Factors affecting calcium phosphate mineralization within bulk alginate hydrogels
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Alginate hydrogels are natural materials which can be used for biomedical purposes in order to trigger natural remineralization of damaged hard tissues. Mineralization of alginate hydrogels by using diverse protocols is extensively studied, with a goal of obtaining biocomposite materials having improved mechanical properties. The majority of the studies described in the literature are focused on the use of alginate in the form of beads, while alginate in bulk form has been more rarely studied. In this work, the influence of parameters, like phosphate concentration, type of media (water, HEPES and TRIS buffer) and pH (5.0, 7.4, 9.0), on gelation and mineralization of bulk alginate hydrogels (approx. 2 × 2 cm) was studied. Hydrogels were produced using semipermeable membranes. In all experiments, calcium chloride solution was added as a mineralizing solution to the alginate dissolved in medium containing disodium phosphate, which simultaneously triggered gelation and mineralization of hydrogels. Hydrogels were mineralized for 5 days with daily exchange of mineralizing solution. Such hydrogels were characterized using a combination of infrared spectroscopy, powder X-ray diffraction and electron microscopy. The obtained results demonstrated that the media and pH have a profound influence on gelation and the stability of the hydrogels. Octacalcium phosphate was formed in all hydrogels except in TRIS buffer at pH = 9.0 where amorphous calcium phosphate (ACP) was formed. ACP was stabilized during the experiments, as well as during the extraction from the hydrogel. The obtained results point to a protocol suitable for fine-tuning the properties of the mineralized hydrogel, by a simple change of experimental conditions.
Keywordsalginate bulk hydrogel octacalcium phosphate amorphous calcium phosphate mineralization
Authors are grateful to Krunoslav Užarević for auxiliary PXRD measurements.
Conceptualization, Maja Dutour Sikirić; Funding acquisition, Damir Kralj; Investigation, Vida Strasser, Nives Matijaković, Daniel Mark Lyons, Tea Mihelj Josipović, Jasminka Kontrec and Damir Kralj; Methodology, Maja Dutour Sikirić; Writing – original draft, Maja Dutour Sikirić, Vida Strasser, Damir Kralj.
This research was funded by the Croatian Science Foundation under project HRZZ-IP-2013-11-5055.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
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