Structure-Related Mechanical Properties and Bioactivity of Silica–Gelatin Hybrid Aerogels for Bone Regeneration

Abstract

We report the synthesis of mesoporous silica–gelatin hybrid aerogels with 15, 25, and 30 wt. % gelatin contents, using 3-glycidoxypropyl trimethoxysilane (GPTMS) as a coupling agent, for tissue-engineering applications. Aerogels were obtained using a one-step sol–gel process followed by CO2 supercritical drying, resulting in crack-free monolith samples with bulk densities ranging from 0.41 g cm−3 to 0.66 g cm−3. Nitrogen adsorption measurements revealed an interconnected mesopore network and a general decrease in the textural parameters: specific surface areas (651–361 m2 g−1), pore volume (1.98–0.89 cm3 g−1), and pore sizes (10.8–8.6 nm), by increasing gelatin content. Thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy and uniaxial compression experiments confirmed that the structure, thermal properties and mechanical behavior of these aerogels changed significantly when the concentration of gelatin reached 25 wt.%, suggesting that this composition corresponds to the percolation threshold of the organic phase. In addition, the samples exhibited hydrophilic behavior and extremely fast swelling in phosphate-buffered saline (PBS), with swelling ratios from 2.32 to 3.32. Furthermore, in vitro bioactivity studies revealed a strong relationship between the kinetics of the nucleation and growth processes of hydroxyapatite in simulated body fluid (SBF) and the gelatin content. The live/dead assay revealed no cytotoxicity in HOB® osteoblasts in vitro and a positive influence on cell growth, focal adhesion development, and cytoskeletal arrangement for cell adhesion. Mineralization assays confirmed the positive effects of the samples on osteoblast differentiation. The biomaterials described are versatile, can be easily sterilized and are suitable for a wide range of applications in bone tissue-engineering, either alone or in combination with bioactive-reinforced phases.

Bioengineering Composite Aerogel-Based Scaffolds That Influence Porous Microstructure, Mechanical Properties and In Vivo Regeneration for Bone Tissue Application

“…This material behavior is observed in the study of the hybrid silica–GPTMS–gelatin-based aerogels developed by Reyes-Peces et al (2023) ( Table 1 ) [ 54 ]. The supercritical dried aerogels showed an elastic behavior to compression and higher stiffness in dry conditions with increasing gelatin content (maximum compressive strain for SG25 was 27.67%) and crosslinking agents [ 54 ].…”

“…In terms of pore size, the studies’ results in Table 1 showed that the pore size scale ranges from 8.6 [ 54 ] to 31 nm [ 41 ] (mesopores) to a few micrometers [ 26 ]. Perez-Moreno et al (2020) developed silica (SiO 2 )/chitosan (CS 0, 4, 8, 16, 20 wt.%) (SCS) composite aerogels with mesopores ranging from 11 to 14 nm [ 7 ].…”

“…The hybrid silica–gelatin-based aerogels developed by Reyes-Peces et al (2023) ( Table 1 ) exhibited lower mean pore diameters (in a nanometer scale), specific surface area and total pore volume with increasing contents of gelatin (from 15 to 30% wt.) and crosslinker (organosilaner 3-glycidoxypropyltrimethoxysilane—GPTMS) [ 54 ]. The authors attributed these results to a more intertwined hybrid structure, due to higher organic network content.…”

“…The authors attributed these results to a more intertwined hybrid structure, due to higher organic network content. Moreover, these hybrid aerogels did not show a micro or macropore distribution [ 54 ]. In a study by Iglesias-Mejuto et al (2021) 3D-printed alginate–hydroxyapatite (Alg–HA) aerogel scaffolds were obtained after scCO 2 drying [ 41 ].…”

Aerogel-Based Materials in Bone and Cartilage Tissue Engineering—A Review with Future Implications

“…Most aerogel-based scaffolds contain one or more natural or synthetic polymeric components with or without inorganic counterparts like silica, graphene, carbon nanotube, calcium phosphates, etc. Although the physical properties are important in bone-related research, only a part of the papers contain relevant data [ 24 , 42 , 58 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 ]. Most recently, a critical review paper has been published describing and summarizing the syntheses, biomechanical properties, and their connection with the porosities of bone substitute aerogel materials by Souto-Lopez and coworkers [ 88 ].…”