Biomedical Engineering Reference
In-Depth Information
noncovalent.interactions—for.example,.hydrogen.bonds,.ionic.bonds.(electrostatic.forces),.
hydrophobic.interactions,.and.van.der.Waals.forces—is.responsible.for.such.a.phenomenon.
(Zhang. 2003).. A. number. of. self-assembling. peptides. and. proteins. have. been. used. to.
generate.nanoibrous.scaffolds..The.process.is.not.limited.to.biomolecules.found.in.nature;.
in.fact,.a.number.of.synthesized.polymers.are.typically.employed.
In.one.study,.a.change.in.pH.triggered.self-assembly.of.peptide.amphiphiles.(PAs).into.
ECM.ibril-like.nanocylinders,.with.the.reaction.being.reversible..These.PAs.possessed.
a. hydrophobic,. long. alkyl. tail. and. a. hydrophilic. peptide. head.. Additional. features.
included.a.phosphorylated.serine.residue.for.interaction.with.calcium.ions.and.to.guide.
mineralization. of. hydroxyapatite,. and. an. RGD. domain. at. the. peptide's. C. terminus. to.
promote.cell.adhesion.(Figure.8.2c;.Hartgerink.et.al..2001)..The.addition.of.various.cell.
adhesive.moieties.to.PAs.has.also.proven.effective.in.a.number.of.other.studies.(Guler.
et.al..2006;.Storrie.et.al..2007;.Ananthanarayanan.et.al..2010;.Shroff.et.al..2010)..Among.
the.more.recent,.bone-marrow.mononuclear.cells.(BMNCs).encapsulated.in.PA.scaffolds.
covalently. linked. to. the. Arg-Gly-Arg-Ser. (RGDS). sequence. retained. viability. and. had.
improved. proliferative. capacity,. as. demonstrated. by. both. in. vitro. and. in. vivo. studies.
(Webber. et. al.. 2010).. Heparin-binding. PA. (HBPA). gels. were. used. to. deliver. vascular.
endothelial. growth. factor. and. basic. ibroblast. growth. factor. into. murine. pancreatic.
islets—a. challenging. area. for. cellular. signaling. due. to. the. presence. of. a. packed. array.
of. clustered. cells.. These. HBPAs. successfully. iniltrated. the. islet. surface,. unlike. their.
counterparts. without. heparin.. This. correlated. to. enhanced. islet. secretion. and. insulin.
production..Furthermore,.a.substantial.angiogenic.response.was.triggered,.as.concluded.
through. observation. of. increased. islet. endothelial. cell. sprouting. (Chow. et. al.. 2010)..
Human. MSCs. encapsulated. in. TGFβ1-binding. PAs. showed. greater. expression. of.
chondrogenic. markers. than. in. PAs. without. bioactive. agents. on. their. surfaces.. In.
vivo. studies. using. a. rabbit. model. indicated. that. TGFβ1-binding. PAs. effectively. aided.
microfracture-generated. chondral. defects. in. repairing. damaged. articular. cartilage.
tissue. (Shah. et. al.. 2010).. A. number. of. other. studies. also. alluded. to. the. role. of. PAs. in.
improving. differentiation. capacity. of. various. cell. types. (Silva. et. al.. 2004;. Galler. et. al..
2008;.Anderson.et.al..2011).
8.2.2 Ordered Topography
8.2.2.1 Dip-Pen Nanolithography
Dip-pen.nanolithography.(DPN).employs.an.atomic.force.microscope.(AFM).tip.to.create.
nanopatterns.on.a.solid.surface.using.high.substrate.afinity.molecules.(Figure.8.3a;.Piner.
et.al..1999)..These.so-called.inks.consist.of.small.organic.molecules,.organic.and.biological.
polymers,. colloidal. particles,. metal. ions,. or. sols. (Ginger. et. al.. 2004).. DPN. enables. direct.
transport.of.the.inks.via.capillary.forces,.in.addition.to.selective.placement..This.technique.
does. not. require. a. stamp,. resist,. or. additional. processing. steps,. enjoying. considerable.
simplicity. compared. with. other. nanopatterning. techniques.. The. characteristics. of. the.
deposited. nanofeatures. depend. on. factors. that. include. the. substrate. material,. AFM. tip,.
environment,.and.spacing..DPN.is.nevertheless.time-consuming,.and.patterning.of.a.large.
surface.area.would.require.an.array.of.tips.
Cell. adhesion. studies. were. conducted. using. protein. nanoarrays. containing. dots. and.
grids.patterned.on.a.gold.surface.with.16-mercaptohexadecanoic.acid.(MHA)..The.lysozyme.
protein. bound. to. the. MHA. nanopatterns. in. a. highly. speciic. fashion.. Retronectin—a.
recombinant. protein. partly. derived. from. ibronectin—successfully. generated. focal.
