Silk – A second skin

Effects – Uniqueness – Why silk?

The skin is a “barrier organ” that protects our bodies. The outermost layer, the stratum corneum, acts as a shield in both directions, preventing harmful environmental agents (pathogenic microorganisms, allergens, chemical substances) from entering, while limiting the release of water from our bodies. To carry out this important protective barrier function, the stratum corneum must maintain the proper hydrolipidic balance, (water content of 10-35% and fats). When this balance is disrupted due to disease, allergies or intolerances, or simply changes in climate, the use of aggressive detergents or cosmetics or wearing clothes that do to respect the skin (insufficient breathability and/or limited ability to absorb and release moisture, etc.), the stratum corneum changes (due to dehydration or conversely hyperhidrosis/maceration) and is no longer able to perform its protective function. This can lead to irritation, itchiness, dryness, inflammation and, in more serious cases, bacterial and fungal infections.

Over the past ten years, the scientific world’s interest in fibroin has grown enormously, with a focus on researching its unique properties, (which make it an “ideal candidate for use in the field of tissue engineering and the study of controlled drug release systems” (Altman GH, Diaz F, Jakuba C, Calabro T, Horan RL, Chen J, Lu H, Richmond J, Kaplan DL. Silk-based biomaterials. Biomaterials 2003; 24: 401-416):

excellent mechanical properties;
biocompatibilty and biodegradability;
good resistance to microbial contamination and relative environmental stability compared to globular proteins, thanks to the wide presence of hydrogen bonds and a significant percentage of crystal domains (Leal-Egaña A, Scheibel T. Silk-based materials for biomedical applications. Biotechnol Appl Biochem 2010; 55: 155-167.);
Fibroin can be considered, for all intents and purposes, a biocompatible polymer on par with the best synthetic and natural polymers like polyglycolic acid, polylactic acid, polystyrene, poly-2-hydroxylmethylacrylate and collagen that are currently used as biomaterials, (Meinel L, Hofmann S, Karageorgiou V, Kirker-Head C, McCool J, Gronowicz G, Zichner L, Langer R, Vunjak-Novakovic G, Kaplan DL – The inflammatory responses to silk films in vitro and in vivo.
Biomaterials 2005; 26: 147-155). Fibroin favours the adhesion of cells to its surface, promoting their growth; fibroin does not induce significant thrombogenic effects and membranes derived from it have been shown to be permeable to oxygen and water vapour (Minoura N, Tsukada M, Nagura M Physico-chemical properties of silk fibroin membrane as a biomaterial. Biomaterials 1990; 11: 430-434. Minoura N, Tsukada M, Nagura M Fine structure and oxygen permeability of silk fibroin membrane treated with methanol. Polymer 1990; 31: 265-269);
highly protective with respect to the human epidermisand induced DNA damage, it can protect the skin when altered, favouring the metabolism of epithelial cells, as well as its balance and function; promotes collagen synthesisand re-epithelialization, and enhances the activity of the cutaneous immune system;
temperature regulating, fighting excess perspiration and maintaining a constant body temperature even in excessive humidity. In contrast to synthetic and plantbased (cotton, linen) materials, the absorbed perspiration does not have a chilling effect and therefore does not stimulate an increase in body temperature that leads to additional perspiration. It breaks the vicious cycle of “perspiringchilling-perspiring” that excessively aggravates dry skin.

Sericin has always been used as an essential component in the cosmetics industry since it has a unique affinity with other human proteins, enabling it to effectively bond with the keratin in skin and hair. It can create a multi-functional, moisturizing protective film and an anti-wrinkle protective film, leaving the skin feeling silky and providing significant aesthetic benefits.

The moisturizing effect is due primarily to formation of a film, without blocking:

Direct: sericin’s high hygroscopicity enables it to fix water on the skin surface. Skin in contact with SERICIN displays less granulation with a reduction in the depth of wrinkles as a result of skin moisturization;

Indirect: the elastic and protective film produced by sericin reduces transepidermal water loss (TEWL), drastically reducing skin dehydration. It acts as a barrier to prevent water loss from the stratum corneum, thereby favouring water accumulation. It replenishes natural moisturizing factor (NMF);

It increases hydroxyproline, which is essential for stabilizing collagen and connective tissue structure by replenishing amino acids.

Anti-aging effect

Elimination of multiple oxidative stress responses (OSRs) caused by UV radiation, with notable antioxidant activity (Dash et al. 2007);
OSRs are responsible for numerous diseases, including cancer. The sericin in silk is an antioxidant protein. The protective effect of sericin is evident in terms of significant reduction in the incidence of skin tumours. The results suggest that sericin has a photo-protective capacity against acute damage from UVB rays and tumour propagation, reducing oxidative stress;
Anti-tyrosinase activity (direct exposure to sunlight induces excessive production of melanin and flaking of the skin surface), thanks to components like flavonoids and carotenoids (Chlapanidas et al. 2013); Anti-elastase activity. The excess production of elastase due to UV rays degrades elastin fibre, causing a loss of skin elasticity and the formation of wrinkles (Chlapanidas et al. 2013);
Recent research has demonstrated that sericin inhibits the effects of the enzymes responsible for skin aging, reducing wrinkles and spots. The three-dimensional structure of sericin leads to zones of varying polarity, attraction and repulsion, hydrogen bonds, repeated zones of bonds or non-bonds that interact with the skin surface (which is also polymeric and made up of repeated units), establishes attractive and bio-adhesive effects that are impossible to achieve with monomers like normal hydrolysed proteins;
Anti-apoptosis (programmed cell death) properties. Sericin stimulates “bcl-2”, an anti-apoptosis regulator (swab test Kitisin et al. 2013);
Sericin displays elevated hydrophilic properties, compatibility and biodegradability. Methionine and cysteine favour cell growth and collagen synthesis, reducing the size of wounds by 90% (Aramwit et al. 2007).

Antimicrobial

Sericin displays antibacterial activity against E. Coli and S. Aureus (Senakoon et al. 2009 & Rajendrana et al. 2012);
In combination with permanent antimicrobial protections, it helps control and prevent bacterial and fungal infections of the skin and is effective in the following disorders: atopic dermatitis, contact dermatitis, mycosis, lichen simplex chronicus, lichen sclerosus, recurrent vulvovaginal candidiasis, vulvitis, hyperhidrosis or maceration, sensitive and hyper-reactive skin and dry, dehydrated, irritated, inflamed, itching, burning, red or injured skin.

Fights asthma, rhinitis and allergies
Tightly woven fibres, like those that can be obtained with silk, are the first barrier against acari colonization. Equally important is the correlation between imperviousness to acari allergens and the breathability of the fabric and/or fill. Airflow is essential not only from the perspective of the thermophysiological comfort of the silk product, but also for the health of the user. The moisture released from the body (for example, approximately 250-300 ml is released during the night), must move freely to the exterior environment not only because it can cause unpleasant odours but also because it can lead to rapid deterioration and an exponential increase in the growth of various species of fungi and moulds, which are the primary cause of asthma and rhinitis symptoms and, in some cases, can also cause allergies. Antimicrobial and antiallergenic treatments that do not release substances increase the excellent natural properties of silk.

But that’s not all:

Fibroin improves lithium batteries

Scientists at the Beijing Institute of Technology have discovered that fibroin from silk is able to increase the lifespan of lithium batteries by five times and improve their performance over time. Fibroin regenerated from natural silk works at a high level of performance for more than 10,000 cycles and stores more than five times more energy than graphite, the most utilized material for lithium battery anodes.

A biocompatible optical fibre

A biocompatible, biodegradable biopolymer derived from silk that can act as an optical fibre has been created by a group of researchers from Tufts University and the University of Illinois. Silk offers new opportunities for the creation of sensors with the potential to transport light to the interior of living tissues. Immediate applications include in vivo monitoring of glucose and the detection of viruses or Alzheimer markers.

Functioning bone marrow created from silk

A collaboration between the University of Pavia and Tufts University in Massachusetts has led to the creation of a three-dimensional system of tissue with silk microtubes that can reproduce the complex structure and physiology of human marrow and generate platelets. This technology could lead to customized medical treatments and the production of materials that can be transfused to patients.

A new biomaterial based on silk proteins that can release drugs to promote bone growth

A group of scientists at Tufts University in the United States has used water and silk proteins to produce three-dimensional biomaterials that have the unique ability to be programmed to carry out biological functions or release drugs.

A super-violin made of silk

A mixture of silkworm silk and Australian spider silk has produced a material that is five times stronger than steel and has excellent structural and acoustic properties tested by luthiers in Cremona.

Silk lengthens the life of fruit

Research published in Scientific Reports has shown that silk has a unique crystal structure that makes it one of the strongest materials in nature. Fibroin, an insoluble, biocompatible and biodegradable protein, can stabilize and protect other materials with which it comes into contact, acting as a sort of “protective shield” to preserve fruit. Analyses demonstrated that the silk coating protects the fruit by making it less permeable to oxygen and carbon dioxide;

A pain-free silk needle

In addition to being thinner than a strand of hair, it has the unique feature of being composed primarily of the silk protein fibroin. This micro-needle, described in the journal Advanced Functional Materials, is so small that it is not detected by nerve tissue and therefore does not cause discomfort.

A silk protein helps preserve vaccines and antibiotics

Research published in the Proceedings of the National Academy of Sciences of the United States has revealed that fibroin functions as a stabilizer, preserving the efficacy of both vaccines and drugs, including when they are exposed to temperatures above 60 degrees. This function of the protein results from chains of amino acids that fold in specific shapes and are composed of crystal sheets that have numerous small pockets that trap the biomolecules and protect them from moisture and high temperatures. In practice, they function like bubble wrap on a nanometric scale. The most important consequences could be for developing countries in which limited infrastructure makes it difficult to keep these drugs refrigerated as required.

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