Bioadhesion, biofilms d bi f liand biofouling

OEST 740020608

OutlineOutline

BioadhesionBioadhesionNonspecific

Specific bacterial adhesionSpecific bacterial adhesion

Substratum effectsSurface chemistry

Conditioning film

Free surface energy

Bioadhesion

Bioadhesion

Biological adhesionBiological adhesionBioadhesive characteristicsChemical composition of surfaceChemical composition of surfacePhysical characteristics of surfaceBi l i l f tBiological features

Nonspecific bacterial adhesion

Primary or initial adhesionPrimary or initial adhesionReversibleO i l t t ith fOccurs once in close contact with surface (< 1 nm)

RandomRandomDirected via motility or chemotaxis

Dependent upon net sum of attractive orDependent upon net sum of attractive or repulsive forces generated between two surfaces

Nonspecific bacterial adhesionNonspecific bacterial adhesion

Physiochemical interactions between the cellPhysiochemical interactions between the cell and surface

Do not involve molecular structure interactionsDo not involve molecular structure interactionsBacterial – living colloidal particles

El i d bl l fElectric double layer forcesSteric stabilization (hydrophobicity)Van der waals forces

Electric Double Layer ForcesElectric Double Layer Forces

Overlap of counter-ion cloudsOverlap of counter-ion cloudsChange in free energy as interaction distance changeschanges

pH importantB t i t ti f hBacteria- net negative surface chargeNegative charged surface

I i t th ( di )Ionic strength (medium)Van der Waals forces - Distance of separation

DLVO TheoryDLVO Theory

Combined interaction of electric doubleCombined interaction of electric double layer repulsive force and van der waals attractive forcesattractive forcesStability is determined by sum of the electrical double layer repulsive and van derelectrical double layer repulsive and van der Waals attractive forces.

DLVO TheoryDLVO Theory

Steric stabilizationSteric stabilization

Theory of interfacesTheory of interfaces

Thermodynamic modelThermodynamic model

Assumes thermodynamic driving force resulting in bacterium/solid interfaceresulting in bacterium/solid interface

ΔahdG = GSB – GSL – GBL− ΔahdG – spontaneous

HoweverHowever

Net repulsion can be overcome by specificNet repulsion can be overcome by specific molecular interactions

Adhesions on cell structuresAdhesions on cell structuresEndurance of primary adhesion depends on

f ll f tsum of all factorsSurface chemistry favors adhesion

O i b i l i fOrganic substances in solution concentrate near surfaces

Specific bacterial adhesionSpecific bacterial adhesion

Recognition of conditioning filmRecognition of conditioning filmIrreversible

Specific bacterial adhesionSpecific bacterial adhesion

Direct protein-protein or protein-ligandDirect protein protein or protein ligand bonds

Selective bindingSelective binding

Effect of SubstratumEffect of Substratum

Surface roughnessSurface roughnessSurface potentialS fSurface net chargeCritical surface tension

Composition of conditioning film

Bioadhesion resistancePolyethyleneoxide (PEO)

L t b l t t iLowest absolute protein coveragePhysical structure – inhibits protein adsorption

Polyethyleleglycol (PEG)Polyethyleleglycol (PEG)Hydrophilic polymerNon-specific protein adsorptionNon specific protein adsorptionShort-term

Poly(sulfobetaine methacrylate) (pSBMA)Poly(sulfobetaine methacrylate) (pSBMA)Long-chain zwitterionic polymerResistant to nonspecific protein adsorption

SummarySummary

The process of bacterial adhesion is dictatedThe process of bacterial adhesion is dictated by a number of factors including species, surface composition environmental factorssurface composition, environmental factors and essential gene products“Rule of thumb” initial adhesion is generallyRule of thumb - initial adhesion is generally mediated by nonspecific (e.g. hydrophobic) interactions where as final adhesion is dictatedinteractions, where as final adhesion is dictated through specific molecular fastening mechanismsmechanisms