Nanotopographical Cues Mediate Osteogenesis of Stem Cells on Virus Substrates through BMP-2 Intermediate.

Recent studies have demonstrated rapid osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) on substrates with plant virus modified nanotopographical cues as a promising strategy for bone repair; however, the mechanisms remain unclear. We hypothesized that the highly structurally ordered virus coat proteins, responsible for targeting specific cellular components, are critical for the osteogenesis promotion. In this study, hybrid viral gold nanorods were prepared to explore the effects of highly ordered arranged virus coat proteins on osteogenic differentiation of BMSCs. The results herein indicate that it is the nanotopographical cues modified by structurally ordered virus nanoparticles, not the chemical properties of virus surface, that mediate osteogenesis. Bone morphogenetic protein 2 (BMP-2) expression is significantly increased and serves as a modulator that mediates the osteogenic differentiation in response to the viral particle coatings. After BMP-2 is inhibited by Noggin, the osteogenesis promoting effects are significantly compromised, demonstrated by lower alkaline phosphatase activity and calcium sequestration. This study reveals that plant virus modified nanotopographical substrates promote osteogenic differentiation of BMSCs through increasing BMP-2 autocrine. It provides key insights to engineering functional materials for rapid bone repair.

Enhanced Bone Defect Repair by Polymeric Substitute Fillers of MultiArm Polyethylene Glycol-Crosslinked Hyaluronic Acid Hydrogels.

Bone regeneration is still one of the greatest challenges for the treatment of bone defects since no current clinical approach has been proven effective. To develop an alternative biodegradable bone graft material, multiarm polyethylene glycol (PEG) crosslinked hyaluronic acid (HA) hydrogels are synthesized and applied to promote osteogenesis of mesenchymal stem cells (MSCs) with the ultimate goal for bone defect repair. The multiarm PEG-HA hydrogels provide a significant improvement of alkaline phosphatase (ALP) activity and calcium mineralization of the in vitro encapsulated MSCs under osteogenic condition after 3, 7, and 28 days. In addition, the multiarm PEG-HA hydrogels also facilitate healing of the cranial bone defects more effectively in a Sprague Dawley rat model after 10 weeks of implantation based on histological evaluations and microcomputed tomography analysis. These promising results set the stage for the development of innovative biodegradable hydrogels to provide a more effective and versatile treatment option for bone regeneration.

Using Plant Virus Based Nanorods to Modulate the Differentiation of Human Bone Marrow Stem Cells.

Tobacco mosaic virus (TMV) is a protypical nanorod-shaped bioparticles that has been used as a building block to construct a variety of self-assembled nanomaterials for different biomedical applications, including drug delivery, in vivo imaging, tumor immunotherapy and tissue engineering. In this work, the roles of TMV and its mutant TMV-RGD1 nanoparticles on the differentiation of human bone marrow stem cells (hBMSCs), an important process in bone regeneration, were carefully investigated. We observed that cells cultured on the TMV-RGD1 nanorods coated substrate showed significantly higher levels of gene and protein expression of osteo-specific markers osteocalcin (OCN) and bone morphogenetic protein 2 (BMP2). Investigation of alkaline phosphatase (ALP) activity and calcium deposition further confirmed that the TMV-RGD1 substrate could promote the osteogenesis and induce the mineralization of hBMSCs. On the other hand, the adipogenesis was downregulated on TMV and TMV-RGD1 coated substrates. Taken together, this study demonstrates for the first time the potential of TMV-RGD1 in promoting osteogenic differentiation of hBMSCs which can lead to future applications in clinical bone engineering.

Fabrication of Plant Virus-Based Thin Films to Modulate the Osteogenic Differentiation of Mesenchymal Stem Cells.

Stem cells can interact and respond to the extracellular nanoscale environment. Viral nanoparticles have been utilized as building blocks to control cell growth and differentiation. By integrating stem cell research and virus nanoparticle chemistry together, a systematic analysis of the effects of nanotopography on stem cell differentiation can be accomplished. The fabrication of thin films of the viral nanoparticles is particularly valuable for such studies. Here, we describe two methods to fabricate plant virus-based thin films and procedures to study the osteogenic differentiation of mesenchymal stem cells on plant virus-based substrates. The method makes use of wild-type tobacco mosaic virus (wt-TMV), RGD-modified TMV (TMV-RGD), turnip yellow mosaic virus (TYMV), cowpea mosaic virus (CPMV), turnip vein clearing virus (TVCV), and potato virus X (PVX) for development of bone tissue engineering biomaterials.

Influence of Cross-Linkers on the in Vitro Chondrogenesis of Mesenchymal Stem Cells in Hyaluronic Acid Hydrogels.

This study aims to investigate the effect of the structures of cross-linkers on the in vitro chondrogenic differentiation of bone mesenchymal stem cells (BMSCs) in hyaluronic acid (HA)-based hydrogels. The hydrogels were prepared by the covalent cross-linking of methacrylated HA with different types of thiol-tailored molecules, including dithiothreitol (DTT), 4-arm poly(ethylene glycol) (PEG), and multiarm polyamidoamine (PAMAM) dendrimer using thiol-ene "click" chemistry. The microstructure, mechanical properties, diffusivity, and degradation rates of the resultant hydrogels were controlled by the structural feature of different cross-linkers. BMSCs were then encapsulated in the resulting hydrogels and cultured in chondrogenic conditions. Overall, chondrogenic differentiation was highly enhanced in the PEG-cross-linked HA hydrogels, as measured by glycosaminoglycan (GAG) and collagen accumulation. The physical properties of hydrogels, especially the mechanical property and microarchitecture, were resulted from the structures of different cross-linkers, which subsequently modulated the fate of BMSC differentiation.

Promotion of In Vitro Chondrogenesis of Mesenchymal Stem Cells Using In Situ Hyaluronic Hydrogel Functionalized with Rod-Like Viral Nanoparticles.

This study focuses on the development of injectable hydrogels to mimic the cartilage microenvironment using hyaluronic acid (HA) derivatives as starting materials. Cysteine-inserted Tobacco mosaic virus (TMV) mutants (TMV1cys) could be cross-linked to methacrylated hyaluronic acid (MeHA) polymers by thiol-ene "click" chemistry and form hydrogels under physiological condition. The resulting hydrogels could promote in vitro chondrogenesis of bone marrow mesenchymal stem cells (BMSCs) significantly higher than that in the TMV-free HA hydrogels by upregulating bone morphogenetic protein-2 (BMP-2) expression and enhancing collagen accumulation.

Tobacco Mosaic Virus Functionalized Alginate Hydrogel Scaffolds for Bone Regeneration in Rats with Cranial Defect.

Plant viruses have been highlighted among material research due to their well-defined structures in nanoscale, monodispersity, stability, and chemical functionalities. Each of the thousands coat protein subunits on a viral nanoparticle can be homogeneously modified, chemically and genetically, with a functional ligand leading to a high-density and spatial distribution of ligands on each particle (multivalency). Previous reports from our group have evidenced that substrates coated with Tobacco mosaic virus (TMV) and its mutant promote early osteogenesis of mesenchymal stem cells (MSCs). We then fabricated a three-dimensional (3D) biopolymeric scaffold with rod-like TMV in the form of a sponge-like hydrogel for tissue engineering purposes. The hydrogel was functionalized with the cellular recognition peptide, arginine-glycine-aspartic acid (RGD), through an incorporation of an RGD mutant of TMV (TMV-RGD). The virus-functionalized hydrogel materials were shown to aid bone differentiation of MSCs in vitro. Herein, we performed an in vivo study based on the TMV and TMV-RGD hydrogels in Sprague-Dawley rats with cranial bone defects. This report substantiated the hypothesis that TMV-functionalized hydrogel scaffolds did not cause systemic toxicity when implanted in the defect site and that the TMV-based hydrogel platform can support cell localization and can be further optimized for bone regeneration and repair.