Sequence-defined positioning of amine and amide residues to control catechol driven wet adhesion

Antibacterial Broad-Spectrum Dendritic/Gellan Gum Hybrid Hydrogels with Rapid Shape-Forming and Self-Healing for Wound Healing Application

Treating wound infections is a difficult task ever since pathogenic bacteria started to develop resistance to common antibiotics. The present study develops hybrid hydrogels based on the formation of a polyelectrolyte complex between the anionic charges of dopamine-functionalized Gellan Gum (GG-DA) and the cationic moieties of the TMP-G2-alanine dendrimer. The hydrogels thus obtained can be doubly crosslinked with CaCl2 , obtaining solid hydrogels. Or, by oxidizing dopamine to GG-DA, possibly causing further interactions such as Schiff Base and Michael addition to take place, hydrogels called injectables can be obtained. The latter have shear-thinning and self-healing properties (efficiency up to 100%). Human dermal fibroblasts (HDF), human epidermal keratinocytes (HaCaT), and mouse monocyte cells (RAW 264.7), after incubation with hydrogels, in most cases show cell viability up to 100%. Hydrogels exhibit adhesive behavior on various substrates, including porcine skin. At the same time, the dendrimer serves to crosslink the hydrogels and endows them with excellent broad-spectrum microbial eradication activity within four hours, evaluated using Staphylococcus aureus 2569 and Escherichia coli 178. Using the same GG-DA/TMP-G2-alanine ratios hybrid hydrogels with tunable properties and potential for wound dressing applications can be produced.

Statistical Copolymers that Mimic Aspects of Mussel Adhesive Proteins: Access to Robust Adhesive-Domains for Non-Covalent Surface PEGylation

Reconstructing functional sequence motifs of proteins, using statistical copolymers greatly reduces the information content, but simplifies synthesis significantly. Key amino acid residues involved in the adhesion of mussel foot proteins are identified. The side-chain functionalities of Dopa, lysine, and arginine are abstracted and incorporated into acrylate monomers to allow controlled radical polymerization. The resulting Dopa-acrylate (Y*-acr), arginine-acrylate (R-acr), and lysine-acrylate (K-acr) monomers are polymerized in different monomer ratios and compositions by reversible addition fragmentation transfer polymerization with a poly(ethylene glycol) (PEG) macrochain transfer agent. This results in two sets of PEG-block-copolymers with statistical mixtures and different monomer ratios of catechol/primary amine and catechol/guanidine side-chain functionalities, both important pairs for mimicking π-cation interactions. The coating behavior of these PEG-block-copolymers is evaluated using quartz crystal microbalance with dissipation energy monitoring (QCM-D), leading to non-covalent PEGylation of the substrates with clear compositional optima in the coating stability and antifouling properties. The coatings prevent non-reversible albumin or serum adsorption, as well as reduce cellular adhesion and fungal spore attachment.

Facile Synthesis of Catechol-Containing Polyacrylamide Copolymers: Synergistic Effects of Amine, Amide and Catechol Residues in Mussel-Inspired Adhesives

The straightforward synthesis of polyamide-derived statistical copolymers with catechol, amine, amide and hydroxy residues via free radical polymerization is presented. In particular, catechol, amine and amide residues are present in natural mussel foot proteins, enabling strong underwater adhesion due to synergistic effects where cationic residues displace hydration and ion layers, followed by strong short-rang hydrogen bonding between the catechol or primary amides and SiO2 surfaces. The present study is aimed at investigating whether such synergistic effects also exist for statistical copolymer systems that lack the sequence-defined positioning of functional groups in mussel foot proteins. A series of copolymers is established and the adsorption in saline solutions on SiO2 is determined by quartz crystal microbalance measurements and ellipsometry. These studies confirm a synergy between cationic amine groups with catechol units and primary amide groups via an increased adsorptivity and increased polymer layer thicknesses. Therefore, the free radical polymerization of catechol, amine and amide monomers as shown here may lead to simplified mussel-inspired adhesives that can be prepared with the readily scalable methods required for large-scale applications.

Water-driven noninvasively detachable wet tissue adhesives for wound closure

Tissue adhesive with on-demand detachment feature is critically important since it can minimize hurt to patient when it is stripped away. Herein, a water-driven noninvasively detachable wet tissue adhesive hydrogel (w-TAgel) was produced by UV-initiated radical copolymerization of N-isopropylacrylamide (NIPAM), acrylamide (AAm), gelatin methacrylate (GelMA), and urushiol. As a w-TAgel, its robust and tough mechanical property makes it suitable for dynamic wound tissue. The polyurushiol segments of it are crucial to the formation of tough adhesion interface with various wet tissues, while polyNIPAM units play an indispensable role in on-demand detachment via thermo-responsive swelling behavior because the hydrophobic aggregation among isopropyl groups is destroyed upon water treatment with temperature of 25 ​°C or less. Additionally, it exhibits multiple merits including good hemocompatibility, cytocompatibility as well as pro-coagulant activity and hemostasis. Therefore, our w-TAgel with strong adhesion and facile detachment is an advanced prospective dressing for wound closure and rapid hemostasis. The wet tissue adhesion and water-driven detachable mechanism may shed new light on the development of on-demand noninvasively detachable wet tissue adhesives.

Imprinted biopolymers as green abiotic route in immunoglobulin affinity plasmonic sensing

The relentless research in material science is pushing towards sustainable building blocks, which may be exploited in the molecularly imprinting technology, a potentially ground-breaking tool for producing affinity mimetic receptors. In this scenario, we report and characterize a novel polynorepinephrine (PNE)-based mimetic for IgG detection, biomolecules of utmost clinical interest, coupled to a label-free and real-time sensing based on Surface Plasmon Resonance (SPR). A "molecular walk" around the Y-shaped IgG structure is performed to select small peptide portions to be used as templates during the epitope imprinting process. For real-time diagnosis, the mimetic receptor is integrated into SPR sensing platform, to directly target the IgG both in standard solutions and human serum specimens using the standard addition method. The designed platform is characterized in terms of binding kinetic/affinity parameters and analytical figures of merit, (selectivity, repeatability, limit of detection and quantification, namely 0.90 ± 0.02 μg mL^-1 and 3.01 ± 0.07 μg mL^-1, respectively), displaying excellent promising outcomes also when the material is subjected to thermal stress. Comprehensively, the excellent analytical performances of the MIP-based SPR sensing and the well-known versatility of such biopolymer encourage the further development of serological point-of-care testing for IgG antibodies detection.

Mussel adhesion: A fundamental perspective on factors governing strong underwater adhesion

Protein-based underwater adhesives of marine organisms exhibit extraordinary binding strength in high salinity based on utilizing a variety of molecular interaction mechanisms. These include acid-base interactions, bidentate bindings or complex hydrogen bonding interactions, and electrochemical manipulation of interfacial bonding. In this Perspective, we briefly review recent progress in the field, and we discuss how interfacial electrochemistry can vary interfacial forces by concerted tuning of surface charging, hydration forces, and tuning of the interfacial ion concentration. We further discuss open questions, controversial findings, and new paths into understanding and utilizing redox-proteins and derived polymers for enhancing underwater adhesion in a complex salt environment.

Principles of Cation-π Interactions for Engineering Mussel-Inspired Functional Materials

Supramolecular assembly is commonly driven by noncovalent interactions (e.g., hydrogen bonding, electrostatic, hydrophobic, and aromatic interactions) and plays a predominant role in multidisciplinary research areas ranging from materials design to molecular biology. Understanding these noncovalent interactions at the molecular level is important for studying and designing supramolecular assemblies in chemical and biological systems. Cation-π interactions, initially found through their influence on protein structure, are generally formed between electron-rich π systems and cations (mainly alkali, alkaline-earth metals, and ammonium). Cation-π interactions play an essential role in many biological systems and processes, such as potassium channels, nicotinic acetylcholine receptors, biomolecular recognition and assembly, and the stabilization and function of biomacromolecular structures. Early fundamental studies on cation-π interactions primarily focused on computational calculations, protein crystal structures, and gas- and solid-phase experiments. With the more recent development of spectroscopic and nanomechanical techniques, cation-π interactions can be characterized directly in aqueous media, offering opportunities for the rational manipulation and incorporation of cation-π interactions into the design of supramolecular assemblies. In 2012, we reported the essential role of cation-π interactions in the strong underwater adhesion of Asian green mussel foot proteins deficient in l-3,4-dihydroxyphenylalanine (DOPA) via direct molecular force measurements. In another study in 2013, we reported the experimental quantification and nanomechanics of cation-π interactions of various cations and π electron systems in aqueous solutions using a surface forces apparatus (SFA).Over the past decade, much progress has been achieved in probing cation-π interactions in aqueous solutions, their impact on the underwater adhesion and cohesion of different soft materials, and the fabrication of functional materials driven by cation-π interactions, including surface coatings, complex coacervates, and hydrogels. These studies have demonstrated cation-π interactions as an important driving force for engineering functional materials. Nevertheless, compared to other noncovalent interactions, cation-π interactions are relatively less investigated and underappreciated in governing the structure and function of supramolecular assemblies. Therefore, it is imperative to provide a detailed overview of recent advances in understanding of cation-π interactions for supramolecular assembly, and how these interactions can be used to direct supramolecular assembly for various applications (e.g., underwater adhesion). In this Account, we present very recent advances in probing and applying cation-π interactions for mussel-inspired supramolecular assemblies as well as their structural and functional characteristics. Particular attention is paid to experimental characterization techniques for quantifying cation-π interactions in aqueous solutions. Moreover, the parameters responsible for modulating the strengths of cation-π interactions are discussed. This Account provides useful insights into the design and engineering of smart materials based on cation-π interactions.

Dendritic Hydrogels Induce Immune Modulation in Human Keratinocytes and Effectively Eradicate Bacterial Pathogens

Infections caused by antibiotic-resistant bacteria are globally a major threat, leading to high mortality rates and increased economic burden. Novel treatment strategies are therefore urgently needed by healthcare providers to protect people. Biomaterials that have inherent antibacterial properties and do not require the use of antibiotics present an attractive and feasible avenue to achieve this goal. Herein, we demonstrate the effect of a new class of cationic hydrogels based on amino-functional hyperbranched dendritic-linear-dendritic copolymers (HBDLDs) exhibiting excellent antimicrobial activity toward a wide range of clinical Gram-positive and Gram-negative bacteria, including drug-resistant strains isolated from wounds. Intriguingly, the hydrogels can induce the expression of the antimicrobial peptides RNase 7 and psoriasin, promoting host-mediated bacterial killing in human keratinocytes (HaCaT). Moreover, treatment with the hydrogels decreased the proinflammatory cytokine IL-1β, reactive nitrogen species (NO), and mitochondrial reactive oxygen species (ROS) in S. aureus-infected HaCaT cells, conjunctively resulting in reduced inflammation.

Biomimetic estrogen sensor based on soft colloidal probes

An increasing number of reports substantiate the link between emerging estrogenic pollutants and a variety of adverse effects including developmental disorders, infertility, cancer and neurological disorders, threatening public health as well as environment. The detection of the diverse classes of estrogenic and antiestrogenic substances is still challenging due to analytics which needs to cover the whole range of compounds acting on estrogen receptors and the complex estrogen pathways. In this proof-of-concept study, we report a novel biomimetic detection scheme based on the specific recognition of estrogenic ligands by estrogen sulfotransferase 1E1 (SULT1E1), which acts as one of the key enzymes in estrogen homeostasis. SULT1E1 was site-specifically immobilized on transparent glass slides via a hexahistidine-tag in a multi-step procedure. Soft colloidal probes (SCPs) covalently functionalized with ligands of SULT1E1, namely estrone and estradiol 17-(β-D-glucuronide), served as adhesion probes. The various functionalization steps were analyzed and optimized using epifluorescence, confocal laser scanning as well as reflection interference contrast microscopy (RICM). A competitive SCP binding assay probing the elastic SCP deformation driven by the specific interaction between SCPs and the SULT1E1 decorated glass slides was employed in conjunction with an optical readout by RICM and automated image analysis to detect estrogenic compounds by their inhibition of SCP adhesion. This sensing concept has demonstrated exceptional specificity for estrogenic steroid compounds compared to structurally related substance classes and provides promising options for multiplexed assays and incorporation of other proteins of the endocrine system to fully capture the whole ensemble of hormonally active substances.