This report provides a perspective on metabolic glycoengineering methodology developed over the past two decades that allows natural sialic acids to be replaced with chemical variants in living cells and animals. Examples are given demonstrating how this technology provides the glycoscientist with chemical tools that are beginning to reproduce Mother Nature's control over complex biological systems – such as the human brain – through subtle modifications in sialic acid chemistry. Several metabolic substrates (e.g., ManNAc, Neu5Ac, and CMP-Neu5Ac analogs) can be used to feed flux into the sialic acid biosynthetic pathway resulting in numerous – and sometime quite unexpected – biological repercussions upon nonnatural sialoside display in cellular glycans. Once on the cell surface, ketone-, azide-, thiol-, or alkyne-modified glycans can be transformed with numerous ligands via bioorthogonal chemoselective ligation reactions, greatly increasing the versatility and potential application of this technology. Recently, sialic acid glycoengineering methodology has been extended to other pathways with analog incorporation now possible in surface-displayed GalNAc and fucose residues as well as nucleocytoplasmic O-GlcNAc-modified proteins. Finally, recent efforts to increase the “druggability” of sugar analogs used in metabolic glycoengineering, which have resulted in unanticipated “scaffold-dependent” activities, are summarized.

This review highlights recent advances in biomimetic neural scaffolds, their clinical applicability, and possible synergy with other nerve regeneration technologies.

Carboxymethyl chitosan (CMCS) with varying molecular weights (M(v) = 40-405 kDa) and degrees of substitution (DS = 0.25-1.19) has been synthesized by alkalization of chitosan, followed by carboxymethylation with monochloroacetic acid. At DS up to 1.19, the locations where carboxymethylation took place were influenced by the alkalization temperature, i.e., both C2 and C6 substitution at ambient temperature (N,O-carboxymethylated) and mainly C6 substitution at the lower temperature, -15 °C (O-carboxymethylated). Generally, carboxymethylation was more favorable at the primary C6 hydroxyl than the C2 position with increasing DS. CMCS synthesized from 405 kDa CS was soluble in water at DS≥0.73 whereas those from 40 and 89 kDa became water-soluble at lower DS of 0.25 and 0.36, respectively. Electrospinning of aqueous solutions of CMCS was facilitated with the addition of water-soluble polymers, including PEO, PAA, PAAm and PVA. The optimal fiber formation was observed at equal mass composition of O-CMCS (89 kDa at 0.36 DS) and PVA, producing nanofibers with an average diameter of 130 nm. Heat-induced esterification (at 140 °C for 30 min) produced inter-molecular covalent cross-links within and among fibers, rendering the fibrous membrane water-insoluble. Membranes containing higher CMCS carboxyl to PVA hydroxyl ratio retained better fiber morphology upon extended water exposure, indicating more favorable inter-molecular cross-links. The fibrous membranes generated with less substituted CMCS were more hydrophilic and retained a greater extent of the desirable amine functionality.