It is a brand name of the product that includes 5 amino acids attached to a carrier molecule. Matrixyl is used to reduce wrinkles by increasing collagen formation and reducing degradation of collagen matrix. Because these amino acids are the parts of skin collagen so it acts as feedback inhibitors to collagen degradation.

Yes and no. Collagen will dissolve in water, but only at the right pH. At physiological pH (pH7.4) collagen is a stable structural protein which forms the scaffolding for skin and connective tissue in a body that is mostly water. What helps collagen stay stable in the body is also that it is crosslinked with glucosaminoglycans such as chondroitin or hyaluronic acid. Collagen can also be crosslinked in a lab with heat in the absence of water or with chemicals such as carbidiimide or glutaraldehyde. Collagen should start dissolving under pH5.

Generally, collagen type of skin is type I collagen

Collagen fibers are made up of many collagen fibrils (smaller individual unit)

what is collagen secreted by