Effect of inorganic and organic bioactive signals decoration on the biological performance of chitosan scaffolds for bone tissue engineering

Chitosan/hydroxyapatite nanocomposite scaffolds to modulate osteogenic and inflammatory response

Considerable attention has been given to the use of chitosan (CS)‐based materials reinforced with inorganic bioactive signals such as hydroxyapatite (HA) to treat bone defects and tissue loss. It is well known that CS/HA based materials possess minimal foreign body reactions, good biocompatibility, controlled biodegradability and antibacterial property. Herein, the bioactivity of these composite systems was analyzed on in vitro bone cell models for their applications in the field of bone tissue engineering (BTE). The combination of sol–gel approach and freeze‐drying technology was used to obtain CS/HA scaffolds with three‐dimensional (3D) porous structure suitable for cell in‐growth. Specifically, our aim was to investigate the influence of bioactive composite scaffolds on cellular behavior in terms of osteoinductivity and anti‐inflammatory effects for treating bone defects. The results obtained have demonstrated that by increasing inorganic component concentration, CS/HA (60 and 70% v/v) scaffolds induced a good biological response in terms of osteogenic differentiation of human mesenchymal stem cells (hMSC) towards osteoblast phenotype. Furthermore, the scaffolds with higher concentration of inorganic fillers are able to modulate the production of pro‐inflammatory (TGF‐β) and anti‐inflammatory (IL‐4, IL‐10) cytokines. Our results highlight the possibility of achieving smart CS/HA based composites able to promote a great osteogenic differentiation of hMSC by increasing the amount of HA nanoparticles used as bioactive inorganic signal. Contemporarily, these materials allow avoiding the induction of a pro‐inflammatory response in bone implant site.

Enhancing Bioactivity of Hydroxyapatite Scaffolds Using Fibrous Type I Collagen

In the field of bone tissue regeneration, the development of osteoconductive and osteoinductive scaffolds is an open challenge. The purpose of this work was the design and characterization of composite structures made of hydroxyapatite scaffold impregnated with a collagen slurry in order to mimic the bone tissue structure. The effect of magnesium and silicon ions enhancing both mechanical and biological properties of partially substituted hydroxyapatite were evaluated and compared with that of pure hydroxyapatite. The use of an innovative freeze-drying approach was developed, in which composite scaffolds were immersed in cold water, frozen and then lyophilized, thereby creating an open-pore structure, an essential feature for tissue regeneration. The mechanical stability of bone scaffolds is very important in the first weeks of slow bone regeneration process. Therefore, the biodegradation behavior of 3D scaffolds was evaluated by incubating them for different periods of time in Tris-HCl buffer. The microstructure observation, the weight loss measurements and mechanical stability up to 28 days of incubation (particularly for HA-Mg_Coll scaffolds), revealed moderate weight loss and mechanical performances reduction due to collagen dissolution. At the same time, the presence of collagen helps to protect the ceramic structure until it degrades. These results, combined with MTT tests, confirm that HA-Mg_Coll scaffolds may be the suitable candidate for bone remodeling.

Bioactivation Routes of Gelatin-Based Scaffolds to Enhance at Nanoscale Level Bone Tissue Regeneration

The present work is focused on the development of gelatin-based scaffolds crosslinked through carbodiimide reaction and their bioactivation by two different methods: (i) surface modification by inorganic signals represented by hydroxyapatite nanoparticles precipitated on scaffold through biomimetic treatment; (ii) analog of BMP-2 peptide decoration. The results showed the effects of polymer concentration and crosslinking time on the physico-chemical, morphological, and mechanical properties of scaffolds. Furthermore, a comparative study of biological response for both bioactivated structures allowed to evaluate the influence of inorganic and organic cues on cellular behavior in terms of adhesion, proliferation and early osteogenic marker expression. The bioactivation by inorganic cues induced positive cellular response compared to neat scaffolds in terms of increased cell proliferation and early osteogenic differentiation of human mesenchymal stem cell (hMSC), as evidenced by the Alkaline phosphatase (ALP) expression. Similarly BMP-2 peptide decorated scaffolds showed higher values of ALP than biomineralized ones at longer time. The overall results demonstrated that the presence of bioactive signals (either inorganic or organic) at nanoscale level allowed an osteoinductive effect on hMSC in a basal medium, making the modified gelatin scaffolds a promising candidate for bone tissue regeneration.

Effect of cellulose nanocrystals on scaffolds comprising chitosan, alginate and hydroxyapatite for bone tissue engineering

In this study, chitosan/alginate/hydroxyapatite/nanocrystalline cellulose scaffolds were successfully fabricated by the using of freeze-drying method, followed by dicationic crosslinking using CaCl₂. The chemical structure and morphology along with mechanical properties of the formed scaffolds respecting to various CNC contents were studied by Fourier-transform infrared spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and mechanical compression test. Chemical interaction and electrostatic attraction between chitosan (CS) and alginate with various CNC ratios were affirmed by FTIR spectroscopy. Results depicted that, scaffolds containing CNC exhibited remarkable improvement in both swelling ratio up to 110% compared without CNC (63%) and compressive strength when compared with other scaffolds. In addition, the average pore size increased, dramatically, with increasing of CNC up to 230 μm. Porosity was also obeyed the sequence and attainted a maximum value at 93.6%. The growth and cell attachment of fibroblast cells of the selected scaffold were examined prolonging to the cell viability by using Alamar Blue (AB) and then confirmed using SEM. The results indicated that the scaffold comprising CNC has a promising cell growth and cell adherence, and thus expected to have a potent possibility for applications in bone tissue culture.