Biomacromolecules as carriers in drug delivery and tissue engineering

Natural biomacromolecules have attracted increased attention as carriers in biomedicine in recent years because of their inherent biochemical and biophysical properties including renewability, nontoxicity, biocompatibility, biodegradability, long blood circulation time and targeting ability. Recent advances in our understanding of the biological functions of natural-origin biomacromolecules and the progress in the study of biological drug carriers indicate that such carriers may have advantages over synthetic material-based carriers in terms of half-life, stability, safety and ease of manufacture. In this review, we give a brief introduction to the biochemical properties of the widely used biomacromolecule-based carriers such as albumin, lipoproteins and polysaccharides. Then examples from the clinic and in recent laboratory development are summarized. Finally the current challenges and future prospects of present biological carriers are discussed.
Natural-origin biomacromolecules perform a diverse set of functions in their native setting. For example, polysaccharides function in membranes, intracellular communication and as storage sites, whereas proteins function as structural materials, transport vehicles, nutrients and catalysts. Transport proteins as carriers for delivery of nutrients and other necessary molecules are of special interest. Inspired by such natural processes in organisms, scientists started to utilize natural and biological macromolecules, including proteins, polysaccharides, and lipoproteins, for the delivery of drugs and tissue engineering. Biomacromolecule-based drug carriers are nontoxic, non-immunogenic and have high drug loading content, good biocompatibility and targeting ability. Meanwhile, they are also capable of controlled and sustained drug release. Many meaningful designs have been reported using biological carriers, some of which are already approved for clinical use. Biomacromolecules used as carriers include proteins (albumin, transferrin, lipoproteins, silk fibroin, collagen, keratin) and polysaccharides (chitosan, cyclodextrin, hyaluronic acid, heparin and pectin). The structural diagrams of these carriers are shown in Fig. 1. These biomacromolecules can be naturally obtained from animals and plants in abundant amounts and are renewable resources. They have good affinity to organisms and weak immune rejection, and can be degraded by in vivo enzymes; the metabolites also have low toxicity to organisms. Biomacromolecule-based carriers have been reported in the form of prodrugs, drug conjugates, nanoparticles, microcapsules, hydrogels and tissue engineering scaffolds. The use of biomacromolecule-based carriers has been shown to improve the pharmacokinetics of the payloads and to reduce systemic toxicity and immunogenicity. Furthermore, the hydroxyl, amine and carboxyl groups on the chains of these biomacromolecules can be utilized for chemical modification, making them of great significance in biomedical field.(Acta Pharm Sin B. 2018 Jan; 8(1): 34–50.)

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