Biomimetic Mineralization of Hydrogel Biomaterials for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 56

peptide amphiphile nanofi brous scaffolds as a template for embedding of
hydroxyapatite nanoparticles, Anderson et al. observed that the resulting
composites possessed the capacity for bone healing using a critical size
femoral defect rat model [27].

3.3 Biomimetic Mineralization in Calcium and/or

Phosphate-Containing Solutions

Two main biomimetic approaches are proposed in the literature to create
a mineral phase on the surface of and inside hydrogels by soaking/incu-
bation in suitable mineralization solutions. The fi rst approach is based on
soaking of the hydrogel samples in mineralization solutions containing
calcium and phosphate ions [28] in order to cause CaP nanocrystal forma-
tion after gel formation. The second approach involves in situ formation
of CaP nanocrystals inside hydrogels during gel formation, which then
serve as nucleation sites for further crystal growth upon incubation in a
mineralization solution.

3.3.1 Soaking in Solutions Containing Calcium and

Phosphate Ions

Baskar et al. showed hydroxyapatite formation on chitosan as a result of
incubation in SBF [29]. Chesnutt et al. showed that degree of deacetylation
of chitosan, concentration of SBF, and incubation time in SBF all infl uence
the amount and composition of CaP formed [30]. Surface-mineralized chi-
tosan hydrogels produced in this way were found to be suitable substrates
for the distribution, attachment, migration and osteogenic diffrentiation
of osteoblast-like cells [31].
SBF has been used to compare mineralizabilities of different hydrogel
materials. Ichibouji et al. compared hydrogels consisting of pectin from
different sources with different zeta potentials and detected differences in
the amount of calcium bound and presence of mineral formed [32].
Skhilnyy et al. showed that poly(ethylene imine) (PEI) hydrogels min-
eralize with apatite and brushite after incubation in SBF, provided that
crosslinking using poly(ethylene glycol) diglycidyl ether takes place
beforehand [33]. The authors suggested that uncrosslinked PEI is more
protonated, and thus can release more protons, leading to a decrease in
pH and increasing solubility of CaP, hindering CaP precipitation.
Alternatives to soaking in the near-physiological solution SBF are (a)
soaking in solutions with superphysiological concentrations of Ca 2+ and
PO 3− and (b) alternate soaking in Ca 2+ and PO 3− solutions. Although these
approaches are not suitable for mimicking mineralization behavior in vivo