Peptides and Proteins as Biomaterials for Tissue Regeneration and Repair

Mario Barbosa, M Cristina L Martins

• Publisher: Woodhead Publishing
• Year: 2017
• Print ISBN: 9780081008034
• eBook ISBN: 9780081008522
• Topic: Technology & Engineering
• Subtopic: Biomedical Science
• Index: Technology & Engineering

Peptides and Proteins as Biomaterials for Tissue Regeneration and Repair highlights the various important considerations that go into biomaterial development, both in terms of fundamentals and applications.After covering a general introduction to protein and cell interactions with biomaterials, the book discusses proteins in biomaterials that mimic the extracellular matrix (ECM). The properties, fabrication and application of peptide biomaterials and protein-based biomaterials are discussed in addition to in vivo and in vitro studies.This book is a valuable resource for researchers, scientists and advanced students interested in biomaterials science, chemistry, molecular biology and nanotechnology.- Presents an all-inclusive and authoritative coverage of the important role which protein and peptides play as biomaterials for tissue regeneration- Explores protein and peptides from the fundamentals, to processing and applications- Written by an international group of leading biomaterials researchers

1

Fundamentals of protein and cell interactions in biomaterials

H.P. Felgueiras*; J.C. Antunes^†; M.C.L. Martins*; M.A. Barbosa* ^* i3S—Instituto de Investigação e Inovação em Saúde, University of Porto, Porto, Portugal
^† INSERM, U1148, Cardiovascular Bioengineering, X Bichat Hospital, Paris, France

Abstract

Protein adsorption is the first process that occurs after implantation of a biomaterial in the human body. This process changes the properties of the surface and can induce structural alterations on the adsorbed/desorbed proteins. Cell-biomaterial interactions are mediated by the type and conformation of the adsorbed proteins that can interact with specific integrins expressed by the cells. These phenomena can be strongly influenced by adsorption of water molecules, a process that is dependent on the surface composition of the biomaterial. In this chapter, fundamentals of protein adsorption, protein conformation, and techniques for protein adsorption quantification will be described. The importance of the adsorbed protein layer on cell adhesion, activation, and wound healing responses will also be discussed.

Keywords

Protein adsorption; Protein quantification; Cell interactions; Biomaterials; Interfaces

1.1 Fundamentals of protein adsorption on biomaterials

The interaction of an implantable biomaterial with the living tissue is a very sensitive phenomenon that in a very short period of time triggers a cascade of events that culminate with cell attachment (Fig. 1.1).

Fig. 1.1 Biomaterial interaction with the living system and correspondent intermediary biochemical and biophysical phenomena. From Sridharan R, Cameron AR, Kelly DJ, Kearney CJ, O'Brien FJ. Biomaterial based modulation of macrophage polarization: a review and suggested design principles. Mater Today 2015;18(6):313–325.

An interface is formed between two different phases solid (biomaterial) and liquid (the surrounding biological environment, i.e., blood) and usually displays high energy that can only be stabilized by the adsorption of ions, molecules and/or macromolecules from the medium, such as proteins. Water molecules bind to the biomaterial initiating a layer that allow proteins to adsorb, modifying their structure and function according to the biomaterials’ outermost layer properties, coat the substrate and promotes interaction with cells. This might appear a simple mechanism but the implications to cells response is enormous, being at the basis of our current interpretation of the interaction of biomaterials with cells and tissues [1–4].

1.1.1 Basics of protein adsorption

One of the first events taking place at the interface tissue-biomaterial is the adsorption of proteins from body fluids. Evidently, water molecules, low molecular weight solutes, and ions adsorb first; still protein adsorption remains the most important. Due to rich, competitive and complex nature, these biological macromolecules have the ability to radically alter the interface, thereby being critical for the host response. Even in the simplest case where a single, well-defined protein adsorbs to a uniform and well-characterized surface, a substantial number of processes is usually involved [5–8].

Proteins are large complex amphipathic molecules composed of amino acids that contain combinations of hydrophobic, hydrophilic, polar, and apolar regions exposed to the environment by a three-dimensional structure [9,10]. These regions grant the protein a “surface active” character allowing it to interact with various biomaterials. The surrounding environment and the biomaterials’ surface properties induce changes in the proteins behavior during adsorption, particularly in their conformation. Van der Waals forces, Lewis acid-base forces, and hydrophobic interactions are some of the many intermolecular events that affect the intrinsic structural stability of the proteins. As proteins are the primary elements to be recognized by cells, response of the latter to the implantable biomaterial is believed to be a consequence of the interfacial protein layer [6,7,11].

1.1.1.1 Function and structural organization

The understanding of protein adsorption requires familiarity with the concepts of protein function and structure. Proteins are high molecular weight macromolecules resultant from the co-polymerization of up to 20 different amino acids (8 have apolar side chains, 7 have polar, and 5 have charged polar). As general rule, a chain of amino acids is only recognized as a protein if superior to 40 units, otherwise it is identified as a peptide. In the human body there are nearly 10⁵ different proteins, each one with a specific role. Proteins are involved in practically all biological processes, managing the transport and storage of vital substances, providing mechanical support and protection, acting as catalysts of biochemical reactions, etc. Thus, in order to accommodate their functions, proteins fold into one or more spatial conformations driven by different noncovalent interactions. Their specificity is therefore determined by the acquired structure and chemical composition [6,7,12].

There are four levels of protein structure: primary, secondary, tertiary, and quaternary (Fig. 1.2). The primary structure refers to the amino acid organization as a linear sequence. The unique and specific amino acid organization is particular to each protein and is held together by covalent bonds (peptide bonds). Hydrogen interactions are then created between amino acids from different positions along the protein chain, causing them to bend and fold, resulting in various secondary structures (i.e., α-helix or β-pleated sheet). A three-dimensional conformation is then created but only reaches full potential by means of intramolecular associations [4,6,14]. Ionic interactions, hydrophobic-hydrophilic interactions, hydrogen bonding, salt bridges, and covalent disulfide bonds are the most common associations observed in tertiary structures. Quaternary structure refers to the regular association of two or more polypeptide chains, in different structure levels, to form a complex. A multisubunit protein is then generated is stabilized mainly by weak interactions between residues exposed by polypeptides within the complex [12–15].

Fig. 1.2 Representation of the four levels of the proteins' structure [13].

1.1.1.2 Structure and orientation of adsorbed proteins

The structure of proteins when adsorbed onto a biomedical surface is difficult to identify and even more difficult to predict. The majority of proteins adsorb as monolayers, generating close-packed formations of mass density of 1–5 mg/m². However, this range cannot be assumed as absolute. It all depends on the protein molecular orientation, conformational state and biomaterials surface properties [12,16–18], namely surface chemical composition, electrical charge, topography, hydrophobicity and mechanical properties [19–21]. Multilayer adsorption is not common but may also occur, particularly in highly concentrated protein solutions [12,16–18].

Norde [12], by studying the adsorption of different types of proteins at solid-liquid interfaces, stated that we cannot assume a definitive structure of a protein on a substrate but only infer about its most likely adsorption orientation. Since proteins are typically asymmetric and only in exceptional cases exhibit a spherical shape (generally, proteins present elliptical, rod-like or heart-like shapes), when adsorbed they adopt a certain orientation that determines which side of the molecule interacts with the material and which side stays in contact with the solution. The local amino acid composition of specific regions of a protein determines its affinity to the surface. Usually, the proteins structure is subdivided into four domains: hydrophobic, hydrophilic, positively and negatively charged, which are exposed to the surface accordingly to their character (Fig. 1.3) [16,17,22,23].

Fig. 1.3 Schematic representation of proteins domains and respective interactions with surfaces of different nature: hydrophilic, hydrophobic, positively charged and negatively charged [22].

Structurally stable proteins can admit two types of orientation: the “side-on,” with the short axis of an elliptically shaped molecule being perpendicular to the surface, or the “end-on,” where the long axis is the perpendicular one. Inevitably, the “end-on” orientation results in a more saturated monolayer than the “side-on” orientation [23]. As a rule, larger proteins possess more binding sites. In consequence, their potential to adsorption increases and its orientation is even harder to predict. In these cases, the unfolding properties of the proteins, as well as their stability, play a major role in the adsorption process. Regardless of the protein original structural rearrangement, its unfolding, can lead to increased active site exposure for protein surface contacts [17,22,24].

1.1.2 Interactions with the surface: hydrophobic and electrostatic bonding

Proteins adsorb ont...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• 1: Fundamentals of protein and cell interactions in biomaterials
• 2: Extracellular matrix constitution and function for tissue regeneration and repair
• 3: Surface functionalization of biomaterials for bone tissue regeneration and repair
• 4: Bioengineered peptide-functionalized hydrogels for tissue regeneration and repair
• 5: Collagen-based biomaterials for tissue regeneration and repair
• 6: Fibrin biomaterials for tissue regeneration and repair
• 7: Fibrous protein-based biomaterials (silk, keratin, elastin, and resilin proteins) for tissue regeneration and repair
• 8: Fabrication of nanofibers and nanotubes for tissue regeneration and repair
• 9: Peptide and protein printing for tissue regeneration and repair
• 10: Self-assembling peptides and their application in tissue engineering and regenerative medicine
• 11: Collagen-like materials for tissue regeneration and repair
• 12: Elastin-like materials for tissue regeneration and repair
• 13: Antimicrobial peptides (AMP) biomaterial coatings for tissue repair
• 14: Antimicrobial peptides as hydrogels for tissue regeneration and repair
• Index