Sodium silicate gel as a precursor for the in vitro nucleation and growth of a bone-like apatite coating in compact and porous polymeric structures

Abstract

In the present work, a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other polymeric biomaterials is proposed. A sodium silicate gel is employed as an alternative nucleating agent to the more typical bioactive glasses for inducing the formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3D architectures aimed at being used on tissue replacement applications and as tissue engineering scaffolds. By means of this treatment, it is possible to observe the formation of an apatite-like layer, only after 6 hours of simulated body fluid immersion. For the porous materials, this layer could also be observed inside the pores, clearly covering the cell walls. Furthermore, an increase of the surface hydrophilicity (higher amount of polar groups in the surface) might contribute to the formation of silanol groups that also act as apatite inductors. After 30 days of SBF immersion, the apatite-like films exhibit a partially amorphous nature and the Ca/P ratios became much closer to the value attributed to hydroxyapatite (1.67). The obtained results are very promising for the development of cancellous bone replacement materials and for pre-calcifying bone tissue engineering scaffolds.

P(EMA-co-HEA)/SiO2 hybrid nanocomposites for guided dentin tissue regeneration: structure, characterization and bioactivity.

“…This increases the ionic activity product of the apatite while maintaining the Ca/P molar ratio, and thereby make the apatite nuclei grow more rapidly (growth stage) [54,60,61] . Table 1.1 shows the ion concentrations and the ionic activity products of the apatite in 2×SBF.…”

“…Oliveira et al [60,74] proposed a methodology to generate apatite nucleating sites on the surface of starch-based biodegradable materials or other polymeric biomaterials (with relatively strong swelling ability) and scaffolds, based on the impregnation of the samples with a sodium silicate gel containing NaOH (procedure type ii). The hydrogen bonding complexes formed between NaOH and hydroxyl groups increase the surface hydrophilicity (higher amount of polar groups in the surface).…”

“…After 14 days in SBF, the peaks corresponding to the coatings are poorly resolved and the broad band corresponding to the hybrid predominates in the three spectra (10-25º). After 35 days, the broad peak at 32 to 34º and the peak at around 26º attributed to XRD HAp crystals [40,50,54,60,61,93,101,102] are well defined. The intensity of these peaks decreases in the order: H15 > H30 > H00.…”

“…After 7 days (SBF7), H00 shows typical intricately intertwined needle-shaped crystals forming some isolated cauliflower HAp structures [38,53,60,94] , with an average diameter of about 1 μm. After 14 days, more cauliflowers appear on the surface, covered in some zones by continuous semitransparent coatings.…”

“…This confirms that the influence of silica is also superficial. This is of great importance since the hydrophilic character of the surfaces plays an important role during apatite formation [50,60,102,105] . The presence of Si-OH groups on the surface (and/or their formation by dissolution of the silica network) is related with the ability to nucleate bone-like hydroxyapatite crystals in contact with body fluids.…”