Glass-ceramic scaffolds containing silica mesophases for bone grafting and drug delivery

Achieving the ideal balance between biological and mechanical requirements in composite bone scaffolds through a voxel-based approach

Achieving successful bone regeneration necessitates the design of scaffolds that meet diverse biological and mechanical requirements, often leading to conflicts in the design parameters. A key conflict arises between scaffold porosity and stiffness. Increasing porosity facilitates cell infiltration and nutrient exchange, promoting bone regeneration. However, higher porosity compromises scaffold stiffness, which is crucial for providing structural support in the defective region. Furthermore, appropriate scaffold stiffness is crucial for preventing stress shielding. Conventional geometry-based design methods utilizing single-phase materials have limited flexibility in resolving such conflicts. To address this challenge, we propose a voxel-based method for designing composite scaffolds composed of hydroxyapatite (HA) and polylactic acid (PLA). Our strategy involves first satisfying primary biological requirements by selecting appropriate porosity, pore shape, and size. Subsequently, scaffold stiffness requirements are met by selecting suitable phase materials and tuning their contents. The study demonstrates that the voxel-based approach effectively balances both biological and mechanical requirements in scaffold design. This method addresses the limitations of traditional designs by achieving an optimal balance between porosity and stiffness, which is crucial for scaffold performance in biomedical applications. Moreover, the scaffolds designed using this method can be manufactured using voxel-based 3D printing technology, which is emerging in the field. Future advancements in voxel-based 3D printing technology will further enhance the feasibility and practicality of this approach for bone tissue engineering applications.

Interaction of alginate with nano-hydroxyapatite-collagen using strontium provides suitable osteogenic platform

Background

Hydrogels based on organic/inorganic composites have been at the center of attention for the fabrication of engineered bone constructs. The establishment of a straightforward 3D microenvironment is critical to maintaining cell-to-cell interaction and cellular function, leading to appropriate regeneration. Ionic cross-linkers, Ca²⁺, Ba²⁺, and Sr²⁺, were used for the fabrication of Alginate-Nanohydroxyapatite-Collagen (Alg-nHA-Col) microspheres, and osteogenic properties of human osteoblasts were examined in in vitro and in vivo conditions after 21 days.

Results

Physicochemical properties of hydrogels illustrated that microspheres cross-linked with Sr²⁺ had reduced swelling, enhanced stability, and mechanical strength, as compared to the other groups. Human MG-63 osteoblasts inside Sr²⁺ cross-linked microspheres exhibited enhanced viability and osteogenic capacity indicated by mineralization and the increase of relevant proteins related to bone formation. PCR (Polymerase Chain Reaction) array analysis of the Wnt (Wingless-related integration site) signaling pathway revealed that Sr²⁺ cross-linked microspheres appropriately induced various signaling transduction pathways in human osteoblasts leading to osteogenic activity and dynamic growth. Transplantation of Sr²⁺ cross-linked microspheres with rat osteoblasts into cranium with critical size defect in the rat model accelerated bone formation analyzed with micro-CT and histological examination.

Conclusion

Sr²⁺ cross-linked Alg-nHA-Col hydrogel can promote functionality and dynamic growth of osteoblasts.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01511-9.

Recent Advances in Application of Azobenzenes Grafted on Mesoporous Silica Nanoparticles in Controlled Drug Delivery Systems Using Light as External Stimulus

Hybrid materials based on Mesoporous Silica Nanoparticles (MSN) have attracted plentiful attention due to the versatility of their chemistry, and the field of Drug Delivery Systems (DDS) is not an exception. MSN present desirable biocompatibility, high surface area values, and a well-studied surface reactivity for tailoring a vast diversity of chemical moieties. Particularly important for DDS applications is the use of external stimuli for drug release. In this context, light is an exceptional alternative due to its high degree of spatiotemporal precision and non-invasive character, and a large number of promising DDS based on photoswitchable properties of azobenzenes have been recently reported. This review covers the recent advances in design of DDS using light as an external stimulus mostly based on literature published within last years with an emphasis on usually overlooked underlying chemistry, photophysical properties, and supramolecular complexation of azobenzenes.

Comparing the Effects of Chitosan Scaffolds Containing Various Divalent Metal Phosphates on Osteogenic Differentiation of Stem Cells from Human Exfoliated Deciduous Teeth

Inducing the differentiation of stem cells from human exfoliated deciduous teeth (SHEDs) proceeds with low efficiency, which greatly limits clinical applications. Divalent metal elements play an important role in osteoinductivity for bone remodeling because they can simulate bone formation and decrease bone resorption. The purpose of this study was to investigate the effect of some divalent metal phosphates on osteogenic differentiation from human exfoliated deciduous teeth. These divalent metal ions can be gradually released from the scaffold into the culture medium and continually induce osteoblastic differentiation. Experimental results revealed that SHEDs cultured in chitosan scaffolds containing divalent metal phosphates had notably increased osteoblastic differentiation compared with cells cultured without divalent metal phosphates. This effect was due to the high activity of alkaline phosphatase, as well as the bone-related gene expression of collagen type I, Runx2, osteopontin, osteocalcin, VEGF, and Ang-1, shown through RT-PCR and bone-related protein immunocytochemistry stains. A calcium-content assay further revealed significant enhancement of deposited minerals on the scaffolds after 21 days of culture, particularly for magnesium phosphate and zinc phosphate. Thus, divalent metals, except for barium phosphate, effectively promoted SHED cell differentiation and osteoblastic cell maturation. This study demonstrated that the divalent metal elements magnesium, strontium, and zinc could effectively induce SHED osteoblastic differentiation for use in tissue engineering and bone repair.

Hydrophilic and Hydrophobic Mesoporous Silica Derived from Rice Husk Ash as a Potential Drug Carrier

This work describes the preparation of mesoporous silica by the green reaction of rice husk ash (RHA) with glycerol, followed by the modification and the potential use as a drug carrier. The reaction was carried out at 215 °C for 2 h. The solution was further hydrolyzed with deionized water and aged for various times (24, 48, 120, 360, 528 and 672 h) before calcinations at 500 °C for 24 h. Further treatment of prepared mesoporous silica was performed using trimethylmethoxysilane (TMMS) to obtain hydrophobic Mesoporous silica. For all synthesized silicas, silica contents were as high as 95 wt %, whereas organic residues were less than 3 wt %. RHA-glycerol showed the highest specific surface area with smallest pore diameter (205.70 m²/g, 7.46 nm) when aged for 48 h. The optimal hydrolysis-ageing period of 120 h resulted in 500.7 m²/g specific surface area, 0.655 cm³/g pore volume and 5.23 nm pore diameter. The surface modification of RHA-glycerol occurred through the reaction with TMMS as confirmed by FTIR (Fourier-transform infrared spectroscopy). Ibuprofen was selected as a model drug for the adsorption experiments. The adsorption under supercritical CO₂ was carried out at isothermal temperature of 40 °C and 100 bar; % ibuprofen loading of TMMS modified mesoporous silica (TMMS-g-MS) was 6 times less than that of mesoporous silica aged for 24 h (MS-24h) due to the hydrophobic nature of modified mesoporous silica, not surface and pore characteristics. The release kinetics of ibuprofen-loaded mesoporous silicas were also investigated in vitro. The release rate of ibuprofen-loaded MS-24h was much faster than that of ibuprofen-loaded TMMS-g-MS, but comparable to the crystalline ibuprofen. The slower release rate was attributed to the diffusion control and the stability of hydrophobic nature of modified silica. This would allow the design of a controlled release drug delivery system.

Composite Biomaterials Based on Sol-Gel Mesoporous Silicate Glasses: A Review

Bioactive glasses are able to bond to bone and stimulate the growth of new tissue while dissolving over time, which makes them ideal materials for regenerative medicine. The advent of mesoporous glasses, which are typically synthesized via sol-gel routes, allowed researchers to develop a broad and versatile class of novel biomaterials that combine superior bone regenerative potential (compared to traditional melt-derived glasses) with the ability of incorporating drugs and various biomolecules for targeted therapy in situ. Mesoporous glass particles can be directly embedded as a bioactive phase within a non-porous (e.g., microspheres), porous (3D scaffolds) or injectable matrix, or be processed to manufacture a surface coating on inorganic or organic (macro)porous substrates, thereby obtaining hierarchical structures with multiscale porosity. This review provides a picture of composite systems and coatings based on mesoporous glasses and highlights the challenges for the future, including the great potential of inorganic-organic hybrid sol-gel biomaterials.

Uniform Surface Modification of 3D Bioglass(®)-Based Scaffolds with Mesoporous Silica Particles (MCM-41) for Enhancing Drug Delivery Capability

The design and characterization of a new family of multifunctional scaffolds based on bioactive glass (BG) of 45S5 composition for bone tissue engineering and drug delivery applications are presented. These BG-based scaffolds are developed via a replication method of polyurethane packaging foam. In order to increase the therapeutic functionality, the scaffolds were coated with mesoporous silica particles (MCM-41), which act as an in situ drug delivery system. These sub-micron spheres are characterized by large surface area and pore volume with a narrow pore diameter distribution. The solution used for the synthesis of the silica mesoporous particles was designed to obtain a high-ordered mesoporous structure and spherical shape – both are key factors for achieving the desired controlled drug release. The MCM-41 particles were synthesized directly inside the BG-based scaffolds, and the drug-release capability of this combined system was evaluated. Moreover, the effect of MCM-41 particle coating on the bioactivity of the BG-based scaffolds was assessed. The results indicate that it is possible to obtain a multifunctional scaffold system characterized by high and interconnected porosity, high bioactivity, and sustained drug delivery capability.

Bioceramics in ophthalmology

The benefits of ceramics in biomedical applications have been universally appreciated as they exhibit an extraordinarily broad set of physico-chemical, mechanical and biological properties which can be properly tailored by acting on their composition, porosity and surface texture to increase their versatility and suitability for targeted healthcare applications. Bioceramics have traditionally been used for the repair of hard tissues, such as bone and teeth, mainly due to their suitable strength for load-bearing applications, wear resistance (especially alumina, zirconia and composites thereof) and, in some cases, bone-bonding ability (calcium orthophosphates and bioactive glasses). Bioceramics have been also applied in other medical areas, like ophthalmic surgery; although their use in such a context has been scientifically documented since the late 1700s, the potential and importance of ceramic ocular implants still seem to be underestimated and an exhaustive, critical assessment is currently lacking in the relevant literature. The present review aims to fill this gap by giving a comprehensive picture of the ceramic-based materials and implants that are currently used in ophthalmology and pointing out the strengths and weaknesses of the existing devices. A prospect for future research is also provided, highlighting the potential of new, smart bioceramics able to carry specific added values which could have a significant impact on the treatment of ocular diseases.

Novel resorbable glass-ceramic scaffolds for hard tissue engineering: from the parent phosphate glass to its bone-like macroporous derivatives

One of the major challenges of hard tissue engineering research focuses on the development of scaffolds that can match the mechanical properties of the host bone and resorb at the same rate as the bone is repaired. The aim of this work was the synthesis and characterization of a resorbable phosphate glass, as well as its application for the fabrication of three dimensional (3-D) scaffolds for bone regeneration. The glass microstructure and behaviour upon heating were analysed by X-ray diffraction, differential scanning calorimetry and hot stage microscopy. The glass solubility was investigated according to relevant ISO standards using distilled water, simulated body fluid (SBF) and Tris-HCl as testing media. The glass underwent progressive dissolution over time in all three media but the formation of a hydroxyapatite-like layer was also observed on the samples soaked in SBF and Tris-HCl, which demonstrated the bioactivity of the material. The glass powder was used to fabricate 3-D macroporous bone-like glass-ceramic scaffolds by adopting polyethylene particles as pore formers: during thermal treatment, the polymer additive was removed and the sintering of glass particles was allowed. The obtained scaffolds exhibited high porosity (87 vol.%) and compressive strength around 1.5 MPa. After soaking for 4 months in SBF, the scaffolds mass loss was 76 wt.% and the pH of the solution did not exceed the 7.55 value, thereby remaining in a physiological range. The produced scaffolds, being resorbable, bioactive, architecturally similar to trabecular bone and exhibiting interesting mechanical properties, can be proposed as promising candidates for bone repair applications.

Mesoporous bioactive glass as a multifunctional system for bone regeneration and controlled drug release

PURPOSE

Coupling the potential for bone regeneration and the ability for in situ controlled drug release in a single device is a challenging field of research in bone tissue engineering; in an attempt to pursue this aim, mesoporous bioactive glass (MBG) membranes belonging to the SiO2-P2O5-CaO ternary system were produced and characterized.

METHODS

The glass was synthesized via a sol-gel route coupled with an evaporation-induced self-assembly process by using a non-ionic block co-polymer as a mesostructure former. MBG structure and morphology, as well as mesopores size and shape, were investigated by x-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption measurements. In vitro bioactivity was investigated by soaking MBG membranes in simulated body fluid (SBF) for different time frames. Ibuprofen was encapsulated into MBG pores and drug release kinetics in SBF were assessed. Biological tests by using SAOS-2 cells were performed to assess the material cytocompatibility.

RESULTS

The material revealed significant ability to induce hydroxyapatite formation on its surface (bioactivity). Drug release kinetics in SBF are very similar to those obtained for mesoporous silica having mesopore size comparable to that of the prepared MBG (∼5 nm). No evidence of cell viability depression was detected during in vitro culture, which demonstrates the good biological compatibility of the material.

CONCLUSIONS

The easiness of tailoring and shaping, the highly bioactive and biocompatible behavior, and the drug uptake/release ability of the prepared materials may suggest their use as "smart" multifunctional grafts for bone reconstructive surgery.

A New Highly Bioactive Composite for Scaffold Applications: A Feasibility Study

Hydroxyapatite (HA) has been widely investigated as scaffolding material for bone tissue engineering, mainly for its excellent biocompatibility. Presently, there is an increasing interest in the composites of hydroxyapatite with bioactive glasses, with the aim to obtain systems with improved bioactivity or mechanical properties. Moreover, modifying the ratio between bioactive glass and hydroxyapatite results in the possibility of controlling the reaction rate of the composite scaffold in the human body. However, high temperature treatments are usually required in order to sinter HA-based composites, causing the bioactive glass to crystallize into a glass-ceramic, with possible negative effects on its bioactivity. In the present research work, a glass composition belonging to the Na₂O-CaO-P₂O₅-SiO₂ system, with a reduced tendency to crystallize, is applied to realize HA-based composites. The novel samples can be sintered at a relative low temperature (750 °C) compared to the widely studied HA/45S5 Bioglass^® composites. This fact greatly helps to preserve the amorphous nature of the glass, with excellent effects in terms of bioactivity, according to in vitro tests. As a first application, the obtained composites are also tested to realize highly porous scaffolds by means of the standard burning out method.