Biomaterials in Modern Medicine

The following sections are included:

• Contents

• List of Contributors

In modern medicine, technology plays a prominent role in the diagnosis of diseases and treatment of patients. As a consequence, healthcare requires new generations of medical doctors and engineers: medical doctors who are familiar with the latest technical developments in their field, and engineers who have knowledge about the human body-anatomy, physiology, pathology, etc. Development of medical products requires a close cooperation between doctors and engineers. Product development is a multidisciplinary and time consuming activity. In this chapter, the artificial kidney and silicone breast implants are described from a historical perspective to emphasize the long development times of medical devices. A list of medical grade materials is enclosed in the Appendix of this book.

The student should be able to explain why BioMedical Engineering is a multidisciplinary research area by its definition, and should understand the meaning of an innovation, a biomaterial and the role of medical doctors and engineers in medical product development.

Biomedical product design involves a complex series of activities that has to be performed by a team which, in order to have sufficient expertise, must be composed of people of various disciplines. Design of biomedical products is quite different from designing consumer products. The main question is how to create high-quality biomedical products that can solve a medical problem.

A new design method has been developed for designing biomedical products, based on an iterative approach and characterized by five phases: an analysis phase, three synthesis phases and the use phase.

To enable medical, technical and industrial experts to work together, the fundamental differences between the three groups must be known and accepted. A second condition for a properly functioning design team is that are the required roles are filled. Finally, a character analysis of the team members can prevent or solve conflicts.

For centuries animals have been used in medical research to obtain more insights into the functioning of the human body. Although animals differ from man, many physiologic processes are comparable and can be studied in more detail in animals than in man. In this regard animals are used for development and testing of new drugs, sera and vaccines, development and validation of new diagnostics, and development and training of surgical techniques under realistic (physiological) conditions. The need for animal experiments in medical research has come into question today. Animal welfare groups raise questions such as, “Are we, as intelligent human beings, allowed to use and harm animals that cannot defend themselves?”, and “Is it ethically acceptable to use animals for medical research while men and animals are so much different?” This chapter deals with animal models that are used in medical devices development and presents three case studies in which animals were used to mimic a clinical situation.

Health care technologies have the potential to increase life expectancy and improve the quality of life of the general public. The general public has high expectations of these technologies and places more and more demands on the effectiveness of these technologies.¹ In recent decades, however, the increased use of health care technology has increased health care expenditures. Technologies that failed have sometimes shown disastrous effects on health outcomes. In response to these impacts on society, an increasing amount of research has focused on the systematic evaluation of the effects of health care technology.

The use of blood-contacting biomaterials is increasing yearly by 12%. Biomaterials are used for implants (stents, heart valves, vascular grafts), for temporary support or monitoring in the body (infusion systems, catheters, drug delivery, heart pumps), or for extracorporeal circulation (dialysis, apheresis, heart-lung machine). In most situations a proper anticoagulation is essential to prevent immediate thrombosis. However, much more knowledge about blood-material interactions must be obtained to reduce other side effects, such as micro-thrombosis and an inflammatory reaction. Those who are involved in the construction of medical devices should be aware of the response of platelets, coagulation, and complement immediately after contact with a biomaterial. Furthermore, they should realize that haemocompatibility of the biomaterial is of major concern for uneventful use of a device. This should be verified with proper testing. Progress is being made with different types of coating, which might be used to cover even the most thrombogenic surface.

Biomaterials serve different purposes in biomedical technology and medicine. In this chapter the reactions of tissues and cells towards biomaterials are described. The focus is on materials that are implanted to support or replace damaged tissue or organs.

The adhesion of cells and tissues to biomaterials is an essential part and determines the overall reaction. Adhesion hardly ever occurs to the materials themselves, but instead to a protein layer covering the materials. The composition of the protein layer, as well as the conformation of the proteins, is determined by the physicochemical properties of the biomaterial surface. Apart from these properties, the tissue/cell response towards degradable and non-degradable materials differs. The foreign-body reaction in particular results in complete removal of the degradable material from the implantation site and subsequent resorption. Non-degradable materials are encapsulated and therefore isolated as a foreign body, although a continuous, mild inflammatory reaction might persist. Materials that are indistinguishable from the bodies' own materials will generally not evoke a foreign-body reaction.

The incidence of wound infection after clean surgery is often underestimated. Infection rates up to 15% can be found by meticulous follow up. The consequences of these infectious complications can be troublesome for the patient involved. Most of the time the post-operative recovery will be delayed and secondary healing of the operative wound will occur. The long-term consequences of these infectious complications will be within acceptable limits. However, when biomaterials are involved in post-operative infectious complications, a totally different scenario is likely to occur — the longevity of these artificial organs and temporary assist devices is limited by biomaterial-associated infection of the implant.

In this chapter we present an overview of the mechanisms of biomaterial-associated infection and its occurrence in various medical disciplines. Surgical procedures are critically reviewed for non-biomaterial associated versus biomaterial-associated surgery and recommendations are given for biomaterial-associated surgery.

Cardiopulmonary bypass is one of the most popularly applied medical technologies of extracorporeal circulation for patients who need a heart operation. It is indicated to be employed during open-heart surgery to replace the function of the natural heart and lungs. The heart-lung machine is a machine system to be used for performing the cardiopulmonary bypass. It consists of a number of heart pumps, an oxygenator, and reservoirs and filters. Since the heart-lung machine contains a large surface area of nonphysiological synthetic materials, it induces tremendous blood activation and a whole-body inflammatory response that contributes to post-operative organ dysfunction. Research and development on optimizing the heart-lung machine system and cardiopulmonary bypass circuit will be of crucial importance in improving the care and post-operative organ function for cardiac surgical patients.

Heart failure can be defined as a situation in which the pump function of the heart is not able to maintain the proper functioning of the vital organs, or in other words, the heart cannot generate enough blood pressure and flow to guarantee adequate organ perfusion. In case pharmaceutical and interventional cardiologic therapies like medication, intracoronary balloon dilatation or stent placement fail in treatment of severe heart failure, mechanical circulatory support of the diseased heart may become a life-saving therapy. In order to understand heart failure and mechanical circulatory support, the reader must be aware of the natural anatomy of the heart and its functioning and the different types of blood pumps that can be applied to assist a failing heart.

Total joint arthroplasty is one of the most cost-effective surgical interventions of the last 50 years. With the development of new metallurgic, physical and chemical techniques, degenerated and destroyed joints, especially the hip and the knee, can be replaced by artificial joints. Patients are again capable to live a pain-free life, with a range of motion adequate for daily activities. On average, modern endoprostheses function in more than 90% of patients for 15 years without wear or loosening problems.

Aseptic loosening, as a result of wear and bone resorption, and infection, form the limits of a successful arthroplasty. New developments in osseo-integration, to promote incorporation of the prosthesis in the bone, and in passive (antibiotic) or active (immunologic) defense against microbial infection are the subject of intensive research. The latest developments are discussed in this chapter.

A laryngectomy has severe consequences for the patient's quality of life. The voice becomes low-pitched, nasal functions are lost and the inevitable visible tracheostoma can be the source of mental problems. An artificial larynx could solve all of these problems. However, the function of the larynx is complex. Whether such a device can be made is questionable and will be discussed. It is important to realize which functions have to be restored and which solutions for those functions are available.

In ophthalmology, biomaterials are frequently used in the treatment of various eye diseases. An example of a biomaterial is the intraocular lens. Intraocular lenses are implanted in the eye when the opacified natural lens has been removed by phacoemulsification cataract surgery. The history of intraocular lenses started in 1947 when the first lens was implanted. Initially, many severe complications occurred with intraocular lenses, but due to continuing improvements cataract surgery with intraocular lens implantation is now a very safe and predictable operative procedure. As a result, intraocular lenses are also used for refractive surgery. Biomaterials are also used in the treatment of retinal detachments. Although they are adequate for this goal, there is still room for improvements in these biomaterials.

Plastic surgery is a very broad surgical specialism covering reconstructive, aesthetic, craniofacial, congenital, burn, and hand surgery. This implies that plastic surgeons operate on a diverse patient population and almost all anatomical sites of the body, both sexes, and all ages.

There are many applications of biomaterials in plastic surgery. One can think of joint reconstruction, osteosynthesis (e.g. plates and screws), reconstruction and creation of the shapes of bones and soft tissues (e.g. breast reconstruction and augmentation), glues, suture materials, and injectables.

Abdominal wall hernia repairs are the second most common surgical procedure performed in the USA, behind only cataract procedures. Although surgical techniques in hernia repair have improved, recurrence used to be a common complication. Therefore, the idea of increasing the strength of the abdominal wall by implanting a mesh was explored. The introduction of a polypropylene mesh in 1962 was a breakthrough with regards to biocompatibility and comfort. The positive effects of the use of a mesh on recurrence of the hernia stimulated the search for an optimal mesh with biocompatibility, low adhesion formation and low infection rates. To date a large number of surgical meshes are available for abdominal wall reconstruction. They all differ concerning tissue ingrowth, change of infection and rate of recurrence. The enormous variety in materials available implies important differences concerning interactions between surgical mesh and micro-organisms. To date, the use of a surgical mesh always forces the clinician to choose between the risks of prosthesis-related complications and a suboptimal treatment without a device and high rates of recurrence.

The following sections are included:

• Index