This review focuses on recently developed alginate injectable hydrogels and alginate composites for applications in bone tissue regeneration, and it evaluates the alternatives to overcome the problems that avoid their utilization in the field. Section 2 covers the properties of alginates that have made them useful for medical applications, in particular their ionic gelling ability for preparing injectable compositions used as delivery drugs systems. The advantages and shortcomings of these preparations are revised together with the chemical modifications assayed. Section 3 describes how it has been taken advantage of alginates into the new field of biofabrication and the developments in bone engineering. The state of the art of this field is reviewed. Finally in Section 4, new developments and approaches that in opinion of the authors can lead to a breakthrough in bone tissue engineering using alginates are introduced.

Abstract:The aims of this paper are: (1) to review the current state of the art in the field of cartilage substitution and regeneration; (2) to examine the patented biomaterials being used in preclinical and clinical stages; (3) to explore the potential of polymeric hydrogels for these applications and the reasons that hinder their clinical success. The studies about hydrogels used as potential biomaterials selected for this review are divided into the two major trends in tissue engineering: (1) the use of cell-free biomaterials; and (2) the use of cell seeded biomaterials. Preparation techniques and resulting hydrogel properties are also reviewed. More recent proposals, based on the combination of different polymers and the hybridization process to improve the properties of these materials, are also reviewed. The combination of elements such as scaffolds (cellular solids), matrices (hydrogel-based), growth factors and mechanical stimuli is needed to optimize properties of the required materials in order to facilitate tissue formation, cartilage regeneration and final clinical application. Polymer combinations and hybrids are the most promising materials for this application. Hybrid scaffolds may maximize cell growth and local tissue integration by forming cartilage-like tissue with biomimetic features.

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The aim of this work is to evaluate the effect of chitosan content (1, 3 and 5 wt %) dispersed in polylactic acid (PLA) on the structure and properties of composites. Also, the hydrolytic degradation, and the cell viability and adhesion of human MG-63 osteoblasts are analyzed to determine the composites’ suitability for use in tissue engineering. For the manufacture of the materials, natural chitosan was extracted chemically from shrimp exoskeleton. The composites were fabricated by extrusion, because it is a low-cost process, it is reproducible, and it does not compromise the biocompatibility of the materials. FT-IR and XRD show that the chitosan does not change the polymer structure, and interactions between the composite components are discarded. In vitro degradation tests show that the composites do not induce significant pH changes in phosphate buffer solution due to their low susceptibility to hydrolytic degradation. The adhesion and morphological characteristics of the osteoblasts are evaluated using confocal microscopy and scanning electron microscopy. The cell viability is determined by the MTT assay. Osteoblasts adhesion is observed on the surface of PLA and composites. A higher amount of chitosan, higher number of cells with osteoblastic morphology, and mineralized nodules are observed on the composite surface. The highest metabolic activity is evidenced at 21 days. The results suggest that the Polylactic acid/chitosan composites are potentially suitable for use as a biomaterial.

HA-based hybrid hydrogels were successfully developed. The polysaccharide (HA) chains were chemically modified and hybridized via amidation of their carboxylic groups with aminosilane molecules. HA-polysaccharide chains were crosslinked by a 3D siloxane organic-inorganic matrix via sol-gel. The novel inorganic crosslinking network − PDMS SiO ( ) 2 provided to sodium hyaluronate (HA) strong chemical bonds, giving restriction to their natural hydrophilicity and stiffness to its structure (improved rheological properties). It was observed that synthesis conditions such as starting HA concentration solution and temperature determined gelling times, efficiency in the polysaccharide chemical modification and in crosslinking hydrolysis-condensation reactions, resulting in the siloxane organic-inorganic matrix. Drying processes influenced crosslinking in HA hybrid hydrogels, either by enhancing polycondensation reactions or inhibiting them. Room temperature-drying produced more densified hybrid structures. Freeze-drying increased porosity and surface hydroxyl groups −OH ( ) resulting in more Q 3 structural units. 60°C-drying boosted polycondensation of monodendate structural units, enhancing the formation of hybrid − D Q bonds.