Yingnan Wu

Simple surface engineering of polydimethylsiloxane with polydopamine for stabilized mesenchymal stem cell adhesion and multipotency.

Polydimethylsiloxane (PDMS) has been extensively exploited to study stem cell physiology in the field of mechanobiology and microfluidic chips due to their transparency, low cost and ease of fabrication. However, its intrinsic high hydrophobicity renders a surface incompatible for prolonged cell adhesion and proliferation. Plasma-treated or protein-coated PDMS shows some improvement but these strategies are often short-lived with either cell aggregates formation or cell sheet dissociation. Recently, chemical functionalization of PDMS surfaces has proved to be able to stabilize long-term culture but the chemicals and procedures involved are not user- and eco-friendly. Herein, we aim to tailor greener and biocompatible PDMS surfaces by developing a one-step bio-inspired polydopamine coating strategy to stabilize long-term bone marrow stromal cell culture on PDMS substrates. Characterization of the polydopamine-coated PDMS surfaces has revealed changes in surface wettability and presence of hydroxyl and secondary amines as compared to uncoated surfaces. These changes in PDMS surface profile contribute to the stability in BMSCs adhesion, proliferation and multipotency. This simple methodology can significantly enhance the biocompatibility of PDMS-based microfluidic devices for long-term cell analysis or mechanobiological studies.

Substrate topography determines the fate of chondrogenesis from human mesenchymal stem cells resulting in specific cartilage phenotype formation

To reproduce a complex and functional tissue, it is crucial to provide a biomimetic cellular microenvironment that not only incorporates biochemical cues, but also physical features including the nano-topographical patterning, for cell/matrix interaction. We developed spatially-controlled nano-topography in the form of nano-pillar, nano-hole and nano-grill on polycaprolactone surface via thermal nanoimprinting. The effects of chondroitin sulfate-coated nano-topographies on cell characteristics and chondrogenic differentiation of human mesenchymal stem cell (MSC) were investigated. Our results show that various nano-topographical patterns triggered changes in MSC morphology and cytoskeletal structure, affecting cell aggregation and differentiation. Compared to non-patterned surface, nano-pillar and nano-hole topography enhanced MSC chondrogenesis and facilitated hyaline cartilage formation. MSCs experienced delayed chondrogenesis on nano-grill topography and were induced to fibro/superficial zone cartilage formation. This study demonstrates the sensitivity of MSC differentiation to surface nano-topography and highlights the importance of incorporating topographical design in scaffolds for cartilage tissue engineering. From the clinical editor: These authors have developed spatially-controlled nano-topography in the form of nano-pillar, nano-hole and nano-grill on polycaprolactone surface via thermal nanoimprinting, and the effects of chondroitin sulfate-coated nano-topographies on cell characteristics and chondrogenic differentiation of human mesenchymal stem cells (MSC) were investigated. It has been concluded that MSC differentiation is sensitive to surface nano-topography, and certain nano-imprinted surfaces are more useful than others for cartilage tissue engineering.

Cross-talk between TGF-beta/SMAD and integrin signaling pathways in regulating hypertrophy of mesenchymal stem cell chondrogenesis under deferral dynamic compression.

The molecular mechanisms of mechanotransduction in regulating mesenchymal stem cell (MSC) chondrogenesis are not fully understood and represent an area of growing investigation. In this study, human MSC was subjected to chondrogenic differentiation in chitosan-coated poly L-lactide-co-ɛ-caprolactone scaffolds under free swelling or deferral dynamic compression conditions. The effect of deferral dynamic compression to MSC chondrogenesis and late stage hypertrophy development was investigated, and the involvement of TGF-β/SMAD pathway and integrin β1 signaling was analyzed. Deferral dynamic compression enhanced cartilage formation and suppressed chondrocyte hypertrophy. Differential cell morphology and cytoskeletal organization were induced under dynamic compression, together with the activation of TGF-β/Activin/Nodal and suppression of the BMP/GDP signaling. This was accompanied by the repression of integrin/FAK/ERK signaling in the non-hypertrophic cells when compared to the free swelling samples. Inhibition studies blocking TGF-β/Activin/Nodal signaling heightened hypertrophy, activate BMP/SMAD1/5/8 and integrin signaling, while inhibition of integrin-ECM interaction suppressed hypertrophy and activate TGF-β/SMAD2/3 in the free-swelling samples. This study demonstrates the roles of TGF-β/SMAD and integrin signaling, and suggests cross-talk between these two signaling pathways, in regulating the compression-driven hypertrophy development.

The influence of scaffold microstructure on chondrogenic differentiation of mesenchymal stem cells

Different forms of biomaterials, including microspheres, sponges, hydrogels and nanofibres have been broadly used in cartilage regeneration; however, effects of internal structures of biomaterials on chondrogenesis of mesenchymal stem cells (MSCs) remain largely unexplored. Here we investigated the effect of physical microenvironments of sponges and hydrogels on chondrogenic differentiation of MSCs. MSCs, cultured in these two scaffold systems, were induced with TGF-β3 in chondrogeneic differentiation medium and the chondrogenic differentiation was evaluated and compared after three weeks. MSCs in the sponges clustered with spindle morphologies, while they distributed homogenously with round morphologies in the hydrogel. The MSCs proliferated faster in the sponge compared to that in the hydrogel. Significantly higher glycosaminoglycan and collagen II were found in the sponges but not in the hydrogels. The different tissue formation ability of MSCs in these two systems could be attributed to the different metabolic requirements and the cellular events prerequisite in the chondrogenic process of MSCs. It is reasonable to conclude that sponges with relatively active microenvironments that facilitate cell-cell contacts and cell-matrix interaction are optimal for early stage of chondrogeneic differentiation.

Microfluidic Assay To Study the Combinatorial Impact of Substrate Properties on Mesenchymal Stem Cell Migration

As an alternative to complex and costly in vivo models, microfluidic in vitro models are being widely used to study various physiological phenomena. It is of particular interest to study cell migration in a controlled microenvironment because of its vital role in a large number of physiological processes, such as wound healing, disease progression, and tissue regeneration. Cell migration has been shown to be affected by variations in the biochemical and physical properties of the extracellular matrix (ECM). To study the combinatorial impact of the ECM physical properties on cell migration, we have developed a microfluidic assay to induce migration of human bone marrow derived mesenchymal stem cells (hBMSCs) on polydimethylsiloxane (PDMS) substrates with varying combinatorial properties (hydrophobicity, stiffness, and roughness). The results show that although the initial cell adhesion and viability appear similar on all PDMS samples, the cell spreading and migration are enhanced on PDMS samples exhibiting intermediate levels of hydrophobicity, stiffness, and roughness. This study suggests that there is a particular range of substrate properties for optimal cell spreading and migration. The influence of substrate properties on hBMSC migration can help understand the physical cues that affect cell migration, which may facilitate the development of optimized engineered scaffolds with desired properties for tissue regeneration applications.

Topological-insulator-based terahertz modulator

Three dimensional topological insulators, as a new phase of quantum matters, are characterized by an insulating gap in the bulk and a metallic state on the surface. Particularly, most of the topological insulators have narrow band gaps, and hence have promising applications in the area of terahertz optoelectronics. In this work, we experimentally demonstrate an electronically-tunable terahertz intensity modulator based on Bi1:5Sb0:5Te1:8Se1:2 single crystal, one of the most insulating topological insulators. A relative frequency-independent modulation depth of ~62% over a wide frequency range from 0.3 to 1.4 THz has been achieved at room temperature, by applying a bias current of 100 mA. The modulation in the low current regime can be further enhanced at low temperature. We propose that the extraordinarily large modulation is a consequence of thermally-activated carrier absorption in the semiconducting bulk states. Our work provides a new application of topological insulators for terahertz technology.

The effect of temporal manipulation of transforming growth factor beta 3 and fibroblast growth factor 2 on the derivation of proliferative chondrocytes from mensenchymal stem cells-A study monitored by quantitative reverse transcription polymerase chain r: EFFECT OF TEMPORAL MANIPULATION OF TGFβ3 AND FGF2

Proliferative chondrocytes are critical to realize regeneration of damaged epiphyseal growth plate. However, acquiring autologous replacement cells involves highly invasive procedures and often results in limited cell quantity. Mesenchymal stem cells (MSCs) are a potential source of chondrogenic cells for the treatment of cartilage disorders and injuries. The temporal effect of transforming growth factor beta 3 (TGFβ3) and fibroblast growth factor 2 (FGF2) on the derivation of proliferative chondrocytes from MSCs in three-dimensional agarose was investigated by manipulating the duration of TGFβ3 and FGF2 treatment. The differentiation process was monitored by quantitative reverse transcription polymerase chain reaction (qRT-PCR) as well as nanosensors containing two molecular beacons that target critical biomarkers for proliferative chondrocytes (i.e., collagen type-II messenger ribonucleic acid [mRNA] and Ki67 mRNA). The molecular beacon-based nanosensors were found to be comparable to qRT-PCR in measuring mRNA expression and thus providing a noninvasive mean to screen and monitor culture samples.

The effect of temporal manipulation of TGFβ3 and FGF2 on the derivation of proliferative chondrocytes from Mensenchymal Stem Cells – a study monitored by qRT‐PCR and Molecular Beacon based Nanosensors

Proliferative chondrocytes are critical to realize regeneration of damaged epiphyseal growth plate. However, acquiring autologous replacement cells involves highly invasive procedures and often results in limited cell quantity. Mesenchymal stem cells (MSCs) are a potential source of chondrogenic cells for the treatment of cartilage disorders and injuries. The temporal effect of transforming growth factor beta 3 (TGFβ3) and fibroblast growth factor 2 (FGF2) on the derivation of proliferative chondrocytes from MSCs in three-dimensional agarose was investigated by manipulating the duration of TGFβ3 and FGF2 treatment. The differentiation process was monitored by quantitative reverse transcription polymerase chain reaction (qRT-PCR) as well as nanosensors containing two molecular beacons that target critical biomarkers for proliferative chondrocytes (i.e., collagen type-II messenger ribonucleic acid [mRNA] and Ki67 mRNA). The molecular beacon-based nanosensors were found to be comparable to qRT-PCR in measuring mRNA expression and thus providing a noninvasive mean to screen and monitor culture samples.

The effect of temporal manipulation of transforming growth factor beta 3 and fibroblast growth factor 2 on the derivation of proliferative chondrocytes from mensenchymal stem cells—A study monitored by quantitative reverse transcription polymerase chain reaction and molecular beacon based nanosensors

Proliferative chondrocytes are critical to realize regeneration of damaged epiphyseal growth plate. However, acquiring autologous replacement cells involves highly invasive procedures and often results in limited cell quantity. Mesenchymal stem cells (MSCs) are a potential source of chondrogenic cells for the treatment of cartilage disorders and injuries. The temporal effect of transforming growth factor beta 3 (TGFβ3) and fibroblast growth factor 2 (FGF2) on the derivation of proliferative chondrocytes from MSCs in three-dimensional agarose was investigated by manipulating the duration of TGFβ3 and FGF2 treatment. The differentiation process was monitored by quantitative reverse transcription polymerase chain reaction (qRT-PCR) as well as nanosensors containing two molecular beacons that target critical biomarkers for proliferative chondrocytes (i.e., collagen type-II messenger ribonucleic acid [mRNA] and Ki67 mRNA). The molecular beacon-based nanosensors were found to be comparable to qRT-PCR in measuring mRNA expression and thus providing a noninvasive mean to screen and monitor culture samples.

Non-invasive Monitoring of 3D Chondrogenic Constructs using Molecular Beacon Nanosensors

Chondrogenic differentiation of human mesenchymal stem cells (MSCs) in three-dimensional hydrogel holds promise as a method for repairing injured articular cartilage. Given MSC plasticity (its potential to mature into alternative lineages), nondestructive monitoring is critical for the optimization of chondrogenic differentiation conditions and the evaluation of the final product. However, conventional validation/assessments of the differentiation process (i.e., quantitative reverse transcription polymerase chain reaction [qRT-PCR] and histology) are end-point assays requiring disruption of the sample. This report introduces molecular beacon (MB)-based nanosensors to achieve noninvasive monitoring of chondrogenic differentiation. These nanosensors consist of biodegradable poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) encapsulating MBs to detect Type II Collagen (Col2) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNAs that serve as lineage-specific and housekeeping biomarkers, respectively. The sustainable release of MBs from MB-NPs allows longitudinal monitoring of MSCs undergoing chondrogenic differentiation over a period of 28 days. Dual-colored MB loading ensures accurate assessment of Col2 mRNA expression level, where potential heterogeneity in nanosensor uptake and retention by MSCs are taken into account. When normalized nanosensor signal was compared against qRT-PCR result, a tight correlation was observed (R2 = 0.9301). Finally, nanosensor usage was compatible with MSC potency with minimal influence on chondrogenic, adipogenic, and osteogenic differentiation.