Why Collagen & Elastin?
For this project, we chose to research collagen and elastin; collagen and elastin are two of the perhaps most common molecules in human tissue; subsequently, they are used a ton in the scaffolding for tissue engineering, as collagen is a key structural protein and elastin, a protein key to stretchiness. Read most any video on mammalian tissue engineering and scaffolding, and you will find that collagen and elastin are present.
Right: Elastin fibers (black) among collagen bundles (pink) inside the interstitium, a connective tissue. (Thiese & Carr-locke 2018).
Collagen
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The proteins known as collagen are the most abundant proteins in your body; collagen makes up about â…“ of all proteins in your body (Ross 2020). If you look in a grocery store in the vitamins and minerals aisle, this is while you’ll find massive supplies of collagen supplement products: collagen water, collage powder, collagen enhanced protein bars and topical creams. Collagen is the structural protein that makes up most of your tissue. “Collagen” is really a family of 28 proteins(1), all with slight variants in amino acid composition ... but the four most common types, Type I through IV, are found in skin, tendons, internal organs and bone (Type I, making up 90%), cartilage (Type II), bone marrow and lymphoid tissues (Type III), and the basement membrane, a type of surrounding tissue (Type IV) (Ross, 2020; Wu et al., 2020). Collagen is known for its rigidity and resistance to stretching, thus it makes a great matrix for skin, connective tissue, bones, and organs (Wu et al., 2020).
For this reason - its sheer commonness - collagen is unavoidable when reusing materials from nature (i.e. porcine and human organs). Natural tissue engineering therefore requires materials that have strong compatibility with collagen. Furthermore, a lot of tissue engineering makes use of collagen anyways because of its strong biomaterial properties, even if the collagen is bolstered by an additive - polymeric, bioceramic, or inorganic. Chonjuan Dong explains, “Collagen can be extracted and purified from a variety of sources and offers low immunogenicity, a porous structure, good permeability, biocompatibility and biodegradability. However, the poor mechanical property of collagen scaffolds limits their applications to some extent. To overcome this shortcoming, collagen scaffolds can be cross-linked by chemical or physical methods or modified with natural/synthetic polymers or inorganic materials” (Dong & Lv, 2016).
We will explore the structures of collagen - to see what makes it so useful in the body and better understand how those same material properties can be applied in tissue engineering; further, we will look into the role of some of those additives.
Elastin
Elastins encompass a family of protein-based polymers which are derived from the sequence of tropoelastin (Conticello and Desai 2012). These materials are typically found in areas of the body as a connector such as the heart, lungs, arteries, and skin. In stores, you can find this material in moisturizing creams or renewing masks as a way to help skin glow and help with wrinkles in the skin; specifically the face.
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Elastin is a protein-based biopolymer that has an elastomeric mechanical quality which is brought 1000 times more elastic than collagen (Kristensen and Karsdal 2016). The elasticity is primarily why elastin is used so much in arteries and lungs. Elastin is less stiff than collagen and allows for the tissue to expand and contract due to aging. In a study about arteries as when individuals get older, the elastin percentage within the artery decreases which leads to a stiffer tissue and thus increasing pulse pressure (Kristensen and Karsdal 2016).
Above: Image of St. Ives renewing moisturizer which markets that it can give the skin a youthful glow with the additions of collagen and elastin.
Elastin is very sensitive to light and pH which makes it a good candidate for scaffolding, but only when crossed with another material to take away the negatives that elastin brings to tissue. In addition, elastin has a tendency to fragment within the body, leading to strange ways of cross-linking (Conticello and Desai 2012) and giving good elasticity to scaffolding which is helpful in cases of skin and lung tissue scaffolding.
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We will continue to compare elastin in engineered tissue and contrast the benefits that adding additives can do for elastin. In addition, we will analyze how elastin compares to collagen in these applications.