Accelerated cell sheet recovery by co-grafting of PEG with PIPAAm onto porous cell culture membranes

Construction of a chondrocyte cell sheet using temperature-responsive poly(N-isopropylacrylamide)-co-acrylamide

In this study, a novel temperature-responsive poly(N-isopropylacrylamide)-co-acrylamide was used to prepare a chondrocyte cell sheet. Chondrocytes were isolated from human articular cartilage and plated on the copolymer film grafted tissue culture plates. The cell attachment on the copolymer film was shown to be similar to that of the ungrafted surface. To harvest a cell sheet, the incubation temperature was reduced to 10°C for 30 minutes to allow the polymer chain to fully extend, changing the copolymer's phase from hydrophobicity to hydrophilicity. Additional incubation at 20°C for 60 minutes was necessary to activate the cellular metabolism required for cytoskeletal organization and cell detachment. A complete cell sheet recovery was achieved when a PVDF membrane was used as a cell sheet carrier. Unfortunately, the shrinkage of the cell sheet was observed. Nonetheless, the harvested cell sheet was shown to be viable and healthy.

Rate control of cell sheet recovery by incorporating hydrophilic pattern in thermoresponsive cell culture dish

Thready stripe-polyacrylamide (PAAm) pattern was fabricated on a thermoresponsive poly(N-isopropylacrylamide) (PIPAAm) surface, and their surface properties were characterized. A PIPAAm surface spin-coated with positive photoresist was irradiated through a 5 µm/5 µm or a 10 µm/10-µm black and white striped photomask, resulting in the radical polymerization of AAm on the photoirradiated area. After staining with Alexa488 bovine serum albumin, the stripe-patterned surface was clearly observed and the patterned surface was also observed by a phase contrast image of an atomic force microscope. NIH-3T3 (3T3) single cells were able to be cultured at 37°C on the patterned surfaces as well as on a PIPAAm surface without pattern, and the detachment of adhered cells was more rapidly from the patterned surface after reducing temperature. Furthermore, the rate of detachment of 3T3 confluent cell sheet on the patterned surface was accelerated, compared with on a conventional PIPAAm surface under the static condition. The rate control of cell sheet recovery should contribute the preservations of cell phenotype and biological functions of cell sheet for applying to clinical trials.

Initiated chemical vapor deposition of thermoresponsive poly(N-vinylcaprolactam) thin films for cell sheet engineering

Poly(N-vinylcaprolactam) (PNVCL) is a thermoresponsive polymer known to be nontoxic, water soluble and biocompatible. Here, PNVCL homopolymer was successfully synthesized for the first time by use of a one-step vapor-phase process, termed initiated chemical vapor deposition (iCVD). Fourier transform infrared spectroscopy results showed that radical polymerization took place from N-vinylcaprolactam monomers without damaging the functional caprolactam ring. A sharp lower critical solution temperature transition was observed at 31°C from the iCVD poly(N-vinylcaprolactam) (PNVCL) film. The thermoresponsive PNVCL surface exhibited a hydrophilic/hydrophobic alteration with external temperature change, which enabled the thermally modulated attachment and detachment of cells. The conformal coverage of PNVCL film on various substrates with complex topography, including fabrics and nanopatterns, was successfully demonstrated, which can further be utilized to fabricate cell sheets with aligned cell morphology. The advantage of this system is that cells cultured on such thermoresponsive surfaces could be recovered as an intact cell sheet by simply lowering the temperature, eliminating the need for conventional enzymatic treatments.

Human corneal endothelial cell sheets for transplantation: thermo-responsive cell culture carriers to meet cell-specific requirements

Corneal endothelial diseases lead to severe vision impairment, motivating the transplantation of donor corneae or corneal endothelial lamellae, which is, however, impeded by endothelial cell loss during processing. Therefore, one prioritized aim in corneal tissue engineering is the generation of transplantable human corneal endothelial cell (HCEC) layers. Thermo-responsive cell culture carriers are widely used for non-enzymatic harvest of cell sheets. The current study presents a novel thermo-responsive carrier based on simultaneous electron beam immobilization and cross-linking of poly(vinyl methyl ether) (PVME) on polymeric surfaces, which allows one to adjust layer thickness, stiffness, switching amplitude and functionalization with bioactive molecules to meet cell type specific requirements. The efficacy of this approach for HCEC, which require elaborate cell culture conditions and are strongly adherent to the substratum, is demonstrated. The developed method may pave the way to tissue engineering of corneal endothelium and significantly improve therapeutic options.

Cell-adhesive and cell-repulsive zwitterionic oligopeptides for micropatterning and rapid electrochemical detachment of cells

In this study, we describe the development of oligopeptide-modified cell culture surfaces from which adherent cells can be rapidly detached by application of an electrical stimulus. An oligopeptide, CGGGKEKEKEK, was designed with a terminal cysteine residue to mediate binding to a gold surface via a gold-thiolate bond. The peptide forms a self-assembled monolayer through the electrostatic force between the sequence of alternating charged glutamic acid (E) and lysine (K) residues. The dense and electrically neutral oligopeptide zwitterionic layer of the modified surface was resistant to nonspecific adsorption of proteins and adhesion of cells, while the surface was altered to cell adhesive by the addition of a second oligopeptide (CGGGKEKEKEKGRGDSP) containing the RGD cell adhesion motif. Application of a negative electrical potential to this gold surface cleaved the gold-thiolate bond, leading to desorption of the oligopeptide layer, and rapid (within 2 min) detachment of virtually all cells. This approach was applicable not only to detachment of cell sheets but also for transfer of cell micropatterns to a hydrogel. This electrochemical approach of cell detachment may be a useful tool for tissue-engineering applications.

Microporous membrane-based liver tissue engineering for the reconstruction of three-dimensional functional liver tissues in vitro

To meet the increasing demand for liver tissue engineering, various three-dimensional (3D) liver cell culture techniques have been developed. Nevertheless, conventional liver cell culture techniques involving the suspending cells in extracellular matrix (ECM) components and the seeding of cells into 3D biodegradable scaffolds have an intrinsic shortcoming, low cell-scaffold ratios. We have developed a microporous membrane-based liver cell culture technique. Cell behaviors and tissue organization can be controlled by membrane geometry, and cell-dense thick tissues can be reconstructed by layering cells cultured on biodegradable microporous membranes. Applications extend from liver parenchymal cell monoculture to multi-cell type cultures for the reconstruction of 3D functional liver tissue. This review focuses on the expanding role for microporous membranes in liver tissue engineering, primarily from our research.

Shear stress-dependent cell detachment from temperature-responsive cell culture surfaces in a microfluidic device

A new approach to quantitatively estimate the interaction between cells and material has been proposed by using a microfluidic system, which was made of poly(dimethylsiloxane) (PDMS) chip bonding on a temperature-responsive cell culture surface consisted of poly(N-isopropylacrylamide) (PIPAAm) grafted tissue culture polystyrene (TCPS) (PIPAAm-TCPS) having five parallel test channels for cell culture. This construction allows concurrently generating five different shear forces to apply to cells in individual microchannels having various resistance of each channel and simultaneously gives an identical cell incubation condition to all test channels. NIH/3T3 mouse fibroblast cells (MFCs) and bovine aortic endothelial cells (BAECs) were well adhered and spread on all channels of PIPAAm-TCPS at 37 °C. In our previous study, reducing culture temperature below the lower critical solution temperature (LCST) of PIPAAm (32 °C), cells detach themselves from hydrated PIPAAm grafted surfaces spontaneously. In this study, cell detachment process from hydrated PIPAAm-TCPS was promoted by shear forces applied to cells in microchannels. Shear stress-dependent cell detachment process from PIPAAm-TCPS was evaluated at various shear stresses. Either MFCs or BAECs in the microchannel with the strongest shear stress were found to be detached from the substrate more quickly than those in other microchannels. A cell transformation rate constant C(t) and an intrinsic cell detachment rate constant k(0) were obtained through studying the effect of shear stress on cell detachment with a peeling model. The proposed device and quantitative analysis could be used to assess the possible interaction between cells and PIPAAm layer with a potential application to design a cell sheet culture surface for tissue engineering.

Rapid cell sheet detachment using spin-coated pNIPAAm films retained on surfaces by an aminopropyltriethoxysilane network

The ability to harvest cell sheets grown on thermoresponsive polymers, such as poly(N-isopropylacrylamide) (pNIPAAm), has been widely studied for use in tissue engineering applications. pNIPAAm is of special interest because of the phase change that it undergoes in a physiologically relevant temperature range. Two primary approaches have been adopted to graft pNIPAAm chains covalently onto tissue culture polystyrene dishes: electron beam irradiation and plasma polymerization. These approaches often involve non-easily accessible (e.g. e-beam) facilities and complicated procedures that have hindered most tissue culture laboratories in adopting this technology for their specific applications. In this study, we developed a simple and cost-effective approach to create thermoresponsive surfaces using commercially available pNIPAAm. Using a simple spin-coating technique, thermoresponsive thin films were deposited on glass slides or silicon wafers using pNIPAAm blended with a small amount of 3-aminopropyltriethoxysilane (APTES), which enhances the retention of pNIPAAm on the surface. We found that the thermoresponsive films created using our method support cell attachment and proliferation without additional adhesive proteins as well as cell sheet detachment within minutes.

Tissue engineering based on electrochemical desorption of an RGD-containing oligopeptide

This paper describes a non-invasive approach for efficient detachment of cells adhered to a gold substrate via a specific oligopeptide. Detachment is effected by an electrical stimulus. The oligopeptide contains cysteine, which spontaneously forms a gold-thiolate bond on a gold surface. This chemical adsorption reaches > 95% equilibrium within 10 min after immersion of a gold-coated substrate in a solution containing the peptide. The peptide is reversibly desorbed from the surface within 5 min of application of a negative electrical potential. By taking advantage of this simple adsorption and desorption mechanism, cells can be grown on an oligopeptide-functionalized gold surface and can be efficiently detached as single cells or cell sheets by application of a negative electrical potential. This approach was also applied to the surface of gold-coated microrods. Capillary-like microchannels were formed in collagen gel by transferring endothelial cells to the internal surfaces of the microchannels. During subsequent perfusion culture, the enveloped endothelial cells migrated into the collagen gel and formed luminal structures, which sprouted from the microchannels. This technique has the potential to provide a fundamental tool for the engineering of thick cell sheets as well as vascularized tissues and organs.

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.

Cell growth as a sheet on three-dimensional sharp-tip nanostructures

Cells in vivo encounter with and react to the extracellular matrix materials on a nanometer scale. Recent advances in nanofabrication technologies allowing the precise control of a nanostructure's pattern, periodicity, shape, and height have enabled a systematic study of cell interactions with three-dimensional nanotopographies. In this report, we examined the behavior of human foreskin fibroblasts on well-ordered dense arrays (post and grate patterns with a 230-nm pitch) of sharp-tip nanostructures with varying three-dimensionalities (from 50 to 600 nm in structural height) over time-until a cell sheet was formed. Although cells started out smaller and proliferated slower on tall nanostructures (both posts and grates) than on smooth surfaces, they became confluent to form a sheet in 3 weeks. On grate patterns, significant cell elongation in alignment with the underlying pattern was observed and maintained over time. On tall nanostructures, cells grew while raised on sharp tips, resulting in a weak total adherence to the solid surface. A sheet of cells was easily peeled off from such surfaces, suggesting that nanoscale topographies can be used as the basis for cell-sheet tissue engineering.

Cell adhesion and accelerated detachment on the surface of temperature-sensitive chitosan and poly(N-isopropylacrylamide) hydrogels

A series of temperature-sensitive poly(NIPAAm-co-CSA) hydrogels were synthesized by the copolymerization of acrylic acid-derivatized Chitosan (CSA) and N-isopropylacrylamide (NIPAAm) in aqueous solution. Their swelling properties and L929 cell adhesion and detachment behaviors were studied. It was found that poly(NIPAAm-co-CSA) hydrogels were temperature-sensitive associated with the roles of the component PNIPAAm. Most significantly, poly(NIPAAm-co-CSA) hydrogels exhibited simultaneously good swelling properties. The investigation of L929 cell adhesion and detachment of poly(NIPAAm-co-CSA) hydrogels indicated the cell adhesion and spreading was higher on the surface of poly(NIPAAm-co-CSA) hydrogels than that of PNIPAAm hydrogel at 37 degrees C due to the incorporation of CS, which having excellent cell affinity. Poly(NIPAAm-co-CSA) hydrogels showed more rapid detachment of cell sheet compared to PNIPAAm hydrogel because of the highly hydrophilic and hygroscopic nature of CS chains when reducing the culture temperature from 37 degrees C to 20 degrees C.

Engineered extracellular matrices with cleavable crosslinkers for cell expansion and easy cell recovery

An unmet need for expansion of primary cells and progenitor cells in three dimensions (3-D) is a synthetic mimic of the extracellular matrix (ECM) with user-controllable composition that would permit rapid recovery of viable cells under mild, non-enzymatic conditions. Three block copolymers based on disulfide-containing polyethylene glycol diacrylate crosslinkers were synthesized, and were used to crosslink thiol-modified hyaluronan and gelatin macromonomers in the presence of cells. The triblock PEGSSDA contained a single disulfide-containing block, the pentablock PEG(SS)(2)DA contained two disulfide blocks, and the heptablock PEG(SS)(3)DA contained three disulfide blocks. For each hydrogel composition, four cell types were encapsulated in 3-D, and growth and proliferation were evaluated. Murine NIH 3T3 fibroblasts, human HepG2 C3A hepatocytes, human bone marrow-derived mesenchymal stem cells (MSCs), and human umbilical vein endothelial cells (HUVECs) all showed excellent viability and growth during expansion in 3-D in the three disulfide block copolymer crosslinkers. After cell expansion, the hydrogels were dissociated using the thiol-disulfide exchange reaction in the presence of N-acetyl-cysteine or glutathione, which dissolved the hydrogel network. After dissolution, cells were recovered in high yield and with high viability by gentle centrifugation.

Intact endothelial cell sheet harvesting from thermoresponsive surfaces coated with cell adhesion promoters

Recently, with the development of smart polymers, research has looked to using thermoresponsive polymers as cell culture substrates. These novel surfaces allow the cultivation of cells without enzymes using the thermoresponsive phase transition property of poly(N-isopropylacrylamide) (PNIPAAm). However, this requires expensive techniques to generate a sufficiently thin film that allows cell adhesion. In this study, we looked at simple solvent cast films which normally show poor cell adhesion, but here the films are coated with cell adhesion promoters (CAPs) to improve cell growth without altering the copolymer thermoresponsive behaviour.A copolymer of PNIPAAm and N-tert-butylacrylamide (NtBAm) with a ratio of 85:15, respectively, was synthesized and solvent cast. The copolymer films were coated with CAPs, such as collagen, fibronectin and laminin, to increase their cell adhesion and growth properties. Cell activity measured by the alamarBlue assay showed similar results for coated copolymer films and standard tissue culture plastic controls. Deposition of CAPs on to the copolymer films was characterized by scanning electron microscopy and atomic force microscopy. Cell detachment from the copolymer films is not affected by the surface coatings of CAPs, and endothelial cells are recovered as an intact sheet, which has great potential for uses in tissue engineering applications. The results demonstrate a versatile method for the cultivation of cells while eliminating the need for the use of digestive enzymes such as trypsin. This study shows that cultivation on physically bonded PNIPAAm copolymers is viable and achievable by relatively simple methods.

Cryogels from poly(2-hydroxyethyl methacrylate): macroporous, interconnected materials with potential as cell scaffolds

Macroporous hydrogels (MHs) have been prepared by cross-linking polymerization of hydroxyethyl methacrylate (HEMA) or cross-linking co-polymerization of HEMA with dimethylacrylamide (DMAA) in semi-frozen state. The MHs are elastic and have a unique structure of large interconnected pores with pore sizes up to 100 µm and total porosity of 94-97%, as demonstrated by micro-computed tomography. The stiffness of such MHs increased with total monomer concentration and with the ratio of DMAA in the composition. Pore-surface modification of the HEMA MHs was achieved by grafting a stimuli-responsive polymer, poly(-isopropylacrylamide) (PNIPAM), with high density using atom transfer radical polymerization (ATRP). The effect of catalytic system, initiator content and the addition of sacrificial initiator on the ATRP process have been studied. The elasticity, possibility of drying and fast re-swelling, tunable mechanical properties and the macroporous, interconnected structure of HEMA MHs are of interest for biomedical applications such as cell culturing.

Thermo-responsive poly(NiPAAm-co-DEGMA) substrates for gentle harvest of human corneal endothelial cell sheets

Gentle harvesting of corneal endothelial cell sheets grown in culture is of interest for the development of cornea replacement strategies. Thin films of a fast responding copolymer of N-isopropylacrylamide (NiPAAm) and diethyleneglycol methacrylate (DEGMA) with a phase transition temperature of 32 degrees C were prepared and evaluated for that purpose. The polymer layers were immobilized onto fluorocarbon substrates using low pressure argon plasma treatment. Cell culture and detachment experiments were performed with L929 mouse fibroblasts and human corneal endothelial cells (HCEC) at standard conditions. The hydrogel-coated supports were found to permit adhesion, spreading, and proliferation of both cell types. Harvesting of cell sheets was achieved upon lowering the temperature to about 30 degrees C. The formation of a closed monolayer as a crucial prerequisite for maintaining ionic pump function in HCEC was proven by ZO-1 immunostainung. Labeling of fibronectin indicated that the vast majority of the extracellular matrix is detached from the hydrogel coatings together with the cell layer. Inspired by this result, the reuse of the hydrogel-coated culture carriers was investigated confirming the suitability of the substrates for repeated cell harvesting. Altogether, the introduced thermoresponsive coating was found advantageous for the efficient generation of HCEC sheets and will be further utilized in transplantation strategies.

Modification of HTPB-based polyurethane with temperature-sensitive poly(N-isopropyl acrylamide) for biomaterial usage

Hydroxyl-terminated polybutadiene (HTPB)-based polyurethane with dimethyol propionic acid (DPA) as chain extender was synthesized by solution polymerization. The HTPB-based polyurethane was modified by UV radiation with N-isopropyl acrylamide monomer to get poly(N-isopropyl acrylamide)-modified polyurethane (PUDPANIPAAm). The cohesive energy (E(coh)), molar volume (V), solubility parameter (delta), molecular weight (W(M)), volume per gram (V(g)), and the density (1/V(g)) of PUDPANIPAAm were calculated by group contribution methods. To evaluate the application of PUDPANIPAAm for wound dressing and transplantation of cell sheet, the measurement of water content, water vapor transmission rate, and gas permeation on the PUDPANIPAAm membrane was evaluated. The biocompatibility of these membranes, cell adhesion, and proliferation assay were conducted in the cell culture. The effect of thermosensitivity of poly(N-isopropyl acrylamide) on cell detachment was also evaluated in the primary study. The results showed that these PUDPANIPAAm membranes are thermosensitive. The modification of PU with poly(N-isopropyl acrylamide) reduced the water vapor transmission rate and permeability of gas through PUDPANIPAAm membrane. PUDPANIPAAm membranes could support cell adhesion and growth. Owing to the thermosensitive nature of poly(N-isopropyl acrylamide), the relative cell numbers detached from PUDPANIPAAm membranes were larger than those detached from the polystyrene dish.

Cell sheet detachment affects the extracellular matrix: A surface science study comparing thermal liftoff, enzymatic, and mechanical methods

This work compares the removal of bovine aortic endothelial cell (BAEC) monolayers via 1) low-temperature liftoff from a "smart polymer," plasma polymerized poly(N-isopropyl acrylamide) (ppNIPAM), 2) enzymatic digestion, and 3) mechanical dissociation from ppNIPAM surfaces. We examine the surfaces after cell removal by using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), immunostaining, and cell adhesion assay. Immunoassay results indicate that low-temperature liftoff nondestructively harvests the cell sheet and most of the underlying extracellular matrix (ECM), whereas enzymatic digestion and mechanical dissociation are damaging to both the cells and ECM. XPS results indicate that amide and alcohol groups attributed to proteins in the ECM are present on postliftoff surfaces. Principal component analysis (PCA) of ToF-SIMS data indicates that molecular ion fragments of amino acids are present on postliftoff surfaces. Finally, a cell adhesion assay seeding new cells on surfaces from which an initial layer of cells was removed via each of the three methods indicates that liftoff and mechanical dissociation leave behind surfaces that better promote cell adhesion. We conclude that the removal of BAEC cells via low-temperature liftoff from ppNIPAM-treated surfaces is less damaging to the ECM proteins remaining at the surface than the other methods.

Grafted thermo- and pH responsive co-polymers: Surface-properties and bacterial adsorption

A series of responsive polymers displaying pH and temperature-mediated phase changes were prepared from N-isopropylacrylamide and omega-carboxylic acid functionalised acrylamides. These polymers were grafted to surfaces and their characteristics probed by atomic force microscopy in aqueous solutions. The effects of pH and temperature induced phase transitions on the short-term adsorption of the bacteria Salmonella typhimurium and Bacillus cereus from pure cultures were assessed. Contact angle studies indicated that pH and temperature-dependent surface properties were exhibited by the graft polymer surfaces. Temperature-dependent surface morphology changes occurred through polymer graft phase transitions as observed in AFM and accompanying changes in adhesion forces underwater were found to correlate with surface properties obtained from contact angle measurements. Adsorption of S. typhimurium and B. cereus was not significantly altered as a function of pH, but attachment of both bacterial strains increased at temperatures above the polymer coil-globule transition indicating the importance of switching surface hydrophobicity in controlling short-term bacterial adsorption.

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

A novel multifunctional linear block copolymer, poly(N-isopropylacrylamide-co-acrylic acid)-b-poly( L-lactic acid) (NAL), was synthesized to expand the concept of cell sheet engineering by using its thermoresponsive property and processibility. The chemical structure of synthesized NAL was confirmed by Fourier transform infrared spectroscopy, and its molar mass (103,500 g.mol(-1)) and molar mass distribution were determined by matrix-assisted laser desorption/ionization-time of flight mass spectroscopy. NAL copolymer was fabricated into thin films by spin-casting. Spin-cast NAL films displayed thermoresponsive properties as demonstrated by surface wettability and topology changes from relatively more hydrophobic (contact angle of 56 degrees) and rougher at 37 degrees C to relatively more hydrophilic (contact angle of 40 degrees) and smoother at 22 degrees C, as assessed by contact angle measurement and atomic force microscopy, respectively. Murine osteoblastic MC3T3-E1 cells displayed comparable adhesion but slower proliferation on NAL films than on poly(L-lactic acid) (PLLA) films and tissue culture polystyrene (TCPS). Within 9 days of cell culture, the highest alkaline phosphatase activity of MC3T3-E1 cells occurred later (on day 9) on NAL films than on PLLA films and TCPS (on day 6). A well-established MC3T3-E1 cell sheet was successfully detached from NAL films, in the absence of enzymes, within about 5 min by simply lowering the temperature from 37 degrees C to room temperature. NAL copolymer has potential for use in the controlled release of therapeutic agents while simultaneously supporting cell growth. In addition, it may be applicable for noninvasive two- or three-dimensional cell sheet harvesting.

Regulation of cell adhesion using a signal-responsive membrane substrate

We have developed a novel cell culture material that regulates cell adhesion by changes in potassium ion concentration. The material is a polyethylene substrate grafted to a copolymer of the thermoresponsive polymer N-isopropylacrylamide (NIPAM) and benzo-18-crown- 6-acrylamide (BCAm), with a pendant crown ether as sensor. The crown ether recognizes potassium ion concentrations and NIPAM conformational changes lead to changes in the hydrophobicity/hydrophilicity balance of the entire polymer at constant cell culture temperatures. Although cells were successfully cultured on the ion recognition material in normal culture medium at 37 degrees C, the cells could be detached from the material surface by adding potassium ions alone, without proteolytic enzymes, because the surface to which the cells were attached altered its surface characteristics to a more hydrophilic state. Therefore, cell layers with intact cell-to-cell junctions and high activities were successfully recovered. Furthermore, by changing the target sensors, this material will be able to control cell adhesion through various cellular signals.