Lecture 13 - Scaffold Modification Flashcards
Biomaterial/Blood Interactions
- Adsorption of inorganic components such as water, metal ions (Na+, K+, Fe2+, Cl-)
- Biomolecule adsorption - proteins, glycoproteins, and polysaccharides
- Blood component adsorption/interaction - platelets, PMNs, coagulation/fibrin clot formation
Biomaterial/Tissue Interactions
- Inorganic components and biomolecules in body fluid adsorption
- Cellular adhesion, proliferation, and differentiation
- Ideally, development of specific biomaterial/tissue interface
Biomaterial/Cell interactions
- Inorganic components and biomolecules in culture medium adsorb onto surface
- Cellular adhesion, spread and proliferation
Surface Properties Relevant to Biomaterial Performance
- Surface chemistry (composition, functional groups)
- Surface energy ( hydrophilicity/hydrophobicity)
- Surface charges (type (ionic, cationic), density)
- Surface structure (topography/roughness, porosity, defects)
Surface Modification Methods
- Plasma treatment and deposition
- Radiation grafting
- Chemical reaction of the surface
- Ion etching
- Self-assembly
- Immobilization of biomolecules
Non-Covalent Modification
- Physical Adsorption —> amphiphilic macromolecules (block copolymer) adsorption, Ex: PEO-PPO-PEO (PEO-hydrophilic, PPO-hydrophobic)
- Electronic Assembly (polyelectrolyte layer-by-layer assembly) —> alternate adsorption of polycations and polyanions on the surface forming multilayers, Ex: substrate (PLA, PCL), polycation (gelatin, PEI, polylysine, polyanion (PAA, alginate)
Plasma Surface Modification
Plasma:
- Typically an ionized gas (can be ions, electrons, free radicals, atoms and/or molecules)
Introduce functional groups:
- O2, CO2, CO (hydroxyl, carboxyl, peroxide)
- NH3 (amine, amide)
- H20 (hydroxyl)
Drawback:
- Surface can contain more than one functional group. Surface properties change versus time
Plasma Surface Modification: Graft Polymerization
- Introduce hydrophilicity onto the surface
- Hydrophilic monomers: HEMA, AA, AAm
- Drawback: can be hard to control the molecular weight/length of polymer chain
Chemical Modification
- Direct surface reaction to introduce functional groups (-OH, -NH2, COOH)
- Surface immobilization of biomolecules
Surface Modification Applications
- Reduce thrombogenicity
- Promote cell attachment
- Reduce bacterial adhesion
Surface Binding Heparin
- Heparin is naturally occurring anticoagulant. Immobilization of heparin can inhibit platelet adhesion
- EX: PLA surface modified with heparin
Highly Hydrophobic Surface
- Inherently weak surface/cell interface
- Reduced interaction with blood components
Surface Coating or Binding Albumin
Albumin:
- High water solubility and stability
- No affinity to proteins and platelets due to lack of peptide sequences (RGD’s) and is unable to interact with platelets or enzyme receptors in the coagulation
Surface Modification to Promote Cell Attachment
- Surface modification should improve protein adsorption on biomaterial surface
- Appropriate surface energy favors protein adsorption on surface
Surface functional groups: - Introduce polar groups (to improve protein adsorption
Cell attachment: - -NH2 > -OH > -CONH2 > -COOH
Introducing Positive Charges
- Many proteins have net negative surface charge
- Positive charge increases protein adsorption, thus improve cell attachment
- Cell has negative charge, it increases the interaction between cell and positive charge surface
