Klausur Biokompatible Werkstoffe

= Acrylonitril Butadiene Styrene

• strong physical bonds: hetero atoms -> Nitrogen

• strain hardeing via stretching of polymers -> long chains

• Heterogeneity

• long elongation at break: due to relativ movement of polymer chains in respect to each other

1. strong physical bonds

2. internal crystal structure

3. heterogenity

4. strain hardening

• linear / branched macromolecules

• Semicrystalline: soft -> hard, tough (plastic flow), opaque due to scattering at inner interface

  • Solvent: swellable, soluble at higher T°C

• Amorphous: hard & brittle, transparent

  • Solvent: easily soluble after previous svelling (in certain organics)

• Heat: softening, become clear, weldable

• tightly crosslined macromolecules

• hard & brittle

• transparent when not filled

• Heat: remain hard, maintain shape until T°C of decomposition

• Solvent: insoluble, almost no swelling

• (mostly) loosely crosslinked

• soft & flexible

• Heat: flexible -> no plastic flow until T°C of decomposition

• Solvent: insoluble -> swellable due to loose network

• Addition to monomer to growing chain with reactive terminus = growth at end of chain

• Decrease of monomer concentration with increasing reaction time

• Increase of Molar mass doesnt change with reaction procedure

• after termination = chains arent active

• Initiator required

• Reaction can occur between any pair of molecular species = growth troughout the matrix

• rapid loss of monomers in favor of low oligomers

• Takes a long time to get long chain

• living polymer = end remain active

• no initiator required

Change of: dc sinkt

• molar mass

• cross link density

• stiffness

• molecule interactions

• crystalinity

Change of: dc steigt

• Plasticizer content

• Filler content

= Device that enables introduction of therapeutic substance into body -> controlls rate, time & place of release

Concept: controlled release

Result: equal level in plasma & tissue over defined period

• transdermal therapeutic system

• reactive agent in reservoir surrounded by polymer membrane

• release by diffusion through rate controlling membrane (

• strong water permeable membrane

• flexible membrean (impermeable for water & drug)

• due to contact to body fluid = water diffusion trough strong membrane

  • due to higher salt concentration in device

  • pressure increase in reservoir = drug release

• Carrier system

• Backbones with pendant drug - degradable system

• main chain bound active agents

• side chain bound active agents

1)Hot:

• steam

• dry heat

2)Cold:

• gas: EO / Formaldehyd

• gasplasma

• chemical: more like desinfection

• irradiation: e-beam, gamma radiation

• Filtration: Retention of microorgs in membrane surface -> liquids & gas

Plasma = 4. state of matter, created when gas is heated / exposed to strong electromagnetic field

• at low T°C: 37-60 °C

• hydrogen peroxid vapors generates free radicals that interact with molecules

Vorteil:

• for heat & moist sensitive devices

• no toxic residues

• shoert aberation time

Nachteil:

• free radicals = influence on molecular structure of polymer

Vorteil:

• low weight

• high strength + stiffness

• biocompatability (TiO2 coating on surface)

Nachteil:

• pure Ti = hexagonal crystal structure = low ductility

• sentitive to oxygen, hydrogen, nitrogen = difficult to process

= CP-Ti instead of Ti-6Al-4V:

• Biocompatability (minimal alloying elements = lower risk of toxicity)

• nearly 100% pure: softer & more ductile

• Corrosion resistance

• small grain size: nano scale powders

• incoorporation of crack stoppers: fibers

• low porosity: by high sintering temperature

• transformation strengthening / toughening

• cleavage of covalent bonds (chemical)

• by macrophages (natural)

  
  

• Polymer dissolution: cleavage of covalent bonds - thermal / mechnical processes - destruction of entire backbone

• Hydrolysis: due to hydrolytic instable bond (amide, ester), reversed polycondensation

• Enzymatic degradation: at specific groups identified by enzymes - hydrolytic, oxidative, chain scission

• Dissociation of PPC: via salvation of macromolecular components - until: gain of free energy > than energy of intermolecular cooperative interaction between 2 polymers

1) Haemostasis (Clotting):

• vasoconstriction

• platelet aggregation + fibrin formation

2) Inflammation (Phagocytosis):

• Differentiation of macrophages: Infiltration of: lymphozytes, neutrophiles, Monocytes

3) Proliferation (Wound closure):

• Angiogensis

• Collagen synthesis

• Re-epithelialisation

4) Remodelling (development of tensile strength):

• collagen modelling + vascular maturation

• give protection

• assist in healing

• restore skin integrity

• haemostatic properties - release of calcium ions

• debridment of slough

• highly absorbant (20x own weigth)

• moist wound healing

• occlusive & waterproof

• low to medium exudate wounds

• for non infected wounds

  
  

• highly absorbant

• non adherent/adherent wound contact layer - hydrocellular foam - waterproof outer layer (silicone, polyurethane)

• ??

• high water content: 96%

• can absorb a lot without dissolving

• good compatability with skin

• can be loaded with therapeutics

• needs secondary protective layer

• help in debridment

• antimicrobial agents

• Iodosorb, Aquacel AG

• Needles + Threads

1) Blood Biomaterial Interaction:

• Proteins (from blood & tissue = albumin, fibrinogen) adsorb onto surfce

2) Acute Inflammation:

• Formation of Temporary Matrix (Wound healing steps)

• Infiltration of: PMN & host cells = wound healig: defense against pathogens

3) Chronic Inflammation:

• Phagozytosis: Macrophages + Monocytes

• M1: pro inflammatory

• M2: pro healing

• exhibit high plasticity: can switch between: polarization / activation = perform different functions

4) Foreign Body Giant Cell Formation:

• Fibroplasts: deposit collagen

• Endothelial cells: angiogenesis -> Formation of granulation tissue = new tissue during healing phase

5) Encapsulation:

• “walls off” material = isolating it

• can cause functional issues around medical implant

• Hydrophylic Implant surface

• attracks water molecules = wettable surface

in FBR:

• lower protein absorption

• reduced cell adhesion

• weaker inflammatory response

zB:

• Hydrogels

• Material coated by polar Molecules

1) FCC: Face centered cubic:

• 8 atoms in corner & 1 on each side

• Kaltverformbarkeit: sehr gut & good ductility

• betaFe, Al, Cu, Pb

2) BCC: Body centered cubic:

• 8 atoms in corner & 1 in middle

• Kaltverformbarkeit: gut

• alphaFe, Cr, Mo, V

3) HCP: Hexagonal close packed:

• atoms arranged in hexagonal pattern: stacked ABAB sequence

• Kaltformbarkeit: gering & low ductility

• Mg, Zn, Ti

1) Alloy, stainless steel:

• Nickel, Chromium, Molybdenum, Iron

• Gut:

  • austensite = primary structure = good corrosion resistance

• Schlecht:

  • elastic deformation limited to 1%

    • Behandelt: Retenosis due to inflammation of tissue

      • smooth muscles proliferate = closing stent

      • corrosion = release of ions = retenosis

2) Nitinol:

• hyperelastic

• shape memory

• biocompatability

• corrosion resistance

for: stents, tools minimal invasive surgery, orthodontic wires

Surface preparation: Electropolishing!

3) Drug eluting stent:

• antiproliferative agent

  • Drug: sirolimus & paclitaxel

  • Composition: stainless steel + polymer coating (non degradable)

• 4th generation: fully degradable polymer stent

  • temporary mechanical support, decrease risk of long term complication

  • Composition: Metal + Polyester

    
    

• Austenite Phase under Low Stress:

  • Austenite phase behaves = elastically

• Martensitic Transformation under Higher Stress:

  • stress increases = austenite phase begins to convert into martensite.

  • more strain without permanent damage = superelasticity.

• Martensite Reversion:

  • stress is removed = martensite transforms back into austenite = material returns to its original shape.

• hybrid material -> glass & crystalline phase

• amorphous

• specific type of glass that interacts with biological tissue

• high strength

• fracture toughness

• for crwon coppings, bridge frameworks, abutments

• by CAD, CAM, AMT

Transformation strengthening:

• Tetragonal -> Monoclin = Increase in Volume = closes cracks (controlled by heterogenousf nucleation)

resistance against elastic deformation (reversible)

resistance against plastic deformation, fracture (irreversible)

Resistance against plastic deformation by indentation

Resistance against crack growth

• 3D network of hydrophilic polymers by:

  • covalent bonds

  • physical cross links through entanglments

  • ionic interaction

• cant dissolve!

• Process:

  • Polymer selection

  • Crosslinking

  • Gelation

• biomechanical phenomenon where implant bears a disproportionate load

  = leading to reduced stress on surrounding bone

• Mechanism:

  • remodelling follows Wolfs Law:

    • bone grows in response to mechanical stress

    • if implant is too stiff = absorbs all the stress

    • reduced bone stimulation

    • bone resorption

• Lösung:

  • Materials with E-Modul close to natural bone (Ti-alloys, porous ceramics)

  • design implant with: tailored geometires, surface treatments to support osseointegration

• ability to undergo plastic deformation before fracture

• allows material to be stretched / to be shaped)

Characteristics:

• Deformation without fracture

• high tensile strain

Factors:

• crystal structure (hexagonal = low ductility)

• T°C

• Impurities & Alloys

• Grain size

• strong physical bonds

• internal crystal structure

• heterogeneity

• strain hardening

• cold working

• grain refinement

• solut solution strengthening

• precipitation strengthening

gut:

• high strenght

• weat & corrosion resistance

• biocompatability

• durability

schlecht:

• brittleness

alloy melted at 1350-1450°C, poured & pressurized into ceramic molds of desired shape

zB: femoral stems, oral implants, cardiac stent

• biodegradable & bioabsorbable!

gut:

• temporary application

• corrosion products = biocompatible (Mg in human body)

• high specific strength & elastic modulus wie knochen

schlecht:

• low corrosion resistance

• formation of hydrogen: bubbles around implant = delay of healing

• low ductility

• to assess compatability of Material through use of isolated cells in vitro

• direct contact procedure

• indirect contace procedure

• extract test

• to determine wheter material contains chemicals that cause local / systemic effects after repeated / prolonged exposure

• intracutaneous test

• primary skin irritation test

• murine local lymph node assay

• to evaluate materials potential to cause pyrogenic repsonse / fever

• pyrogenic = substance that can cause fever when in body / blood (injections)

• in vitro

• in vivo - rabbit pyrogen test

• to determine potentially harmfull effects from longer term / multiple exposure

• test during in life phase

  • hematology

  • clinical chemistry

• to detect mutagens

• can cause cancer

• Mutagenicity & Carciagenicity

• in vivo / vitro

• to evaluate interaction between MD & living tissue

• cellular & immunologic response

• Materials used in blood containing devices must be assest for blood compatability

• Hemolysis assay

• coagulation assay

• complement activation

• to investigate metabolic processes of: absorption, distribution, etc of toxic leachables from test materials

• for: bioabsorbable material, durg-device combination

• to asses pot. effects of material on fertility / reproductive function

• weil: oft permanent contact with internal tissue