Biointegration of Medical Implant Materials

Chandra P. Sharma

• Publisher: Woodhead Publishing
• Year: 2019
• eBook ISBN: 9780081026816
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Biotechnology in Medicine
• Index: Technology & Engineering

Biointegration of Medical Implant Materials, Second Edition, provides a unique and comprehensive review of recent techniques and research into material and tissue interaction and integration. New sections discuss soft tissue integration, with chapters on the biocompatibility of engineered stem cells, corneal tissue engineering, and vascular grafts. Other sections review tissue regeneration, inorganic nanoparticles for targeted drug delivery, alginate based drug delivery devices, and design considerations, with coverage of the biocompatibility of materials and their relevance to drug delivery and tissue engineering. With its distinguished editor and team of international contributors, this book is ideal for medical materials scientists and engineers in industry and academia.- Provides a unique and comprehensive review of recent techniques and research into material and tissue interaction and integration- Discusses soft tissue biointegration, with chapters on the biocompatibility of engineered stem cells, corneal tissue engineering, vascular grafts and replacement materials for facial reconstruction- Includes new information on a variety of tissue regeneration techniques and applications

1

Biointegration

an introduction

Sunita Prem Victor, C.K.S. Pillai, and Chandra P. Sharma Sree Chitra Tirunal Institute for Medical Sciences and Technology, Thiruvananthapuram, Kerala, India

Abstract

This introductory chapter discusses the relevance of the basic aim of the book, reflecting on the importance of the interfacial concepts related to the biointegration of the implants with respect to their design and structure–function relationship. Various examples, including orthopedic implants, are discussed.

Keywords

Biointegration; Biomaterials; Design; Interface; Medical implants

1. 1.1 Introduction
2. 1.2 Biointegration of biomaterials for orthopedics
3. 1.3 Biointegration of biomaterials for dental applications
4. 1.4 AlphaCor artificial corneal experience
5. 1.5 Biointegration and functionality of tissue engineering devices
6. 1.6 Percutaneous devices
7. 1.7 Future trends
8. References

1.1. Introduction

Biointegration has been defined as an interconnection between a biomaterial and the recipient tissue at the microscopic level. This implant-to-tissue interface could be a distinct boundary or a zone of interaction between the corresponding biomaterial and tissue. So when biomaterials are designed, a set of properties are built in such a way as to ensure that, after implantation, they will assist the body to heal itself. Thus, it is of critical importance that these materials are integrated into organ-specific repair mechanisms such as the physiologic process required for the biologization of implants (Amling et al., 2006). It should further involve a direct structural and functionally stable connection between the living part and the surface of an implant. Although various materials have been developed in recent years with enhanced physical, surface, and mechanical properties, the use of these materials in certain biological applications is often limited by minimal tissue integration. The rate of implant failures and economic impacts are slowly being documented (Carr et al., 2012; Zhang et al., 2011). This takes us back to the query on how biomaterials could be converted to “living tissues” after implantation. Biomaterials are defined as “materials intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ, or function of the body” (Williams, 1999). To cite an example, the bonding of hydroxyapatite (HA) to bone, which is considered as a true case of biointegration, is thought to involve a direct biochemical bond of the bone to the surface of an implant at the electron microscopic level and is independent of any mechanical interlocking mechanism (Cochran, 1996; Meffert et al., 1987). To this end, several groups working on various aspects of the design, development, and application of improved devices are concerned with how the physical, chemical, and biological properties of materials can be tuned to integrate with soft and hard tissues in the human body (Kim et al., 2013; Yu et al., 2013; Patel et al., 2010).

1.2. Biointegration of biomaterials for orthopedics

The biological interface between an orthopedic implant and the host tissue results from a direct, structural, and functional connection between ordered, living bone and the surface of a load-carrying implant (Branemark et al., 1985). Desired effects include osteoinduction, vascularization, and osseointegration, leading to augmented mechanical stability (Svensson et al., 2013; Jain and Kapoor, 2015). Orthopedic research is developing and advancing at a rapid pace as latest techniques are being applied in the repair of musculoskeletal tissues (Jain and Kapoor, 2015). The discovery of biological solutions to important problems, such as fracture-healing, soft tissue repair, osteoporosis, and osteoarthritis, continues to be an important research focus. In orthopedic applications, there is a significant need and demand for the development of bone substitutes that are bioactive and exhibit material properties (mechanical and surface) comparable with those of natural, healthy bone. Conventional biomaterials including ceramics, polymers, metals, and composites have limitations involving suitable cellular responses resulting in diminished osteointegration (Balasundaram and Webster, 2006; Barrere et al., 2008). Numerous strategies are now being envisaged to prevent potential drawbacks such as inflammation, infection, and fibrous encapsulation resulting in implant loosening with deleterious clinical effects (Hacking et al., 2000). For instance, the surfaces of orthopedic implants have dramatically evolved from solid to porous structures in an effort to increase vascularization and promote optimal and unparalleled biological fixation (www.azom, 2004; http://academic.uprm.edu).

Several metallic materials based on titanium, tantalum, cobalt, stainless steel, and magnesium have been widely used for orthopedic applications (Dabrowski et al., 2010; Jafari et al., 2010; Babis and Mavrogenis, 2014). Of these, titanium-based materials in particular are considered for load-bearing applications, which include pin structure, and the fabrication of plates and femoral stems. Titanium's ability to integrate with bone has been known for quarter of a century, and it forms the basis of orthopedic research and implant technology today (Meneghini et al., 2010). These titanium implant surfaces are subjected to various surface treatments and are designed to exhibit varying roughness to promote osseointegration between the implant and host tissue (Barbas et al., 2012). Roughness was evaluated by measuring root mean square (RMS) values and RMS/average height ratio, in different dimensional ranges, varying from 100 microns square to a few hundreds of nanometers. The results showed that titanium presented a lower roughness than the other materials analyzed, frequently reaching statistical significance (Covani et al., 2007). In particular, this study focuses attention on AP40 and especially RKKP, which proved to have a significant higher roughness at low dimensional ranges. This determines a large increase in surface area, which is strongly connected with osteoblast adhesion and growth in addition to protein adsorption. In addition, roughened titanium surfaces augment focal contacts for cellular adherence and in turn enhance cytoskeletal assembly and membrane receptor organization (Wall et al., 2009; Borsari et al., 2005; Stevens and George, 2005).

One should mention here the famous osseointegration concept evolved by Per Ingvar Brånemark, closely coupled with the design of a cylindrical titanium screw (Albrektsson et al., 1981; Branemark et al., 1985) having a specific surface treatment to enhance its bioacceptance (Adell et al., 1990). The titanium screw underwent many animal and, subsequently, human clinical trials to test the concept, design, and success rate associated with the implant. A fixture is believed to have osseointegrated if it provides a stable and apparently immobile support of prosthesis under functional loads, without pain, inflammation, or loosening. Direct bonding of orthopedic biomaterials with collagen is rarely considered; however, several noncollagenic proteins have been shown to adhere to biomaterial surfaces (Rey, 1981). According to Yazdani et al. (2018), osseointegration involves close proximity between implant and bone with no collagen or fibrous tissue, and biointegration represents a continuity of implant to bone without intervening space (Fig. 1.1).

Osseointegration of an implant is thus defined as a direct structural and functionally stable connection between living bone and the surface of an implant that is exposed to mechanical load (http://www.dental-oracle.org). This integration of the implant to bone essentially involves two processes: interlocking with bone tissue and chemical interactions with the surrounding bone constituents. The two processes in turn depend on the chemical composition and the morphology of the surface of the implant. Irradiation with laser light (Nd:YAG [λ = 1064 nm, τ = 100 ns]) is used for the surface modification of Ti-6Al-4V—which is widely used in implantation to enhance biointegration (Mirhosseini et al., 2007). Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method for generating HA films on metallic substrates to promote osteoconduction and oesteintegration; however, the as-sputtered films are usually amorphous, which can cause some serious adhesion problems when postdeposition heat treatment is necessitated. Nearly stoichiometric, highly crystalline HA films strongly bound to the substrate were obtained by an opposing radio frequency magnetron sputtering approach. HA films have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tiss...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• 1. Biointegration: an introduction
• Part One. Soft tissue biointegration
• Part Two. Tissue regeneration
• Part Three. Drug delivery
• Part Four. Design considerations
• Index