Mechanoregulation of stem cell fate via micro-/nano-scale manipulation for regenerative medicine

Macrophage cell morphology-imprinted substrates can modulate mesenchymal stem cell behaviors and macrophage M1/M2 polarization for wound healing applications

Mesenchymal stem cells and macrophages (MQ) are two very important cells involved in the normal wound healing process. It is well understood that topological cues and mechanical factors can lead to different responses in stem cells and MQ by influencing their shape, cytoskeleton proliferation, migration, and differentiation, which play an essential role in the success or failure of biomaterial implantation and more importantly wound healing. On the other hand, the polarization of MQ from proinflammatory (M1) to prohealing (M2) phenotypes has a critical role in the acceleration of wound healing. In this study, the morphology of different MQ subtypes (M0, M1, and M2) was imprinted on a silicon surface (polydimethylsiloxane [PDMS]) to prepare a nano-topography cell-imprinted substrate with the ability to induce anti-inflammatory effects on the mouse adipose-derived stem cells (ADSCs) and RAW264.7 monocyte cell line (MO). The gene expression profiles and flow cytometry of MQ revealed that the cell shape microstructure promoted the MQ phenotypes according to the specific shape of each pattern. The ELISA results were in agreement with the gene expression profiles. The ADSCs on the patterned PDMS exhibited remarkably different shapes from no-patterned PDMS. The MOs grown on M2 morphological patterns showed a significant increase in expression and section of anti-inflammatory cytokine compared with M0 and M1 patterns. The ADSCs homing in niches heavily deformed the cytoskeletal, which is probably why the gene expression and phenotype unexpectedly changed. In conclusion, wound dressings with M2 cell morphology-induced surfaces are suggested as excellent anti-inflammatory and antiscarring dressings.

Current advances in anisotropic structures for enhanced osteogenesis

Bone defects are a challenge to healthcare systems, as the aging population experiences an increase in bone defects. Despite the development of biomaterials for bone fillers and scaffolds, there is still an unmet need for a bone-mimetic material. Cortical bone is highly anisotropic and displays a biological liquid crystalline (LC) arrangement, giving it exceptional mechanical properties and a distinctive microenvironment. However, the biofunctions, cell-tissue interactions, and molecular mechanisms of cortical bone anisotropic structure are not well understood. Incorporating anisotropic structures in bone-facilitated scaffolds has been recognised as essential for better outcomes. Various approaches have been used to create anisotropic micro/nanostructures, but biomimetic bone anisotropic structures are still in the early stages of development. Most scaffolds lack features at the nanoscale, and there is no comprehensive evaluation of molecular mechanisms or characterisation of calcium secretion. This manuscript provides a review of the latest development of anisotropic designs for osteogenesis and discusses current findings on cell-anisotropic structure interactions. It also emphasises the need for further research. Filling knowledge gaps will enable the fabrication of scaffolds for improved and more controllable bone regeneration.

Bioactivation of 3D Cell-Imprinted Polydimethylsiloxane Surfaces by Bone Protein Nanocoating for Bone Tissue Engineering

Physical and chemical parameters that mimic the physiological niche of the human body have an influence on stem cell fate by creating directional signals to cells. Micro/nano cell-patterned polydimethylsiloxane (PDMS) substrates, due to their ability to mimic the physiological niche, have been widely used in surface modification. Integration of other factors such as the biochemical coating on the surface can achieve more similar microenvironmental conditions and promote stem cell differentiation to the target cell line. Herein, we investigated the effect of physical topography, chemical functionalization by acid bone lysate (ABL) nanocoating, and the combined functionalization of the bone proteins' nanocoated surface and the topographically modified surface. We prepared four distinguishing surfaces: plain PDMS, physically modified PDMS by 3D cell topography patterning, chemically modified PDMS with bone protein nanocoating, and chemically modified nano 3D cell-imprinted PDMS by bone proteins (ABL). Characterization of extracted ABL was carried out by Bradford staining and sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, followed by the MTT assay for evaluation of cell viability on ABL-coated PDMS. Moreover, field emission scanning electron microscopy and profilometry were used for the determination of optimal coating thickness, and the appropriate coating concentration was identified and used in the study. The binding and retention of ABL to PDMS were confirmed by Fourier transform infrared spectroscopy and bicinchoninic acid assay. Sessile drop static water contact angle measurements on substrates showed that the combined chemical functionalization and nano 3D cell-imprinting on the PDMS surface improved surface wettability by 66% compared to plain PDMS. The results of ALP measurement, alizarin red S staining, immunofluorescence staining, and real-time PCR showed that the nano 3D cell-imprinted PDMS surface functionalized by extracted bone proteins, ABL, is able to guide the fate of adipose derived stem cellss toward osteogenic differentiation. Eventually, chemical modification of the cell-imprinted PDMS substrate by bone protein extraction not only improved the cell adhesion and proliferation but also contributed to the topographical effect itself and caused a significant synergistic influence on the process of osteogenic differentiation.

Direct reuse of electronic plastic scraps from computer monitor and keyboard to direct stem cell growth and differentiation

Reuse of electronic wastes is a critical aspect for a more sustainable circular economy as it provides the simplest and most direct route to extend the lifespan of non-renewable resources. Herein, the distinctive surface and micro topographical features of computer electronic-plastic (E-plastic) scraps were unconventionally repurposed as a substrate material to guide the growth and differentiation of human adipose-derived mesenchymal stem cells (ADSCs). Specifically, the E-plastics were scavenged from discarded computer components such as light diffuser plate (polyacrylates), prismatic sheet (polyethylene terephthalate), and keyboards (acrylonitrile butadiene styrene) were cleaned, sterilized, and systematically characterized to determine the identity of the plastics, chemical constituents, surface features, and leaching characteristics. Multiparametric analysis revealed that all the E-plastics could preserve stem-cell phenotype and maintain cell growth over 2 weeks, rivalling the performance of commercial tissue-culture treated plates as cell culture plastics. Interestingly, compared to commercial tissue-culture treated plastics and in a competitive adipogenic and osteogenic differentiation environment, ADSCs cultured on the keyboard and light diffuser plastics favoured bone cells formation while the grating-like microstructures of the prismatic sheet promoted fat cells differentiation via the process of contact guidance. Our findings point to the real possibility of utilizing discarded computer plastics as a "waste-to-resource" material to programme stem cell fate without further processing nor biochemical modification, thus providing an innovative second-life option for E-plastics from personal computers.

Sustainable aquaculture side-streams derived hybrid biocomposite for bone tissue engineering

Despite being a rich source of bioactive compounds, the current exploitation of aquatic biomass is insufficient. Majority of the aquaculture industry side-streams are currently used for low-value purposes such as animal feed or composting material, with low economical returns. To maximize resource reuse and minimize waste generation, valorization efforts should be augmented with the aim to produce high-value products. Herein, we present a novel aquaculture wastes-derived multi-scale osteoconductive hybrid biocomposite that is composed of chemically crosslinked American bullfrog (Rana catesbeiana) skin-derived type I tropocollagen nanofibrils (~22.3 nm) network and functionalized with micronized (~1.6 μm) single-phase hydroxyapatite (HA) from discarded snakehead (Channa micropeltes) fish scales. The bioengineered construct is biocompatible, highly porous (>90%), and exhibits excellent osteoconductive properties, as indicated by robust adhesion and proliferation of human fetal osteoblastic 1.19 cell line (hFOB 1.19). Furthermore, increased expression level of osteo-related ALPL and BGLAP mRNA transcripts, as well as enhanced osteocalcin immunoreactivity and increasing Alizarin red S staining coverage on the hybrid biocomposite was observed over 21 days of culture. Collectively, the devised "waste-to-resource" platform represents a sustainable waste valorization strategy that is amendable for advanced bone repair and regeneration applications.

Clarifying the in-situ cytotoxic potential of electronic waste plastics

Plastics in waste electronics (E-plastics) account for approximately 20% of the entire global electronic waste (E-waste) stream. Most of the E-plastics are not recycled as the presence of toxic additives (e.g. heavy metals, brominated flame retardants (BFRs), antimony, etc.) have associated environmental and health concerns. However, the majority of the studies are focused on quantitative assessment of the toxic constituents in E-plastics, while empirical information regarding the potential toxic effects in humans is largely lacking. To gain a deeper appreciation into the toxicological profile of E-plastics, in situ time-dependent exposures of 6 different human cell lines to a panel of 8 representative E-plastics recovered from liquid crystal displays (LCD), keyboards, screen frames, and wire insulators were conducted. Although several hazardous elements (e.g. Pb, As, Sb, Zn, Cu, etc) were detected at concentrations that far exceed the limit values permitted by the Restriction of Hazardous Substances Directive and EU Directives in the panel E-plastics, in-depth analysis of the 144 unique cell viability data points and live-dead staining experiments suggest that the acute and sub-chronic toxic effects of E-plastics in direct contact with human cells are negligible. These observations agreed with the inductively coupled plasma-optical emission spectrometry data, which revealed that leaching of these toxic additives into the biological milieu is not sufficiently high to trigger a cytotoxic response up to a continuous culture period of 2 weeks. The novel insights gained from this study are posited to further clarify the uncertainty associated with the safety and circular economy implementation of E-plastics.

Microfluidic and Microscale Assays to Examine Regenerative Strategies in the Neuro Retina

Bioengineering systems have transformed scientific knowledge of cellular behaviors in the nervous system (NS) and pioneered innovative, regenerative therapies to treat adult neural disorders. Microscale systems with characteristic lengths of single to hundreds of microns have examined the development and specialized behaviors of numerous neuromuscular and neurosensory components of the NS. The visual system is comprised of the eye sensory organ and its connecting pathways to the visual cortex. Significant vision loss arises from dysfunction in the retina, the photosensitive tissue at the eye posterior that achieves phototransduction of light to form images in the brain. Retinal regenerative medicine has embraced microfluidic technologies to manipulate stem-like cells for transplantation therapies, where de/differentiated cells are introduced within adult tissue to replace dysfunctional or damaged neurons. Microfluidic systems coupled with stem cell biology and biomaterials have produced exciting advances to restore vision. The current article reviews contemporary microfluidic technologies and microfluidics-enhanced bioassays, developed to interrogate cellular responses to adult retinal cues. The focus is on applications of microfluidics and microscale assays within mammalian sensory retina, or neuro retina, comprised of five types of retinal neurons (photoreceptors, horizontal, bipolar, amacrine, retinal ganglion) and one neuroglia (Müller), but excludes the non-sensory, retinal pigmented epithelium.

Robust Fabrication of Composite 3D Scaffolds with Tissue-Specific Bioactivity: A Proof-of-Concept Study

The basic requirement of any engineered scaffold is to mimic the native tissue extracellular matrix (ECM). Despite substantial strides in understanding the ECM, scaffold fabrication processes of sufficient product robustness and bioactivity require further investigation, owing to the complexity of the natural ECM. A promising bioacive platform for cardiac tissue engineering is that of decellularized porcine cardiac ECM (pcECM, used here as a soft tissue representative model). However, this platform's complexity and batch-to-batch variability serve as processing limitations in attaining a robust and tunable cardiac tissue-specific bioactive scaffold. To address these issues, we fabricated 3D composite scaffolds (3DCSs) that demonstrate comparable physical and biochemical properties to the natural pcECM using wet electrospinning and functionalization with a pcECM hydrogel. The fabricated 3DCSs are non-immunogenic in vitro and support human mesenchymal stem cells' proliferation. Most importantly, the 3DCSs demonstrate tissue-specific bioactivity in inducing spontaneous cardiac lineage differentiation in human induced pluripotent stem cells (hiPSC) and further support the viability, functionality, and maturation of hiPSC-derived cardiomyocytes. Overall, this work illustrates the technology to fabricate robust yet tunable 3D scaffolds of tissue-specific bioactivity (with a proof of concept provided for cardiac tissues) as a platform for basic materials science studies and possible future R&D application in regenerative medicine.

Mechanotransduction, nanotechnology, and nanomedicine

Mechanotransduction, a conversion of mechanical forces into biochemical signals, is essential for human development and physiology. It is observable at all levels ranging from the whole body, organs, tissues, organelles down to molecules. Dysregulation results in various diseases such as muscular dystrophies, hypertension-induced vascular and cardiac hypertrophy, altered bone repair and cell deaths. Since mechanotransduction occurs at nanoscale, nanosciences and applied nanotechnology are powerful for studying molecular mechanisms and pathways of mechanotransduction. Atomic force microscopy, magnetic and optical tweezers are commonly used for force measurement and manipulation at the single molecular level. Force is also used to control cells, topographically and mechanically by specific types of nano materials for tissue engineering. Mechanotransduction research will become increasingly important as a sub-discipline under nanomedicine. Here we review nanotechnology approaches using force measurements and manipulations at the molecular and cellular levels during mechanotransduction, which has been increasingly play important role in the advancement of nanomedicine.

Repair of Osteochondral Defects With Predifferentiated Mesenchymal Stem Cells of Distinct Phenotypic Character Derived From a Nanotopographic Platform

BACKGROUND

Articular cartilage has a zonal architecture and biphasic mechanical properties. The recapitulation of surface lubrication properties with high compressibility of the deeper layers of articular cartilage during regeneration is essential in achieving long-term cartilage integrity. Current clinical approaches for cartilage repair, especially with the use of mesenchymal stem cells (MSCs), have yet to restore the hierarchically organized architecture of articular cartilage.

HYPOTHESIS

MSCs predifferentiated on surfaces with specific nanotopographic patterns can provide phenotypically stable and defined chondrogenic cells and, when delivered as a bilayered stratified construct at the cartilage defect site, will facilitate the formation of functionally superior cartilage tissue in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

MSCs were subjected to chondrogenic differentiation on specific nanopatterned surfaces. The phenotype of the differentiated cells was assessed by the expression of cartilage markers. The ability of the 2-dimensional nanopattern-generated chondrogenic cells to retain their phenotypic characteristics after removal from the patterned surface was tested by subjecting the enzymatically harvested cells to 3-dimensional fibrin hydrogel culture. The in vivo efficacy in cartilage repair was demonstrated in an osteochondral rabbit defect model. Repair by bilayered construct with specific nanopattern predifferentiated cells was compared with implantation with cell-free fibrin hydrogel, undifferentiated MSCs, and mixed-phenotype nanopattern predifferentiated MSCs. Cartilage repair was evaluated at 12 weeks after implantation.

RESULTS

Three weeks of predifferentiation on 2-dimensional nanotopographic patterns was able to generate phenotypically stable chondrogenic cells. Implantation of nanopatterned differentiated MSCs as stratified bilayered hydrogel constructs improved the repair quality of cartilage defects, as indicated by histological scoring, mechanical properties, and polarized microscopy analysis.

CONCLUSION

Our results indicate that with an appropriate period of differentiation, 2-dimensional nanotopographic patterns can be employed to generate phenotypically stable chondrogenic cells, which, when implanted as stratified bilayered hydrogel constructs, were able to form functionally superior cartilage tissue.

CLINICAL RELEVANCE

Our approach provides a relatively straightforward method of obtaining large quantities of zone-specific chondrocytes from MSCs to engineer a stratified cartilage construct that could recapitulate the zonal architecture of hyaline cartilage, and it represents a significant improvement in current MSC-based cartilage regeneration.

Epithelial-mesenchymal transition of cancer cells using bioengineered hybrid scaffold composed of hydrogel/3D-fibrous framework

Cancer cells undergoing epithelial-mesenchymal transition (EMT) acquire stem cell-like phenotype associated with malignant behaviour, chemoresistance, and relapse. Current two-dimensional (2D) in-vitro culture models of tumorigenesis are inadequate to replicate the complexity of in-vivo microenvironment. Therefore, the generation of functional three-dimensional (3D) constructs is a fundamental prerequisite to form multi-cellular tumour spheroids for studying basic pathological mechanisms. In this study, we focused on two major points (i) designing and fabrication of 3D hybrid scaffolds comprising electrospun fibers with cancer cells embedded within hydrogels, and (ii) determining the potential roles of 3D hybrid scaffolds associated with EMT in cancer progression and metastasis. Our findings revealed that 3D hybrid scaffold enhances cell proliferation and induces cancer cells to undergo EMT, as demonstrated by significant up-regulation of EMT associated transcriptional factors including Snail1, Zeb1, and Twist2; and mesenchymal markers whereas epithelial marker, E-Cadherin was downregulated. Remarkably, this induction is independent of cancer cell-type as similar results were obtained for breast cancer cells, MDA-MB-231 and gastric cancer cells, MKN74. Moreover, the hybrid scaffolds enrich aggressive cancer cells with stem cell properties. We showed that our 3D scaffolds could trigger EMT of cancer cells which could provide a useful model for studying anticancer therapeutics against metastasis.

Layer-by-layer ultraviolet assisted extrusion-based (UAE) bioprinting of hydrogel constructs with high aspect ratio for soft tissue engineering applications

One of the major challenges in the field of soft tissue engineering using bioprinting is fabricating complex tissue constructs with desired structure integrity and mechanical property. To accomplish such requirements, most of the reported works incorporated reinforcement materials such as poly(ϵ-caprolactone) (PCL) polymer within the 3D bioprinted constructs. Although this approach has made some progress in constructing soft tissue-engineered scaffolds, the mechanical compliance mismatch and long degradation period are not ideal for soft tissue engineering. Herein, we present a facile bioprinting strategy that combines the rapid extrusion-based bioprinting technique with an in-built ultraviolet (UV) curing system to facilitate the layer-by-layer UV curing of bioprinted photo-curable GelMA-based hydrogels to achieve soft yet stable cell-laden constructs with high aspect ratio for soft tissue engineering. GelMA is supplemented with a viscosity enhancer (gellan gum) to improve the bio-ink printability and shape fidelity while maintaining the biocompatibility before crosslinking via a layer-by-layer UV curing process. This approach could eventually fabricate soft tissue constructs with high aspect ratio (length to diameter) of ≥ 5. The effects of UV source on printing resolution and cell viability were also studied. As a proof-of-concept, small building units (3D lattice and tubular constructs) with high aspect ratio are fabricated. Furthermore, we have also demonstrated the ability to perform multi-material printing of tissue constructs with high aspect ratio along both the longitudinal and transverse directions for potential applications in tissue engineering of soft tissues. This layer-by-layer ultraviolet assisted extrusion-based (UAE) Bioprinting may provide a novel strategy to develop soft tissue constructs with desirable structure integrity.

Mechanoregulation of Cancer-Associated Fibroblast Phenotype in Three-Dimensional Interpenetrating Hydrogel Networks

Tumor stromal residing cancer-associated fibroblasts (CAFs) are significant accomplices in the growth and development of malignant neoplasms. As cancer progresses, the stroma undergoes a dramatic remodeling and stiffening of its extracellular matrix (ECM). However, exactly how these biomechanical changes influence the CAF behavior and the functional paracrine crosstalk with the neighboring tumor cells in a 3-dimensional (3D) microenvironment remains elusive. Herein, a collagen and alginate interpenetrating network (CoAl-IPN) hydrogel system was employed as a 3D in vitro surrogate of the cancerous breast tissue stromal niche. In this study, the mechanical properties of CoAl-IPN were precisely fine-tuned with Young's modulus ( E) values of ∼108 and 898 Pa. The results revealed that the 3D polymeric network mechanics and microstructure are critical biophysical determinants of the human breast CAF (b-CAF) morphology, phenotype, and paracrine dialogue with MDA-MB-231 tumoroids. A compliant hydrogel network favors b-CAF spreading, nuclear translocation of the YAP/TAZ mechanosignaling protein, and upregulation of CAF hallmark transcripts. Conversely, a rigid and highly cross-linked hydrogel network imposed a physical entrapment effect on the b-CAFs that limited their spreading and phenotype in a manner that effectively muted their pro-tumorigenic paracrine activity. Collectively, the CoAl-IPN 3D culture system has proven to be a versatile platform in defining the 3D biophysical parameters that could either promote or restrain the protumorigenic activity of b-CAFs and sheds critical mechano-mediated light onto the phenotypic plasticity and corresponding specific bioactivity of b-CAFs in the 3D microenvironment.

Migration and Phenotype Control of Human Dermal Fibroblasts by Electrospun Fibrous Substrates

Electrospun fibrous matrices, mimicking extracellular matrix (ECM) hierarchical structures, are potential scaffolds for wound healing. To design functional scaffolds, it is important to explore the interactions between scaffold topographic features and cellular responses, especially directional migration and phenotypic changes, which are critical functional aspects during wound healing. Here, accelerated and persistent migration of human dermal fibroblasts (HDFs) is observed on fibers with aligned orientation. Furthermore, aligned fibers can induce fibroblast-to-myofibroblast differentiation of HDFs. During wound healing, the presence of myofibroblasts advances wound repair by rendering contractile force and ECM deposition within the early and middle courses, but its continuous persistence in the later event may not be desired due to the contribution in pathological scarring. To tune the balance, it is noted in this work that the introduction of matricellular protein angiopoietin-like 4 (ANGPTL4) is capable of reversing the phenotypic alteration induced by aligned fibers, in a time-dependent manner. These results indicate fibrous matrices with oriented configuration are functional in mediating directional cell migration and phenotypic change. The discoveries further suggest that tissue-engineered fibrous grafts with precise alignment modulation and ANGPTL4 releasing properties may thus be promising to promote wound repair with minimizing scar formation.

The relationship between substrate topography and stem cell differentiation in the musculoskeletal system

It is well known that biomaterial topography can exert a profound influence on various cellular functions such as migration, polarization, and adhesion. With the development and refinement of manufacturing technology, much research has recently been focused on substrate topography-induced cell differentiation, particularly in the field of tissue engineering. Even without biological and chemical stimuli, the differentiation of stem cells can also be initiated by various biomaterials with different topographic features. However, the underlying mechanisms of this biological phenomenon remain elusive. During the past few decades, many researchers have demonstrated that cells can sense the topography of materials through the assembly and polymerization of membrane proteins. Following the activation of RHO, TGF-b or FAK signaling pathways, cells can be induced into various differentiation states. But these signaling pathways often coincide with canonical mechanical transduction pathways, and no firm conclusion has been reached among researchers in this field on topography-specific signaling pathways. On the other hand, some substrate topographies are reported to have the ability to inhibit differentiation and maintain the 'stemness' of stem cells. In this review, we will summarize the role of topography in musculoskeletal system regeneration and explore possible topography-related signaling pathways involved in cell differentiation.

An engineered cell-imprinted substrate directs osteogenic differentiation in stem cells

A cell-imprinted poly(dimethylsiloxane)/hydroxyapatite nanocomposite substrate was fabricated to engage topographical, mechanical, and chemical signals to stimulate and boost stem cell osteogenic differentiation. The physicochemical properties of the fabricated substrates, with nanoscale resolution of osteoblast morphology, were probed using a wide range of techniques including scanning electron microscopy, atomic force microscopy, dynamic mechanical thermal analysis, and water contact angle measurements. The osteogenic differentiation capacity of the cultured stem cells on these substrates was probed by alizarin red staining, ALP activity, osteocalcin measurements, and gene expression analysis. The outcomes revealed that the concurrent roles of the surface patterns and viscoelastic properties of the substrate provide the capability of directing stem cell differentiation toward osteogenic phenotypes. Besides the physical and mechanical effects, we found that the chemical signaling of osteoinductive hydroxyapatite nanoparticles, embedded in the nanocomposite substrates, could further improve and optimize stem cell osteogenic differentiation.

Contractility of Airway Smooth Muscle Cell in Response to Zinc Oxide Nanoparticles by Traction Force Microscopy

Zinc oxide nanoparticles (ZnO-NPs) have been widely used in engineering and biomedicine. However, their adverse pathological effects and mechanisms, especially the biomechanical effects on respiratory system where airway smooth muscle cell (ASMC) contractility regulates the airway response and lung function, are not fully understood. Herein, we used traction force microscopy (TFM) method to investigate whether ZnO-NPs of different concentrations (0.1-10 μg/mL) can alter ASMC contractility (basal and agonist-stimulated) after a short-term exposure and the potential mechanisms. We found that ZnO-NPs exposure led to a decrease of ASMC viability in a dose-dependent manner. Notably, basal contractility was enhanced when the concentration of ZnO-NPs was less than 0.1 μg/mL and decreased afterwards, while KCl-stimulated contractility was reduced in all cases of ZnO-NPs treated groups. Cytoskeleton structure was also found to be significantly altered in ASMC with the stimulation of ZnO-NPs. More importantly, it seems that ZnO-NPs with low concentration (< 0.1 μg/mL) would change ASMC contractility without any apparent cytotoxicity through disruption of the microtubule assembly. Moreover, our results also emerged that ASMC contractility responses were regulated by clathrin-mediated endocytosis and cytoskeleton remodeling. Together, these findings indicate the susceptibility of cell mechanics to NPs exposure, suggesting that cell mechanical testing will contribute to uncover the pathological mechanisms of NPs in respiratory diseases.

Effects of Transplanted Heparin-Poloxamer Hydrogel Combining Dental Pulp Stem Cells and bFGF on Spinal Cord Injury Repair

Spinal cord injury (SCI) is one of serious traumatic diseases of the central nervous system and has no effective treatment because of its complicated pathophysiology. Tissue engineering strategy which contains scaffolds, cells, and growth factors can provide a promising treatment for SCI. Hydrogel that has 3D network structure and biomimetic microenvironment can support cellular growth and embed biological macromolecules for sustaining release. Dental pulp stem cells (DPSCs), derived from cranial neural crest, possess mesenchymal stem cell (MSC) characteristics and have an ability to provide neuroprotective and neurotrophic properties for SCI treatment. Basic fibroblast growth factor (bFGF) is able to promote cell survival and proliferation and also has beneficial effect on neural regeneration and functional recovery after SCI. Herein, a thermosensitive heparin-poloxamer (HP) hydrogel containing DPSCs and bFGF was prepared, and the effects of HP-bFGF-DPSCs on neuron restoration after SCI were evaluated by functional recovery tests, western blotting, magnetic resonance imaging (MRI), histology evaluation, and immunohistochemistry. The results suggested that transplanted HP hydrogel containing DPSCs and bFGF had a significant impact on spinal cord repair and regeneration and may provide a promising strategy for neuron repair, functional recovery, and tissue regeneration after SCI.

Ice-Templated Protein Nanoridges Induce Bone Tissue Formation

Little is known about the role of biocompatible protein nanoridges in directing stem cell fate and tissue regeneration due to the difficulty in forming protein nanoridges. Here an ice-templating approach is proposed to produce semi-parallel pure silk protein nanoridges. The key to this approach is that water droplets formed in the protein films are frozen into ice crystals (removed later by sublimation), pushing the surrounding protein molecules to be assembled into nanoridges. Unlike the flat protein films, the unique protein nanoridges can induce the differentiation of human mesenchymal stem cells (MSCs) into osteoblasts without any additional inducers, as well as the formation of bone tissue in a subcutaneous rat model even when not seeded with MSCs. Moreover, the nanoridged films induce less inflammatory infiltration than the flat films in vivo. This work indicates that decorating biomaterials surfaces with protein nanoridges can enhance bone tissue formation in bone repair.

Arsenite-loaded nanoparticles inhibit the invasion and metastasis of a hepatocellular carcinoma: in vitro and in vivo study

Postoperative recurrence and metastasis are the major problems for the current treatment of hepatocellular carcinomas (HCC) in the clinic, including hepatectomy and liver transplantation. Here, we report that arsentic-loaded nanoparticles (ALNPs) are able to reduce the invasion of HCC cells in vitro, and, more importantly, can strongly suppress the invasion and metastasis of HCC in vivo without adverse side effects. Compared to free drug arsenic trioxide , ALNPs can deliver the drug into cancer cells more efficiently, destroy the structure of microtubules and reduce the aggregation of microfilaments in cell membranes more significantly. Furthermore, our results also reveal that tumor cells in murine blood were reduced remarkably after intravenous injection of ALNPs, indicating that this nano-drug may efficiently kill circulating tumor cells in vivo. In conclusion, our nano-drug ALNPs have great potential for the suppression of metastasis of HCC, which may open up a new avenue for the effective treatment of HCC without metastasis and recurrence.

Bone-Inspired Spatially Specific Piezoelectricity Induces Bone Regeneration

The extracellular matrix of bone can be pictured as a material made of parallel interspersed domains of fibrous piezoelectric collagenous materials and non-piezoelectric non-collagenous materials. To mimic this feature for enhanced bone regeneration, a material made of two parallel interspersed domains, with higher and lower piezoelectricity, respectively, is constructed to form microscale piezoelectric zones (MPZs). The MPZs are produced using a versatile and effective laser-irradiation technique in which K_0.5Na_0.5NbO₃ (KNN) ceramics are selectively irradiated to achieve microzone phase transitions. The phase structure of the laser-irradiated microzones is changed from a mixture of orthorhombic and tetragonal phases (with higher piezoelectricity) to a tetragonal dominant phase (with lower piezoelectricity). The microzoned piezoelectricity distribution results in spatially specific surface charge distribution, enabling the MPZs to bear bone-like microscale electric cues. Hence, the MPZs induce osteogenic differentiation of stem cells in vitro and bone regeneration in vivo even without being seeded with stem cells. The concept of mimicking the spatially specific piezoelectricity in bone will facilitate future research on the rational design of tissue regenerative materials.

Engineering a Cell Home for Stem Cell Homing and Accommodation

Distilling complexity to advance regenerative medicine from laboratory animals to humans, in situ regeneration will continue to evolve using biomaterial strategies to drive endogenous cells within the human body for therapeutic purposes; this approach avoids the need for delivering ex vivo-expanded cellular materials. Ensuring the recruitment of a significant number of reparative cells from an endogenous source to the site of interest is the first step toward achieving success. Subsequently, making the "cell home" cell-friendly by recapitulating the natural extracellular matrix (ECM) in terms of its chemistry, structure, dynamics, and function, and targeting specific aspects of the native stem cell niche (e.g., cell-ECM and cell-cell interactions) to program and steer the fates of those recruited stem cells play equally crucial roles in yielding a therapeutically regenerative solution. This review addresses the key aspects of material-guided cell homing and the engineering of novel biomaterials with desirable ECM composition, surface topography, biochemistry, and mechanical properties that can present both biochemical and physical cues required for in situ tissue regeneration. This growing body of knowledge will likely become a design basis for the development of regenerative biomaterials for, but not limited to, future in situ tissue engineering and regeneration.

Hierarchical macropore/nano surface regulates stem cell fate through a ROCK-related signaling pathway

Synergistic cytoskeleton distribution accompanying higher ROCK activity activated FAK-ERK1/2 signaling pathway and promotion of BMSC osteogenesis on hierarchical surface.

Soft Material Approach to Induce Oxidative Stress in Mesenchymal Stem Cells for Functional Tissue Repair

Biomimicking hydrogel-based cell culture platforms with physiologically relevant stiffness are powerful tools to modulate the behaviors of stem cells. Herein, the use of fibronectin-conjugated polyacrylamide (PAA) hydrogel biointerface is exploited to modulate the intracellular oxidative stress of human bone marrow derived mesenchymal stem cells (MSCs). We show that compliant culture surface with kPa range matrix stiffness can augment the expression level of reactive oxygen species (ROS) in MSCs by approximately 2-4 fold compared with cells grown on conventional FN coated glass control surface in a noncytotoxic manner. Via an unbiased proteomics approach and mechanistic studies, we show that the secretion level of a sub series of "mechano-sensitive" chemokines and trophic factors is heavily dependent on the PAA matrix stiffness mediated ROS level. Importantly, the secretome harvested from the cells that were grown on the PAA hydrogel was found to enhance wound healing in both in vitro and in vivo full thickness mouse excisional wound model. The devised "soft approach" to induce oxidative stress in MSCs is posited to pave the way for novel cell-free therapeutic interventions targeting a wide variety of diseases and to foster functional tissue repair.

Nanoarchitectonics for Dynamic Functional Materials from Atomic-/Molecular-Level Manipulation to Macroscopic Action

Objects in all dimensions are subject to translational dynamism and dynamic mutual interactions, and the ability to exert control over these events is one of the keys to the synthesis of functional materials. For the development of materials with truly dynamic functionalities, a paradigm shift from "nanotechnology" to "nanoarchitectonics" is proposed, with the aim of design and preparation of functional materials through dynamic harmonization of atomic-/molecular-level manipulation and control, chemical nanofabrication, self-organization, and field-controlled organization. Here, various examples of dynamic functional materials are presented from the atom/molecular-level to macroscopic dimensions. These systems, including atomic switches, molecular machines, molecular shuttles, motional crystals, metal-organic frameworks, layered assemblies, gels, supramolecular assemblies of biomaterials, DNA origami, hollow silica capsules, and mesoporous materials, are described according to their various dynamic functions, which include short-term plasticity, long-term potentiation, molecular manipulation, switchable catalysis, self-healing properties, supramolecular chirality, morphological control, drug storage and release, light-harvesting, mechanochemical transduction, molecular tuning molecular recognition, hand-operated nanotechnology.

Nanoscale topography, semiconductor polarity and surface functionalization: additive and cooperative effects on PC12 cell behavior

This work compares the behavior of PC12 cells on planar and patterned III-nitride materials with nanostructured topographies.

Highly Ordered 1D Fullerene Crystals for Concurrent Control of Macroscopic Cellular Orientation and Differentiation toward Large-Scale Tissue Engineering

A highly aligned 1D fullerene whisker (FW) scaffold in a centimeter area is fabricated by interfacial alignment. The resulting aligned FW scaffold enables concurrent control over cellular orientation and differentiation to muscle cells. This aligned FW scaffold is made by a facile method, and hence the substrate is a promising alternative to other cell scaffolds for tissue engineering.

Role of Cytoskeletal Tension in the Induction of Cardiomyogenic Differentiation in Micropatterned Human Mesenchymal Stem Cell

The role of biophysical induction methods such as cell micropatterning in stem cell differentiation has been well documented previously. However, the underlying mechanistic linkage of the engineered cell shape to directed lineage commitment remains poorly understood. Here, it is reported that micropatterning plays an important role in regulating the optimal cytoskeletal tension development in human mesenchymal stem cell (hMSC) via cell mechanotransduction pathways to induce cardiomyogenic differentiation. Cells are grown on fibronectin strip patterns to control cell polarization and morphology. These patterned cells eventually show directed commitment toward the myocardial lineage. The cell's mechanical properties (cell stiffness and cell traction forces) are observed to be very different for cells that have committed to the myocardial lineage when compared with that of control. These committed cells have mechanical properties that are significantly lower indicating a correlation between the micropatterning-induced differentiation and actomyosin-generated cytoskeletal tension within patterned cells. To study this correlation, patterned cells are treated with RhoA pathway inhibitor. Severely down-regulated cardiomyogenic marker expression is observed in those treated patterned cells, thus emphasizing the direct dependence of hMSCs differentiation fate on the cytoskeletal tension.

Environmental physical cues determine the lineage specification of mesenchymal stem cells

BACKGROUND

Physical cues of cellular environment affect cell fate and differentiation. For example, an environment with high stiffness drives mesenchymal stem cells (MSCs) to undergo osteogenic differentiation, while low stiffness leads to lipogenic differentiation. Such effects could be independent of chemical/biochemical inducers.

SCOPE OF REVIEW

Stiffness and/or topography of cellular environment can control MSC differentiation and fate determination. In addition, physical factors such as tension, which resulted from profound cytoskeleton reorganization during MSC differentiation, affect the gene expression essential for the differentiation. Although physical cues control MSC lineage specification probably by reorganizing and tuning cytoskeleton, the full mechanism is largely unclear. It also remains elusive how physical signals are sensed by cells and transformed into biochemical and biological signals. More importantly, it becomes pivotal to define explicitly the physical cue(s) essential for cell differentiation and fate decision. With a focus on MSC, we present herein current understanding of the interplay between i) physical cue and factors and ii) MSC differentiation and fate determination.

MAJOR CONCLUSIONS

Biophysical cues can initiate or strengthen the biochemical signaling for MSC fate determination and differentiation. Physical properties of cellular environment direct the structural adaptation and functional coupling of the cells to their environment.

GENERAL SIGNIFICANCE

These observations not only open a simple avenue to engineer cell fate in vitro, but also start to reveal the physical elements that regulate and determine cell fate.

Investigating the spatial distribution of integrin β₁ in patterned human mesenchymal stem cells using super-resolution imaging

Lineage commitment of human mesenchymal stem cells (hMSCs) could be directed through micro/nanopatterning of the extracellular matrix (ECM) between cells and substrate. Integrin receptors, integrator of the ECM and cell cytoskeleton, function as molecular bridges linking cells to different biophysical cues translated from patterned ECM. Here we report the distinct recruitment of active integrin β1 (ITG-β1) in hMSCs when they were committed toward the cardiomyogenic lineage on a micropatterned surface. In addition, a systematic study of the distribution of ITG-β1 was performed on focal adhesions (FAs) using a direct stochastic optical reconstruction microscopy (dSTORM) technique, a super-resolution imaging technique to establish the relationship between types of integrin expression and its distribution pattern that are associated with cardiomyogenic differentiation of hMSCs. We ascertained that elongated FAs of ITG-β1 expressed in patterned hMSCs were more prominent than FAs expressed in unpatterned hMSCs. However, there was no significant difference observed between the widths of FAs from both experimental groups. It was found in patterned hMSCs that the direction of FA elongation coincides with cell orientation. This phenomenon was however not observed in unpatterned hMSCs. These results showed that the biophysical induction methods like FAs patterning could selectively induce hMSCs lineage commitment via integrin-material interaction.

Influence of micropattern width on differentiation of human mesenchymal stem cells to vascular smooth muscle cells

In recent years, various approaches have been taken to generate functional muscle tissue by tissue engineering. However, in vitro methods to generate smooth muscle with physiologically aligned structure remains limited. In order to mimic the in vivo highly organized structure of smooth muscle cells, we used micropatterning technology for engineering parallel aligned cells. In this study, a gradient micropattern of different width of cell-adhesive polystyrene stripes (5, 10, 20, 40, 60, 80, 100, 200, 400, 600, 800 and 1000μm) was prepared and the effects of micropattern width on human mesenchymal stem cells (hMSCs) orientation, morphology and smooth muscle cell differentiation were investigated. The width of micropattern stripes showed obvious effect on cell orientation, morphology and smooth muscle cell differentiation. The cells showed higher degree of orientation when the micropattern stripes became narrower. Higher expression of calponin and smooth muscle actin was observed among the narrow micropatterns ranging from 200μm to 20μm, compared to the non-patterned area and wide micropattern areas which showed similar levels of expression.

Nanoparticles strengthen intracellular tension and retard cellular migration

Nanoparticles can have profound effects on cell biology. Here, we show that after TiO2, SiO2, and hydroxyapatite nanoparticles treatment, TR146 epithelial cell sheet displayed slower migration. Cells after exposure to the nanoparticles showed increased cell contractility with significantly impaired wound healing capability however without any apparent cytotoxicity. We showed the mechanism is through nanoparticle-mediated massive disruption of the intracellular microtubule assembly, thereby triggering a positive feedback that promoted stronger substrate adhesions thus leading to limited cell motility.