Preparation of macroporous alginate-based aerogels for biomedical applications

Abstract

Highlights • alginate-starch Ca-crosslinked aerogels by CO 2 induced gelation and sc-drying; • macroporosity due to CO 2 expansion and intrinsically high mesoporosity; • alginate-starch aerogels are bioactive and non-cytotoxic. ABSTRACT Aerogels are a special class of ultra-light porous materials with growing interest in biomedical applications due to their open pore structure and high surface area. However, they usually lack macroporosity, while mesoporosity is typically high. In this work, carbon dioxide induced gelation followed by expansion of the dissolved CO 2 was performed to produce hybrid calcium-crosslinked alginate-starch hydrogels with dual meso-and macroporosity. The hydrogels were subjected to solvent exchange and supercritical drying to obtain aerogels. Significant increase in macroporosity from 2 to 25 % was achieved by increasing expansion rate from 0.1 to 30 bar/min with retaining mesoporosity (BET surface and BJH pore volume in the range 183-544 m 2 /g and 2.0-6.8 cm 3 /g, respectively). In vitro bioactivity studies showed that the alginate-starch aerogels are bioactive, i.e. they form hydroxyapatite crystals when immersed in a simulated body fluid solution. Bioactivity is attributed to the presence of calcium in the matrix. The assessment of the biological performance showed that the aerogels do not present a cytotoxic effect and the cells are able to colonize and grow on their surface. Results presented in this work provide a good indication of the potential of the alginate-starch aerogels in biomedical applications, particularly for bone regeneration. KEYWORDS aerogels, alginate, starch, tissue engineering, supercritical fluids, CO 2 induced gelation INTRODUCTION An ideal scaffold for tissue engineering must meet particular requirements to achieve the desired biological response: the scaffold should possess interconnecting pores of appropriate size to favor tissue integration and vascularization, be made from material with controlled biodegradability, have appropriate surface chemistry to favor cellular attachment, differentiation and proliferation, possess adequate mechanical properties to match the intended site of implantation and handling, should not induce any adverse response and be easily fabricated into a variety of shapes and sizes [1]. Some attempts have recently been made to address tissue engineering and regenerative medicine (TERM) problems using aerogels as scaffolds. Aerogels are well known ultra-light highly porous materials with an open structure, large specific surface area and pore volume. High mesoporosity comparable to the native extracellular matrix (ca. 80% porosity) is favorable condition for cell growth, making aerogels an ideal candidate for a number of biomedical applications, including tissue engineering. Nevertheless, macroporosity of these structures should be improved to promote cell migration into the matrices and enhance mass transfer between the scaffold and the bulk phase. The fact that biopolymers can be used for aerogel production was recognized by Samuel...

Preparation of Biopolymer Aerogels Using Green Solvents

“…Fast depressurization can lead to increased macroporosity of the gels. This phenomena can be applied for tissue engineering applications where macroporosity of the material with interconnectivity is an important feature for the growth and proliferation of cells 13,14 . In addition, the crosslinking degree in Protocol Section 1 plays an important role in the syneresis and swelling property of the amidated pectin hydrogels.…”

Preparation and Characterization of Graphene Oxide Aerogels: Exploring the Limits of Supercritical CO2 Fabrication Methods

“…Straight sol-gel gelling induced by compressed CO 2 has only been described for polymeric aerogelsi nvolving highly reactive monomers, such as silsesquioxanes, [35] and some biopolymers. [36][37][38][39] In the developed supercritical CO 2 procedure, the mechanism of gelling and drying was visually followed through the sapphire windowso ft he high-pressure reactor,w hich allow the acquisition of optical pictures ( Figure 4).…”

Synthesis and Characterization of a New Collagen-Alginate Aerogel for Tissue Engineering

“…Nowadays, there has been considerable interest in carbon-based nanomaterials to fabricate a new class of materials with unique properties [20]. In this study, a method to improve the mechanical and biological properties of the scaffold by the incorporation of alginate and GO was used, since it has been previously reported as successful [6,28,[35][36][37]. Even though it has been established that both materials could be employed to improve general properties of biomaterials, results in this study showed that the incorporation of GO could negatively affect cell attachment, proliferation, and response.…”

“…Baldino et al [36] also confirmed that the supercritical process does not modify the gel organization and avoids gel collapse during drying. Martins et al [35] reported an alginate-based aerogel for TE; to obtain an adequate porosity in the structure, Martins et al proposed different pressuring and depressurizing rates. In this study, a collagen-alginate-GO aerogel with a highly porous structure is presented; the incorporation of collagen type I and the crosslinking performed by UV light allow a porous three-dimensional structure to be formed, even without the use of specific pressuring and depressurizing rates; also, the biological characteristics of collagen added to the aerogel provide adequate properties for its use in TE.…”