CHAPTER 1 Clinical Problems Requiring Implants for Solution: Defining the Problem 1.1 Objectives of Subject 1.2 Related Subjects at MIT 1.3 Terminology 1.4 How Selected Tissues/Organs Function 1.5 Effects of Trauma and Disease on Function 1.6 Restoration of Function with Implants 1.7 Applications of Medial Devices and Examples Demonstrating the Successful and Unsuccessful Performance of Medical Devices/Implants 1.8 Design Considerations for Medical Devices and Non- medical Structures 1.1 OBJECTIVES OF THE SUBJECT MEDICAL DEVICE DESIGN PROJECTS CONNECTIVE TISSUE Musculoskeletal System Joint Replacement Prostheses - Ankle prosthesis - Prosthesis for intervertebral disk regeneration Fracture fixation device - "Smart" bone plate Bone Substitute Material Tendon/Ligament Replacement Meniscus Replacement Articular Cartilage Prosthesis Oral, Maxillofacial, and Otologic Dental Implants Temporomandibular Joint Prostheses Ossicular Replacement Prostheses Augumentation of G ingiva Cardiovascular System Angioplasty Balloon Catheter Heart Valve Vascular Prosthesis NERVE TISSUE Nervous System Nerve - Prosthesis for peripheral nerve regeneration EPITHELIA Reproductive System Intrauterine Device Ophthalmalogic System Prosthesis for Retina Regeneration 1.3 TERMINOLOGY Biomaterials "Any substance (other than a drug) or combination of substances, synthetic or natural in origin, which can be used at any period of time as a whole or in part of a system which treat s, augments or place any tissue, organ or function of the body." J. W. Boretos and M. Eden Contemporary Biomaterials , 1984 "A non- variable material used in a medical device intended to interact with biological systems." D. F. Williams Definitio ns of Biomaterials, 1987 Implant A device that is placed into a surgically or naturally formed cavity of the human body if it is intended to remain there for a period of 30 days or more. (FDA, Fed. Register) Tissue An aggregation of similarly speciali zed cells united in the performance of a particular function. Cells serving the same general function and having the same extracellular matrix. Organ Two or more tissues combined to form a larger functional unit. Connective Tissue The matrix- continuo us tissue which binds together and is the support of the all of the structures of the body. The predominant structural protein comprising the extracellular matrix of connective tissue is collagen. Regeneration The renewal of a tissue or organ at the com pletion of healing. Repair The formation of scar at a site of injury at the completion of healing. Remodeling/ Maintenance/ Turnover The process by which extracellular matrix is replaced in a process of degradation followed by synthesis. 1.7 APPLICAT IONS OF MEDICAL DEVICES (Ratner, 1993) Clinical Applications Numbers used of Medical Devices per year in the US Ophthalmologic Intraocular lenses Contact lenses Retinal surgery implants Prostheses after enucleat ion Cardiovascular Vascular grafts Arteriovenous shunts Heart valves Pacemakers Blood bags Reconstructive Breast prostheses Nose, chin Penile Dental Orthopedic Hips Knees Shoulders, finger joints Other Devices Ventricular shunts Catheters Oxygenators Renal dialyzers Wound drains Sutures 1 400 000 2 500 000 50 000 5 000 350 000 150 000 75 000 130 000 30 000 000 100 000 10 000 40 000 20 000 90 000 60 000 50 000 21 500 200 000 000 500 000 16 000 000 3 000 000 20,000,000 1.8 DESIGN CONSIDERATION S FOR MEDICAL DEVICES AND NON- MEDICAL STRUCTURES Define the problem Problem to be solved Required Performance (Mech., chem., electr., therm., optical) - Scale of performance (living element) - Material selection criteria - Geometric considerations Design Parameters Effect of the design on the environment - Time constant - Governmental regulations Effect of the environment on the design - Mechanical, chemical (+water), thermal, light, ionizing radiation - Mechanisms of failure (fracture, wear, corrosion) - Permanent vs. temporary (Insoluble vs. soluble) Laboratory testing/simulation - Models and mock- ups Non- medical + Extend human capabilities + mm, m (human organism) + + + Inert Years, decades + (EPA) + + Permanent + Mech. and chem. Medical + Replace missing organ + n m, m m, mm (cell) + + (anatomic) + Inert and bioactive (biocompatibility) Days, months, years + (FDA) + + Permanent and temporary (scaffolds for regeneration - tissue engineering) + Mech. a nd chem. Cell/tissue culture Animal implantation * " + " means a consideration to be addressed. Nonedical Medical Mathematical modeling + (Often) Evaluation of performance in use Controlled use/ Assessment of value Engineering disciplines responsible for product Nonengineering responsibility Consumer Consumer education Role of marketing Cost as an issue Cost per pound instrumented Exceeds safety factor (Threshold risk) Aero., chem., civil, mat'l., mech, etc. None Varied Variable Tech. spec./ aesthetics + Low Generally not available Clinical trial Benefit/risk Biomedical Engineering Physician Physician Variable Tech. spec. (?) + High