Photo-based diagnosis and treatment methods are gaining prominence due to increased spatial imaging resolution, minimally invasive modalities involved as well as localized treatment. Recently, nanoparticles (NPs) have been developed and used in photo-based therapeutic applications. While some nanomaterials have inherent photo-based imaging capabilities, others including polymeric NPs act as nanocarriers to deliver various fluorescent dyes or photosensitizers for photoimaging and therapeutic applications. These applications can vary from Magnetic Resonance Imaging (MRI) and optical imaging to photothermal therapy (PTT) and chemotherapy. Materials commonly used for development of photo-based NPs ranges from metal-based (gold, silver and silica) to polymer-based (chitosan, dextran, poly ethylene glycol (PEG) and poly lactic-co-glycolic acid (PLGA)). Recent research has paved the way for multi-modal 'theranostic' (a combination of therapy and diagnosis) nano-carriers capable of active targeting using cell-specific ligands and carrying multiple therapeutic and imaging agents for accurate diagnosis and controlled drug delivery. This review summarizes the different materials used today to synthesize photo-based NPs, their diagnostic and therapeutic applications as well as the current challenges faced in bringing these novel nano-carriers into clinical practices.

To develop materials with improved controllability and specificity, we have investigated composite hydrogels with temperature‐sensitive properties using photo cross‐linking. Specifically, our novel composite materials are composed of nanoparticles made of poly(N‐isopropylacrylamide) (PNIPAAm), temperature‐sensitive hydrogels, and a photo cross‐linker, poly(ethylene glycol) diacrylate (PEGDA). PNIPAAm particles were synthesized by emulsion polymerization and by varying concentration of four main factors: monomers (N‐isopropylacrylamide), cross‐linkers (N, N′‐methylenebisacrylamide), surfactants (sodium dodecyl sulfate, SDS), and initiators (potassium persulfate). We found that the surfactant, SDS, was the most important factor affecting the particle size using the factorial design analysis. Additionally, both nano‐ and micro‐PNIPAAm particles had excellent loading efficiency (>80% of the incubated bovine serum albumin (BSA)), and their release kinetics expressed an initial burst effect followed by a sustained release over time. Furthermore, BSA‐loaded PNIPAAm nanoparticles were used to form three‐dimensional gel networks by means of a photocuring process using a photo cross‐linker, PEGDA, and a photoinitiator, Irgacure‐2959 (I‐2959). Results from scanning electron microscopy and in vitro BSA release studies from these hydrogels demonstrated that PNIPAAm nanoparticles were embedded inside the PEG polymeric matrix and the composite material was able to release BSA in response to changes in temperature. These PNIPAAm nanoparticle hydrogel networks may have advantages in applications of controlled drug delivery systems because of their temperature sensitivity and their ability of in situ photopolymerization to localize at the specific region in the body.

Mussel-inspired bioadhesives gain increasing interests in healthcare applications. In this review, adhesive mechanism, mussel-inspired bioadhesive synthesis and applications in healthcare are summarized and discussed.