Viscoelastic, Antimicrobial and Recyclable Biomedical Bioplastic with Compactly Entangled Silk Structure

Global endeavors for a sustainable society have recently translated into the successful development of performance-advantaged bioplastics. Nevertheless, current healthcare service still demands considerable advances regarding sustainability. Each hospital bed generates an average of 0.5 kg of medical plastic waste daily and a total of 6 million tons annually in the United States. Particularly in dentistry, a tremendous waste of dental care plastic has been released. For instance, every week, a dentist changes the polyethylene terephthalate-based orthodontic aligner to a new one and discards the used one. Thereby, 40-50 plastic aligner wastes are inevitably generated from one patient. Bioplastic could be a promising substitutive material of typical biomedical plastics with healthcare purposes. However, there is a big challenge resulting from the intrinsic characteristics of the human physiological system. Herein, we propose a new category of bioplastic, so-called biomedical bioplastic, that is desirable for a sustainable healthcare future.<br/>Biomedical bioplastic should exhibit excellent durability for a prolonged period under the deformation stress from the body's essential activities. For instance, dental plastic should endure repetitive and substantial loads from tongue and tooth movements. Moreover, biomedical bioplastic should show a viscoelastic behavior to accomplish a mechanical match with human organizations. Hence, biomedical bioplastic should be flexible, tough, and viscoelastic at the same time. Biomedical bioplastic should be microbially clean regardless of the microbe, cell, and protein-abundant physiological environment. The contamination of biomedical bioplastic could damage microbiological homeostasis and cause severe complications. In summary, the desirable biomedical bioplastic should yield flexibility, toughness, viscoelasticity, and antimicrobial properties in balance.<br/>In this study, we have developed a biomedical bioplastic composed of compactly entangled silk fibroin strands. Recent studies demonstrates that the entangled structure could cause viscoelastic behavior and reinforce the toughness. From this background, we synthesize a molecular template that can induce the compact entanglement of silk fibroin. This template also involves a quaternary ammonium group to impart antimicrobial properties to the biomedical bioplastic. The prepared biomedical bioplastic harmoniously exhibits great flexibility, toughness, and viscoelasticity. Thereby the successful dental care of misaligned rabbit incisors is demonstrated <i>in vivo</i>. Moreover, the biomedical bioplastic shows an intense resistance to pathogens growth, proved by <i>ex vivo</i> human saliva biofilm test. Remarkably, the silk fibroin and molecular templates are extracted with high selectivity through an acid-mediated disentanglement of entangled domains. This extracted silk fibroin is recycled into a new biomedical bioplastic with mechanical properties comparable to the original values. In conclusion, we anticipate that this study could be a cornerstone to establish a greener healthcare future.