Cell Adhesion to Polymer Surfaces - PowerPoint PPT Presentation

1 / 18
About This Presentation
Title:

Cell Adhesion to Polymer Surfaces

Description:

Cell Adhesion to Polymer Surfaces George Tulevski Colloids and Surface phenomena Introduction Cell adhesion to polymer surfaces has obvious implications in the field ... – PowerPoint PPT presentation

Number of Views:48
Avg rating:3.0/5.0
Slides: 19
Provided by: engBuffal
Category:

less

Transcript and Presenter's Notes

Title: Cell Adhesion to Polymer Surfaces


1
Cell Adhesion to Polymer Surfaces
  • George Tulevski
  • Colloids and Surface phenomena

2
Introduction
  • Cell adhesion to polymer surfaces has obvious
    implications in the field of tissue engineering
  • Facilitating cellular adhesion, growth and
    differentiation onto a surface can aid in wound
    healing and tissue growth
  • a polymer can provide mechanical stability for
    the newly forming tissue
  • understanding adhesion mechanisms can prevent
    bacterial cell adhesion and aid in infection
    control

3
Composition of biomaterial surfaces1
  • Substrate - polymer surface
  • Conditioning layer - adsorbed macromolecues (i.e.
    polysaccharides, proteins
  • Cells - adhesion of cells to conditioned
    biosurface
  • Needs to be a clear understanding of composition
    of the three components and how they interact

4
Surface Characterization3
  • Use contact angle measurements to obtain surface
    energy of substrate
  • surface energy of substrate, along with that of
    the protein, governs the protein adsorption,
    including which proteins adsorb and to what
    degree

5
Surface spectroscopy General Method4
  • The solid sample is irradiated with a primary
    beam of electrons, photons, ions or molecules
  • The impact of this beam, then generates a
    secondary beam which is sent to the analyzer

6
Surface spectroscopy Examples4
7
XPS4
  • X-ray photoelectron spectroscopy
  • a photon of a monochromatic x-ray beam displaces
    an electron from an orbital of the atom
  • Eb hv EK w
  • The ejected electrons kinetic energy, Ek,, is
    measured and can be used to determine Eb,, which
    is characteristic of the atom.



  • Elemental composition, functionality, oxidation
    states and structure can be elucidated

8
SIMS and SEM4
  • SIMS - secondary ion mass spectrometry
  • the surface is bombarded with beams of 5 to 20
    keV ions, such as Ar, Cs, N2 or O2 by an ion
    gun.
  • The surface is stripped of its molecules and the
    resultant charged molecules are sent to the mass
    analyzer (i.e. quadropole, flight tube)
  • SEM - scanning electron microscopy
  • surface is scanned with a beam of energetic
    electrons
  • the secondary beam is created and consists of
    backscattered electrons and secondary electrons
  • the secondary beam is then sent to the analyzer
    and morphological and topographical information
    is obtained

9
Formation of the conditioning film2
  • The interaction between proteins on the surface
    and the cells has an enormous impact on cell
    adhesion
  • Adhesion of animal cells is mediated by adhesion
    receptor proteins in the cells membrane (the
    integrin family is primarily responsible for
    cell/foreign substance adhesion)
  • Adhesion proteins bind to ligand proteins
    adsorbed to the surface (i.e. fibrinogen, von
    Willebrand, vitronectin and fibronectin)
  • Adsorbing these proteins to a surface and
    maintaining their bio-activity can facilitate
    cell growth

10
Protein adsorption3
  • Proteins are surfactants- they have hydrophobic
    and hydrophilic portions and adsorb to virtually
    any surface
  • the degree of adsorption is governed by the
    interfacial free energy between the protein and
    substrate
  • ?GIF1w2 ?GLW1w2 ?GAB1w2
  • A favorable interaction corresponds to a negative
    value of ?GIF1w2
  • this value can be obtained from tensiometric
    measurements such as contact angle or wicking

11
Vroman Effect
  • Protein adsorption is essentially irreversible if
    no other proteins are present
  • Proteins can replace themselves at the surface
  • Different proteins have different affinities for
    a surface, proteins with a stronger affinity can
    displace proteins with a weaker affinity at the
    surface
  • When proteins are allowed to adsorb to steady
    state, and isotherm is formed in which (1) an
    adsorption plateau occurs at high bulk
    concentrations (2) at lower concentrations,
    adsorption is linear until it reaches a plateau

12
Protein adsorption (van Oss 1991)14
  • Maximum cell (absence of protein) and protein
    adhesion occurs at surface tension of 33 mJ/M2
  • Despite this, minimal cell adhesion occurs at
    this surface tension
  • since proteins adhere first, the hydrated surface
    of the adsorbed protein is hydrophilic in nature
    and results in minimal cell adhesion
  • correlates well with previous data showing that
    cells adhere least to polymer surfaces of this
    energy in vivo (Baier 1984)10

13
Protein adsorption and cell adhesion (Busscher
1989)6
  • This work displays that cell adhesion increases
    with increasing surface energy
  • cell adhesion moves from poor to good at around
    ?s 55 mJ/m2
  • higher surface energy facilitates cell growth
    (fibroblasts, smooth muscle cells, epithelial
    cells
  • bulk measurements can elucidate macroscopic
    interactions, but there needs to be a correlation
    between surface chemistry and cell adhesion to
    develop control over the system. Conformational
    changes occur regularly upon adsorption of a
    protein and can alter bio-activity. This also
    effects cell adhesion and cannot be explained by
    energetics alone.

14
Microscopic correlation (van Oss 1995)14
  • The adsorption of H.S.A. onto glass is
    energetically disfavored
  • despite this, the elbow can overcome the
    macroscopic repulsion and obtain a local point of
    attachment via a divalent metal cation (i.e.
    Ca2) electron acceptor interacting with an
    electron donor in the protein with little
    conformational changes
  • Determined by adding EDTA and then observing
    detachment of the protein

15
Minimal Peptide Sequences
  • One can circumvent problems with conformational
    changes in the protein by using minimal peptide
    sequences.
  • The most influential sequence in many ligand
    proteins is the RGDS (arg-gly-asp-ser) sequence
  • this sequence can be covalently linked to the
    surface and be used to bind to the adhesion
    receptor protein in the cells membrane and
    encourage adhesion
  • Example Brandley and Schnaar 1988
  • used (tyr-ala-val-gly-arg-gly-asp-ser) sequence
    and covalently immobilized it to a polyacrylamide
    gel surface
  • the surface was coated with a density of 2 nmol
    peptide/cm2 and supported long-term fibroblast
    growth
  • tertiary structure must have some importance and
    a role in mediating cell adhesion.

16
Specific case (Busscher 1992)12
  • The author used e-PTFE vascular grafts that were
    luminally modified and implanted into rabbit
    carotid artery
  • the interior was modified by ion etching and was
    followed by oxygen glow-discharge to render the
    surface highly hydrophobic
  • the water contact angle went from 109 to 140-150
    degrees for the modified surface
  • the graft was implanted and then removed after
    one week and inspected with SEM
  • the lumen had some platelet adhesion, but did not
    experience a cascade of platelet adhesion which
    would have led to clotting
  • the outside, anastomic side, had some endothelial
    outgrowth, as desired
  • the biomaterial succeeded on both fronts in
    providing a pathway for blood flow and tissue
    growth around the outside.

17
SEM images12
18
Conclusions
  • Four aspects to address
  • Biomaterial substrate must be well characterized
    including its chemical composition, morphology
    and structure.
  • .A firm understanding of macromolecular film
    conditioning structure, conformation and
    interaction with the substrate.
  • Cell processes such as retention, adhesion,
    differentiation and growth should be
    quantitatively measured.
  • Short and long term effects should be evaluated
  • Future trend ability to control formation of
    conditioning layer with selectivity and
    conformational control of adsorbed protein.
    Correlations between surface chemistry and
    protein conformation and how to modify the
    surface chemistry to obtain desired results
Write a Comment
User Comments (0)
About PowerShow.com