An ideal hydrogel for biomedical engineering should mimic the intrinsic properties of natural tissue, especially high toughness and self-healing ability, in order to withstand cyclic loading and repair skin and muscle damage. In addition, excellent cell affinity and tissue adhesiveness enable integration with the surrounding tissue after implantation. Inspired by the natural mussel adhesive mechanism, we designed a polydopamine-polyacrylamide (PDA-PAM) single network hydrogel by preventing the overoxidation of dopamine to maintain enough free catechol groups in the hydrogel. Therefore, the hydrogel possesses super stretchability, high toughness, stimuli-free self-healing ability, cell affinity and tissue adhesiveness. More remarkably, the current hydrogel can repeatedly be adhered on/stripped from a variety of surfaces for many cycles without loss of adhesion strength. Furthermore, the hydrogel can serve as an excellent platform to host various nano-building blocks, in which multiple functionalities are integrated to achieve versatile potential applications, such as magnetic and electrical therapies.

Surface-adherent polydopamine (PDA) films as multifunctional coatings can be easily deposited onto a wide range of materials through dopamine self-polymerization. However, a lack of in-depth understanding of PDA aggregation and deposition processes and definite structure elucidation of PDA make it challenging to tailor the surface characteristic and functionality of the PDA films. Herein, we demonstrate that the surface characteristics of the PDA films can be readily tuned by controlling the competitive interplay between PDA aggregation in solution and deposition on the substrate. Moreover, a structural investigation of the PDA films using analytical tools such as X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) allows us to propose a new structure model for the PDA building block. The (DHI)2/PCA trimer complex, which consists of two 5,6-dihydroxyindole (DHI) units and one pyrrolecarboxylic acid (PCA) moiety, is definitely identified as a primary building block of PDA, and its formation is steered by covalent interactions in the initial stages of polymerization. In latter stages, the (DHI)2/PCA trimer complexes are further linked primarily through noncovalent interactions to build up the supramolecular structure of PDA. This study provides new insights into the mechanisms of PDA buildup.

Wearable and implantable bioelectronics are receiving a great deal of attention because they offer huge promise in personalized healthcare. Currently available bioelectronics generally rely on external aids to form an attachment to the human body, which leads to unstable performance in practical applications. Self‐adhesive bioelectronics are highly desirable for ameliorating these concerns by offering reliable and conformal contact with tissue, and stability and fidelity in the signal detection. However, achieving adequate and long‐term self‐adhesion to soft and wet biological tissues has been a daunting challenge. Recently, mussel‐inspired hydrogels have emerged as promising candidates for the design of self‐adhesive bioelectronics. In addition to self‐adhesiveness, the mussel‐inspired chemistry offers a unique pathway for integrating multiple functional properties to all‐in‐one bioelectronic devices, which have great implications for healthcare applications. In this report, the recent progress in the area of mussel‐inspired self‐adhesive bioelectronics is highlighted by specifically discussing: 1) adhesion mechanism of mussels, 2) mussel‐inspired hydrogels with long‐term and repeatable adhesion, 3) the recent advance in development of hydrogel bioelectronics by reconciling self‐adhesiveness and additional properties including conductivity, toughness, transparency, self‐healing, antibacterial properties, and tolerance to extreme environment, and 4) the challenges and prospects for the future design of the mussel‐inspired self‐adhesive bioelectronics.

A one-step method to deposit a functional amine-rich coating in dopamine and hexamethylendiamine mixed solution through simple dip-coating of objects.

Engineering heterogeneous micro-mechano-microenvironments of extracellular matrix is of great interest in tissue engineering, but spatial control over mechanical heterogeneity in three dimensions is still challenging given the fact that geometry and stiffness are inherently intertwined in fabrication. Here, we develop a layer-by-layer three-dimensional (3D) printing paradigm which achieves orthogonal control of stiffness and geometry by capitalizing on the conventionally adverse effect of oxygen inhibition on free-radical polymerization. Controlled oxygen permeation and inhibition result in photo-cured hydrogel layers with thicknesses only weakly dependent to the ultraviolet exposure dosage. The dosage is instead leveraged to program the crosslink density and stiffness of the cured structures. The programmable stiffness spans nearly an order of magnitude (E ~ 2–15 kPa) within the physiologically relevant range. We further demonstrate that extracellular matrices with programmed micro-mechano-environments can dictate 3D cellular organization, enabling in vitro tissue reconstruction.

A combined experimental and computational approach was employed to investigate the feasibility and effectiveness of characterizing carbonated apatite (CAp) by infrared (IR) spectroscopy. First, an experimental comparative study was conducted to identify characteristic IR vibrational bands of carbonate substitution in the apatite lattice. The IR spectra of pure hydroxyapatite (HA), carbonate adsorbed on the HA surface, a physical mixture of HA and sodium carbonate monohydrate, a physical mixture of HA and calcite, synthetic CAps prepared using three methods (precipitation method, hydrothermal route, and solid-gas reaction at high temperature) and biological apatites (human enamel, human cortical bone, and two animal bones) were compared. Then, the IR vibrational bands of carbonate in CAp were calculated with density functional theory. The experimental study identified characteristic IR bands of carbonate that cannot be generated from surface adsorption or physical mixtures and the results show that the bands at ∼880, 1413, and 1450 cm(-1) should not be used as characteristic bands of CAp since they could result from carbonate adsorbed on the apatite crystals surface or present as a separate phase. The combined experimental and computational study reveals that the carbonate v3 bands at ∼1546 and 1465 cm(-1) are, respectively, the IR signature bands for type A CAp and type B CAp.

For a basic understanding and potential biomedical applications of surface topographical effects on bacterial responses, this study focuses on not only the bacterial retention but also the bacterial growth, proliferation, and viability that are significant post-retentive behaviors playing critical roles in infections of medical implants. Specifically, periodic micropillar arrays (SiPA ) with nine different feature sizes were fabricated on silicon substrates with photolithography and dry etching methods. The SiPA was cultured with Staphylococcus aureus or Escherichia coli for different periods to investigate the bacterial retention, growth and proliferation behavior on a patterned surface. The experimental results show that a significant reduction of bacterial retention, growth, and proliferation can be achieved when the pillar size is reduced to the submicrometer level. However, micropillars have no obvious influence on the viability of the bacteria within 24 h. On the basis of the bacterial experiment results, it is inferred that the topographical effects may have resulted from bacterial confinement by micropillars, either limiting the attachment area for individual bacterium or trapping a bacterium between pillars. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek theoretical analysis indicates the effects might have come from the topographic induced surface property changes, mainly hydrophobicity, which is represented by the changes in the interaction free energy of Lifshitz-van der Waals among different periodic micropillar arrays. This study could help to deepen the understanding about the surface topographical effects on bacterial responses and may provide a guidance for the future medical implant surface design to decrease the infection risk by avoiding the surface topography which could attract more bacteria.

It is great challenge to generate multifunctionality of vascular grafts and stents to enable vascular cell selectivity and improve hemocompatibility. Micro/nanopatterning of vascular implant surfaces for such multifunctionality is a direction to be explored. We developed a novel patterned platform featuring two typical geometries (groove and pillar) and six pattern sizes (0.5-50 μm) in a single substrate to evaluate the response of vascular cells and platelets. Our results indicate that targeted multifunctionality can be indeed instructed by rationally designed surface topography. The pillars nonselectively inhibited the growth of endothelial and smooth muscle cells. By contrast, the grooves displayed selective effects: in a size-dependent manner, the grooves enhanced endothelialization but inhibited the growth of smooth muscle cells. Moreover, our studies suggest that topographic cues can affect response of vascular cells by regulating focal adhesion and stress fiber development, which define cytoskeleton organization and cell shape. Notably, both the grooves and the pillars at 1 μm size drastically reduced platelet adhesion and activation. Taken together, these findings suggest that the topographic pattern featuring 1 μm grooves may be the optimal design of surface multifunctionality that favors vascular cell selectivity and improves hemocompatibility.