materials:
Figures, Tables and Solutions Manual.
1 Biomaterials – An Introductory Overview
1.1 Introduction
Materials have been used to treat, replace, or augment tissues and organs in the human body since antiquity but their use and degree of sophistication have increased significantly over time, particularly over the last several decades. Advances in materials science, biological sciences, physical sciences, and engineering along with an evolution in medical treatment over the last several decades have led to the creation of biomaterials with more reproducible properties, better performance, and increased functionality. These advances have resulted in a considerable increase in the range of use and the efficacy of biomaterials. Nowadays, millions of lives are being improved or saved by the use of biomaterials in fracture fixation plates, implants for total hip and knee joint replacement, dental implants and restorations, heart valves, vascular grafts and stents, contact and intraocular lenses, skin substitutes, and wound healing materials, for example (Figure 1.1).
Figure 1.1 Examples of biomaterials in use for medical and dental applications. (a) Fracture fixation plate; (b) implant for total hip replacement; (c) implant for total knee replacement; (d) dental implant; (e) heart valve; (f) vascular graft; (g) intravascular stent; (h) intraocular lens; (i) degradable suture; (j) degradable screw for fracture fixation; (k) degradable polymer microsphere for delivery of therapeutics; (l) functional skin substitute.
The applications of biomaterials are many. Table 1.1 provides a list of selected applications and the types of materials used in these applications. Many of the biomaterials used in these applications were selected from durable, chemically inert materials that were available off the shelf, and they were designed to serve, mainly, a mechanical (or physical) function. The last few decades have seen a shift in emphasis in which the biological sciences are playing a role in the design of biomaterials of significance comparable to that of materials science. Biomaterials are now no longer designed to be chemically inert or to just serve a mechanical function. Instead, advances in biological sciences are being used to design biomaterials to regenerate tissues and organs and to direct the response of specific cells and tissues. In doing so, these biomaterials stimulate the body to heal itself. An example is the creation of functional skin substitutes to treat patients with severe burns (Figure 1.1l).
Table 1.1 Key applications of synthetic materials and modified natural materials in medicinea.
Source: Modified from Ratner (2013).
| Application | Biomaterial | Number used per year worldwide (or market in US$) |
|---|---|---|
| Skeletal system | ||
| Joint replacement (hip; knee; shoulder) | Titanium; stainless steel; polyethylene | 2.5 million |
| Bone fixation plates and screws | Metals; polylactic acid | 1.5 million |
| Spine repair | Titanium; polyether ether ketone; silicon nitride | 800 000 |
| Bone cement | Polymethylmethacrylate | ($600 million) |
| Bone defect repair | Calcium phosphates | — |
| Artificial tendon or ligament | Polyester fibers | — |
| Dental implants | Titanium | ($4 billion) |
| Cardiovascular system | ||
| Blood vessel prosthesis | Dacron; expanded polyethylene | 200 000 |
| Heart valve | Dacron; carbon; metal; treated natural tissue | 400 000 |
| Pacemaker | Titanium; polyurethane | 600 000 |
| Implantable defibrillator | Titanium; polyurethane | 300 000 |
| Stents | Stainless steel; cobalt–chromium alloy; nickel–titanium alloy | 1.5 million |
| Catheters | Teflon; silicone; polyurethane | 1 billion ($20 billion) |
| Organs | ||
| Heart assist devices | Polyurethane; titanium; stainless steel | 4000 |
| Hemodialysis | Polysulfone; silicone | 1.8 million patients ($70 billion) |
| Blood oxygenator | Silicone | 1 million |
| Skin substitute | Collagen; cadaver skin; nylon; silicone | ($1 billion) |
| Ophthalmologic | ||
| Contact lens | Acrylate, methacrylate and silicone polymers | 150 million |
| Intraocular lens | Acrylate and methacrylate polymers | 7 million |
| Corneal bandage lens | Hydrogel | — |
| Glaucoma drain | Silicone; polypropylene | ($200 million) |
| Other | ||
| Cochlear prosthesis | Platinum; platinum–iridium; silicone | 250 000 users |
| Breast implant | Silicone | |