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this design criterion is met when a new biomaterial is under development. Chapter 5.2 provides an overview of methods in biomaterials toxicology. The implications of toxicity are addressed in Chapters 4.2 and 4.4.

Blocompatibilfcy

The understanding and measurement of biocompatibiiity is unique to biomaterials science. Unfortunately, we do not have precise definitions or accurate measurements of biocompaability. More often than not, tr is defined in terms of performance or success at a specific rask. Thus, for a patient who is alive and doing well, with a vascular prosthesis that is unoccluded, few would argue that this prosthesis is, in this case, not "biocompatible." However, this operational definition offers us little to use in designing new or improved vascular prostheses. It is probable that bioeotnpatihility may have to be specifically defined for applications id soft tissue, hard tissue, and the cardiovascular system (blood compatibility!, in fact, Incom patibility may have to be uniquely defined for each application. The problems and meanings of biocompatibility will be explored and expanded upon throughout this textbook, in partic ular, see Chapters 4 and

Heading

Special processes are invoked when a material or device heals in the body. Injury to tissue will stimulate the well-defined inflammatory reaction sequence that leads to healing, Where a foreign body (e.g., an implant) is involved, the reaction sequence is referred to as the "foreign body reaction" {Chapter 4.2). The normal response of the body will he modulated because of the solid implant. Furthermore, this reaction will differ m intensity and duration depending upon the anatomical site involved. An understanding of how a foreign object alters the normal inflammatory reaction sequence is an important concern tor ihe biomaterials scientist.

Unique Anatomical Sites

Consideration of the anatomical site of an implant is essential. An intraocular lens may go into the lens capsule or the anterior chamber. A hip joint wilt be implanted in bone 3cross an articulating joint space. A heart valve will be sutured into cardiac muscle. A cathetet may be placed in a vein. Each of these sites challenges the biomedical device designer with special requirements for geometry, si/.e. mechanical properties, and bioreaction. Chapter 1,4 introduces these ideas.

Mechanical and Performance Requirements

Each biomatenal and device has imposed upon it mechanical and performance requirements that originate from the physical (bulk) properties of the material. These requirements can be divided into three categories: mechanical performance, mechanical durability, and physical properties. First, consider mechanical performance. A hip prosthesis must he strong and rigid. A tendon material must be strong and flexible. A heart valve leaflet must he flexible and rough. A dialysis membrane must be strong and flexible, but not elastomeric. An articular cartilage substitute must be soft and elastomeric. Then, we must address mechanical durability. A catheter may only have to perform lor ) days A bone plate may fulfill its function in 6 months or longer. A leaflet m a heart valve must flex 60 rimes per minute w ithout tearing for the lifetime of the patient fit is hoped, foe 10 or more years). A hip |omt must not fail under heavy loads for more than 10 years. Finally, the bulk physical properties will address performance. The dialysis membrane has a specified permeability, the articular cup of the hip joint has a lubricity, and the intraocular lens has a clarity and refraction requirement, lo meet these requirements, design principles arc borrowed from mechanical engineering; chemical engineering, and materials science.

Industrial Involvement

At the same time as a significant basic research effort is under way to understand how biomaterials function and how to optimize them, companies are producing millions of implants for use in humans and earning billions of dollars on the sale of medical devices. Thus, although we are now only learning about the fundamentals of biointeraction, we manufacture and implant materials and devices. How is this dichotomy explained? Basically, as a result of considerable experience, trial and error, inspired guesses, and just plain luck, we now have a set of materials that performs satisfactorily in the body. The medical practitioner can use them with reasonable confidence, and the performance in the patient is largely acceptable. In cssence, the complications of the devices are less than the complicatons of the original diseases. Companies make impressive profits on these devices. Yet, in some respects, the patient is trading one disease for another, and there is much evidence that better materials and devices can be made through basic science and engineering exploration. So, in the field of biomaterials, we always see two sides of the coin—a basic science and engineering effort, and a commercial sector.

The balance between the desire to alleviate loss of life and suffering, and the corporate imperative to turn a profit forces us to look further afield for guidance. Obviously, ethical concerns enter into the picture. Companies have large investments in the manufacture, quality control, clinical testing, regulatory clearance, and distribution of medical devices. How much of an advantage will be realized in introducing an improved device? The improved device may indeed work better for the patient. However, the company will incur a large expense that will, in the short term, be perceived by the stockholders as a cut in the profits. Moreover, product liability issues are a major concern of manufacturers. When looking at the industrial side of the biomaterials field, questions are asked about the ethics of withholding an improved device from people who need it, the market share advantages of having a better product, and the gargantuan costs (possibly nonrecoverable) of introducing a new product into the medical marketplace. If companies did not have the profit incentive, would there be medical devices, let alone improved ones, available for clinical application?

When the industrial segment of the biomaterials field is examined, we see other contributions to our field. Industry deals well with technological developments such as packaging, sterilization, and quality control and analysis. These subjects require a strong technological base, and have generated stimulating research questions. Also, many companies support in-house basic research laboratories and contribute in important ways to the fundamental study of biomaterials science.

Ethics

There are a wide range of other ethical considerations in biomaterials science. Some key ethical questions in biomaterials science are summarized in Table 3. Like most ethical questions, an absolute answer may be difficult to come by. Some articles have addressed ethical questions in biomaterials and debated the important points (Saha and Saha, 1987; Schiedermayer and Shapiro, 1989),

Regulation

The consumer (the patient) demands safe medical devices. To prevent inadequately tested devices and materials from

TABLE 3 Some Ethical Concerns Relevant to Biomaterials Science

Is the use of animal models justified? Specifically, is the experiment well designed and important so that the data obtained will justify the suffering and sacrifice of the life of a living creature?

How should research using humans be conducted to minimize risk to the patient and offer a reasonable risk-to-benefit ratio? How can we best ensure informed consent?

Companies fund much biomaterials research and own proprietary hiomaterials. How can the needs of the patient be best balanced with the financial goals of a company? Consider that someone must manufacture devices—these would not be available if a company did not choose to manufacture them.

Since researchers often stand to benefit financially from a successful biomedical device and sometimes even have devices named after them, how can investigator bias be minimized in biomaterials research?

For life-sustaining devices, what is the tradeoff between sustaining life and the quality of life with the device for the patient? Should the patient be permitted to "pull the plug" if the quality of life is not satisfactory?

With so many unanswered questions about the basic science of biomaterials, do government regulatory agencies have sufficient information to define adequate tests for materials and devices and to properly regulate biomaterials?

coming on the market, and to screen out individuals clearly unqualified to produce biomaterials, a complex national regulatory system has been erected by the United States government through the Food and Drug Administration (FDA). Through the International Standards Organization (ISO), international regulatory standards have been developed for the world community. Obviously, a substantial base of biomaterials knowledge went into these standards. The costs to meet the standards and to demonstrate compliance with material, biological, and clinical testing are enormous. Introducing a new biomedical device to the market requires a regulatory investment of many millions of dollars. Are the regulations and standards truly addressing the safety issues? Is the cost of regulation inflating the cost of health care and preventing improved devices from reaching those who need them? Under this regulation topic, we see the intersection of all the players in the biomaterials community: government, industry, ethics, and basic science. The answers are not simple, but the problems are addressed every day. Chapters 10.2 and 10.3 expand on standards and regulatory concerns.

biomaterials literature

Over the past 40 years, the field of biomaterials has developed from individual medical researchers "trying things out," to the defined discipline we have today. Concurrent with the evolution of the discipline, a literature has also developed. A bibliography is provided at the end of this introduction to s highlight key reference works and technical journals in the biomaterials field.

summary

This chapter provides a broad overview of the biomaterials field, it is intended to provide a vantage point from which the reader can begin to place all the subthemes (chapters) within the perspective of the larger whole.

To reiterate a key point, biomaterials science may be the most interdisciplinary of all the sciences. Consequently, biomaterials scientists must master material from many fields of science, technology, engineering, and medicine in order to be competent in this profession. The reward for mastering this volume of material is involvement in an intellectually stimulating endeavor that advances our understanding of basic sciences and also contributes to reducing human suffering.

Bibliography

References

Saha, S., and Saha, P. (1987). Bioethics and applied biomaterials, ].

liiomed. Mater. Res: Appl. Biomat. 21: 181-190. Schiedermayer, D. L., and Shapiro, R. S. (1989). The artificial heart as a bridge to transplant: Ethical and legal issues at the bedside. J. Heart Transplant 8: 471-473. Society For Biomaterials Educational Directory (1992). Society For

Biomaterials, Minneapolis, MN. Williams, I). P., (1987). Definitions in Biomaterials. Proceedings of a Consensus Conference of the European Society for Biomaterials, Chester, England, March 3-5 1986, Vol. 4, Elsevier, New York.

Biomaterials journals

Advanced Drug Delivery Reviews (Elsevier)

American Society of Artificial Internal Organs Transactions

Annals of Biomedical Engineering (Blackwell—Official Publication of the Biomedical Engineering Society) Artificial Organs (Raven Press)

Artificial Organs Today (T. Agishi, ed., VSP Publishers) Biofouling (Harwood Academic Publishers)

Biomaterial-Living System Interactions (Sevastianov, ed., BioMir) Biomaterials (including Clinical Materials) (Elsevier) Biomaterials, Artificial Cells and Artificial Organs (T. M. S. Chang, ed.) Biomaterials Forum (Society For Biomaterials)

Biomaterials: Processing, Testing and Manufacturing Technology

(Butterworth) Biomedical Materials (Elsevier/

Biomedical Materials and Engineering (T. Yokobori, ed., Pergamon Press)

Biosensors and Bioelectronics (Elsevier) Cell Transplantation (Pergamon)

Cells and Materials (Scanning Microscopy International) Colloids and Surfaces B: Biointerfaces (Elsevier) Drug Targeting and Delivery (Academic Press)

Frontiers of Medical and Biological Engineering (Y. Sakurai, ed.,

VSP Publishers) International Journal of Artificial Organs (Wichtig Editore) Journal of Applied Biomaterials (Wiley)1 Journal of Bioactive and Compatible Polymers (Technomics) Journal of Biomaterials Applications (Technomics) Journal of Biomaterials Science: Polymer Edition (VSP Publishers) Journal of Biomedical Materials Research (Wiley— Official Publication of the Society For Biomaterials) Journal of Controlled Release (Elsevier) Journal of Drug Targeting (Harwood Academic Publishers) Journal of Long Term Effects of Medical Implants (CRC Press) Materials in Medicine (Chapman and Hall—Official Publication of the European Society for Biomaterials) Medical Device and Diagnostics Industry (Canon Publications) Medical Device Research Report (AAMI) Medical Device Technology (Astor Publishing Corporation) Medical Plastics and Biomaterials (Canon Communications, Inc.) Nanohiology (Carfax Publishing Co.) Nanotechnology (an institute of Physics Journal) Tissue Engineering (Marv Ann Liebert, Inc.)

J. Black, Biological Performance of Materials: Fundamentals of Bio-compatibility, 2nd ed., Marcel Dekker, New York, 1992.

J. W. Boretos, and M. Eden (eds.), Contemporary Biomaterials— Material and Host Response, Clinical Applications, New Technology and Legal Aspects. Noyes Publ., Park Ridge, NJ, 1984.

A. I. Glasgold, and F. H. Silver, Applications of Biomaterials in Facial Plastic Surgery, CRC Press, Boca Raton, FL, 1991.

G. Heimke, Osseo-lntegrated Implants. CRC Press, Boca Raton, FL, 1990.

L. I.. Hench, and E. C. Ethridge, Biomaterials: An Interfacial Approach, Academic Press, New York, 1982,

J. B. Park, Biomaterials: An introduction, Plenum Publ., New York, 1979.

J. B. Park (ed.), Biomaterials Science and Engineering. Plenum Publ., New York, 1984.

F. J. Schoen, Interventional and Surgical Cardiovascular Pathology: Clinical Correlations and Basic Principles, W. B, Saunders, Philadelphia, 1989.

F. H. Silver and C. Doillon, Biocompatibility: Interactions of Biological and Implanted Materials, Vol. 1 - Polymers, VCH Publ., New-York, 5989.

A. F. Von Recum, (ed.), Handbook of Biomaterials Flvaluation, 1st ed., Macmillan, New York, 1986.

D. Williams fed.), Concise Encyclopedia of Medical and Dental Materials, 1st ed., Pergamon Press, Oxford, UK, 1990.

T. Yamamuro, L. L. Hench, and J. Wilson, CRC Handbook of Bioactive Ceramics. CRC Press, Boca Raton, FI„ 1990.

"Now a subsection oi journal of Biomedical Materials' Research.

Some Biomaterials Books part

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