Direct laser machining-induced topographic pattern promotes up-regulation of myogenic markers in human mesenchymal stem cells

Electrospun Poly(L-lactide-co-ε-caprolactone) Scaffold Potentiates C2C12 Myoblast Bioactivity and Acts as a Stimulus for Cell Commitment in Skeletal Muscle Myogenesis

Tissue engineering combines a scaffold, cells and regulatory signals, reproducing a biomimetic extracellular matrix capable of supporting cell attachment and proliferation. We examined the role of an electrospun scaffold made of a biocompatible polymer during the myogenesis of skeletal muscle (SKM) as an alternative approach to tissue regeneration. The engineered nanostructure was obtained by electrospinning poly(L-lactide-co-ε-caprolactone) (PLCL) in the form of a 3D porous nanofibrous scaffold further coated with collagen. C2C12 were cultured on the PLCL scaffold, and cell morphology and differentiation pathways were thoroughly investigated. The functionalized PLCL scaffold recreated the SKM nanostructure and performed its biological functions, guiding myoblast morphogenesis and promoting cell differentiation until tissue formation. The scaffold enabled cell-cell interactions through the development of cellular adhesions that were fundamental during myoblast fusion and myotube formation. Expression of myogenic regulatory markers and muscle-specific proteins at different stages of myogenesis suggested that the PLCL scaffold enhanced myoblast differentiation within a shorter time frame. The functionalized PLCL scaffold impacts myoblast bioactivity and acts as a stimulus for cell commitment, surpassing traditional 2D cell culture techniques. We developed a screening model for tissue development and a device for tissue restoration.

Investigating Potential Effects of Ultra-Short Laser-Textured Porous Poly-ε-Caprolactone Scaffolds on Bacterial Adhesion and Bone Cell Metabolism

Developing antimicrobial surfaces that combat implant-associated infections while promoting host cell response is a key strategy for improving current therapies for orthopaedic injuries. In this paper, we present the application of ultra-short laser irradiation for patterning the surface of a 3D biodegradable synthetic polymer in order to affect the adhesion and proliferation of bone cells and reject bacterial cells. The surfaces of 3D-printed polycaprolactone (PCL) scaffolds were processed with a femtosecond laser (λ = 800 nm; τ = 130 fs) for the production of patterns resembling microchannels or microprotrusions. MG63 osteoblastic cells, as well as S. aureus and E. coli, were cultured on fs-laser-treated samples. Their attachment, proliferation, and metabolic activity were monitored via colorimetric assays and scanning electron microscopy. The microchannels improved the wettability, stimulating the attachment, spreading, and proliferation of osteoblastic cells. The same topography induced cell-pattern orientation and promoted the expression of alkaline phosphatase in cells growing in an osteogenic medium. The microchannels exerted an inhibitory effect on S. aureus as after 48 h cells appeared shrunk and disrupted. In comparison, E. coli formed an abundant biofilm over both the laser-treated and control samples; however, the film was dense and adhesive on the control PCL but unattached over the microchannels.

Biomimetic Hierarchical Structuring of PLA by Ultra-Short Laser Pulses for Processing of Tissue Engineered Matrices: Study of Cellular and Antibacterial Behavior

The influence of ultra-short laser modification on the surface morphology and possible chemical alteration of poly-lactic acid (PLA) matrix in respect to the optimization of cellular and antibacterial behavior were investigated in this study. Scanning electron microscopy (SEM) morphological examination of the processed PLA surface showed the formation of diverse hierarchical surface microstructures, generated by irradiation with a range of laser fluences (F) and scanning velocities (V) values. By controlling the laser parameters, diverse surface roughness can be achieved, thus influencing cellular dynamics. This surface feedback can be applied to finely tune and control diverse biomaterial surface properties like wettability, reflectivity, and biomimetics. The triggering of thermal effects, leading to the ejection of material with subsequent solidification and formation of raised rims and 3D-like hollow structures along the processed zones, demonstrated a direct correlation to the wettability of the PLA. A transition from superhydrophobic (θ > 150°) to super hydrophilic (θ < 20°) surfaces can be achieved by the creation of grooves with V = 0.6 mm/s, F = 1.7 J/cm2. The achieved hierarchical architecture affected morphology and thickness of the processed samples which were linked to the nature of ultra-short laser-material interaction effects, namely the precipitation of temperature distribution during material processing can be strongly minimized with ultrashort pulses leading to non-thermal and spatially localized effects that can facilitate volume ablation without collateral thermal damage The obtained modification zones were analyzed employing Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray analysis (EDX), and optical profilometer. The modification of the PLA surface resulted in an increased roughness value for treatment with lower velocities (V = 0.6 mm/s). Thus, the substrate gains a 3D-like architecture and forms a natural matrix by microprocessing with V = 0.6 mm/s, F = 1.7 J/cm2, and V = 3.8 mm/s, F = 0.8 J/cm2. The tests performed with Mesenchymal stem cells (MSCs) demonstrated that the ultra-short laser surface modification altered the cell orientation and promoted cell growth. The topographical design was tested also for the effectiveness of bacterial attachment concerning chosen parameters for the creation of an array with defined geometrical patterns.

Bioactive micropatterned platform to engineer myotube-like cells from stem cells

Skeletal muscle has the capacity to repair and heal itself after injury. However, this self-healing ability is diminished in the event of severe injuries and myopathies. In such conditions, stem cell-based regenerative treatments can play an important part in post injury restoration. We herein report the development of a bioactive (integrin-β1 antibody immobilized) gold micropatterned platform to promote human mesenchymal stem cells (hMSCs) differentiation into the myotube-like cells. hMSCs grown on bioactive micropattern differentiated into the myotube-like cells within two weeks. Further, up-regulation of myogenic markers, multi-nucleated state with continuous actin cytoskeleton and absence of proliferation marker confirmed the formation of myotube-like cells on bioactive micropattern. Prominent expression of elongated integrin-β1 focal adhesions (ITG-β1 FAs) and development of anisotropic stress fibres in those differentiated cells elucidated their importance in stem cell myogenesis. Together these findings delineate the synergistic role of engineered cell anisotropy and ITG-β1 mediated signaling in the development of myotube-like cells from hMSCs.

The Role of the Microenvironment in Controlling the Fate of Bioprinted Stem Cells

The field of tissue engineering and regenerative medicine has made numerous advances in recent years in the arena of fabricating multifunctional, three-dimensional (3D) tissue constructs. This can be attributed to novel approaches in the bioprinting of stem cells. There are expansive options in bioprinting technology that have become more refined and specialized over the years, and stem cells address many limitations in cell source, expansion, and development of bioengineered tissue constructs. While bioprinted stem cells present an opportunity to replicate physiological microenvironments with precision, the future of this practice relies heavily on the optimization of the cellular microenvironment. To fabricate tissue constructs that are useful in replicating physiological conditions in laboratory settings, or in preparation for transplantation to a living host, the microenvironment must mimic conditions that allow bioprinted stem cells to proliferate, differentiate, and migrate. The advances of bioprinting stem cells and directing cell fate have the potential to provide feasible and translatable approach to creating complex tissues and organs. This review will examine the methods through which bioprinted stem cells are differentiated into desired cell lineages through biochemical, biological, and biomechanical techniques.

Enhanced Biocompatibility and Differentiation Capacity of Mesenchymal Stem Cells on Poly(dimethylsiloxane) by Topographically Patterned Dopamine

Controlling the behavior of mesenchymal stem cells (MSCs) through topographic patterns is an effective approach for stem cell studies. We, herein, reported a facile method to create a dopamine (DA) pattern on poly(dimethylsiloxane) (PDMS). The topography of micropatterned DA was produced on PDMS after plasma treatment. The grid-topographic-patterned surface of PDMS-DA (PDMS-DA-P) was measured for adhesion force and Young's modulus by atomic force microscopy. The surface of PDMS-DA-P demonstrated less stiff and more elastic characteristics compared to either nonpatterned PDMS-DA or PDMS. The PDMS-DA-P evidently enhanced the differentiation of MSCs into various tissue cells, including nerve, vessel, bone, and fat. We further designed comprehensive experiments to investigate adhesion, proliferation, and differentiation of MSCs in response to PDMS-DA-P and showed that the DA-patterned surface had good biocompatibility and did not activate macrophages or platelets in vitro and had low foreign body reaction in vivo. Besides, it protected MSCs from apoptosis as well as excessive reactive oxygen species (ROS) generation. Particularly, the patterned surface enhanced the differentiation capacity of MSCs toward neural and endothelial cells. The stromal cell-derived factor-1α/CXantiCR4 pathway may be involved in mediating the self-recruitment and promoting the differentiation of MSCs. These findings support the potential application of PDMS-DA-P in either cell treatment or tissue repair.

Biological evaluation of bone substitute

Critical-sized defects (CSDs) caused by trauma, tumor resection, or skeletal abnormalities create a high demand for bone repair materials (BRMs). Over the years, scientists have been trying to develop BRMs and evaluate their efficacy using numerous developed methods. BRMs are characterized by osteogenesis and angiogenesis promoting properties, the latter of which has rarely been studied in vitro and in vivo. While blood vessels are required to provide nutrients. Bone mass maintains a dynamic balance under the joint action of osteolytic and osteogenic activity in which monocytes differentiate into osteolytic cells, and osteoprogenitor cells differentiate into osteogenic cells. This review would be helpful for inexperienced researchers as well as present a comprehensive overview of methods used to investigate the effect of BRMs on osteogenic cells, osteolytic cells, and blood vessels, as well as their biocompatibility and biological performance. This review is expected to facilitate further research and development of new BRMs.

Facile Method for Fabrication of Meter-Long Multifunctional Hydrogel Fibers with Controllable Biophysical and Biochemical Features

Hydrogel structures with microscale morphological features have extensive application in tissue engineering owing to their capacity to induce desired cellular behavior. Herein, we describe a novel biofabrication method for fabrication of grooved solid and hollow hydrogel fibers with control over their cross-sectional shape, surface morphology, porosity, and material composition. These fibers were further configured into three-dimensional structures using textile technologies such as weaving, braiding, and embroidering methods. Additionally, the capacity of these fibers to integrate various biochemical and biophysical cues was shown via incorporating drug-loaded microspheres, conductive materials, and magnetic particles, extending their application to smart drug delivery, wearable or implantable medical devices, and soft robotics. The efficacy of the grooved fibers to induce cellular alignment was evaluated on various cell types including myoblasts, cardiomyocytes, cardiac fibroblasts, and glioma cells. In particular, these fibers were shown to induce controlled myogenic differentiation and morphological changes, depending on their groove size, in C2C12 myoblasts.

Recent advances in three-dimensional bioprinting of stem cells

In spite of being a new field, three-dimensional (3D) bioprinting has undergone rapid growth in the recent years. Bioprinting methods offer a unique opportunity for stem cell distribution, positioning, and differentiation at the microscale to make the differentiated architecture of any tissue while maintaining precision and control over the cellular microenvironment. Bioprinting introduces a wide array of approaches to modify stem cell fate. This review discusses these methodologies of 3D bioprinting stem cells. Fabricating a fully operational tissue or organ construct with a long life will be the most significant challenge of 3D bioprinting. Once this is achieved, a whole human organ can be fabricated for the defect place at the site of surgery.

Laser Surface Microstructuring of a Bio-Resorbable Polymer to Anchor Stem Cells, Control Adipocyte Morphology, and Promote Osteogenesis

New strategies in regenerative medicine include the implantation of stem cells cultured in bio-resorbable polymeric scaffolds to restore the tissue function and be absorbed by the body after wound healing. This requires the development of appropriate micro-technologies for manufacturing of functional scaffolds with controlled surface properties to induce a specific cell behavior. The present report focuses on the effect of substrate topography on the behavior of human mesenchymal stem cells (MSCs) before and after co-differentiation into adipocytes and osteoblasts. Picosecond laser micromachining technology (PLM) was applied on poly (L-lactide) (PLLA), to generate different microstructures (microgrooves and microcavities) for investigating cell shape, orientation, and MSCs co-differentiation. Under certain surface topographical conditions, MSCs modify their shape to anchor at specific groove locations. Upon MSCs differentiation, adipocytes respond to changes in substrate height and depth by adapting the intracellular distribution of their lipid vacuoles to the imposed physical constraints. In addition, topography alone seems to produce a modest, but significant, increase of stem cell differentiation to osteoblasts. These findings show that PLM can be applied as a high-efficient technology to directly and precisely manufacture 3D microstructures that guide cell shape, control adipocyte morphology, and induce osteogenesis without the need of specific biochemical functionalization.

Electroactive polymers for tissue regeneration: Developments and perspectives

Human body motion can generate a biological electric field and a current, creating a voltage gradient of -10 to -90 mV across cell membranes. In turn, this gradient triggers cells to transmit signals that alter cell proliferation and differentiation. Several cell types, counting osteoblasts, neurons and cardiomyocytes, are relatively sensitive to electrical signal stimulation. Employment of electrical signals in modulating cell proliferation and differentiation inspires us to use the electroactive polymers to achieve electrical stimulation for repairing impaired tissues. Electroactive polymers have found numerous applications in biomedicine due to their capability in effectively delivering electrical signals to the seeded cells, such as biosensing, tissue regeneration, drug delivery, and biomedical implants. Here we will summarize the electrical characteristics of electroactive polymers, which enables them to electrically influence cellular function and behavior, including conducting polymers, piezoelectric polymers, and polyelectrolyte gels. We will also discuss the biological response to these electroactive polymers under electrical stimulation. In particular, we focus this review on their applications in regenerating different tissues, including bone, nerve, heart muscle, cartilage and skin. Additionally, we discuss the challenges in tissue regeneration applications of electroactive polymers. We conclude that electroactive polymers have a great potential as regenerative biomaterials, due to their ability to stimulate desirable outcomes in various electrically responsive cells.

Reliable laser fabrication: the quest for responsive biomaterials surface

This review presents current efforts in laser fabrication, focusing on the surface features of biomaterials and their biological responses; this provides insight into the engineering of bio-responsive surfaces for future medical devices.

Generation of a co-culture cell micropattern model to simulate lung cancer bone metastasis for anti-cancer drug evaluation

A549/OB co-culture micropattern was fabricated through μ-eraser strategy to mimic lung cancer bone metastasis for DOX efficacy evaluation.

Relationship between nanotopographical alignment and stem cell fate with live imaging and shape analysis

The topography of a biomaterial regulates cellular interactions and determine stem cell fate. A complete understanding of how topographical properties affect cell behavior will allow the rational design of material surfaces that elicit specified biological functions once placed in the body. To this end, we fabricate substrates with aligned or randomly organized fibrous nanostructured topographies. Culturing adipose-derived stem cells (ASCs), we explore the dynamic relationship between the alignment of topography, cell shape and cell differentiation to osteogenic and myogenic lineages. We show aligned topographies differentiate cells towards a satellite cell muscle progenitor state - a distinct cell myogenic lineage responsible for postnatal growth and repair of muscle. We analyze cell shape between the different topographies, using fluorescent time-lapse imaging over 21 days. In contrast to previous work, this allows the direct measurement of cell shape at a given time rather than defining the morphology of the underlying topography and neglecting cell shape. We report quantitative metrics of the time-based morphological behaviors of cell shape in response to differing topographies. This analysis offers insights into the relationship between topography, cell shape and cell differentiation. Cells differentiating towards a myogenic fate on aligned topographies adopt a characteristic elongated shape as well as the alignment of cells.

Automated Robotic Dispensing Technique for Surface Guidance and Bioprinting of Cells

This manuscript describes the introduction of cell guidance features followed by the direct delivery of cells to these features in a hydrogel bioink using an automated robotic dispensing system. The particular bioink was selected as it allows cells to sediment towards and sense the features. The dispensing system bioprints viable cells in hydrogel bioinks using a backpressure assisted print head. However, by replacing the print head with a sharpened stylus or scalpel, the dispensing system can also be employed to create topographical cues through surface etching. The stylus movement can be programmed in steps of 10 µm in the X, Y and Z directions. The patterned grooves were able to orientate mesenchymal stem cells, influencing them to adopt an elongated morphology in alignment with the grooves' direction. The patterning could be designed using plotting software in straight lines, concentric circles, and sinusoidal waves. In a subsequent procedure, fibroblasts and mesenchymal stem cells were suspended in a 2% gelatin bioink, for bioprinting in a backpressure driven extrusion printhead. The cell bearing bioink was then printed using the same programmed coordinates used for the etching. The bioprinted cells were able to sense and react to the etched features as demonstrated by their elongated orientation along the direction of the etched grooves.

Bioprinting and Differentiation of Stem Cells

The 3D bioprinting of stem cells directly into scaffolds offers great potential for the development of regenerative therapies; in particular for the fabrication of organ and tissue substitutes. For this to be achieved; the lineage fate of bioprinted stem cell must be controllable. Bioprinting can be neutral; allowing culture conditions to trigger differentiation or alternatively; the technique can be designed to be stimulatory. Such factors as the particular bioprinting technique; bioink polymers; polymer cross-linking mechanism; bioink additives; and mechanical properties are considered. In addition; it is discussed that the stimulation of stem cell differentiation by bioprinting may lead to the remodeling and modification of the scaffold over time matching the concept of 4D bioprinting. The ability to tune bioprinting properties as an approach to fabricate stem cell bearing scaffolds and to also harness the benefits of the cells multipotency is of considerable relevance to the field of biomaterials and bioengineering.

Development and Characterization of Organic Electronic Scaffolds for Bone Tissue Engineering

Bones have been shown to exhibit piezoelectric properties, generating electrical potential upon mechanical deformation and responding to electrical stimulation with the generation of mechanical stress. Thus, the effects of electrical stimulation on bone tissue engineering have been extensively studied. However, in bone regeneration applications, only few studies have focused on the use of electroactive 3D biodegradable scaffolds at the interphase with stem cells. Here a method is described to combine the bone regeneration capabilities of 3D-printed macroporous medical grade polycaprolactone (PCL) scaffolds with the electrical and electrochemical capabilities of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). PCL scaffolds have been highly effective in vivo as bone regeneration grafts, and PEDOT is a leading material in the field of organic bioelectronics, due to its stability, conformability, and biocompatibility. A protocol is reported for scaffolds functionalization with PEDOT, using vapor-phase polymerization, resulting in a conformal conducting layer. Scaffolds' porosity and mechanical stability, important for in vivo bone regeneration applications, are retained. Human fetal mesenchymal stem cells proliferation is assessed on the functionalized scaffolds, showing the cytocompatibility of the polymeric coating. Altogether, these results show the feasibility of the proposed approach to obtain electroactive scaffolds for electrical stimulation of stem cells for regenerative medicine.

The Regulation of Cellular Responses to Mechanical Cues by Rho GTPases

The Rho GTPases regulate many cellular signaling cascades that modulate cell motility, migration, morphology and cell division. A large body of work has now delineated the biochemical cues and pathways, which stimulate the GTPases and their downstream effectors. However, cells also respond exquisitely to biophysical and mechanical cues such as stiffness and topography of the extracellular matrix that profoundly influence cell migration, proliferation and differentiation. As these cellular responses are mediated by the actin cytoskeleton, an involvement of Rho GTPases in the transduction of such cues is not unexpected. In this review, we discuss an emerging role of Rho GTPase proteins in the regulation of the responses elicited by biophysical and mechanical stimuli.

Micropatterning Extracellular Matrix Proteins on Electrospun Fibrous Substrate Promote Human Mesenchymal Stem Cell Differentiation Toward Neurogenic Lineage

In this study, hybrid micropatterned grafts constructed via a combination of microcontact printing and electrospinning techniques process were utilized to investigate the influencing of patterning directions on human mesenchymal stem cells (hMSCs) differentiation to desired phenotypes. We found that the stem cells could align and elongate along the direction of the micropattern, where they randomly distributed on nonmicropatterned surfaces. Concomitant with patterning effect of component on stem cell alignment, a commensurate increase on the expression of neural lineage commitment markers, such as microtubule associated protein 2 (MAP2), Nestin, NeuroD1, and Class III β-Tubulin, were revealed from mRNA expression by quantitative Real Time PCR (qRT-PCR) and MAP2 expression by immunostaining. In addition, the effect of electrospun fiber orientation on cell behaviors was further examined. An angle of 45° between the direction of micropatterning and orientation of aligned fibers was verified to greatly prompt the outgrowth of filopodia and neurogenesis of hMSCs. This study demonstrates that the significance of hybrid components and electrospun fiber alignment in modulating cellular behavior and neurogenic lineage commitment of hMSCs, suggesting promising application of porous scaffolds with smart component and topography engineering in clinical regenerative medicine.

Induction of predominant tenogenic phenotype in human dermal fibroblasts via synergistic effect of TGF-β and elongated cell shape

Micropattern topography is widely investigated for its role in mediating stem cell differentiation, but remains unexplored for phenotype switch between mature cell types. This study investigated the potential of inducing tenogenic phenotype in human dermal fibroblasts (hDFs) by artificial elongation of cultured cells. Our results showed that a parallel microgrooved topography could convert spread hDFs into an elongated shape and induce a predominant tenogenic phenotype as the expression of biomarkers was significantly enhanced, such as scleraxis, tenomodulin, collagens I, III, VI, and decorin. It also enhanced the expression of transforming growth factor (TGF)-β1, but not α-smooth muscle actin. Elongated hDFs failed to induce other phenotypes, such as adiopogenic, chondrogenic, neurogenic, and myogenic lineages. By contrast, no tenogenic phenotype could be induced in elongated human chondrocytes, although chondrogenic phenotype was inhibited. Exogenous TGF-β1 could enhance the tenogenic phenotype in elongated hDFs at low dose (2 ng/ml), but promoted myofibroblast transdifferentiation of hDFs at high dose (10 ng/ml), regardless of cell shape. Elongated shape also resulted in decreased RhoA activity and increased Rho-associated protein kinase (ROCK) activity. Antagonizing TGF-β or inhibiting ROCK activity with Y27632 or depolymerizing actin with cytochalasin D could all significantly inhibit tenogenic phenotype induction, particularly in elongated hDFs. In conclusion, elongation of cultured dermal fibroblasts can induce a predominant tenogenic phenotype likely via synergistic effect of TGF-β and cytoskeletal signaling.

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.

Femtosecond laser induced periodic surface structure on poly-L-lactic acid

Laser-induced periodic surface structure (LIPSS) is one of the most remarkable nanostructures formed only by a simple procedure of laser irradiation that enables to control cell behaviors. To the best of our knowledge, however, LIPSS formation on a scaffold-usable biodegradable polymer had not been succeede d probably due to relatively-low glass transition temperature and melting temperature of such polymers. In this study, we demonstrate LIPSS formation on a poly-L-lactic acid (PLLA), a versatile biodegradable polymer which has been widely used in clinical practice. Experimental results revealed that the repetition rate of femtosecond laser is one of the key parameters for LIPSS formation on PLLA, suggesting that thermal properties and photochemical reactions should be considered. The present study expands the potential of femtosecond laser processing for fabrication of highly-biocompatible scaffold in tissue engineering.

Multifunctional wettability patterns prepared by laser processing on superhydrophobic TiO2nanostructured surfaces

An ultrafast laser technique is developed to construct a three-dimensional pattern with high wettability contrast on a superhydrophobic TiO₂nanotube array surface for droplet manipulation and biomedical scaffold.

Modulating human mesenchymal stem cell plasticity using micropatterning technique

In our previous work, we have reported that enforced elongation of human mesenchymal stem cells (hMSCs) through micropatterning promoted their myocardial lineage commitment. However, whether this approach is robust enough to retain the commitment when subsequently subjected to different conditions remains unsolved. This de-differentiation, if any, would have significant implication on the application of these myocardial-like hMSCs either as tissue engineered product or in stem cell therapy. Herein, we investigated the robustness of micropatterning induced differentiation by evaluating the retention of myocardial differentiation in patterned hMSCs when challenged with non-myocardial differentiation cues. Altogether, we designed four groups of experiments; 1) Patterned hMSCs cultured in normal growth medium serving as a positive control; 2) Patterned hMSCs cultured in normal growth medium for 14 days followed by osteogenic and adipogenic media for next 7 days (to study the robustness of the effect of micropatterning); 3) Patterned hMSCs (initially grown in normal growth medium for 14 days) trypsinized and recultured in different induction media for next 7 days (to study the robustness of the effect of micropatterning without any shape constrain) and 4) Patterned hMSCs cultured in osteogenic and adipogenic media for 14 days (to study the effects of biochemical cues versus biophysical cues). It was found that hMSCs that were primed to commit to myocardial lineage (Groups 2 and 3) were able to maintain myocardial lineage commitment despite subsequent culturing in osteogenic and adipogenic media. However, for hMSCs that were not primed (Group 4), the biochemical cues seem to dominate over the biophysical cue in modulating hMSCs differentiation. It demonstrates that cell shape modulation is not only capable of inducing stem cell differentiation but also ensuring the permanent lineage commitment.

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.

Microfabrication and microfluidics for muscle tissue models

The relatively recent development of microfluidic systems with wide-ranging capabilities for generating realistic 2D or 3D systems with single or multiple cell types has given rise to an extensive collection of platform technologies useful in muscle tissue engineering. These new systems are aimed at (i) gaining fundamental understanding of muscle function, (ii) creating functional muscle constructs in vitro, and (iii) utilizing these constructs a variety of applications. Use of microfluidics to control the various stimuli that promote differentiation of multipotent cells into cardiac or skeletal muscle is first discussed. Next, systems that incorporate muscle cells to produce either 2D sheets or 3D tissues of contractile muscle are described with an emphasis on the more recent 3D platforms. These systems are useful for fundamental studies of muscle biology and can also be incorporated into drug screening assays. Applications are discussed for muscle actuators in the context of microrobotics and in miniaturized biological pumps. Finally, an important area of recent study involves coculture with cell types that either activate muscle or facilitate its function. Limitations of current designs and the potential for improving functionality for a wider range of applications is also discussed, with a look toward using current understanding and capabilities to design systems of greater realism, complexity and functionality.

Enhancing mesenchymal stem cell response using uniaxially stretched poly(ε-caprolactone) film micropatterns for vascular tissue engineering application

Regeneration of tunica media with anisotropic architecture still remains a challenging issue for vascular tissue engineering (TE). Herein, we present the development of flexible poly(ε-caprolactone) (PCL) film micropatterns to regulate mesenchymal stem cells (MSCs) function for tunica media construction. Results showed that uniaxial thermal stretching of PCL films resulted in topographical micropatterns comprising of ridges/grooves, and improved mechanical properties, including yield stress, Young's modulus, and fracture stress without sacrificing film elasticity. Culturing on such PCL film micropatterns, MSCs self-aligned along the ridges with a more elongated morphology as compared to that of the un-stretched film group. Moreover, MSCs obtained a contractile SMCs-like phenotype, with ordered organization of cellular stress filaments and upregulated expression of the contractile makers, including SM-α-actin, calponin, and SM-MHC. The PCL film micropatterns could be rolled into a small-diameter 3D tubular scaffold with circumferential anisotropy of ridges/grooves, and in the incorporation of MSCs, which facilitated a hybrid sandwich-like vascular wall construction with ordered cell architecture similar to that of the tunica media. These results provide insights of how geometric cues are able to regulate stem cells with desired functions and have significant implications for the designing of a functionalized vascular TE scaffold with appropriate topographical geometries for guiding tunica media regeneration with microscale control of cell alignment and genetic expression.

Stem cell delivery systems inspired by tissue-specific niches

Since stem cells have the capacity to differentiate into a variety of cell types, stem cell delivery systems (SCDSs) can be effective therapeutic strategies for a multitude of diseases and disorders. For stem cell-based therapy, stem cells are introduced directly (or peripherally) into a target tissue via different delivery systems. Despite initial promising results obtained from preclinical studies, a number of technical hurdles must be overcome for ultimate clinical utility of stem cells. A key aspect of SCDSs is how to create local environments, called stem cell niches, for improvement of survival and engraftment as well as the fate of transplanted stem cells. The stem cell niches encompassing a wide range of biochemical, biophysical, and biomechanical cues play a guidance role to modulate stem cell behaviors such as adhesion, proliferation, and differentiation. Recent studies have tried to decipher the complex interplay between stem cells and niches, and thereafter to engineer SCDS, mimicking dynamic stem cell niches encompassing a wide range of biochemical, biophysical, and biomechanical cues. Here, we discuss the biological role of stem cell niches and highlight recent progress in SCDS to mimic stem cell niches, particularly focusing on important biomaterial properties for modulating stem cell fate.

Induction of myogenic differentiation of human mesenchymal stem cells cultured on Notch agonist (Jagged-1) modified biodegradable scaffold surface

Engineered scaffold surface provides stem cells with vital cues that could determine the eventual fate of stem cells. In this work, biodegradable poly(L-lactide-co-ε-caprolactone) (PLCL) scaffold conjugated with Notch agonist-Jagged-1(JAG) peptide (2.1 kDa) was prepared to initiate myogenic differentiation of human mesenchymal stem cells (hMSCs). The scaffold surface was activated with oxygen plasma and acrylic acid was engrafted via UV polymerization to form a surface bearing carboxylic groups. JAG peptide was subsequently immobilized onto the carboxylated scaffold surface. Surface chemistry and topography were examined using attenuated total reflection Fourier transform infrared, X-ray photoelectron spectroscopy, and atomic force microscopy. Quantitative real time polymerase chain reaction analysis revealed activation of the Notch pathway; furthermore, several specific markers associated with myogenic but not osteogenic differentiation were shown to be up-regulated in hMSCs cultured on the engineered surface. The pro-myocardial effect of surface bound JAG peptide was further affirmed via immunodetection of the distinct myocardial marker, cardiac troponin T. Collectively, our results suggest that PLCL conjugated JAG peptide is a viable strategy to enhance the functional potential of scaffolds to be used as a bioengineered cardiac patch in myocardial infarction repair.

A generic micropatterning platform to direct human mesenchymal stem cells from different origins towards myogenic differentiation

Human mesenchymal stem cells (MSCs) derived from various origins show varied differentiation capability. Recent work shows that cell shape manipulation via micropatterning can modulate the differentiation of bone-marrow-derived MSCs. Herein, the effect of micropatterning on the myogenesis of MSCs isolated from three different sources (bone marrow, fetal tissue, and adipose) is reported. All the well-aligned cells, regardless of source, predominantly commit to myogenic lineage, as shown by the significant upregulation of myogenic gene markers and positive myosin heavy chain staining. It is demonstrated that our novel micropattern can be used as a generic platform for inducing myogenesis of MSCs from different sources and may also have the potential to be extended to induce other lineage commitment.

Biomimetic three-dimensional anisotropic geometries by uniaxial stretch of poly(ε-caprolactone) films for mesenchymal stem cell proliferation, alignment, and myogenic differentiation

Anisotropic geometries are critical for eliciting cell alignment to dictate tissue microarchitectures and biological functions. Current fabrication techniques are complex and utilize toxic solvents, hampering their applications for translational research. Here, we present a novel simple, solvent-free, and reproducible method via uniaxial stretching for incorporating anisotropic topographies on bioresorbable films with ambitions to realize stem cell alignment control. Uniaxial stretching of poly(ε-caprolactone) (PCL) films resulted in a three-dimensional micro-ridge/groove topography (inter-ridge-distance: ~6 μm; ridge-length: ~90 μm; ridge-depth: 200-900 nm) with uniform distribution and controllable orientation by the direction of stretch on the whole film surface. When stretch temperature (Ts) and draw ratio (DR) were increased, the inter-ridge-distance was reduced and ridge-length increased. Through modification of hydrolysis, increased surface hydrophilicity was achieved, while maintaining the morphology of PCL ridge/grooves. Upon seeding human mesenchymal stem cells (hMSCs) on uniaxial-stretched PCL (UX-PCL) films, aligned hMSC organization was obtained. Compared to unstretched films, hMSCs on UX-PCL had larger increase in cellular alignment (>85%) and elongation, without indication of cytotoxicity or reduction in cellular proliferation. This aligned hMSC organization was homogenous and stably maintained with controlled orientation along the ridges on the whole UX-PCL surface for over 2 weeks. Moreover, the hMSCs on UX-PCL had a higher level of myogenic genes' expression than that on the unstretched films. We conclude that uniaxial stretching has potential in patterning film topography with anisotropic structures. The UX-PCL in conjunction with hMSCs could be used as "basic units" to create tissue constructs with microscale control of cellular alignment and elongation for tissue engineering applications.

Modulation of osteogenic, adipogenic and myogenic differentiation of mesenchymal stem cells by submicron grooved topography

Topographic cues have been recognized crucial on the modulation of cell behavior, and subsequent important for the design of implants, cell-based biomedical devices and tissue-engineered products. Grooved topography direct cells to align anisotropically on the substrates, resulting in an obvious morphological difference compared with the flat and the other topographies. This study aimed at investigating the effects of grooved topography on the differentiation of mesenchymal stem cells (MSCs) into osteoblasts, adipocytes and myoblasts. A series of submicron-grooved polystyrene substrates with equal groove-to-ridge ratio but different width and depth (width/depth (nm): 450/100, 450/350, 900/100, and 900/550) were fabricated based on electron beam lithography and soft lithography techniques. Primary rat MSCs (rMSCs) were cultured on these substrates without induction for differentiation for 6 days, and then subjected to induction for osteogenesis, adipogenesis and myogenesis. While the alignment of rMSCs strongly complied with the direction of the grooves and increased with groove depths, cell attachment on day 1 (~1.5 × 10(4)/cm(2)) and cell proliferation after 6 days of culture (~5 × 10(4)/cm(2)) were not significantly affected by substrate types. Osteogenesis, indicated by alkaline phosphatase activities and calcium deposit, was not significantly modulated by the grooved substrates, compared with the flat control, suggesting that cell alignment may not determine osteoinduction of rMSCs. On the other hand, adipogenesis, indicated by lipid production, was significantly enhanced by the grooved substrates compared with the flat surface (P < 0.001). On the other hand, myogenesis, indicated by desmin and MHC staining, was enhanced by the grooves in a time- and groove size-dependent manner compared with the flat control. The results suggested that grooved topography has an in-depth potential for modulating the commitment of the stem cell lineages, which could benefit the development of advanced biomaterials for biomedical applications.

Understanding the nano-topography changes and cellular influences resulting from the surface adsorption of human hair keratins

Recent interest in the use of human hair keratins as a biomaterial has grown, fuelled by improvements in keratin extraction methods and better understanding of keratin bioactivity. The use of keratins as a bioactive coating for in vitro cell culture studies is an attractive proposition. In this light, the surface adsorption of human hair keratins onto tissue culture polystyrene surfaces has been investigated. Keratin density, nano-topography and hydrophobicity of keratin coated surfaces were characterized. To understand the cellular influence of these coated surfaces, murine L929 fibroblasts were cultured on them and evaluated for cytotoxicity, proliferation, metabolic activity and detachment behaviors compared to collagen type 1 coated surfaces. Keratins were deposited up to a density of 650 ng/cm(2) when a coating concentration of 80 μg/ml or higher was used. The surface features formed by adsorbed keratins also changed in a coating concentration dependent manner. These surfaces improved L929 mouse fibroblast adhesion and proliferation in comparison to uncoated and collagen type 1 coated tissue culture polystyrene. Furthermore, the expression of fibronectin was accelerated on surfaces coated with solutions of higher keratin concentrations. These results suggest that human hair keratins can be used as a viable surface coating material to enhance substrate compliance for culturing cells.