Biomedical Engineering

Biomedical Engineer responsibilty

• Responsible for the development of useful devices to replace human tissue and bone

• Desigining surgical equipment

Biocompatibility ( Biomedical engineers must be)

• Choosing a material that will not suffer greatly fron fatigue, corrode, rejected by body tissues

Examples of Biomedical devices

• Artifical hearts

• Bionic Ear

• Artifical limbs

Training of the Profession * What UNI

• UNSW has a biomedical engineering course on offer

Careers in Biomedical engineering

• Not as many jobs as civil, mechanical, electrical engineering offer

• However expansion could be likely

Relations with the community ( Community thoughts on Biomed engineering)

• Has great support from community

Ethics

Ethics is the system of moral principles that guides people in deciding what is right and wrong and how they should act

Example of Ethics in BIOMED ENGINEERING (DEVICE NAME)

Steam Engine

Ethical : yes or no (depends)

Finish sentence “Ethics play an important role in..

• The testing of new developed devices

Example of ethical failure: ABIOMED ( JARVIK-7 artifical heart)

Jarvik-7 artificial heart was placed into William Schroeder (terminal patient), however infected the blood, suffered fever for 420 days and sufered 4 strokes of clots forming

Terminal Patient: disease or condition that cannot be cured and is expected to lead to death, even with treatment.

Engineers as Managers ( Very Important) (2)

1. Design Process

- Overseeing development of a project, coordinating teams

2. Company Management

- Improved income, greater autonomy (control)

Historical Background to Biomedical engineering

Initally (1500’s)

• Most products were wooden, then metal was used

After WWI (limbs)

• The manufacutre of prosthetic limbs expanded, with the development of quality artifical legs, using metal and rubber

• Artifical limbs developed into myoelectic limbs which use electrical signals

1960 ( hip joint), consited of,.+ removing need for nails..

• First artifical hip joint , consisted of a metal ball fitted onto a plastic socket

• Newer joints now allow bone to grow removing the need for nail or screw attachment

1961 (heart valve)

• First artifical heart valve, prior was pig heart vakves

1978 (Cochlear Implant) + FAMOUS PERSON

• A bionic ear

• DR Graeme Clark was the developer

1980 (LVAD)

• Left ventricular assist device

2000 (ABIOCAR) what is it made out of

• It was made of proprietary polyether-based polyurethane called Angioflx and titatnium alloys

• Abiomed released a new electro hydraulic heartthe *abiocar

2020 (current ) SynCard…

• The SynCardia TAH

Effect of Biomedical engineering to peoples lives

• The development of heart monitors, various scanners “(CAT), MRI, Nuclear cameras”

is of paramount importance to medical world

Orders of Levers

1st Order

2nd Order

3rd Order

1st Order lever

USED IN: See saw, retractors, pliers

• Can be interchangable, effort and load can switch

• Far ends arrows

2nd Order Lever

Used in: Wheel barrow, brake pedal, bottle opener

• Both arrows left/right to fulcrum

• Effort up, load down

3rd Order Lever

• Load down, effort up

• Used in: Fishing rod

• Effort always larger then load in third order lever

Mechanical Advantage Formula

MA = LOAD/EFFORT

VELOCITY RATIO (VR)

VR= distance effort/distance load

Effiency

• MA/VR X 100

• Percentage

The Human Structure

What is the body built upn on and comprised of what…

• The body is built upon a structure known as the skeleton, and comprised of bone

Bone property + adantage, disavantge

• Hard and brittle

• More capabale of carrying compressive loads of body

• Shock loads are not well recieved

Soft Tissues + examples

• Cloakced in the skeleton to take up shock loads and impacts

• Intervertterbral discs, muscles, tendons, cartilage, flesh

Material Compatibilty and relation to human body

• Biocompatibility is the ability of a material to safely interact with the human body without causing harm or disrupting normal body functions.

• The human body is a corrosive environment, so biomedical materials must be biocompatible to resist corrosion, avoid immune reactions, and function safely over a long period.

Engineering Materials (3) FORMING METHODS

• Forging

• Casting

• Fabricating

1. Forging + 1 advantage

• Proccess of shaping a metal with forceful blows usually by hammering or pressing (The metal is often heated first to make it easier to shape)

• One of the biggest advantages of forging is that it improves the grain structure of the metal

Hot Forging

• Carried out above the recrystillisation temperature

• Easier and quicker, results in rough surface finish

Cold forging

• Forging near room temperature

• Slower and harder results in smoother, accurate finish

Grain structure of forging

• Forging grain structure is conformed to the shape of article

• A well-aligned grain structure increases the strength and toughness of the metal, therfore forged materials are stronger and tougher

What biomedical engineering items are forged to maximise strentgh

• Artifical Hip

• Joints

2. Casting

Process of Casting

• Involves pouring moulten metal into a mould, allowed to cool and solidify, and then removed to form the required shape.

Products made from casting (P, ECH, EB, S

• Pistons

• Engine cylinder heads

• Engine blocks

• Statues

Solidification of Molten Metals + solidification meaning

• When a molten metal is poured into a mould it begins to solidify by the formation of small crystal nuclei

• Solidification is the process of molten (liquid) metal turning into a solid. (cooling)

Dendritic Solidification of Molten Metal (4 steps)

1. Refer to Image

3.

4.

Fast cooling/ solidification

• Lots of crystal starting points → small grains.

Slow cooling

• Fewer starting points → large grains.

Reality of solidification

In reality, metals don't always cool evenly, so the grains can end up with different shapes.

Structure of Moulding in Ingots, what determines grain stucture

• When molten metal is poured into a Ingot, the cooling rate determines the grain structure:

Metal moulds remove heat much faster than sand moulds.

1. Sand Mould + ISOTROPIC

Grain structure: Chill crystals → Columnar grains → Equiaxed centre

• Isotropic: Strong in all directions and does not lose heat easily

Cssting temperature is correct

2. Metal/Sand Mould + ANSIOTROPIC

Grain structure: Mostly columnar grains with chill crystals at the surface

Ansiotropic: Only strong in one direction, as heat loses fast in metal sides

Casting to a high temperature

Which one is better and why

• Sand Mould,

- Has equiaxed grains in the centre.

- More uniform strength in all directions (isotropic).

while metal mould, does not provide overall uniform toughness because it contains mainly columnar grains, which produce anisotropic properties

Piping in Casting

• If we cast molten metal into an ingot we get primary or secondary pipe

• When a molten metal solidifies it shrinks

Primary Pipe

• Occurs as the metal solidifies from the outside in the molten metal

• A shrinkage cavity at the top of the ingot.

Secondary Pipe

• Internal shrinkage cavity

Sand Casting

• The most common casting procedures

1. drag + green

• The lower box “The Drag” is placed on a board with the object

• Green sand is pakced tightly around the pattern

2. Cop… , r and r

• The Drag is inverted and the top box “cope” is placed on top

• The cope is filled with sand and there riser and runners in place

3. Sepe..

• The cope and drag are seperated, the pattern, riser, and runner pins are removed and boxes reassblemed

4. Molten….

• Molten metal is poured into the runner pin until riser and runner are filled

5. Solidi…

• Casting is allowed to solidify

6. Casting is….

• Casting is removed and the runner and riser parts are ground off

Who uses sand casting (engine bl..

• Engine blocks and heads

Advantages of Sand Casting

• Cheap, easy castings, good final grain structure

Permanent Mould Casting (Die Casting) (2). very important

1. Gravity die casting

2. Pressure die casting

Cannot be broken down, and have to be reused many times

1. Gravity die casting + advantages + disadvantage,( production runs..)

• Molten metal flows into the mould by gravity (no pressure).

• Mould is able to be seperated

• Produces a better surface finish than sand casting

• Over long prodcution runs, the cost is reduced as there are many parts

• Over small prodcution runs, the cost is expensive

2. Pressure die casting + WHAT IS IT USED WITH (2 METALS)

• Molten metal is forced under pressure

• Used with low melting point alloys, such as aliminum and zinc

• Produces denser, stronger castings with excellent surface finish.

• Cost effecitve for long prodcution runs

Investment Casting (another name)

• Lost Wax Casting

What is investment casting used in + example + why is it costly

• The manufacturing of high quaility castinfg where dimensional accuracy and surface finish are excellent

• Manufacture rocker arms for automotive engines

• Costly as a new one has to be made each time

Final result of invesemtent casting

• Excellent replica of the wax mould that is superior in finish to other casting methods with no further machining required

Proccess of investment casting

A wax pattern of the desired object is made.

A refractory ceramic is coated around the wax and allowed to set

The mould is heated so the wax melts and drains out, leaving a hollow cavity that is an exact copy of the object.

4

Molten metal is poured into the ceramic mould and allowed to solidify

The ceramic mould is broken away to remove the finished casting.

3. Fabricating + example

Using numerous pieces cut and assembled to form the material

Bicycle frame

Structure + Properties of Appropriate Materials (3)

• Crsytal strucure

• Microstructure

• Macroscructure

Amorphous

• Amorphous means non-crystalline.

  An amorphous material does not have a crystalline structure because its atoms are arranged randomly, rather than in a regular, repeating pattern.

1. Crystal Structure + 3 (how atoms are arranged)

• The crystal structure refers to how the atoms are arranged in a solid material

FCC- AUSTENTITE *atoms every corner and face

BCC- ROOM TEMPERATURE “atoms every corner and one centre

HCP- When steel becomes heated until a Red Hot (FCC) stucture, then rapidly quenched to form a HCP Structure (Martensite)- Diagram shown

Vulcanised Rubber (what type of polymer)

• Vulcanised rubber is a cross-linked polymer where sulfur bonds connect polymer chains, increasing stiffness, strength, and durability.

Bakelite (what type of polymer)

Theremosett

Microscture + carbon percenatge

• When a material is viewed under a microscope

0.2 - More ferrite less pearlite (hypo-eutectoid)

0.83- All pearlite (eutectoid)

1.2- Cementite + Pearlite (hyper-eutectoid)

Macrostructure

• Can be seen with the naked eye

Stainless Steel (what does it contain…)

• Alays contain more than 10 percent chromium but not always nickel

Main stainless steel for “Biomedical Engineering’

• Austenitic stainless steel

Different types of stainless steels (number 3 most important) (FMADP

1. Ferritic stainless steel

2. Martensite stainless steel

3. Austenitic stainless steel

4. Duplex Stainless steel

5. Precipitation Hardening Stainless steel

1. Ferritc stainless steel (definiton, property, usage)

• Have a ferrite structure and have chromium added (11-27 percent) and a low carbon content

• Good strength and moderate ductility

• Used in marine application and outdoor construction

2. Martensitic Stainless Steel

• Both chromium and carbon added

• High hardness and tensile strength

• Used in Knife blades and stainless tools with a cutting edge

3. Austenitic Stainless Steel (MORE IMPORTANT)

• Accounts for 70 percent of production of all stainless steels

Austenitic Stainless Steel properties

• Have chromium, nickel and low carbon content

• Excellent ductility, formability and corrosion resistance

• Non Magnetic, making them unique

How can austentic stainless steel be welded? (mig or tig)

TIG WELDING

4. Duplex Stainless Steel (definiton + usage)

• Have a dual phase structure mix of ferrite and austenitic structure

• Used in marine and chloride rich environments

Precipitation Hardening stainless steel + MAIN PROPERTY (high yi…)

• Can be hardned through the precipitaiton hardening method

• Very high yield strength

Precipitation Hardening

Precipitation hardening is a heat-treatment process used to make a metal stronger and harder.

Why is there Heat Treatment of a precipitation hardned steel? (to achieve..)

• To achieve its peak strentgh

Steps in heat treatment of precipitation hardened stainless steel (refer to graph)

1. Anneal to more than 1000 degress

2. Slowly cool

3. Fabricate

4. Left there for a long time

5. Precipitates form, making steel stronger