Intro to Biomaterials and Biocompatibility and Overview of Materials Science

Biomaterial

a material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ of funnction of the body

Biomaterials Science

the study of biomaterials and their interactions with the biological environment; includes material science/engineering, immunology, toxicology, wound healing, anatomy, industrial involvement, and ethics/regulations

Biomaterial Scientist

both the material properties and the biological reaction to ensure that the chosen material is appropriate for the given application (will it properly function in the body)

Biocompatibility

the ability of a material to perform with an appropriate host response in a specfic application (defined by application otherwise hard to define)

Biocompatibility Appropriate Host Response

resistance to blood clotting or to bacteria colonization (can lead to infection), normal healing, calicification (desired for bone grafts but not good if happens on a breat implant or something bc soft tissues), and fibrosis (can help some degree to fix implant in place but can also create unhelpful barriers - glucose sensor)

Tissue Engineering

the application of the principles of life sciences and engineering to develop biological substitutes for the restoration or replacement of tissue or organ function (ex. scaffolds, cells, and chemicals like gfs)

Biomaterial Examples

hard/soft tissue replacement and others

Hard Tissue Replacement Biomaterials

metals and ceramics like orthopedic and dental materials; ex. bones and teeth

Soft Tissue Replacement Biomaterials

polymer like vascular grafts, nerve grafts, and general plastic surgey; ex. neural and vascular tissue

Other Biomaterials

surgical materials like sutures and adhesion prevention, bioelectrodes, and sensors (ex. fixation, monitoring, and prevention)

Skeletal System Biomaterial Applications

joint replacements (hip/knee) - titanium, Ti-Al-V alloy, stainless steel, polyethylene

bone plate for fracture fixation - stainless steel, cobalt-chromium alloy

bone cement - poly(methyl methacrylate)

bony defect repair - hydroxylapatite (ceramics)

artificial tendon/ligament - teflon, dacron

dental implant for tooth fixation - titanium, alumina, calcium phosphate

Cardiovascular System Biomaterial Applications

blood vessel prosthesis - dacron, teflon, polyurethane

heart valve - reprocessed tissue, stainless steel, carbon

cathetar - silicone rubber, teflon, polyurethane

all have polymers bc don’t want them that stiff

Organ Biomaterial Applications

artificial heart - polyurethane

skin repair template - silicone-collagen composite

artificial kidney (hemodialyzer) - cellulose, polyacrylonitrile

heart-lung machine - silicone rubber

Senses Biomaterial Applications

cochlear replacement - platinum electrodes

intraocular lens - poly(methyl methacrylate), silicone rubber, hydrogel

contact lens - silicone-acrylate, hydrogel

comeal bandage - collagen, hydrogel

Cardiovascular System Devices - Occulded Artery

thrombolytic therapy - meds to dissolve blood clots

balloon angioplasty - opens/clears vessel/artery

stent placement - keeps blood vessel and helps keep it open

these 3 help reestablish coronoary patency, salvage the myocardium, and improve survival

Cardiovascular System Devices - Pacemaker

sensor detects low/adnormal BPM and sends out electrical stimulation to get the heart back on track; cons - insulation coudl fail so electrical charges end up in wrong areas

Skeletal System Device - Total Hip Joint Replacement

usually very successful but can have complications because of the polymer material wearing out

Nervous System Device - Cochlear Implants

lower f - inner ear and higher f - outer ear; cons - electrodes can have fibrosis which can decrease the stimulation and regeneration of nerve cells and the sounds sound artifical

HIstory of Biomaterials

before/early civilization - dental implants (sea shells, iron), sutures (linen and metallic), prostheses

before WWII - basic concepts of biocompatibility

post WWII (surgeon/physician hero era) - high performance metal ,ceramic, and polymeric material became available. intraocular lenses, hip/knee prosthese, dental implants, artificial kidney, vascular grafts, stents, pacemakers (wars = bad but promote technology advancements) → no regulations

since 1960s - materials/devices are specifically designed for biomedical applications

contemporary era - modern biology/materials

Development of Biomaterials

inert materials → bio-active and degradable materials → smart materials (can detect changes) and nanotechnology

Smart Materials/Nanotechnology

can detect changes like temp., pH, solvent responsive, electric activity, piezoelectric.ferroelectric (ion balance), and nanostructured

Clinical Need to Medical Device Time Line - Full Details

identify a need (treat a condition, replace organ, cosmetic) - physician/dentist, researcher, inventor, entreprenuer

device design - physician consults and engineer implements

material synthesis - ceramicist, metalurgist, polymer chemist

materials testing (mechanical properties, toxicology, bioreaction to material (protein interactions, cell activiation, or tissue reaction), biostability (mechanical or chemical)) - bio or mechanical engineer, biochemist, cell biologist, veterinary surgeon

fabrication - engineer or machinist

sterilization/packaging - bioengineer or industrial designer

device testing (toxicology, in vitro, animal testing) - bioengineer, vet surgeon, physician/dentist

regulatory (pre-market approval, limited clinical studt, clinical studies, long-term follow-up) - regulatory specialist/agency or legislators

clincial use - physician, dentist, or optometrist

explant anaylsis (explant registry, pathological examination testing to understand failure) - pathologist or bioegineer

Clinical Need to Medical Device Short Timeline

identify a need → device design → materials synthesis → materials testing → fabrication → sterilization and packaging → device testing → regulatory → clincial use → explant analysis

Material Science Basics

processing → structure —> properties —> performance

Processinf

the way be making a material into a device; ex. heat treatment, mechanical forces, electrical field, etc.

Structure

this determines properties; can atomic, microscopt, or macroscopic

Properties

determined by structure; ex. mechanical and chemical (always important), electrical (pacemaker), magnetic (MRI), thermal, and optical (intraocular lenses)

Subatomic Species

nucleus, electron, atomic #, and atomic mass

Nucleus of an Atom

combination of protons (+ 1.67 × 10^-19 C) and neutrals (no charge)

Electrons

have a negative charge of - 1.67 × 10^-19 C

Atomic #

the # of protons in an atom

Isotope

same element but have different #’s of neutrons; ex. C12, C13, and C14

Atomic Models

Bohr and wave-mechanical

Atomic Orbitals

have shells (n) and subshells (orbitals, s, p, d, and f) → 1 energy state for s, 3 for p, 5 for d, and 7 for F; lower energy states filled first; must follow Pauli exclusion principle and Hund’s rule

Pauli Exclusion

no energy state can be occupied by more than 2 e- and they must be a different orientation (have opposite spins)

Hund’s Rule

when filling subshells with more than one energy state, fill each subshell with one e’ first then add a 2nd with opposing spin

Valenc Electrons

electrons that occupy the outermost filled shell; participate in bonding between atoms; physical/chemical properties of solids are based on these

Periodic Table Picture

Ionic Bonds

type of primary bond that involves sharing/transferring ve-; occure between atoms with large differences in electronegativity; non-directional (jave the same magnitude in all direction); each ion must be surrounded by oppsoitely charged ions in all direction → constraints on crystal structure → brittle and hard

Ionic Bond Picture

Covalent Bond

formed through the sharing of ve-; both atoms are electronegative; has hyridization; have sigma and pi bonds; directional bc shared e- lie in line between the 2 atoms

Hybridization

the spatial orientation of the hybrid orbital that determines where bonding occurs and the bond angle

Covalent Bond Picture

Sigma Bond

type of covalent bond that is along the internuclear axis; stronger bc more overlap; allows for rotation

Pi Bond

type of covalent bond that is perpendicular (vertical)

Metallic Bond

bond between electropositive elements with attractive force between ion cores and the e sea; non-directional; bc of the mobility of e- in the “sea”, these are electrical conductors

Primary Bondings

ionic - betwen cation/anion, strongly attracted by electrostatic effect; 150-370 kccal/mol; poor electrical conductors; intrinsicially brittle; low chemical reactivity

metallic - atoms arranged in order with ve- cloud floating around; 25-200 kcal/mol; high electrical/thermal conductivity; undergo more plastic deformation (change shape w/o breaking); varies a lot in reactivity

covalent - ve- from 2 atoms make a pair; 75-300 kcal/mol; poor electrical conductors (usually); have a higher chemical reactivity

Secondary Bondings

bondings betwene molecules that are usually weaker than primary bonds; ex. Van de Waals and hydrogen (H) bonds

Van der Waals

secondary bonds that form from atomic/molecular dipoles (either permanent, polar molecule-induced, or fluctation induced); 10 kcal/mol

Hydrogen Bonds

secondary bonds that are formed between H-F, H-O, or H-N (X~H-Y where X/Y are F, O, or N); important for synthetic polymers and biomocules

H Bonds in Water Picture

adnormal because of the structure of these bonds so that is why ice expands

Crystalline and Noncrystalline Materials

single crystals, polycrystalline materials, and amorphous materials

Single Crystals

the periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen w/o interruption

Polycrystalline Materials

collection of many small crystals or grains that have order but not a perfect/repeated structure

Amorphous Materials

do not have a systemic or regular arrangement of atoms over a relatively large atomic distance

Bragg’s Law and Diffraction

explains where constructive interference happens

X-ray Diffraction

helps determine interference type; crystalline if see a lot of spikes (constrauctive interference) and amorphous if just a broad peak and no specific orders

Electron Diffraction

use this instead of an X-ray because it is a much smaller wavelength so more precise picture of interference

Classification of Material Types

metal, ceramics, polymers, carbon materials, glass, and composite materials

Metals

have metallic bonding and a simple crystal structure

Ceramics

have a combo of ionic and covalent bonding and a complicated crystal structure or amorphouse

Polymers

use primarily covalent bonding; can be amorphous or polycrystalline or a mixture

Structure-Property Relationship

the arrangement of atoms in diff. ways (diff. crystal type like graphite vs. diamond); polycrystalline vs. amorphouse → opaque vs. translucent and a smaller grain size = higher mechanical strength

Stress and Strain - Mechanical Properties

tensile stress (sigma = F (load) / A (area)) → N/m² = pascal (Pa)

tensile strain (epsilon = delta L (change in length) / (lo) initial length) → no units

Elastic Constant

sigma = Ee (tension or compression)

E - Young’s modulus (slope of stress-strain curve) and represents the inherent properties of the materials

Stress-Strain Curve Pictures

Plastic Deformation

large scale displacement of atoms w/o the complete ruptire of the material’ only metals and alloy materials can truly undergo this; useful for shaping materials; can’t go back to original shape

Mechanical Properties Table Picture

Fatigue

a process by which structures fail as a result of cyclic stresses that may be less than the ultimate tensile stress; this type of failure is one of the major challenges in many prosthetic devices (ex. heart valve, prosthetic joint); many factors influence this; can’t test staticallt

What can repetitive loading do to a material?

can produce microscopic cracks that then can propagate by small steps at each load cycle

Factors that Influence Fatigue Life

stress and cycle rate

internal isses like stress conc. at crack tip, surface scratch, or a sharp corner

environmental issues like temp., corrosion, or deterioration

Fatigue Test

a dynamic measumrent that counts the # of loadings until failure

Mechanical Property Considerations for Load-bearing Biomaterials

at all time points, stress needs to be safely below the yield strength and if cyclic loads are involved, the service stresses must be kept below the fatigue strength

Mechanical Property Considerations for non-load-bearing Biomaterials

these should match those of the host tisse to minimize foreign body reaction