Biointerfaces: Where Material Meets Biology: Volume 10 (Smart Materials Series) - Hardcover

Hardcover

ISBN 10: 1849738769 ISBN 13: 9781849738767

Publisher: Royal Society of Chemistry, 2014

Synopsis

An up to date overview of the knowledge and methods used to control living organism responses to implantable devices.

About this title

About the Author

Dr Chrzanowski has over 12 years in the area of biomaterials with over 50 papers, 2 books (monographs). He graduated from the Silesian University of Technology, where he also obtained my PhD. After receiving a prestigious fellowship I moved to University College London to work in Biomaterials and Tissue Engineering laboratory and develop novel osteogenic materials. In 2008 he moved to the University of Glasgow where I joined large EU consortium providing his expertise in the synthesis of materials for orthopaedic applications. In 2010 he moved to the University of Sydney where I established my laboratory working currently with six PhD students.

From the Back Cover

In order to design and develop new biomaterials it is essential to understand the biointerface, the interconnection between a synthetic or natural material and tissue, microorganism, cell, virus or biomolecule.

Biointerfaces: Where Material Meets Biology provides an up to date overview of the knowledge and methods used to control living organism responses to implantable devices. The book starts with an introduction to the biointerface - past, present and the future perspectives and covers the key areas of biomolecular interface for cell modulation, topographical biointerface, mechano structural biointerafce, chemo-structural biointerfaces and interface that control bacteria responses. By combining the cellular, antimicrobial, antibacterial and therapeutic aspects of the interface with the methodology of fabrication and testing of the synthetic biomaterials used in a variety of medical applications the text provides a handbook for researchers.

Edited by leading researchers, the book integrates the understanding of cell, microorganism and biomolecule interactions with surfaces and the methods used for assessment which will appeal to materials scientists, chemists, biotechnologists, (molecular-) biologists, biomedical engineers interested in the fundamentals and applications of biomaterials and biointerfaces.

Excerpt. © Reprinted by permission. All rights reserved.

Biointerfaces

Where Material Meets Biology

By Dietmar Hutmacher, Wojciech Chrzanowski

The Royal Society of Chemistry

Copyright © 2015 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84973-876-7

Contents

Section A Biomolecular Interfaces for Cell Modulations, 
Chapter 1 Protein-based Biointerfaces to Control Stem Cell Differentiation Jorge Alfredo Uquillas Paredes, Alessandro Polini and Wojciech Chrzanowski, 3, 
Chapter 2 Additive Manufacturing and Surface Modification of Biomaterials using Self-assembled Monolayers Jayasheelan Vaithilingam, Ruth D. Goodridge, Steven D. R. Christie, Steve Edmondson and Richard J. M. Hague, 30, 
Chapter 3 Probing Biointerfaces: Electrokinetics Ralf Zimmermann, Jérôme F. L. Duval and Carsten Werner, 55, 
Chapter 4 Growth Factor Delivery Systems for the Treatment of Cardiovascular Diseases Natalia Zapata, Elisa Garbayo, Maria J. Blanco-Prieto and Felipe Prosper, 74, 
Section B Structural Biointerfaces, 
Chapter 5 Titanium Phosphate Glass Microspheres as Microcarriers for In VitroBone Cell Tissue Engineering Nilay J. Lakhkar, Carlotta Peticone, David De Silva-Thompson, Ivan B. Wall, Vehid Salih and Jonathan C. Knowles, 105, 
Chapter 6 Biointerfaces Between Cells and Substrates in Three Dimensions Adam S. Hayward, Neil R. Cameron and Stefan A. Przyborski, 133, 
Section C Multi-functional Biointerfaces, 
Chapter 7 Interfaces in Composite Materials Ensanya A. Abou Neel, Wojciech Chrzanowski and Anne M. Young, 153, 
Chapter 8 Bioactive Conducting Polymers for Optimising the Neural Interface Josef Goding, Rylie Green, Penny Martens and Laura Poole-Warren, 192, 
Chapter 9 Polycaprolactone-based Scaffolds Fabricated Using Fused Deposition Modelling or Melt Extrusion Techniques for Bone Tissue Engineering Patrina S. P. Poh, Michal Bartnikowski, Travis J. Klein, Giles T. S. Kirby and Maria A. Woodruff, 221, 
Section D Chemo-structural Biointerfaces, 
Chapter 10 High Throughput Techniques for the Investigation of Cell–Material Interactions Lauren R. Clements, Helmut Thissen and Nicolas H. Voelcker, 259, 
Chapter 11 Grafting of Functional Monomers on Biomaterials Lisbeth Grøndahl and Jing Zhong Luk, 312, 
Chapter 12 Design of Mobile Supramolecular Biointerfaces for Regulation of Biological Responses Ji-Hun Seo and Nobuhiko Yui, 343, 
Section E Interfaces that Control Bacterial Responses, 
Chapter 13 Bacterial Adhesion and Interaction with Biomaterial Surfaces Li-Chong Xu and Christopher A. Siedlecki, 365, 
Chapter 14 Antimicrobial Interfaces Sabeel P. Valappil, 399, 
Subject Index, 424, 

CHAPTER 1

Protein-based Biointerfaces to Control Stem Cell Differentiation

JORGE ALFREDO UQUILLAS PAREDES, ALESSANDRO POLINI AND WOJCIECH CHRZANOWSKI

Faculty of Pharmacy, University of Sydney, Sydney, Australia

1.1 Modification of Biomaterial Surfaces with Proteins

It is already well-established that cellular responses to foreign materials when implanted in vivo are guided mainly by the surface characteristics. The modulation of characteristics such as roughness, porosity, chemical and biological composition allows the regulation of material integration within the body as well as the guidance of specific responses, e.g., cell adhesion, cell detachment, cell proliferation, differentiation, or metabolic activity. Material integration within the body is critically important for orthopedic implantable devices. Desired integration results in successful single surgery, thus reduces costs and complications related to adverse reactions and implant revisions. In this chapter, we described the methods of surface modification and functionalization, which enable the effective regulation of stem cells behavior for orthopedic applications. In particular, the chapter focuses on immobilization of different signaling molecules such as proteins, peptides, growth factors on the surface and, in three dimensions, to modulate cell adhesion and to trigger and regulate osteogenesis, osteointegration, and osteoregeneration. Furthermore, examination methods for the immobilization of biomolecules on surfaces are described in detail to explain the advantages and disadvantages of each method.

1.1.1 Introduction

Implantation of exogenous materials into the body triggers common body responses, and in some cases adverse inflammatory reactions. The body tries to ward-off the foreign object and protect from its 'perceived' negative influence on healthy cells and tissues. As a consequence the exogenous materials are encapsulated in a vascular, fibrous sacks which often limit the functionality of the implanted material. In the last decades research has been focused on the possibility of addressing this problem and creating surfaces that mimic the body's environment, thus enabling the host cells to accept and interact with the foreign object. Such interactions are facilitated by different cues incorporated into the surface, which includes topographical, mechanical, structural, chemical and biochemical signals. These are capable of stimulating specific cellular responses which include cell adhesion, proliferation, differentiation and, ultimately, cell death. The design of specific cues, single or combined, is guided by the application and tailored for specific needs.

Historically, one of the most successful approaches, which can be called biomimetic, was a deposition of hydroxyapatite coatings on the surface of implants that were placed within the bone environment. Hydroxyapatite, a natural component of bone tissues, when present on surfaces of metallic or polymeric devices allows for significant improvement of implant integration within the body. The most significant limitation is the adhesion of the coating to the substrate. It has to be noted that some of the implants are heavily bent (pre-operatively) and 'hammered' into the host tissue. This creates significant sheer and bending stresses that can lead to failure of the coating. Nevertheless, hydroxyapatite coatings have been clinically used and verified.

The cross-talk between a bioactive layer and the tissue can similarly be achieved using different types of mineral, ceramic, glass–ceramic materials that include tri-calcium phosphate, bioglasses and phosphate glasses. These materials are coated onto the surface or are used as a base component to produce implants. The primary advantage of these materials is that they can be degradable and compounded with different ions (Zn, Ag, Co, Sr), which provides additional biochemical cues for cells at the interface. Zn, Co and Ag have been reported to have antimicrobial activity, while Sr and Zn have been demonstrated to support bone formation and are used clinically in the treatment of osteoporosis. Furthermore, each of these materials interacts with body fluids differently and can guide the adsorption of proteins and growth factors and other components from the body fluids and blood. Subsequently, these biomolecules modulate interactions with cells and tissues. Hence, by a careful selection of the material it is possible to stimulate cellular responses through the structural and chemical composition, and also to guide the adsorption of desired biomolecules that stimulates biological responses, e.g., adsorption of cell adhesive proteins to hydroxyapatite.

1.1.2 Influence of Modified Surfaces on Cell Adhesion

The communication of cells with surfaces is mediated by pre-adsorbed protein layers. The composition of this layer is critical to obtain specific responses such as cell adhesion/repulsion, or differentiation. It is well established that specific proteins, peptides, growth factors and drugs can stimulate cells. These biomolecules are used to enhance the implant integration and also treat some dysfunction/diseases when released from the surface. The most common approach to enhance cell adhesion to the surface of implantable materials using biomolecules is to incorporate the cell binding motif Arg-Gly-Asp (RGD). RGD, together with the integrins that serve as receptors for them, constitute a primary recognition system for cell adhesion. The RGD sequence is the cell attachment site of many adhesive extracellular matrix, blood, and cell surface proteins, and nearly half of the over 20 known integrins recognize this sequence in their adhesion protein ligands. The integrin-binding activity of adhesion proteins can be achieved by engineering short synthetic peptides that contain the RGD sequence. Interestingly, it was reported that such peptides promote cell adhesion when immobilized onto a surface, and inhibit it when presented to cells in solution. Importantly, integrin-mediated cell attachment regulates further cell migration, growth, differentiation, and apoptosis. The ability to target cell adhesion receptors, which are responsible not only for cell–matrix adhesion but also for signaling bidirectionally across the cell membrane, provides an opportunity to design new drugs (Figure 1.1). Because integrins are involved in many biological processes such as angiogenesis, thrombosis, inflammation, osteoporosis and cancer, these drugs, which are based on the RGD structure, can be used for the treatment of diseases such as thrombosis, osteoporosis and cancer (Figure 1.1).

It is well established that tethering of protein and peptides facilitates communication with the cell. In fact, adhesion of cells is a prerequisite for the subsequent proliferation and differentiation of cells. Recent studies by Webster demonstrated that adsorbed proteins including fibronectin, laminin and vitronectin play an important role in limiting bacteria colonization. Hence fibronectin-functionalized surfaces can be considered as multi-functional with a dual purpose: preventing bacteria adhesion and enhancing cell adhesion.

While fibronectin and vitronectin receive the most attention to enhance cell adhesion to surfaces of biomaterials, there are several types of proteins and peptides that have been attempted to use for the same purpose. The use of fibronectin and vitronectin is primarily dictated by their composition, in which the RGD sequence plays a critical role. RDG is recognized and bind via integrins (α5β1, αvβ1, αvβ3, αvβ5, αvβ6, αvβ8, and αIIbβ3) cell adhesion receptors that bind to the extracellular matrix (ECM) proteins. It has been demonstrated that laminins and collagens also contain RGD sequences but these are inaccessible, thus are not typically used for surface modifications.

Many integrins are expressed in various tissues; however there is some population which are expressed only in a certain type of cell or tissues. The integrin receptors, which were found in human osteoblasts and are typically used to regulate bone cell responses, are the fibronectin receptor (α5β1), vitronectin receptor (αvβ3), and the type I collagen receptor (α2β1). For this reason modification — functionalization — of implant surfaces with biomolecules/protein to mediated cell adhesion to substrates via integrins has recently become one of the most interesting approaches in the development of new biomaterials including drug carriers that are capable of targeting specific sides.

It has been already suggested that the RGD peptide, which interacts with the αvβ3 and αvβ5 integrin sub-units, commonly associated with vitronectin, increases biointegration of implants. Matsuura also demonstrated that RGD contributes to the osteoconductive effect of hydroxyapatite more than titanium. This phenomenon is associated with higher affinity and adsorption capability of protein to hydroxyapatite surface than to titanium surface.

The positive effects of the RGD peptide on regulation of cell adhesion have been confirmed in many in vitro as well as in vivo studies. Elmengaard has shown that RGD peptide-coated porous-coated titanium implant significantly increased bone formation on and around the implant. In this study a cyclic RGD (Figure 1.2), which interacts with both αvβ3 and αvβ5 integrin sub-units has been immobilized on unloaded press-fit titanium implants. Not only was the increase in bone formation observed, but also a significant reduction in presence of fibrous tissue around the implant was evidenced. Because the RGD coating can be relatively easily applied to the surface it offers a cost-effective way to enhance the early osseo-integration of press-fitted clinical implants.

One of the interesting features of this approach was the use of cyclic peptide. Cells typically show higher integrin binding affinity to the cyclic RGD sequence and previous studies have shown that cyclic peptides are more stable when immobilized to complex and three-dimensional substrates. Another important feature of cyclic RGD peptides is their high selectiveness toward the αv integrin, which regulates activation of the osteoblast-specific transcription factor (core binding factor alpha-1/runt related transcription factor 2 during osteogenesis). These peptides show also more resistance to enzymatic cleavage, and may also promote a more stable cell–ligand bond. The integrin affinity and specificity to the RGD peptide is affected by both steric conformation and the amino-acid sequences flanking the RGD peptide. Mooney has also demonstrated that a linear RGD peptide promoted osteogenic differentiation of pre-osteoblasts (MC3T3-E1) but did not induce differentiation of hBMSCs or D1 stem cells. At the same time matrices that presented the higher-affinity cyclic form of this adhesion ligand enhanced osteoprogenitor differentiation in three dimensions.

In vivo studies by Elmengaard on press-fit titanium alloy implants coated with cyclic RGD and its effect on bone ongrowth showed that after 4 weeks, cyclic RGD coating significantly stimulated bone formation directly at the interface. A two-fold increase in bone growth was found for RGD-coated implants compared to the uncoated. Importantly, RGD-coated implants showed less fibrous tissue around the implant, which is considered very positive. However, a significantly higher amount of bone for RGD coated implants was observed mostly at the interface (0–100 µm), and the difference in bone volume between both coated and uncoated groups gradually decreased with distance from the surface. There were no significant differences between both groups at a distance of 750 µm from the implant surface. Furthermore, an increase in the mechanical fixation was also observed; apparent shear stiffness was significantly higher for RGD-coated implants. A similar study on the osteoconductive hydroxyapatite coating with titanium alloy implants using the same press-fit implant model showed only a significant increase in bone ongrowth but no difference in mechanical fixation.

To immobilize RGD on amino-functionalized glass surfaces Dechantsreiter et al. suggested the use of isothiocyanate-terminated peptides. It was demonstrated that RGD peptides were fused to an isothiocyanate anchor during synthesis and bound to amino-terminated surfaces. Importantly, two types of linear peptides and one cyclic peptide were investigated and were shown to enhance cell spreading and induce the formation of focal adhesions in murine fibroblasts. The authors also concluded that formed adhesions were specific because cells did not recognize the corresponding negative control peptides and did not spread in the presence of soluble H-RGDS-OH peptide. This coupling method was shown to be effective also for patterning, where cells selectively recognized areas coated with RGD-containing peptides.

Better integration and deposition of the bone on the surface is directly linked to pullout strength of the implants. O'Toole suggested the use of bone sialoproteins (BSPs) to improve the pullout strength. In his approach two scenarios were considered: (1) BSPs were coated on the surface and (2) BSPs were not placed directly on the surface but BSP-containing gelatin was used as a plug where the implant was placed. Results failed to demonstrate the benefits of the BSP. In general, BSP-coated acid-etched implants perform more poorly, mechanically, than do uncoated implants. It was concluded that BSP forms an insulating barrier on the implant surface, preventing the direct apposition of the bone on the implants. At the same time, histology tests showed that the BSP coating failed at the BSP–implant interface but osteoinductive behaviors were confirmed at the BSP–bone interface. It was postulated that a better method of coating is required to allow the formation of bone at the interface with the implant. Similar results were found for the second group where BSP-containing gelatin was used. These implants performed poorly both histologically and mechanically. Histologically, osteoid, osteoblasts and osteocytes are stimulated by the presence of BSP, but it was not observed at the surface. This distant osteoinduction does not correspond with better mechanical performances when implants are subjected to pull-out testing analysis.

With respect to proteins, peptides benefit from a lower immunogenic activity as well as from the ability to be synthesized and handled. In addition, over the last decade, highly active and αvβ3,- and αvβ5-integrin selective cyclic pentapeptide ligands such as cyclo(-RGDfX) have been developed. It was thus demonstrated that in addition to the RGD binding sequence a D-amino acid, especially D-Phe following the Asp residue in the cycle, is essential for high activities and αv selectivity. Cyclic pentapeptides with D-amino acid in other positions and/or a non-hydrophobic amino acid following Asp as well as linear peptides have lower activity and are less selective towards αv integrins. Our results clarify that osteoprogenitor cells exhibit a differential binding to RGD peptides displaying a specific conformation (linear RGDC and cyclo-DfKRG). Such a behavior has to be related to the different signal transduction pathways implied by both peptides. Indeed, some of us have shown that linear GRGDSPC peptide interacts preferentially with αxβ1 integrins while cyclo-DfKRG peptide interacts with αvβ3 and αvβ5 integrins. Consequently, different cell adhesion at 24 h seeding may be linked to the different cellular activity, as extracellular proteins synthesis, implied by the signal transduction pathways that both RGD-containing peptides induce, respectively. In addition, cell adhesion behavior has to be related to the accessibility of integrins receptors by peptides displaying conformation. However, both cyclo-DfKRG and linear RGDC appear to be good candidates for developing hybrid biomaterials made of titanium alloys and human osteogenic cells.

(Continues...)

Excerpted from Biointerfaces by Dietmar Hutmacher, Wojciech Chrzanowski. Copyright © 2015 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2014
• Language: English
• ISBN 10: 1849738769
• ISBN 13: 9781849738767
• Binding: Hardcover
• Number of pages: 469
• Editor: Dietmar Hutmacher