BME 430 - Exam 2

Composites

- 2+ parts with distinct interface at nano to micro to macro scale range - 1+ discontinuous phase embedded in continuous phase

Silicones

- Biocompatibility and durability (ex: PDMS) - Soft tissue implants (hydrophobic so fibrous encapsulation) - Low Tg, elastomeric, gas and drug permeable - Thermoset (network of polymers with covalent bonds) - Can NOT be further processed after polymerization

PEG/PEO (polyethylene glycol)

- Biologically inert (resistant to protein adsorption, hides from immune system) and hydrophilic hydrogel - 4 arm PEG -> cross-linking agent fro hydrogel - Amorphous, Tg=-60

Cold working/heating

- Change grain sizes (decreases), increases strength, decreases ductility. - Heat treatment will increase grain size, decreasing strength, increasing ductility.

Acrylics

- Contain methacrylate (double bond) group, - Workable viscosity after combination (prepolymer)

Textile processing

- Continuous monofilament or multifilament (stronger) yarn with different lengths

Networks of polymers

- Covalent bonds between polymer chains - Cross-linking => covalent bonds

Hydroxyapetite

- Crystalline mineral, mimics bone/dentin - Ca substitutions (Pb, Ca, P, Zn, etc.) = destabilize, increase solubility and enhance bone growth - Osteoinductive (generate bone), but osteoconductive (bone grow on surface but no penetration) - Preparation: sintering

Elemental carbon

- Diversity of structure/properties - Graphite: sheet of carbon, soft with anisotropic, hexagonal covalent bonding (in plane) AND inter plane van der Waals. Lubricating, mechanical strength. - Bucky balls - Diamonds: hard, tetrahedral crystal (isotropic), covalent bonds

Poly(N-isopropylacrylamine)

- Example of smart hydrogel (phobic when warm, philic when cold) - Transmittance increases as temperature increases due to precipitation of hydrogel

Alumina

- Extracted from ores (Bayer process) by acid wash, then addition of salt and calcination - Inert, resistant to corrosion, elicit minimal FBR, stable for years - High wetability (low friction) and strong af in pure forms (superseded by diamonds) - Use: joint replacement prostheses, teeth replacement, extend implant life with matrix ceramics (combination of: Zirconia/CrO=mechanical properties, Alumina=hardness and wear resistance)

Cross-links

- Forms hydrogels by assembling multifunctional cross-linkers or polymers (various structures)

Pyrolytic carbon

- Graphite based, NOT ceramic - Resist thrombus formation, structural properties for long-term use (heart valves) - Need anticoagulant, carbon coating - Synthesis in fluidized bed reactor to coat substrate Mechanical properties: high flexure/structural strength, low density (movement with circulating blood), mechanical match with bone, brittle but good fatigue/wear resistance (limited deformation) -needs diamond/alumina oxide materials for machining

Cobalt based alloys

- Hard to process - Used in femoral stems and oral implants (corrosion resistant layer by adding chromium) - Investment casting for fabrication

Fluorinated polymers

- Hydrocarbons with lots of fluorine pendant atoms (high EN) - Chemical resistance (doesn't react to anything due to helical axis) - Low interfacial energy/friction (chemical inertness) - High tensile properties and temperature resistance - Can NOT be further polarized ex: PTFE, PVDF, FEP

Ceramics, glass, glass-ceramics

- Inorganic, nonmetallic elements - Made with isostatic pressure and annealing - Difference between them: microstructure

Stainless steel

- Iron and carbon alloy with impurities (Cr, Ni, Mo, some N, Mg, P, C (316)) - L = 0.03 % Carbon content - Oxide layers added for corrosion resistance

Crystallinity

- Level of close-packing between polymer strands

Surface immobilized biomolecules

- Many ways biomolecules can be immobilized on substrate. - Important to keep bioactivity - Materials with surface: -OH, carbonyl, primary amide (reactive) - Molecules used to covalently bind to surface: azide, alkyne, -SH

Textured/porous materials

- Materials that stimulate tissue ingrowth, disrupt fibrosis, promote angiogenesis - Optimal pore/texture size and method depend on tissue and material

MW of polymers between crosslinks

- Mc definition - Describes basic function of hydrogel

Fabrication of metallic biomaterials

- Mine from mineral deposit - Physical manipulation/processing - Fabricate into shape - Surface preparation - Cleaning/quality control/packaging

Polymer

- Molecule composed of many units (monomers) - Largest class of materials used in medicine

Acrylic monomer

- Monomer used to form hydrogels - Double bonds before polymerization, easily polymerize (Free radical) - Different properties ex: PHEMA

Addition reaction

- Monomer with at least one double bond (multiple double bonds lead to branching/network) - Radical process yields random polymers with high PDI

Matrices (composites)

- Most composites have polymer _______, not bioresorbable - ex: PEEK, UHMWPE, PTFE, PMMA - Absorbable composite implant from polyester (PLA, PLGA, PGA) - Bioresorbable natural polymers (collagen and chitosan. Matrices, scaffold, drug delivery)

PHEMA

- Most widely used FDA approved hydrogel - Contact lenses - Biologically inert, permeable to metabolites, swelling upon hydration

Alginate

- Natural bioinert polysaccharide - Linear anionic form brown algae - Homopolymer blocks - Ionically cross-linked or covalently - Encapsulate cells

Native collagen

- Natural material example - 14 forms - Triple helix with amino acids - Type 1 (abundant, skin/bond/tendon) - Type 2 (cartilage) - Type 3 (blood vessel wall) - Type 4 (basement membrane - between epithelial and mesenchymal/meat of tissue)

Extracellular matrix proteins

- Natural material example - Mechanical support for cells, sequester growth factor, secreted by cell - Bioresorbable - Large proteins isolated from other biological sources

Decellularized matrices

- Natural matrix - Detergent treatment removes cell/debris - Maintain ECM structure and protein, clear (immunogenic) - Perfused with cells=new tissue (limited success/viability/length) ex: pork tissue = FDA approval for heart valve, submucosa, pulmonary artery patch application

Fibrin

- Natural polymer - Forms mesh - Produced after coagulation - No mechanical strength

Elastin

- Natural polymer - Tropoelastin (soluble) to elastin (insoluble), from intermolecular cross-links (gamma, chemical)

Chitosan

- Natural polysaccharide (polycationic copolymer) - From exoskeleton of crustacean - Ionic cross linking with polyelectrolyte complexes, covalent crosslinking with aldehyde - No cell adhesive motif

GAGs

- Natural proteoglycan (covalent bond) - Alternating hexamine and sugar units ex: HA, CS and Heparin

Hydrophilic polymers

- Natural, synthetic, or combinations (customize) - Most hydrogels - With hydrophobic polymer => reduce swelling

Nitinol Martensite Austenite (stress 800-1500)

- Nickel and titanium allot - Shape memory => different cubic structure when cooled (_________) vs heated (__________)

PVA (polyvinyl alcohol)

- Nontoxic, hydrophilic polymer (blood contact) - Drug delivery matrix - Freeze and thaw to crosslink (no crosslinking agent) - Pack tightly b/c o small side groups

Collagen

- Not helical, 3 protein chain assemble into microfibrils - Covalently crosslinked (aldehyde, dehydration, enzymatic modification), less elastic

Erosion

- Physical change of shape, size, mass of device - May not involve degradation

Stress strain curve

- Records changes due to physical forces (MTS machine-tension and compression) - Determine tensile (young's) modulus, tensile (yield) strength, ultimate tensile strength, ultimate strain/elongation at break

- Increases/decreases - Decreases/increates

- SMALL/multiple grains _________ strength and ________ ductility - LARGE/less grains _________ strength and ________ ductility

Ceramics

- Sintered polycrystalline powers (powder fuses) - Ionic covalent bonds, minimal porosity, ultra-fine grain formation - Small grain

Glass

- Solid with no/little crystalline formation - Fine particulates are melted, homogenized, cool rapidly (prevent crystals/grains)

Swelling (medical applications)

- Solute diffusion within/out of porous hydrogel network (controlled release of drugs-swell in drug, controlled drug release) - Surface property/mobility of polymer network (more hydrophilic, more lubricated) - Pptical (contact lenses) and mechanical (dissolution and biodegradation) properties

Glass-ceramics

- Start as glass, end as ceramics - Rapid cooling - Mechanical properties while maintaining translucency, less brittle than glass

Tacticity

- Stereochemistry of repeat unit - Synthesis of isotactic/syndiotactic requires catalyst - Can affect crystallinity (close-packing)

Smart hydrogel

- Stimuli responsive hydrogel - They separate/precipitate out of solution due to temperature change - Change swelling based on pH - Change from solid to gel for injections

Bioceramics

- Success as implant - Classified by bioreactivity (rate of formation of interfacial bond with tissue) - Level of reactivity of implant influences thickness of interfacial zone/layer between material and tissue

Titanium alloys

- Ti with O, Al, Vanadium - Al is an alpha phase (HCP) stabilizer - Vanadium is a beta phase (BCC) stabilizer - Ti/Al oxide => corrosion resistance - O, C, N => strengthen metal (durability)

Surface Patterning

- Use of surface modification methods to make chemically/physically demarcated regions on surface - Methods derived from microelectronics industry

Polyurethanes

- Used in blood contacting applications - Mechanical stability and good biocompatibility - Biodegradation=ether groups (hydrolysis reaction in body) - Can be further processed after synthesis with heat

Polymer molecular weight average (MW)

- Used to describe polymer molecular weight - Can have variable degrees of polymerization (weight) due to synthesis - Calculation

Hydrogels

- Water-swollen polymer system (compatible with human tissue due to water content - Made with at least one hydrophilic polymer for swelling purposes

Bioactive fixation stages of type 3 bioceramics

1 - Ion exchange from implant and hydronium from solution 2- Silica structure breaks down/dissolve at interface 3- Repolymerization of silica oxide on inactive glass surface 4- Calcium phosphate film on silica and crystallization 5- Forms HA crystals

Diffusion, hydrogel degradation, swelling after diffusion

3 driving forces for drug delivery hydrogels:

Non absorbable composite

Absorbable or non absorbable composite? - Life-long implant, total joint replacement - Femoral stems: composite materials generate elastic and strong implant (mechanical matching)

Absorbable composite

Absorbable or non absorbable composite? - Time varying mechanical properties - Complete dissolution of implant matrix and reinforcement - Prevents bone resorption b/c of stress shielding, secondary surgery to remove potentially corrosive implant - PLLA, HA=bone fixation (biodegrade, osteoconductive)

Corrosion resistant Bioinert Mech similar to bone Light weight and high strength

Advantages of titanium alloys

Improves, cell phenotype

Alligning and collecting eletrospinning fibers on mandrel _______ (improve or not) mechanical and optical properties, as well as affecting _______

Biodegradation

Biological agent causes breakdown

Physiochemical surface modification

Can be specific or non-specific - Only changes surface, material stays same inside - Influences biointeractions - Thin as possible - Resist delamination by covalent bonding, intermixing surface film and substrate (interfacial zone-IPN), adhesion primer layer (buffer layer) - Driven by minimizing interfacial energy (ex: causes F to blossom)

Charge formation

Chemical mechanism of bioerosion - Ionization and protonation of R-groups - Change in pH

Solubilization

Chemical mechanism of bioerosion - Material forms hydrogen-bonding with water

Chemical degradation with hydrolysis

Chemical mechanism of bioerosion - Occurs with most polymers, proteins, sugars - Cleave cross links => dissolve - Side chains degrade => change polymer chemistry - Break backbone => dissolve hydrogel

Enzyme catalyzed

Chemical mechanism of bioerosion - Reaction with specific bond to cause erosion - Nonspecific fashion

Degradation

Chemical process resulting in cleavage of covalent chemical bonds (hydrolysis, oxidative, enzymatic mechanisms)

Bioactivity

Common term in surface patterning - Biologics that denature in harsh processing - Patterning method works in aqueous conditions at ambient temps

Contrast

Common term in surface patterning - Degree to which components in pattern are distinguishable from background - *Passivation step*: prevent nonspecific adsorption to background regions - PEG monolayer

Shelf life/durability

Common term in surface patterning - Ideal storage -> ambient conditions for unlimited time - Hard for patterning soft-wet materials, may require using patterned substrate immediately before use

Throughput

Common term in surface patterning - Measure of SA patterned in period of time

Resolution

Common term in surface patterning - Smallest feature size reasonable created by patterning technique - Lower may not be applicable for all situations

Filament winding process

Composite fabrication by aligning fibers by a spinning mandrel. High tensile strength, hollow cylinder implants.

Continuous pultrusion

Composite fabrication by pulling aligned fibers, coated in matrix

Hand lay-up process

Composite fabrication example where material is laminate-reinforced. Can laminate in different directions.

- A: bioactive bone boundary, bind with bone - B: silicate glasses, like type 2 - C: resorbable glasses, disappear - D: too weak - in dashed region = collagenous soft tissue bind to silicate glass

Composition of Type 3 bioceramics (Si, Ca, P) affects binding behavior. Label:

Composite fabrication

Compression/injection molding or extrusion are most common. Polymer pellets are heated and mixed, injected into mold (mix matrix with filler and form shape). - Establishment of strong interface between reinforcement and matrix is key

-Primary amines, hydroxyl, CA -Primary amines, aromatics, CA

Covalent attachement - Groups doing immobilizing (3) - To be immobilized (3)

Yarn linear density

Decitex = mass in grams of 10,000 meters of fiver

Glaucoma drainage device

Device placed in sclera or eye, tube under iris into anterior chamber, *allows for drainage* - GDD plate enclosed by fibrous capsule - Makes "bleb" of non-pressurized space, liquid drained to be resorbed into tissue - If fibrous capsule *too thick*=not permeable and device failure

Amorphous - no particular shape, elastic Semi-crystalline - polymers form lattice (stronger mech properties)

Difference between amorphous and semi-crystalline hydrogels

Surface erosion

Erosion when water penetration SLOWER than material transformation into water-soluble, maintain structure/integrity

Bulk erosion

Erosion when water penetration is FASTER than polymer transformation into water-soluble, crumbles

CS

Example of GAG - Anionic, major part of cartilage, absorb water (compressive strength)

Heparin

Example of GAG - Highly sulfonated - Binds to growth factors in ECM - Used in catheters and stents

HA

Example of GAGs - Non-sulfonated GAG, found in all body tissues, not a proteoglycan, higher MW

Fabrication in location

Example of composite fabrication. Bone cement is mixed and placed in cavity, cement in place.

Higher Coat Less More Sutures

Fluorinated polymers - High MW and helical confirmation: ____ (higher or lower) melt viscosity - Prefers to _____ (coat or not coat) material's air surface - More fluorines = ____ (more or less) crystalline, ____ (more or less) elastic - Used for _______

Denatured

Gelatin is the ________ version of collagen

Increased osteoinduction Decreased strength

Generating porous HAP causes _____ in osteoinduction (pores >100 microns) and ______ in strength

Good: Stability, Mechanical strength Bad: Stress leads to corrosion, Stress-shielding

Good and bad of using metal devices

Fatigue resistance

Hard and soft segments in polyurethanes give it ______ resistance

Slower

Higher MW and PDI causes _____ (faster or slower) erosion

Increased mechanical properties

Higher molecular weight polymers show _____ mechanical properties due to more interactions (more energy to break bonds)

Addition of filler particles

How can the yield strength of silicone be improved?

- Primary covalent crosslinks - Ionic forces - Hydrogen bonds - Affinity (bio-recognition) - Hydrophobic interactions - Polymer crystallites - Physical entanglements - Combination

Hydrogels are held together by: (8)

Higher Lower Lower Higher

Impact of structure on Tg and Tm: - More intermolecular forces (H bonding) = _____ Tg and Tm - Less pendant groups (free bonds) = ____ Tg and Tm - Less bulky pendant groups = _____ Tg and similar Tm - Pendant group chemistry => more EN atoms => interact with H groups = _____ Tg and Tm

Water interaction

Impact on crystallinity - Chemistry and degree of crystallization affects hydrophobia - Closer packing => less interaction => hydrophobic (high crystalline)

Absence of pendant groups

Impact on crystallinity - More rotational freedom => increased free energy => increase elasticity and decrease crystallization - Not entropically favorable to be immobilized, doesn't freeze under normal conditions (freedom in bond)

Intermolecular forces

Impact on crystallinity - Not covalent bonds - Van der Waals, hydrogen bonding, ionic interactions, pi-stacking (aromatics) - Stronger forces => attraction => closer packing - PET => pi stacking (high crystallinity), PTFE/PVC => ionic interactions and H-bond

Bulkiness

Impact on crystallinity Bulkier groups and irregularities leads to less closely packed

Decreased filler dimensions

Interface in composites is important in _______ (decreased or increased) filler dimensions?

1 - Glass 3/4 - Ceramics 5 - Glass-ceramics

Label 1, 3/4 and 5

A - Cross-linked film B - Grafted brush C - Alkanethiol SAM D - Surfactant

Label PEG:

A = Linear amorphous B = Semi-chrystalline C = Crosslinking

Label the stages of glass transition

A = Young's modulus B = Yield strength C = Ultimate strength D = Fracture

Label:

Difunctional

Linear monomer that has reactive groups on both ends

Biomimetic materials

Materials designed to replicate natural material, four types of mimicry (functional, molecular, process, structure)

Degradable and resorbable biomaterials

Materials for short term application without secondary intervention -ex: temporary support devices (sutures, fixation), temporary barriers (tissue adhesion, skin lesions/burns), drug delivery matrix -can be multifunctional

PDI (polydispersity index)

Measure of distribution of molecular masses in polymer system - If = 1 then polymers are of same length (ideal) - Narrow distribution better than broad molar mass distribution

Mechanical properties of pyrolytic carbon

Mechanical properties - High flexure/structural strength - Low density (movement with circulating blood) - Mechanical match with bone - Brittle but good fatigue/wear resistance (limited deformation) - Needs diamond/alumina oxide materials for machining

Salt/particle leaching Gas forming Freeze drying

Methods of making textured/porous materials: - ________ _______: salt not dissolved in polymer solution, add water, salt dissolves and leaves pores (not interconnected) - _______ _________: add gas, when dries leaves interconnected and large pores - __________ ________: freeze, low vacuum pressure removes water/ice molecules, highly porous/interconnected

Microstructure of pyrolytic carbon

Microstructure - Small crystalline size, lattice imperfections = mechanical strength - Order within layers (not between), lattice vacancies (curved/kinked planes=strength)

Branching or network

Monomers with 3+ functional groups can form ______ polymers

PLG and PLA

Most widely used bioerodible polymer

- Random - Alternating

Name the following polymer arrangements: AABABBABABBAAB ABABABABABABAB

FCC non-magnetic 316 or 316L

Names of stainless steel used for implantation in body, crystal structure and what is it done for corrosion prevention

Polysaccharides Proteins GAGs

Natural materials for hydrogels example (3)

Network contracts

Network _____ when hydrogel is cross linked in swelled state

Network expands

Network ______ when hydrogel is cross linked in dried state, then swells

Protein concentration Pluronics Kosmotropes

Non-fouling behaviors influenced by: - _________: longer hydrophilic changes provide non-fouling behavior - ________: block non-specific protein adsorption and cell adhesion (polymers with zwitterionic groups - albumin, casein) - ________: creates non-fouling surfaces since they order surrounding water molecules.

Plasma treatment

Nonspecific surface modification - Oxidizes surfaces and gases and it is reactive - Deposition: make surface free radicals/reactive species (polymerize with molecules from gas phase) *OR* small molecules and high MW units in gas phase precipitate on surface - Pros: coats any surface, film easy to make, sterile when removed - Con: surface particles will react randomly

Degree of polymerization (n)

Number of repeat units in polymer

Crystalline structure

Ordered structure with similar regions close to each other, promoted by intermolecular interactions between polymer chains

PTFE FEP PVDF

PTFE, PVDF and FEP in order of more elongation

Lithography

Patterning with mask - Etched stones with ink, create imprint - Mask => template with spatially modulate field/radiation that passes through it, control exposure

Positive Negative

Photoresist in photolithography - __________ => soluble when exposed to light, rinse off photoresist that contacted with light (w/out=pattern) - __________ => insoluble when exposed to light, wash negative pattern (w/=pattern)

PEG

Poly(ethylene glycol) - 2-15 units immobilized many ways - Longer oligo chain means lower surface density for non-fouling - Minimum of 3 EG units for effective protein absorption (within SAMs) - Variables are conformation and surface density

Homopolymer

Polymer arrangement: - 1 monomer subunit AAAAAAA

Block copolymer

Polymer arrangements - Large blocks - Phase separation - Can lead to combination of properties (PDMS - higher elasticity, with, PP - higher mech strength, combination: elastic but reinforced) AAAABBBBAAAABBBB

Diffusion coefficient

Pore volume fraction affects:

Mesopores, micropores

Pores >2 nm, <50 nm and pores <2 nm for solute/drug diffusion

Macropores

Pores >50 nm, <300 micrometer for tissue and cell penetration

Burst release

Rapid diffusion of molecules at surface of polymer matrix of hydrogel (affected by bulk vs surface erosion)

Number of oxygen bonds (and double bonds) and amines

Rate of hydrolysis of polymers increases with the increase of and decrease with increase of:

Condensation reaction

Reaction - 2 monomers form covalent bond with elimination of small molecule (H2O) - Ester bonds are liable to hydrolysis (interstitial fluid), control crystallinity/hydrophobicity to control rate of degradation

Anisotropic fibers

Reinforcement material in composites, anisotropic is more effective. Used in orthopedics, dentistry, ligament/tendon, and eletrospun nets

Oligomer

Short chain of monomers (just few repeating units)

Surface modifying additives

Specific surface modification - Added in low concentration during bulk material fabrication (doping/imbed) - Spontanteously rise to dominate surface by minimization of interfacial energies (fluoropolymers)

Conversion coating

Specific surface modification - Dense oxide rich outer layer added - Impart corrosion protection, enhanced adhesion, altered appearance, lubricity (Cr oxide) - Induced with acid wash

Layer by layer deposition and multilayer polyelectrolyte deposition

Specific surface modification - Dip coat of charged/oxidized substrate into molecules with alternating charged - Natural polyanions or polycations to coat (HA or chitosan)

Langmuir-Blodgett deposition

Specific surface modification - Dip coat surface with 1+ layers of surfactant molecules (hydrophobically bound) - Multiple layers - Stabilized by cross-linking after formation

Silanization

Specific surface modification - Hydroxylated surface - Densely presented on glass, Si/Al/Ti/quartz/metal oxide - Bind to self-assembled, covalently bound monolayers on hydroxlyated surfaces - Con: prone to hydrolysis, resistance in vivo varies

Ion bean implantation

Specific surface modification - Injection of accelerated ions one surface Zoe - To modify hardness, lubricity, toughness, corrosion, conductivity and bioreactivity. - Used on materials with crystal lattice structure (metals, ceramics, glasses, semi-conductor)

Self-assembled monolayers

Specific surface modification - Reactive group next to alkyl chain, covalent bond with substrate (gold, silver, copper) - most common - Formation requires moderate-strong adsorption of chemical anchoring group to substrate, van der waals interactions of alkyl chains leads to quasi-crystallization Other examples: -n-alkyl silanes on hydroxylated substrates -alkane thiols on gold/silver/copper coated -amines/alcohols on platinum substrates -CA on Al oxide -Silver/phosphate on Ti or tantalum

Parylene coating 1- vaporize 2- pyrolyze 3- deposit

Specific surface modification - Simultaneous evaporation, pyrolysis deposition, polymerization of di-para-xylene monomer - Insulates electrical components (moisture barrier, water/oxygen resistance) - Name steps (1, 2, 3)

Initiation Propagation Termination

Stages of free radical polymerization: - ______ - generates free radical - ______ - interaction, bind, disrupt double bond in adjacent monomer - ______ - form double bone with another monomer radical

Bone implants

Stimulating tissue growth implant - Ideally has similar mechanical properties, biocompatible, degrades with bone remodeling - Textured fixation layers minimize prostheses loosening - Fixation also improved using porous material (osteointegration), reducing stress shielding

Orbital implant

Stimulation of tissue growth implant - In eye when enucleated (trauma, ocular cancer, blind/painful eye) - Implant success if integrated into tissue/muscle - HAP, PE, Al oxide with pores of 400 micrometers (fibrovascularization) or porous hydrogels - Mechanical mismatch can cause inflammation

Nonspecific surface modification

Surface modification with distribution of different functional groups on surface

Specific surface modification

Surface modification with well defined reactive chemical groups on surface

Direct write patterning

Surface patterning technique - DPN, nanoimprinting/engraving, inkjet - Scanning patterning element across substrate - Generate patterns with arbitrary feature shape/size - High resolution/low throughput

Non-fouling surface

Surface type - Resists protein adsorption/cell adhesion (hydrogel - hydrophilic) - Resistance is related to resistance of interfacial groups to release bound water. - Application: catheters, biosensor, microfluidic, IV tubing

Free water Osmotic

Swelling behavior of hydrogel: - Solute diffuse through ________ ____ channels - Equilibrium due to ______ force

True

T/F Discontinuous phase is harder (reinforce) than continuous phase (matrix)

Atactic

Tacticity name for material with random stereochemistry

Syndiotactic

Tacticity name for material with repeating pattern of stereochemistry (closer packing)

Isotactic

Tacticity name for material with same stereochemistry (closer packing)

Melt temperature

Temperature of transition from solid to liquid (Tm), affected by molecular chem and structure

Glass transition temperature

Temperature of when there is no intermolecular rotation or movement (Tg), affected by molecular chem/structure, three phases: - Glassy state - Semi-crystalline phase => regular lattice structure achieved (only iso/syndio polymers) - Rubbery state => plateau above Tg where modulus changes slowly (soft and extensible)

Biotextiles

Textiles - Nonviable, permanent or temporary, fibrous structures - Synthetic or natural materials - Thin, strong, flexible, lightweight, porous structures - Good fatigue properties, large SA

Pendant groups

The chains or groups coming off the backbone of the polymer

Structure-property relationship

The molecular characteristics determine the physiochemical material properties and the material's application - Molecular structure/processing => morphology => function => use - Relationship

Volume and porosity

The strength of calcium phosphate in Type 4 bioceramics depend on:

Decrease

The volume of acrylics may _____ after polymerization

7 polyesters

There are _ degradable and resorbable polymers that are FDA approved, mostly _________

-Physical adsorption -Physical entrapment -Covalent attachment

Three methods of immobilization: - _________ _____: van der Waals, electrostatic interactions, affinity recognition - _________ ______: microcapsules, hydrogels, physical mixtures (matrix drug delivery), porous layer - ________ ________: soluble polymer conjugates, on solid surfaces/within hydrogels (attached by PEG arms - remains bioactive)

Use chain transfer agent

To produce polymers with low PDI by free radical polymerization

1. stable attachment to connective tissue 2. stimulating repair/regenerate tissue

Two reasons why bioceramics are successful implants

Entropic Osmotic

Two types of repulsion mechanism (entropic or osmotic) - _________ due to random polymer coils retain expanded volume - _________ highly order water layer (PEG resistance) to release H2O from hydrated cells, prevent molecule interaction at surface

Type 1

Type of bioceramics - Dense, nonporous, inert - No biological bonding at interface - Implanted by compression loading - Movement at interface can wear particles, cause fibrosis capsule (good for bone movement)

Type 3

Type of bioceramics - Interfacial bond between tissue and material from bioresponse (bioactive fixation) - Can bind to bone, soft tissue -ex: hydroxyapetite, bioactive glass/glass-ceramics

Type 2

Type of bioceramics - Nearly inert, microporous - Strength from ingrowth of tissue (biological fixation pores must be > 100 micron) - Application: nonloading, space filler - Increase porosity, decrease strength - Derived from hydroxyapatite

Type 4

Type of bioceramics - Resorbable biomaterials (replaced by tissue) ex: PLGA suture, CaP ceramics - Good if mech requirements and short term performances work - Used as plasma sprayed coating for porous overlay - Biodegrade by physiochemical dissolution, disintegration, or biological factors

DPN, nanoimprinting/engraving

Type of direct write patterning - Direct writing with rigid stylus and control of atomic force microscope (AFM) - Cantilever beam deflects laser to measure topography

Photolithography

Type of direct write patterning - Focused beam of light to pattern substrate, mask based - Resolution based on *diffraction limit of light* (200nm) - Photochemical or physical modification - Use: generate electrode array for stimulating and recording signals culture neuronal cells

Focused ion beam lithography

Type of direct write patterning - High mass ions to bombard/ablate surface molecules - Engrave sub-micron features

Electron beam

Type of direct write patterning - Pattern at resolution: 10-100 nanometers - High vacuum and dry sample - Focused beam of electrons=stylus, crosslinking/functionalization rxns - Low throughput, not continuous - Make patterns for adsorption/functionalized with biologics

Inkjet

Type of direct write patterning - Pump ink through nozzle onto substrate as 10-20 pL droplets in pattern - Lateral resolution: 10-100 micrometers - Contact free, ambient conditions, positional accuracy, high throughput, low resolution, clean airspace (less contamination)

Ionic hydrogels

Type of hydrogel - Has charges on polymer backbone

Complexation hydrogel

Type of hydrogel - Held together by special forces (h-bond, hydrophobic group, affinity complexes)

IPN

Type of hydrogel - network of two different hydrogels - cohydrogel

Soft lithography

Type of lithography - Make stamp (pattern on substrate) off of PDMS - Fabricated with photolithography - Cost-effective, pattern nano to microscale patterns, high throughput

Multiphoton lithography

Type of litrography - Confocal: single photon/plane (2D) or multiphoton: 2 photon (3D - dot) - Laser based direct writing - 3D photopolymerized polymers - Moderate throughput, 250 nm resolution

Aramid fiber

Type of reinforcing fiber - Aromatic polyamide fiber (Kevlar) - Low density, low strength, resists impact via energy dissipation (microfibers), shock absorbent - Hygroscopic

Glass fiber

Type of reinforcing fiber - Good strength-to-weight ratio, dimensional stability, thermal/moisture/corrosion resistance and electrical insulation - Low cost

Carbon fiber

Type of reinforcing fiber - Turbostratic cylinder, coated with PE or PVA - Lightweight, flexible, high strength, stiff - Wear debris can cause inflammation

PCL fiber

Type of reinforcing fiber - Use with PLA, PLGA, PGA (to control release) - Hydrophobic, slowly degrading, semi-crystalline polymer

Nanoparticles and nanofibers (nanofillers)

Type of reinforcing fiber/particulate - Small amounts => mechanical/functional properties (high interface) - ex: silica, nanoclay, nanotubes, POSS (atoms in cubic form) - Release of debris affect cell function

PLA, PLGA, PGA fibers

Type of reinforcing fibers - Bioresorbable application (suture, etc.)

PET fibers

Type of reinforcing fibers - Darcon - Arterial graft implant/fabrics for implant fixation

UHMWPE fibers

Type of reinforcing fibers - High modulus, high energy dissipation, good biocompatibility, low density - Low melting point bc only few resins bond well (no high temp fabrication processes)

Ceramics particulates

Type of reinforcing particulate - Decreased strength and brittle properties - ex: Ca/P, Al/Zn based phosphate, glass/glass ceramics, HAP - Ca/P and HAP are bioactive particulates, used in coating on metal implant (osteointegration)

Cell adhesion

Type of surface-immobilization - *Covalent immobilization* of *peptide* motifs from ECM proteins that engage integrin receptors (RGD) - Nanoscale clustering (<70 nm separation) increases adhesion signaling, forming focal adhesion - Material elicits functions/reactors through immobilizing polypeptide growth factors (maintain bioactivity upon covalent immobilization)

Wet/gel spinning

Type of textile processing - For polymer (natural material) that degrade at high temp - Dissolved into solvent, extruded through spinneret into nonsolvent spin bath (precipitate into solid filament) - 10 micrometers for multifilament, 500 micrometers for monofilament

Melt spinning

Type of textile processing - Heating polymer resin to melting temp, extruding through spinneret - Number/shape of holes in spinneret = filament count and cross-sectional shape - Thermoplastic polymer - Lubricate fiber with spin finish or twisted or entangled WHEN spooling to reduce friction

Bi-component spinning

Type of textile processing - Multiple polymer components brought together at spinneret hole - Make filaments with all polymer components in separate parts of cross-section - Unique combined chemical properties - Achieve smaller fiber dimension by *split/separate after spinning*

Electrospinning

Type of textile processing - Polymer solution charged in syringe shot at electrostatic field onto collector plate - Collect as network of non-woven fibers (100 nm) - Nanoscale architecture of ECM (network of interconnected pores, cell integration) - Synthetic modification with bioactive molecules for cell adhesion and growth

-functional -molecular -process -structure

Types of biomemetic - _______ - copy physical/chemical properties - ________ - atoms/molecules used to produce biomaterial - ________ - pathway/mech. of how biomaterial produced - _________ - pattern of molecular organization

IPN (interpenetration network hydrogels) Ionic Complexation

Types of hydrogels (3)

Use: bone screw, implant, superelastic Bad: Ni is allergenic but Ti oxide prevents reaction

Uses of nitinol and bad sides of it (and how is it fixed)

Type of polymer, solvent solution, solution conc, melt viscosity/conductivity, strength/uniformity of E field, geometry, operating conditions of spinning system

Variables that affect electrospinning (7)

- Solute diffusion - Surface property - Molecule mobility - Optical property - Mech property

Volume of swelling affects: (5)

Tacticity, intermolecular forces, bulkiness/sterics, charge

What can crystallinity be affected by? (4 things)

The free rotation on the Si-O bond

What causes the low Tg in silicones?

Necking

What happens past the material's ultimate strength

Calcium and phosphate ion

What ions in glass/ceramics provide nucleation sites for crystallization? (2)

Gly-Pro-X or Gly-HydroxyPro-Y

What motifs in collagen lead to h-bonding

MAA - hydrophobic

What polymer used in PHEMA to decrease its swelling behavior due to _______

Photopolymerization

What polymerization is used to make acrylics? (used in orthondontics)

Hydroscopic

When a fiber absorbs moisture, can be a problem in vivo

Bioerodible

When a water-soluble polymer is converted to a water-soluble material in physiological conditions

High, increases, brittle

____ degrees of crystallinity ______ mechanical properties (tensile modulus and strength) but can make it _______

Volume of swelling (1/Q or U)

_____ = Volume at dry state / volume at swollen state

Tight

_____ cross linking can make stiffer materials, impeding crystallization

Light

_____ cross linking can product elastic materials

Covalent

_____ cross linking, increases tensile modulus/strength, impedes crystallization, used for hydrogel synthesis (light or tight)

Higher

______ (higher or lower) MW can increase mechanical properties of polymer due to random interactions

Porosity Texture

______ - disrupts fibrotic scar, less uniform collagen, promotes tissue ingrowth and vascularization around tissue _____ - improves ingrowth at implant interface, less FB fibrosis, disrupts collagen

Crosslinking Decreases

______ density affects hydrogel porosity and mechanical properties - High density ______ mech properties

Linear, branched

______ polymers crystallize more easily than _____ polymers

Grain boundaries

_______ boundaries in metals that provide force distribution

Formula for filament #

filament# X density X length X cross-sectional area = textile unit #