Bioresorbable Polymers for Biomedical Applications

From Fundamentals to Translational Medicine

Giuseppe Perale, Jöns Hilborn

• Publisher: Woodhead Publishing
• Year: 2016
• ISBN:
  9780081002667
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Bioresorbable Polymers for Biomedical Applications: From Fundamentals to Translational Medicine provides readers with an overview of bioresorbable polymeric materials in the biomedical field. A useful resource for materials scientists in industry and academia, offering information on the fundamentals and considerations, synthesis and processing, and the clinical and R and D applications of bioresorbable polymers for biomedical applications.

• Focuses on biomedical applications of bioresorbable polymers
• Features a comprehensive range of topics including fundamentals, synthesis, processing, and applications
• Provides balanced coverage of the field with contributions from academia and industry
• Includes clinical and R and D applications of bioresorbable polymers for biomedical applications

Part One

Fundamentals and considerations of bioresorbable polymers for biomedical applications

Outline

1. Introduction to bioresorbable polymers for biomedical applications

2. Natural polymers: a source of inspiration

3. Bioresorbability of polymers: chemistry, mechanisms, and modeling

4. The innate immune response: a key factor in biocompatibility

5. Form and function of resorbable materials–based medical devices

6. Quality management and safety of bioresorbable polymers for biomedical applications

7. Bringing bioresorbable polymers to market

1

Introduction to bioresorbable polymers for biomedical applications

G. Pertici University of Applied Sciences and Arts of Southern Switzerland, SUPSI, Manno, Switzerland Industrie Biomediche Insubri SA, Mezzovico-Vira, Switzerland

Abstract

The processing techniques of consolidated bioresorbable polymers are discussed. Because of their delicate molecular structures, these materials must be handled with care, especially regarding their degradation behavior and hydrophilicity. Moreover, a review is reported of the main types of bioresorbable materials used in medical applications such as drug delivery and orthopedic surgery. The bioresorbable materials discussed include aliphatic polyesters, natural polymers, polyanhydrides, poly(ortho esters), polyphosphazenes, poly(amino acids) and “pseudo”-poly(amino acids), polyalkylcyanoacrylates, poly(propylene fumarate), poly(ester-ether), and poly(vinyl alcohol).

Keywords

Aliphatic polyesters; Bioresorbable polymers; Degradation; Natural polymers

1.1. General concepts

The bioresorbable polymers in medicine represent a diverse family within the field of biomaterials. To understand properly all the science behind these attractive materials, it is necessary to start with general definitions.

The term biomaterial was articulated in 1982 at the NIH Consensus Development Conference (Galletti and Boretos 1983) on the Clinical Application of Biomaterials as follows: “any substances, other than a drug, or combination of substances, synthetic or natural in origin, which can be used for any period of time, as a whole or a part of a system, which treats, augments or replaces any tissue, organ or function of the body”.

Other definitions have been described in the William Dictionary of Biomaterials (1999) and include “non-viable material used in a medical device, intended to interact with biological systems” (ESB Consensus Conference I); “material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body” (ESB Consensus Conference II); “synthetic, natural, modified natural material intended to be in contact and interact with the biological system” (ISO, 1988); and “any substance (other than a drug), synthetic or natural, that can be used as a system or part of a system that treats, augments, or replaces a tissue, organ or function of the body” (Dorland's Medical Dictionary).

Materials used in biomedical applications are in contact with the body and must therefore satisfy specific requirements: they must be nontoxic, biocompatible, and suitable for the specific application, which may require them to have adequate biomechanical properties and physical structure. The first-generation biomaterials were designed initially to achieve adequate mechanical strength and a relative state of “bioinertness.” However, it is impossible to achieve total inertness; therefore, second-generation materials are still being developed. These materials are being designed specifically to evoke surface-specific reactions or responses from the biomaterials and particular cells within the body.

The most commonly materials used in clinical applications are natural and modified natural materials, but also metals, ceramics, synthetic polymers, and composites.

Due to their mechanical properties of toughness, high strength, and ductility, metals and their alloys are used for implants in dental and orthopedic applications. However, metallic implants may cause problems (eg, irritation caused by corrosion and erosion in the biological environment, second fracture of the operated bone caused by stress shielding, aseptic loosening of the implant) severe enough to lead to a second operation to remove the device.

Due to their chemical nature, ceramics and glasses (bioactive and nonbioactive) have been used in several biomedical applications, in particular for bone replacement, but their brittleness makes them unsuitable for load-bearing applications.

Compared to ceramics, glasses, and metals, polymers are relatively weak and ductile, but because of their versatility, ease of processing, and biocompatibility, many natural and synthetic polymers are widely and successfully used for replacement, support, augmentation, or fixation of living tissues.

To achieve specific properties not possessed by single-phase materials, it is possible to design composites combining polymers, ceramics, and metals to obtain tailor-made devices for applications in various biomedical fields. In particular, synthetic polymeric composites are very attractive biomaterials because of their similarities with most of the structural living tissues, composed of macromolecular composites.

According to their function in the biological environment, biomaterials can also be classified as biostable, bioabsorbable, and bioactive, and they can have applications in tissue engineering systems.

The biostable materials such as metals, ceramics, glasses, polymers, and stable composites are intended to stay in a body for the patient's lifetime and function appropriately. They should be physiologically inert, cause only minimal response of the surrounding tissues, and retain their properties for years in vivo. Biostable materials have wide application in permanent prostheses such as joint prostheses, sutures, and other implants.

Usually, tissues have sufficient healing or regeneration capacity and need only the temporary presence of a biomaterial to support, augment, or replace tissues or to guide their regrowth. For example, bioabsorbable (biodegradable or resorbable) polymeric materials are adsorbed by the body and then disappear when, after healing, the device is no longer needed (Törmälä et al., 1986). Biodegradable polymers are applicable to those medical devices in which tissue repair or remodeling is the goal (eg, artificial skin, cartilage repair, peripheral nerve repair), but not where long-term material stability is required (eg, artificial heart, kidney, liver). Other typical products for this kind of biomaterial are absorbable sutures, bone fracture fixation devices, and tendon or ligament fixation tacks.

Biologically active (bioactive) materials that are...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• Dedication
• List of contributors
• Woodhead Publishing Series in Biomaterials
• Foreword
• Part One. Fundamentals and considerations of bioresorbable polymers for biomedical applications
• Part Two. Synthesis and processing of bioresorbable polymeric materials for medical applications
• Part Three. Clinical and research and development (R&D) applications of bioresorbable polymers
• Conclusions
• Index