Silk a natural biomaterial
Recent advancements in understanding silk structure and processing open up new opportunities in the use of silk in tissue regeneration
The limited supply of donors and increasing morbidity have put new demands on tissue engineering (TE) as a treatment of organ failures . Materials like polymers, metals and ceramics are widely used as cell scaffolds for tissue engineering. Both synthetic and natural polymers have been trialed, though each has its own limitations. While the former allows easy processing and modiﬁcations, the later offers better cyto- and bio-compatibility . Protein, being a component of natural tissues, is a rational choice for applications in tissue engineering. Structural proteins such as collagen, elastin, elastin-like-peptides, albumin and ﬁbrin are used as sutures, tissue scaffolds, haemostatic and drug delivery agents . Silk ﬁbroin of silk a commonly available natural biopolymer with a long history of applications in the human body as sutures. Currently silk sutures are used in lips, eyes, oral surgeries and in the treatment of skin wounds . Increasingly, silk ﬁbroin is exploited in other areas of biomedical science, as a result of new knowledge of its processing and properties like mechanical strength, elasticity, biocompatibility, and controllable biodegradability . These properties of silk ﬁbroin are particularly useful for tissue engineering.
Silk has several major advantages over other protein based biomaterials, which are derived from tissues of allogeneic or xenogeneic origins. As such, the risk of infection is high for those materials. Processing of such materials is also expensive due to the stringent protein isolation and puriﬁcation protocols. In contrast, silk is an established textile ﬁber and nearly 1000 metric tons of silk are produced and processed annually. Silk ﬁber puriﬁcation is routinely carried out using a simple alkali or enzyme based degumming procedure, which yields the starting material for sericin free silk based biomaterials. It is also economically advantageous to use silk for biomedical applications, because of available large scale processing infrastructure of traditional silk textile industries .
The major advantage of silk compared to other natural biopolymers is its excellent mechanical property. Other important advantages include good biocompatibility, water based processing, biodegradability and the presence of easy accessible chemical groups for functional modiﬁcations. Silk based designs allow easy control on matrix morphology, degradation rate and conformal adhesion to underlying tissues with low immune-toxicity and good biocompatibility.
Recent advancements in understanding silk structure and processing open up new opportunities in the use of various forms of silk in tissue regeneration. Silk systems will be particularly useful for applications where slow biodegradation and good mechanical properties are critically required, such as for bone, ligament and musculoskeletal tissues. Successful applications of silk based materials in tissue engineering depends on further understanding of the long term biocompatibility, biodegradability and its degraded products, along with the ability to tune silk morphologies for tissue speciﬁc requirements. Hybrid materials, incorporating 100% silk in different matrix morphologies show promising results in this regard.
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