The stimulatory effect of silica nanoparticles on osteogenic differentiation of human mesenchymal stem cells

Delivery of miRNAs Using Porous Silicon Nanoparticles Incorporated into 3D Hydrogels Enhances MSC Osteogenesis by Modulation of Fatty Acid Signaling and Silicon Degradation

Strategies incorporating mesenchymal stromal cells (MSC), hydrogels and osteoinductive signals offer promise for bone repair. Osteoinductive signals such as growth factors face challenges in clinical translation due to their high cost, low stability and immunogenicity leading to interest in microRNAs as a simple, inexpensive and powerful alternative. The selection of appropriate miRNA candidates and their efficient delivery must be optimised to make this a reality. This study evaluated pro-osteogenic miRNAs and used porous silicon nanoparticles modified with polyamidoamine dendrimers (PAMAM-pSiNP) to deliver these to MSC encapsulated within gelatin-PEG hydrogels. miR-29b-3p, miR-101-3p and miR-125b-5p are strongly pro-osteogenic and are shown to target FASN and ELOVL4 in the fatty acid biosynthesis pathway to modulate MSC osteogenesis. Hydrogel delivery of miRNA:PAMAM-pSiNP complexes enhanced transfection compared to 2D. The osteogenic potential of hBMSC in hydrogels with miR125b:PAMAM-pSiNP complexes is evaluated. Importantly, a dual-effect on osteogenesis occurred, with miRNAs increasing expression of alkaline phosphatase (ALP) and Runt-related transcription factor 2 (RUNX2) whilst the pSiNPs enhanced mineralisation, likely via degradation into silicic acid. Overall, this work presents insights into the role of miRNAs and fatty acid signalling in osteogenesis, providing future targets to improve bone formation and a promising system to enhance bone tissue engineering.

Precision Nanomedicine with Bio-Inspired Nanosystems: Recent Trends and Challenges in Mesenchymal Stem Cells Membrane-Coated Bioengineered Nanocarriers in Targeted Nanotherapeutics

In the recent past, the formulation and development of nanocarriers has been elaborated into the broader fields and opened various avenues in their preclinical and clinical applications. In particular, the cellular membrane-based nanoformulations have been formulated to surpass and surmount the limitations and restrictions associated with naïve or free forms of therapeutic compounds and circumvent various physicochemical and immunological barriers including but not limited to systemic barriers, microenvironmental roadblocks, and other cellular or subcellular hinderances-which are quite heterogeneous throughout the diseases and patient cohorts. These limitations in drug delivery have been overcome through mesenchymal cells membrane-based precision therapeutics, where these interventions have led to the significant enhancements in therapeutic efficacies. However, the formulation and development of nanocarriers still focuses on optimization of drug delivery paradigms with a one-size-fits-all resolutions. As mesenchymal stem cell membrane-based nanocarriers have been engineered in highly diversified fashions, these are being optimized for delivering the drug payloads in more and better personalized modes, entering the arena of precision as well as personalized nanomedicine. In this Review, we have included some of the advanced nanocarriers which have been designed and been utilized in both the non-personalized as well as precision applicability which can be employed for the improvements in precision nanotherapeutics. In the present report, authors have focused on various other aspects of the advancements in stem cells membrane-based nanoparticle conceptions which can surmount several roadblocks and barriers in drug delivery and nanomedicine. It has been suggested that well-informed designing of these nanocarriers will lead to appreciable improvements in the therapeutic efficacy in therapeutic payload delivery applications. These approaches will also enable the tailored and customized designs of MSC-based nanocarriers for personalized therapeutic applications, and finally amending the patient outcomes.

Nanoparticle-Based Drug Delivery Systems for Enhancing Bone Regeneration

The treatment of bone defects has been a long-standing challenge in clinical practice. Among the various bone tissue engineering approaches, there has been substantial progress in the development of drug delivery systems based on functional drugs and appropriate carrier materials owing to technological advances in recent years. A large number of materials based on functional nanocarriers have been developed and applied to improve the complex osteogenic microenvironment, including for promoting osteogenic activity, inhibiting osteoclast activity, and exerting certain antibacterial effects. This Review discusses the physicochemical properties, drug loading mechanisms, advantages and disadvantages of nanoparticles (NPs) used for constructing drug delivery systems. In addition, we provide an overview of the osteogenic microenvironment regulation mechanism of drug delivery systems based on nanoparticle (NP) carriers and the construction strategies of drug delivery systems. Finally, the advantages and disadvantages of NP carriers are summarized along with their prospects and future research trends in bone tissue engineering. This Review thus provides advanced strategies for the design and application of drug delivery systems based on NPs in the treatment of bone defects.

Effect of Silicon Dioxide and Magnesium Oxide on the Printability, Degradability, Mechanical Strength and Bioactivity of 3D Printed Poly (Lactic Acid)-Tricalcium Phosphate Composite Scaffolds

BACKGROUND

Poly (lactic acid) (PLA) is a biodegradable polyester that has been exploited for a variety of biomedical applications, including tissue engineering. The incorporation of β-tricalcium phosphate (TCP) into PLA has imparted bioactivity to the polymeric matrix.

METHODS

We have modified a 90%PLA-10%TCP composite with SiO2 and MgO (1, 5 and 10 wt%), separately, to further enhance the material bioactivity. Filaments were prepared by extrusion, and scaffolds were fabricated using 3D printing technology associated with fused filament fabrication.

RESULTS

The PLA-TCP-SiO2 composites presented similar structural, thermal, and rheological properties to control PLA and PLA-TCP. In contrast, the PLA-TCP-MgO composites displayed absence of crystallinity, lower polymeric molecular weight, accelerated degradation ratio, and decreased viscosity within the 3D printing shear rate range. SiO2 and MgO particles were homogeneously dispersed within the PLA and their incorporation increased the roughness and protein adsorption of the scaffold, compared to a PLA-TCP scaffold. This favorable surface modification promoted cell proliferation, suggesting that SiO2 and MgO may have potential for enhancing the bio-integration of scaffolds in tissue engineering applications. However, high loads of MgO accelerated the polymeric degradation, leading to an acid environment that imparted the composite biocompatibility. The presence of SiO2 stimulated mesenchymal stem cells differentiation towards osteoblast; enhancing extracellular matrix mineralization, alkaline phosphatase (ALP) activity, and bone-related genes expression.

CONCLUSION

The PLA-10%TCP-10%SiO2 composite presented the most promising results, especially for bone tissue regeneration, due to its intense osteogenic behavior. PLA-10%TCP-10%SiO2 could be used as an alternative implant for bone tissue engineering application.

Silica Replicas Derived from Mammalian Cells as an Innovative Approach to Physically Direct Cell Lineage Decisions of Mesenchymal Stem Cells

By means of a "live-cell" template strategy, silica replicas displaying the same morphology and topography of the mammalian cells used as templates are fabricated. The replicas are used as substrates to direct the differentiation of mesenchymal stem cells (MSCs) to predefined cell lineages. Upregulation of specific genes shows how the silica replica-based substrates have the ability to induce the molecular characteristics of the mature cell types from which they have been derived from. Thus, MSCs cultured in the presence of silica replicas of human osteoblasts (HObs) differentiate into HObs-like cells, as shown by the upregulation of specific osteogenic genes. Likewise, when MSCs are incubated with silica replicas derived from human chondrocytes, an enhanced expression of chondrogenic markers is observed. Importantly, the effects of the silica replicas are cell type-specific since the incubation of MSCs with HObs silica replicas does not result in upregulation of chondrogenic markers and vice versa. What is more, for both cases, the differentiation rate is enhanced when the silica replicas are used in combination with growth factors, suggesting a potential synergistic effect. These results demonstrate the potential of this innovative method as an efficient and cheap approach with the potential to eliminate, or at least reduce, the use of biochemically soluble compounds in stem cells research.

Bioactive silica nanoparticles target autophagy, NF-κB, and MAPK pathways to inhibit osteoclastogenesis

Spherical 50 nm silica-based nanoparticles (SiNPs) promote healthy bone homeostasis and maintenance by supporting bone forming osteoblast lineage cells while simultaneously inhibiting the differentiation of bone resorbing osteoclasts. Previous work demonstrated that an intraperitoneal injection of SiNPs in healthy mice - both young and old - increased bone density and quality, suggesting the possibility that SiNPs represent a dual action therapeutic. However, the underlying mechanisms governing the osteoclast response to SiNPs have yet to be fully explored and defined. Therefore, the goals of this study were to investigate the cellular and molecular mechanisms by which SiNPs inhibit osteoclastogenesis. SiNPs strongly inhibited RANKL-induced osteoclast differentiation within the first hours and concomitantly inhibited early transcriptional regulators such as Nfatc1. SiNPs simultaneously stimulated expression of autophagy related genes p62 and LC3β dependent on ERK1/2 signaling pathway. Intriguingly, SiNPs were found to stimulate autophagosome formation while inhibiting the autophagic flux necessary for RANKL-stimulated osteoclast differentiation, resulting in the inhibition of both the canonical and non-canonical NF-κB signaling pathways and stabilizing TRAF3. These results suggest a model in which SiNPs inhibit osteoclastogenesis by inhibiting the autophagic machinery and RANKL-dependent functionality. This mechanism of action defines a novel therapeutic strategy for inhibiting osteoclastogenesis.

Inorganic nanoparticle-integrated mesenchymal stem cells: A potential biological agent for multifaceted applications

Mesenchymal stem cell (MSC)-based therapies are flourishing. MSCs could be used as potential therapeutic agents for regenerative medicine due to their own repair function. Meanwhile, the natural predisposition toward inflammation or injury sites makes them promising carriers for targeted drug delivery. Inorganic nanoparticles (INPs) are greatly favored for their unique properties and potential applications in biomedical fields. Current research has integrated INPs with MSCs to enhance their regenerative or antitumor functions. This model also allows the in vivo fate tracking of MSCs in multiple imaging modalities, as many INPs are also excellent contrast agents. Thus, INP-integrated MSCs would be a multifunctional biologic agent with great potential. In this review, the current roles performed by the integration of INPs with MSCs, including (i) enhancing their repair and regeneration capacity via the improvement of migration, survival, paracrine, or differentiation properties, (ii) empowering tumor-killing ability through agent loaded or hyperthermia, and (iii) conferring traceability are summarized. An introduction of INP-integrated MSCs for simultaneous treatment and tracking is also included. The promising applications of INP-integrated MSCs in future treatments are emphasized and the challenges to their clinical translation are discussed.

Nano-SiO2 reinforced alginate-chitosan-gelatin nanocomposite hydrogels with improved physicochemical properties and biological activity

Alginate (Alg) hydrogels possess desirable advantages for application in tissue engineering; however, they are limited by their weak mechanical properties, poor chronical stability in phosphate buffered saline, and absence of mammalian cell recognition sites, severely restricting their biomedical applications. To overcome these limitations, we integrated Alg hydrogels with nano-silica (SiO2) to produce nano-SiO2 reinforced Alg-chitosan-gelatin nanocomposite hydrogels (Alg/SiO2-CHI-GA NCH) for biomedical purposes, utilizing Chitosan (CHI) and gelatin (GA) in an alternate electrostatic adsorption. Specifically, we investigated the regulatory and promotional effects of the nano-SiO2 on the morphological structure, mechanical properties, thermal stability, rheological properties, swelling, biodegradability, biomineralization and cytocompatibility of the resultant Alg/SiO2-CHI-GA NCH. The experimental findings demonstrate that the constructed Alg/SiO2-CHI-GA NCH exhibited uniform morphology and a regular structure. Upon freeze-drying, the internal cross-sections of the NCH exhibited a honeycomb porous structure. Furthermore, the physicochemical properties and biological activities of the prepared Alg/SiO2-CHI-GA NCH were regulated to some extent by nano-SiO2 content. Notably, nano-SiO2 inclusion enhanced the attachment and viability of MG63 and MC3T3-E1 cells and induced three-dimensional cell growth in ALG/SiO2-CHI-GA NCH. Among the fabricated NCH, Alg/SiO2-CHI-GA NCH with 0.5% and 1.0% (w/v) nano-SiO2 exhibited significant proliferative activity, which is attributable to their high porosity and uniform cell adhesion. Furthermore, the alkaline phosphatase activity in the cells gradually increased with increasing of nano-SiO2 amount, indicating the favorable effect of nano-SiO2 on the osteogenic differentiation of MG63 and MC3T3-E1 cells. Our study findings provide a comprehensive foundation for the structural- and property-related limitations of Alg hydrogels in biomedicine, thereby expanding their potential applications in tissue engineering.

Silica Nanoparticles Promote the Megakaryocyte Maturation and Differentiation: Potential Implications for Hematological Homeostasis

Silica nanoparticles (SiO₂ NPs) have been widely applied in diverse areas, thus causing the extensive release through multiple routes. Their toxicological effects, especially for the disturbance in hematological homeostasis, have raised public concern. Considering the detrimental role of excessive platelets in many cardiovascular diseases, the regulation of platelet formation offers a unique aspect for studying the blood compatibility of nanomaterials. In this study, the effects of SiO₂ NPs with four sizes (80, 120, 200, and 400 nm) were investigated on the maturation and differentiation of the megakaryocytes into platelets. The results showed that SiO₂ NPs promoted megakaryocyte development as manifested by the occurrence of irregular cell morphology, enlargement of cell size, increases in DNA content and DNA ploidy, and formation of spore-like protrusions. The expression of megakaryocyte-specific antigen (CD41a) was up-regulated, due to SiO₂ NP treatments. The correlation analysis of SiO₂ NP size with the above test bioindicators showed that the smaller the SiO₂ NPs were, the stronger effects they induced. Moreover, exposure to SiO₂ NPs induced the up-regulation of both GATA-1 and FLI-1, while the transcriptional expressions of aNF-E2 and fNF-E2 remained unchanged. The significant positive correlation of GATA-1 and FLI-1 with megakaryocytic maturation and differentiation suggested their crucial roles in the SiO₂ NP-promoted effect. The finding herein provided new insight into the potential health risk of SiO₂ NPs by perturbing the platelet-involved hematological homeostasis.

Advanced Glycation End Products Effects on Adipocyte Niche Stiffness and Cell Signaling

Adipose tissue metabolism under hyperglycemia results in Type II diabetes (T2D). To better understand how the adipocytes function, we used a cell culture that was exposed to glycation by adding intermediate carbonyl products, which caused chemical cross-linking and led to the formation of advanced glycation end products (AGEs). The AGEs increased the cells and their niche stiffness and altered the rheological viscoelastic properties of the cultured cells leading to altered cell signaling. The AGEs formed concomitant with changes in protein structure, quantified by spectroscopy using the 8-ANS and Nile red probes. The AGE effects on adipocyte differentiation were viewed by imaging and evidenced in a reduction in cellular motility and membrane dynamics. Importantly, the alteration led to reduced adipogenesis, that is also measured by qPCR for expression of adipogenic genes and cell signaling. The evidence of alteration in the plasma membrane (PM) dynamics (measured by CTxB binding and NP endocytosis), also led to the impairment of signal transduction and a decrease in AKT phosphorylation, which hindered downstream insulin signaling. The study, therefore, presents a new interpretation of how AGEs affect the cell niche, PM stiffness, and cell signaling leading to an impairment of insulin signaling.

3D Biocomposites Comprising Marine Collagen and Silica-Based Materials Inspired on the Composition of Marine Sponge Skeletons Envisaging Bone Tissue Regeneration

Ocean resources are a priceless repository of unique species and bioactive compounds with denouement properties that can be used in the fabrication of advanced biomaterials as new templates for supporting the cell culture envisaging tissue engineering approaches. The collagen of marine origin can be sustainably isolated from the underrated fish processing industry by-products, while silica and related materials can be found in the spicules of marine sponges and diatoms frustules. Aiming to address the potential of biomaterials composed from marine collagen and silica-based materials in the context of bone regeneration, four different 3D porous structure formulations (COL, COL:BG, COL:D.E, and COL:BS) were fabricated by freeze-drying. The skins of Atlantic cod (Gadus morhua) were used as raw materials for the collagen (COL) isolation, which was successfully characterized by SDS-PAGE, FTIR, CD, and amino acid analyses, and identified as a type I collagen, produced with a 1.5% yield and a preserved characteristic triple helix conformation. Bioactive glass 45S5 bioglass® (BG), diatomaceous earth (D.E.) powder, and biosilica (BS) isolated from the Axinella infundibuliformis sponge were chosen as silica-based materials, which were obtained as microparticles and characterized by distinct morphological features. The biomaterials revealed microporous structures, showing a porosity higher than 85%, a mean pore size range of 138-315 μm depending on their composition, with 70% interconnectivity which can be favorable for cell migration and ensure the needed nutrient supply. In vitro, biological assays were conducted by culturing L929 fibroblast-like cells, which confirmed not only the non-toxic nature of the developed biomaterials but also their capability to support cell adhesion and proliferation, particularly the COL:BS biomaterials, as observed by calcein-AM staining upon seven days of culture. Moreover, phalloidin and DAPI staining revealed well-spread cells, populating the entire construct. This study established marine collagen/silica biocomposites as potential scaffolds for tissue engineering, setting the basis for future studies, particularly envisaging the regeneration of non-load-bearing bone tissues.

Zn-Loaded and Calcium Phosphate-Coated Degradable Silica Nanoparticles Can Effectively Promote Osteogenesis in Human Mesenchymal Stem Cells

Nanoparticles such as mesoporous bioactive glasses (MBGs) and mesoporous silica nanoparticles (MSN) are promising for use in bone regeneration applications due to their inherent bioactivity. Doping silica nanoparticles with bioinorganic ions could further enhance their biological performance. For example, zinc (Zn) is often used as an additive because it plays an important role in bone formation and development. Local delivery and dose control are important aspects of its therapeutic application. In this work, we investigated how Zn incorporation in MSN and MBG nanoparticles impacts their ability to promote human mesenchymal stem cell (hMSC) osteogenesis and mineralization in vitro. Zn ions were incorporated in three different ways; within the matrix, on the surface or in the mesopores. The nanoparticles were further coated with a calcium phosphate (CaP) layer to allow pH-responsive delivery of the ions. We demonstrate that the Zn incorporation amount and ion release profile affect the nanoparticle's ability to stimulate osteogenesis in hMSCs. Specifically, we show that the nanoparticles that contain rapid Zn release profiles and a degradable silica matrix were most effective in inducing hMSC differentiation. Moreover, cells cultured in the presence of nanoparticle-containing media resulted in the highest induction of alkaline phosphate (ALP) activity, followed by culturing hMSC on nanoparticles immobilized on the surface as films. Exposure to nanoparticle-conditioned media did not increase ALP activity in hMSCs. In summary, Zn incorporation mode and nanoparticle application play an important role in determining the bioactivity of ion-doped silica nanoparticles.

Silicon-Gold Nanoparticles Affect Wharton's Jelly Phenotype and Secretome during Tri-Lineage Differentiation

Multiple studies have demonstrated that various nanoparticles (NPs) stimulate osteogenic differentiation of mesenchymal stem cells (MSCs) and inhibit adipogenic ones. The mechanisms of these effects are not determined. The aim of this paper was to estimate Wharton’s Jelly MSCs phenotype and humoral factor production during tri-lineage differentiation per se and in the presence of silicon–gold NPs. Silicon (SiNPs), gold (AuNPs), and 10% Au-doped Si nanoparticles (SiAuNPs) were synthesized by laser ablation, characterized, and studied in MSC cultures before and during differentiation. Humoral factor production (n = 41) was analyzed by Luminex technology. NPs were nontoxic, did not induce ROS production, and stimulated G-CSF, GM-CSF, VEGF, CXCL1 (GRO) production in four day MSC cultures. During MSC differentiation, all NPs stimulated CD13 and CD90 expression in osteogenic cultures. MSC differentiation resulted in a decrease in multiple humoral factor production to day 14 of incubation. NPs did not significantly affect the production in chondrogenic cultures and stimulated it in both osteogenic and adipogenic ones. The major difference in the protein production between osteogenic and adipogenic MSC cultures in the presence of NPs was VEGF level, which was unaffected in osteogenic cells and 4–9 times increased in adipogenic ones. The effects of NPs decreased in a row AuNPs > SiAuNPs > SiNPs. Taken collectively, high expression of CD13 and CD90 by MSCs and critical level of VEGF production can, at least, partially explain the stimulatory effect of NPs on MSC osteogenic differentiation.

Calcium phosphate and silicate-based nanoparticles: history and emerging trends

Bulk calcium phosphates and silicate-based bioglasses have been extensively studied since the early 1970s due to their unique capacity to bind to host bone, which led to their clinical translation and commercialization in the 1980s. Since the mid-1990s, researchers have synthesized nanoscale calcium phosphate and silicate-based particles of increased specific surface area, chemical reactivity and solubility which offer specific advantages as compared to their bulk counterparts. This review provides a critical perspective on the history and emerging trends of these two classes of ceramic nanoparticles. Their synthesis and functional properties in terms of particle composition, size, shape, charge, dispersion, and toxicity are discussed as a function of relevant processing parameters. Specifically, emerging trends such as the influence of ion doping and mesoporosity on the biological and pharmaceutical performance of these nanoparticles are reviewed in more detail. Finally, a broad comparative overview is provided on the physicochemical properties and applicability of calcium phosphate and silicate-based nanoparticles within the fields of i) local delivery of therapeutic agents, ii) functionalization of biomaterial scaffolds or implant coatings, and iii) bio-imaging applications.

Fabrication of Antibacterial, Osteo-Inductor 3D Printed Aerogel-Based Scaffolds by Incorporation of Drug Laden Hollow Mesoporous Silica Microparticles into the Self-Assembled Silk Fibroin Biopolymer

In this study, the novel biomimetic aerogel-based composite scaffolds through a synergistic combination of wet chemical synthesis and advanced engineering approaches have successfully designed. To this aim, initially the photo-crosslinkable methacrylated silk fibroin (SF-MA) biopolymer and methacrylated hollow mesoporous silica microcapsules (HMSC-MA) as the main constituents of the novel composite aerogels were synthesized. Afterward, by incorporation of drug-loaded HMSC-MA into the self-assembled SF-MA, printable gel-based composite inks are developed. By exploiting micro-extrusion-based three-dimensional (3D) printing, SF-MA-HMSC composite gels are printed by careful controlling their viscosity to provide a means to control the shape fidelity of the resulted printed gel constructs. The developed scaffold has shown a multitude of interesting biophysical and biological performances. Namely, thanks to the photo-crosslinking of the gel components during the 3D printing, the scaffolds become mechanically more stable than the pristine SF scaffolds. Also, freeze-casting the printed constructs generates further interconnectivity in the printed pore struts resulting in the scaffolds with hierarchically organized porosities necessary for cell infiltration and growth. Importantly, HMSC incorporated scaffolds promote antibacterial drug delivery, cellular ingrowth and proliferation, promoting osteoblastic differentiation by inducing the expression of osteogenic markers and matrix mineralization. Finally, the osteoconductive, -inductive, and anti-infective composite aerogels are expected to act as excellent bone implanting materials with an extra feature of local and sustained release of drug for efficient therapy of bone-related diseases.

Fabrication and in vitro study of 3D novel porous hydroxyapatite/polyether ether ketone surface nanocomposite

The unique characteristics of polyether ether ketone (PEEK) including low elastic modulus, high mechanical strength, and biocompatibility have made it an attractive alternative for the metallic biomaterials. However, its bioinert property is always the main concern, which could lead to poor osseointegration and subsequent clinical failure of the implant. Changing the surface structure to porous structure and mixing it with bioactive hydroxyapatite (HA) are the common methods, which could be used to enhance the properties of the PEEK-based implants. In this study, friction stir processing was utilized for the fabrication of porous HA/PEEK surface nanocomposite. Scanning electron microscopic image of the nanocomposite surface showed nano-scale roughness of the porous structure. Water contact angle test confirmed the increase in the wettability of the treated specimens. In vitro bioactivity test via simulated body fluid solution, initial cell adhesion, cell proliferation, and cell differentiation assay also confirmed the enhancement in bioactivity of the treated surface in comparison to the bare PEEK. This surface modification method requires no special equipment and would not damage the heat-sensitive PEEK substrate due to the low temperature used during the fabrication process.

Facile synthesis of multi-functional nano-composites by precise loading of Cu2+ onto MgO nano-particles for enhanced osteoblast differentiation, inhibited osteoclast formation and effective bacterial killing

Biomaterials with multi-functions including enhancing osteogenesis, inhibiting osteoclastogenesis and effectively removing bacteria are urgently needed in the treatment of osteoporotic bone defects. In this study, MgO nano-particles were employed as a platform for precise Cu²⁺ loading. By immersing MgO into CuSO₄ solution with a pre-defined concentration (0.1, 1 or 10 mM), 1 mg MgO adsorbed 3.25, 32.5 or 325 μg Cu²⁺ from the solution. As-synthesized nano-composites were referred as MgO-0.1Cu, MgO-1Cu or MgO-10Cu depending on the concentration of employed CuSO₄ solution. The results revealed that MgO-xCu (x = 0.1, 1 and 10) nano-composites were lamella-shaped and composed of amorphous Cu(OH)₂, crystalline Mg(OH)₂ and minor MgO. The extracellular release of Cu²⁺ was rather limited due the capture of Cu²⁺ by Mg(OH)₂. In vitro results revealed that MgO-xCu (x = 0.1, 1 and 10) nano-composites modulated osteoblast, osteoclast and bacterium response in a Cu²⁺ loading amount-dependent manner. MgO-0.1Cu nano-composite exhibited stimulatory function on osteoblast proliferation without influencing osteoblast maturation, osteoclast formation and bacterial survival. MgO-1Cu nano-composite enhanced osteoblast proliferation and differentiation, inhibited osteoclast formation and effectively killed bacteria. When larger amount of Cu²⁺ was loaded, MgO-10Cu nano-composite exhibited stronger stimulatory effect on osteoblast maturation, enhanced inhibitory function on osteoclast formation and promoted bactericidal performance, although it showed a certain degree of initial cyto-toxicity. Together, the results suggest that MgO nano-particles could be employed as potential platform for precise Cu²⁺ loading and intracellular Cu²⁺ delivery. MgO-xCu (x = 1 and 10) nano-composites are promising to be employed as multi-functional fillers in bone tissue engineering scaffolds for osteoporotic bone regeneration.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

Antibacterial and osteogenic activities of clindamycin-releasing mesoporous silica/carboxymethyl chitosan composite hydrogels

Conventional treatment of jaw bone infection is often ineffective at controlling bacterial infection and enhancing bone regeneration. Biodegradable composite hydrogels comprised of carboxymethyl chitosan (CMCS) and clindamycin (CDM)-loaded mesoporous silica nanoparticles (MCM-41), possessing dual antibacterial activity and osteogenic potency, were developed in the present study. CDM was successfully loaded into both untreated and plasma-treated MCM-41 nanoparticles, denoted as (p)-MCM-41, followed by the incorporation of each of CDM-loaded (p)-MCM-41 into CMCS. The resulting CDM-loaded composite hydrogels, (p)-MCM-41-CDM-CMCS, demonstrated slow degradation rates (about 70% remaining weight after 14-day immersion), while the CDM-free composite hydrogel entirely disintegrated after 4-day immersion. The plasma treatment was found to improve drug loading capacity and slow down initial drug burst effect. The prolonged releases of CDM from both (p)-MCM-41-CDM-CMCS retained their antibacterial effect against Streptococcus sanguinis for at least 14 days in vitro. In vitro assessment of osteogenic activity showed that the CDM-incorporated composite hydrogel was cytocompatible to human mesenchymal stem cells (hMSCs) and induced hMSC mineralization via p38-dependent upregulated alkaline phosphatase activity. In conclusion, novel (p)-MCM-41-CDM-CMCS hydrogels with combined controlled release of CDM and osteogenic potency were successfully developed for the first time, suggesting their potential clinical benefit for treatment of intraoral bone infection.

Chemically induced hypoxia by dimethyloxalylglycine (DMOG)-loaded nanoporous silica nanoparticles supports endothelial tube formation by sustained VEGF release from adipose tissue-derived stem cells

Inadequate vascularization leading to insufficient oxygen and nutrient supply in deeper layers of bioartificial tissues remains a limitation in current tissue engineering approaches to which pre-vascularization offers a promising solution. Hypoxia triggering pre-vascularization by enhanced vascular endothelial growth factor (VEGF) expression can be induced chemically by dimethyloxalylglycine (DMOG). Nanoporous silica nanoparticles (NPSNPs, or mesoporous silica nanoparticles, MSNs) enable sustained delivery of molecules and potentially release DMOG allowing a durable capillarization of a construct. Here we evaluated the effects of soluble DMOG and DMOG-loaded NPSNPs on VEGF secretion of adipose tissue-derived stem cells (ASC) and on tube formation by human umbilical vein endothelial cells (HUVEC)-ASC co-cultures. Repeated doses of 100 µM and 500 µM soluble DMOG on ASC resulted in 3- to 7-fold increased VEGF levels on day 9 (P < 0.0001). Same doses of DMOG-NPSNPs enhanced VEGF secretion 7.7-fold (P < 0.0001) which could be maintained until day 12 with 500 µM DMOG-NPSNPs. In fibrin-based tube formation assays, 100 µM DMOG-NPSNPs had inhibitory effects whereas 50 µM significantly increased tube length, area and number of junctions transiently for 4 days. Thus, DMOG-NPSNPs supported endothelial tube formation by upregulated VEGF secretion from ASC and thus display a promising tool for pre-vascularization of tissue-engineered constructs. Further studies will evaluate their effect in hydrogels under perfusion.

Applications of nanotechnology in 3D printed tissue engineering scaffolds

Tissue engineering is an interdisciplinary field that aims to combine life sciences and engineering to create therapies that regenerate functional tissue. Early work in tissue engineering mostly used materials as inert scaffolding structures, but research has shown that constructing scaffolds from biologically active materials can help with regeneration by enabling cell-scaffold interactions or release of factors that aid in regeneration. Three-dimensional (3D) printing is a promising technique for the fabrication of structurally intricate and compositionally complex tissue engineering scaffolds. Such scaffolds can be functionalized with techniques developed by nanotechnology research to further enhance their ability to stimulate regeneration and interact with cells. Nanotechnological components, nanoscale textures, and microscale/nanoscale printing can all be incorporated into the manufacture of 3D printed scaffolds. This review discusses recent advancements in the merging of nanotechnology with 3D printed tissue engineering scaffolds, with a focus on applications of nanoscale components, nanoscale texture, and innovative printing techniques and the effects observed in vitro and in vivo.

Development of methods for detecting the fate of mesenchymal stem cells regulated by bone bioactive materials

The fate of mesenchymal stem cells (MSCs) is regulated by biological, physical and chemical signals. Developments in biotechnology and materials science promoted the occurrence of bioactive materials which can provide physical and chemical signals for MSCs to regulate their fate. In order to design and synthesize materials that can precisely regulate the fate of MSCs, the relationship between the properties of materials and the fate of mesenchymal stem cells need to be clarified, in which the detection of the fate of mesenchymal stem cells plays an important role. In the past 30 years, a series of detection technologies have been developed to detect the fate of MSCs regulated by bioactive materials, among which high-throughput technology has shown great advantages due to its ability to detect large amounts of data at one time. In this review, the latest research progresses of detecting the fate of MSCs regulated by bone bioactive materials (BBMs) are systematically reviewed from traditional technology to high-throughput technology which is emphasized especially. Moreover, current problems and the future development direction of detection technologies of the MSCs fate regulated by BBMs are prospected. The aim of this review is to provide a detection technical framework for researchers to establish the relationship between the properties of BMMs and the fate of MSCs, so as to help researchers to design and synthesize BBMs better which can precisely regulate the fate of MSCs.

Biocompatibility of a Marine Collagen-Based Scaffold In Vitro and In Vivo

Scaffold material is essential in providing mechanical support to tissue, allowing stem cells to improve their function in the healing and repair of trauma sites and tissue regeneration. The scaffold aids cell organization in the damaged tissue. It serves and allows bio mimicking the mechanical and biological properties of the target tissue and facilitates cell proliferation and differentiation at the regeneration site. In this study, the developed and assayed bio-composite made of unique collagen fibers and alginate hydrogel supports the function of cells around the implanted material. We used an in vivo rat model to study the scaffold effects when transplanted subcutaneously and as an augment for tendon repair. Animals' well-being was measured by their weight and daily activity post scaffold transplantation during their recovery. At the end of the experiment, the bio-composite was histologically examined, and the surrounding tissues around the implant were evaluated for inflammation reaction and scarring tissue. In the histology, the formation of granulation tissue and fibroblasts that were part of the inclusion process of the implanted material were noted. At the transplanted sites, inflammatory cells, such as plasma cells, macrophages, and giant cells, were also observed as expected at this time point post transplantation. This study demonstrated not only the collagen-alginate device biocompatibility, with no cytotoxic effects on the analyzed rats, but also that the 3D structure enables cell migration and new blood vessel formation needed for tissue repair. Overall, the results of the current study proved for the first time that the implantable scaffold for long-term confirms the well-being of these rats and is correspondence to biocompatibility ISO standards and can be further developed for medical devices application.

Nanomaterials-based Cell Osteogenic Differentiation and Bone Regeneration

With the rapid development of nanotechnology, various nanomaterials have been applied to bone repair and regeneration. Due to the unique chemical, physical and mechanical properties, nanomaterials could promote stem cells osteogenic differentiation, which has great potentials in bone tissue engineering and exploiting nanomaterials-based bone regeneration strategies. In this review, we summarized current nanomaterials with osteo-induction ability, which could be potentially applied to bone tissue engineering. Meanwhile, the unique properties of these nanomaterials and their effects on stem cell osteogenic differentiation are also discussed. Furthermore, possible signaling pathways involved in the nanomaterials- induced cell osteogenic differentiation are also highlighted in this review.

Mesenchymal Cell Growth and Differentiation on a New Biocomposite Material: A Promising Model for Regeneration Therapy

Mesenchymal stem cells serve as the body’s reservoir for healing and tissue regeneration. In cases of severe tissue trauma where there is also a need for tissue organization, a scaffold may be of use to support the cells in the damaged tissue. Such a scaffold should be composed of a material that can biomimic the mechanical and biological properties of the target tissues in order to support autologous cell-adhesion, their proliferation, and differentiation. In this study, we developed and assayed a new biocomposite made of unique collagen fibers and alginate hydrogel that was assessed for the ability to support mesenchymal cell-proliferation and differentiation. Analysis over 11 weeks in vitro demonstrated that the scaffold was biocompatible and supports the cells viability and differentiation to produce tissue-like structures or become adipocyte under differentiation medium. When the biocomposite was enriched with nano particles (NPs), mesenchymal cells grew well after uptake of fluorescein isothiocyanate (FITC) labeled NPs, maintained their viability, migrated through the biocomposite, reached, and adhered to the tissue culture dish. These promising findings revealed that the scaffold supports the growth and differentiation of mesenchymal cells that demonstrate their full physiological function with no sign of material toxicity. The cells’ functionality performance indicates and suggests that the scaffold is suitable to be developed as a new medical device that has the potential to support regeneration and the production of functional tissue.

Gold nanoparticles biosynthesized by Nocardiopsis dassonvillei NCIM 5124 enhance osteogenesis in gingival mesenchymal stem cells

Gold nanoparticles are widely used for biomedical applications owing to their biocompatibility, ease of functionalization and relatively non-toxic nature. In recent years, biogenic nanoparticles have gained attention as an eco-friendly alternative for a variety of applications. In this report, we have synthesized and characterized gold nanoparticles (AuNPs) from an Actinomycete, Nocardiopsis dassonvillei NCIM 5124. The conditions for biosynthesis were optimized (100 mg/ml of cell biomass, 2.5 mM tetrachloroauric acid (HAuCl₄) at 80 °C and incubation time of 25 min) and the nanoparticles were characterized by TEM, SAED, EDS and XRD analysis. The nanoparticles were spherical and ranged in size from 10 to 25 nm. Their interactions with human gingival tissue-derived mesenchymal stem cells (GMSCs) and their potential applications in regenerative medicine were evaluated further. The AuNPs did not display cytotoxicity towards GMSCs when assessed by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay, DNA fragmentation patterns and Annexin V/propidium iodide staining techniques. These AuNPs induced faster cell migration when monitored by the in vitro wound healing assay. The effect of these nanoparticles on osteogenesis of GMSCs was also studied. Based on the results obtained from alkaline phosphatase, Von Kossa staining and Alizarin Red S staining, the AuNPs were seen to positively affect differentiation of GMSCs and enhance mineralization of the synthesized matrix. We therefore conclude that the biogenic, non-toxic AuNPs are of potential relevance for tissue regeneration applications.

Genipin crosslinked bioactive collagen/chitosan/hyaluronic acid injectable hydrogels structurally amended via covalent attachment of surface-modified silica particles

Collagen, chitosan and hyaluronic acid based multicomponent injectable and in situ gellating biomimetic hybrid materials for bone tissue engineering applications were prepared in one-step procedure. The bioactive phase in the form of surface-modified silica particles was introduced to the solutions of biopolymers and simultaneously crosslinked with genipin both the biopolymer matrix and dispersed particles at 37 °C. The novel approach presented here involved the use of silica particles which surfaces were priory functionalized with amino groups. That modification makes possible the covalent attachment of silica particles to the polymeric hydrogel network on crosslinking with genipin. That methodology is especially important as it makes possible to obtain the hybrid materials (biopolymer-silica particles) in which the problems related to the potential phase separation of mineral particles, hindering their in vivo application can be eliminated. The hybrids of various compositions were obtained and their physicochemical and biological properties were determined. The in vitro experiments performed under simulated body fluid conditions revealed that the amino-functionalized silica particles covalently attached to the biopolymeric network are still bioactive. Finally, the in vitro cell culture studies shown that the materials developed are biocompatible as they supported MG-63 cells adhesion, proliferation as well as Alkaline phosphatase (ALP) expression.

A brief review of cytotoxicity of nanoparticles on mesenchymal stem cells in regenerative medicine

Multipotent mesenchymal stem cells have shown great promise for application in regenerative medicine owing to their particular therapeutic effects, such as significant self-renewability, low immunogenicity, and ability to differentiate into a variety of specialized cells. However, there remain certain complicated and unavoidable problems that limit their further development and application. One of the challenges is to noninvasively monitor the delivery and biodistribution of transplanted stem cells during treatment without relying on behavioral endpoints or tissue histology, and it is important to explore the potential mechanisms to clarify how stem cells work in vivo. To solve these problems, various nanoparticles (NPs) and their corresponding imaging methods have been developed recently and have made great progress. In this review, we mainly discuss NPs used to label stem cells and their toxic effects on the latter, the imaging techniques to detect such NPs, and the current existing challenges in this field.

Bioactive effects of silica nanoparticles on bone cells are size, surface, and composition dependent

Silica based nanoparticles have been demonstrated to have intrinsic biologic activity towards the skeleton and to function by promoting the differentiation of bone forming osteoblasts while inhibiting the differentiation of bone resorbing osteoclasts. The excitement surrounding nanomedicine in part revolves around the almost unlimited possibilities for varying the physicochemical properties including size, composition, and surface charge. To date few studies have attempted to manipulate these characteristics in concert to optimize a complex biologic outcome. Towards this end, spherical silica nanoparticles of various sizes (50-450 nm), of different surface properties (OH, CO₂H, NR₄+, mNH₂), and of different composition (silica, gold, and polystyrene) were synthesized and evaluated for biological activity toward skeletal cells. Osteoblast activity was most influenced by composition and size variables, whereas osteoclasts were most affected by surface property variation. The study also establishes nanoparticle mediated suppression of Nfatc1, a key transcriptional regulator for osteoclast differentiation, identifying a novel mechanism of action. Collectively, the study highlights how during the design of bioactive nanoparticles, it is vital to consider not only the myriad of physical properties that can be manipulated, but also that the characteristics of the target cell plays an equally integral role in determining biological outcome. STATEMENT OF SIGNIFICANCE: Silica nanomaterials represent a promising biomaterial for beneficial effects on bone mass and quality as well as regenerative tissue engineering and are currently being investigated for intrinsic bioactivity towards the primary cells responsible for skeletal homeostasis; osteoblasts and osteoclasts. The goal of the current study was to assess the physical properties of silica nanoparticles that impart intrinsic bioactivity by evaluating size, surface charge, and composition. Results reveal differential influences of the physical properties of nanoparticles towards osteoblasts and osteoclasts. This study provides new insights into the design of nanoparticles to specifically target different aspects of bone metabolism and highlights the opportunities provided by nanotechnology to modulate a range of cell specific biological responses for therapeutic benefit.

The Impact of Metallic Nanoparticles on Stem Cell Proliferation and Differentiation

Nanotechnology has a wide range of medical and industrial applications. The impact of metallic nanoparticles (NPs) on the proliferation and differentiation of normal, cancer, and stem cells is well-studied. The preparation of NPs, along with their physicochemical properties, is related to their biological function. Interestingly, various mechanisms are implicated in metallic NP-induced cellular proliferation and differentiation, such as modulation of signaling pathways, generation of reactive oxygen species, and regulation of various transcription factors. In this review, we will shed light on the biomedical application of metallic NPs and the interaction between NPs and the cellular components. The in vitro and in vivo influence of metallic NPs on stem cell differentiation and proliferation, as well as the mechanisms behind potential toxicity, will be explored. A better understanding of the limitations related to the application of metallic NPs on stem cell proliferation and differentiation will afford clues for optimal design and preparation of metallic NPs for the modulation of stem cell functions and for clinical application in regenerative medicine.

Incorporation of silica nanoparticles to PLGA electrospun fibers for osteogenic differentiation of human osteoblast-like cells

The development of bone tissue engineering scaffolds still remains a challenging field, although various biomaterials have been developed for this purpose. Electrospinning is a promising approach to fabricate nanofibers with an interconnected porous structure, which can support cell adhesion, guide cell proliferation and regulate cell differentiation. The aim of this study is to fabricate composite fibers composed of poly(lactic-co-glycolic acid) (PLGA) and silica nanoparticles (NPs) via electrospinning and investigate the effect of PLGA/SiO2 composite fibers on the cellular response of osteoblast-like cells (SaOS-2 cells). SEM and EDX analysis showed that silica NPs were homogenously dispersed in the composite fibers. The mechanical behavior of the fibers showed that silica NPs acted as reinforcements at concentrations of 2.5 and 5 mg/ml. The incorporation of silica NPs led to enhancement of cell attachment and spreading on PLGA/SiO2 composite fibers. SaOS-2 cells cultured on PLGA/SiO2 composite fibers exhibited increased alkaline phosphatase activity, collagen secretion and bone nodules formation. The bone nodules formation of SaOS-2 cells increased along with the amount of incorporated silica NPs. The present findings indicate that PLGA/SiO2 composite fibers can stimulate osteogenic differentiation of SaOS-2 cells and may be a promising candidate scaffold for bone tissue engineering.

In Vitro Uptake of Hydroxyapatite Nanoparticles and Their Effect on Osteogenic Differentiation of Human Mesenchymal Stem Cells

There have been many applications in biomedical fields based on hydroxyapatite nanoparticles (HA NPs) over the past decades. However, the biocompatibility of HANPs is affected by exposure dose, particle size, and the way of contact with cells. The objective of this study is to investigate the effect of HA NPs with different sizes on osteogenesis using human mesenchymal stem cells (hMSCs). Three different-sized HA NPs (~50, ~100, and ~150 nm, resp.) were synthesized to study the cytotoxicity, cellular uptake, and effect on osteogenic differentiation of hMSCs. The results clearly showed that each size of HA NPs had dose-dependent cytotoxicity on hMSCs. It was found that HA NPs could be uptaken into hMSCs. The osteogenic differentiation of hMSCs was evaluated through alkaline phosphatase (ALP) activity measurement, ALP staining, immunofluorescent staining for osteopontin (OPN), and real-time polymerase chain reaction (RT-PCR) examination. As expected, HA NPs of all sizes could promote the differentiation of hMSCs towards osteoblast lineage. Among the three sizes, smaller-sized HA NPs (~50 and ~100 nm) appeared to be more effective in stimulating osteogenic differentiation of hMSCs.

Effects of silica-gentamicin nanohybrids on osteogenic differentiation of human osteoblast-like SaOS-2 cells

INTRODUCTION

In recent years, there has been an increasing interest in silica (SiO2) nanoparticles (NPs) as drug delivery systems. This interest is mainly attributed to the ease of their surface functionalization for drug loading. In orthopedic applications, gentamicin-loaded SiO2 NPs (nanohybrids) are frequently utilized for their prolonged antibacterial effects. Therefore, the possible adverse effects of SiO2-gentamicin nanohybrids on osteogenesis of bone-related cells should be thoroughly investigated to ensure safe applications.

MATERIALS AND METHODS

The effects of SiO2-gentamicin nanohybrids on the cell viability and osteogenic differentiation of human osteoblast-like SaOS-2 cells were investigated, together with native SiO2 NPs and free gentamicin.

RESULTS

The results of Cell Count Kit-8 (CCK-8) assay show that both SiO2-gentamicin nanohybrids and native SiO2 NPs reduce cell viability of SaOS-2 cells in a dose-dependent manner. Regarding osteogenesis, SiO2-gentamicin nanohybrids and native SiO2 NPs at the concentration range of 31.25-125 μg/mL do not influence the osteogenic differentiation capacity of SaOS-2 cells. At a high concentration (250 μg/mL), both materials induce a lower expression of alkaline phosphatase (ALP) but an enhanced mineralization. Free gentamicin at concentrations of 6.26 and 9.65 μg/mL does not significantly influence the cell viability and osteogenic differentiation capacity of SaOS-2 cells.

CONCLUSIONS

The results of this study suggest that both SiO2-gentamicin nanohybrids and SiO2 NPs show cytotoxic effects to SaOS-2 cells. Further investigation on the effects of SiO2-gentamicin nanohybrids on the behaviors of stem cells or other regular osteoblasts should be conducted to make a full evaluation of the safety of SiO2-gentamicin nanohybrids in orthopedic applications.

Injectable nanosilica-chitosan microparticles for bone regeneration applications

This study was aimed at assessing the effects of silica nanopowder incorporation into chitosan-tripolyphosphate microparticles with the ultimate goal of improving their osteogenic properties. The microparticles were prepared by simple coacervation technique and silica nanopowder was added at 0% (C), 2.5% (S1), 5% (S2) and 10% (S3) (w/w) to chitosan. We observed that this simple incorporation of silica nanopowder improved the growth and proliferation of osteoblasts along the surface of the microparticles. In addition, the composite microparticles also showed the increased expression of alkaline phosphatase and osteoblast specific genes. We observed a significant increase ( p < 0.05) in the expression of alkaline phosphatase by the cells growing on all sample groups compared to the control (C) groups at day 14. The morphological characterization of these microparticles through scanning electron microscopy showed that these microparticles were well suited to be used as the injectable scaffolds with perfectly spherical shape and size. The incorporation of silica nanopowder altered the nano-roughness of the microparticles as observed through atomic force microscopy scans with roughness values going down from C to S3. The results in this study, taken together, show the potential of chitosan-tripolyphosphate-silica nanopowder microparticles for improved bone regeneration applications.

Aggregation Behavior of Nano-Silica in Polyvinyl Alcohol/Polyacrylamide Hydrogels Based on Dissipative Particle Dynamics

Due to the aggregation behavior of nano-silica in aqueous solution, the use of nano-silica without surface modification for synthesizing hydrogels is still a challenging task. This paper presents our study on the use of dissipative particle dynamics simulations to discover the aggregation behavior of nano-silica in polyvinyl alcohol (PVA)/polyacrylamide (PAM) blended hydrogels. By simulations, we aimed at investigating the effects of such factors as nano-silica content, polymer component ratio, temperature and shear rate on the aggregation behavior of nano-silica in terms of the mesoscopic morphologies and the relative concentration distribution functions. Our results reveal that the dispersion of nano-silica is seen if the nano-silica content is increased to 1.5%, and the aggregation of nano-silica becomes noticeable in blended hydrogels with an increase in the nano-silica content. This finding agrees well with the experimental results obtained by means of scanning electron microscopy. Furthermore, it is also found that the dispersion of nano-silica becomes more uniform with an increase in PAM content, temperature and shear rate. These findings greatly enrich our understanding of the aggregation behavior of nano-silica in PVA/PAM blended hydrogels.

The negative effect of silica nanoparticles on adipogenic differentiation of human mesenchymal stem cells

Nanoparticles have drawn much attention for a wide variety of applications in biomedical and bioengineering fields. The combined use of nanoparticles and human mesenchymal stem cells (hMSCs) in tissue engineering and regenerative medicine requires more knowledge of the influence of nanoparticles on cell viability and differentiation potential of hMSCs. The objective of this study is to investigate the in vitro uptake of silica nanoparticles (silica NPs) and their effect on adipogenic differentiation of hMSCs. After exposure of hMSCs to silica NPs, the uptake and localization of silica NPs were assessed using transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). The adipogenic differentiation potential of hMSCs was examined by analyzing the formation and accumulation of lipids droplets, triglyceride (TG) content and the expression of adipogenic marker genes/proteins. The results showed that silica NPs did not affect the cell viability but significantly decreased the differentiation of hMSCs to adipocytes. These findings improve the understanding of the influence of silica NPs on adipogenic differentiation of hMSCs and will provide a reference for the applications of silica NPs in biomedical and bioengineering fields.

Cell behavior of human mesenchymal stromal cells in response to silica/collagen based xerogels and calcium deficient culture conditions

Herein, we aim to elucidate osteogenic effects of two silica-based xerogels with different degrees of bioactivity on human bone-derived mesenchymal stromal cells by means of scanning electron microscopy, quantitative PCR enhanced osteogenic effects and the formation of an extracellular matrix which could be ascribed to the sample with lower bioactivity. Given the high levels of bioactivity, the cells revealed remarkable sensitivity to extremely low calcium levels of the media. Therefore, additional experiments were performed to elucidate cell behavior under calcium deficient conditions. The results refer to capacity of the bone-derived stromal cells to overcome calcium deficiency even though proliferation, migration and osteogenic differentiation capabilities were diminished. One reason for the differences of the cellular response (on tissue culture plates versus xerogels) to calcium deficiency seems to be the positive effect of silica. The silica could be detected intracellularly as shown by time of flight-secondary ion mass spectrometry after cultivation of primary cells for 21 days on the surfaces of the xerogels. Thus, the present findings refer to different osteogenic differentiation potentials of the xerogels according to the different degrees of bioactivity, and to the role of silica as a stimulator of osteogenesis. Finally, the observed pattern of connexin-based hemichannel gating supports the assumption that connexin 43 is a key factor for calcium-mediated osteogenesis in bone-derived mesenchymal stromal cells.