Digital light 4D printing of bioresorbable shape memory elastomers for personalized biomedical implantation.

Four-dimensional (4D) printing unlocks new potentials for personalized biomedical implantation, but still with hurdles of lacking suitable materials. Herein, we demonstrate a bioresorbable shape memory elastomer (SME) with high elasticity at both below and above its phase transition temperature (Ttrans). This SME can be digital light 3D printed by co-polymerizing glycerol dodecanoate acrylate prepolymer (pre-PGDA) with acrylic acid monomer to form crosslinked Poly(glycerol dodecanoate acrylate) (PGDA)-Polyacrylic acid (PAA), or PGDA-PAA network. The printed complex, free-standing 3D structures with high-resolution features exhibit shape programming properties at a physiological temperature. By tuning the pre-PGDA weight ratios between 55 wt% and 70 wt%, Ttrans varies between 39.2 and 47.2 ℃ while Young's moduli (E) range 40-170 MPa below Ttrans with fractural strain (εf) of 170 %-200 %. Above Ttrans, E drops to 1-1.82 MPa which is close to those of soft tissue. Strikingly, εf of 130-180 % is still maintained. In vitro biocompatibility test on the material shows > 90 % cell proliferation and great cell attachment. In vivo vascular grafting trials underline the geometrical and mechanical adaptability of these 4D printed constructs in regenerating the aorta tissue. Biodegradation of the implants shows the possibility of their full replacement by natural tissue over time. To highlight its potential for personalized medicine, a patient-specific left atrial appendage (LAA) occluder was printed and implanted endovascularly into an in vitro heart model. STATEMENT OF SIGNIFICANCE: 4D printed shape-memory elastomer (SME) implants particularly designed and manufactured for a patient are greatly sought-after in minimally invasive surgery (MIS). Traditional shape-memory polymers used in these implants often suffer from issues like unsuitable transition temperatures, poor biocompatibility, limited 3D design complexity, and low toughness, making them unsuitable for MIS. Our new SME, with an adjustable transition temperature and enhanced toughness, is both biocompatible and naturally degradable, particularly in cardiovascular contexts. This allows implants, like biomedical scaffolds, to be programmed at room temperature and then adapt to the body's physiological conditions post-implantation. Our studies, including in vivo vascular grafts and in vitro device implantation, highlight the SME's effectiveness in aortic tissue regeneration and its promising applications in MIS.

4D printing of biocompatible, hierarchically porous shape memory polymeric structures.

Conventional implants tend to have significant limitations, as they are one-size-fits-all, require monitoring, and have the potential for immune rejection. However, 4D Printing presents a method to manufacture highly personalized, shape-changing, minimally invasive biomedical implants. Shape memory polymers (SMPs) with a glass transition temperature (Tg) between room and body temperature (20-38 °C) are particularly desirable for this purpose, as they can be deformed to a temporary shape before implantation, then undergo a shape change within the body. Commonly used SMPs possess either an undesirable Tg or lack the biocompatibility or mechanical properties necessary to match soft biological tissues. In this work, Poly(glycerol dodecanoate) acrylate (PGDA) with engineered pores is introduced to solve these issues. Pores are induced by porogen leaching, where microparticles are mixed with the printing ink and then are dissolved in water after 3D printing, creating a hierarchically porous texture to improve biological activity. With this method, highly complex shapes were printed, including overhanging structures, tilted structures, and a "3DBenchy". The porous SMP has a Tg of 35.6 °C and a Young's Modulus between 0.31 and 1.22 MPa, comparable to soft tissues. A one-way shape memory effect (SME) with shape fixity and recovery ratios exceeding 98 % was also demonstrated. Cultured cells had a survival rate exceeding 90 %, demonstrating cytocompatibility. This novel method creates hierarchically porous shape memory scaffolds with an optimal Tg for reducing the invasiveness of implantation and allows for precise control over elastic modulus, porosity, structure, and transition temperature.

A Photocured Bio-based Shape Memory Thermoplastics for Reversible Wet Adhesion.

Development of reversible wet or underwater adhesives remains a grand challenge. Because weakened intermolecular interactions by water molecules or/and low effective contact area cause poor interface to the wet surfaces, which significantly decreases adhesive strength. Herein, a new photocured, bio-based shape memory polymer (SMP) that shows both chemical and structural wet adhesion to various types of surfaces is developed. The SMP is polymerized from three monomers mainly from bio-sources to form linear polymer chains dangled with hydrophobic side chains. The hydrogen acceptor and donor groups in the chains form hydrogen bonding with the surfaces, which is protected by the hydrophobic chains in the interface. The SMP shows tunable phase transition temperature (Tg) of 17-38 °C. In a rubbery state above Tg, the adhesive forms conformable contact with the targeted surfaces. Below Tg, a transition to a glassy state locks the conformed shapes to largely increase the effective contact area. As a result, the adhesive exhibits long-term underwater adhesion of > 15 days with the best adhesion strength of ~ 0.9 MPa. Its applications in leak repair, underwater on-skin sensors were demonstrated. This new, general strategy would pave avenues to designing bio-based, long-lasting, and reversible adhesives from renewable feedstocks for widespread applications.