Osteostatin potentiates the bioactivity of mesoporous glass scaffolds containing Zn2+ ions in human mesenchymal stem cells

Osteostatin, a peptide for the future treatment of musculoskeletal diseases

Nowadays, the treatment of musculoskeletal diseases represents a major challenge in the developed world. Diseases such as osteoporosis, osteoarthritis and arthritis have a high incidence and prevalence as a consequence of population aging, and they are also associated with a socioeconomic burden. Many efforts have been made to find a treatment for these diseases with various levels of success, but new approaches are still needed to deal with these pathologies. In this context, one peptide derived for the C-terminal extreme of the Parathormone related Peptide (PTHrP) called Osteostatin can be useful to treat musculoskeletal diseases. This pentapeptide (TRSAW) has demonstrated both in different in vitro and in vivo models, its role as a molecule with anti-resorptive, anabolic, anti-inflammatory, and anti-antioxidant properties. Our aim with this work is to review the Osteostatin main features, the knowledge of its mechanisms of action as well as its possible use for the treatment of osteoporosis, bone regeneration and fractures and against arthritis given its anti-inflammatory properties.

Engineering mesoporous bioactive glasses for emerging stimuli-responsive drug delivery and theranostic applications

Mesoporous bioactive glasses (MBGs), which belong to the category of modern porous nanomaterials, have garnered significant attention due to their impressive biological activities, appealing physicochemical properties, and desirable morphological features. They hold immense potential for utilization in diverse fields, including adsorption, separation, catalysis, bioengineering, and medicine. Despite possessing interior porous structures, excellent morphological characteristics, and superior biocompatibility, primitive MBGs face challenges related to weak encapsulation efficiency, drug loading, and mechanical strength when applied in biomedical fields. It is important to note that the advantageous attributes of MBGs can be effectively preserved by incorporating supramolecular assemblies, miscellaneous metal species, and their conjugates into the material surfaces or intrinsic mesoporous networks. The innovative advancements in these modified colloidal inorganic nanocarriers inspire researchers to explore novel applications, such as stimuli-responsive drug delivery, with exceptional in-vivo performances. In view of the above, we outline the fabrication process of calcium-silicon-phosphorus based MBGs, followed by discussions on their significant progress in various engineered strategies involving surface functionalization, nanostructures, and network modification. Furthermore, we emphasize the recent advancements in the textural and physicochemical properties of MBGs, along with their theranostic potentials in multiple cancerous and non-cancerous diseases. Lastly, we recapitulate compelling viewpoints, with specific considerations given from bench to bedside.

Osteogenic-angiogenic coupled response of cobalt-containing mesoporous bioactive glasses in vivo

The incorporation of cobalt ions into the composition of bioactive glasses has emerged as a strategy of interest for bone regeneration purposes. In the present work, we have designed a set of bioactive mesoporous glasses SiO2-CaO-P2O5-CoO (Co-MBGs) with different amounts of cobalt. The physicochemical changes introduced by the Co2+ ion, the in vitro effects of Co-MBGs on preosteoblasts and endothelial cells and their in vivo behaviour using them as bone grafts in a sheep model were studied. The results show that Co2+ ions neither destroy mesoporous ordering nor inhibit in vitro bioactive behaviour, exerting a dual role as network former and modifier for CoO concentrations above 3 % mol. On the other hand, the activity of Co-MBGs on MC3T3-E1 preosteoblasts and HUVEC vascular endothelial cells is dependent on the concentration of CoO present in the glass. For low Co-MBGs concentrations (1mg/ml) cell viability is not affected, while the expression of osteogenic (ALP, RUNX2 and OC) and angiogenic (VEGF) genes is stimulated. For Co-MBGs concentration of 5 mg/ml, cell viability decreases as a function of the CoO content. In vivo studies show that the incorporation of Co2+ ions to the MBGs improves the bone regeneration activity of these materials, despite the deleterious effect that this ion has on bone-forming cells for any of the Co-MBG compositions studied. This contradictory effect is explained by the marked increase in angiogenesis that takes place inside the bone defect, leading to an angiogenesis-osteogenesis coupling that compensates for the partial decrease in osteoblast cells. STATEMENT OF SIGNIFICANCE: The development of new bone grafts implies to address the need for osteogenesis-angiogenesis coupling that allows bone regeneration with viable tissue in the long term. In this sense the incorporation of cobalt ions into the composition of bioactive glasses has emerged as a strategy of great interest in this field. Due to the potential cytotoxic effect of cobalt ions, there is an important controversy regarding the suitability of their incorporation in bone grafts. In this work, we address this controversy after the implantation of cobalt-doped mesoporous bioactive glasses in a sheep model. The incorporation of cobalt ions in bioactive glasses improves the bone regeneration ability of these bone grafts, due to enhancement of the angiogenesis-osteogenesis coupling.

Bio-response of copper-magnesium co-substituted mesoporous bioactive glass for bone tissue regeneration

Mesoporous bioactive glass (MBG) is widely acknowledged in bone tissue engineering due to its mesoporous structure, large surface area, and bioactivity. Recent research indicates that introduction of metallic ions has beneficial impacts on bone metabolism and angiogenesis. Thus, the features of MBG can be modified by incorporating combinations of ions, such as magnesium (Mg) and copper (Cu), which can play a considerable role in bone formation, influencing angiogenesis, osteogenesis, as well as antibacterial properties. In this study, Mg and Cu were co-doped for the first time (in a ratio of 1 : 1) in 80SiO2-5P2O5-(15 - 2x)CaO-xMgO-xCuO glass composition with x = 0, 0.5, 1, and 2 mol%, synthesized using the sol-gel and evaporation-induced self-assembly method. X-ray diffraction analysis confirmed the amorphous nature of the powders, while inductively coupled plasma-optical emission spectrometry verified the existence of dopant ions in the respective amounts. The nitrogen sorption method indicated the formation of uniform cylindrical mesopores which are open at both ends and a high surface area of the powders. TEM images show fringes, indicating an ordered mesoporous structure in all MgCu co-doped systems. In vitro bioactivity was observed in all MBG powders, confirmed by the formation of an apatite phase when placed in simulated body fluid (SBF). Flake-like microstructure characteristics of HAp crystals found on the surface of MBG powders were visualized using FESEM. Cytotoxicity tests at lower concentrations (0.1 and 1 wt/vol%) of co-doped 2MC MBG (co-doping up to 2 mol%) showed cell proliferation and viability of osteoblast-like MG-63 cells and normal human dermal fibroblast (NHDF) cells similar to the basic glass 80S. Antibacterial study of MBG pellets showed an increment in the zone of inhibition with the sequential addition of doping ions. The turbidity measurement of bacterial cultures revealed that the optimal concentration for effectively inhibiting bacterial growth was 1 wt/vol% (i.e., 10 mg mL-1) concentration of MBG extracts. The result suggested that the incorporation of Mg and Cu ions in MBG in lower concentrations of up to 2 mol% can be useful in bone regeneration owing to bioactivity, cell proliferation, and antibacterial characteristics.

Osteogenic Potential of a Biomaterial Enriched with Osteostatin and Mesenchymal Stem Cells in Osteoporotic Rabbits

Mesoporous bioactive glasses (MBGs) of the SiO2-CaO-P2O5 system are biocompatible materials with a quick and effective in vitro and in vivo bioactive response. MBGs can be enhanced by including therapeutically active ions in their composition, by hosting osteogenic molecules within their mesopores, or by decorating their surfaces with mesenchymal stem cells (MSCs). In previous studies, our group showed that MBGs, ZnO-enriched and loaded with the osteogenic peptide osteostatin (OST), and MSCs exhibited osteogenic features under in vitro conditions. The aim of the present study was to evaluate bone repair capability after large bone defect treatment in distal femur osteoporotic rabbits using MBGs (76%SiO2-15%CaO-5%P2O5-4%ZnO (mol-%)) before and after loading with OST and MSCs from a donor rabbit. MSCs presence and/or OST in scaffolds significantly improved bone repair capacity at 6 and 12 weeks, as confirmed by variations observed in trabecular and cortical bone parameters obtained by micro-CT as well as histological analysis results. A greater effect was observed when OST and MSCs were combined. These findings may indicate the great potential for treating critical bone defects by combining MBGs with MSCs and osteogenic peptides such as OST, with good prospects for translation to clinical practice.

Zinc-based biomaterials for bone repair and regeneration: mechanism and applications

Zinc (Zn) is one of the most important trace elements in the human body and plays a key role in various physiological processes, especially in bone metabolism. Zn-containing materials have been reported to enhance bone repair through promoting cell proliferation, osteogenic activity, angiogenesis, and inhibiting osteoclast differentiation. Therefore, Zn-based biomaterials are potential substitutes for traditional bone grafts. In this review, the specific mechanisms of bone formation promotion by Zn-based biomaterials were discussed, and recent developments in their application in bone tissue engineering were summarized. Moreover, the challenges and perspectives of Zn-based biomaterials were concluded, revealing their attractive potential and development directions in the future.

Nanodevices based on mesoporous glass nanoparticles enhanced with zinc and curcumin to fight infection and regenerate bone

Nanotechnology-based approaches are emerging as promising strategies to treat different bone pathologies such as infection, osteoporosis or cancer. To this end, several types of nanoparticles are being investigated, including those based on mesoporous bioactive glasses (MGN) which exhibit exceptional structural and textural properties and whose biological behaviour can be improved by including therapeutic ions in their composition and loading them with biologically active substances. In this study, the bone regeneration capacity and antibacterial properties of MGNs in the SiO2-CaO-P2O5 system were evaluated before and after being supplemented with 2.5% or 4% ZnO and loaded with curcumin. in vitro studies with preosteoblastic cells and mesenchymal stem cells allowed determining the biocompatible MGNs concentrations range. Moreover, the bactericidal effect of MGNs with zinc and curcumin against S. aureus was demonstrated, as a significant reduction of bacterial growth was detected in both planktonic and sessile states and the degradation of a pre-formed bacterial biofilm in the presence of the nanoparticles also occurred. Finally, MC3T3-E1 preosteoblastic cells and S. aureus were co-cultured to investigate competitive colonisation between bacteria and cells in the presence of the MGNs. Preferential colonisation and survival of osteoblasts and effective inhibition of both bacterial adhesion and biofilm formation of S. aureus in the co-culture system were detected. Our study demonstrated the synergistic antibacterial effect of zinc ions combined with curcumin and the enhancement of the bone regeneration characteristics of MGNs containing zinc and curcumin to obtain systems capable of simultaneously promoting bone regeneration and controlling infection. STATEMENT OF SIGNIFICANCE: In search of a new approach to regenerate bone and fight infections, a nanodevice based on mesoporous SiO2-CaO-P2O5 glass nanoparticles enriched with Zn2+ ions and loaded with curcumin was designed. This study demonstrates the synergistic effect of the simultaneous presence of zinc ions and curcumin in the nanoparticles that significantly reduces the bacterial growth in planktonic state and is capable to degrade pre-formed S. aureus biofilms whereas the nanosystem exhibits a cytocompatible behaviour in the presence of preosteoblasts and mesenchymal stem cells. Based on these results, the designed nanocarrier represents a promising alternative for the treatment of acute and chronic infections in bone tissues, while avoiding the significant current problem of bacterial resistance to antibiotics.

Pleiotrophin-Loaded Mesoporous Silica Nanoparticles as a Possible Treatment for Osteoporosis

Osteoporosis is the most common type of bone disease. Conventional treatments are based on the use of antiresorptive drugs and/or anabolic agents. However, these treatments have certain limitations, such as a lack of bioavailability or toxicity in non-specific tissues. In this regard, pleiotrophin (PTN) is a protein with potent mitogenic, angiogenic, and chemotactic activity, with implications in tissue repair. On the other hand, mesoporous silica nanoparticles (MSNs) have proven to be an effective inorganic drug-delivery system for biomedical applications. In addition, the surface anchoring of cationic polymers, such as polyethylenimine (PEI), allows for greater cell internalization, increasing treatment efficacy. In order to load and release the PTN to improve its effectiveness, MSNs were successfully internalized in MC3T3-E1 mouse pre-osteoblastic cells and human mesenchymal stem cells. PTN-loaded MSNs significantly increased the viability, mineralization, and gene expression of alkaline phosphatase and Runx2 in comparison with the PTN alone in both cell lines, evidencing its positive effect on osteogenesis and osteoblast differentiation. This proof of concept demonstrates that MSN can take up and release PTN, developing a potent osteogenic and differentiating action in vitro in the absence of an osteogenic differentiation-promoting medium, presenting itself as a possible treatment to improve bone-regeneration and osteoporosis scenarios.

Delivery of Therapeutic Biopolymers Employing Silica-Based Nanosystems

The use of nanoparticles is crucial for the development of a new generation of nanodevices for clinical applications. Silica-based nanoparticles can be tailored with a wide range of functional biopolymers with unique physicochemical properties thus providing several advantages: (1) limitation of interparticle interaction, (2) preservation of cargo and particle integrity, (3) reduction of immune response, (4) additional therapeutic effects and (5) cell targeting. Therefore, the engineering of advanced functional coatings is of utmost importance to enhance the biocompatibility of existing biomaterials. Herein we will focus on the most recent advances reported on the delivery and therapeutic use of silica-based nanoparticles containing biopolymers (proteins, nucleotides, and polysaccharides) with proven biological effects.

Antibacterial effect of 3D printed mesoporous bioactive glass scaffolds doped with metallic silver nanoparticles

The development of new biomaterials for bone tissue regeneration with high bioactivity abilities and antibacterial properties is being intensively investigated. We have synthesized nanocomposites formed by mesoporous bioactive glasses (MBGs) in the ternary SiO₂, CaO and P₂O₅ system doped with metallic silver nanoparticles (AgNPs) that were homogenously embedded in the MBG matrices. Ag/MBG nanocomposites have been directly synthesized and silver species were spontaneously reduced to metallic AgNPs by high temperatures (700 °C) obtained of last MBG synthesis step. Three-dimensional silver-containing mesoporous bioactive glass scaffolds were fabricated showing uniformly interconnected ultrapores, macropores and mesopores. The manufacture method consisted of a combination of a single-step sol-gel route in the mesostructure directing agent (P123) presence and a biomacromolecular polymer such as (hydroxypropyl)methyl cellulose (HPMC) as the macrostructure template, followed by rapid prototyping (RP) technique. Biological properties of Ag/MBG nanocomposites were evaluated by MC3T3-E1 preosteoblastic cells culture tests and bacterial (E. coli and S. aureus) assays. The results showed that the MC3T3-E1 cells morphology was not affected while preosteoblastic proliferation decreased when the presence of silver increased. Antimicrobial assays indicated that bacterial growth inhibition and biofilm destruction were directly proportional to the increased presence of AgNPs in the MBG matrices. Furthermore, in vitro co-culture of MC3T3-E1 cells and S. aureus bacteria confirmed that AgNPs presence was necessary for antibacterial activity, and AgNPs slightly affected cell proliferation parameters. Therefore, 3D printed scaffolds with hierarchical pore structure and high antimicrobial capacity have potential applications in bone tissue regeneration. STATEMENT OF SIGNIFICANCE: This study combines three key scientific aspects for bone tissue engineering: (i) materials with high bioactivity to repair and regenerate bone tissue that (ii) contain antibacterial agents to reduce the infection risk (iii) in the form of three-dimensional scaffolds with hierarchical porosity. Innovative methodology is described here: sol-gel method, which is employed to obtain mesoporous bioactive glass matrices doped with metallic silver nanoparticles where different polymer templates facilitate the different size scales presence, and rapid prototyping technique that provides ultra-large macroporosity according to computer-aided design. The dual scaffolds obtained are biocompatible and deliver active doses of silver capable of combating bone infections, which represent one of the most serious complications associated to surgical treatments of bone diseases and fractures.

Achievements in Mesoporous Bioactive Glasses for Biomedical Applications

Nowadays, mesoporous bioactive glasses (MBGs) are envisaged as promising candidates in the field of bioceramics for bone tissue regeneration. This is ascribed to their singular chemical composition, structural and textural properties and easy-to-functionalize surface, giving rise to accelerated bioactive responses and capacity for local drug delivery. Since their discovery at the beginning of the 21st century, pioneering research efforts focused on the design and fabrication of MBGs with optimal compositional, textural and structural properties to elicit superior bioactive behavior. The current trends conceive MBGs as multitherapy systems for the treatment of bone-related pathologies, emphasizing the need of fine-tuning surface functionalization. Herein, we focus on the recent developments in MBGs for biomedical applications. First, the role of MBGs in the design and fabrication of three-dimensional scaffolds that fulfil the highly demanding requirements for bone tissue engineering is outlined. The different approaches for developing multifunctional MBGs are overviewed, including the incorporation of therapeutic ions in the glass composition and the surface functionalization with zwitterionic moieties to prevent bacterial adhesion. The bourgeoning scientific literature on MBGs as local delivery systems of diverse therapeutic cargoes (osteogenic/antiosteoporotic, angiogenic, antibacterial, anti-inflammatory and antitumor agents) is addressed. Finally, the current challenges and future directions for the clinical translation of MBGs are discussed.

Influence of Copper-Strontium Co-Doping on Bioactivity, Cytotoxicity and Antibacterial Activity of Mesoporous Bioactive Glass

Mesoporous bioactive glass (MBG) is an extensively studied biomaterial used for the healing of bone defects. Its biological applications can be tailored by introducing metallic ions, such as strontium (Sr) and copper (Cu), which can enhance its functionalities, including osteogenetic, angiogenetic and antibacterial functionalities. In this study, Cu and Sr ions were co-doped (ratio 1:1) with x = 0.5, 1 and 2 mol% each in glass with an intended nominal composition of 80SiO2-(15-2x)CaO-5P2O5-xCuO-xSrO and synthesized with an evaporation-induced self-assembly (EISA)-based sol-gel technique. XRD confirmed the amorphous nature of the glass, while compositional analysis using ICP-OES confirmed the presence of dopant ions with the required amounts. A TEM study of the MBG powders showed fringes that corresponded to the formation of a highly ordered mesoporous structure. The Cu-Sr-doped MBG showed a positive effect on apatite formation when immersed in SBF, although the release of Cu and Sr ions was relatively slow for 1 mol% of each co-dopant, which signified a stable network structure in the glass. The impact of the Cu and Sr ions on the osteoblast-like cell line MG-63 was assessed. At the particle concentrations of 1 wt./vol.% or lower, the cell viability was above 50%. An antibacterial test was conducted against Gram-negative E. coli and Gram-positive S. aureus bacteria. With a sequential increase in the co-doped ion content in the glass, the zone of inhibition for bacteria increased. The results suggest that the doping of MBG with Cu and Sr ions at up to 2 mol% can result in tailored sustained release of ions to enhance the applicability of the studied glass as a functional biomaterial for bone regeneration applications.

An Extracellular Matrix-like Surface for Zn Alloy to Enhance Bone Regeneration

Zn-based alloys are promising biodegradable implants for bone defect repair due to their good mechanical performance and degradability. However, local Zn²⁺ released from Zn-based implants can seriously affect adhering cell behaviors as well as new bone formation on implant surfaces. To address this issue, we have fabricated a bone-mimetic extracellular matrix (ECM)-like surface on Zn-1Ca implants using a hybrid process of anodization, hydrothermal treatment (HT), and fluorous-curing. The ECM-like surface consisted of Zn₂SiO₄ nanorods layered with collagen I (Col-I). The Zn₂SiO₄ nanorods were hemicrystallized and transformed by the reaction of Zn(OH)₂ and SiO₄^4- during the HT. The Zn₂SiO₄ nanorods effectively protected the substrate from corrosion; the Col-I layer decreased the degradation of Zn₂SiO₄ nanorods and further reduced Zn²⁺ release into the medium. This ECM-like surface generated a microenvironment with appropriate Zn²⁺ levels, nanorod-like topography, and Col-I. It significantly improved adhesion, proliferation, and differentiation of osteoblasts on implant surfaces and vascularization of endothelial cells in the extract medium. The in vivo results are in good agreement with in vitro tests, with the ECM-like surface significantly enhancing new bone formation and bone-implant contact compared to the bare implant surface. Overall, this bone-mimetic ECM-like material of Col-I layered Zn₂SiO₄ nanorods is a promising scaffold that promotes the bone regeneration of Zn-based implants.

Engineering mesoporous silica nanoparticles for drug delivery: where are we after two decades?

The present review details a chronological description of the events that took place during the development of mesoporous materials, their different synthetic routes and their use as drug delivery systems. The outstanding textural properties of these materials quickly inspired their translation to the nanoscale dimension leading to mesoporous silica nanoparticles (MSNs). The different aspects of introducing pharmaceutical agents into the pores of these nanocarriers, together with their possible biodistribution and clearance routes, would be described here. The development of smart nanocarriers that are able to release a high local concentration of the therapeutic cargo on-demand after the application of certain stimuli would be reviewed here, together with their ability to deliver the therapeutic cargo to precise locations in the body. The huge progress in the design and development of MSNs for biomedical applications, including the potential treatment of different diseases, during the last 20 years will be collated here, together with the required work that still needs to be done to achieve the clinical translation of these materials. This review was conceived to stand out from past reports since it aims to tell the story of the development of mesoporous materials and their use as drug delivery systems by some of the story makers, who could be considered to be among the pioneers in this area.

Effects of Zinc, Magnesium, and Iron Ions on Bone Tissue Engineering

Large-sized bone defects are a great challenge in clinics and considerably impair the quality of patients' daily life. Tissue engineering strategies using cells, scaffolds, and bioactive molecules to regulate the microenvironment in bone regeneration is a promising approach. Zinc, magnesium, and iron ions are natural elements in bone tissue and participate in many physiological processes of bone metabolism and therefore have great potential for bone tissue engineering and regeneration. In this review, we performed a systematic analysis on the effects of zinc, magnesium, and iron ions in bone tissue engineering. We focus on the role of these ions in properties of scaffolds (mechanical strength, degradation, osteogenesis, antibacterial properties, etc.). We hope that our summary of the current research achievements and our notifications of potential strategies to improve the effects of zinc, magnesium, and iron ions in scaffolds for bone repair and regeneration will find new inspiration and breakthroughs to inspire future research.

Cu-Doped Hollow Bioactive Glass Nanoparticles for Bone Infection Treatment

In search of new approaches to treat bone infection and prevent drug resistance development, a nanosystem based on hollow bioactive glass nanoparticles (HBGN) of composition 79.5SiO₂-(18-x)CaO-2.5P₂O₅-xCuO (x = 0, 2.5 or 5 mol-% CuO) was developed. The objective of the study was to evaluate the capacity of the HBGN to be used as a nanocarrier of the broad-spectrum antibiotic danofloxacin and source of bactericidal Cu²⁺ ions. Core-shell nanoparticles with specific surface areas close to 800 m²/g and pore volumes around 1 cm³/g were obtained by using hexadecyltrimethylammonium bromide (CTAB) and poly(styrene)-block-poly(acrylic acid) (PS-b-PAA) as structure-directing agents. Flow cytometry studies showed the cytocompatibility of the nanoparticles in MC3T3-E1 pre-osteoblastic cell cultures. Ion release studies confirmed the release of non-cytotoxic concentrations of Cu²⁺ ions within the therapeutic range. Moreover, it was shown that the inclusion of copper in the system resulted in a more gradual release of danofloxacin that was extended over one week. The bactericidal activity of the nanosystem was evaluated with E. coli and S. aureus strains. Nanoparticles with copper were not able to reduce bacterial viability by themselves and Cu-free HBGN failed to reduce bacterial growth, despite releasing higher antibiotic concentrations. However, HBGN enriched with copper and danofloxacin drastically reduced bacterial growth in sessile, planktonic and biofilm states, which was attributed to a synergistic effect between the action of Cu²⁺ ions and danofloxacin. Therefore, the nanosystem here investigated is a promising candidate as an alternative for the local treatment of bone infections.

Osteostatin improves the Osteogenic differentiation of mesenchymal stem cells and enhances angiogenesis through HIF-1α under hypoxia conditions in vitro

BACKGROUND

Hypoxia conditions induced by bone defects would prolong the duration of bone regeneration. The effect of osteostatin (OST) on the osteogenic differentiation of mesenchymal stem cells (MSCs) and angiogenesis under hypoxia conditions remain unexplored.

METHODS

SPF mice were obtained, and MSCs were isolated from bone marrow. MSCs were treated with 1% oxygen for hypoxia induction, and 200 nM of OST was used to treat cells under nomorxia or hypoxia conditions. Cell proliferation was evaluated using CCK8 assay, and trypan blue staining was implemented for determining cell death ratio. Alkaline phosphatase activity and alizarin redS staining was conducted to histologically evaluated osteogenic differentiation. Flow cytometry was used for the detection of CD31^hiEmcn^hi cells (Type H ECs), whose migration was detected by Transwell assay and angiogenesis was measured by tube formation assay. Protein level was measured by western blotting and mRNA level was monitored via RT-qPCR.

RESULTS

The MSC proliferation was enhanced by OST under hypoxia conditions. The osteogenic differentiation of MSCs was decreased under hypoxia conditions, and treatment of OST significantly reversed its inhibitory effect. The hypoxia treated culture medium of MSCs promoted the proliferation, migration, and angiogenesis of type H ECs, while the effects were further strengthened by OST addition. HIF-1α was found to be upregulated in hypoxia treated MSCs, whereas silencing of HIF-1α had reversed effects on the angiogenic capacity of Type H ECs.

CONCLUSION

OST improved the proliferation and osteogenic differentiation of MSCs and further promoted angiogenesis of type H ECs through upregulating HIF-1α expression.

The Role of Zinc in Bone Mesenchymal Stem Cell Differentiation

Zinc is an essential trace element for bone growth and bone homeostasis in the human body. Bone mesenchymal stem cells (BMSCs) are multipotent progenitors existing in the bone marrow stroma with the capability of differentiating along multiple lineage pathways. Zinc plays a paramount role in BMSCs, which can be spurred differentiating into osteoblasts, chondrocytes, or adipocytes, and modulates the formation and activity of osteoclasts. The expression of related genes also changed during the differentiation of various cell phenotypes. Based on the important role of zinc in BMSC differentiation, using zinc as a therapeutic approach for bone remodeling will be a promising method. This review explores the role of zinc ion in the differentiation of BMSCs into various cell phenotypes and outlines the existing research on their molecular mechanism.

Mesoporous Bioglasses Enriched with Bioactive Agents for Bone Repair, with a Special Highlight of María Vallet-Regí’s Contribution

Throughout her impressive scientific career, Prof. María Vallet-Regí opened various research lines aimed at designing new bioceramics, including mesoporous bioactive glasses for bone tissue engineering applications. These bioactive glasses can be considered a spin-off of silica mesoporous materials because they are designed with a similar technical approach. Mesoporous glasses in addition to SiO₂ contain significant amounts of other oxides, particularly CaO and P₂O₅ and therefore, they exhibit quite different properties and clinical applications than mesoporous silica compounds. Both materials exhibit ordered mesoporous structures with a very narrow pore size distribution that are achieved by using surfactants during their synthesis. The characteristics of mesoporous glasses made them suitable to be enriched with various osteogenic agents, namely inorganic ions and biopeptides as well as mesenchymal cells. In the present review, we summarize the evolution of mesoporous bioactive glasses research for bone repair, with a special highlight on the impact of Prof. María Vallet-Regí´s contribution to the field.

Our contributions to applications of mesoporous silica nanoparticles

Our contributions to mesoporous silica materials in the field of biomedicine are reported in this article. This perspective article represents our work in the basics of the material, preparing different ranges of mesoporous silica nanoparticles with different diameters and with varied pore sizes. We demonstrated the high loading capacity of these materials. Additionally, the possibility of functionalizing both internal and external surface with different organic or inorganic moieties allowed the development of stimuli-responsive features which allowed a proper control on the administered dose. In addition, we have demonstrated that these carriers are not toxic, and we have also ensured that the load reaches its destination without affecting healthy tissues. STATEMENT OF SIGNIFICANCE: This paper presents my personal opinion and background on a hot topic as mesoporous silica nanoparticles for drug delivery. To this aim it provides a comprehensive and historical overview on the innovative contributions of my research group to this rapidly expanding field of research.

The Role of Transmission Electron Microscopy in the Early Development of Mesoporous Materials for Tissue Regeneration and Drug Delivery Applications

For the last 20 years, silica-based mesoporous materials have provided a sound platform for the development of biomedical technology applied to tissue engineering and drug delivery. Their unique structural and textural characteristics, chiefly, the ordered distribution of homogeneous and tunable pores with high surface areas and large pore volume, and their excellent biocompatibility provide an excellent starting point for bone tissue regeneration on the mesoporous surface, and also to load species of interest inside the pores. Adequate control of the synthesis conditions and functionalization of the mesoporous surface are critical factors in the design of new systems that are suitable for use in specific medical applications. Simultaneously, the use of appropriate characterization techniques in the several stages of design and manufacture of mesoporous particles allows us to ascertain the textural, structural and compositional modifications induced during the synthesis, functionalization and post-in vitro assays processes. In this scenario, the present paper shows, through several examples, the role of transmission electron microscopy and associated spectroscopic techniques in the search for useful information in the early design stages of mesoporous systems, with application in the fields of tissue regeneration and drug delivery systems.

Incorporation of Zinc into Binary SiO2-CaO Mesoporous Bioactive Glass Nanoparticles Enhances Anti-Inflammatory and Osteogenic Activities

During the healing and repair of bone defects, uncontrolled inflammatory responses can compromise bone regeneration. Biomaterials with anti-inflammatory activity are favorable for bone tissue regeneration processes. In this work, multifunctional Zn-containing mesoporous bioactive glass nanoparticles (Zn-MBGs) exhibiting favorable osteogenic and anti-inflammatory activities were produced employing a sol-gel method. Zn-MBGs exhibited a mesoporous spherical shape and nanoscale particle size (100 ± 20 nm). They were degradable in cell culture medium, and could release Si, Ca, and Zn in a sustained manner. Zn-MBGs also exhibited a concentration-dependent cellular response. The extract of Zn-MBGs obtained by incubation at 0.1 mg/mL (in culture medium) for 24 h could enhance in vitro mineralization, alkaline phosphatase activity, the expression of osteogenesis-related genes, and the production of intracellular protein osteocalcin of rat bone marrow stromal cells (BMSCs). Moreover, the extract of Zn-MBGs at 0.1 mg/mL could significantly downregulate the expression of inflammatory genes and the production of inducible nitric oxide in RAW 264.7 cells, particularly under stimulation of inflammatory signals interferon-γ (IFN-γ) and lipopolysaccharide (LPS). Zn-MBGs also inhibited the pro-inflammatory M1 polarization of RAW264.7 cells induced by LPS and IFN-γ. In summary, we successfully synthesized Zn-MBGs with concentration-dependent osteogenic and anti-inflammatory activities. Zn-MBGs show their great potential in immunomodulation strategies for bone regeneration, representing a multifunctional biomaterial that can be applied to regenerate bone defects under inflammatory conditions.

Design of 3D Scaffolds for Hard Tissue Engineering: From Apatites to Silicon Mesoporous Materials

Advanced bioceramics for bone regeneration constitutes one of the pivotal interests in the multidisciplinary and far-sighted scientific trajectory of Prof. Vallet Regí. The different pathologies that affect osseous tissue substitution are considered to be one of the most important challenges from the health, social and economic point of view. 3D scaffolds based on bioceramics that mimic the composition, environment, microstructure and pore architecture of hard tissues is a consolidated response to such concerns. This review describes not only the different types of materials utilized: from apatite-type to silicon mesoporous materials, but also the fabrication techniques employed to design and adequate microstructure, a hierarchical porosity (from nano to macro scale), a cell-friendly surface; the inclusion of different type of biomolecules, drugs or cells within these scaffolds and the influence on their successful performance is thoughtfully reviewed.

Mesoporous bioactive glasses for regenerative medicine

Stem cells are the central element of regenerative medicine (RM). However, in many clinical applications, the use of scaffolds fabricated with biomaterials is required. In this sense, mesoporous bioactive glasses (MBGs) are going to play an important role in bone regeneration because of their striking textural properties, quick bioactive response, and biocompatibility. As other bioactive glasses, MBGs are mainly formed by silicon, calcium, and phosphorus oxides whose ions play an important role in cell proliferation as well as in homeostasis and bone remodeling process. A common improvement of bioactive glasses for RM is by adding small amounts of oxides of elements that confer them additional biological capacities, including osteogenic, angiogenic, antibacterial, anti-inflammatory, hemostatic, or anticancer properties. Moreover, MBGs are versatile in terms of the different ways in which they can be processed, such as scaffolds, fibers, coatings, or nanoparticles. MBGs are unique because their textural properties are so high that they still exhibit outstanding bioactive responses even after adding extra inorganic ions or being processed as scaffolds or nanoparticles. Moreover, they can be further improved by loading with biomolecules, drugs, and stem cells. This article reviews the state of the art and future perspectives of MBGs in the field of RM of hard tissues.

3D Printed Zn-doped Mesoporous Silica-incorporated Poly-L-lactic Acid Scaffolds for Bone Repair

Poly-L-lactic acid (PLLA) lacks osteogenic activity, which limits its application in bone repair. Zinc (Zn) is widely applied to strengthen the biological properties of polymers due to its excellent osteogenic activity. In the present study, Zn-doped mesoporous silica (Zn-MS) particles were synthesized by one-pot hydrothermal method. Then, the particles were induced into PLLA scaffolds prepared by selective laser sintering technique, aiming to improve their osteogenic activity. Our results showed that the synthesized particles possessed rosette-like morphology and uniform mesoporous structure, and the composite scaffold displayed the sustained release of Zn ion in a low concentration range, which was attributed to the shield effect of the PLLA matrix and the strong bonding interaction of Si-O-Zn. The scaffold could evidently promote osteogenesis differentiation of mouse bone marrow mesenchymal stem cells by upregulating their osteogenesis-related gene expression. Besides, Zn-MS particles could significantly increase the compressive strength of the PLLA scaffold because of their rosette-like morphology and mesoporous structure, which can form micromechanical interlocking with the PLLA matrix. The Zn-MS particles possess great potential to improve various polymer scaffold properties due to their advantageous morphology and physicochemical properties.

Strontium-Modified Scaffolds Based on Mesoporous Bioactive Glasses/Polyvinyl Alcohol Composites for Bone Regeneration

In the search of a new biomaterial for the treatment of bone defects resulting from traumatic events, an osteoporosis scenario with bone fractures, tumor removal, congenital pathologies or implant revisions for infection, we developed 3D scaffolds based on mesoporous bioactive glasses (MBGs) (85 − x)SiO₂–5P₂O₅–10CaO–xSrO (x = 0, 2.5 and 5 mol.%). The scaffolds with meso-macroporosity were fabricated by pouring a suspension of MBG powders in polyvinyl alcohol (PVA) into a negative template of polylactic acid (PLA), followed by removal of the template by extraction at low temperature. SrO-containing MBGs exhibited excellent properties for bone substitution including ordered mesoporous structure, high textural properties, quick in vitro bioactive response in simulated body fluid (SBF) and the ability of releasing concentrations of strontium ions able to stimulate expression of early markers of osteoblastic differentiation. Moreover, the direct contact of MC3T3-E1 pre-osteoblastic cells with the scaffolds confirmed the cytocompatibility of the three compositions investigated. Nevertheless, the scaffold containing 2.5% of SrO induced the best cellular proliferation showing the potential of this scaffold as a candidate to be further investigated in vitro and in vivo, aiming to be clinically used for bone regeneration applications in non-load bearing sites.

Development and evaluation of copper-containing mesoporous bioactive glasses for bone defects therapy

Mesoporous bioactive glasses (MBGs) are gaining increasing interest in the design of new biomaterials for bone defects treatment. An important research trend to enhance their biological behavior is the inclusion of moderate amounts of oxides with therapeutical action such as CuO. MBGs with composition (85-x)SiO₂-10-CaO-5P₂O₅-xCuO (x = 0, 2.5 or 5 mol-%) were synthesized, investigating the influence of the CuO content and some synthesis parameters in their properties. Two series were developed; first one used HCl as catalyst and chlorides as CaO and CuO precursors, second one, used HNO₃ and nitrates. MBGs of chlorides family exhibited calcium/copper phosphate nanoparticles between 10 and 20 nm in size. Nevertheless, CuO-containing MBGs of nitrates family showed metallic copper nanoparticles larger than 50 nm as well as quicker in vitro bioactive responses. Thus, MBGs of the nitrate series were coated by an apatite-like layer after 24 h soaked in simulated body fluid (SBF) a remarkably short period for a MBG containing 5% of CuO. A model, focused in the location of copper in the glass network, was proposed to relate nanostructure and in vitro behaviour. Moreover, after 24 h soaked in MEM or THB culture media, all the MBGs released therapeutic amounts of Ca²⁺ and Cu²⁺ ions. Because the quick bioactive response in SBF, the capacity to host biomolecules in their pores and to release therapeutic concentrations of Ca²⁺ and Cu²⁺ ions, MBGs of the nitrate families are proposed as excellent biomaterials for bone regeneration.

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO₂-10.3CaO-3.3P₂O₅-4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice.

Multifunctional antibiotic- and zinc-containing mesoporous bioactive glass scaffolds to fight bone infection

Bone regeneration is a clinical challenge which requires multiple approaches. Sometimes, it also includes the development of osteogenic and antibacterial biomaterials to treat the emergence of possible infection processes arising from surgery. This study evaluates the antibacterial properties of gelatin-coated meso-macroporous scaffolds based on the bioactive glass 80%SiO₂-15%CaO-5%P₂O₅ (mol-%) before (BL-GE) and after being doped with 4% of ZnO (4ZN-GE) and loaded with both saturated and the minimal inhibitory concentrations of one of the antibiotics: levofloxacin (LEVO), vancomycin (VANCO), rifampicin (RIFAM) or gentamicin (GENTA). After physical-chemical characterization of materials, release studies of inorganic ions and antibiotics from the scaffolds were carried out. Moreover, molecular modelling allowed determining the electrostatic potential density maps and the hydrogen bonds of antibiotics and the glass matrix. Antibacterial in vitro studies (in planktonic, inhibition halos and biofilm destruction) with S. aureus and E. coli as bacteria models showed a synergistic effect of zinc ions and antibiotics. The effect was especially noticeable in planktonic cultures of S. aureus with 4ZN-GE scaffolds loaded with VANCO, LEVO or RIFAM and in E. coli cultures with LEVO or GENTA. Moreover, S. aureus biofilms were completely destroyed by 4ZN-GE scaffolds loaded with VANCO, LEVO or RIFAM and the E. coli biofilm total destruction was accomplished with 4ZN-GE scaffolds loaded with GENTA or LEVO. This approach could be an important step in the fight against microbial resistance and provide needed options for bone infection treatment. STATEMENT OF SIGNIFICANCE: Antibacterial capabilities of scaffolds based on mesoporous bioactive glasses before and after adding a 4% ZnO and loading with saturated and minimal inhibitory concentrations of levofloxacin, vancomycin, gentamicin or rifampicin were evaluated. Staphylococcus aureus and Escherichia coli were the infection model strains for the performed assays of inhibition zone, planktonic growth and biofilm. Good inhibition results and a synergistic effect of zinc ions released from scaffolds and antibiotics were observed. Thus, the amount of antibiotic required to inhibit the bacterial planktonic growth was substantially reduced with the ZnO inclusion in the scaffold. This study shows that the ZnO-MBG osteogenic scaffolds are multifunctional tools in bone tissue engineering because they are able to fight bacterial infections with lower antibiotic dosage.

Drug Delivery Applications of Three-Dimensional Printed (3DP) Mesoporous Scaffolds

Mesoporous materials are structures characterized by a well-ordered large pore system with uniform porous dimensions ranging between 2 and 50 nm. Typical samples are zeolite, carbon molecular sieves, porous metal oxides, organic and inorganic porous hybrid and pillared materials, silica clathrate and clathrate hydrates compounds. Improvement in biochemistry and materials science led to the design and implementation of different types of porous materials ranging from rigid to soft two-dimensional (2D) and three-dimensional (3D) skeletons. The present review focuses on the use of three-dimensional printed (3DP) mesoporous scaffolds suitable for a wide range of drug delivery applications, due to their intrinsic high surface area and high pore volume. In the first part, the importance of the porosity of materials employed for drug delivery application was discussed focusing on mesoporous materials. At the end of the introduction, hard and soft templating synthesis for the realization of ordered 2D/3D mesostructured porous materials were described. In the second part, 3DP fabrication techniques, including fused deposition modelling, material jetting as inkjet printing, electron beam melting, selective laser sintering, stereolithography and digital light processing, electrospinning, and two-photon polymerization were described. In the last section, through recent bibliographic research, a wide number of 3D printed mesoporous materials, for in vitro and in vivo drug delivery applications, most of which relate to bone cells and tissues, were presented and summarized in a table in which all the technical and bibliographical details were reported. This review highlights, to a very cross-sectional audience, how the interdisciplinarity of certain branches of knowledge, as those of materials science and nano-microfabrication are, represent a growing valuable aid in the advanced forum for the science and technology of pharmaceutics and biopharmaceutics.

Novel three-dimensional bioglass functionalized gelatin nanofibrous scaffolds for bone regeneration

The clinical use of FDA-approved bone morphogenetic proteins (BMPs) are impeded by high costs, super-high dosage requirement, short half-life, and other undesirable side effects. Therefore, designing a biomaterial that can promote new bone formation without using exogenous BMPs is highly desirable in clinical applications. In the present work, a new kind of nanofibrous scaffold composed of gelatin and 45S5 bioglass (GF/45S5 BG) was prepared through thermally induced phase separation method together with the particle leach technique (TIPS&P). In addition to the significantly higher mechanical strength, the composite scaffolds (GF/45S5 BG) significantly increased osteogenic differentiation of human mesenchymal stem cells (hMSCs) in vitro compared with the neat scaffold (GF) without adding other biological agents, for example, BMPs or hormones. Most importantly, our in vivo studies also indicated that GF/45S5 BG scaffolds could directly promote ectopic bone regeneration in SD rats without exogenous BMP2. In summary, both in vitro and in vivo results indicated that the novel 45S5 bioglass functionalized GF nanofibrous scaffold is a promising alternative for bone tissue engineering.

Mesoporous Silica Nanoparticles as Carriers for Therapeutic Biomolecules

The enormous versatility of mesoporous silica nanoparticles permits the creation of a large number of nanotherapeutic systems for the treatment of cancer and many other pathologies. In addition to the controlled release of small drugs, these materials allow a broad number of molecules of a very different nature and sizes. In this review, we focus on biogenic species with therapeutic abilities (proteins, peptides, nucleic acids, and glycans), as well as how nanotechnology, in particular silica-based materials, can help in establishing new and more efficient routes for their administration. Indeed, since the applicability of those combinations of mesoporous silica with bio(macro)molecules goes beyond cancer treatment, we address a classification based on the type of therapeutic action. Likewise, as illustrative content, we highlight the most typical issues and problems found in the preparation of those hybrid nanotherapeutic materials.

Cu(II) ion loading in silk fibroin scaffolds with silk I structure

Metal ions play important roles in the diverse biochemical reactions associated with many cell signalling pathways. The modification of biomaterials with metal ions may offer a promising approach to stimulate cellular activity for improving tissue regeneration. Here, copper ion loading as a potential therapeutic agent in silk fibroin (SF) scaffolds was investigated. Freezing-annealing was used to induce silk I crystallization for forming water-insoluble SF scaffolds. Cu(II) ions were entrapped into SF scaffolds with different ratios by forming silk I crystal networks when copper chloride dihydrate was less than 5.0 wt%, producing water-stable materials. Moreover, it was found that copper ion chelation further enhanced SF stability when a low amount copper chloride was loaded. Increasing copper chloride content weakened silk I crystallization and Cu(II) ion chelation, rendering SF scaffolds unstable in water. Above 5.0 wt% copper chloride dihydrate, silk I crystallization was prevented. Finally, silk I scaffold with 1.5 wt% copper chloride dihydrate showed the strongest water-stability and highest loading efficiency. The results provide valuable data for understanding the effect of metal ions in freezing-induced SF crystallization, and also offer options for preparing novel Cu(II)-functionalized SF scaffolds.

Double-edged effects and mechanisms of Zn2+ microenvironments on osteogenic activity of BMSCs: osteogenic differentiation or apoptosis

Zinc-incorporated biomaterials show promoting effects on osteogenesis; however, excessive zinc ions lead to cytotoxic reactions and also have other adverse effects. Therefore, the double-edged effects of Zn²⁺ microenvironments on osteogenesis may become critical issues for new material development. This study systematically investigated the bidirectional influences of diverse Zn²⁺ microenvironments on the cell adhesion, proliferation, osteogenic differentiation and apoptosis of rBMSCs. Furthermore, the mechanisms of zinc-induced osteogenic differentiation of rBMSCs and of cell apoptosis induced by high concentration of Zn²⁺ were both discussed in detail. The results indicated that the Zn²⁺ microenvironments of 2 μg mL⁻¹ and 5 μg mL⁻¹ effectively improved the initial adhesion and proliferation of rBMSCs, while that of 15 μg mL⁻¹ had exactly the opposite effect. More importantly, the suitable Zn²⁺ microenvironments (2 μg mL⁻¹ and 5 μg mL⁻¹) moderately increased the intracellular Zn²⁺ concentration by regulating zinc transportation, and then activated the MAPK/ERK signaling pathway to induce the osteogenic differentiation of rBMSCs. In contrast, the high Zn²⁺ concentration (15 μg mL⁻¹) not only inhibited the osteogenic differentiation of rBMSCs by damaging intracellular zinc homeostasis, but also induced rBMSC apoptosis by enhancing intracellular ROS generation. The current study clarified the double-edged effects of Zn²⁺ microenvironments on the osteogenic properties of rBMSCs and the related mechanisms, and may provide valuable guidance for optimizing the design of zinc-doped biomaterials and zinc-based alloys.

Dual-directional regulation of diverse Zn²⁺ microenvironments on osteogenic activity of BMSCs plays important roles in the design of zinc-containing biomaterials.

The effect of biomimetic mineralization of 3D-printed mesoporous bioglass scaffolds on physical properties and in vitro osteogenicity

Three-dimensional Mesoporous bioactive glasses (MBGs) scaffolds has been widely considered for bone regeneration purposes and additive manufacturing enables the fabrication of highly bioactive patient-specific constructs for bone defects. Commonly, this process is performed with the addition of polymeric binders that facilitate the printability of scaffolds. However, these additives cover the MBG particles resulting in the reduction of their osteogenic potential. The present work investigates a simple yet effective phosphate-buffered saline immersion method for achieving polyvinyl alcohol binder removal while enables the maintenance of the mesoporous structure of MBG 3D-printed scaffolds. This resulted in significantly modifying the surface of the scaffold via the spontaneous formation of a biomimetic mineralized layer which positively affected the physical and biological properties of the scaffold. The extensive surface remodeling induced by the deposition of the apatite-like layer lead to a 3-fold increase in surface area, a 5-fold increase in the roughness, and 4-fold increase in the hardness of the PBS-immersed scaffolds when compared to the as-printed counterpart. The biomimetic mineralization also occurred throughout the bulk of the scaffold connecting the MBGs particles and was responsible for the maintenance of structural integrity. In vitro assays using MC3T3-E1 pre-osteoblast like cells demonstrated a significant upregulation of osteogenic-related genes for the scaffolds previously immersed in PBS when compared to the as-printed PVA-containing scaffolds. Although the pre-immersion scaffolds performed equally towards osteogenic cell differentiation, our data suggest that a short immersion in PBS of MBG scaffolds is beneficial for the osteogenic properties and might accelerate bone formation after implantation.