Biomaterials polypeptides/proteins

In this book, a large number of biomaterials are reported. These include polypeptides/proteins, carbohydrates, lipids/triglycerides and synthetic polymers. In addition, it is understood that many of the polymeric materials involved in all the chapters can potentially be used as biomaterials although they may not be specified as such. 

Manipulation of DNA in such a precise manner demonstrates what can be achieved when the nature of nanoscale interactions is well understood and can be controlled. As more and more becomes known about similar molecular recognition motifs in the natural world the potential to use other biomaterials as structural components will increase. Other structural biomolecules that could be targets for unnatural manipulation include collagen [8] and clathrin proteins [9], shown in Fig. 8.2. The former is a polypeptide that forms a triple helical coil in which the individual strands are left handed but the resulting supercoil is right handed. It provides structure to bone and cartilage and has many other rigidifying functions. 

A major research trend is to tailor the structure of proteins and polypeptides so they can function for a wide range of advanced material applications. In their paper, Kiick et al (5) described their work in using biosynthetic routes to produce polypeptides with non-natural amino acids that have desired conformation and side-chain placement. Montclare et al (6) described novel research on elastins where the aim is to generate new biomaterials that have the desired biological activity, optimal function in delivery of therapeutics, and more applications. 

The focus of this review is drug dehvery and tissue regeneration using natural biomaterials consisting of proteins and polymer chains of naturally occurring amino acids, or polyfamino acids) (PAAs). PAAs or polypeptides are biopolymers made from repeating units of amino acids. They differ chiefly from proteins in that they contain only one type of amino acid (monomer) and are polydisperse, whereas proteins are assemblies of various amino acids and are monodisperse [12]. In both proteins and PAAs, the amino acid side chains offer sites for attachment of various moieties that can modify the physical and biochemical... 

Figure 16 Three-dimensional cell culture constructs derived from elastin-mimetic polypeptides, (a) Photograph of a chemically cross-linked scaffold derived from an elastin-like, protein-engineered biomaterial.

Besides the naturally occurring proteins, coiled-coil protein, amphiphilic block-copolypeptide, and two-component protein are also used for constructing self-assemblies with interest to biomaterial and biomedical engineering fields [3]. Figure 6.7 depicts the self-assemblies built from these proteins or polypeptides. 

Polypeptides represent a class of molecules, which are uniquely qualified to serve as biomaterials. They imdergo self-assembly to form macroscopic stmctures and are s)mthesized from renewable resources. Chemoenzymatic synthesis, identification of new enz)nne sequences and native chemical ligation has advanced the more traditional routes of polypeptide production. Despite the successes outlined above, these techniques have been modest in their production of new biomaterials. Progress in the development of next -generation biomaterials wiU require media and protein engineering as well as combining these methods reviewed above. One of the major limitations in the chemoenz3unatic... 

The question whether silk fibroin filaments are resorbable or permanent is open to interpretation. Having a polypeptide chemical structure, silk fibroin, like any other protein, is susceptible to proteolytic degradation, and will become weaker and eventually over a period of 2 years will be totally resorbed in vzvo. However, given the definition for an absorbable suture in the United States Pharmacopeia as a material that loses most of its tensile strength within 60 days post-implantation silk can therefore be classified as a permanent biomaterial. 

Prototypical examples of engineering peptide-based biomaterials include polyamino acids, elastin-Uke polypeptides, sdk-hke proteins, coiled-coil domains. 

A. Minato, H. Ise, M. Goto, T. Akaike, Cardiac differentiation of embryonic stem cells by substrate immobilization of insulin-like growth factor binding protein 4 with elastin-like polypeptides, Biomaterials 33 (2012) 515-523. 

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