Photodegradable Iron(III) Cross-Linked Alginate Gels

Abstract

Biocompatible photoresponsive materials are of interest for targeted drug delivery, tissue engineering, 2D and 3D protein patterning, and other biomedical applications. We prepared light degradable hydrogels using a natural alginate polysaccharide cross-linked with iron(III) cations. The "hard" iron(III) cations used to cross-link the alginate hydrogel were found to undergo facile photoreduction to "soft" iron(II) cations in the presence of millimolar concentrations of sodium lactate. The "soft" iron(II) cations have a decreased ability to cross-link the alginate which results in dissolution of the hydrogel and the formation of a homogeneous solution. The photodegradation is done using long wave UV or visible light at neutral pH. The very mild conditions required for the photodegradation and the high rate at which it occurs suggest applications for iron(III) cross-linked alginate hydrogels as light-controlled biocompatible scaffolds.

Photochemical Patterning of Ionically Cross-Linked Hydrogels

“…Presence of sodium lactate in the gel increases this maximum concentration from 20 mM to 30 mM [59]. At higher concentrations of either iron(II) chloride or sodium alginate, the formation of white precipitate of iron(II) alginate took place, as has been observed in the literature [58].…”

“…After 1 min of irradiation the Petri dish with the hydrogel was separated from the solution of lactic acid and the absorbance of the irradiated zone of the hydrogel was measured. As expected, the absorbance of the gel below 400 nm decreased after every irradiation cycle for first five minutes due to decreased concentration of iron(III) cations which provide the most important contribution to UV absorbance [59]. Along with it there was a minor increase in absorption above 400 nm which can be attributed to increased roughness of the gel surface due to photodegradation which results in scattering of light passing through the hydrogel.…”

“…The resultant iron(III) cations in the gel can be reduced photochemically in the presence of 10-20 mM of α-hydrocarboxylic acids salts such as sodium lactate that work as sacrificial reductants (Figure 1). Incorporation of lactic acid into iron(II)-alginate solution before the air oxidation stage produces photoresponsive gel that easily dissolves upon irradiation with UV or visible light after treatment with water or 0.9% saline [59]. Here we report on using the photoresponsive iron(III) cross-linked alginate hydrogel as a biocompatible photoresist and photochemical patterning of the hydrogel under biocompatible conditions.…”

“…Based on previously reported process of photodegradation of iron(III) cross-linked alginate hydrogel [59] we investigated properties of this material for photochemical patterning of surfaces. A layer of the hydrogel (2.0 mm thickness) was irradiated through a mask.…”

Fabrication of Tissue Engineering Scaffold from Hydroxyapatite/Alginate Composite

“…In particular, freeze drying is a technique including solvent casting method, in which the solvent removing may be accompanied by freeze drying to a more porous structure to be obtained. In this procedure, cavities is produced in the scaffold due to the space occupied by the solvent after drying, and the smaller pores arising from sublimation of the solvent serves as interconnection between the macropores [18].…”