The adhesion of some marine organisms to almost any kind of surface in wet conditions has aroused increasing interest in recent decades. Numerous fundamental studies have been performed to understand the scientific basis of this behaviour, with catechols having been found to play a key role. Several novel bio-inspired adhesives and coatings with value-added performances have been developed by taking advantage of the knowledge gained from these studies. To date there has been no detailed overview focusing exclusively on the complex mode of action of these materials. The aim of this Review is to present recent investigations that elucidate the origin of the strong and versatile adsorption capacities of the catechol moiety and the effects of extrinsic factors that play important roles in the overall adhesion process, such as pH value, solvent, and the presence of metal ions. The aim is to detail the chemistry behind the astonishing properties of natural and synthetic catechol-based adhesive materials.

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The Chemistry behind Catechol-Based Adhesion

Production of bioplastic through food waste valorization.

Electrospinning for Tissue Engineering Applications

http://pubs.acs.org/doi/pdf/10.1021/acs.biomac.7b00969

Degradable Adhesives for Surgery and Tissue Engineering.

The rapid and robust adhesion of marine mussels to diverse solid surfaces in wet environments is mediated by the secreted mussel adhesive proteins which are abundant in a catecholic amino acid, l-3,4-dihydroxyphenylalanine (Dopa). Over the last two decades, enormous efforts have been devoted to the development of synthetic mussel-inspired adhesives with water-resistant adhesion and cohesion properties by modifying polymer systems with Dopa and its analogues. In the present review, an overview of the unique features of various mussel foot proteins is provided in combination with an up-to-date understanding of catechol chemistry, which contributes to the strong interfacial binding via balancing a variety of covalent and noncovalent interactions including oxidative cross-linking, electrostatic interaction, metal-catechol coordination, hydrogen bonding, hydrophobic interactions and π-π/cation-π interactions. The recent developments of novel Dopa-containing adhesives with on-demand mechanical properties and other functionalities are then summarized under four broad categories: viscous coacervated adhesives, soft adhesive hydrogels, smart adhesives, and stiff adhesive polyesters, where their emerging applications in engineering, biological and biomedical fields are discussed. Limitations of the developed adhesives are identified and future research perspectives in this field are proposed.

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Recent progress in synthesis and application of mussel-inspired adhesives

Adhesion properties of catechol-based biodegradable amino acid-based poly(ester urea) copolymers inspired from mussel proteins.

A new class of l-phenylalanine-based poly(ester urea)s (PEU) was developed that possess tunable mechanical properties and degradation rates. Our preliminary data have shown that 1,6-hexanediol-l-phenylalanine-based poly(ester urea)s possess an elastic modulus nearly double that of poly(lactic acid). The data in this article detail the synthesis of a series of l-phenylalanine-based poly(ester urea)s possessing a variation in diol chain length and how these subtle structural differences influence the mechanical properties and in vitro biodegradation rates. The mechanical data span a range of values that overlaps with several currently clinically available degradable polymers. Increasing the diol chain lengths increases the amount of flexible segment in the chemical structure, which results in reduced elastic modulus values and increased values of elongation at break. The l-phenylalanine-based poly(ester urea)s also exhibited a diol length dependent degradation process that varied between 1 and 5% over 16 we...

Phenylalanine-Based Poly(ester urea): Synthesis, Characterization, and in vitro Degradation

An off-the-shelf, small diameter tissue engineered vascular graft (TEVG) would be transformative to surgeons in multiple subspecialties. Herein, the results of a small diameter (ID ≈ 1 mm) vascular graft constructed from resorbable, amino acid-based poly(ester urea) (PEU) are reported. Electrospun PEU grafts of two different wall thicknesses (type A: 250 μm; type B: 350 μm) are implanted as abdominal infra-renal aortic grafts in a severe combined immune deficient/beige mouse model and evaluated for vessel remodeling over one year. Significantly, the small diameter TEVG does not rupture or lead to acute thrombogenic events during the intervals tested. The pilot TEVG in vivo shows long-term patency and extensive tissue remodeling with type A grafts. Extensive tissue remodeling in type A grafts leads to the development of well-circumscribed neovessels with an endothelial inner lining, a neointima containing smooth muscle cells. However, due to slow degradation of the PEU scaffold materials in vivo, the grafts remain after one year. The type B grafts, which have 350 μm thick walls, experience occlusion over the one year interval due to intimal hyperplasia. This study affords significant findings that will guide the design of future generations of small diameter vascular grafts.

/pdf/pilot-mouse-study-of-1-mm-inner-diameter-id-vascular-graft-b756jf8rca.pdf

Pilot Mouse Study of 1 mm Inner Diameter (ID) Vascular Graft Using Electrospun Poly(ester urea) Nanofibers.

Poly(ester urea)s (PEUs) derived from α-amino acids are promising for vascular tissue engineering applications. The objective of this work was to synthesize and characterize l-leucine-based PEUs and evaluate their suitability for vascular tissue engineering. Four different PEUs were prepared from di-p-toluenesulfonic acid salts of bis-l-leucine esters and triphosgene using interfacial condensation polymerizations. Mechanical testing indicated that the elastic moduli of the respective polymers were strongly dependent on the chain length of diols in the monomers. Three of the resulting PEUs showed elastic moduli that fall within the range of native blood vessels (0.16 to 12 MPa). The in vitro degradation assays over 6 months indicated that the polymers are surface eroding and no significant pH drop was observed during the degradation process. Human umbilical vein endothelial cells (HUVECs) and A-10 smooth muscle cells (A-10 SMCs) were cultured on PEU thin films. Protein adsorption studies showed the PEUs di...

l-Leucine-Based Poly(ester urea)s for Vascular Tissue Engineering.

Recombinant human growth hormone (rhGH) has been used clinically for several decades. However, rhGH has a short half-life in vivo and therefore for efficacy requires frequent subcutaneous injection, leading to pain and poor patient compliance. An effective rhGH delivery system able to continuously release rhGH over a comparatively long period (generally over a month) would be a significant clinical advance. In this study, a novel long-duration release strategy of rhGH was developed by encapsulating sugar glass-stabilized rhGH in electrospun, bioresorbable poly(ester urea) (PEU) nanofibers. The rhGH was found to be randomly dispersed among the fibers, and sustained rhGH release with only a modest burst was observed for at least 6 weeks as studied by a bicinchoninic acid (BCA) protein assay. Significantly, the released rhGH remained bioavailable and bioactive as determined by an Nb2 cell bioassay specific for rhGH. Our results suggest the feasibility of this system as an effective long-term sustained releas...

Yaohua Gao

Papers

Adhesion properties of catechol-based biodegradable amino acid-based poly(ester urea) copolymers inspired from mussel proteins.

Phenylalanine-Based Poly(ester urea): Synthesis, Characterization, and in vitro Degradation

Pilot Mouse Study of 1 mm Inner Diameter (ID) Vascular Graft Using Electrospun Poly(ester urea) Nanofibers.

l-Leucine-Based Poly(ester urea)s for Vascular Tissue Engineering.

Sustained Release of Recombinant Human Growth Hormone from Bioresorbable Poly(ester urea) Nanofibers