Bacterial Nanocellulose Hydrogels Designed as Bioartificial Medical Implants 179
Besides. its. cytocompatibility,. the. lack. of. contaminating. bacterial. or.
medium. components. derived. from. the. biotechnological. production. process.is.an.important.criterion.for.the.biocompatibility.of.BNC..An.effective.
cleaning.process.for.BNC.is.essential.to.remove.substances.that.are.associated. with. the. biosynthesis. and. to. prepare. the. hydrogels. for. implantation.
as. a. scaffold. for. tissue. engineering.. Impurities. of. the. material. may. cause.
immunological. responses. and. rejection. reactions.. In. particular,. lipopolysaccharides. (LPS). from. the. outer. membrane. of. Gluconacetobacter. species.
induce. systemic. reactions. by. activation. of. monocytes. (Langstein. et. al..
2000).and.have.to.be.removed.from.the.material..The.most.common.cleaning. process. after. cultivation. of. BNC. referred. to. in. the. literature. is. a. treatment.with.aqueous.sodium.hydroxide.(0.1–1.M.at.60°C–120°C).(Grande.et al..
2009;. Helenius. et. al.. 2006;. Watanabe. et. al.. 1993).. A. flat. implant. of. defined.
size.(e.g.,.8.mm.×.8.mm.×.2.mm).has.to.be.cleaned.under.such.conditions.
for.20–60.min..An.additional.treatment.with.the.detergent.sodium.dodecyl.
sulfate. has. also. been. described. (Svensson. et. al.. 2005).. Also,. boiling. BNC.
hydrogels.in.alkali.sodium.hydroxide.solution.leads.to.depyrogenation.and.
effectively.reduces.the.biological.activity.of.LPS.(Williams.2007).
Bioactivity
Bioactivity. means. that. a. biomaterial. has. a. direct. influence. on. the. physiology. and. morphology. of. living. cells. by. controlling. their. adhesion,. migration,.proliferation,.differentiation,.and.release.of.extracellular.matrix.(ECM).
molecules. leading. to. the. formation. of. new. tissue.. Several. factors,. such. as.
structural. and. surface. properties,. the. inclusion. of. composite. partners,.
and/or. the. ability. to. release. incorporated. substances. (e.g.,. growth. factors,.
cytokines).contribute.to.the.bioactivity.of.biomaterials..BNC.shows.a.texture.
of.irregular,.randomly,.and.three-dimensionally.oriented.nanofibers.that.is.
very. similar. to. that. of. the. collagen. network.. This. biomimetic. structure. of.
BNC—mimicking.a.body’s.own.tissue—offers.a.good.matrix.for.in.vitro.cell.
seeding. prior. to. tissue. engineering. applications.. Due. to. increased. surface.
area.and.the.possibility.of.3D.seeding,.BNC.both.supports.efficient.adhesion.
of.the.cells.and.prevents.dedifferentiation.(Bodin.et.al..2010)..In.addition,.the.
BNC.structure.allows.the.mass.transport.of.nutrients.and.oxygen.to.support.
the.survival.of.cells..Finally,.the.BNC.nanofibers.may.participate.in.guiding.
the.orientation.of.the.ECM.molecules.deposited.by.the.cells.
Besides. the. structural.aspects,. the. surface. chemistry. plays. an.important.
role. in. the. bioactivity. of. BNC.. Several. authors. have. shown. that. chemical.
modification.of.the.surface.leads.to.augmented.adhesion.of.cells..Modification.
of.the.BNC.surface.by.phosphorylation.and.sulfation.in.order.to.mimic.glucosaminoglycans.of.native.cartilage,.for.example,.increased.the.adhesion.of.
bovine. chondrocytes. to. the. material,. but. did. not. augment. their. proliferation.(Svensson.et.al..2005)..The.finding.that.very.strong.adhesion.prevents.
proliferation.has.also.been.confirmed.by.others.(Sieminski.and.Gooch.2000)..