Bioengineered Protein-based Adhesives for Biomedical Applications

Expanding the Genetic Code of Bioelectrocatalysis and Biomaterials

Genetic code expansion is a promising genetic engineering technology that incorporates noncanonical amino acids into proteins alongside the natural set of 20 amino acids. This enables the precise encoding of non-natural chemical groups in proteins. This review focuses on the applications of genetic code expansion in bioelectrocatalysis and biomaterials. In bioelectrocatalysis, this technique enhances the efficiency and selectivity of bioelectrocatalysts for use in sensors, biofuel cells, and enzymatic electrodes. In biomaterials, incorporating non-natural chemical groups into protein-based polymers facilitates the modification, fine-tuning, or the engineering of new biomaterial properties. The review provides an overview of relevant technologies, discusses applications, and highlights achievements, challenges, and prospects in these fields.

Glycopolymer-Based Antiswelling, Conductive, and Underwater Adhesive Hydrogels for Flexible Strain Sensor Application

With the fast development of soft electronics, underwater adhesion has become a highly desired feature for various sensing uses. Currently, most adhesive hydrogels are based on catechol-based structures, such as polydopamine, pyrogallol, and tannic acid, with very limited structural variety. Herein, a new type of glycopolymer-based underwater adhesive hydrogel has been prepared straightforwardly by random copolymerization of acrylic acid, acetyl-protected/unprotected glucose, and methacrylic anhydride in dimethyl sulfoxide (DMSO). By employing a DMSO-water solvent exchange strategy, the underwater adhesion was skillfully induced by the synergetic effects of hydrophobic aggregation and hydrogen bonding, leading to excellent adhesion behaviors on various surfaces, including pig skins, glasses, plastics, and metals, even after 5 days of storage in water. In addition, the underwater adhesive hydrogels with simple and low-cost protected/unprotected carbohydrate compositions showed good mechanical and rheological properties, together with cytocompatibility and antiswelling behavior in water, all of which are beneficial for underwater adhesions. In application as a flexible strain sensor, the adhesive hydrogel exhibited stable and reliable sensing ability for monitoring human motion in real time, suggesting great potential for intelligent equipment design.

Genetically Engineered Protein-Based Bioadhesives with Programmable Material Properties

Silk-amyloid-mussel foot protein (SAM) hydrogels made from recombinant fusion proteins containing β-amyloid peptide, spider silk domain, and mussel foot protein (Mfp) are attractive bioadhesives as they display a unique combination of tunability, biocompatibility, bioabsorbability, strong cohesion, and underwater adhesion to a wide range of biological surfaces. To design tunable SAM hydrogels for tailored surgical repair applications, an understanding of the relationships between protein sequence and hydrogel properties is imperative. Here, we fabricated SAM hydrogels using fusion proteins of varying lengths of silk-amyloid repeats and Mfps to characterize their structure and properties. We found that increasing silk-amyloid repeats enhanced the hydrogel's β-sheet content (r = 0.74), leading to higher cohesive strength and toughness. Additionally, increasing the Mfp length beyond the half-length of the full Mfp sequence (1/2 Mfp) decreased the β-sheet content (r = -0.47), but increased hydrogel surface adhesion. Among different variants, the hydrogel made of 16xKLV-2Mfp displayed a high ultimate strength of 3.0 ± 0.3 MPa, an ultimate strain of 664 ± 119%, and an attractive underwater adhesivity of 416 ± 20 kPa to porcine skin. Collectively, the sequence-structure-property relationships learned from this study will be useful to guide the design of future protein adhesives with tunable characteristics for tailored surgical applications.

Engineered Bicomponent Adhesives with Instantaneous and Superior Adhesion Performance for Wound Sealing and Healing Applications

Surgical adhesives are playing an important role in wound repair and emergency hemostasis in clinical treatment. However, the development of strong bioglue with rapid in situ adhesion, durable adhesiveness, and flexibility in dynamic and moist physiological environments is still challenging. Herein, a new type of biosynthetic protein bioadhesives with superior adhesion performance is reported by developing a protein aldimine condensation strategy. Lysine‐rich recombinant proteins are designed and massively biosynthesized to instantaneously react with aldehyde cross‐linkers to realize in situ strong adhesion. The obtained bioadhesives show an ultra‐high adhesion strength of ≈101.6 kPa on porcine skin, outperforming extant clinical bioglues. In addition, they possess super biocompatibility, flexibility, biodegradability, and compliance with the tissues. Owing to the strong and instantaneous adhesion properties, the bioadhesives are qualified for dynamic wound closure, facilitating wound repair, and noncompressible hemorrhage. Importantly, they can be industrially encapsulated into custom‐made cartridge delivery tubes at low cost for clinical use. Therefore, biosynthetic bioadhesives have great potential for biological applications and are capable of scaling up to the industrial level for clinical transformation, which will be a successful paradigm for reforming existing clinical products.

Ternary Synergy of Lys, Dopa, and Phe Results in Strong Cohesion of Peptide Films

Synergistic interactions between 3,4-dihydroxyphenylalanine (Dopa, Y*), cationic residues, and the aromatic rings have been recently highlighted as influential factors that enhance the underwater adhesion strength of mussel foot proteins and their derivatives. In this study, we report the first ever evidence of a cation-catechol-benzene ternary synergy between Y*, lysine (Lys, K), and phenylalanine (Phe, F) in adhesive peptides. We synthesized three hexapeptides containing a different combination of Y*, K, and F, i.e., (KY*)₃, (KF)₃, and (KY*F)₂, respectively, exploring the relationship between the cohesive performance and molecular architecture of peptides. The peptide with the (KY*F)₂ sequence displays the strongest underwater cohesion energy of 10.3 ± 0.3 mJ m^-2 from direct nanoscale surface force measurements. Combined with molecular dynamics simulation, we demonstrated that there are more bonding interactions (including cation-π, π-π, and hydrogen bond interactions) in (KY*F)₂ compared to the other two peptides. In addition, peptide (KY*F)₂ still shows the strongest cohesive energies of 7.6 ± 0.7 and 3.7 ± 0.5 mJ m^-2 in acidic and high-ionic strength environments, respectively, although the cohesive energy decreases compared to the value in pure water. Our results further explain the underwater cohesion mechanisms combining multiple interactions and offer insights on designing Dopa containing underwater adhesives.

Branched short elastin-like peptides with temperature responsiveness obtained by EDTA-mediated multimerization

Elastin-like peptides (ELPs) exhibit a reversible phase transition, known as coacervation, triggered by temperature changes. This property makes them useful as stimuli-responsive molecular materials for various applications. Among ELPs, short peptide chain lengths have some advantages over long peptide chain lengths because short ELPs can be easily obtained by chemical synthesis, allowing the use of various amino acids, including D-type and unnatural amino acids, at any position in the sequence. Moreover, the incorporated amino acids readily affect the temperature-responsive behavior of ELPs. However, to be utilized in various applications, it is necessary to develop short ELPs and to investigate their temperature-responsive properties. To obtain further insights into the temperature-responsive behavior of the short ELPs, we investigated branched short ELP analogs composed of (FPGVG)_n chains (n = 1 or 2, abbreviated as F1 and F2, respectively). We synthesized multimers composed of four F1 chains or two to four F2 chains using ethylenediaminetetraacetic acid (EDTA) as a central component of multimerization. Our results show that the multimers obtained exhibited coacervation in aqueous solutions whereas linear F1 or F2 did not. Furthermore, the structural features of the obtained multimers were the same as those of linear (FPGVG)₄ . In this study, we demonstrated that molecules capable of coacervation can be obtained by multimerization of F1 or F2. The temperature-responsive molecules obtained using short ELPs make it possible to use them as easy-to-synthesize peptide tags to confer temperature responsiveness to various molecules, which will aid the development of temperature-responsive biomaterials with a wide variety of functions.

Molecularly Engineered Protein Glues with Superior Adhesion Performance

Naturally inspired proteins are investigated for the development of bioglues that combine adhesion performance and biocompatibility for biomedical applications. However, engineering such adhesives by rational design of the proteins at the molecular level is rarely reported. Herein, it is shown that a new generation of protein-based glues is generated by supramolecular assembly through de novo designed structural proteins in which arginine triggers robust liquid-liquid phase separation. The encoded arginine moieties significantly strengthen multiple molecular interactions in the complex, leading to ultrastrong adhesion on various surfaces, outperforming many chemically reacted and biomimetic glues. Such adhesive materials enable quick visceral hemostasis in 10 s and outstanding tissue regeneration due to their robust adhesion, good biocompatibility, and superior antibacterial capacity. Remarkably, their minimum inhibitory concentrations are orders of magnitude lower than clinical antibiotics. These advances offer insights into molecular engineering of de novo designed protein glues and outline a general strategy to fabricate mechanically strong protein-based materials for surgical applications.

Flexible customization of the self-assembling abilities of short elastin-like peptide Fn analogs by substituting N-terminal amino acids

Elastin-like peptides (ELPs) are thermoresponsive biopolymers inspired by the characteristic repetitive sequences of natural elastin. As ELPs exhibit temperature-dependent reversible self-assembly, they are expected to be biocompatible thermoresponsive materials for drug delivery carriers. One of the most widely studied ELPs in this field is the repetitive pentapeptide, (VPGXG)_n . We previously reported that phenylalanine-containing ELP (Fn) analogs, in which the former Val residue of the repetitive sequence (VPGVG)_n is replaced by Phe, show coacervation with a short chain length (n = 5). Owing to their short sequences, Fn analogs are easily modified in amino acid sequences via simple chemical synthesis, and are useful for investigating the relationship between peptide sequences and temperature responsiveness. In this study, we developed Fn analogs by replacing Phe residue(s) with other amino acids or introducing another amino acid at the N-terminus. The temperature responsiveness of the Fn analogs changed drastically with the substitution of a single Phe residue, suggesting that aromatic amino acids play an important role in their self-assembly. In addition, the self-assembling ability of Fn was enhanced by increasing the bulkiness of the N-terminal amino acids. Therefore, the N-terminal residue was considered to be important for hydrophobicity-induced intermolecular interactions between the peptides during coacervation.