Biomedical Engineering Reference
In-Depth Information
researched.to.overcome.the.drawbacks.of.PEG.hydrogels.including.non-natural.and.non-
biodegradable. properties. leading. to. failure. to. recreate. the. complexity. of. native. ECM..
Dang.et.al..developed.a.method.to.fabricate.cell.laden.alginate.microcapsules.patterned.
by. commercially. available. polypropylene. meshes.
96
. The. meshes. having. different. shapes.
and.sizes.are.dipped.into.cell.suspended.alginate.solution.and.CaCl
2
.solution.sequentially.
to. form. alginate. microcapsules.. This. method. provides. a. cheap. and. convenient. way. to.
create.non-photopatternable.hydrogels,.but.the.size.and.shape.of.fabricated.hydrogels.are.
limited. by. available. meshes. and. further. assembly. of. hydrogels. should. be. proposed. to.
build.complex.3D.cell.structures..Liu.and.Chan-Park.studied.modiied.dextran.and.gelatin.
to.investigate.the.viability,.proliferation.and.spreading.of.human.umbilical.artery.smooth.
muscle. cells. (SMCs). under. different. synthetic. conditions.
73
. The. mechanical. stiffness. of.
hydrogels. was. adjusted. by. changing. relative. concentrations. of. dextran. and. gelatin,. or.
precursor.solutions.
12.5.2 Porous Polymers
An. important. aspect. of. generating. engineered. tissue. is. to. direct. the. 3D. organization. of.
cells. by. biomaterial. construct. and. to. establish. the. conditions. necessary. for. the. cells. to.
reconstruct.a.functional.tissue.structure..Porous.polymer.structures.may.provide.a.suit-
.provide.a.suit-
able.chance.to.construct.3D.cellular.microenvironment.when.cells.are.cultured.inside.the.
polymers.and.the.porous.space.is.used.as.a.channel.to.supply.oxygen.and.nutrients.and.
allow.for.removing.waste..This.approach.may.assist.to.overcome.ongoing.major.challenge.
in.tissue.engineering.which.is.to.create.functional,.integrated.microvasculature..Fibrous.
structure.is.one.example.of.porous.polymers.typically.fabricated.by.electrospinning.pro-
cess.
97
.The.polymer.stream.ejected.from.an.electrically.biased.needle.forms.a.thin.ibrous.
structure.on.a.target.plate.which.is.electrically.grounded..A.high.surface.to.volume.ratio.
and.iber.network.similar.to.natural.ECM.is.beneicial.to.mimic.3D.cellular.environment,.
but. cell. seeding. and. migration. can. be. dificult. due. to. the. small. pore. size. of. the. ibrous.
structures..Acceptable.pore.sizes.for.cell.seeding.and.migration.in.the.porous.structures.
have.been.obtained.by.mixing.polymers.with.porogens.(or.water.to.be.removed.by.freeze.
dry).and.removing.porogens.selectively.by.appropriate.solvents.to.form.pores.where.the.
porogens. existed.. The. pore. size. can. be. controlled. from. sub-micron. to. a. few. hundred.
microns.by.chemical.composition.and.processing.condition..Akay.et.al..reported.a.high.
internal.phase.emulsion.(HIPE).polymerization.process.to.construct.different.pore.sizes.
of. 40,. 60,. and. 100. μm. with. the. varied. porosity. from. 70%. to. 97%.
98
. They. built. bone-like.
matrix. by. culturing. osteoblasts. for. 35. days. to. allow. the. cells. to. migrate. to. a. maximum.
depth.of.1.4mm..Cheng.et.al..created.3D.porous.structures.by.removing.porogens.through.
temperature.induced.phase.separations.without.applying.chemicals.
99
.Sieved.ammonium.
bicarbonate. particles. were. mixed. with. high. viscous. polymer. solution. and. removed. by.
decomposition.into.ammonia.over.36°C.leaving.void.spaces.they.occupied..
Porous.polymer.structures.may.provide.a.suit-
may.provide.a.suit-
12.5.3 Computer-Aided Structuring
Recently,. computer. aided. structuring. has. emerged. to. take. advantages. such. as. rapid. pro-
computer. aided. structuring. has. emerged. to. take. advantages. such. as. rapid. pro-
totyping,. customization. of. 3D. structures. and. automation. of. manufacturing. process.. This.
concept.has.become.an.attractive.approach.since.it.has.a.great.potential.of.providing.delicate.
3D.structures.
100,101
.By.dispensing.polymers.mixed.with.cells.using.a.bioplotter,.3D.scaffolds.
were.fabricated.with.a.particle.size.of.30-75.μm.
102
.Concentration,.viscosity,.and.dispensing.
