-term intradermal sensing nanomaterials that provide users with biomedically relevant information in the form of an observable color change.

Vascular grafts are widely used for vascular surgeries, to bypass a diseased artery or function as a vascular access for hemodialysis. Bioengineered or tissue-engineered vascular grafts have long been envisioned to take the place of bioinert synthetic grafts and even vein grafts under certain clinical circumstances. However, host responses to a graft device induce adverse remodeling, to varied degrees depending on the graft property and host’s developmental and health conditions. This in turn leads to invention or failure. Herein, we have mapped out the relationship between the design constraints and outcomes for vascular grafts, by analyzing impairment factors involved in the adverse graft remodeling. Strategies to tackle these impairment factors and counteract adverse healing are then summarized by outlining the research landscape of graft innovations in three dimensions—cell technology, scaffold technology and graft translation. Such a comprehensive view of cell and scaffold technological innovations in the translational context may benefit the future advancements in vascular grafts. From this perspective, we conclude the review with recommendations for future design endeavors.

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