The concept of self-healing synthetic materials emerged a couple of decades ago and continues to attract scientific community. Driven primarily by an opportunity to develop lifelike materials on one hand, and sustainable technologies on the other, several successful approaches to repair mechanically damaged materials have been explored. This review examines chemical and physical processes occurring during self-healing of polymers as well as examines the role of interfaces in rigid nano-objects in multicomponent composites. The complex nature of processes involved in self-healing demands understanding of multi-level molecular and macroscopic events. Two aspects of self-healing are particularly intriguing: physical flow (macro) of matter at or near a wound and chemical re-bonding (molecular)of cleaved bonds. These events usually occur concurrently, and depending upon interplay between kinetics and thermodynamics of the processes involved, these transient relations as well as efficiency are critical in designing self-healing materials. This review examines covalent bonding and supramolecular chemistry in the context of molecular heterogeneities in repair processes. Interfacial regions in nanocomposites also facilitate an opportunity for supramolecular assemblies or covalent bonding which, if designed properly, are capable of self-repairs.

Porous synthetic grafts made of poly(glycerol sebacate) (PGS) can transform into autologous vascular conduits in vivo upon degradation of PGS. A long-held doctrine in tissue engineering is the necessity to match degradation of the scaffolds to tissue regeneration. Here, we tested the impact of degradation of PGS and its derivative in an interposition model of rat common carotid artery (CCA). Previous work indicates a complete degradation of PGS within approximately 2 weeks, likely at the fast end of the spectrum. Thus, the derivation of PGS focuses on delay degradation by conjugating the free hydroxy groups in PGS with a long chain carboxylic acid: palmitic acid, one of the most common lipid components. We evaluated two of the resultant palmitate-PGS (PPGS) in this study: one containing 9% palmitate (9-PPGS) and the other16% palmitate (16-PPGS). 16-PPGS grafts had the highest patency. Ultrasound imaging showed that the lumens of 16-PPGS grafts were similar to CCA and smaller than 9-PPGS and PGS grafts 12 weeks post-operation. Immunohistological and histological examination showed an endothelialized lumens in all three types of grafts within 4 weeks. Inflammatory responses to 16-PPGS grafts were limited to the adventitial space in contrast to a more diffusive infiltration in 9-PPGS and PGS grafts in week 4. Examination of calponin + and αSMA + cells revealed that 16-PPGS grafts remodeled into a distinctive bi-layered wall, while the walls of 9-PPGS grafts and PGS grafts only had one thick layer of smooth muscle-like cells. Correspondingly, the expression of collagen III and elastin displayed an identical layered structure in the remodeled 16-PPGS grafts, in contrast to a more spread distribution in 9-PPGS and PGS grafts. All the three types of grafts exhibited the same collagen content and burst pressure after 12 weeks of host remodeling. However, the compliance and elastin content of 16-PPGS grafts in week 12 were closest to those

Autologous veins are the most widely used grafts for bypassing small arteries in coronary and peripheral arterial occlusive diseases. However, they have limited availability and cause donor-site morbidity. Here, we report a direct comparison of acellular biodegradable synthetic grafts and autologous veins as interposition grafts of rat carotid arteries, which is a good model for clinically relevant small arteries. Notably, extensive but transient infiltration of circulating monocytes at day 14 in synthetic grafts leads to a quickly-resolved inflammation and arterial-like tissue remodeling. The vein graft exhibits a similar inflammation phase except the prolonged presence of inflammatory monocytes. The walls of the remodeled synthetic graft contain many circumferentially aligned contractile non-proliferative smooth muscle cells (SMCs), collagen and elastin. In contrast, the walls of the vein grafts contain disorganized proliferating SMCs and thicken over time, suggesting the onset of stenosis. At 3 months, both grafts have a similar patency, extracellular matrix composition, and mechanical properties. Furthermore, synthetic grafts exhibit recruitment and re-orientation of newly synthesized collagen fibers upon mechanical loading. To our knowledge, this is the first demonstration of a biodegradable synthetic vascular graft with a performance similar to an autologous vein in small artery grafting.

Molecularly imprinted polymer nanoparticles (MIPNPs) are an increasingly important area of research with potential in applications such as biosensors, solid phase extractions and bioassays. Advantages over the traditional molecularly imprinted polymers typically include a higher binding capacity, greater selectivity and affinity for target species, and aqueous compatibility. Recent research efforts have sought to impart MIPNPs with additional capabilities by introducing nanoparticle size‐control, stimuli‐responsiveness, biocompatibility, and optoelectronic properties. This short review describes the molecular imprinting principle and then discusses recent advances in the field of MIPNPs with particular focus on surface polymerization techniques to imprint both small and macro molecules.

Here we define hydrogels crosslinked by weak bonds as physical hydrogels. They possess unique features including reversible bonding, shear thinning and stimuli-responsiveness. Unlike covalently crosslinked hydrogels, physical hydrogels do not require triggers to initiate chemical reactions for in situ gelation. The drug can be fully loaded in a pre-formed hydrogel for delivery with minimal cargo leakage during injection. These benefits make physical hydrogels useful as delivery vehicles for applications in biomedical engineering. This review focuses on recent advances of physical hydrogels crosslinked by weak bonds: hydrogen bonds, ionic interactions, host-guest chemistry, hydrophobic interactions, coordination bonds and π-π stacking interactions. Understanding the principles and the state of the art of gels with these dynamic bonds may give rise to breakthroughs in many biomedical research areas including drug delivery and tissue engineering.