Magnetic Nanofibrous Hydrogels for Dynamic Control of Stem Cell Differentiation

The extracellular matrix in tissue consists of complex heterogeneous soft materials with hierarchical structure and dynamic mechanical properties dictating cell and tissue level function. In many natural matrices, there are nanofibrous structures that serve to guide cell activity and dictate the form and function of tissue. Synthetic hydrogels with integrated nanofibers can mimic the structural properties of native tissue; however, model systems with dynamic mechanical properties remain elusive. Here we demonstrate modular nanofibrous hydrogels that can be reversibly stiffened in response to applied magnetic fields. Iron oxide nanoparticles were incorporated into gelatin nanofibers through electrospinning, followed by chemical stabilization and fragmentation. These magnetoactive nanofibers can be mixed with virtually any hydrogel material and reversibly stiffen the matrix at a low fiber content (≤3%). In contrast to previous work, where a large quantity of magnetic material disallowed cell encapsulation, the low nanofiber content allows matrix stiffening with cells in 3D. Using adipose derived stem cells, we show how nanofibrous matrices are beneficial for both osteogenesis and adipogenesis, where stiffening the hydrogel with applied magnetic fields enhances osteogenesis while discouraging adipogenesis. Skeletal myoblast progenitors were used as a model of tissue morphogenesis with matrix stiffening augmenting myogenesis and multinucleated myotube formation. The ability to reversibly stiffen fibrous hydrogels through magnetic stimulation provides a useful tool for studying nanotopography and dynamic mechanics in cell culture, with a scope for stimuli responsive materials for tissue engineering.

Alginate/Gelatin Hydrogel Scaffold Containing nCeO2 as a Potential Osteogenic Nanomaterial for Bone Tissue Engineering

Background

Clinicians frequently face difficulties when trying to fix bone abnormalities. Gelatin-Alginate (GA) is frequently employed as a carrier because it is non-toxic, biodegradable, and has a three-dimensional network structure. Meanwhile, cerium oxide nanoparticles (nCeO₂) demonstrated high antioxidant enzyme simulation activity. Therefore, in order to develop a porous hydrogel scaffold for the application of bone tissue engineering, an appropriate-type GA-nCeO₂ hydrogel scaffold was developed and evaluated.

Methods

 GA-nCeO₂ hydrogel scaffold was prepared by the lyophilized method and characterized. The surface morphology and cell adhesion of the scaffold were observed by the scanning electron microscope. CCK8 and live-dead staining methods were used to evaluate its biological safety and cell proliferation. Then the osteogenic differentiation in early and late stages was discussed. The expression of osteogenic genes was also detected by RT-PCR. Finally, a bone defect model was made in SD rats, and bone formation in vivo was detected.

Results

 The results showed that GA-nCeO₂ hydrogel scaffold exhibited a typical three-dimensional porous structure with a mean pore ratio of 70.61 ± 1.94%. The GA-nCeO₂ hydrogel was successfully endowed with simulated enzyme activity including superoxide dismutase (SOD) and catalase (CAT) after the addition of nCeO₂. Osteoblasts demonstrated superior cell proliferation and adhesion on composite scaffolds, and both mineralization test and gene expression demonstrated the strong osteogenic potential of GA-nCeO₂ hydrogel. The outcomes of hematoxylin and eosin (H&E) staining and Masson trichrome staining in the femoral defect model of SD rats further supported the scaffold's favorable biocompatibility and bone-promoting capacity.

Conclusion

Due to its favorable safety, degradability, and bone formation property, GA-nCeO₂ hydrogel was anticipated to be used as a potential bone defect healing material.

Collagen hydrogels with controllable combined cues of elasticity and topography to regulate cellular processes

The elasticity, topography, and chemical composition of cell culture substrates influence cell behavior. However, the cellular responses toin vivoextracellular matrix (ECM), a hydrogel of proteins (mainly collagen) and polysaccharides, remain unknown as there is no substrate that preserves the key features of native ECM. This study introduces novel collagen hydrogels that can combine elasticity, topography, and composition and reproduce the correlation between collagen concentration (C) and elastic modulus (E) in native ECM. A simple reagent-free method based on radiation-cross-linking altered ECM-derived collagen I and hydrolyzed collagen (gelatin or collagen peptide) solutions into hydrogels with tunable elastic moduli covering a broad range of soft tissues (E= 1-236 kPa) originating from the final collagen density in the hydrogels (C= 0.3%-14%) and precise microtopographies (⩾1 μm). The amino acid composition ratio was almost unchanged by this method, and the obtained collagen hydrogels maintained enzyme-mediated degradability. These collagen hydrogels enabled investigation of the responses of cell lines (fibroblasts, epithelial cells, and myoblasts) and primary cells (rat cardiomyocytes) to soft topographic cues such as thosein vivounder the positive correlation betweenCandE. These cells adhered directly to the collagen hydrogels and chose to stay atop or spontaneously migrate into them depending onE, that is, the density of the collagen network,C. We revealed that the cell morphology and actin cytoskeleton organization conformed to the topographic cues, even when they are as soft asin vivoECM. The stiffer microgrooves on collagen hydrogels aligned cells more effectively, except HeLa cells that underwent drastic changes in cell morphology. These collagen hydrogels may not only reducein vivoandin vitrocell behavioral disparity but also facilitate artificial ECM design to control cell function and fate for applications in tissue engineering and regenerative medicine.

Combined macromolecule biomaterials together with fluid shear stress promote the osteogenic differentiation capacity of equine adipose-derived mesenchymal stem cells

Background

Combination of mesenchymal stem cells (MSCs) and biomaterials is a rapidly growing approach in regenerative medicine particularly for chronic degenerative disorders including osteoarthritis and osteoporosis. The present study examined the effect of biomaterial scaffolds on equine adipose-derived MSC morphology, viability, adherence, migration, and osteogenic differentiation.

Methods

MSCs were cultivated in conjunction with collagen CultiSpher-S Microcarrier (MC), nanocomposite xerogels B30 and combined B30 with strontium (B30Str) biomaterials in osteogenic differentiation medium either under static or mechanical fluid shear stress (FSS) culture conditions. The data were generated by histological means, live cell imaging, cell viability, adherence and migration assays, semi-quantification of alkaline phosphatase (ALP) activity, and quantification of the osteogenic markers runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP) expression.

Results

The data revealed that combined mechanical FSS with MC but not B30 enhanced MSC viability and promoted their migration. Combined osteogenic medium with MC, B30, and B30Str increased ALP activity compared to cultivation in basal medium. Osteogenic induction with MC, B30, and B30Str resulted in diffused matrix mineralization. The combined osteogenic induction with biomaterials under mechanical FSS increased Runx2 protein expression either in comparison to those cells cultivated in BM or those cells induced under static culture. Runx2 and ALP expression was upregulated following combined osteogenic differentiation together with B30 and B30Str regardless of static or FSS culture.

Conclusions

Taken together, the data revealed that FSS in conjunction with biomaterials promoted osteogenic differentiation of MSCs. This combination may be considered as a marked improvement for clinical applications to cure bone defects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02146-7.

Influence of Cell Spreading Area on the Osteogenic Commitment and Phenotype Maintenance of Mesenchymal Stem Cells

Osteogenic differentiation and commitment of mesenchymal stem cells (MSCs) is a complex process that is induced and regulated by various biological factors and biophysical cues. Although cell spreading area, as a biophysical cue, has been demonstrated to play a critical role in the regulation of osteogenic differentiation of MSCs, it is unclear how it affects the maintenance of the committed phenotype after osteogenic differentiation of MSCs. In this study, poly (vinyl alcohol) was micropatterned on a tissue culture polystyrene surface, and the micropatterns were used to culture MSCs to control their cell spreading area. The influence of cell spreading area on osteogenic differentiation and maintenance of the differentiated phenotype of MSCs was investigated. MSCs with a larger spreading area showed a higher degree of osteogenic differentiation, slower loss of differentiated phenotype and slower re-expression of stem cell markers compared with MSCs with a smaller spreading area. A large cell spreading area was beneficial for osteogenic differentiation of MSCs and maintenance of their differentiated phenotype.

Modulating smooth muscle cell response by the release of TGFβ2 from tubular scaffolds for vascular tissue engineering

Tissue engineering has gained considerable attention in the development of small diameter tissue engineered vascular grafts (TEVGs) for treating coronary heart disease. A properly designed acellular and biodegradable TEVG must encourage the infiltration and growth of vascular smooth muscle cells (SMCs). Our group has previously shown that increasing levels of TGFβ2 can differentially modulate SMC migration and proliferation. In this study, tubular electrospun scaffolds loaded with TGFβ2 were fabricated using various ratios of gelatin/polycaprolactone (PCL), resulting in scaffolds with porous nano-woven architecture suitable for tissue ingrowth. Scaffold morphology, degradation rate, TGβ2 release kinetics, and bioactivity were assessed. TGFβ2 was successfully integrated into the electrospun biomaterial that resulted in a differential release profile depending on the gelatin/PCL ratio over the course of 42 days. Higher TGFβ2 elution was obtained in scaffolds with higher gelatin content, which may be related to the biodegradation of gelatin in culture media. The biological activity of the released TGFβ2 was evaluated by its ability to affect SMC proliferation as a function of its concentration. SMCs seeded on TGFβ2-loaded scaffolds also showed higher densities and infiltration after 5 days in culture as compared to scaffolds without TGFβ2. Our results demonstrate that the ratio of synthetic and natural polymers in electrospun blends can be used to tune the release of TGFβ2. This method can be used to intelligently modulate the SMC response in gelatin/PCL scaffolds making the TGFβ2-loaded conduits attractive for cardiovascular tissue engineering applications.

Influence of Cell Morphology on Mesenchymal Stem Cell Transfection

Gene transfection has broad applications in bioengineering and biomedical fields. Although many gene carrier materials and transfection methods have been developed, it remains unclear how cell morphology including cell spreading and elongation affects gene transfection. In this study, human bone marrow-derived mesenchymal stem cells (hMSCs) were cultured on micropatterns and transfected with cationic pAcGFP1-N1 plasmid complexes. The relationship between the cell morphology of hMSCs and gene transfection was investigated using micropatterning techniques. Spreading and elongation of hMSCs were precisely controlled by micropatterned surfaces. The results showed that well-spread and elongated hMSCs had high transfection efficiency. Analysis of the uptake of exogenous genes and DNA synthesis activity indicated that the well-spread and elongated cell morphology promoted gene transfection through enhanced uptake of the cationic complexes and accelerated DNA synthesis. The results should provide useful information for understanding of cell morphology on gene transfection and development of efficient gene transfection methods.

Regulation of mesenchymal stem cell functions by micro-nano hybrid patterned surfaces

Micro- and nano-structured substrates have been widely used in the biomedical engineering field. Their precise control of cell morphology makes them promising for investigating various cell behaviors. However, regulation of cell functions using micro-nano hybrid patterns is rarely achieved. Since the cell microenvironment in vivo has complex micro- and nano-structures, it is desirable to use micro-nano hybrid patterns to mimic the microenvironment to control cell morphology and disclose its influence on stem cell differentiation. In this study, poly(vinyl alcohol) (PVA) micro-stripes with different spacings (50 μm, 100 μm and 200 μm) were constructed on polystyrene (PS) nano-grooves to prepare micro-nano hybrid patterns where the direction of the PVA micro-stripes and PS nano-grooves was parallel or orthogonal. Human bone marrow-derived mesenchymal stem cells (hMSCs) cultured on the micro-nano hybrid patterns showed a different cell alignment and elongation dependent on the PVA micro-stripe spacing and orientation of the PS nano-grooves. Comparison of the influence of cell alignment and aspect ratio on differentiation of hMSCs indicated that myogenic differentiation was predominantly regulated by cell alignment and osteogenic differentiation by cell elongation, while adipogenic differentiation was regulated neither by cell alignment nor by cell elongation.