Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 12

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 medicine^a.

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	700 000
Hernia mesh	Silicone; polypropylene; teflon	200 000 ($4 billion)
Sutures	Polylactic acid; polydioxanone; polypropylene; stainless steel	($2 billion)
Blood bags	Polyvinyl chloride	—
Ear tubes (Tympanostomy)	Silicone; teflon	1.5 million
Intrauterine device	Silicone; copper	1 million

^a Data compiled from many sources – these numbers should be considered rough estimates that are growing with changing markets and new technologies. Where only US numbers are available, world usage is estimated at 2.5 times the US usage.

The importance of biomaterials to society has been increasing significantly in the last several decades, both as an academic field, an area of research to develop new or improved devices, and as an industry (Figure 1.2). The number of biomedical engineering (or bioengineering) departments in academic institutions has increased rapidly over the last few decades. There are over 75 biomedical engineering (or bioengineering) departments in the United States alone. Biomaterials are an important area of teaching and research in these departments and they are often emphasized in engineering disciplines such as materials science and engineering, chemical engineering, and mechanical engineering.

Figure 1.2 Schematic showing the major components of the biomaterials field.

Outside of academic institutions, biomaterials are also an important area of research, development, and manufacturing in several industries, such as in the production of medical devices, dental restorations, and devices for drug delivery. The size of companies that manufacture biomaterials and devices for these applications cover a wide range, from small start‐up companies to large established companies that are among the so‐called Fortune 500 companies in the United States. The commercial market for devices that incorporate biomaterials is immense and it is projected to grow at a healthy rate. Estimates of the commercial market and the number of implantable medical devices that incorporate biomaterials annually are presented in Table 1.1.