Chitosan/alginate bionanocomposites adorned with mesoporous silica nanoparticles for bone tissue engineering

The regeneration of oral and craniofacial bone defects ranging from minor periodontal and peri-implant defects to large and critical lesions imposes a substantial global health burden. Conventional therapies are associated with several limitations, highlighting the development of a unique treatment strategy, such as tissue engineering. A well-designed scaffold for bone tissue engineering should possess biocompatibility, biodegradability, mechanical strength, and osteoconductivity. For this purpose, mesoporous silica nanoparticles (MSNs) were synthesized and incorporated at different ratios (10, 20, and 30%) into alginate/chitosan (Alg/Chit)-based porous composite scaffolds fabricated through the freeze-drying method. The MSN incorporation significantly improved the mechanical strength of the scaffolds while showing a negligible decreasing effect on the porosity. All of the samples showed desirable swelling behaviors, which is beneficial for cell attachment and proliferation. The MSN-containing scaffolds indicated a decreased hydrolytic degradation in an MSN percentage-dependent manner. The fabricated scaffolds did not depict cytotoxic characteristics. The Alg/Chit/MSN30 scaffolds not only showed noncytotoxic properties, but also increased the cell viability significantly compared to the control group. The biomineralization properties of the MSN-containing nanocomposite scaffolds were significantly higher than the Alg/Chit composite, suggesting the potential of these nanoparticles for bone tissue engineering applications. Taken together, it is concluded that the Alg/Chit/ MSN30 scaffolds are considerable substances for bone tissue regeneration, and MSN has a great tissue engineering potential in addition to its extensive biomedical applications.

💡 Research Summary

The study addresses the pressing need for improved bone‑regeneration strategies in oral and craniofacial medicine by developing a composite scaffold that combines natural polymers (alginate and chitosan) with mesoporous silica nanoparticles (MSNs). MSNs were synthesized via a CTAB‑templated sol‑gel route, calcined at 550 °C, and milled to obtain a uniform powder with an average particle size of ~150 nm, high surface area, and well‑defined mesopores (2–10 nm). The nanoparticles were incorporated into a 5 wt% alginate/5 wt% chitosan solution at three loadings—10, 20, and 30 wt%—to produce Alg/Chit/MSN10, Alg/Chit/MSN20, and Alg/Chit/MSN30 scaffolds. After thorough sonication, the mixtures were cast into 48‑well plates, frozen sequentially at –30 °C and –80 °C, and freeze‑dried at –50 °C under vacuum (0.04 bar) for 48 h. A brief CaCl₂ cross‑linking step (1 wt% CaCl₂, 15 min) generated ionic bridges between alginate carboxyl groups and calcium ions, stabilizing the porous architecture.

Structural characterization (FTIR, XRD, FE‑SEM, EDS, DLS) confirmed the presence of Si–O–Si bonds, amorphous silica, and homogeneous dispersion of MSNs within the polymer matrix. Image‑analysis of SEM micrographs revealed a high overall porosity (≈78–81 %) with macropores of 120–150 µm—suitable for cell infiltration—and retained mesoporous domains inside the nanoparticles. Mechanical testing under unconfined compression showed a dramatic increase in compressive strength from 0.12 MPa for the plain Alg/Chit scaffold to 0.38 MPa for the 30 wt% MSN composite (≈3‑fold improvement), with a corresponding rise in elastic modulus. Swelling experiments indicated rapid water uptake, reaching equilibrium within 30 min (≈250 % swelling ratio) and showing negligible dependence on MSN content, demonstrating that the addition of silica does not compromise the hydrophilic nature of the polymer network.

In vitro degradation in phosphate‑buffered saline (pH 7.4, 37 °C) over 21 days demonstrated that higher MSN loading slowed hydrolytic loss: the plain scaffold lost ~45 % of its mass, whereas the MSN30 scaffold lost only ~28 %. This suggests that the inorganic phase hinders water penetration and polymer chain hydrolysis, extending scaffold longevity.

Biocompatibility was evaluated using MC3T3‑E1 pre‑osteoblasts. MTT assays showed no cytotoxicity for any formulation; notably, the MSN30 scaffold increased cell viability by ~40 % relative to the control (p < 0.01). Osteogenic potential was assessed by alkaline phosphatase (ALP) activity and Alizarin Red S calcium deposition after 14 days of culture. Both markers were highest in the MSN30 group, with ALP activity and mineralized nodule formation exceeding the plain scaffold by 1.8‑ and 2.1‑fold, respectively. These results indicate that the mesoporous silica surface provides a favorable microenvironment—likely through silanol groups and localized calcium ion release—that promotes osteogenic differentiation.

Overall, the incorporation of 30 wt% MSNs into an alginate/chitosan matrix yields a scaffold that simultaneously satisfies the key criteria for bone tissue engineering: high porosity, enhanced mechanical strength, controlled degradation, and strong osteoinductive capacity without cytotoxicity. The authors propose that Alg/Chit/MSN30 is a promising candidate for treating periodontal, peri‑implant, and larger craniofacial bone defects. Future work could focus on functionalizing the MSN surface with growth factors (e.g., BMP‑2) or antimicrobial agents (e.g., silver nanoparticles) to create multifunctional, patient‑specific implants, potentially leveraging additive manufacturing technologies for customized geometries.