Topics In Biomaterials: 9

Proteins followed by a monolayer followed by cells

Receptors on cells bind to ligand proteins on the surface of biomaterials which affect cell proliferation, differentiation, migration, and death.

Hydrophilic RESISTS proteins because strongly bound water molecules repel protein

Hydrophobic FAVORS proteins

1. Improve tissue compatibility

2. Blood compatibility

3. Antibacterial properties

4. Corrosion resistance

5. Wear resistance

A process that alters one or more surface properties while retaining the bulk properties of a material.

1. Surface composition

2. Topography

3. Surface charges

1. Simple

2. Robust

3. Cost-effective

1. Abrasive Blasting

2. Plasma Glow Discharge Treatment

Preparing material surfaces for further treatment, cleaning, or finishing of a surface, and shot peening.

A process used to increase strength and durability by replacing tensile surface stresses with compressive stresses.

1. Remove surface contaminants,

2. Roughen implant surfaces,

3. Increase the surface area,

4. Enhance cellular-biomaterial interaction

5. Improve the adhesion of coatings.

1. Blast media

2. Accessories in the blasting equipment

3. Air compressor

Use of air compressor to propel a stream of blasting media against a surface under pressure

1. Type of abrasive media used

2. Size and shape of abrasive media

3. Substrate type

4. Gas or air pressure

5. Type of nozzle used

6. Nozzle to substrate distance

1. Glass beads

2. Sodium bicarbonate

3. Alumina (cuz its hard)

4. Calcium phosphates (resorbable blast media)

10 to 50 um with round or irregular shapes

RBM like calcium phosphate are used because they're biocompatible and may have osteoconductive properties.

1. Surface preparation: roughen to improve adhesion

2. Surface finish: roughen for resorbable blast media like dental implants

The embedment of abrasive media in the substrates which can lead to stress concentration points.

1. Local thermal equilibrium (LTE)

2. Non-local thermal equilibrium (non-LTE)

1. Chamber

2. Electrodes

3. Reactive or inert gas

Gas molecules in the chamber are ionized due to a potential difference being applied between to electrodes. Positively charged ions bombard the cathode thereby releasing secondary electrons.

The material to be modified

Excitation or elevation of energy levels of the gas molecules being ionized followed by their decay

All plasma species in localized area exhibit similar temperatures.

1. Cutting

2. Welding

3. Spraying

4. Analytical analysis such as Inductively Coupled Plasma (ICP)

5. Any applications that require high uniform temperature

Deposition of layers or etching where high temperatures are not required

Inserting a cathode and an anode into the cell or by having the walls of the cell act as these electrodes.

The physical removal of electrons from an atom or molecule in the gaseous state at low pressure where they are accelerated toward the anode.

Production of positive ions and electrons

Plasma is created when a potential difference of a few hundred volts to a few kilovolts is applied between the two electrodes.

1. The inability to use a non-conducting electrode in the chamber or cell.

2. Buildup of electrons due to constant current leads to burn-out of the glow discharge

1. Capacitively coupled RF glow discharge

2. Inductively coupled RF glow discharge

A RF power supply and the electrodes and their sheaths form a capacitor.

A electrodeless discharge in which the chamber is surrounded by a coil thus allowing the RF power to be inductively coupled to the plasma.

Thermal spraying

A line-of-sight process that uses a gas stream to carry powders, which are then passed through a plasma.

Argon and nitrogen

Hydrogen and Helium

1. Type of gas used

2. Gas ratios

Thinner coating

1. Electric heat source in plasma spraying; chemical heat source in flame spraying

2. Media supply

3. A feeder or mechanism to introduce the powder particles to the heat source

It is prepared by plasma spraying to enhance coating-substrate adhesion.

Vacuum spraying (instead of air plasma spraying)

1. Plasma spraying (highest temp)

2. Flame spraying (highest deposition rate)

3. High-velocity oxyfuel (fastest velocity)

Higher the decomposition

Thicker coatings

1. Lower bond strength

2. Higher porosity

1. Distance between nozzle and substrates

2. Powder size

3. Speed and temperature of the plasma

4. Rate of cooling

5. Gas used and flow rate

6. Energy output

7. Spray time

Flattened lamallae upon depositing on the substrate surface whose thickness and lateral dimensions depend on the size of the powders.

Metals. Differences in metal and ceramic coatings can lead to cracks

To alter the plasma characteristics and energy level

Increase the substrate temperature leading to oxidation that can be detrimental to the coating-substrate bond.

Amorphous

Cracks in the coating

Flame spraying uses an oxy-acetylene burner as the heat source.

Denser with high coating-substrate bond strength than coatings done by flame or plasma spraying.

Term that refers to a family of line-of-sight vaporization coating techniques for depositing thin films on substrates.

1. Evaporation of target material

2. Transportation of the dislodged atoms to the substrate

3. Possible reaction of dislodged atoms with reactive gas

4. Deposition of the atoms on the substrate surface

The transfer of material on an atomic level in a vacuum chamber

1. Evaporative

2. Pulsed Laser

3. Ion Implantation

4. Sputter deposition

1. Target material is melted using an electric heater

2. Rise in vapor pressure allows vapor to be deposited on the substrate

Results in electronic excitation of the target due to the removal of electrons from its atoms which then go on to collide with target atoms and gas atoms in the chamber.

A plasma plume being formed which then bombards the substrate surface with target materials.

1. Erosion of target material by high energy gaseous ions

2. Energy of the ejected atoms is transported to the substrate

1. DC sputtering

2. Radiofrequency sputtering

3. RF magnetron sputtering

4. Ion beam sputtering

DC sputtering

A continuous potential difference between the cathode and anode

A short breakdown, followed by the creation of a surface charge on the cathode

Radiofrequency sputter deposition

Radiofrequency sputter deposition

More effecient sputtering rate, minimal growth of insulating films, and independent control of bombardment of the growing film

1. Ion beam-assisted deposition (IBAD)

2. Dual ion beam sputter deposition

A cathode and thus the electrical conductivity of the target is no longer of important

The interaction of the accelerated ions generated by the ion source with the coating atoms from the PVD process as they are being deposited on the substrate surface.

1. Thinner

2. Denser

A process whereby high-energy accelerated ions penetrate or embed into the substrate material.

Penetration of ions into the substrate, causing structural damages to the surface.

Alters mechanical properties through formation of new phases at the near-surface region

A chemical process using thermal energy to heat up gases in the coating chamber and drive the deposition reaction.

Metal and ceramic coatings

1. Introduction of gas reactants in chamber

2. Moving gas reactants towards the heated substrate

3. Absorbing gas reactants on the heated substrate surface

4. Chemical reaction at the substrate forms coating

5. Desorption and evacuation of gas by-products from chamber

1. Volatile at high temps

2. Stable for delivery to heated surface

1. Homogenous

2. Heterogenous

As they move toward the heated substrates which results in the formation of gas-phase aggregates.

When the gas reactants first adsorb on the heated substrate surfaces

Homogenous reactions!

Heterogeneous reactions!

Many of the reactants or gases used are toxic, corrosive, explosive, and flammable.

Surface modification technique used to alter surface properties for selective protein adsorption.

The reaction of 1+ polymeric species or functional groups to the main chain of the polymeric macromolecules.

1. Covalent coupling

2. Surface graft polymerization

3. Surface segregation

4. Interpenetration

1. Chemical activation

2. Radiation

1. MW of polymer

2. Degree of chain branching

3. Density of functional and charged groups

4. Solubility of polymer

OH, COOH, NH2

1. Substrate surface contains active H

2. Solution contains functional species

Remove active hydrogen to create active sites or free radicals

The need to remove oxygen from the aqueous solution

Radiation grafting

1. Gamma radiation

2. UV

3. Corona discharge

4. Radiofrequency glow discharge

5. Electron beam radiation

1. Pre-radiation of substrate while in solution to create active sites by breaking bonds

2. Monomers covalently bond to substrate at the active site

3. Propagation of monomer through C-C bonds

1. Type of radiation

2. Dose or total energy absorbed

3. Dose rate

4. Radiation sensitivity of substrate

SAM deposits a monolayer thin film of organic molecules on surfaces to improve surface properties for corrosion rates, reducing friction, or enhancing wetting or adhesion.

Samples are immersed in a solution containing SAM molecules

Amphiphilic molecules containing both hydrophobic and hydrophilic properties

Hydrophilic heads

Hydrophobic tail ends

Hydrophobic tail ends

1. Chemisorption of the head group to the substrate surface

2. 2D organization of SAM molecules through inter-chain interactions of hydrocarbon backbone

To form densely packed, semi-crystalline or crystalline monolayers

1. Time of annealing

2. Cleanliness of substrate surface

3. Purity of solution

4. Properties of head and tail groups

More packed monolayer

More interactions

1. Initial solution concentration

2. Temp

Concentrated solutions

1. Simple and rapid

2. Can be used for planar and non-planar substrates

1. Micro-contact printing (planar or rolling stamp)

2. Dip-pen nanolithography

Bottom-up

Films are formed by alternatively dipping the substrate into soluble anionic and cationic polyelectrolytes

Proteins and growth factors

1. Chemical structure and MW of polyelectrolytes

2. Ionic strength of polyelectrolytes

3. pH of electrolyte

4. Time in between dipping

1. Spin-coating

2. Spray

1. Restriction in the substrate size

2. Inability to effectively deposit monolayers on non-planar substrates

1. Spraying time

2. Polyelectrolyte solution

3. Distance and angle of spray