Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

Evasion of the accelerated blood clearance phenomenon by polysarcosine coating of liposomes

Using polyethylene glycol (PEG) to functionalize liposomes improves their stealth properties and stability in blood. However, PEG is known to induce the accelerated blood clearance (ABC) phenomenon, which occurs for multiple doses owing to anti-PEG IgM being produced after the initial injection. In this study, as an alternative to PEG, polysarcosine (PSar) was selected owing to its low antigenicity and its highly dense chains with controllable lengths, similar to PEG. Furthermore, we directly evaluate the potential of PSar for avoiding the ABC phenomenon by comparing PSar with PEG on the same liposome platform, which has similar physicochemical properties such as hydrophobic region, membrane fluidity, and size. PEG- and PSar-liposomes were prepared and characterized for comparison. PSar-liposomes showed similar physicochemical properties to PEG-liposomes in terms of size control, zeta potential, membrane polarity, and fluidity; however, ELISA results showed noticeably lower levels and faster production speeds of both IgM and IgG for PSar-liposomes than for PEG-liposomes. In addition, a pharmacokinetics experiment with multiple injections showed that PSar-PE coating of liposomes may help to circumvent the ABC phenomenon.