Search

Amino acids (AAs) attract attention for elucidating the role of proteins in biomineralization and the preparation of functionalized biomaterials. The influence that AAs exert on calcium phosphate (CaP) mineralization is still not completely understood, as contradictory results have been reported. In this paper, the influence of the addition of different classes of AAs, charged (L-aspartic acid, Asp, L-lysine, Lys), polar (L-asparagine, Asn, L-serine, Ser, L-tyrosine, Tyr), and non-polar (L-phenylalanine, Phe), on CaP growth in the presence of octacalcium phosphate (OCP) and calcium hydrogenphosphate dihydrate (DCPD) seeds was investigated. In control systems (without AAs), a calcium-deficient apatite (CaDHA) layer was formed on the surface of OCP, while a mixture of CaDHA and OCP in the form of spherical aggregates was formed on the surface of DCPD crystals. Charged and non-polar promoted, while polar AAs inhibited CaDHA formation on the OCP seeds. In the case of DCPD, Lys, Asp, and Phe promoted CaP formation, while the influence of other AAs was negligible. The most efficient promotor of precipitation in both cases was non-polar Phe. No significant influence of AAs on the composition and morphology of precipitates was observed. The obtained results are of interest for understanding biomineralization processes and additive controlled material synthesis.

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 semi- permeable 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.