Mussel-Inspired Catechol Functionalisation as a Strategy to Enhance Biomaterial Adhesion: A Systematic Review

Biomaterials have long been explored in regenerative medicine strategies for the repair or replacement of damaged organs and tissues, due to their biocompatibility, versatile physicochemical properties and tuneable mechanical cues capable of matching those of native tissues. However, poor adhesion under wet conditions (such as those found in tissues) has thus far limited their wider application. Indeed, despite its favourable physicochemical properties, facile gelation and biocompatibility, gellan gum (GG)-based hydrogels lack the tissue adhesiveness required for effective clinical use. Aiming at assessing whether substitution of GG by dopamine (DA) could be a suitable approach to overcome this problem, database searches were conducted on PubMed® and Embase® up to 2 March 2021, for studies using biomaterials covalently modified with a catechol-containing substituent conferring improved adhesion properties. In this regard, a total of 47 reports (out of 700 manuscripts, ~6.7%) were found to comply with the search/selection criteria, the majority of which (34/47, ~72%) were describing the modification of natural polymers, such as chitosan (11/47, ~23%) and hyaluronic acid (6/47, ~13%); conjugation of dopamine (as catechol “donor”) via carbodiimide coupling chemistry was also predominant. Importantly, modification with DA did not impact the biocompatibility and mechanical properties of the biomaterials and resulting hydrogels. Overall, there is ample evidence in the literature that the bioinspired substitution of polymers of natural and synthetic origin by DA or other catechol moieties greatly improves adhesion to biological tissues (and other inorganic surfaces).

Ynamide: A New Coupling Reagent for Amide and Peptide Synthesis

The discovery and application of ynamide coupling reagents is highlighted with a brief summary of the development history of coupling reagents in amide and peptide synthesis. As novel coupling reagents, ynamides are not only effective for simple amide and dipeptide synthesis but also can be used for peptide fragment condensation. More importantly, no racemization was detected during the activation of α-chiral carboxylic acids by employing ynamide coupling reagents.1 Introduction2 Carbodiimide Coupling Reagents3 Uronium/Guanidinium Salt Coupling Reagents4 Phosphonium Salt Coupling Reagents5 Ethoxyacetylene as a Coupling Reagent6 Ynamine Coupling Reagents7 Ynamide Coupling Reagents8 Summary and Outlook