Improved light-induced cell detachment on rutile TiO₂ nanodot films

Tailoring cell sheets for biomedical applications

Cell sheet technology has emerged as a novel scaffold-free approach for cell-based therapies in regenerative medicine. Techniques for harvesting cell sheets are essential to preserve the integrity of living cell sheets. This review provides an overview of fundamental technologies to fabricate cell sheets and recent advances in cell sheet-based tissue engineering. In addition to the commonly used temperature-responsive systems, we introduce alternative approaches, such as ROS-induced, magnetic-controlled, and light-induced cell sheet technologies. Moreover, we discuss the modification of the cell sheet to improve its function, including stacking, genetic modification, and vascularization. With the significant advances in cell sheet technology, cell sheets have been widely applied in various tissues and organs, including but not limited to the lung, cornea, cartilage, periodontium, heart, and liver. This review further describes both the preclinical and clinical applications of cell sheets. We believe that the progress in cell sheet technology would further propel its biomedical applications.

Fine-Tuning the Nanostructured Titanium Oxide Surface for Selective Biological Response

Cardiovascular diseases are a pre-eminent global cause of mortality in the modern world. Typically, surgical intervention with implantable medical devices such as cardiovascular stents is deployed to reinstate unobstructed blood flow. Unfortunately, existing stent materials frequently induce restenosis and thrombosis, necessitating the development of superior biomaterials. These biomaterials should inhibit platelet adhesion (mitigating stent-induced thrombosis) and smooth muscle cell proliferation (minimizing restenosis) while enhancing endothelial cell proliferation at the same time. To optimize the surface properties of Ti6Al4V medical implants, we investigated two surface treatment procedures: gaseous plasma treatment and hydrothermal treatment. We analyzed these modified surfaces through scanning electron microscopy (SEM), water contact angle analysis (WCA), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analysis. Additionally, we assessed in vitro biological responses, including platelet adhesion and activation, as well as endothelial and smooth muscle cell proliferation. Herein, we report the influence of pre/post oxygen plasma treatment on titanium oxide layer formation via a hydrothermal technique. Our results indicate that alterations in the titanium oxide layer and surface nanotopography significantly influence cell interactions. This work offers promising insights into designing multifunctional biomaterial surfaces that selectively promote specific cell types' proliferation─which is a crucial advancement in next-generation vascular implants.

Current status and future prospects of stomatology research

Research in stomatology (dental medicine) continues to expand globally and is oriented towards solving clinical issues, focusing on clarifying the clinical relevance and potential mechanisms of oral‍-‍systemic connections via clinical epidemiology, oral microecological characterization, and the establishment of animal models. Interdisciplinary integration of materials science and tissue engineering with stomatology is expected to lead to the creation of innovative materials and technologies to better resolve the most prevalent and challenging clinical issues such as peri-implantitis, soft and hard tissue defects, and dentin hypersensitivity. With the rapid development of artificial intelligence (AI), 5th generation mobile communication technology (5G), and big data applications, "intelligent stomatology" is emerging to build models for better clinical diagnosis and management, accelerate the reform of education, and support the growth and advancement of scientific research. Here, we summarized the current research status, and listed the future prospects and limitations of these three aspects, aiming to provide a basis for more accurate etiological exploration, novel treatment methods, and abundant big data analysis in stomatology to promote the translation of research achievements into practical applications for both clinicians and the public.

Nanomaterial-based cell sheet technology for regenerative medicine and tissue engineering

Nanomaterial-based cell sheet technology has been reported to be an effective method in regenerative medicine and tissue engineering. Here, we summarized several types of nanomaterials used to harvest cell sheets. Currently, the technology is divided into four categories according to the mechanisms: light-induced cell sheet technology, thermo-responsive cell sheet technology, magnetic-controlled cell sheet technology, and reactive oxygen species (ROS)-induced cell sheet technology. Furthermore, some studies have been conducted to show that nanomaterial-based cell sheets produce satisfying outcomes in the regeneration of bone, skeletal muscle, cardiac tissue, and tendon, as well as angiogenesis and osseointegration. Nevertheless, some shortcomings still exist, such as comprehensive preparation, unclear safety, and cell quality. Thus, future studies should aim to produce more types of nanomaterials to solve this problem.

Hydroxyapatite-modified micro/nanostructured titania surfaces with different crystalline phases for osteoblast regulation

Surface structures and physicochemical properties critically influence osseointegration of titanium (Ti) implants. Previous studies have shown that the surface with both micro- and nanoscale roughness may provide multiple features comparable to cell dimensions and thus efficiently regulate cell-material interaction. However, less attention has been made to further optimize the physicochemical properties (e.g., crystalline phase) and to further improve the bioactivity of micro/nanostructured surfaces. Herein, micro/nanostructured titania surfaces with different crystalline phases (amorphous, anatase and anatase/rutile) were prepared and hydroxyapatite (HA) nanorods were deposited onto the as-prepared surfaces by a spin-assisted layer-by-layer assembly method without greatly altering the initial multi-scale morphology and wettability. The effects of crystalline phase, chemical composition and wettability on osteoblast response were investigated. It is noted that all the micro/nanostructured surfaces with/without HA modification presented superamphiphilic. The activities of MC3T3-E1 cells suggested that the proliferation trend on the micro/nanostructured surfaces was greatly influenced by different crystalline phases, and the highest proliferation rate was obtained on the anatase/rutile surface, followed by the anatase; but the cell differentiation and extracellular matrix mineralization were almost the same among them. After ultrathin HA modification on the micro/nanostructured surfaces with different crystalline phases, it exhibited similar proliferation trend as the original surfaces; however, the cell differentiation and extracellular matrix mineralization were significantly improved. The results indicate that the introduction of ultrathin HA to the micro/nanostructured surfaces with optimized crystalline phase benefits cell proliferation, differentiation and maturation, which suggests a favorable biomimetic microenvironment and provides the potential for enhanced implant osseointegration in vivo.

Graphene/Si-Promoted Osteogenic Differentiation of BMSCs through Light Illumination

Graphene (Gr) presents promising applications in regulating the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Light illumination is regarded as a spatiotemporally controllable, easily applicable, and noninvasive mean to modulate material responses. Herein, Gr-transferred silicon (Gr/Si) with a Schottky junction is utilized to evaluate the visible-light-promoted osteogenic differentiation of BMSCs. Under light illumination, light-induced charges, owing to the formation of the Schottky junction at the interface of Gr and Si, accumulated on the surface and then changed the surface potential of Gr/Si. The Schottky junction and surface potential at the interface of Gr and Si was measured by photovoltaic test and scanning Kelvin probe microscopy. Alkaline phosphatase (ALP) activity and quantitative real-time polymerase chain reaction (PCR) measurement showed that such variations of surface improved the osteogenic differentiation of BMSCs, and the activation of the voltage-gated calcium channels through surface potential and accumulation of cytosolic Ca²⁺ could be the reason. Moreover, X-ray photoelectron spectroscopy characterization showed that surface charge could also affect BMSCs differentiation through the promotion or inhibition of the adsorption of osteogenic growth factors. Such light-promoted osteogenic differentiation of BMSCs on Gr/Si may have huge potential for biomedical materials or devices for bone regeneration application.

Light-Induced Cell Alignment and Harvest for Anisotropic Cell Sheet Technology

Well-organized orientation of cells and anisotropic extracellular matrix (ECM) are crucial in engineering biomimetic tissues, such as muscles, arteries, and nervous system, and so on. This strategy, however, is only beginning to be explored. Here, we demonstrated a light-induced cell alignment and harvest for anisotropic cell sheets (ACS) technology using light-responsive TiO₂ nanodots film (TNF) and photo-cross-linkable gelatin methacrylate (GelMA). Cell initial behaviors on TNF might be controlled by micropatterns of light-induced distinct surface hydroxyl features, owing to a sensing mechanism of myosin II-driven retraction of lamellipodia. Further light treatment allowed ACS detachment from TNF surface while simultaneously solidified the GelMA, realizing the automatic transference of ACS. Moreover, two detached ACS were successfully stacked into a 3D bilayer construct with controllable orientation of individual layer and maintained cell alignment for more than 7 days. Interestingly, the anisotropic HFF-1 cell sheets could further induce the HUVECs to form anisotropic capillary-like networks via upregulating VEGFA and ANGPT1 and producing anisotropic ECM. This developed integrated-functional ACS technology therefore provides a novel route to produce complex tissue constructs with well-defined orientations and may have a profound impact on regenerative medicine.

Visible-Light-Responsive Surfaces for Efficient, Noninvasive Cell Sheet Harvesting

Effective regulation of cell-surface interactions is critical for regenerative medicine and other cell-based therapies. Herein, visible-light-induced cell sheet harvesting based on silicon wafers with a p/n junction [Si(p/n)] is introduced. Cell sheets could quickly detach from the Si(p/n) surface after 10 min of visible-light illumination with maintained cell viability and functions. It is found that preadsorbed proteins on the Si(p/n) surface like BSA and collagen-I show light-induced desorption behaviors. Molecular dynamics simulation also indicates that long-range force caused by the photovoltaic effect of Si(p/n) under visible-light illumination plays a key role in triggering the release of the preadsorbed protein. It is suggested that such protein desorption behavior mediated by the photovoltaic effect is responsible for cell release. This work not only shows promising potential for cell sheet harvesting, but also provides new insights into protein-material interactions.

Enhanced osteogenic activity of anatase TiO2 film: Surface hydroxyl groups induce conformational changes in fibronectin

In this study, with an attempt to identify the effects of TiO₂ crystalline phase compositions on the osteogenic properties, the anatase and rutile TiO₂ thin films with similar film thickness, surface topography and hydrophilicity were prepared on Si (100) substrates by atomic layer deposition (ALD), subsequent thermal annealing and ultraviolet irradiation. The films were studied with XRD, XPS, FE-SEM, AFM, FTIR and contact angle measurements. In vitro cellular assays showed that the anatase phase led to better osteoblast compatibility in terms of adhesion, proliferation, differentiation, mineralization as well as osteogenesis-related gene expression when compared with the rutile phase. We investigated the difference between the anatase and rutile TiO₂ films at the biomolecular level to explain the enhanced osteogenic activity of the anatase film. It was found that the presence of more TiOH groups on anatase surface induced more cell-binding sites of fibronectin (FN) exposed on its surface, causing a more active conformation of the adsorbed FN for subsequent osteoblast behaviors.

SiO2/TiO2 Nanocomposite Films on Polystyrene for Light-Induced Cell Detachment Application

Light-induced cell detachment shows much potential in in vitro cell culture and calls for high-performance light-responsive films. In this study, a smooth and dense SiO₂/TiO₂ nanocomposite thin film with thickness of around 250 nm was first fabricated on H₂O₂ treated polystyrene (PS) substrate via a low-temperature sol-gel method. It was observed that the film could well-adhere on the PS surface and the bonding strength became increasingly high with the increase of SiO₂ content. The peeling strength and shear strength reached 3.05 and 30.02 MPa, respectively. It was observed the surface of the film could transform into superhydrophilic upon 20 min illumination of ultraviolet with a wavelength of 365 nm (UV365). In cell culture, cells, i.e., NIH3T3 and MC3T3-E1 cells, cultured on SiO₂/TiO₂ nanocomposite film were easily detached after 10 min of UV365 illumination; the detachment rates reached 90.8% and 88.6%, respectively. Correspondingly, continuous cell sheets with good viability were also easily obtained through the same way. The present work shows that SiO₂/TiO₂ nanocomposite thin film could be easily prepared on polymeric surface at low temperature. The corresponding film exhibits excellent biocompatibility, high bonding strength, and good light responses. It could be a good candidate for the surface of cell culture utensils with light-induced cell detachment property.

Laminin-521 Promotes Rat Bone Marrow Mesenchymal Stem Cell Sheet Formation on Light-Induced Cell Sheet Technology

Rat bone marrow mesenchymal stem cell sheets (rBMSC sheets) are attractive for cell-based tissue engineering. However, methods of culturing rBMSC sheets are critically limited. In order to obtain intact rBMSC sheets, a light-induced cell sheet method was used in this study. TiO₂ nanodot films were coated with (TL) or without (TN) laminin-521. We investigated the effects of laminin-521 on rBMSCs during cell sheet culturing. The fabricated rBMSC sheets were subsequently assessed to study cell sheet viability, reattachment ability, cell sheet thickness, collagen type I deposition, and multilineage potential. The results showed that laminin-521 could promote the formation of rBMSC sheets with good viability under hyperconfluent conditions. Cell sheet thickness increased from an initial 26.7 ± 1.5 μm (day 5) up to 47.7 ± 3.0 μm (day 10). Moreover, rBMSC sheets maintained their potential of osteogenic, adipogenic, and chondrogenic differentiation. This study provides a new strategy to obtain rBMSC sheets using light-induced cell sheet technology.

Engineering prevascularized composite cell sheet by light-induced cell sheet technology

Light-induced cell sheet technology based on light-responsive TiO₂ nanodots film realized an optimal and transferable prevascularized MSC–EC composite cell sheet.

Controlling mesenchymal stem cells differentiate into contractile smooth muscle cells on a TiO2 micro/nano interface: Towards benign pericytes environment for endothelialization

Building healthy and oriented smooth muscle cells (SMCs) environment is an effective method for improving the surface endothelialization of the cardiovascular implants. However, a long-term and stable source of SMCs for implantation without immune rejection and inflammation has not been solved, and mesenchymal stem cells (MSCs) differentiation may be a good choice. In this work, two types of TiO2 micro/nano interfaces were fabricated on titanium surface by photolithography and anodic oxidation. These TiO2 micro/nano interfaces were used to regulate the differentiation of the MSCs. The X-ray diffraction (XRD) detection showed that the TiO2 micro/nano interfaces possessed the anatase crystal structure, suggesting good cytocompatibility. The CCK-8 results indicated the TiO2 micro/nano interfaces improved MSC proliferation, further immunofluorescence staining and calculation of the cell morphology index proved the micro/nano surfaces also elongated MSCs and regulated MSCs oriented growth. The specific staining of α-SMA, CNN-1, vWF, CD44 and CD133 markers revealed that the micro/nano surfaces induced MSCs differentiation to contractile SMCs, and the endothelial cells (ECs) culture experiment indicated that the MSCs induced by micro/nano interfaces contributed to the ECs attachment and proliferation. This method will be further studied and applied for the surface modification of the cardiovascular implants.