Biomaterials: An Overview

• The following notes cover the topic of Biomaterials from the content provided.

Course Overview

• The course explores biomaterials from the perspectives of Material Sciences and Biomedical Sciences, leading to various applications.
• Course assessment includes assignments, short tests, and a final exam.
• Assignment: group report of at least 15 pages.
• One short test will be given that lasts 30 minutes.
• The final exam will be writing based.
• Assignments should include references in Endnote, Zotero, or Mendeley.

Materials Science

• Materials are substances or mixtures that constitute an object, whether pure, impure, living, or non-living.
• Materials are categorized based on physical/chemical properties, geological origin, or biological function.
• Materials science studies materials and their applications.
• The four main types of materials include: metals, ceramics, polymers, and composites.

Biomaterials

• Biomaterials: Materials used in contact with biological systems for evaluation, treatment, augmentation, or replacement of tissues, organs, or bodily functions.
• Biomaterials can be natural or synthetic, used in prosthetic, diagnostic, therapeutic or storage applications without harming living organisms.
• Requirements for a material to become a biomaterial: applicability, biocompatibility, preparation, structural/chemical/physical characterizations.
• Concerns with Biomaterials are with the materials properties, biological properties and social requirements
  • Materials: Physical, chemical, mechanical, surface, and corrosion/degradation.
  • Biological: Biocompatibility, inflammation/rejection/healing, coagulation/sterilization, adsorption/resorption, toxicity, carcinogenic/allergic effects.
  • Social: cost effectiveness, ethical considerations, and regulatory compliance.
• From research to clinical use/ applications it takes 10 - 15 years.
• Challenges: replicating complex tissue architecture in vitro, developing compatible materials/processing techniques, understanding cell function modulators, finding better immune acceptance strategies.

Types of Biomaterials

• Biomaterials can be classified based on: origin (synthetic, natural), type (polymers, ceramics, metals, composites), properties (degradable, inert/active, conductive/inductive), and applications (orthopedics, cardiovascular, dentistry, tissue engineering, drug delivery).
• Metals are characterized by high electrical/thermal conductivity, malleability, ductility, and light reflectivity.
• Suited for load-bearing/internal fixation devices due to crystal structure and bonding.
• They processed to contribute high tensile, fatigue, and yield strengths, low reactivity, and good ductility.
• A key issue with metals can be stress shielding.
• Ceramics are inorganic compounds with metallic/non-metallic elements, formed at high temperatures with ionic/covalent bonding.
  • Ceramics are generally inert (or bioactive), with high wear resistance, high modulus/compressive strength, and fine esthetic properties.
  • A disadvantages of ceramics is that they can be brittle with low fracture resistance, low tensile strength (except fibers), and poor fatigue resistance.
• Polymers are made of organic macromolecules with repeating units in long, flexible chains.
  • Flexible structure can be useful for many applications from garbage bags to rubber tires.
  • Polymers are soft, light, and have controllable molecular structures.
  • Can also be used to store genetic information.
  • Processing conditions can induce polymer chain linking.
  • Polymers can be easily varied in order to suit current biomedical applications.
• Composites: Hybrid materials that combine ceramics, metals and polymers to compensate for individual weaknesses.
  • Each material has individual strengths and weaknesses depend on the intended applications.
  • Composites take on the desires characteristics of different the materials and adapt them for use in living tissue. -Composite designs combine strength and flexibility by reinforcing a flexible material with a harder, stronger one.

Material sciences

• Interdisciplinary field that covers the design and discovery of new materials, also referred to as materials science and engineering.

History of Biomaterials

• Ancient Egyptians used artificial toes in mummies.
• Mayans used blue nacre shells for dental implants.
• 1881: Etienne-Jules Marey designed an artificial heart.
• (460-370BC) Hippocrates suggested bandages seeped in egg white and vinegar for fracture fixation.
• 1829: Henry Levert used metal sutures in dogs; platinum was superior.
• 1860s: Lister developed aseptic surgical techniques.
• 1900s: Macewan implanted glass in bone.
• The European Society of Biomaterials defines biomaterials.
• Biomaterials are nonviable materials used in medical devices that interact with biological systems (ESB, 1987).
• Biomaterials interface with biological systems to evaluate, treat, augment, or replace tissues (ESB, 1992).
• 1950s: Marked the "biomaterials revolution".
• 1962: Drug Amendments and Consumer Bill of Rights occurred.
• Understanding biocompatibility.
• Varies and can be described as a material or device's capacity to avoid toxic or injurious effects on biological systems.
• Before 1950, low implant success rates happened because of immune system rejection.

Generations of Biomaterials

• First Generation (1960s-1970s): "Ad hoc" implants mimicking lost tissue, preferably inert and not interacting with the host.
  • Materials included: gold fillings, wooden teeth, PMMA dental prostheses, steel/gold/ivory bone plates, glass eyes, and dacron/parachute cloth vascular implants.
• Second Generation (1990s): Bioactive materials actively interacting/integrating with the biological environment.
  • Materials included: titanium alloy dental/orthopedic implants, cobalt-chromium-molybdenum orthopedic implants, UHMW polyethylene bearing surfaces, and heart valves/pacemakers.
• Third Generation (2000s): Combined bioactive/resorbable materials activating genes and stimulating tissue regeneration.
  • Examples include: engineered implants, Integra LifeSciences artificial skin, Genzyme cartilage cell procedure, resorbable bone repair cements, and genetically engineered components.
• Fourth Generation: Nanomaterials and nanotechnology designed to manipulate/monitor cellular bioelectrical signals.
• Electrical processes are important for inter- and intracellular signaling.