A review on recent trends and concept of silk beyond textile

Introduction

Sericulture is an age old agro based industry that weaves together the tapestry of history, culture and wonder of nature. 'Silk' is the main output of this industry holding the crown of 'Queen of Textile' among the different textile fibers. Due of its versatility and wide range of application silk is not limited to the textile industry. It continues to bridging the gap between ancient tradition and modern innovation. Silk has many industrial and commercial uses.

Recent trends and concepts in sericultural innovations

Silkworms are the lepidopteran insect. The mulberry silkworm Bombyx mori L. being a useful model for the biological research, in the field of genetic engineering techniques like bioengineering, nanotechnology it is used as highly potent tool for developing some novel concepts. For the production of foreign protein study on silk gland become a modern trend after the making of transgenic silkworm by the piggyBack transposon mediated technology. More than 10 numbers of foreign proteins were expressed successfully in transgenic silkworm in last decade (Sharma et al., 2022) [16] .

Silk micrococoons, a novel approach

Researchers have manufactured microscopic version of the cocoons spun by silkworms, which could be used to store sensitive proteins and other molecules for a wide range of uses. These micrococoons are more than a thousand times smaller than the natural one crafted by the silkworms. These are comprises of a solid and tough shell of silk nano-fibrils that surround and protect a centre of liquid cargo. Micrococoons are prepared from the native silk feedstocks extracted from the silk gland of 5 th instar B. mori larvae that had just started to construct the cocoon (Laity et al., 2015) [10] . These nanostructures are utilized to fabricate structurally and functionally efficient materials such as hydrogel, fibers, films, coating and 3D materials (Wang et al., 2018) [22] . Some of the potential application of these micrococoons are-It is an extremely versatile drug delivery nanomaterial from the silk. The major silk protein fibroin's molecules possess amine, hydroxyl, carboxyl and thiol as a functional group of amino acid which can anchor many biomolecules as marker for active targeting and can be modified to manage to entrap drug properties (Phama and Tiyaboonchaia, 2020) [15] . Because of its high entrapping efficiency, increases drug solubility and stability, drug loaded fibroin nanoparticles are found promising to fix the obstacles of the pharmaceutical products that are available as small molecules in the market (Sharma et al., 2022) [16] . To revitalize cell growth and differentiation during tissue regeneration some growth factors and enzymes are highly used in therapeutic proteins. But there are so many limitations like limited tissue penetration, low stability level and potential toxicity in the clinical application of enzymes. Fibroin nanoparticles have the potential to deliver big molecules to achieve therapeutic protein delivery (Sharma et al., 2022) [16] . Fibroin nanoparticles have been used in delivering bovine serum albumin, vascular endothelial growth factor etc. (Chen et al., 2018; Kundu et al., 2010) [2,9] . Micrococoons can be effectively used in gene delivery and vaccine delivery due to its verified higher transfection efficiency and higher degree of specificity of fibroin (Sharma et al., 2022) [16] . Dong et al. (2015) [6] reported the better cell adhesion in human corneal epithelial cells when silk fibroin coated liposomes loaded with ibuprofen used for ocular delivery. Filon et al. (2015) [7] reported that fibroin nanoparticles serve as a promising vehicle for drug delivery through transdermal surfaces. Micrococoon can increase the stability and lifetime of an antibody and have potential to treat the major protein misfold disorders such as Alzimer and Parkinson's disease (Shimanovich et al., 2017) [17] .

Innovation of different biomaterials from the silk:

 Seri surgical scaffolds: It is a bioresorbable, silkderived scaffold for soft tissue support. Ultra-pure strands of fibroin in Seri Surgical Scaffold prompt a muted immune response also having highly moldable and drapable nature extracted from the silk from the Bombyx mori (Jewell et al., 2015) [8] . These are used in plastic surgery like breast reconstruction, body contouring, brachioplasty etc.  Silk solutions: Solubilized aqueous form of B. mori silk has been investigated for a range of therapeutic applications, including treatment of diabetes, chronic wounds and inflammation. Studies have been made to utilize the silk solution for the treatment of ocular conditions like dry eye and corneal injury (Sharma et al., 2022) [16] .  Skin grafts/ artificial skin from silk: Skin is the largest organ and the protective barrier to the other organs of our body. Due to some illness it can get damaged in such a way that it needs some replacement in form of graft. A good graft should have the property to cover or to protect the intended place without any negative immune response. The biomaterial derived from the silk has the ability to mimic the human skin (Altman et al., 2003) [1] . Electrospun fibroin from the muga silkworm (A. assamensis) and eri silkworm (S. ricini) have been successfully used in wound healing (chouhan et al., 2017) [3] .  Bone grafts: Among the different biomaterials to develop scaffold based bone tissue, fibroin has almost all the properties suitable for developing osteoinductive functional bone graft that resemble collagen (Wittmer et al., 2011) [23] . Silk fibroin extracted from the tropical tasar silkworm i.e A. mylitta can be used to make porous scaffolds that mimic borne tissue (Mandal and Kundu, 2009) [12] .  Surgical sutures: Silk has been used as surgical sutures in cardiovascular, ocular and neural surgery because of its super knot strength, wound safty and biocompatibility (Chu, 2013) [4] .

 Hydrogels: Silk fibroin hydrogels are emerging as useful tool for therapeutic delivery of stem cells (Sharma et al., 2022) [16] .  Electrospun silk: Silk fibroin fabricated by electrospinning has been explored for a wide range of application starting from wound dressing to the vascular grafting.

Commercial uses of silk proteins:

The 'core' protein fibroin and the sericin represents a unique family of structural proteins which are biocompatible, biodegradable, anti-inflammatory and also offering a wide range of properties. Because of these properties they have been used in different commercial sectors:  In cosmetic industry: The silk protein sericin can be used in cosmetic industry to prepare cosmetic formulations such as gels, creams, shampoos etc. due to its gelling property, moisture retention capacity, easy skin adhesion, elasticity, anti-aging, anti-wrinkle, antiinflammatory effects (Padamwar and Pawar, 2004, Singh et al., 2014) [14,18] .  In food industry: Proper food packaging not only maintain the cost-benefit ratio to the food companies it also prevents the food from contamination. But some low grade packaging and food coating materials has become the contributing factors of migration of chemical substances from that material to the food. Currently scientists are searching for alternative sources of coating materials to use in food industries and they found the low cost edible coating materials prepared from sericin which serves as a alternative coating materials (Tarangini et al., 2022) [20] . Sericin coating on fruits like apple, mango, banana, strawberries, mushrooms and vegetables prevents browning, weight loss and polyphenol oxidase activity to a great extent (Thongsook and Tiyaboonchai, 2011; Cuervo et al., 2021) [21,5] . Apart from the coating and packaging materials, food products prepared with sericin helps in controlling the diabetics. Sericin can be use as an ingredient in salad dressing and making jelly desert (Matran et al., 2023) [13] .

Conclusion

Global developments are switching towards sustainable and friendly materials along with production process. Accordingly, natural fiber applications are gaining acceptance universally. Silk, the natural protein fiber has recently experienced more attention due to the innovative technologies that has extended the use of silk fiber beyond the traditional textile industry. The unique and versatile properties of silk make it suitable to produce diversified products and extensive use has been recorded in biochemical field as sutures. Therefore, it is crucial to enhance the production of silk in regard to annual global demand for future needs.

References

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