Controlled Nanoscale Topographies for Osteogenic Differentiation of Mesenchymal Stem Cells

Integrating Mechanics and Bioactivity: A Detailed Assessment of Elasticity and Viscoelasticity at Different Scales in 2D Biofunctionalized PEGDA Hydrogels for Targeted Bone Regeneration

Methods for promoting and controlling the differentiation of human mesenchymal stem cells (hMSCs) in vitro before in vivo transplantation are crucial for the advancement of tissue engineering and regenerative medicine. In this study, we developed poly(ethylene glycol) diacrylate (PEGDA) hydrogels with tunable mechanical properties, including elasticity and viscoelasticity, coupled with bioactivity achieved through the immobilization of a mixture of RGD and a mimetic peptide of the BMP-2 protein. Despite the key relevance of hydrogel mechanical properties for cell culture, a standard for its characterization has not been proposed, and comparisons between studies are challenging due to the different techniques employed. Here, a comprehensive approach was employed to characterize the elasticity and viscoelasticity of these hydrogels, integrating compression testing, rheology, and atomic force microscopy (AFM) microindentation. Distinct mechanical behaviors were observed across different PEGDA compositions, and some consistent trends across multiple techniques were identified. Using a photoactivated cross-linker, we controlled the functionalization density independently of the mechanical properties. X-ray photoelectrin spectroscopy and fluorescence microscopy were employed to evaluate the functionalization density of the materials before the culturing of hMSCs on them. The cells cultured on all functionalized hydrogels expressed an early osteoblast marker (Runx2) after 2 weeks, even in the absence of a differentiation-inducing medium compared to our controls. Additionally, after only 1 week of culture with osteogenic differentiation medium, cells showed accelerated differentiation, with clear morphological differences observed among cells in the different conditions. Notably, cells on stiff but stress-relaxing hydrogels exhibited an overexpression of the osteocyte marker E11. This suggests that the combination of the functionalization procedure with the mechanical properties of the hydrogel provides a potent approach to promoting the osteogenic differentiation of hMSCs.

Manipulating Stem Cell Fate with Disordered Bioactive Cues on Surfaces: The Role of Bioactive Ligand Selection

The development of 2D or 3D bioactive platforms for rapidly isolating pure populations of cells from adult stem cells holds promise for advancing the understanding of cellular mechanisms, drug testing, and tissue engineering. Over the years, methods have emerged to synthesize bioactive micro- and nanostructured 2D materials capable of directing stem cell fate. We introduce a novel method for randomly micro- or nanopatterning any protein/peptide onto both 2D and 3D scaffolds via spray technology. Our goal is to investigate the impact of arranging bioactive micropatterns (ordered vs disordered) on surfaces to guide human mesenchymal stem cell (hMSC) differentiation. The spray technology efficiently coats materials with controlled, cost-effective bioactive micropatterns in various sizes and shapes. BMP-2 mimetic peptides were covalently grafted, individually or in combination with RGD peptides, onto activated polyethylene terephthalate (PET) surfaces through a spraying process, incorporating nano/microscale parameters like size, shape, and composition. The study explores different peptide distributions on surfaces and various peptide combinations. Four surfaces were homogeneously functionalized with these peptides (M1 to M4 with various densities of peptides), and six surfaces with disordered micro- and nanopatterns of peptides (S0 to S5 with different sizes of peptide patterns) were synthesized. Fluorescence microscopy assessed peptide distribution, followed by hMSC culture for 2 weeks, and evaluated osteogenic differentiation via immunocytochemistry and RT-qPCR for osteoblast and osteocyte markers. Cells on uniformly peptide-functionalized surfaces exhibited cuboidal forms, while those on surfaces with disordered patterns tended toward columnar or cuboidal shapes. Surfaces S4 and S5 showed dendrite-like formations resembling an osteocyte morphology. S5 showed significant overexpression of osteoblast (OPN) and osteocyte markers (E11, DMP1, and SOST) compared to control surfaces and other micropatterned surfaces. Notably, despite sharing an equivalent quantity of peptides with a homogeneous functionalized surface, S5 displayed a distinct distribution of peptides, resulting in enhanced osteogenic differentiation of hMSCs.

Morphology of Nanostructured Tantalum Oxide Controls Stem Cell Differentiation and Improves Corrosion Behavior

Tantalum is receiving increasing attention in the biomedical field due to its biocompatible nature and superior mechanical properties. However, the bioinert nature of tantalum still poses a challenge and limits its integration into the bone tissue. To address these issues, we fabricated nanotubular (NT), nanocoral (NC), and nanodimple morphologies on tantalum surfaces via anodization. The size of these nanofeatures was engineered to be approximately 30 nm for all anodized samples. Thus, the influence of the anodized nanostructured morphology on the chemical and biological properties of tantalum was evaluated. The NT and NC samples exhibited higher surface roughness, surface energy, and hydrophilicity compared to the nonanodized samples. In addition, the NT samples exhibited the highest corrosion resistance among all of the investigated samples. Biological experiments indicated that NT and NC samples promoted human adipose tissue-derived mesenchymal stem cell (hADMSC) spreading and proliferation up to 5 days in vitro. ALP, COL1A1, and OSC gene expressions as well as calcium mineral synthesis were upregulated on the NT and NC samples in the second and third weeks in vitro. These findings highlight the significance of nanostructured feature morphology for anodized tantalum, where the NT morphology was shown to be a potential candidate for orthopedic applications.

Direct Mapping of Cytomechanical Homeostasis Destruction in Osteoarthritis Based on Silicon Nanopillar Array

Osteoarthritis (OA) is the most prevalent joint degenerative disease characterized by chronic joint inflammation. The pathogenesis of OA has not been fully elucidated yet. Cartilage erosion is the most significant pathological feature in OA, which is considered the result of cytomechanical homeostasis destruction. The cytomechanical homeostasis is maintained by the dynamic interaction between cells and the extracellular matrix, which can be reflected by cell traction force (CTF). It is critical to assess the CTF to provide a deeper understanding of the cytomechanical homeostasis destruction and progression in OA. In this study, a silicon nanopillar array (Si-NP) with high spatial resolution and aspect ratio is fabricated to investigate the CTF in response to OA. It is discovered that the CTF is degraded in OA, which is attributed to the F-actin reorganization induced by the activation of RhoA/ROCK signaling pathway. Si-NP also shows promising potential as a mechanopharmacological assessment platform for OA drug screening and evaluation.

Controlling differentiation of stem cells via bioactive disordered cues

Ideal bone tissue engineering is to induce bone regeneration through the synergistic integration of biomaterial scaffolds, bone progenitor cells, and bone-forming factors. Biomimetic scaffolds imitate the native extracellular matrix (ECM) and are often utilized in vitro as analogues of the natural ECM to facilitate investigations of cell-ECM interactions and processes. In vivo, the cellular microenvironment has a crucial impact on regulating cell behavior and functions. A PET surface was activated and then functionalized with mimetic peptides to promote human mesenchymal stem cell (hMSC) adhesion and differentiation into an osteogenic lineage. Spray technology was used to randomly micropattern peptides (RGD and BMP-2 mimetic peptides) on the PET surface. The distribution of the peptides grafted on the surface, the roughness of the surfaces and the chemistry of the surfaces in each step of the treatment were ascertained by atomic force microscopy, fluorescence microscopy, time-of-flight secondary ion mass spectrometry, Toluidine Blue O assay, and X-ray photoelectron spectroscopy. Subsequently, cell lineage differentiation was evaluated by quantifying the expression of immunofluorescence markers: osteoblast markers (Runx-2, OPN) and osteocyte markers (E11, DMP1, and SOST). In this article, we hypothesized that a unique combination of bioactive micro/nanopatterns on a polymer surface improves the rate of morphology change and enhances hMSC differentiation. In DMEM, after 14 days, disordered micropatterned surfaces with RGD and BMP-2 led to a higher osteoblast marker expression than surfaces with a homogeneous dual peptide conjugation. Finally, hMSCs cultured in osteogenic differentiation medium (ODM) showed accelerated cell differentiation. In ODM, our results highlighted the expression of osteocyte markers when hMSCs were seeded on PET surfaces with random micropatterns.

Engineered Nano-Bio Interfaces for Stem Cell Therapy

Engineered nanomaterials (ENMs) with different topographies provide effective nano-bio interfaces for controlling the differentiation of stem cells. The interaction of stem cells with nanoscale topographies and chemical cues in their microenvironment at the nano-bio interface can guide their fate. The use of nanotopographical cues, in particular nanorods, nanopillars, nanogrooves, nanofibers, and nanopits, as well as biochemical forces mediated factors, including growth factors, cytokines, and extracellular matrix proteins, can significantly impact stem cell differentiation. These factors were seen as very effective in determining the proliferation and spreading of stem cells. The specific outgrowth of stem cells can be decided with size variation of topographic nanomaterial along with variation in matrix stiffness and surface structure like a special arrangement. The precision chemistry enabled controlled design, synthesis, and chemical composition of ENMs can regulate stem cell behaviors. The parameters of size such as aspect ratio, diameter, and pore size of nanotopographic structures are the main factors for specific termination of stem cells. Protein corona nanoparticles (NPs) have shown a powerful facet in stem cell therapy, where combining specific proteins could facilitate a certain stem cell differentiation and cellular proliferation. Nano-bio reactions implicate the interaction between biological entities and nanoparticles, which can be used to tailor the stem cells' culmination. The ion release can also be a parameter to enhance cellular proliferation and to commit the early differentiation of stem cells. Further research is needed to fully understand the mechanisms underlying the interactions between engineered nano-bio interfaces and stem cells and to develop optimized regenerative medicine and tissue engineering designs.

Silicon nanowire array overcomes chemotherapeutic resistance by inducing the differentiation of breast cancer stem cells

Currently, traditional cancer treatment strategies are greatly challenged by the existence of cancer stem cells (CSCs), which are root cause of chemotherapy resistance. Differentiation therapy presents a novel therapeutic strategy for CSC-targeted therapy. However, there are very few studies on the induction of CSCs differentiation so far. Silicon nanowire array (SiNWA) with many unique properties is considered to be an excellent material for various applications ranging from biotechnology to biomedical applications. In this study, we report the SiNWA differentiates MCF-7-derived breast CSCs (BCSCs) into non-CSCs by modulating the morphology of cells. In vitro, the differentiated BCSCs lose the stemness properties and thus become sensitive to chemotherapeutic drugs, eventually leading to the death of BCSCs. Therefore, this work suggests a potential approach for overcoming chemotherapeutic resistance.

Impact of In-Process Crystallinity of Biodegradable Scaffolds Fabricated by Material Extrusion on the Micro- and Nanosurface Topography, Viability, Proliferation, and Differentiation of Human Mesenchymal Stromal Cells

Due to affordability, and the ability to parametrically control the vital processing parameters, material extrusion is a widely accepted technology in tissue engineering. Material extrusion offers sufficient control over pore size, geometry, and spatial distribution, and can also yield different levels of in-process crystallinity in the resulting matrix. In this study, an empirical model based on four process parameters—extruder temperature, extrusion speed, layer thickness, and build plate temperature—was used to control the level of in-process crystallinity of polylactic acid (PLA) scaffolds. Two sets of scaffolds were fabricated, with low- and high-crystallinity content, and subsequently seeded with human mesenchymal stromal cells (hMSC). The biochemical activity of hMSC cells was tested by examining the DNA content, lactate dehydrogenase (LDH) activity, and alkaline phosphatase (ALP) tests. The results of this 21-day in vitro experiment showed that high level crystallinity scaffolds performed significantly better in terms of cell response. Follow-up tests revealed that the two types of scaffolds were equivalent in terms of hydrophobicity, and module of elasticity. However, detailed examination of their micro- and nanosurface topographic features revealed that the higher crystallinity scaffolds featured pronounced nonuniformity and a larger number of summits per sampling area, which was the main contributor to a significantly better cell response.

Nanoenabled Trainable Systems: From Biointerfaces to Biomimetics

In the dynamic biological system, cells and tissues adapt to diverse environmental conditions and form memories, an essential aspect of training for survival and evolution. An understanding of the biological training principles will inform the design of biomimetic materials whose properties evolve with the environment and offer routes to programmable soft materials, neuromorphic computing, living materials, and biohybrid robotics. In this perspective, we examine the mechanisms by which cells are trained by environmental cues. We outline the artificial platforms that enable biological training and examine the relationship between biological training and biomimetic materials design. We place emphasis on nanoscale material platforms which, given their applicability to chemical, mechanical and electrical stimulation, are critical to bridging natural and synthetic systems.

Strategies to improve bioactive and antibacterial properties of polyetheretherketone (PEEK) for use as orthopedic implants

Polyetheretherketone (PEEK) has gradually become the mainstream material for preparing orthopedic implants due to its similar elastic modulus to human bone, high strength, excellent wear resistance, radiolucency, and biocompatibility. Since the 1990s, PEEK has increasingly been used in orthopedics. Yet, the widespread application of PEEK is limited by its bio-inertness, hydrophobicity, and susceptibility to microbial infections. Further enhancing the osteogenic properties of PEEK-based implants remains a difficult task. This article reviews some modification methods of PEEK in the last five years, including surface modification of PEEK or incorporating materials into the PEEK matrix. For surface modification, PEEK can be modified by chemical treatment, physical treatment, or surface coating with bioactive substances. For PEEK composite material, adding bioactive filler into PEEK through the melting blending method or 3D printing technology can increase the biological activity of PEEK. In addition, some modification methods such as sulfonation treatment of PEEK or grafting antibacterial substances on PEEK can enhance the antibacterial performance of PEEK. These strategies aim to improve the bioactive and antibacterial properties of the modified PEEK. The researchers believe that these modifications could provide valuable guidance on the future design of PEEK orthopedic implants.

Antibacterial nanopatterned coatings for dental implants

Dental implants, usually made of titanium, are exposed to hostile oral microflora that facilitate bacterial infections and subsequent inflammation. To mitigate these processes, we coated titanium substrates with block copolymer nanopatterns and investigated the bactericidal effect of these coatings against Gram-positive and Gram-negative bacteria. We found that the bactericidal efficacy of the coatings depends on their morphology and surface chemistry as well as on the bacterial strain: an optimal combination can lead to significant bacterial death for a short time, i.e. 90% for 90 min. Human gingival fibroblasts in contact with the nanopatterned coatings showed similar cell attachment and morphology as on bare Ti. Immunostaining assays showed similar levels of CCR7 and CD206 in macrophages cultured over the nanopatterns and bare Ti, demonstrating adequate properties for tissue integration. The nanopatterns induced a small increase in macrophage aspect ratio, which might indicate early states of M2 polarization, given the absence of CD206.

Block copolymer nanopatterns affect cell spreading: Stem versus cancer bone cells

Bone healing after a tumor removal can be promoted by biomaterials that enhance the bone regeneration and prevent the tumor relapse. Herein, we obtained several nanopatterns by self-assembly of polystyrene-block-poly-(2-vinylpyridine) (PS-b-P2VP) with different molecular weights and investigated the adhesion and morphology of human bone marrow mesenchymal stem cells (BMMSC) and osteosarcoma cell line (SaOS-2) on these patterns aiming to identify topography and chemistry that promote bone healing. We analyzed > 2000 cells per experimental condition using imaging software and different morphometric descriptors, namely area, perimeter, aspect ratio, circularity, surface/area, and fractal dimension of cellular contour (FDC). The obtained data were used as inputs for principal component analysis, which showed distinct response of BMMSC and SaOS-2 to the surface topography and chemistry. Among the studied substrates, micellar nanopatterns assembled from the copolymer with high molecular weight promote the adhesion and spreading of BMMSC and have an opposite effect on SaOS-2. This nanopattern is thus beneficial for bone regeneration after injury or pathology, e.g. bone fracture or tumor removal.

Interplay of matrix stiffness and stress relaxation in directing osteogenic differentiation of mesenchymal stem cells

The aim of this study is to investigate the impact of the stiffness and stress relaxation of poly(acrylamide-co-acrylic acid) hydrogels on the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Varying the amount of the crosslinker and the ratio between the monomers enabled the obtainment of hydrogels with controlled mechanical properties, as characterized using unconfined compression and atomic force microscopy (AFM). Subsequently, the surface of the hydrogels was functionalized with a mimetic peptide of the BMP-2 protein, in order to favor the osteogenic differentiation of hMSCs. Finally, hMSCs were cultured on the hydrogels with different stiffness and stress relaxation: 15 kPa - 15%, 60 kPa - 15%, 140 kPa - 15%, 100 kPa - 30%, and 140 kPa - 70%. The cells on hydrogels with stiffnesses from 60 kPa to 140 kPa presented a star-like shape, typical of osteocytes, which has only been reported by our group for two-dimensional substrates. Then, the extent of hMSC differentiation was evaluated by using immunofluorescence and by quantifying the expression of both osteoblast markers (Runx-2 and osteopontin) and osteocyte markers (E11, DMP1, and sclerostin). It was found that a stiffness of 60 kPa led to a higher expression of osteocyte markers as compared to stiffnesses of 15 and 140 kPa. Finally, the strongest expression of osteoblast and osteocyte differentiation markers was observed for the hydrogel with a high relaxation of 70% and a stiffness of 140 kPa.

Nanoimprinting for high-throughput replication of geometrically precise pillars in fused silica to regulate cell behavior

Developing high-throughput nanopatterning techniques that also allow for precise control over the dimensions of the fabricated features is essential for the study of cell-nanopattern interactions. Here, we developed a process that fulfills both of these criteria. Firstly, we used electron-beam lithography (EBL) to fabricate precisely controlled arrays of submicron pillars with varying values of interspacing on a large area of fused silica. Two types of etching procedures with two different systems were developed to etch the fused silica and create the final desired height. We then studied the interactions of preosteoblasts (MC3T3-E1) with these pillars. Varying interspacing was observed to significantly affect the morphological characteristics of the cell, the organization of actin fibers, and the formation of focal adhesions. The expression of osteopontin (OPN) significantly increased on the patterns, indicating the potential of the pillars for inducing osteogenic differentiation. The EBL pillars were thereafter used as master molds in two subsequent processing steps, namely soft lithography and thermal nanoimprint lithography for high-fidelity replication of the pillars on the substrates of interest. The molding parameters were optimized to maximize the fidelity of the generated patterns and minimize the wear and tear of the master mold. Comparing the replicated feature with those present on the original mold confirmed that the geometry and dimensions of the replicated pillars closely resemble those of the original ones. The method proposed in this study, therefore, enables the precise fabrication of submicron- and nanopatterns on a wide variety of materials that are relevant for systematic cell studies. STATEMENT OF SIGNIFICANCE: Submicron pillars with specific dimensions on the bone implants have been proven to be effective in controlling cell behaviors. Nowadays, numerous methods have been proposed to produce bio-instructive submicron-topographies. However, most of these techniques are suffering from being low-throughput, low-precision, and expensive. Here, we developed a high-throughput nanopatterning technique that allows for control over the dimensions of the features for the study of cell-nanotopography interactions. Assessing the adaptation of preosteoblast cells showed the potential of the pillars for inducing osteogenic differentiation. Afterward, the pillars were used for high-fidelity replication of the bio-instructive features on the substrates of interest. The results show the advantages of nanoimprint lithography as a unique technique for the patterning of large areas of bio-instructive surfaces.

Endowing Polyetheretherketone Implants with Osseointegration Properties: In Situ Construction of Patterned Nanorod Arrays

Polyetheretherketone (PEEK) is widely used in orthopedic and craniomaxillofacial surgeries as it exhibits excellent biocompatibility, mechanical property, and chemical stability. However, its clinical application is limited by the biological inertness of PEEK. Numerous efforts have been made to improve the bioactivity of this polymer over the years. However, modification methods that can not only promote osteogenesis but also maintain excellent properties are still limited. Hence, a facile hot die formation technique is developed for establishing patterned nanorod arrays on the PEEK surface in situ. This method can maintain the excellent properties of PEEK and can be used in implantation as it can facilitate osteogenic activity in the absence of any organic/inorganic differentiation-inducing factors. PEEK with 200-nm patterned nanorod arrays on the surface exhibits excellent osteogenic properties. This result is obtained by assessing the osteogenic differentiation properties of rat adipose-derived stem cells at the gene and protein levels in vitro. In vivo experimental results reveal that the surface-modified cylindrical PEEK 200 implants present with excellent osseointegration properties. Moreover, they can tightly bind with the surrounding bone tissue. A practical method for manufacturing single-component PEEK implants with excellent osseointegration properties is reported, and the materials can be possibly used as orthopedic implants.

Incorporating nanocrystalline cellulose into a multifunctional hydrogel for heart valve tissue engineering applications

Functional tissue engineered heart valves (TEHV) have been an elusive goal for nearly 30 years. Among the persistent challenges are the requirements for engineered valve leaflets that possess nonlinear elastic tissue biomechanical properties, support quiescent fibroblast phenotype, and resist osteogenic differentiation. Nanocellulose is an attractive tunable biological material that has not been employed to this application. In this study, we fabricated a series of photocrosslinkable composite hydrogels mNCC-MeGel (mNG) by conjugating TEMPO-modified nanocrystalline cellulose (mNCC) onto the backbone of methacrylated gelatin (MeGel). Their structures were characterized by FTIR, 1 HNMR and uniaxial compression testing. Human adipose-derived mesenchymal stem cells (HADMSC) were encapsulated within the material and evaluated for valve interstitial cell phenotypes over 14 days culture in both normal and osteogenic media. Compared to the MeGel control group, the HADMSC encapsulated within mNG showed decreased alpha smooth muscle actin (αSMA) expression and increased vimentin and aggrecan expression, suggesting the material supports a quiescent fibroblastic phenotype. Under osteogenic media conditions, HADMSC within mNG hydrogels showed lower expression of osteogenic genes, including Runx2 and osteocalcin, indicating resistance toward calcification. As a proof of principle, the mNG hydrogel, combined with a viscosity enhancing agent, was used to 3D bioprint a tall, self-standing tubular structure that sustained cell viability. Together, these results identify mNG as an attractive biomaterial for TEHV applications.

The restricted adhesion of bone marrow mesenchymal stem cells by stepped structures on surfaces of hydroxyapatite

Currently, many researches have developed several strategies to design the surface structures of hydroxyapatite (HA), and have proved that the surface structures are pivotal in guiding the adhesion of bone marrow mesenchymal stem cells (BMSCs) as well as subsequent cellular behaviours. Most of these strategies, such as altering roughness and constructing surface patterning of HA, involve the construction of geometric topographies at the micro/nanoscale. However, besides geometric topographies, crystal defects are also important characteristics of surface structures and would alter many local physicochemical properties, which is critical for contact between cells and bioceramic surfaces. For the practical applications of crystal defects, a major hindrance is that crystal defects are usually unstable and easily eliminated during crystallization, which limits the large-scale fabrication of materials with crystal defects. In this work, given that stepped structures contain massive stable crystal defects on their step edges and kinks, we proposed a feasible and efficient method to fabricate HA dishes with stepped structures on their surfaces. First, plate-like HA mesocrystals were prepared from CaHPO₄via topotactic transformation, and were shaped into HA dishes by vacuum-filtration. Then, a sintering process was applied to facilitate the formation of stepped structures on the surfaces. We demonstrated that the generation of stepped structures could restrict the adhesion of BMSCs and showed the restriction effect is highly correlated with the density of exposed stepped structures. This phenomenon is interesting and the construction of a cell adhesion model is robust and easy, the underlying mechanisms of which deserve further exploration. Furthermore, constructing stepped structures on surfaces may be a new useful strategy to regulate cell adhesion and could also cooperate with other methods that do not need change in the surface crystal structure.

Stepped structures largely exposed on surfaces of HA significantly restrict the adhesion of bone marrow mesenchymal stem cells.

Nanotopography in directing osteogenic differentiation of mesenchymal stem cells: potency and future perspective

Severe bone injuries can result in disabilities and thus affect a person's quality of life. Mesenchymal stem cells (MSCs) can be an alternative for bone healing by growing them on nanopatterned substrates that provide mechanical signals for differentiation. This review aims to highlight the role of nanopatterns in directing or inducing MSC osteogenic differentiation, especially in bone tissue engineering. Nanopatterns can upregulate the expression of osteogenic markers, which indicates a faster differentiation process. Combined with growth factors, nanopatterns can further upregulate osteogenic markers, but with fewer growth factors needed, thereby reducing the risks and costs involved. Nanopatterns can be applied in scaffolds for tissue engineering for their lasting effects, even in vivo, thus having great potential for future bone treatment.

Nanofabrication Techniques: Challenges and Future Prospects

Nanofabrication of functional micro/nano-features is becoming increasingly relevant in various electronic, photonic, energy, and biological devices globally. The development of these devices with special characteristics originates from the integration of low-cost and high-quality micro/nano-features into 3D-designs. Great progress has been achieved in recent years for the fabrication of micro/nanostructured based devices by using different imprinting techniques. The key problems are designing techniques/approaches with adequate resolution and consistency with specific materials. By considering optical device fabrication on the large-scale as a context, we discussed the considerations involved in product fabrication processes compatibility, the feature's functionality, and capability of bottom-up and top-down processes. This review summarizes the recent developments in these areas with an emphasis on established techniques for the micro/nano-fabrication of 3-dimensional structured devices on large-scale. Moreover, numerous potential applications and innovative products based on the large-scale are also demonstrated. Finally, prospects, challenges, and future directions for device fabrication are addressed precisely.

Analyte Co-localization at Electromagnetic Gap Hot-Spots for Highly Sensitive (Bio)molecular Detection by Plasmon Enhanced Spectroscopies

Electromagnetic hot-spots at ultranarrow plasmonic nanogaps carry immense potential to drive detection limits down to few molecules in sensors based on surface-enhanced Raman or fluorescence spectroscopies. However, leveraging the EM hot-spots requires access to the gaps, which in turn depends on the size of the analyte in relation to gap distances. Herein, we leverage a well-calibrated process based on self-assembly of block copolymer colloids on a full-wafer level to produce high-density plasmonic nanopillar arrays exhibiting a large number (>10¹⁰ cm^-2) of uniform interpillar EM hot-spots. The approach allows convenient handles to systematically vary the interpillar gap distances down to a sub-10 nm regime. The results show compelling trends of the impact of analyte dimensions in relation to the gap distances toward their leverage over interpillar hot-spots and the resulting sensitivity in SERS-based molecular assays. Comparing the detection of labeled proteins in surface-enhanced Raman and metal-enhanced fluorescence configurations further reveal the relative advantage of fluorescence over Raman detection while encountering the spatial limitations imposed by the gaps. Quantitative assays with limits of detection down to picomolar concentrations are realized for both small organic molecules and proteins. The well-defined geometries delivered by a nanofabrication approach are critical to arriving at realistic geometric models to establish meaningful correlation between the structure, optical properties, and sensitivity of nanopillar arrays in plasmonic assays. The findings emphasize the need for the rational design of EM hot-spots that takes into account the analyte dimensions to drive ultrahigh sensitivity in plasmon-enhanced spectroscopies.

Tanfloc/heparin polyelectrolyte multilayers improve osteogenic differentiation of adipose-derived stem cells on titania nanotube surfaces

In this study, a surface modification strategy using natural biopolymers on titanium is proposed to improve bone healing and promote rapid and successful osseointegration of orthopedic implants. Titania nanotubes were fabricated via an anodization process and the surfaces were further modified with polyelectrolyte multilayers (PEMs) based on Tanfloc (a cationic tannin derivative) and glycosaminoglycans (heparin and hyaluronic acid). Scanning electron microscopy (SEM), water contact angle measurements, and X-ray photoelectron spectroscopy were used to characterize the surfaces. Adipose-derived stem cells (ADSCs) were seeded on the surfaces, and the cell viability, adhesion, and proliferation were investigated. Osteogenesis was induced and osteogenic differentiation of human ADSCs on the surfaces was evaluated via mineralization and protein expression assays, immunofluorescent staining, and SEM. The Tanfloc/heparin PEMs on titania nanotubes improved the rate of osteogenic differentiation of ADSCs as well as the bone mineral deposition, and is therefore a promising approach for use in orthopedic implants.

Fabrication of multilayered electrospun poly(lactic-co-glycolic acid)/polyvinyl pyrrolidone + poly(ethylene oxide) scaffolds and biocompatibility evaluation

Poly(lactic-co-glycolic acid)/polyvinyl pyrrolidone + poly(ethylene oxide) [PLGA/(PVP + PEO)] scaffolds with different polymer concentrations were fabricated using multilayered electrospinning, and their physicochemical properties and biocompatibility were examined to screen for scaffolds with excellent performance in tissue engineering (TE). PLGA solution (15% w/v) was used as the bottom solution, and a mixed solution of 12% w/v PVP + PEO was applied as the surface layer solution. The mass ratios of PVP vs. PEO in each 10 ml surface layer mixed solution were 1.08 g: 0.12 g; 0.96 g: 0.24 g; and 0.84 g: 0.36 g. Compared to the conventional electrospinning method used to fabricate the pure PVP + PEO (0.96 g: 0.24 g, Group A) scaffold and pure PLGA (Group E) scaffold, the multilayer electrospinning technique of alternating sprays of the bottom layer solution and the surface layer solution was adopted to fabricate multilayer nanofiber scaffolds, including PLGA/(PVP + PEO) (1.08 g: 0.12 g, Group B), PLGA/(PVP + PEO) (0.96 g: 0.24 g, Group C), and PLGA/(PVP + PEO) (0.84 g: 0.36 g, Group D). The morphology and characteristics of the five scaffolds were analyzed, and the biocompatibilities of the cell-scaffold composites were assessed through methods including Cell Counting Kit-8 (CCK8) analysis, 4',6-diamidino-2-phenylindole (DAPI) staining, and scanning electron microscopy. Therefore, with a PVP-to-PEO mass ratio of 0.96 g: 0.24 g, an optimal multilayer nanofiber scaffold was fabricated by the multilayer electrospinning technique. The excellent biocompatibility and mechanical properties of the scaffold were confirmed by in vitro experiments, which demonstrated the scaffold's promising application potential in the field of TE.

F-actin Regulates Osteoblastic Differentiation of Mesenchymal Stem Cells on TiO2 Nanotubes Through MKL1 and YAP/TAZ

Titanium and titanium alloys are widely used in orthopedic implants. Modifying the nanotopography provides a new strategy to improve osseointegration of titanium substrates. Filamentous actin (F-actin) polymerization, as a mechanical loading structure, is generally considered to be involved in cell migration, endocytosis, cell division, and cell shape maintenance. Whether F-actin is involved and how it functions in nanotube-induced osteogenic differentiation of mesenchymal stem cells (MSCs) remain to be elucidated. In this study, we fabricated TiO₂ nanotubes on the surface of a titanium substrate by anodic oxidation and characterized their features by scanning electron microscopy (SEM), X-ray energy dispersive analysis (EDS), and atomic force microscopy (AFM). Alkaline phosphatase (ALP) staining, Western blotting, qRT-PCR, and immunofluorescence staining were performed to explore the osteogenic potential, the level of F-actin, and the expression of MKL1 and YAP/TAZ. Our results showed that the inner diameter and roughness of TiO₂ nanotubes increased with the increase of the anodic oxidation voltage from 30 to 70 V, while their height was 2 μm consistently. Further, the larger the tube diameter, the stronger the ability of TiO₂ nanotubes to promote osteogenic differentiation of MSCs. Inhibiting F-actin polymerization by Cyto D inhibited osteogenic differentiation of MSCs as well as the expression of proteins contained in focal adhesion complexes such as vinculin (VCL) and focal adhesion kinase (FAK). In contrast, after Jasp treatment, polymerization of F-actin enhanced the expression of RhoA and transcription factors YAP/TAZ. Based on these data, we concluded that TiO₂ nanotubes facilitated the osteogenic differentiation of MSCs, and this ability was enhanced with the increasing diameter of the nanotubes within a certain range (30-70 V). F-actin mediated this process through MKL1 and YAP/TAZ.

On the Interaction between 1D Materials and Living Cells

One-dimensional (1D) materials allow for cutting-edge applications in biology, such as single-cell bioelectronics investigations, stimulation of the cellular membrane or the cytosol, cellular capture, tissue regeneration, antibacterial action, traction force investigation, and cellular lysis among others. The extraordinary development of this research field in the last ten years has been promoted by the possibility to engineer new classes of biointerfaces that integrate 1D materials as tools to trigger reconfigurable stimuli/probes at the sub-cellular resolution, mimicking the in vivo protein fibres organization of the extracellular matrix. After a brief overview of the theoretical models relevant for a quantitative description of the 1D material/cell interface, this work offers an unprecedented review of 1D nano- and microscale materials (inorganic, organic, biomolecular) explored so far in this vibrant research field, highlighting their emerging biological applications. The correlation between each 1D material chemistry and the resulting biological response is investigated, allowing to emphasize the advantages and the issues that each class presents. Finally, current challenges and future perspectives are discussed.

Directional Osteo-Differentiation Effect of hADSCs on Nanotopographical Self-Assembled Polystyrene Nanopit Surfaces

Introduction

Cells exhibit high sensitivity and a diverse response to the nanotopography of the extracellular matrix, thereby endowing materials with instructive performances formerly reserved for growth factors. This finding leads to opportunities for improvement. However, the interplay between the topographical surface and cell behaviors remains incompletely understood.

Methods

In the present study, we showed nanosurfaces with various dimensions of nanopits (200–750 nm) fabricated by self-assembling polystyrene (PS) nanospheres. Human adipose-derived stem cell behaviors, such as cell morphology, adhesion, cytoskeleton contractility, proliferation, and differentiation, were investigated on the prepared PS nanopit surface.

Results

The osteogenic differentiation can be enhanced by nanopits with a diameter of 300–400 nm.

Discussion

The present study provided exciting new avenues to investigate cellular responses to well-defined nanoscale topographic features, which could further guide bone tissue engineering and stem cell clinical research. The capability to control developing biomaterials mimicking nanotopographic surfaces promoted functional tissue engineering, such as artificial joint replacement, bone repair, and dental applications.

Coating biopolymer nanofibers with carbon nanotubes accelerates tissue healing and bone regeneration through orchestrated cell- and tissue-regulatory responses

Tailoring the surface of biomaterial scaffolds has been a key strategy to modulate the cellular interactions that are helpful for tissue healing process. In particular, nanotopological surfaces have been demonstrated to regulate diverse behaviors of stem cells, such as initial adhesion, spreading and lineage specification. Here, we tailor the surface of biopolymer nanofibers with carbon nanotubes (CNTs) to create a unique bi-modal nanoscale topography (500 nm nanofiber with 25 nm nanotubes) and report the performance in modulating diverse in vivo responses including inflammation, angiogenesis, and bone regeneration. When administered to a rat subcutaneous site, the CNT-coated nanofiber exhibited significantly reduced inflammatory signs (down-regulated pro-inflammatory cytokines and macrophages gathering). Moreover, the CNT-coated nanofibers showed substantially promoted angiogenic responses, with enhanced neoblood vessel formation and angiogenic marker expression. Such stimulated tissue healing events by the CNT interfacing were evidenced in a calvarium bone defect model. The in vivo bone regeneration of the CNT- coated nanofibers was significantly accelerated, with higher bone mineral density and up-regulated osteogenic signs (OPN, OCN, BMP2) of in vivo bone forming cells. The in vitro studies using MSCs could demonstrate accelerated adhesion and osteogenic differentiation and mineralization, supporting the osteo-promoting mechanism behind the in vivo bone forming event. These findings highlight that the CNTs interfacing of biopolymer nanofibers is highly effective in reducing inflammation, promoting angiogenesis, and driving adhesion and osteogenesis of MSCs, which eventually orchestrate to accelerate tissue healing and bone regeneration process. STATEMENT OF SIGNIFICANCE: Here we demonstrate that the interfacing of biopolymer nanofibers with carbon nanotubes (CNTs) could modulate multiple interactions of cells and tissues that are ultimately helpful for the tissue healing and bone regeneration process. The CNT-coated scaffolds significantly reduced the pro-inflammatory signals while stimulating the angiogenic marker expressions. Furthermore, the CNT-coated scaffolds increased the bone matrix production of bone forming cells in vivo as well as accelerated the adhesion and osteogenic differentiation of MSCs in vitro. These collective findings highlight that the CNTs coated on the biopolymer nanofibers allow the creation of a promising platform for nanoscale engineering of biomaterial surface that can favor tissue healing and bone regeneration process, through a series of orchestrated events in anti-inflammation, pro-angiogenesis, and stem cell stimulation.

3D Printing of Large Areas of Highly Ordered Submicron Patterns for Modulating Cell Behavior

Fabricating large areas of geometrically complex and precisely controlled topographies is required for the studies of cell behavior on patterned surfaces. Direct laser writing (DLW) is an advanced 3D-fabrication technique, which facilitates the manufacturing of structures within various scales (from a few hundred nanometers to millimeters). However, this method requires improvements in the accuracy and reproducibility of the submicron and nanoscale features that are printed over a large area. Here, we present a scheme to both improve the uniformity of the printed submicron patterns and decrease the printing time. The effects of various processing parameters (e.g., laser power and writing field) on the dimensions and uniformity of submicron pillars as well as on their Young's modulus and surface wettability were assessed. Decreasing the writing field to 33 × 33 μm2 significantly improved the uniformity of submicron pillars that were printed over an area of 4 mm2 in a single-step process. Preosteoblast cells (MC3T3-E1) were used to assess the cytocompatibility of the used material (IP-L780 resin) with a focus on cell morphology, cell proliferation, cytoskeletal organization, and the elastic modulus of the cells. The cells cultured for 2 days on the submicron pillars showed a polarized shape and a higher Young's modulus of the area corresponding to the nucleus relative to those cultured on flat surfaces. Taken together, the results of the current study clearly show that the submicron patterns created using DLW are both cytocompatible and could modulate the morphology and mechanical properties of cells. This work paves the way for direct printing of submicron features with controlled Young's moduli over large areas in a single-step process, which is necessary for systematically studying how such patterns modulate cellular functions.

Mechanics-Controlled Dynamic Cell Niches Guided Osteogenic Differentiation of Stem Cells via Preserved Cellular Mechanical Memory

Stem cells sense and respond to their local dynamic mechanical niches, which further regulate the cellular behaviors. While in naturally, instead of instantly responding to real-time mechanical changes of their surrounding niches, stem cells often present a delayed cellular response over a time scale, namely cellular mechanical memory, which may finally influence their lineage choice. Here, we aim to build a dynamic mechanical niche model with alginate-based hydrogel, therein the dynamic mechanical switching can be easily realized via the introduce or removal of Ca²⁺. The results show that stiffening hydrogel (from soft to stiff) suppresses osteogenic differentiation of human mesenchymal stem cells (hMSCs) early on, though it finally promoted osteogenic differentiation over a long time period. Instead, softening hydrogel (from stiff to soft) still retains the strong osteogenic differentiation in the early days, though it finally showed a lower level of osteogenic differentiation compared with stiff hydrogel. Further, microRNA miR-21 has been found as a long-term mechanical memory sensor of the osteogenic program in hMSCs, as its level remains to match early mechanics of substrate over a period of time. Regulation of miR-21 level is efficient to erase the past mechanical memory and resensitize hMSCs to subsequent substrate mechanics. Our findings highlight cellular mechanical memory effect as a key factor of cell and cellular microenvironment interactions, which has been largely neglected before, and as a crucial design element of biomaterials for cell culture.