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Abstract Catechol is an oft‐used crosslinking precursor and adhesive molecule for designing in situ curable biomaterials and adhesives and the addition of chemical or enzymatic oxidants is required to initiate fast curing. Here, the feasibility for 6‐hydroxydopamine (6‐OHDA)‐modified 8‐armed polyethylene glycol (PEG) (8‐arm PEG‐DA‐OH) to cure through autoxidation is evaluated. The modification of catechol side chain with an electron‐donating hydroxyl group at the six‐position drastically increased the rate of oxidation and the adhesive cured in just over 1 min through autoxidation. The cure time is decreased to under 40 s with the addition of branched polyethyleneimine (PEI). UV–vis spectra revealed that the deprotonated quinone of 6‐OHDA is a key oxidation intermediate for chemical crosslinking between 6‐OHDA and with primary amine. PEG functionalized with unmodified catechol do not solidify through autoxidation, which highlights the contribution of the electron‐donating hydroxyl group in promoting fast oxidation and crosslinking. Eight‐arm PEG‐DA‐OH and PEI mixture also demonstrated significantly higher adhesion strength to pericardium tissues when compared to a commercial PEG‐based adhesive, DuraSeal. This report highlights 6‐OHDA as an effective crosslinking precursor and adhesive molecule for designing injectable adhesives that do not require externally added oxidants and the adhesive is activated by simple dissolution in an aqueous solution. 

Hemorrhage is one of the leading preventable causes of death associated with trauma, which is often complicated by wound infection. Current hemostatic materials are not ideal and lack antimicrobial properties needed for infection prevention. Here, we tested the feasibility for 6-chlorodopamine-functionalized gelatin (GDC) nanoparticles to function as a hemostatic powder with strong tissue adhesion and antibacterial properties. 6-Chlorodopamine contains a catechol sidechain that is further modified with an electron withdrawing chlorine atom, and provides strong tissue adhesion and antimicrobial property. These gelatin nanoparticles are not covalently crosslinked, which enablde them to rapidly transition into an adhesive film when hydrated with an aqueous solution or blood. The chlorination of catechol significantly increased structural integrity, interfacial bonding to tissue surface, and the rate of film formation. Additionally, GDC nanoparticles are noncytotoxic and nonhemolytic, and effectively killed Gram-positive (Staphylococcus epidermidis, Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. Finally, GDC nanoparticles achieved significantly faster hemostasis and reduced blood loss when compared to a commercial fibrin glue, Tisseel, in tail transection and liver hemorrhage models performed in mice. These findings highlight the potential of GDC nanoparticle as a versatile, multifunctional hemostatic agent capable of both rapid hemorrhage control and infection prevention. 

Representation learning is a powerful tool that enables learning over large multitudes of agents or domains by enforcing that all agents operate on a shared set of learned features. However, many robotics or controls applications that would benefit from collaboration operate in settings with changing environments and goals, whereas most guarantees for representation learning are stated for static settings. Toward rigorously establishing the benefit of representation learning in dynamic settings, we analyze the regret of multi-task representation learning for linear-quadratic control. This setting introduces unique challenges. Firstly, we must account for and balance the misspecification introduced by an approximate representation. Secondly, we cannot rely on the parameter update schemes of single-task online LQR, for which least-squares often suffices, and must devise a novel scheme to ensure sufficient improvement. We demonstrate that for settings where exploration is benign, the regret of any agent after T timesteps scales with the square root of T/H, where H is the number of agents. In settings with difficult exploration, the regret scales as the square root of the input dimension times the parameter dimension multiplied by T, plus a term which scales with T to the three quarters divided by H to the one fifth. In both cases, by comparing to the minimax single-task regret, we see a benefit of a large number of agents. Notably, in the difficult exploration case, by sharing a representation across tasks, the effective task-specific parameter count can often be small. Lastly, we validate the trends we predict. 

Physically crosslinked gelatin microgels were functionalized with a bioadhesive molecule, catechol, to study the effect of in situ generated H2O2 on full-thickness wound repair in diabetic mice. Due to the physically crosslinked nature of the microgels, they transition into a hydrogel film upon hydration. The formation of a hydrogel film was confirmed by the changes in their morphology and viscoelastic properties. Additionally, these microgels released up to 86 μM of H2O2 as a result of catechol autoxidation. The generated H2O2 completely eradicated Staphylococcus epidermidis with an initial concentration of 103 CFU mL−1. These microgels were not cytotoxic and promoted VEGF upregulation in immortalized human keratinocytes (HaCaT) in vitro. When the microgels were applied to a full-thickness dermal wound in diabetic mice, dermal wound closure was accelerated over 14 days, achieving a wound closure of 90% based on the wound area. Microgel-treated wounds also resulted in complete re-epithelialization and regeneration of new dermal tissues with morphology and structure resembling those of native tissues. These results indicate that the release of micromolar concentrations of H2O2 can accelerate wound healing in a healing-impaired animal. 

An SHAM-containing adhesive was combined with PVDF to form a novel structural adhesive. SHAM provides interfacial bonding capability while PVDF increases cohesion through hydrogen bonding with the adhesive polymer backbone.