Abstract
Humans have long appreciated silk for its lustrous appeal and remarkable physical properties, yet as the mysteries of silk are unraveled, it becomes clear that this outstanding biopolymer is more than a high-tech fiber. This progress report provides a critical but detailed insight into the biomedical use of silk. This journey begins with a historical perspective of silk and its uses, including the long-standing desire to reverse engineer silk. Selected silk structure-function relationships are then examined to appreciate past and current silk challenges. From this, biocompatibility and biodegradation are reviewed with a specific focus of silk performance in humans. The current clinical uses of silk (e.g., sutures, surgical meshes, and fabrics) are discussed, as well as clinical trials (e.g., wound healing, tissue engineering) and emerging biomedical applications of silk across selected formats, such as silk solution, films, scaffolds, electrospun materials, hydrogels, and particles. The journey finishes with a look at the roadmap of next-generation recombinant silks, especially the development pipeline of this new industry for clinical use.
Highlights
The biological definition of a silk is a structural protein that is spun into a fiber for use outside the body.[4a,8] In the wild, silks have undergone over 400 million years of “research and development” via natural selection, and after solutions to biological challenges that range from predation to housing and protection.[4a,8] The ubiquity and widespread use of silk is a clear testament to its success, especially as it has arisen numerous times in independent convergent evolutionary events.[2c]. Adv
While gaps still undoubtedly exist in our knowledge surrounding the process of reconstitution and how this affects the integrity and application of the silk proteins undergoing it,[40] the unspinning process has been widely adopted throughout the biomaterials field
The amino acid sequences that form the β-sheet are 7–9mer alanine sequences for Nephila clavipes dragline silk and GAGAGS for Bombyx mori,[58] whereas other silkworm silk species use polyalanine sequences to form the β-sheet structure.[6a]. The influence of the number of alanine residues on the secondary structure and assembly behaviors of silk molecules has been studied using wide angle X-ray crystallography as well as solid-state nuclear magnetic resonance (NMR) spectroscopy
Summary
For the purpose of this progress review, we use the term silk to refer to protein-based fiber-forming materials spun by living. Beyond the replication of silk fibers for textile use, these feedstocks were originally intended for reprocessing into solid form to harness silk’s excellent insulating properties[26b] and enable the casting of films (to make fabrics water and air impermeable[31]) This was mainly because naturally derived materials were still superior in many aspects when compared to those arising from the burgeoning field of industrial polymers.[32]. While gaps still undoubtedly exist in our knowledge surrounding the process of reconstitution and how this affects the integrity and application of the silk proteins undergoing it,[40] the unspinning process has been widely adopted throughout the biomaterials field This is perhaps best evidenced by the impact of the landmark review of Altman et al.[41] 15 years ago and the more recent protocol of Rockwood et al.,[42] which leads us in the present day
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