Thiolactone chemistry, a versatile platform for macromolecular engineering

This review covers the extensive use of γ-thiolactone chemistry as a versatile and powerful tool for macromolecular engineering and the preparation of various polymer architectures, such as functional, alternating, or sequence-controlled (co)polymers.

Design and investigation of salecan/chitosan hydrogel formulations with improved antibacterial performance and 3D cell culture function

Hydrogel formulations are considered to be promising dosage forms for clinical delivery of antibiotics but suffer from many limitations such as polymers selection and crosslinking methods. Herein, dynamic Schiff base reaction crosslinked hydrogels (denoted as CO) with 'switchable' channels were designed based on Chitosan and Salecan. Chitosan maintains the pH sensitive property while providing functional groups for the reversible bond formation. Equilibrium water content, swelling and degradation behavior, dynamic rheology and cytotoxicity assay were investigated to characterize the hydrogels' properties. By simulating and comparing four classic models, the drug release kinetics and mechanism were studied in detail. HeLa cells were encapsulated to further exploring the feasibility of 3D cell culture. All the results revealed CO hydrogels possessed excellent biological functions to maintain cell growth. Therefore, CO hydrogels can be served as a promising carrier for drug delivery and also expected to apply in many other medical fields.

In situ forming oxidized salecan/gelatin injectable hydrogels for vancomycin delivery and 3D cell culture

Antibiotics are widely used in clinical medicine. As an important member, vancomycin often plays an irreplaceable role in some serious infections, but its use still lacks suitable carriers and effective formulations. In order to find a vancomycin carrier with potential for clinical application, a new class of oxidized salecan/gelatin based injectable hydrogels are constructed through dynamic covalent Schiff base reaction. The sodium periodate oxidized salecan (OS) precursor was synthesized, and then the gelatin/oxidized salecan (GS) hydrogels are formed by blending gelatin and OS buffer solutions without any additives under physiological condition. The chemical structure, as well as internal morphologies, mechanical properties, In vitro enzymatic degradation profile of hydrogels are investigated with proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), compression test and rheological experiments. The resulted hydrogels exhibit excellent antibacterial ability and variable characteristics. Moreover, the hydrogels display ideal drug release kinetics and mechanisms, and are applied successfully to the controlled release of vancomycin. Importantly, benefitting from the excellent biocompatibility and the reversibly crosslinked networks, GS hydrogels can function as suitable three dimensional (3D) extracellular matrix for HeLa cells, leading to the encapsulated cells maintaining a high viability and proliferative capacity. Therefore, the injectable GS hydrogels demonstrated attractive properties for future application in pharmaceutics and tissue engineering.

Dynamic crosslinked and injectable biohydrogels as extracellular matrix mimics for the delivery of antibiotics and 3D cell culture

Antibiotics are widely used in clinical medicine. As an important member, vancomycin often plays an irreplaceable role in some serious infections but for its use, there is still a lack of suitable carriers and effective formulations. To find a vancomycin carrier with potential for clinical applications, a new class of poly(γ-glutamic acid)/dextran-based injectable hydrogels have been constructed through dynamic covalent hydrazone linkages. Adipic dihydrazide (ADH)-grafted poly(γ-glutamic acid) (PGAADH) and sodium periodate-oxidized dextran (OD) precursors were synthesized; then, the hydrogels were formed by blending PGAADH and OD buffer solutions without any additives under physiological conditions. The newly formed precursor structures, mechanical properties, morphologies, hydrogel degradation profiles, and the interaction between the drug and precursors were investigated with FTIR spectroscopy, ¹H NMR spectroscopy, rheological experiments, compression tests, SEM, and isothermal titration calorimetric (ITC) measurements. The resulting hydrogels exhibited excellent antibacterial ability and ideal variable performances. Moreover, the hydrogels exhibited different drug release kinetics and mechanisms and were applied effectively towards the controlled release of vancomycin. Significantly, benefitting from the reversibly cross-linked systems and the excellent biocompatibility, the hydrogels can work as the ideal material for HeLa cell culture, leading to encapsulated cells with higher viability and capacity that is proliferative. Therefore, the injectable PGAADH/OD hydrogels demonstrated attractive properties for future applications in pharmaceutics and tissue engineering.

Polysaccharides-polypeptide derived biohydrogels were formed using hydrazone chemistry as crosslinking strategy, which have controllable drug release rate and many other potential applications, especially in sustained drug delivery and cell scaffold.

Protein-Engineered Biomaterials for Cancer Theranostics

Proteins are an important class of biomaterials promising a variety of applications such as drug delivery, and imaging or therapy, owing to their biodegradability, biocompatibility, as well as inherent biological activities acting as enzymes, recognizing molecules, or therapeutics by themselves. Over the few past decades, different types of proteins with desired properties have been widely explored for biomedical applications. Many therapeutic proteins have now entered clinical use. This review therefore summarizes various strategies in the engineering of biomaterials for delivery of therapeutic proteins, as well as the recent development of protein-based biomaterials for cancer theranostics.

Coupling of sterically demanding peptides by β-thiolactone-mediated native chemical ligation

The ligation of sterically demanding peptidyl sites such as those involving Val-Val and Val-Pro linkages has proven to be extremely challenging with conventional NCL methods that rely on exogenous thiol additives. Herein, we report an efficient β-thiolactone-mediated additive-free NCL protocol that enables the establishment of these connections in good yield. The rapid NCL was followed by in situ desulfurization. Reaction rates between β-thiolactones and conventional thioesters towards NCL were also investigated, and direct aminolysis was ruled out as a possible pathway. Finally, the potent cytotoxic cyclic-peptide axinastatin 1 has been prepared using the developed methodology.

Poly(glutamic acid) hydrogels crosslinked via native chemical ligation

Poly(glutamic acid) hydrogels crosslinked by NCL have good biocompatibility and tunable properties.