Bioinspired silk protein modification to develop instant dissolvable microneedles with superior mechanical properties and long-term biomolecule stabilization

Dissolvable microneedles (DMNs) obtained from silk proteins have been considered most promising due to the biocompatibility, tuneable mechanical properties, and superior biomolecule stabilization properties of their silk matrix, required for cold chain-free storage and transport of therapeutic biomolecules and vaccines. However, despite their excellent potential, silk-based microneedles with instant dissolvability, superior mechanical properties, and storage stability have not yet been reported. Reported DMNs prepared with <5% silk concentration without β-sheets show poor mechanical and storage stability. Conversely, silk MNs prepared using <5% silk treated with an organic solvent or >5% silk may have sufficient mechanical properties but lose their instant dissolubility due to β-sheet formation during solvent treatment and storage, respectively. Thus, herein, we address these challenges for the first time <i>via</i> the biomimetic modification of silk proteins to mimic the molecular structure of human serum albumin (HSA) and silk protein molecules in the silk gland lumen of silkworms, resulting in high solubility and low viscosity. Our biomimetic modified silk (MS) allowed us to prepare DMNs in higher concentrations (>10% w/v up to 20% w/v) with a stabilizing agent (>10% w/v), exhibiting superior mechanical properties of >45 N and instant dissolvability even after 6 months of storage at RT without inducing β-sheet formation. Furthermore, MS-DMN facilitated the exceptional storage stability of platelet-rich plasma (PRP) with >80% retention for six months when stored at 4 °C or 25 °C and >90% at 40 °C at 75% RH for one month, as confirmed through <i>in vitro</i> cell proliferation assay, in ova (CAM assay), and <i>in vivo</i> diabetic wound studies. Thus, our novel biomimetic MS-DMN exhibits superior mechanical properties and exceptional biomolecule storage stability, enabling potential cold chain-free preservation and transportation for various biomedical applications.