Multiscale patterned transplantable stem cell patches for bone tissue regeneration

Stem Cell-Laden Engineered Patch: Advances and Applications in Tissue Regeneration

Stem cell-based therapies are emerging as significant approaches in tissue engineering and regenerative medicine, applicable to both fundamental scientific research and clinical practice. Despite remarkable results in clinical studies, challenges such as poor standardization of graft tissues, limited sources, and reduced functionality have hindered the effectiveness of these therapies. In this review, we summarize the engineering approaches involved in fabricating stem cell assisted patches and the substantial strategies for designing stem cell-laden engineered patches (SCP) to complement the existing stem cell-based therapies. We then outline the potential applications of SCP in advancing tissue regeneration and regenerative medicine. By combining living stem cells with engineered patches, SCP can enhance the functions of both components, particularly for tissue engineering applications. Finally, we addressed current challenges, such as ethical considerations, high costs, and regulatory hurdles and proposed future research directions to overcome these barriers.

Liquefied capsules containing nanogrooved microdiscs and umbilical cord-derived cells for bone tissue engineering

Background

Surface topography has been shown to influence cell behavior and direct stromal cell differentiation into distinct lineages. Whereas this phenomenon has been verified in two-dimensional cultures, there is an urgent need for a thorough investigation of topography's role within a three-dimensional (3D) environment, as it better replicates the natural cellular environment.

Methods

A co-culture of Wharton's jelly-derived mesenchymal stem/stromal cells (WJ-MSCs) and human umbilical vein endothelial cells (HUVECs) was encapsulated in a 3D system consisting of a permselective liquefied environment containing freely dispersed spherical microparticles (spheres) or nanogrooved microdiscs (microdiscs). Microdiscs presenting 358 ± 23 nm grooves and 944 ± 49 nm ridges were produced via nanoimprinting of spherical polycaprolactone microparticles between water-soluble polyvinyl alcohol counter molds of nanogrooved templates. Spheres and microdiscs were cultured in vitro with umbilical cord-derived cells in a basal or osteogenic medium within liquefied capsules for 21 days.

Results

WJ-MSCs and HUVECs were successfully encapsulated within liquefied capsules containing spheres and microdiscs, ensuring high cellular viability. Results show an enhanced osteogenic differentiation in microdiscs compared to spheres, even in basal medium, evidenced by alkaline phosphatase activity and osteopontin expression.

Conclusions

This work suggests that the topographical features present in microdiscs induce the osteogenic differentiation of adhered WJ-MSCs along the contact guidance, without additional differentiation factors. The developed 3D bioencapsulation system comprising topographical features might be suitable for bone tissue engineering approaches with minimum in vitro manipulation.

3D cotton-type anisotropic biomimetic scaffold with low fiber motion electrospun via a sharply inclined array collector for induced osteogenesis

Electrospinning is an effective method to fabricate fibrous scaffolds that mimic the ECM of bone tissue on a nano- to macro-scale. However, a limitation of electrospun fibrous scaffolds for bone tissue engineering is the structure formed by densely compacted fibers, which significantly impedes cell infiltration and tissue ingrowth. To address this problem, several researchers have developed numerous techniques for fabricating 3D fibrous scaffolds with customized topography and pore size. Despite the success in developing various 3D electrospun scaffolds based on fiber repulsion, the lack of contact points between fibers in those scaffolds has been shown to hinder cell attachment, migration, proliferation, and differentiation due to excessive movement of the fibers. In this article, we introduce a Dianthus caryophyllus-inspired scaffold fabricated using SIAC-PE, a modified collector under specific viscosity conditions of PCL/LA solution. The developed scaffold mimicking the structural similarities of the nature-inspired design presented enhanced cell proliferation, infiltration, and increased expression of bone-related factors by reducing fiber movements, presenting high space interconnection, high porosity, and controlled fiber topography.

Graphene Hybrid Tough Hydrogels with Nanostructures for Tissue Regeneration

Over the past few decades, hydrogels have attracted considerable attention as promising biomedical materials. However, conventional hydrogels require improved mechanical properties, such as brittleness, which significantly limits their widespread use. Recently, hydrogels with remarkably improved toughness have been developed; however, their low biocompatibility must be addressed. In this study, we developed a tough graphene hybrid hydrogel with nanostructures. The resultant hydrogel exhibited remarkable mechanical properties while representing an aligned nanostructure that resembled the extracellular matrix of soft tissue. Owing to the synergistic effect of the topographical properties, and the enhanced biochemical properties, the graphene hybrid hydrogel had excellent stretchability, resilience, toughness, and biocompatibility. Furthermore, the hydrogel displayed outstanding tissue regeneration capabilities (e.g., skin and tendons). Overall, the proposed graphene hybrid tough hydrogel may provide significant insights into the application of tough hydrogels in tissue regeneration.

Nanotechnology-based bone regeneration in orthopedics: a review of recent trends

Nanotechnology has revolutionized the field of bone regeneration, offering innovative solutions to address the challenges associated with conventional therapies. This comprehensive review explores the diverse landscape of nanomaterials - including nanoparticles, nanocomposites and nanofibers - tailored for bone tissue engineering. We delve into the intricate design principles, structural mimicry of native bone and the crucial role of biomaterial selection, encompassing bioceramics, polymers, metals and their hybrids. Furthermore, we analyze the interface between cells and nanostructured materials and their pivotal role in engineering and regenerating bone tissue. In the concluding outlook, we highlight emerging frontiers and potential research directions in harnessing nanomaterials for bone regeneration.

Artificial Periosteum with Oriented Surface Nanotopography and High Tissue Adherent Property

Massive periosteal defects often significantly impair bone regeneration and repair, which have become a major clinical challenge. Unfortunately, current engineered periosteal materials can hardly currently focus on achieving high tissue adhesion property, being suitable for cell growth, and inducing cell orientation concurrently to meet the properties of nature periosteum. Additionally, the preparation of oriented surface nanotopography often relies on professional equipment. In this study, inspired by the oriented collagen structure of nature periosteum, we present a composite artificial periosteum with a layer of oriented nanotopography surface containing carbon nanotubes (CNTs), cross-linked with adhesive polydopamine (PDA) hydrogel on both terminals. An oriented surface structure that can simulate the oriented alignment of periosteal collagen fibers can be quickly and conveniently obtained via a simple stretching of the membrane in a water bath. With the help of CNTs, our artificial periosteum exhibits sufficient mechanical strength and desired oriented nanotopological structure surface, which further induces the directional arrangement of human bone marrow mesenchymal stem cells (hBMSCs) on the membrane. These oriented hBMSCs express significantly higher levels of osteogenic genes and proteins, while the resultant composite periosteum can be stably immobilized in vivo in the rat model of massive calvarial defect through the PDA hydrogel, which finally shows promising bone regeneration ability. We anticipate that the developed functional artificial periosteum has great potential in biomedical applications for the treatment of composite defects of the bone and periosteum.

Substrate mechanical properties bias MSC paracrine activity and therapeutic potential

Mesenchymal stromal cells (MSCs) have significant therapeutic potential due to their ability to differentiate into musculoskeletal lineages suitable for tissue-engineering, as well as the immunomodulatory and pro-regenerative effects of the paracrine factors that these cells secrete. Cues from the extracellular environment, including physical stimuli such as substrate stiffness, are strong drivers of MSC differentiation, but their effects upon MSC paracrine activity are not well understood. This study, therefore sought to determine the impact of substrate stiffness on the paracrine activity of MSCs, analysing both effects on MSC fate and their effect on T-cell and macrophage activity and angiogenesis. The data show that conditioned medium (CM) from MSCs cultured on 0.2 kPa (soft) and 100 kPa (stiff) polyacrylamide hydrogels have differing effects on MSC proliferation and differentiation, with stiff CM promoting proliferation whilst soft CM promoted differentiation. There were also differences in the effects upon macrophage phagocytosis and angiogenesis, with the most beneficial effects from soft CM. Analysis of the media composition identified differences in the levels of proteins including IL-6, OPG, and TIMP-2. Using recombinant proteins and blocking antibodies, we confirmed a role for OPG in modulating MSC proliferation with a complex combination of factors involved in the regulation of MSC differentiation. Together the data confirm that the physical microenvironment has an important influence on the MSC secretome and that this can alter the differentiation and regenerative potential of the cells. These findings can be used to tailor the culture environment for manufacturing potent MSCs for specific clinical applications or to inform the design of biomaterials that enable the retention of MSC activity after delivery into the body. STATEMENT OF SIGNIFICANCE: • MSCs cultured on 100 kPa matrices produce a secretome that boosts MSC proliferation • MSCs cultured on 0.2 kPa matrices produce a secretome that promotes MSC osteogenesis and adipogenesis, as well as angiogenesis and macrophage phagocytosis • IL-6 secretion is elevated in MSCs on 0.2 kPa substrates • OPG, TIMP-2, MCP-1, and sTNFR1 secretion are elevated in MSCs on 100 kPa substrates.

Hierarchical Topography with Tunable Micro- and Nanoarchitectonics for Highly Enhanced Cardiomyocyte Maturation via Multi-Scale Mechanotransduction

Enhancing cardiomyocyte (CM) maturation by topographical cues is a critical issue in cardiac tissue engineering. Thus far, single-scale topographies with a broad range of feature shapes and dimensions have been utilized including grooves, pillars, and fibers. This study reports for the first time a hierarchical structure composed of nano-pillars (nPs) on micro-wrinkles (µWs) for effective maturation of CMs. Through capillary force lithography followed by a wrinkling process, vast size ranges of topographies are fabricated, and the responses of CMs are systematically investigated. Maturation of CMs on the hierarchical structures is highly enhanced compared to a single-scale topography: cardiac differentiation of H9C2s (rat cardiomyocytes) on the hierarchical topography is ≈ 2.8 and ≈ 1.9 times higher than those consisting of single-scale µWs and nPs. Both nPs and µWs have important roles in cardiac maturation, and the aspect ratio (height/diameter) of the nPs and the wavelength of the µWs are important in CM maturation. This enhancement is caused by strong focal adhesion and nucleus mediated mechanotransduction of CMs from the confinement effects of the different wavelengths of µWs and the cellular membrane protrusion on the nPs. This study demonstrates how a large family of hierarchical structures is used for cardiac maturation.

Tissue-engineered tendon nano-constructs for repair of chronic rotator cuff tears in large animal models

Chronic rotator cuff tears (RCTs) are one of the most common injuries of shoulder pain. Despite the recent advances in surgical techniques and improved clinical outcomes of arthroscopically repaired rotator cuffs (RCs), complete functional recovery-without retear-of the RC tendon through tendon-to-bone interface (TBI) regeneration remains a key clinical goal to be achieved. Inspired by the highly organized nanostructured extracellular matrix in RC tendon tissue, we propose herein a tissue-engineered tendon nano-construct (TNC) for RC tendon regeneration. When compared with two currently used strategies (i.e., transosseous sutures and stem cell injections), our nano-construct facilitated more significant healing of all parts of the TBI (i.e., tendon, fibrocartilages, and bone) in both rabbit and pig RCT models owing to its enhancements in cell proliferation and differentiation, protein expression, and growth factor secretion. Overall, our findings demonstrate the high potential of this transplantable tendon nano-construct for clinical repair of chronic RCTs.

Therapeutic strategies of three-dimensional stem cell spheroids and organoids for tissue repair and regeneration

Three-dimensional (3D) stem cell culture systems have attracted considerable attention as a way to better mimic the complex interactions between individual cells and the extracellular matrix (ECM) that occur in vivo. Moreover, 3D cell culture systems have unique properties that help guide specific functions, growth, and processes of stem cells (e.g., embryogenesis, morphogenesis, and organogenesis). Thus, 3D stem cell culture systems that mimic in vivo environments enable basic research about various tissues and organs. In this review, we focus on the advanced therapeutic applications of stem cell-based 3D culture systems generated using different engineering techniques. Specifically, we summarize the historical advancements of 3D cell culture systems and discuss the therapeutic applications of stem cell-based spheroids and organoids, including engineering techniques for tissue repair and regeneration.

Periosteal topology creates an osteo-friendly microenvironment for progenitor cells

The periosteum on the skeletal surface creates a unique micro-environment for cortical bone homeostasis, but how this micro-environment is formed remains a mystery. In our study, we observed the cells in the periosteum presented elongated spindle-like morphology within the aligned collagen fibers, which is in accordance with the differentiated osteoblasts lining on the cortical surface. We planted the bone marrow stromal cells(BMSCs), the regular shaped progenitor cells, on collagen-coated aligned fibers, presenting similar cell morphology as observed in the natural periosteum. The aligned collagen topology induced the elongation of BMSCs, whichfacilitated the osteogenic process. Transcriptome analysis suggested the aligned collagen induced the regular shaped cells to present part of the periosteum derived stromal cells(PDSCs) characteristics by showing close correlation of the two cell populations. In addition, the elevated expression of PDSCs markers in the cells grown on the aligned collagen-coated fibers further indicated the function of periosteal topology in manipulating cells' behavior. Enrichment analysis revealed cell-extracellular matrix interaction was the major pathway initiating this process, which created an osteo-friendly micro-environment as well. At last, we found the aligned topology of collagen induced mechano-growth factor expression as the result of Igf1 alternative splicing, guiding the progenitor cells behavior and osteogenic process in the periosteum. This study uncovers the key role of the aligned topology of collagen in the periosteum and explains the mechanism in creating the periosteal micro-environment, which gives the inspiration for artificial periosteum design.

Therapeutic strategies and enhanced production of stem cell-derived exosomes for tissue regeneration

Exosomes are nanovesicles surrounded by a plasma membrane and carry bioactive molecules (e.g., proteins, lipids, and nucleic acids) of the origin cell type. The bioactive molecules delivered by exosomes to the recipient cells have attracted considerable attention, as they play an important role in intercellular communication. Moreover, exosomes have unique properties, including the ability to penetrate the biological barrier with minimal immunogenicity and side effects, which can influence various physiological and pathological processes. Thus, exosomes are a promising therapeutic platform for various diseases (e.g., malignancies and allergies), as well as for the regeneration of damaged tissues. However, challenges of obtaining exosomes, such as complex extraction procedures, low yield, and difficulty in quantification are yet to be overcome, which limits the use of exosomes in clinical settings. In this review, we describe the state-of-the-art engineering techniques and strategies for highly efficient mass production of exosomes. Moreover, we discuss the functional aspects and potential therapeutic applications of stem cell-derived exosomes, and deliberate upon various engineering techniques and platform combinations for improved tissue regeneration by exosomes.

3D-printed bioactive ceramic scaffolds with biomimetic micro/nano-HAp surfaces mediated cell fate and promoted bone augmentation of the bone–implant interface in vivo

Calcium phosphate bio-ceramics are osteo-conductive, but it remains a challenge to promote the induction of bone augmentation and capillary formation. The surface micro/nano-topography of materials can be recognized by cells and then the cell fate are mediated. Traditional regulation methods of carving surface structures on bio-ceramics employ mineral reagents and organic additives, which might introduce impurity phases and affect the biological results. In a previous study, a facile and novel method was utilized with ultrapure water as the unique reagent for hydrothermal treatment, and a uniform hydroxyapatite (HAp) surface layer was constructed on composite ceramics (β-TCP/CaSiO₃) in situ. Further combined with 3D printing technology, biomimetic hierarchical structure scaffolds were fabricated with interconnected porous composite ceramic scaffolds as the architecture and micro/nano-rod hybrid HAp as the surface layer. The obtained HAp surface layer favoured cell adhesion, alleviated the cytotoxicity of precursor scaffolds, and upregulated the cellular differentiation of mBMSCs and gene expression of HUVECs in vitro. In vivo studies showed that capillary formation, bone augmentation and new bone matrix formation were upregulated after the HAp surface layer was obtained, and the results confirmed that the fabricated biomimetic hierarchical structure scaffold could be an effective candidate for bone regeneration.

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Simple and practical process to construct surface structure layer in situ with little impurities.

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Combined with the 3D printing technology to fabricate architecture of the pre-treated matrix.

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Study the angiogenesis and osteogenesis (for mesenchymal stem cells) separately.

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Improving tissue growth in vivo: capillary formation, bone-augmentation and new bone matrix formation.

Improve endothelialization of metallic cardiovascular stent via femtosecond laser induced micro/nanostructure dependent cells proliferation and drug delivery control

Regarding restenosis occurrence risk after metallic stent deployment in artery, stents with vascular smooth muscle cells antiproliferative agents sustained released from poly(lactic-co-glycolic acid) (PLGA) coating and endothelial cells proliferation favored surface textures were both attempted for endothelialization enhancement. In order to explore the interaction between the surface texture and performance of drug loaded PLGA coating, femtosecond laser surface treatment was used to change the surface characteristics of 316L stainless steel. Two different surface patterns in form of stripe (FSL100) and isolated island-like structure (FSL800) were firstly generated by femtosecond laser processing with 100 and 800 mW energy, then Rapamycin loaded PLGA coating was further deposited to polished and femtosecond laser processed 316L surfaces via a dip-coating method. The subsequent drug loading capacity and release profile studies confirmed the roles of surface texture. Morphological transition characteristics of the PLGA coating on the FLS100 sample indicate that the coating has integrity during degradation compared to the polished one. Finally, rapamycin eluting FLS100 stent was deployed to iliac arteries of New Zealand White rabbits with vascular plaques to demonstrate its endothelialization potential and resistance to restenosis.

Developing biomaterials to mediate the spatial distribution of integrins

Innovation in material design to regulate cell behavior and function is one of the primary tasks in materials science. Integrins, a family of cell surface-adhesion receptors that mechanically connect the extracellular matrix (ECM) to the intracellular cytoskeleton, have long served as primary targets for the design of biomaterials because their activity is not only critical to a wide range of cell and tissue functions but also subject to very tight and complex regulations from the outside environment. To review the recent progress of material innovations targeting the spatial distribution of integrins, we first introduce the interaction mechanisms between cells and the ECM by highlighting integrin-based cell adhesions, describing how integrins respond to environmental stimuli, including variations in ligand presentation, mechanical cues, and topographical variations. Then, we overview the current development of soft materials in guiding cell behaviors and functions via spatial regulation of integrins. Finally, we discuss the current limitations of these technologies and the advances that may be achieved in the future. Undoubtedly, synthetic soft materials that mediate the spatial distribution of integrins play an important role in biomaterial innovations for advancing biomedical applications and addressing fundamental biological questions.

Plasma-assisted multiscale topographic scaffolds for soft and hard tissue regeneration

The design of transplantable scaffolds for tissue regeneration requires gaining precise control of topographical properties. Here, we propose a methodology to fabricate hierarchical multiscale scaffolds with controlled hydrophilic and hydrophobic properties by employing capillary force lithography in combination with plasma modification. Using our method, we fabricated biodegradable biomaterial (i.e., polycaprolactone (PCL))-based nitrogen gas (N-FN) and oxygen gas plasma-assisted flexible multiscale nanotopographic (O-FMN) patches with natural extracellular matrix-like hierarchical structures along with flexible and controlled hydrophilic properties. In response to multiscale nanotopographic and chemically modified surface cues, the proliferation and osteogenic mineralization of cells were significantly promoted. Furthermore, the O-FMN patch enhanced regeneration of the mineralized fibrocartilage tissue of the tendon-bone interface and the calvarial bone tissue in vivo in rat models. Overall, the PCL-based O-FMN patches could accelerate soft- and hard-tissue regeneration. Thus, our proposed methodology was confirmed as an efficient approach for the design and manipulation of scaffolds having a multiscale topography with controlled hydrophilic property.

Enhanced Osteogenesis of Dental Pulp Stem Cells In Vitro Induced by Chitosan-PEG-Incorporated Calcium Phosphate Cement

The use of bone graft materials is required for the treatment of bone defects damaged beyond the critical defect; therefore, injectable calcium phosphate cement (CPC) is actively used after surgery. The application of various polymers to improve injectability, mechanical strength, and biological function of injection-type CPC is encouraged. We previously developed a chitosan–PEG conjugate (CS/PEG) by a sulfur (VI) fluoride exchange reaction, and the resulting chitosan derivative showed high solubility at a neutral pH. We have demonstrated the CPC incorporated with a poly (ethylene glycol) (PEG)-grafted chitosan (CS/PEG) and developed CS/PEG CPC. The characterization of CS/PEG CPC was conducted using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The initial properties of CS/PEG CPCs, such as the pH, porosity, mechanical strength, zeta potential, and in vitro biocompatibility using the WST-1 assay, were also investigated. Moreover, osteocompatibility of CS/PEG CPCs was carried out via Alizarin Red S staining, immunocytochemistry, and Western blot analysis. CS/PEG CPC has enhanced mechanical strength compared to CPC, and the cohesion test also demonstrated in vivo stability. Furthermore, we determined whether CS/PEG CPC is a suitable candidate for promoting the osteogenic ability of Dental Pulp Stem Cells (DPSC). The elution of CS/PEG CPC entraps more calcium ion than CPC, as confirmed through the zeta potential test. Accordingly, the ion trapping effect of CS/PEG is considered to have played a role in promoting osteogenic differentiation of DPSCs. The results strongly suggested that CS/PEG could be used as suitable additives for improving osteogenic induction of bone substitute materials.

Nano-Topographical Control of Ti-Nb-Zr Alloy Surfaces for Enhanced Osteoblastic Response

Nano-scale surface roughening of metallic bio-implants plays an important role in the clinical success of hard tissue reconstruction and replacement. In this study, the nano-topographical features of titanium-niobium-zirconium (TNZ) alloy surfaces were controlled by using the target-ion induced plasma sputtering (TIPS) technique to improve the in vitro osteoblastic response. The TIPS technique is a novel strategy for etching the surface of metallic bio-implants using bombardment of target metal cations, which were accelerated by an extremely high negative bias voltage applied to the substrates. The nano-topography of the TNZ surfaces was successfully controlled by modulating experimental variables (such as the ion etching energy and the type of substrate or target materials) of TIPS. As a result, various nanopatterns (size: 10–210 nm) were fabricated on the surface of the TNZ alloys. Compared with the control group, experimental groups with nanopattern widths of ≥130 nm (130 and 210 nm groups) exhibited superior cell adhesion, proliferation, and differentiation. Our findings demonstrate that TIPS is a promising technology that can impart excellent biological functions to the surface of metallic bio-implants.

Periosteal Tissue Engineering: Current Developments and Perspectives

Periosteum, a highly vascularized bilayer connective tissue membrane plays an indispensable role in the repair and regeneration of bone defects. It is involved in blood supply and delivery of progenitor cells and bioactive molecules in the defect area. However, sources of natural periosteum are limited, therefore, there is a need to develop tissue-engineered periosteum (TEP) mimicking the composition, structure, and function of natural periosteum. This review explores TEP construction strategies from the following perspectives: i) different materials for constructing TEP scaffolds; ii) mechanical properties and surface topography in TEP; iii) cell-based strategies for TEP construction; and iv) TEP combined with growth factors. In addition, current challenges and future perspectives for development of TEP are discussed.

Radially patterned transplantable biodegradable scaffolds as topographically defined contact guidance platforms for accelerating bone regeneration

BACKGROUND

The healing of large critical-sized bone defects remains a clinical challenge in modern orthopedic medicine. The current gold standard for treating critical-sized bone defects is autologous bone graft; however, it has critical limitations. Bone tissue engineering has been proposed as a viable alternative, not only for replacing the current standard treatment, but also for producing complete regeneration of bone tissue without complex surgical treatments or tissue transplantation. In this study, we proposed a transplantable radially patterned scaffold for bone regeneration that was defined by capillary force lithography technology using biodegradable polycaprolactone polymer.

RESULTS

The radially patterned transplantable biodegradable scaffolds had a radial structure aligned in a central direction. The radially aligned pattern significantly promoted the recruitment of host cells and migration of osteoblasts into the defect site. Furthermore, the transplantable scaffolds promoted regeneration of critical-sized bone defects by inducing cell migration and differentiation.

CONCLUSIONS

Our findings demonstrated that topographically defined radially patterned transplantable biodegradable scaffolds may have great potential for clinical application of bone tissue regeneration.

Eggshell membrane as a bioactive agent in polymeric nanotopographic scaffolds for enhanced bone regeneration

A bone regeneration scaffold is typically designed as a platform to effectively heal a bone defect while preventing soft tissue infiltration. Despite the wide variety of scaffold materials currently available, such as collagen, critical problems in achieving bone regeneration remain, including a rapid absorption period and low tensile strength as well as high costs. Inspired by extracellular matrix protein and topographical cues, we developed a polycaprolactone-based scaffold for bone regeneration using a soluble eggshell membrane protein (SEP) coating and a nanotopography structure for enhancing the physical properties and bioactivity. The scaffold exhibited adequate flexibility and mechanical strength as a biomedical platform for bone regeneration. The highly aligned nanostructures and SEP coating were found to regulate and enhance cell morphology, adhesion, proliferation, and differentiation in vitro. In a calvaria bone defect mouse model, the scaffolds coated with SEP applied to the defect site promoted bone regeneration along the direction of the nanotopography in vivo. These findings demonstrate that bone-inspired nanostructures and SEP coatings have high potential to be applicable in the design and manipulation of scaffolds for bone regeneration.

Application of Inorganic Nanocomposite Hydrogels in Bone Tissue Engineering

Bone defects caused by trauma and surgery are common clinical problems encountered by orthopedic surgeons. Thus, a hard-textured, natural-like biomaterial that enables encapsulated cells to obtain the much-needed biophysical stimulation and produce functional bone tissue is needed. Incorporating nanomaterials into cell-laden hydrogels is a straightforward tactic for producing tissue engineering structures that integrate perfectly with the body and for tailoring the material characteristics of hydrogels without hindering nutrient exchange with the surroundings. In this review, recent developments in inorganic nanocomposite hydrogels for bone tissue engineering that are of vital importance but have not yet been comprehensively reviewed are summarized.

Synergistic effects of gelatin and nanotopographical patterns on biomedical PCL patches for enhanced mechanical and adhesion properties

Biomedical patches have been known as important biomaterial-based medical devices for the clinical treatment of tissue and organ diseases. Inspired by the extracellular matrix-like aligned nanotopographical pattern as well as the unique physical and biocompatible properties of gelatin, we developed strength-enhanced biomedical patches by coating gelatin onto the nanopatterned surface of polycaprolactone (PCL). The relative contributions of the nanotopographical pattern (physical factor) and gelatin coating (chemical factor) in enhancing the mechanical and adhesive properties of PCL were quantitatively investigated. The nanotopographical pattern increased the surface area of PCL, allowing more gelatin to be coated on its surface. The biomedical patch made from gelatin-coated nanopatterned PCL showed strong mechanical and adhesive properties (tensile strength: ~14.5 MPa; Young's modulus: ~60.2 MPa; and normal and shear adhesive forces: ~1.81 N/cm² and ~352.3 kPa) as well as good biocompatibility. Although the nanotopographical pattern or gelatin coating alone could enhance these physical properties of PCL in both dry and wet environmental conditions, both factors in combination further strengthened the properties, indicating the importance of synergistic cues in driving the mechanical behavior of biomedical materials. This strength-enhanced biomedical patch will be especially useful for the treatment of tissues such as cartilage, tendon, and bone.

Smart Surface-Enhanced Resonance Raman Scattering Nanoprobe for Monitoring Cellular Alkaline Phosphatase Activity during Osteogenic Differentiation

High-efficiency induction of bone marrow mesenchymal stem cells (BMSCs) to osteogenic differentiation in vitro can help solve a series of bone diseases such as bone injury, fracture repair, and osteoporosis. In order to explore the optimal conditions for different chemical inducers to promote BMSCs differentiation and the possible differentiation mechanisms, we developed a smart nanoprobe that can achieve in situ alkaline phosphatase (ALP) activity detection during osteogenic differentiation in cells. The smart nanoprobe (Au@BCIP) was designed as the surface decoration of gold nanoparticles (AuNPs) with 5-bromo-4-chloro-3-indolyl phosphate (BCIP). The nanoprobe was co-cultured with differentiated BMSCs at different stages to monitor ALP activity based on an ALP-catalyzed hydrolysis reaction with BCIP as a substrate. The product can be quickly oxidized by dissolved oxygen to obtain a Raman-active species (5,5'-dibromo-4,4'-dichloro-1H,1H-[2,2'] biindolylidene-3,3'-dione). The SERS sensitivity was greatly improved by resonating the excitation wavelength of 632.8 nm. It is a new strategy for tracing bone disease-related ALP activity in an in vivo model with high sensitivity and selectivity and non-invasion. By using this nanoprobe, osteogenic differentiation of cells under osteogenic supplements was assessed and the p38 MAPK signaling pathway for osteogenic differentiation was experimentally evidenced, which are of significance for understanding BMSCs and regulating their osteogenic differentiation process.

Tendon-Inspired Nanotopographic Scaffold for Tissue Regeneration in Rotator Cuff Injuries

Acute and chronic rotator cuff (RC) tears are common etiologies of shoulder disabilities. Despite the advanced surgical techniques and graft materials available for tendon repair, the high re-tear rate remains a critical challenge in RC healing. Inspired by the highly organized nanotopography of the extracellular matrix (ECM) in tendon tissue of the shoulder, nanotopographic scaffolds are developed using polycaprolactone for the repair and regeneration of RC tendons. The scaffolds show appropriate flexibility and mechanical properties for application in tendon tissue regeneration. It is found that the highly aligned nanotopographic cues of scaffolds could sensitively control and improve the morphology, attachment, proliferation, and differentiation of tendon-derived cells as well as promote their wound healing capacity in vitro. In particular, this study showed that the scaffolds could promote tendon regeneration along the direction of the nanotopography in the rabbit models of acute and chronic RC tears. Nanotopographic scaffold-augmented rotator cuff repair showed a more appropriate healing pattern compared to the control groups in a rabbit RC tear model. We demonstrated that the tendon ECM-like nanoscale structural cues of the tendon-inspired patch may induce the more aligned tissue regeneration of the underlying tissues including tendon-to-bone interface.

Mechanochemical Patternable ECM-Mimetic Hydrogels for Programmed Cell Orientation

Native human tissues are supported by a viscoelastic extracellular matrix (ECM) that can adapt its intricate network to dynamic mechanical stimuli. To recapitulate the unique ECM biofunctionality, hydrogel design is shifting from typical covalent crosslinks toward covalently adaptable networks. To pursue such properties, herein hybrid polysaccharide-polypeptide networks are designed based on dynamic covalent assembly inspired by natural ECM crosslinking processes. This is achieved through the synthesis of an amine-reactive oxidized-laminarin biopolymer that can readily crosslink with gelatin (oxLAM-Gelatin) and simultaneously allow cell encapsulation. Interestingly, the rational design of oxLAM-Gelatin hydrogels with varying aldehyde-to-amine ratios enables a refined control over crosslinking kinetics, viscoelastic properties, and degradability profile. The mechanochemical features of these hydrogels post-crosslinking offer an alternative route for imprinting any intended nano- or microtopography in ECM-mimetic matrices bearing inherent cell-adhesive motifs. Different patterns are easily paved in oxLAM-Gelatin under physiological conditions and complex topographical configurations are retained along time. Human adipose-derived mesenchymal stem cells contacting mechanically sculpted oxLAM-Gelatin hydrogels sense the underlying surface nanotopography and align parallel to the anisotropic nanoridge/nanogroove intercalating array. These findings demonstrate that covalently adaptable features in ECM-mimetic networks can be leveraged to combine surface topography and cell-adhesive motifs as they appear in natural matrices.

Design of hydroxyapatite bioceramics with micro-/nano-topographies to regulate the osteogenic activities of bone morphogenetic protein-2 and bone marrow stromal cells

Biomimicking the nanostructure of natural bone apatite to enhance the bioactivity of hydroxyapatite (HA) biomaterials is an eternal topic in the bone regeneration field. In the present study, we designed four kinds of HA bioceramics with micro- to nanosized grains and investigated the effects of bioceramic topographies on the structures of bone morphogenetic protein-2 (BMP-2) and the effects on the responses of bone marrow stromal cells (BMSCs). Compared to the samples with submicron-scale crystalline particles, HA bioceramics with grain sizes of 104.6 ± 27.8 nm exhibited increased roughness, improved hydrophilicity and enhanced mechanical properties. The synergistic effects of these surface characteristics could well maintain the conformation of BMP-2, facilitate cell adhesion and spreading, and activate the osteogenic differentiation of BMSCs. Furthermore, SBF immersion and in vivo canine intramuscular implantation confirmed that the HA bioceramics with nanotopography also processed excellent bone-like apatite forming ability and outstanding osteoinductivity. In summary, these findings suggest that the nanotopography of HA bioceramics is a critical factor to enhance their bioactivity and osteoinductivity.

Topographical patterning: characteristics of current processing techniques, controllable effects on material properties and co-cultured cell fate, updated applications in tissue engineering, and improvement strategies

Topographical patterning has recently attracted lots of attention in regulating cell fate, understanding the mechanism of cell-microenvironment interactions, and solving the great issues of regenerative medicine. The introduced patterns offer topographical cues that can affect the reconstruction of the cytoskeleton or stimulate cell membrane receptors. Numerous studies have focused on these effects on cell behavior including attachment, migration, proliferation, and differentiation. In this review, five aspects of topographical patterning are discussed: (1) the process of typical micro-/nanotechniques and their advantages and limitations; (2) the effects of patterning on the mechanical properties and surface properties of substrates; (3) the influences of micro-/nanopatterns on the behavior of mesenchymal stem cells, as well as the underlying mechanisms; (4) the application of patterns to solve the issues of targeted organs (e.g., skin, nerves, blood vessels, bones, and heart). In the end, future perspectives that would help promote the efficiency of topographical patterning are proposed.

Hydrogel Nanospike Patch as a Flexible Anti-Pathogenic Scaffold for Regulating Stem Cell Behavior

Vertically aligned nanomaterials, such as nanowires and nanoneedles, hold strong potential as efficient platforms onto which living cells or tissues can be interfaced for use in advanced biomedical applications. However, their rigid mechanical properties and complex fabrication processes hinder their integration onto flexible, tissue-adaptable, and large-area patch-type scaffolds, limiting their practical applications. In this study, we present a highly flexible patch that possesses a spiky hydrogel nanostructure array as a transplantable platform for enhancing the growth and differentiation of stem cells and efficiently suppressing biofilm formation. In vitro studies show that the hydrogel nanospike patch imposes a strong physical stimulus to the membranes of stem cells and enhances their osteogenic, chondrogenic, and adipogenic differentiation and the secretion of crucial soluble factors without altering cell viability. At the same time, the array exhibits effective bactericidal properties against Gram-positive and Gram-negative bacteria. In vivo studies further demonstrate that the flexible hydrogel patch with its spiky vertical nanostructures significantly promotes the regeneration of damaged cranial bone tissues while suppressing pathogenic bacterial infections in mouse models.

Cell-substrate traction force regulates the fusion of osteoclast precursors through cell-cell interaction

The adhesion morphology of a cell monolayer results in a mechanical force inside cells, between cells, or between cells and substrates. The mechanical force regulates the differentiation of stem cells, but its influence on cell fusion is seldom studied. The present study is focused on osteoclast precursors, RAW264.7 monocytes, which can fuse into multinucleated cells (MNCs) responsible for bone resorption. Cells were cultured on circular and ring-like patterned substrates. Then, cell fusion, cell-substrate traction force, and force-sensitive molecules in different regions were measured and analyzed. Results showed that MNCs mainly appeared in the interior of the ring-like pattern and the central zone of the circular pattern, where both cell-substrate traction force and in-plane maximal shear stress were smaller than that at the patterns' edge. The immunostaining results revealed that F-actin, vinculin, β-catenin, and E-cadherin were highly distributed at the edge of patterns. High seeding density of cells promoted mechanical force-dependent fusion. When calcium-dependent cell-cell connections were inhibited by E-cadherin antibody or low-calcium medium, the fusion into MNCs was greatly reduced. Thus, the morphology of cell monolayer decides the mechanical state of cell-substrate interaction and cell-cell connection, ultimately regulating the fusion of osteoclast precursors.

Bioinspired Adhesive Architectures: From Skin Patch to Integrated Bioelectronics

The attachment phenomena of various hierarchical architectures found in nature have extensively drawn attention for developing highly biocompatible adhesive on skin or wet inner organs without any chemical glue. Structural adhesive systems have become important to address the issues of human-machine interactions by smart outer/inner organ-attachable devices for diagnosis and therapy. Here, advances in designs of biologically inspired adhesive architectures are reviewed in terms of distinct structural properties, attachment mechanisms to biosurfaces by physical interactions, and noteworthy fabrication methods. Recent demonstrations of bioinspired adhesive architectures as adhesive layers for medical applications from skin patches to multifunctional bioelectronics are presented. To conclude, current challenges and prospects on potential applications are also briefly discussed.

Bone marrow mesenchymal stem cells: Aging and tissue engineering applications to enhance bone healing

Bone has well documented natural healing capacity that normally is sufficient to repair fractures and other common injuries. However, the properties of bone change throughout life, and aging is accompanied by increased incidence of bone diseases and compromised fracture healing capacity, which necessitate effective therapies capable of enhancing bone regeneration. The therapeutic potential of adult mesenchymal stem cells (MSCs) for bone repair has been long proposed and examined. Actions of MSCs may include direct differentiation to become bone cells, attraction and recruitment of other cells, or creation of a regenerative environment via production of trophic growth factors. With systemic aging, MSCs also undergo functional decline, which has been well investigated in a number of recent studies. In this review, we first describe the changes in MSCs during aging and discuss how these alterations can affect bone regeneration. We next review current research findings on bone tissue engineering, which is considered a promising and viable therapeutic solution for structural and functional restoration of bone. In particular, the importance of MSCs and bioscaffolds is highlighted. Finally, potential approaches for the prevention of MSC aging and the rejuvenation of aged MSC are discussed.

Combination of polyetherketoneketone scaffold and human mesenchymal stem cells from temporomandibular joint synovial fluid enhances bone regeneration

Therapies using human mesenchymal stem cells (MSCs) combined with three-dimensional (3D) printed scaffolds are a promising strategy for bone grafting. But the harvest of MSCs still remains invasive for patients. Human synovial fluid MSCs (hSF-MSCs), which can be obtained by a minimally invasive needle-aspiration procedure, have been used for cartilage repair. However, little is known of hSF-MSCs in bone regeneration. Polyetherketoneketone (PEKK) is an attractive bone scaffold due to its mechanical properties comparable to bone. In this study, 3D-printed PEKK scaffolds were fabricated using laser sintering technique. hSF-MSCs were characterized and cultured on PEKK to evaluate their cell attachment, proliferation, and osteogenic potential. Rabbit calvarial critical-sized bone defects were created to test the bone regenerative effect of PEKK with hSF-MSCs. In vitro results showed that hSF-MSCs attached, proliferated, and were osteogenic on PEKK. In vivo results indicated that PEKK seeded with hSF-MSCs regenerated twice the amount of newly formed bone when compared to PEKK seeded with osteogenically-induced hSF-MSCs or PEKK scaffolds alone. These results suggested that there was no need to induce hSF-MSCs into osteoblasts prior to their transplantations in vivo. In conclusion, the combined use of PEKK and hSF-MSCs was effective in regenerating critical-sized bone defects.

Scaffold Structural Microenvironmental Cues to Guide Tissue Regeneration in Bone Tissue Applications

In the process of bone regeneration, new bone formation is largely affected by physico-chemical cues in the surrounding microenvironment. Tissue cells reside in a complex scaffold physiological microenvironment. The scaffold should provide certain circumstance full of structural cues to enhance multipotent mesenchymal stem cell (MSC) differentiation, osteoblast growth, extracellular matrix (ECM) deposition, and subsequent new bone formation. This article reviewed advances in fabrication technology that enable the creation of biomaterials with well-defined pore structure and surface topography, which can be sensed by host tissue cells (esp., stem cells) and subsequently determine cell fates during differentiation. Three important cues, including scaffold pore structure (i.e., porosity and pore size), grain size, and surface topography were studied. These findings improve our understanding of how the mechanism scaffold microenvironmental cues guide bone tissue regeneration.

Enhanced osteodifferentiation of MSC spheroids on patterned electrospun fiber mats - An advanced 3D double strategy for bone tissue regeneration

2D cell culture has been widely developed with various micropatterning and microfabrication techniques over the past few decades for creating and controlling cellular microenvironments including cell-matrix interactions, cell-cell interactions, and bio-mimicking the in-vivo tissue hierarchy and functions. However, the drawbacks of 2D culture have currently paved the way to 3D cell culture which is considered clinically and biologically more relevant. Here we report a 3D double strategy for osteodifferentiation of MSC spheroids on nano- and micro-patterned PLGA/Collagen/nHAp electrospun fiber mats. A comparison of cell alignment, proliferation and differentiation of 2D and 3D MSCs on patterned and non-patterned substrate was done. The study demonstrates the synergistic effect of geometric cues and 3D culture on differentiation of MSC spheroids into osteogenic lineage even in absence of osteoinduction medium.

The effect of ordered and partially ordered surface topography on bone cell responses: a review

Current understanding of the role of ordered and partially ordered surface topography in bone cell responses for bone implant design.

Cellular behavior controlled by bio-inspired and geometry-tunable nanohairs

A cicada wing has a biocidal feature of rupturing the membrane of cells, while the cactus spine can transmit a water drop to the stem of the plant. Both of these properties have evolved from their respective unique structures. Here, we endeavor to develop geometry-controllable nanohairs that mimic the cicada's wing-like vertical hairs and the cactus spine-like stooped hairs, and to quantitatively characterize the cell migration behavior of the hairy structures. It was found that the neuroblastoma cells are highly sensitive to the variation of surfaces: flat, vertical, and stooped nanohairs (100 nm diameter and 900 nm height). The cells on the vertical hairs showed significantly decreased proliferation. It was found that the behavior of cells cultured on stooped nanohairs is strongly influenced by the direction of the stooped pattern of hairs when we quantitatively measured the migration of cells on flat, vertical, and stooped structures. However, the cells on the flat structures showed random movement and the cells on the vertical nanohairs restricted the nanohair movement. Cells on the stooped structure showed higher forward migration preference compared to that of the other structures. Furthermore, we found that these cellular behaviors on the different patterns of nanohairs were affected by intracellular actin flament change. Consistent with these results, the vertical and stooped structures can facilitate the control of cell viability and guide directional migration for biomedical applications such as organogenesis.

Graphene as an Enabling Strategy for Dental Implant and Tissue Regeneration

Graphene-based approaches have been influential in the design and manipulation of dental implants and tissue regeneration to overcome the problems associated with traditional titanium-based dental implants, such as their low biological affinity. Here, we describe the current progress of graphene-based platforms, which have contributed to major advances for improving cellular functions in in vitro and in vivo applications of dental implants. We also present opinions on the principal challenges and future prospects for new graphene-based platforms for the development of advanced graphene dental implants and tissue regeneration.

Spatially and Temporally Controlled Hydrogels for Tissue Engineering

Recent years have seen tremendous advances in the field of hydrogel-based biomaterials. One of the most prominent revolutions in this field has been the integration of elements or techniques that enable spatial and temporal control over hydrogels' properties and functions. Here, we critically review the emerging progress of spatiotemporal control over biomaterial properties towards the development of functional engineered tissue constructs. Specifically, we will highlight the main advances in the spatial control of biomaterials, such as surface modification, microfabrication, photo-patterning, and three-dimensional (3D) bioprinting, as well as advances in the temporal control of biomaterials, such as controlled release of molecules, photocleaving of proteins, and controlled hydrogel degradation. We believe that the development and integration of these techniques will drive the engineering of next-generation engineered tissues.

Mechanoresponsiveness of human adipose stem cells on nanocomposite and micro-hybrid composite

Resin-based composites are used for bone repair applications and comprise resin matrix and different sized filler particles. Nanometer-sized filler particles improve composite's mechanical properties compared with micrometer-sized filler particles, but whether differences exist in the biological response to these composites is unknown. Natural bone comprises a nanocomposite structure, and nanoscale interactions with extracellular matrix components influence stem cell differentiation. Therefore we hypothesized that nanometer-sized filler particles in resin-based composites enhance osteogenic differentiation of stem cells showing a more bone cell-like response to mechanical loading compared with micrometer-sized filler particles. Pulsating fluid flow (PFF; 5 Hz, mean shear stress: 0.7 Pa; 1 h) rapidly, within 5 min, increased nitric oxide production in human adipose stem cells (hASCs) on nanocomposite, but not on micro-hybrid composite. PFF increased RUNX2 expression in hASCs on micro-hybrid composite, but not on nanocomposite after 2 h post-incubation. PFF did not affect mean cell orientation and shape index of hASCs on both composites. In conclusion, the PFF-increased nitric oxide production in hASCs on nanocomposite, and increased osteogenic differentiation of hASCs on micro-hybrid composite suggest different responses to mechanical loading of hASCs on composite with nanometer-sized and micrometer-sized filler particles. This might have important implications for bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2986-2994, 2017.

A biomaterial approach to cell reprogramming and differentiation

Cell reprogramming of somatic cells into pluripotent states and subsequent differentiation into certain phenotypes has helped progress regenerative medicine research and other medical applications. Recent research has used viral vectors to induce this reprogramming; however, limitations include low efficiency and safety concerns. In this review, we discuss how biomaterial methods offer potential avenues for either increasing viability and downstream applicability of viral methods, or providing a safer alternative. The use of non-viral delivery systems, such as electroporation, micro/nanoparticles, nucleic acids and the modulation of culture substrate topography and stiffness have generated valuable insights regarding cell reprogramming.

Effect of the Microenvironment on Mesenchymal Stem Cell Paracrine Signaling: Opportunities to Engineer the Therapeutic Effect

Cues from the extracellular environment, including physical stimuli, are well known to affect mesenchymal stem cell (MSC) properties in terms of proliferation and differentiation. Many therapeutic strategies are now targeting this knowledge to increase the efficacy of cell therapies, typically employed to repair tissue functions in the event of injury, either by direct engraftment into the target tissue or differentiation into mature tissues. However, it is now envisioned that harnessing the repertoire of factors secreted by MSCs (termed the secretome) may provide an alternate to these cell therapies. Of current interest are both direct protein secretions and two major subpopulations of bioactive extracellular vesicles (EVs), namely exosomes and microvesicles. EVs released by MSCs are reflective of their cells of origin, able to impact upon the activities of other cells in the local microenvironment, making the rational design of MSC paracrine activities an encouraging strategy to reproducibly modulate cell therapies. The precise mechanisms by which the secretome is modulated by the microenvironment, however, remain elusive. Controlling MSC growth conditions with oxygen tension, growth factor composition, and mechanical properties may serve to directly influence paracrine activity. Our growing understanding implicates components of the mechanotransduction machinery in translating both mechanical and chemical cues from the environment into alterations in gene regulation and varied paracrine activity. As technologies are developed to manufacture MSCs, advances in bioengineering and novel insight of how the extracellular environment affects MSC paracrine activity will play a pivotal role in the generation of widespread, successful, clinical MSC therapies.

Biophysical Regulation of Cell Behavior-Cross Talk between Substrate Stiffness and Nanotopography

The stiffness and nanotopographical characteristics of the extracellular matrix (ECM) influence numerous developmental, physiological, and pathological processes in vivo. These biophysical cues have therefore been applied to modulate almost all aspects of cell behavior, from cell adhesion and spreading to proliferation and differentiation. Delineation of the biophysical modulation of cell behavior is critical to the rational design of new biomaterials, implants, and medical devices. The effects of stiffness and topographical cues on cell behavior have previously been reviewed, respectively; however, the interwoven effects of stiffness and nanotopographical cues on cell behavior have not been well described, despite similarities in phenotypic manifestations. Herein, we first review the effects of substrate stiffness and nanotopography on cell behavior, and then focus on intracellular transmission of the biophysical signals from integrins to nucleus. Attempts are made to connect extracellular regulation of cell behavior with the biophysical cues. We then discuss the challenges in dissecting the biophysical regulation of cell behavior and in translating the mechanistic understanding of these cues to tissue engineering and regenerative medicine.

Spatial charge manipulated set-selective apatite deposition on micropatterned piezoceramic

Apatite was selectively deposited with the manipulation of spatial charge on the micropatterned piezoelectric K_0.5Na_0.5NbO₃.

Hierarchically Micro- and Nanopatterned Topographical Cues for Modulation of Cellular Structure and Function

Living cells receive biochemical and physical information from the surrounding microenvironment and respond to this information. Multiscale hierarchical substrates with micro- and nanogrooves have been shown to mimic the native extracellular matrix (ECM) better than conventional nanopatterned substrates; therefore, substrates with hierarchical topographical cues are considered suitable for investigating the role of physical factors in tissue functions. In this study, precisely controllable, multiscale hierarchical substrates that could mimic the micro- and nanotopography of complex ECMs were fabricated and used to culture various cell types, including fibroblasts, endothelial cells, osteoblasts, and human mesenchymal stem cells. These substrates had both microscale wrinkles and nanoscale patterns and enhanced the alignment and elongation of all the cells tested. In particular, the nanotopography on the microscale wrinkles promoted not only the adhesion, but also the functions of the cells. These findings suggest that the hierarchical multiscale substrates effectively regulated cellular structure and functions and that they can be used as a platform for tissue engineering and regenerative medicine.

Modulation of human multipotent and pluripotent stem cells using surface nanotopographies and surface-immobilised bioactive signals: A review

The ability to control the interactions of stem cells with synthetic surfaces is proving to be effective and essential for the quality of passaged stem cells and ultimately the success of regenerative medicine. The stem cell niche is crucial for stem cell self-renewal and differentiation. Thus, mimicking the stem cell niche, and here in particular the extracellular matrix (ECM), in vitro is an important goal for the expansion of stem cells and their applications. Here, surface nanotopographies and surface-immobilised biosignals have been identified as major factors that control stem cell responses. The development of tailored surfaces having an optimum nanotopography and displaying suitable biosignals is proposed to be essential for future stem cell culture, cell therapy and regenerative medicine applications. While early research in the field has been restricted by the limited availability of micro- and nanofabrication techniques, new approaches involving the use of advanced fabrication and surface immobilisation methods are starting to emerge. In addition, new cell types such as induced pluripotent stem cells (iPSCs) have become available in the last decade, but have not been fully understood. This review summarises significant advances in the area and focuses on the approaches that are aimed at controlling the behavior of human stem cells including maintenance of their self-renewal ability and improvement of their lineage commitment using nanotopographies and biosignals. More specifically, we discuss developments in biointerface science that are an important driving force for new biomedical materials and advances in bioengineering aiming at improving stem cell culture protocols and 3D scaffolds for clinical applications. Cellular responses revolve around the interplay between the surface properties of the cell culture substrate and the biomolecular composition of the cell culture medium. Determination of the precise role played by each factor, as well as the synergistic effects amongst the factors, all of which influence stem cell responses is essential for future developments. This review provides an overview of the current state-of-the-art in the design of complex material surfaces aimed at being the next generation of tools tailored for applications in cell culture and regenerative medicine.

STATEMENT OF SIGNIFICANCE

This review focuses on the effect of surface nanotopographies and surface-bound biosignals on human stem cells. Recently, stem cell research attracts much attention especially the induced pluripotent stem cells (iPSCs) and direct lineage reprogramming. The fast advance of stem cell research benefits disease treatment and cell therapy. On the other hand, surface property of cell adhered materials has been demonstrated very important for in vitro cell culture and regenerative medicine. Modulation of cell behavior using surfaces is costeffective and more defined. Thus, we summarise the recent progress of modulation of human stem cells using surface science. We believe that this review will capture a broad audience interested in topographical and chemical patterning aimed at understanding complex cellular responses to biomaterials.

miR-29b-Loaded Gold Nanoparticles Targeting to the Endoplasmic Reticulum for Synergistic Promotion of Osteogenic Differentiation

Precise control of stem cells, such as human bone marrow-derived mesenchymal stem cells (hMSCs), is critical for the development of effective cellular therapies for tissue engineering and regeneration medicine. Emerging evidence suggests that several miRNAs act as key regulators of diverse biological processes, including differentiation of various stem cells. In this study, we have described a delivery system for miR-29b using PEI-capped gold nanoparticles (AuNPs) to synergistically promote osteoblastic differentiation. The cell proliferation assay revealed that AuNPs and AuNPs/miR-29b exert negligible cytotoxicity to hMSCs and MC3T3-E1 cells. With the assistance of AuNPs as a delivery vector, miR-29b could efficiently enter the cytoplasm and regulate osteogenesis. AuNPs/miR-29b more effectively promoted osteoblast differentiation and mineralization through induced the expression of osteogenesis genes (RUNX2, OPN, OCN, ALP) for the long-term, compared to the widely used commercial transfection reagent, Lipofectamine. With no obvious cytotoxicity, PEI-capped AuNPs showed great potential as an adequate miRNA vector for osteogenesis differentiation. Interestingly, we observed loading of AuNPs as well as AuNPs/miR-29b into the lumen of the endoplasmic reticulum (ER). Our findings collectively suggest that AuNPs, together with miR-29b, exert a synergistic promotory effect on osteogenic differentiation of hMSCs and MC3T3-E1 cells.

Biomimicking Nano-Micro Binary Polymer Brushes for Smart Cell Orientation and Adhesion Control

A new biomimetic surface named nano-micro binary polymer brushes is fabricated by large-area bench-top dip-pen nanodisplacement lithography technique. It is composed of gelatin-modified poly(glycidyl methacrylate) nanolines which are spaced by microstripes of poly(N-isopropylacrylamide). Cells are not only adhered and oriented well on the re-used surface, but also detachable from the surface with well-preserved extracellular matrix and aligned morphology.