Intro to Biomed exam 1

Biomaterials

A nonviable material used in a medical device, intended to interact with biological systems

Bulk properties

composition, mechanical properties (strength, wear,etc), electrical properties

surface properties

interaction with surrounding environment, targeting

biological properties

interactions with cells and tissues

Pros and cons of Metals

Pros: Strong, ductile, conduct electricity, Cons: Hard to make, corrode. examples- Screws, joint replacement

Properties of metals

Held together by metallic bonds in a crystalline structure (sea of electrons), high melting point and high density

Pros and cons of Ceramics

Pros: bioactive, wear-resistant, strong in compression Cons: brittle and not resilient

Examples: Dental and joint replacement, coatings for metals to interact with bones

Properties of ceramics

Non-metallic inorganic compounds formed from

metallic and non-metallic elements

Strong, BUT brittle, Note stress strength curve

Pros and cons of Polymers

Pros: Easy to manipulate, resilient, can be made transparent, flexible, light,

Cons: not strong and can deform with time, Polymer chains are held together by weak forces

Ex: contact lenses, soft tissues, blood vessels

Properties of Polymers

Various amount of connectivity of monomers that are covalently connected (cross-linking, branching, network) creates a wide-range of properties. 

Titanium Alloy

METAL

Ultimate strength (1 Giga Pascal)

corrosion resistant

lightweight 

excellent fatigue resistance

Poor shear strength and wear resistance

ex: joints

fatigue resistant

can take million of cycles of tension and compression (repeated stress or strain without breaking down)

Nitinol

METAL

(50/50 nickel and titanium)

Very elastic

good shape memory

good thermal memory

Ex: stents (Can return to original shape when inserted into body because of body temperature), braces

Cobalt Chrome

METAL

CoCrWNi

very hard and great wear properties (unlike titanium)

difficult to work with 

Corrosion resistant and biocompatible

ex: Dental and medical implants

Platinum

METAL

good electrical conductor

Electrical applications

very expensive

soft

Ex: Pacemaker

Alumina

CERAMIC

Al2O3

Very hard, but brittle

excellent wear resistance

Used for bearing surface like hip joints

Porcelain

CERAMIC

Mixture of ceramics, including clay.

reinforced with metals or tougher ceramics

can be polished to a glassy and smooth surface that mimics enamel (aestethic)

Ex: dental crown, veneers

Hydroxyapatite

CERAMIC-hydrophobic

mineral component of teeth and bone

brittle

non-toxic

coatings on titanium implants to enhance osseointegration

Ex: bone repair, dental restorations

Bioglass

CERAMIC

Highly bioactive

used for coating to promote new bone growth

not very strong

silica-based material

ex: bone grafts

ossification

New bone tissue is formed and existing bone is remodeled

Silicone

POLYMER

Flexible 

heat resistant

non-toxic

ex: Catheters and tubing

Polyethylene

POLYMER

long chains of C-H2 units

Ultrahigh molecular weight 

one of the best wear resistant plastics

low friction

shock absorbing

ex: used in bulk for lining or bearing surfaces

osteolysis

Active destruction or resorption of bone tissues by cells

pHEMA

POLYMEr

Hydrophilic polymer

forms hydrogels 

ex: Contact lenses

PTFE

POLYMER

Hydrophobic

low friction

coating on devices 

ex: Teflon, used as liner material for stents,surgical instruments, catheters

PGA

POLYMER

BIODEGRADABLE 

encapsulates a drug and releases it gradually as the polymer breaks down

ex: tissue engineering scaffolds (PGA degrades as new tissue forms)

Hydrolysis

breaking a chemical bond by addition of water (component in biodegradation)

Enzymatic Degration

Breakdown of materials by enzymes

can be corrosion

Why biodegradation is desired?

No need for follow up surgery

Temporary function

Allows time for bone to form while the substance degrades

Is it Biocompatible?

How does it function in the environment/ works as intended in the body 

Does the material exhibit bioactivity/ no harm to biological systems 

Host/body response to the material

Host-response following implantation

Injury

blood-material interaction

provisional matrix formation

acute inflammation

chronic inflammation

Granulation tissue formation

Foreign body reaction

Fibrous Capsule Development

Injury

Causes tissue and vascular damage

Release of blood at wound

Coagulation Cascade

(Blood clotting) in the blood-material formaton and Provisional matrix formation stages

Acute inflammation

short- term affects such as rash, burn, infection

Chronic Inflammation

weeks-months affects

disease from the material

Granulation Tissue Formation

Natural healing process

new connective tissue that form on the surface of the healing wound.

Foreign body reaction

Presence of foreign body giant cells and components of granulation tissue formation surrounding the implanted material. 

Fibrous Capsule Development

fibroblasts deposit a fibrous encapsulation layer (mainly collagen) that separates the host from the implant

isolates the foreign object

Large Femoral heads

increase stability and range of motion,

reduce risk of dislocation

increased wear

Small Femoral heads

experience less friction and inertial stress

yield strength

Point at which elasticity doesn’t go back to original shape

tensile strength

point where any material breaks (rubber band)

Biomechanics

Study of mechanics as it relates to the functional and anatomical analysis of biological movement

Fluids

Incompressible and compressible

Deformable bodies

Do change shape

Rigid bodies

Do not change shape

Statics and dynamics

Statics

Systems in constant state of motion or at rest (a=0)

All forces acting on a body being in balance and sum of Fnet is 0

Dynamics

Systems in motion WITH acceleration

2 different dynamics

Kinematics- description of motion without regard to forces (Displacement, velocity,etc)

Kinetics- study of forces associated with motion of body (Forces, torque, mass, etc.)

Areas and Application

Helmet and bike design- outer shell spreads impact force, inner foam liner absorbs energy by controlled deformation and the shape and weight minimize rotational acceleration and neck strain.

car safety standards

fluid flow: Blood, gas

Dr. William Harvey

Discovered blood circulation

CV system is a closed-loop

Dr. Stephen Hales

First measured blood pressure

Used his horse in his backyard to test this

Giovanni Alfonso Borelli

Figures illustrating biomechanical concepts such as locomotion, lifting, and joint equilibrium

Dr. Jean Poiseuille

studied blood flow and how it changes in smaller diameter tubes

Hagen-Poiseuille law

Describes the pressure drop of a fluid in a laminar flow through a cylindrical pipe

Dr. Thomas Young

Measured the stiffness of an elastic material

modules of elasticity

Dr. Julius Wolff

bone architecture

Law of bone remodeling

Wolff’s law of bone remodeling

bone adapts its internal architecture in response to external constraints and loads

ex: Right-handed tennis player: racquet-holding arm becomes much stronger

Dr. Wilhelm roux

Bifurcation of blood vessels

Bifurcation of blood vessels

Dr. Wilhelm Roux

a point where a single vessel splits into two smaller branches

Types of muscle movements

Only pull or contract

That’s why there are muscles surrounding the eye, so it can pull the eye in any direction

moment

tendency of rotation about a certain point