Among the different types of the biological materials available for producing bioactive wound dressings, silk fibroin (SF) obtained from Bombyx mori silkworm has gained significant importance as a bioactive wound dressing.
A wound, be it a minor cut or a major injury, needs to be properly taken care of. One way of wound care is by using wound dressings. A wound dressing is a material such as a gauze, lint, plaster, bandages, cotton wool, hydrogels and semi-permeable films etc. that protects the wound and promotes wound healing. Wound dressings can be classified into two categories; passive dressings and interactive dressings. Passive dressings are the traditional wound dressings such as gauze, lint, and bandages, that only protect the wound from external factors. Modern wound dressings belong to the category of interactive dressings as they interact with the wound and provide an optimum environment (i.e. moisture, oxygen circulation, and prevention from microbial contamination) that promotes wound healing. Interactive wound dressings include hydrogels, semi-permeable films, dressings made from bioactive materials, engineered skin grafts, and the medicated dressings.
Bioactive wound dressings
Bioactive wound dressing is a new and promising approach for wound treatment. These wound dressings are synthesized from biological materials such as collagen, chitosan, alginate, hyaluronic acid, silk fibroin, and elastin. These dressings are being preferred over traditional and synthetic wound dressings for their biodegradability, biocompatibility, low immunogenicity and non-toxic nature. Polymers of these biological materials, alone or in combination (depending on the nature of the wound), are used to synthesize wound dressings. All these biomaterials have unique properties that promote the process of wound healing. Bioactive wound dressings can be incorporated with antimicrobial agents and growth factors that enhance the process of wound healing.
Silk Fibroin wound dressing
Among the different types of the biological materials available for producing bioactive wound dressings, silk fibroin (SF) obtained from Bombyx mori silkworm has gained significant importance as a bioactive wound dressing. Silk is a protein polymer, present in the glands of arthropods such as silkworms, spiders, mites, scorpions, and bees. Arthropods use this silk for various purposes, such as to make webs (spiders) and spin it around themselves during metamorphosis. Silk is composed of two major proteins; silk fibroin (SF) and sericin. Sericin is the glue-like protein that wraps around the SF. The SF of Bombyx mori has a diameter of 10-25 μm and consists of two chains i.e. a light chain (approximately 26 kDa) and a heavy chain (390 kDa) linked with a disulphide bond.
SF shows low immunogenicity and degrades into nontoxic compounds that the body can metabolize. It is also cost effective and can be acquired in large quantities – Bombyx mori can be abundantly cultured in laboratory where sericin is separated from SF by thermal-chemical treatment. Moreover, SF has a good water absorbance capacity, flexibility, gas exchange property, excellent mechanical property and a high solubility in salt solution. SF also has a high thermal-stability which makes possible to sterilize it in an autoclave at >250°C without losing its functional and mechanical properties.
SF can be easily processed to produce different types of wound dressings, each with its own unique property that makes them suitable for the treatment of different types of wounds and injuries. The different forms of SF include nanofibers, hydrogels, films, and sponges. The ‘Silk Fibroin Nanofiber Wound Dressing’ is made up of nano fibers prepared from silk fibroin polymers that range from several micrometers to 10 nanometers in size. ‘Hydrogel Dressing’, as the name indicates, is gel based, containing 90% water and helps in fluid exchange from the wound. In case of ‘Silk Fibroin Hydrogels’, the gel matrix is composed of silk fibroin polymers. ‘Silk Fibroin Films’ are thin films composed of silk polymers, and silk fibroin sponges (sponges based on silk polymers).
Researchers have experimented for the effectiveness of SF wound dressings on mice models that has provided with many encouraging results. They observed that loading antimicrobial agents onto SF nanofibers can prevent infection on the site of injury. SF based hydrogels can be used on irregular surfaces such as burns and diabetic wounds. SF mats accelerate the process of burn healing as it can prevent the loss of water, has good oxygen permeability, and can enhance fluid drainage to prevent the accumulation of fluid at the burnt site. For the treatment of diabetic wounds, SF dressing has been loaded with insulin that helps to accelerate wound repair by proliferation and migration of keratinocytes (skin cells) at site of injury.
Future prospects of biological wound dressing
Besides its great many benefits, SF has yet not been approved as artificial skin. Moreover, the future research work has to bring out such SF based dressings which would minimize or completely overcome the problem of scar tissue formation. Scaffold based engineering and investigations into the molecular bases of scarring process would help overcome these shortcomings and bring out many more interesting facts to the surface.
This article is collectively written by Andleeb Khizar, Gull-e-Lalah Saleem, and Mayra Ahmed, from Kinnaird College for Women Lahore, BSc. (Hons) Biotechnology Department.