Thermoresponsive Terpolymeric Films Applicable for Osteoblastic Cell Growth and Noninvasive Cell Sheet Harvesting

Culturing bone marrow cells with dexamethasone and ascorbic acid improves osteogenic cell sheet structure

Objectives

To assess the structure and extracellular matrix molecule expression of osteogenic cell sheets created via culture in medium with both dexamethasone (Dex) and ascorbic acid phosphate (AscP) compared either Dex or AscP alone.

Methods

Osteogenic cell sheets were prepared by culturing rat bone marrow stromal cells in a minimal essential medium (MEM), MEM with AscP, MEM with Dex, and MEM with Dex and AscP (Dex/AscP). The cell number and messenger (m)RNA expression were assessed in vitro, and the appearance of the cell sheets was observed after mechanical retrieval using a scraper. β-tricalcium phosphate (β-TCP) was then wrapped with the cell sheets from the four different groups and subcutaneously implanted into rats.

Results

After mechanical retrieval, the osteogenic cell sheets from the MEM, MEM with AscP, and MEM with Dex groups appeared to be fragmented or incomplete structures. The cell sheets cultured with Dex/AscP remained intact after mechanical retrieval, without any identifiable tears. Culture with Dex/AscP increased the mRNA and protein expression of extracellular matrix proteins and cell number compared with those of the other three groups. More bridging bone formation was observed after transplantation of the β-TCP scaffold wrapped with cell sheets cultured with Dex/AscP, than in the other groups.

Conclusions

These results suggest that culture with Dex/AscP improves the mechanical integrity of the osteogenic cell sheets, allowing retrieval of the confluent cells in a single cell sheet structure. This method may be beneficial when applied in cases of difficult tissue reconstruction, such as nonunion, bone defects, and osteonecrosis.

Cite this article: M. Akahane, T. Shimizu, T. Kira, T. Onishi, Y. Uchihara, T. Imamura, Y. Tanaka. Culturing bone marrow cells with dexamethasone and ascorbic acid improves osteogenic cell sheet structure. Bone Joint Res 2016;5:569–576. DOI: 10.1302/2046-3758.511.BJR-2016-0013.R1.

Osteogenic Ability of Canine Adipose-Derived Mesenchymal Stromal Cell Sheets in Relation to Culture Time

Cell sheets could be used for bone regeneration without requiring a scaffold and can be easily produced from autologous mesenchymal stromal cells (MSCs). We compared the osteogenic potential of MSC-derived cell sheets in relation to culture time. Undifferentiated cell sheets (U-CS) and osteogenic differentiated cell sheets (O-CS) were generated using canine adipose-derived MSCs. Undifferentiated cells (UCs) were used as the control. Osteogenic differentiation was assessed by assaying alkaline phosphatase (ALP) activity. Expression of osteogenesis-related genes was evaluated by reverse transcription-polymerase chain reaction at 4, 7, 14, and 21 days after initiation of culture. The calcium content in cells was measured, and the cells were stained with Alizarin red S (ARS). The mRNA expression of transforming growth factor-β in U-CS and O-CS at day 4 was higher than that in UCs (p < 0.05). The level of bone morphogenetic protein 7 mRNA in O-CS increased significantly at day 4 and was significantly higher than that of U-CS at day 7. The mRNA level of runt-related transcription factor-2 in both sheet types increased significantly at 7 days of culture. The mRNA level of ALP in O-CS and U-CS increased significantly at day 7, and ALP activity was highest at days 7 and 14, respectively (p < 0.05). The mRNA level of osteocalcin in U-CS and O-CS increased significantly at day 21. O-CS and U-CS showed negative ARS staining but their calcium contents increased marginally at day 21. The O-CS cells started to aggregate at days 10-12, and only a partial sheet remained at day 21. The upregulation of expression of genes related to osteogenic differentiation, peak in ALP activity, and morphological changes in cell sheets suggest that the optimal time for application of O-CS and U-CS is between 7 and 10 days and after 14 days of culture, respectively.

Cell sheet injection as a technique of osteogenic supply

We previously reported a new cell transplantation method utilizing injections of mesenchymal stem cell (MSC) sheets that have osteogenic potential. After subcutaneous transplantation without any scaffold, the sheet demonstrated in vivo bone formation. In the present study, we transplanted such sheets by injection into implanted ceramics and assessed whether the injectable MSC sheets could stimulate osteogenic integration of the ceramics. To fabricate MSC sheets, bone marrow cells cultured from femur shafts of 7-week-old rats were subcultured in regular 10-cm dishes containing dexamethasone and ascorbic acid phosphate until confluent. Each cell sheet was then lifted using a scraper. Porous β-tricalcium phosphate (β-TCP) disks (5 mm Φ×2 mm) were transplanted subcutaneously into the backs of the rats. Immediately following implantation, the sheets were injected around the disks via a 16G needle (immediate group). Cell sheets were also injected into the remaining implanted disks 1 week after disk implantation (1-wk group). Four weeks following sheet injection, radiography and histology revealed calcification and bone tissue around the harvested disks of the immediate group (eight disks exhibited bone formation/eight implanted disks), whereas calcification and bone tissue were observed in 50% of the samples in the 1-wk group (four disks exhibited bone formation/eight implanted disks). The present study indicates that injected cell sheets can supply osteogenic potential to implanted ceramics. Owing to the usage of a needle for cell sheet transplantation, such an injection method can be applied as a minimally invasive technique of osteogenic supply to implanted ceramics.

Thermoresponsive cellulosic hydrogels with cell-releasing behavior

Here we report the preparation and characterization of thermoresponsive cellulosic hydrogels with cell-releasing behavior. Hydroxypropyl cellulose (HPC) was modified with methacrylic anhydride (MA). The resultant macromonomer, HPC-MA, retains the characteristic thermoresponsive phase behavior of HPC, with an onset temperature of 36 °C and a lower critical solution temperature (LCST) of 37-38 °C, as determined by turbidity measurement. Homogenous HPC-MA hydrogels were prepared by UV-cross-linking the aqueous solutions of the macromonomer at room temperature, and characterized by water contact angle and swelling ratio measurements, and dynamic mechanical analysis. These hydrogels exhibit temperature-dependent surface hydrophilicity and hydrophobicity, equilibrium water content as well as mechanical properties. Cell-releasing characteristics were demonstrated using African green monkey kidney cell line (COS-7 cells) and murine-derived embryonic stem cell line (Oct4b2). By reducing temperature to 4 °C, the cultivated cells spontaneously detached from the hydrogels without the need of trypsin treatment. These unique properties make our HPC-MA hydrogels potential substrates for cell sheet engineering.

Self assembled temperature responsive surfaces for generation of cell patches for bone tissue engineering

One of the major challenges in the fabrication of tissue engineered scaffolds is the ability of the scaffold to biologically mimic autograft-like tissues. One of the alternate approaches to achieve this is by the application of cell seeded scaffolds with optimal porosity and mechanical properties. However, the current approaches for seeding cells on scaffolds are not optimal in terms of seeding efficiencies, cell penetration into the scaffold and more importantly uniform distribution of cells on the scaffold. Also, recent developments in scaffold geometries to enhance surface areas, pore sizes and porosities tend to further complicate the scenario. Cell sheet-based approaches for cell seeding have demonstrated a successful approach to generate scaffold-free tissue engineering approaches. However, the method of generating the temperature responsive surface is quite challenging and requires carcinogenic reagents and gamma rays. Therefore, here, we have developed temperature responsive substrates by layer-by-layer self assembly of smart polymers. Multilayer thin films prepared from tannic acid and poly N-isopropylacrylamide were fabricated based on their electrostatic and hydrogen bonding interactions. Cell attachment and proliferation studies on these thin films showed uniform cell attachment on the substrate, matching tissue culture plates. Also, the cells could be harvested as cell patches and sheets from the scaffolds, by reducing the temperature for a short period of time, and seeded onto porous scaffolds for tissue engineering applications. An enhanced cell seeding efficiency on scaffolds was observed using the cell patch-based technique as compared to seeding cells in suspension. Owing to the already pre-existent cell-cell and cell-extracellular matrix interactions, the cell patch showed the ability to reattach rapidly onto scaffolds and showed enhanced ability to proliferate and differentiate into a bone-like matrix.

Scaffold-free cell sheet injection results in bone formation

We previously reported a new cell transplantation method in which mesenchymal stem cells (MSCs) were cultured as cell sheets. The cultured MSC sheets showed high alkaline phosphatase (ALP) activities and osteocalcin (OC) contents. In the present study, we transplanted such sheets by injection to assess whether the injectable MSC sheets could form bone tissue at subcutaneous sites. At 4 weeks after the subcutaneous injection, the injected areas showed hard mass formation. Each mass consisted of newly formed bone, as evaluated by radiographic, histological and gene expression analyses as well as three-dimensional computed tomography (3D-CT). Histological analyses revealed extracellular bone matrix together with osteocytes and active osteoblasts. Real-time PCR analyses showed high ALP and OC mRNA expressions. We also injected the cell sheets into dead bone to determine whether the lost osteogenic potential could be rescued, and histological analyses revealed that the injected cell sheets supplied osteogenic potential to the dead bone. The present study clearly indicates that osteogenic MSC sheets can be transplanted via injection through a needle and that bone formation results in the injected areas. Owing to its usage of a needle for fabrication of in vivo bone tissue, this injection method can be applied as a minimally invasive approach for hard tissue reconstruction.

Engineering the extracellular environment: Strategies for building 2D and 3D cellular structures

Cell fate is regulated by extracellular environmental signals. Receptor specific interaction of the cell with proteins, glycans, soluble factors as well as neighboring cells can steer cells towards proliferation, differentiation, apoptosis or migration. In this review, approaches to build cellular structures by engineering aspects of the extracellular environment are described. These methods include non-specific modifications to control the wettability and stiffness of surfaces using self-assembled monolayers (SAMs) and polyelectrolyte multilayers (PEMs) as well as methods where the temporal activation and spatial distribution of adhesion ligands is controlled. Building on these techniques, construction of two-dimensional cell sheets using temperature sensitive polymers or electrochemical dissolution is described together with current applications of these grafts in the clinical arena. Finally, methods to pattern cells in three-dimensions as well as to functionalize the 3D environment with biologic motifs take us one step closer to being able to engineer multicellular tissues and organs.

Thermoresponsive copolymer nanofilms for controlling cell adhesion, growth, and detachment

This study reports the development and use of a novel thermoresponsive polymeric nanofilm for controlling cell adhesion and growth at 37 °C, and then cell detachment for cell recovery by subsequent temperature drop to the ambient temperature, without enzymatic cleavage or mechanical scraping. A copolymer, poly(N-isopropylacrylamide-co-hydroxypropyl methacrylate-co-3-(trimethoxysilyl)propyl methacrylate) (abbreviated PNIPAAm copolymer), was synthesized by free radical polymerization. The thermoresponses of the copolymer in aqueous solution were demonstrated by dynamic light scattering (DLS) through detecting the sensitive changes of copolymer aggregation against temperature. The DLS measurements revealed the lower critical solution temperature (LCST) at approximately 30 °C. The PNIPAAm film stability and robustness was provided through silyl cross-linking within the film and with the hydroxyl groups on the substrate surface. Film thickness, stability, and reversibility with respect to temperature switches were examined by spectroscopic ellipsometry (SE), atomic force microscopy (AFM), and contact angle measurements. The results confirmed the high extent of thermosensitivity and structural restoration based on the alterations of film thickness and surface wettability. The effective control of adhesion, growth, and detachment of HeLa and HEK293 cells demonstrated the physical controllability and cellular compatibility of the copolymer nanofilms. These PNIPAAm copolymer nanofilms could open up a convenient interfacial mediation for cell film production and cell expansion by nonenzymatic and nonmechanical cell recovery.

Films of dextran-graft-polybutylmethacrylate to enhance endothelialization of materials

We have synthesized new structures obtained from amphiphilic copolymers of dextran and polybutylmethacrylate with the aim of endothelialization of biomaterials. Grafting of butylmethacrylate onto dextran has been carried out using ceric ammonium nitrate as initiator. Three copolymers were obtained (11, 30 and 37 wt.% dextran) and homogeneous thin films were successfully prepared. In contrast to dextran, the resulting films were stable in water, and copolymers characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry and dynamic mechanical analysis showed evidence of hybrid properties between the parent homopolymers. Surfaces of films were smooth when analyzed by atomic force microscopy (roughness 2+/-1 nm) but greatly differed in their hydrophilicity by increasing the dextran content (water contact angle from 99 degrees to 57 degrees). In contrast to polybutylmethacrylate, where the proliferation of vascular smooth muscle cells (VSMCs) was excellent but that of endothelial cells was very low, the copolymer containing 11% of dextran was excellent for endothelial cells but very limited for VSMCs. An in vitro wound assay demonstrated that copolymer with 11% dextran is even more favorable for endothelial cell migration than tissue-culture polystyrene. Increasing the dextran content in the copolymers decreased the proliferation for both vascular cell types. Altogether, these results show that transparent and water-insoluble films made from copolymers of dextran and butylmethacrylate copolymers with an appropriate composition could enhance endothelial cell proliferation and migration. Therefore, a potential benefit of this approach is the availability of surfaces with tunable properties for the endothelialization of materials.

Cell sheet transplantation of cultured mesenchymal stem cells enhances bone formation in a rat nonunion model

Orthopedic surgeons have long been troubled by cases involving nonunion of fractured bones. This study aimed to enhance bone union by cell sheet transplantation of mesenchymal stem cells. A nonunion model was made in rat femur, and rat bone marrow cells were cultured in medium containing dexamethasone and ascorbic acid phosphate to create a cell sheet that could be scraped off as a single sheet. Cell sheets were transplanted onto fractured femurs without a scaffold in the model. X-ray and histological analysis were performed at 2, 4 and 8 weeks. Ultrasonography and biomechanical analysis were performed at 8 weeks. X-ray photographs and histological sections showed callus formation around the fracture site in the cell sheet-transplanted group (sheet group). Bone union was obtained in the sheet group at 8 weeks. By contrast, the control group (without sheet transplantation) showed nonunion of the femur. The results of pullout evaluation in the vertical direction of the femur in the sheet group were significantly better than that of the control group. Analysis of the origin of de novo formed bone using the Sry gene, which was used as a marker for donor cells, showed that transplanted cells without scaffolds could survive and differentiate into osteogenic lineage cells in vivo. These results showed that the femoral fracture in our model was completely cured by the transplantation of a cell sheet created by tissue engineering techniques. Thus, we think that cell sheet transplantation can contribute to hard tissue reconstruction in cases involving nonunion, bone defects and osteonecrosis.

Molecular rearrangement of metal-chelating lipid monolayers upon protein adsorption

The controlled adsorption of proteins to well-defined monolayers is critical to advances in sensor and nanotechnology applications where selective adsorption of targeted species is of interest. In the studies reported here, we developed vibrational spectroscopic methods to gain molecular insight into the effect of single-site versus multiple-site binding of proteins to metal-chelating monolayers at an air-water interface. Analysis of real-time planar array infrared reflection-absorption spectra revealed that a Cu(II)-chelated DSIDA lipid monolayer (Cu(2+)-DSIDA) was readily disrupted by adsorption of myoglobin as demonstrated by a blue shift of 1.7 cm(-1) in the v(as)(CH(2)) stretching mode and a reduced peak intensity over a period of 5 h. However, a Zn(II)-chelated monolayer was not affected by the adsorption of either protein, suggesting that multisite binding of protein on the Cu(2+)-DSIDA results in monolayer disruption. Further studies demonstrated that in film form, adsorption of myoglobin to the Cu(2+)-DSIDA perturbed the secondary structures of myoglobin, especially the alpha-helical, random structure, and extended structures. However, no distinct change was observed during adsorption of lysozyme. These results demonstrate the utility of these methods for monitoring the molecular rearrangement of both metal-charged lipid monolayers and proteins that occur during adsorption of a protein with a strong affinity for the monolayer.

Osteogenic matrix sheet-cell transplantation using osteoblastic cell sheet resulted in bone formation without scaffold at an ectopic site

We previously reported that in vivo bone formation could be observed in composites of porous hydroxyapatite (HA) scaffolds and cultured mesenchymal stem cells (MSCs). In the present study, we developed a new method for transplantation of cultured MSCs without the necessity of using a scaffold to form bone tissue. MSCs were culture-expanded and lifted as cell sheet structures. These cell sheets, designated osteogenic matrix sheets, showed positive alkaline phosphatase (ALP) staining, high ALP activities and high osteocalcin (OC) contents, indicating their osteogenic potential. We transplanted these sheets into subcutaneous sites in rats to assess whether they possessed in vivo bone-forming capability. The transplanted sheets showed mineralized matrix together with osteocytes and an active osteoblast lining, indicating new bone formation, at 6 weeks after transplantation. HA scaffolds were also wrapped with the sheets to make HA/sheet composites and implanted into subcutaneous sites in rats. Histological sections of the composites revealed bone formation in the HA pores at 4 weeks after implantation. Our present results indicate that MSCs can be cultured as sheet structures, and the resulting sheets themselves or HA-sheet composites represent osteogenic implants that can be used for hard tissue reconstruction.

Engineering cell de-adhesion dynamics on thermoresponsive poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) (PIPAAm) has been demonstrated as an effective thermoresponsive polymer for non-invasive cell regeneration/recovery. However, little is known about the intricate relationship between the biophysical response of cells and physiochemical properties of PIPAAm during cell recovery. In this study, the de-adhesion kinetics of smooth muscle cell (SMC) on PIPAAm surfaces is probed with unique biophysical techniques. Water-immersion atomic force microscope (AFM) first showed that the nanotopology of PIPAAm surfaces is dependent on the polymerization time and collagen coating. It is found that the initial rate of cell de-adhesion increases with the increase in polymerization time. Moreover, the degree of cell deformation (a/R) and average adhesion energy are reduced with the increase of grafted PIPAAm density during 40min of cell de-adhesion. It has been shown that collagen coating regulates cell adhesion on biomaterial surface. Interestingly, lower collagen density on PIPAAm leads to higher adhesion energy per cell during the initial 20min compared with as-prepared PIPAAm, while the initial rate of cell de-adhesion remains unchanged. In contrast, higher collagen density leads to 50% reduction in the initial rate of cell de-adhesion and higher adhesion energy per cell during the entire 90min. Furthermore, immunostaining of actin provides supporting evidence that the de-adhesion kinetics is correlated with the cytoskeleton transformation during cell de-adhesion below the lower solution critical temperature (LCST).

Surface energy effects on osteoblast spatial growth and mineralization

While short-term surface energy effects on cell adhesion are relatively well known, little is revealed as regards its later stage effects on cell behavior. We examined surface energy effects on osteoblastic cell growth and mineralization by using human fetal osteoblastic (hFOB) cells cultured on plasma-treated quartz (contact angle, theta=0 degrees) and octadecyltrichlorosilane (OTS)-treated quartz (theta=113 degrees). hFOB cells formed a homogeneous cell layer on plasma-treated quartz, while those cultured on OTS-treated quartz produced randomly distributed clump-like structures that were filled with cells (confirmed by confocal microscopy). Mineral deposition by hFOB cells was spatially homogeneous when cultured on hydrophilic surfaces. Furthermore, cells on hydrophilic surfaces exhibited increased mineralized area as well as enhanced mineral-to-matrix ratio (assessed by Fourier transform infrared spectroscopy), relative to cells on hydrophobic surfaces. Experiments using other types of osteoblast-like cells (MC3T3-E1, MG63, and SAOS-2) revealed more or less similar effects in spatial growth morphology. It was concluded that hydrophilic surfaces induce homogeneous spatial osteoblastic cell growth and mineral deposition and enhance the quantity (e.g., area) and quality (e.g., mineral-to-matrix ratio) of mineralization relative to hydrophobic surfaces. Our data suggest that surface energy effects on osteoblastic cell differentiation, especially mineralization, may be correlated with surface energy dependent changes in spatial cell growth.

Cellular control of tissue architectures using a three-dimensional tissue fabrication technique

Tissue engineering seeks to provide regenerated tissue architectures in vitro but has not yet successfully created thick, highly vascularized, multi-functional tissues replicating native structure. We describe a novel method to fabricate pre-vascularized tissue equivalents using multi-layered cultures combining micro-patterned endothelial cells as vascular pre-cursors with fibroblast monolayer sheets as tissue matrix. Stratified tissue equivalents are constructed by alternately layering fibroblast monolayer sheets with patterned endothelial cell sheets harvested from newly developed thermo-responsive micro-patterned surfaces alternating 20 microm-wide cell-adhesive lanes with 60 microm non-adhesive zones. Cell culture substrates covalently grafted with different thermo-responsive polymers permit spatial switching of cell adhesion and detachment using applied small temperature changes. Endothelial cell patterning fidelity was maintained within the multi-layer tissue constructs after assembly, leading to self-organization into microvascular-like networks after 5-day tissue culture. This novel technique holds promise for the study of cell-cell communications and angiogenesis in reconstructed, three-dimensional environments as well as for the fabrication of tissues with complex, multicellular architecture.

Adhesion behavior of human bone marrow stromal cells on differentially wettable polymer surfaces

An appropriate cellular response to implanted surfaces is essential for tissue regeneration and integration. In this study, we investigated how human bone marrow stromal cells (hBMSCs) respond to scaffold substrates. We prepared wettable polymer surfaces by exposing polymer sheets to radio frequency plasma discharge, which gradually oxidizes the polymer surface, increasing the roughness and greatly reducing the hydrophobicity. We found that hBMSCs adhered better to highly hydrophilic and rough surfaces than to hydrophobic and smooth surfaces. In addition, the cells flattened extensively on hydrophilic surfaces. Further, c-fos gene expression increased in parallel with the degree of hydrophilicity, whereas the expression of the c-myc gene was higher on hydrophobic than on hydrophilic surfaces. Finally, p53 gene expression was higher on more hydrophobic or hydrophilic surfaces than on moderately hydrophobic or hydrophilic surfaces. These results indicate that the biological signals induced by cell adhesion depend on the wettability of the surface to which the cells attach.

Patterned biofunctional designs of thermoresponsive surfaces for spatiotemporally controlled cell adhesion, growth, and thermally induced detachment

In the present study, we report advanced patterned biofunctionalization of thermoresponsive surfaces for achievement of spatiotemporally controlled cell adhesion, growth, and thermally induced detachment. These patterned biofunctional thermoresponsive surfaces were prepared using dual surface modification techniques: electron beam-induced surface patterning of carboxyl-functional thermoresponsive polymers with appropriate metal masks and following site-selective biofunctionalization with biomolecules, the cell adhesive peptide (RGDS) and/or the cell growth factor (insulin; INS). Patterned co-immobilization of RGDS-INS onto thermoresponsive surfaces dominated site-selective cell adhesion and growth along with patterned biofunctional domains in the serum-free culture. Spatiotemporal detachment of sparsely adherent and confluent cells from these patterned biofunctional thermoresponsive surfaces were both achieved only by reducing temperature. Furthermore, RGDS-INS-patterned thermoresponsive surfaces also successfully demonstrated the selective fabrication and recovery of either contiguous monolayer or mesh-like designed monolayer tissue constructs on the identical surfaces. Thus, patterned biofunctional designs would be utilized for the creation and harvest of biomimetic-designed vascular networks having sufficient biofunctional activities in facilitated cell sheet engineering and regenerative medicine.

Hydrogels as Extracellular Matrices for Skeletal Tissue Engineering: State-of-the-Art and Novel Application in Organ Printing

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Cell Sensing and Response to Micro- and Nanostructured Surfaces Produced by Chemical and Topographic Patterning

Chemical and topographic substrate surface patterning is recognized as a powerful tool for regulating cell functions. We discuss the relative role of scale and pattern of chemically and topographically patterned surfaces in regulating cell behavior. Chemical patterning achieved using spatial cell-adhesive molecular organization regulates different cell functions depending on its scale (micropattern for cell patterning and derived cell functions, nanopattern for collective cell functions such as adhesion, proliferation, and differentiation). In chemical patterning, a direct and specific cell-sensing mechanism such as integrin-ligand binding governs. Alternatively, topographic modification affects different cell functions depending on its pattern (anisotropic ridges and grooves for contact-guided cell alignment, isotropic textures having randomly or evenly distributed topographic features for collective functions). For all topographic patterns, micro- or nanotopographic scale determines whether specific cell reactions occur. If the topography effect were assessed under the same surface chemistry, cell adaptation processes would play a major role in cell sensing and response to topography, largely independent of mediation via differences in adsorbed proteins. Controlling scale and pattern in chemical and topographic substrate patterning would help significantly to develop purpose-specific cell-regulating cues in various biomedical applications, including tissue engineering, implants, cell-based biosensors, microarrays, and basic cell biology.

Polymer carriers for drug delivery in tissue engineering

Growing demand for tissues and organs for transplantation and the inability to meet this need using by autogeneic (from the host) or allogeneic (from the same species) sources has led to the rapid development of tissue engineering as an alternative. Tissue engineering aims to replace or facilitate the regrowth of damaged or diseased tissue by applying a combination of biomaterials, cells and bioactive molecules. This review focuses on synthetic polymers that have been used for tissue growth scaffold fabrication and their applications in both cell and extracellular matrix support and controlling the release of cell growth and differentiation supporting drugs.

Novel living cell sheet harvest system composed of thermoreversible methylcellulose hydrogels

In this study, a novel yet simple method, using a thermoreversible hydrogel system coated on tissue culture polystyrene (TCPS) dishes, was developed for harvesting living cell sheets. The hydrogel system was prepared by simply pouring aqueous methylcellulose (MC) solutions blended with distinct salts on TCPS dishes at 20 degrees C. For the applications to cell culture, only those aqueous MC compositions that may form a gel at 37 degrees C were chosen for the study. It was found that the hydrogel coating composed of 8% MC blended with 10 g/L PBS (phosphate buffered saline) (the MC/PBS hydrogel, with a gelation temperature of approximately 25 degrees C) stayed intact throughout the entire course of cell culture. To improve cell attachments, the MC/PBS hydrogel at 37 degrees C was evenly spread with a neutral aqueous collagen at 4 degrees C. The spread aqueous collagen gradually reconstituted with time and thus formed a thin layer of collagen (the MC/PBS/collagen hydrogel). After cells reached confluence, a continuous monolayer cell sheet formed on the surface of the MC/PBS/collagen hydrogel. When the grown cell sheet was placed outside of the incubator at 20 degrees C, it detached gradually from the surface of the thermoreversible hydrogel spontaneously, without treating with any enzymes. The results obtained in the MTT assay demonstrated that the cells cultured on the surface of the MC/PBS/collagen hydrogel had an even better activity than those cultured on an uncoated TCPS dish. After harvesting the detached cell sheet, the remaining viscous hydrogel system is reusable. Additionally, the developed hydrogel system can be used for culturing a multilayer cell sheet. The obtained living cell sheets may be used for tissue reconstructions.

Osteoblast Adhesion on Poly(l-lactic Acid)/Polystyrene Demixed Thin Film Blends: Effect of Nanotopography, Surface Chemistry, and Wettability

Biomaterial surface characteristics are critical cues that regulate cell function. We produced a novel series of poly(l-lactic acid) (PLLA) and polystyrene demixed nanotopographic films to provide nonbiological cell-stimulating cues. The increase in PLLA weight fraction (phi) in blend solutions resulted in topography changes in spin-cast films from pit-dominant to island-dominant morphologies having nanoscale depth or height (3-29 nm). Lower molecular weight PLLA segregated to the top surface of demixed films, as observed by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS). For phi > or = 0.5, the topmost film layer was predominantly filled with PLLA (>96% by SIMS at 20-A depth). Nanotextured substrata stimulated osteoblastic cell adhesion to a greater degree than did flat PLLA (phi = 1), and this effect was more pronounced for nanoisland (phi = 0.7 and 0.9) relative to nanopit topographies (phi = 0.5). Demixed films having relatively lower water contact angles generally enhanced cell adhesion and spreading. Our results reveal that cell adhesion is affected by surface chemistry, topography, and wettability simultaneously and that nanotextured surfaces may be utilized in regulating cell adhesion.