The use of electron beam lithographic graft-polymerization on thermoresponsive polymers for regulating the directionality of cell attachment and detachment

The Impact of Polyethylene Glycol-Modified Chitosan Scaffolds on the Proliferation and Differentiation of Osteoblasts

The objective of this study was to investigate the influence of polyethylene glycol (PEG) incorporated chitosan scaffolds on osteoblasts proliferation and differentiation. The chitosan polymer was initially modified by the predetermined concentration of the photoreactive azido group for UV-crosslinking and with RGD peptides (N-acetyl-GRGDSPGYG-amide). The PEG was mixed at different ratios (0, 10, and 20 wt%) with modified chitosan in 96-well tissue culture polystyrene plates to prepare CHI-100, CHI-90, and CHI-80 scaffolds. PEG-containing scaffolds exhibited bigger pore size and higher water content compared to unmodified chitosan scaffolds. After 10 days of incubation, the cell number of CHI-90 (1.1 × 106 cells/scaffold) surpasses that of CHI-100 (9.2 × 105 cells/scaffold) and the cell number of CHI-80 (7.6 × 105 cells/scaffold) were significantly lower. The ALP activity of CHI-90 was the highest on the fifth day indicating the favored osteoblasts' early-stage differentiation. Moreover, after 14 days of osteogenic culture, calcium deposition in the CHI-90 scaffolds (2.7 μmol Ca/scaffold) was significantly higher than the control (2.2 μmol Ca/scaffold) whereas on CHI-80 was 1.9 μmol/scaffold. The results demonstrate that PEG-incorporated chitosan scaffolds favored osteoblasts proliferation and differentiation; however, mixing relatively excess PEG (≥20% wt.) had a negative impact on osteoblasts proliferation and differentiation.

Thermoresponsive surfaces designed for the proliferation and differentiation of human pluripotent stem cells

Thermoresponsive surfaces enable the detachment of cells or cell sheets by decreasing the temperature of the surface when harvesting the cells. However, human pluripotent stem cells (hPSCs), such as embryonic stem cells and induced pluripotent stem cells, cannot be directly cultured on a thermoresponsive surface; hPSCs need a specific extracellular matrix to bind to the integrin receptors on their surfaces. We prepared a thermoresponsive surface by using poly(N-isopropylacrylamide-co-butylacrylate) and recombinant vitronectin to provide an optimal coating concentration for the hPSC culture. hPSCs can be cultured on the same thermoresponsive surface for 5 passages by partial detachment of the cells from the surface by decreasing the temperature for 30 min; then, the remaining hPSCs were subsequently cultured on the same dishes following the addition of new cultivation media. The detached cells, even after continual culture for five passages, showed high pluripotency, the ability to differentiate into cells derived from the 3 germ layers and the ability to undergo cardiac differentiation.

UV-Laser Interference Lithography for Local Functionalization of Plasmonic Nanostructures with Responsive Hydrogel

A novel approach to local functionalization of plasmonic hotspots at gold nanoparticles with biofunctional moieties is reported. It relies on photocrosslinking and attachment of a responsive hydrogel binding matrix by the use of a UV interference field. A thermoresponsive poly(N-isopropylacrylamide)-based (pNIPAAm) hydrogel with photocrosslinkable benzophenone groups and carboxylic groups for its postmodification was employed. UV-laser interference lithography with a phase mask configuration allowed for the generation of a high-contrast interference field that was used for the recording of periodic arrays of pNIPAAm-based hydrogel features with the size as small as 170 nm. These hydrogel arrays were overlaid and attached on the top of periodic arrays of gold nanoparticles, exhibiting a diameter of 130 nm and employed as a three-dimensional binding matrix in a plasmonic biosensor. Such a hybrid material was postmodified with ligand biomolecules and utilized for plasmon-enhanced fluorescence readout of an immunoassay. Additional enhancement of the fluorescence sensor signal by the collapse of the responsive hydrogel binding matrix that compacts the target analyte at the plasmonic hotspot is demonstrated.

Injection Molded Microfluidics for Establishing High-Density Single Cell Arrays in an Open Hydrogel Format

Here, we develop an injection molded microfluidic approach for single cell analysis by making use of (1) rapidly curing injectable hydrogels, (2) a high density microfluidic weir trap array, and (3) reversibly bonded PDMS lids that are strong enough to withstand the injection molding process, but which can be peeled off after the hydrogel sets. This approach allows for single cell patterns to be created with densities exceeding 40 cells per mm2, is amenable to high speed imaging, and creates microfluidic devices that enable efficient nutrient and gas exchange and the delivery of specific biological and chemical reagents to individual cells. We show that it is possible to organize up to 10 000 single cells in a few minutes on the device, and we developed an image analysis program to automatically analyze the single-cell capture efficiency. The results show single cell trapping rates were better than 80%. We also demonstrate that the genomic DNA of the single cells trapped in the hydrogel can be amplified via localized, multiple displacement amplification in a massively parallel format, which offers a promising strategy for analyzing single cell genomes. Finally, we show the ability to perform selective staining of individual cells with a commercial bioprinter, providing proof of concept of its ability to deliver tailored reagents to specific cells in an array for future downstream analysis. This injection molded microfluidic approach leverages the benefits of both closed and open microfluidics, allows multiday single cell cultures, direct access to the trapped cells for genotypic end point studies.

The design of a thermoresponsive surface for the continuous culture of human pluripotent stem cells

Commonly, stem cell culture is based on batch-type culture, which is laborious and expensive. We continuously cultured human pluripotent stem cells (hPSCs) on thermoresponsive dish surfaces, where hPSCs were partially detached on the same thermoresponsive dish by decreasing the temperature of the thermoresponsive dish to be below the lower critical solution temperature for only 30 min. Then, the remaining cells were continuously cultured in fresh culture medium, and the detached stem cells were harvested in the exchanged culture medium. hPSCs were continuously cultured for ten cycles on the thermoresponsive dish surface, which was prepared by coating the surface with poly(N-isopropylacrylamide-co-styrene) and oligovitronectin-grafted poly(acrylic acid-co-styrene) or recombinant vitronectin for hPSC binding sites to maintain hPSC pluripotency. After ten cycles of continuous culture on the thermoresponsive dish surface, the detached cells expressed pluripotency proteins and had the ability to differentiate into cells derived from the three germ layers in vitro and in vivo. Furthermore, the detached cells differentiated into specific cell lineages, such as cardiomyocytes, with high efficiency.

Dynamically Tunable Cell Culture Platforms for Tissue Engineering and Mechanobiology

Human tissues are sophisticated ensembles of many distinct cell types embedded in the complex, but well-defined, structures of the extracellular matrix (ECM). Dynamic biochemical, physicochemical, and mechano-structural changes in the ECM define and regulate tissue-specific cell behaviors. To recapitulate this complex environment in vitro, dynamic polymer-based biomaterials have emerged as powerful tools to probe and direct active changes in cell function. The rapid evolution of polymerization chemistries, structural modulation, and processing technologies, as well as the incorporation of stimuli-responsiveness, now permit synthetic microenvironments to capture much of the dynamic complexity of native tissue. These platforms are comprised not only of natural polymers chemically and molecularly similar to ECM, but those fully synthetic in origin. Here, we review recent in vitro efforts to mimic the dynamic microenvironment comprising native tissue ECM from the viewpoint of material design. We also discuss how these dynamic polymer-based biomaterials are being used in fundamental cell mechanobiology studies, as well as towards efforts in tissue engineering and regenerative medicine.

A method of packaging molecule/cell-patterns in an open space into a glass microfluidic channel by combining pressure-based low/room temperature bonding and fluorosilane patterning

A fabrication method of a “post-molecule/cell patterned” glass microchip was developed by pressure-based bonding and patterning with a fluorosilane coupling reagent.

Electron-Beam Lithographic Grafting of Functional Polymer Structures from Fluoropolymer Substrates

Well-defined submicrometer structures of poly(dimethylaminoethyl methacrylate) (PDMAEMA) were grafted from 100 μm thick films of poly(ethene-alt-tetrafluoroethene) after electron-beam lithographic exposure. To explore the possibilities and limits of the method under different exposure conditions, two different acceleration voltages (2.5 and 100 keV) were employed. First, the influence of electron energy and dose on the extent of grafting and on the structure's morphology was determined via atomic force microscopy. The surface grafting with PDMAEMA was confirmed by advanced surface analytical techniques such as time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. Additionally, the possibility of effective postpolymerization modification of grafted structures was demonstrated by quaternization of the grafted PDMAEMA to the polycationic QPDMAEMA form and by exploiting electrostatic interactions to bind charged organic dyes and functional proteins.

Vapor-based micro/nano-partitioning of fluoro-functional group immobilization for long-term stable cell patterning

This study developed a simple vapor-based immobilization method using a compound with fluoro-functional-group on a cell culture surface with micro/nano scale patterns.

Microcasting with agarose gel via degassed polydimethylsiloxane molds for repellency-guided cell patterning

A simple method for micro-casting with agarose gel was developed. Vacuum pressure in a degassed PDMS elastomer acted as a driving force for introducing agarose solution into micro-channels. The repellency of agarose well-guided cell adhesion area.

Lithography-free fabrication of reconfigurable substrate topography for contact guidance

Mammalian cells detect and respond to topographical cues presented in natural and synthetic biomaterials both in vivo and in vitro. Micro- and nano-structures influence the adhesion, morphology, proliferation, migration, and differentiation of many phenotypes. Although the mechanisms that underpin cell-topography interactions remain elusive, synthetic substrates with well-defined micro- and nano-structures are important tools to elucidate the origin of these responses. Substrates with reconfigurable topography are desirable because programmable cues can be harmonized with dynamic cellular responses. Here we present a lithography-free fabrication technique that can reversibly present topographical cues using an actuation mechanism that minimizes the confounding effects of applied stimuli. This method utilizes strain-induced buckling instabilities in bilayer substrate materials with rigid uniform silicon oxide membranes that are thermally deposited on elastomeric substrates. The resulting surfaces are capable of reversible of substrates between three distinct states: flat substrates (A = 1.53 ± 0.55 nm; Rms = 0.317 ± 0.048 nm); parallel wavy grating arrays (A∥= 483.6 ± 7.8 nm; λ∥= 4.78 ± 0.16 μm); perpendicular wavy grating arrays (A⊥= 429.3 ± 5.8 nm; λ⊥= 4.95 ± 0.36 μm). The cytoskeleton dynamics of 3T3 fibroblasts in response to these surfaces was measured using optical microscopy. Fibroblasts cultured on dynamic substrates that are switched from flat to topographic features (FLAT-WAVY) exhibit a robust and rapid change in gross morphology as measured by a reduction in circularity from 0.30 ± 0.13 to 0.15 ± 0.08 after 5 min. Conversely, dynamic substrate sequences of FLAT-WAVY-FLAT do not significantly alter the gross steady-state morphology. Taken together, substrates that present topographic structures reversibly can elucidate dynamic aspects of cell-topography interactions.

Advances in the surface modification techniques of bone-related implants for last 10 years

At the time of implanting bone-related implants into human body, a variety of biological responses to the material surface occur with respect to surface chemistry and physical state. The commonly used biomaterials (e.g. titanium and its alloy, Co-Cr alloy, stainless steel, polyetheretherketone, ultra-high molecular weight polyethylene and various calcium phosphates) have many drawbacks such as lack of biocompatibility and improper mechanical properties. As surface modification is very promising technology to overcome such problems, a variety of surface modification techniques have been being investigated. This review paper covers recent advances in surface modification techniques of bone-related materials including physicochemical coating, radiation grafting, plasma surface engineering, ion beam processing and surface patterning techniques. The contents are organized with different types of techniques to applicable materials, and typical examples are also described.

Cell division orientation on biospecific peptide gradients

An assay was developed for determining cell division orientation on gradients. The methodology is based on permeating microfluidic devices with alkanethiols and subsequent printing of cell adhesive peptide gradient self-assembled monolayers (SAMs) for examining oriented cell divisions. To our knowledge, there has been no study examining the correlation between cell division orientations based on an underlying ligand gradient. These results implicate an important role for how the extracellular matrix may control cell division. These surfaces would allow for a range of cell behavior (polarization, migration, division, differentiation) studies on tailored biospecific gradients and as a potential biotechnological platform to assess small molecule perturbations of cell function.

Switchable micropatterned surface topographies mediated by reversible shape memory

Reversibly switching topography on micrometer length scales greatly expands the functionality of stimuli-responsive substrates. Here we report the first usage of reversible shape memory for the actuation of two-way transitions between microscopically patterned substrates, resulting in corresponding modulations of the wetting properties. Reversible switching of the surface topography is achieved through partial melting and recrystallization of a semi-crystalline polyester embossed with microscopic features. This behavior is monitored with atomic force microscopy (AFM) and contact angle measurements. We demonstrate that the magnitude of the contact angle variations depends on the embossment pattern.

Nanoimprinting of topographical and 3D cell culture scaffolds

The extracellular matrix exhibits several nanostructures such as fibers, filaments, nanopores and ridges that can be mimicked by topographical and 3D substrates for cell and tissue cultures for an environment closer to in vivo conditions. This review summarizes and discusses a growing number of reports employing nanoimprint lithography to obtain such scaffolds. The different nanoimprint lithography methods as well as their advantages and disadvantages are described and special attention is paid to cell culture applications. We discuss the impact of materials, nanotopography, size, geometry, fabrication method, and cell type on growth guidance and differentiation. We present examples of cell guidance, inhibition of cell growth, cell pinning and engineering of 3D cell sheets or spheroids. As current applications are limited and not systematically compared for various cell types, this review only suggests promising substrates for particular applications. Future possible directions are also proposed in which this field may proceed.

Development of functional biomaterials with micro- and nanoscale technologies for tissue engineering and drug delivery applications

Micro- and nanotechnologies have emerged as potentially effective fabrication tools for addressing the challenges faced in tissue engineering and drug delivery. The ability to control and manipulate polymeric biomaterials at the micron and nanometre scale with these fabrication techniques has allowed for the creation of controlled cellular environments, engineering of functional tissues and development of better drug delivery systems. In tissue engineering, micro- and nanotechnologies have enabled the recapitulation of the micro- and nanoscale detail of the cell's environment through controlling the surface chemistry and topography of materials, generating 3D cellular scaffolds and regulating cell-cell interactions. Furthermore, these technologies have led to advances in high-throughput screening (HTS), enabling rapid and efficient discovery of a library of materials and screening of drugs that induce cell-specific responses. In drug delivery, controlling the size and geometry of drug carriers with micro- and nanotechnologies have allowed for the modulation of parametres such as bioavailability, pharmacodynamics and cell-specific targeting. In this review, we introduce recent developments in micro- and nanoscale engineering of polymeric biomaterials, with an emphasis on lithographic techniques, and present an overview of their applications in tissue engineering, HTS and drug delivery.

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.

Novel temperature-responsive polymer brushes with carbohydrate residues facilitate selective adhesion and collection of hepatocytes

Temperature-responsive glycopolymer brushes were designed to investigate the effects of grafting architectures of the copolymers on the selective adhesion and collection of hypatocytes. Homo, random and block sequences of N-isopropylacrylamide and 2-lactobionamidoethyl methacrylate were grafted on glass substrates via surface-initiated atom transfer radical polymerization. The galactose/lactose-specific lectin RCA120 and HepG2 cells were used to test for specific recognition of the polymer brushes containing galactose residues over the lower critical solution temperatures (LCSTs). RCA120 showed a specific binding to the brush surfaces at 37 °C. These brush surfaces also facilitated the adhesion of HepG2 cells at 37 °C under nonserum conditions, whereas no adhesion was observed for NIH-3T3 fibroblasts. When the temperature was decreased to 25 °C, almost all the HepG2 cells detached from the block copolymer brush, whereas the random copolymer brush did not release the cells. The difference in releasing kinetics of cells from the surfaces with different grafting architectures can be explained by the correlated effects of significant changes in LCST, mobility, hydrophilicity and mechanical properties of the grafted polymer chains. These findings are important for designing 'on-off' cell capture/release substrates for various biomedical applications such as selective cell separation.

Micropatterned thermoresponsive surfaces by polymerization of monomer crystals: modulating cellular morphology and cell-substrate interactions

A novel and facile approach has been developed to create thermoresponsive surfaces with macroscale patterns together with microscale features. The surface patterns were formed by applying macroscale nucleation agent patterns onto saturated N-isopropylacrylamide monomer solution membranes to induce the divergent growth of needlelike monomer crystals; the patterned monomer crystals were then photopolymerized to form patterned thermoresponsive films. A series of analytical tools (i.e., scanning electron microscopy, profilometry, and contact angle measurement) were used to characterize the properties of the patterned films. Cell coculture on this patterned thermoresponsive films enables cell separation and sorting by modulating temperature- and topography-dependent cell-substrate interactions and cell morphology, respectively. This versatile technique allows the formation of various macroscale patterns with microscale features over large areas, and on most solid substrates, within minutes, all of this without the need for expensive equipment and facilities. Such patterned surfaces can act as both in vitro tumor models and separation platforms for cancer studies. This method can also be applied to other cell-based biological studies and clinical applications.

Functional polymers in protein detection platforms: optical, electrochemical, electrical, mass-sensitive, and magnetic biosensors

The rapidly growing field of proteomics and related applied sectors in the life sciences demands convenient methodologies for detecting and measuring the levels of specific proteins as well as for screening and analyzing for interacting protein systems. Materials utilized for such protein detection and measurement platforms should meet particular specifications which include ease-of-mass manufacture, biological stability, chemical functionality, cost effectiveness, and portability. Polymers can satisfy many of these requirements and are often considered as choice materials in various biological detection platforms. Therefore, tremendous research efforts have been made for developing new polymers both in macroscopic and nanoscopic length scales as well as applying existing polymeric materials for protein measurements. In this review article, both conventional and alternative techniques for protein detection are overviewed while focusing on the use of various polymeric materials in different protein sensing technologies. Among many available detection mechanisms, most common approaches such as optical, electrochemical, electrical, mass-sensitive, and magnetic methods are comprehensively discussed in this article. Desired properties of polymers exploited for each type of protein detection approach are summarized. Current challenges associated with the application of polymeric materials are examined in each protein detection category. Difficulties facing both quantitative and qualitative protein measurements are also identified. The latest efforts on the development and evaluation of nanoscale polymeric systems for improved protein detection are also discussed from the standpoint of quantitative and qualitative measurements. Finally, future research directions towards further advancements in the field are considered.

Patterning methods for polymers in cell and tissue engineering

Polymers provide a versatile platform for mimicking various aspects of physiological extracellular matrix properties such as chemical composition, rigidity, and topography for use in cell and tissue engineering applications. In this review, we provide a brief overview of patterning methods of various polymers with a particular focus on biocompatibility and processability. The materials highlighted here are widely used polymers including thermally curable polydimethyl siloxane, ultraviolet-curable polyurethane acrylate and polyethylene glycol, thermo-sensitive poly(N-isopropylacrylamide) and thermoplastic and conductive polymers. We also discuss how micro- and nanofabricated polymeric substrates of tunable elastic modulus can be used to engineer cell and tissue structure and function. Such synergistic effect of topography and rigidity of polymers may be able to contribute to constructing more physiologically relevant microenvironment.

Using polymeric materials to control stem cell behavior for tissue regeneration

Patients with organ failure often suffer from increased morbidity and decreased quality of life. Current strategies of treating organ failure have limitations, including shortage of donor organs, low efficiency of grafts, and immunological problems. Tissue engineering emerged about two decades ago as a strategy to restore organ function with a living, functional engineered substitute. However, the ability to engineer a functional organ is limited by a limited understanding of the interactions between materials and cells that are required to yield functional tissue equivalents. Polymeric materials are one of the most promising classes of materials for use in tissue engineering, due to their biodegradability, flexibility in processing and property design, and the potential to use polymer properties to control cell function. Stem cells offer potential in tissue engineering because of their unique capacity to self-renew and differentiate into neurogenic, osteogenic, chondrogenic, and myogenic lineages under appropriate stimuli from extracellular components. This review examines recent advances in stem cell-polymer interactions for tissue regeneration, specifically highlighting control of polymer properties to direct adhesion, proliferation, and differentiation of stem cells, and how biomaterials can be designed to provide some of the stimuli to cells that the natural extracellular matrix does.

Effect of polymer deposition method on thermoresponsive polymer films and resulting cellular behavior

Poly(N-isopropyl acrylamide) or pNIPAM is a thermoresponsive polymer that is widely studied for use in bioengineering applications. The interest in this polymer lies in the polymer's unique capability to undergo a sharp property change near physiological temperature, which aids in the spontaneous release of biological cells from substrates. Currently, there are many methods for depositing pNIPAM onto substrates, including atom-transfer radical polymerization (ATRP) and electron beam ionization. Each method yields pNIPAM-coated substrates with different surface characteristics that can influence cell behavior. In this work, we compare two methods of pNIPAM deposition: plasma deposition and codeposition with a sol-gel. The resulting pNIPAM films were analyzed for use as substrates for mammalian cell culture based on surface characterization (XPS, ToF-SIMS, AFM, contact angles), cell attachment/detachment studies, and an analysis of exocytosis function using carbon-fiber microelectrode amperometry (CFMA). We find that although both methods are useful for the deposition of functional pNIPAM films, plasma deposition is much preferred for cell-sheet engineering applications because of the films' thermoresponse, minimal change in cell density, and maintenance of supported cell exocytosis function.

Shape-memory surface with dynamically tunable nano-geometry activated by body heat

Shape-memory surfaces with on-demand, tunable nanopatterns are developed to observe time dependent changes in cell alignment using temperature-responsive poly(ϵ-caprolactone) (PCL) films. Temporary grooved nanopatterns are easily programmed on the films and triggered to transition quickly to permanent surface patterns by the application of body heat. A time-dependent cytoskeleton remodeling is also observed under biologically relevant conditions.

Thermo-responsive poly(N-isopropylacrylamide) grafted onto microtextured poly(dimethylsiloxane) for aligned cell sheet engineering

Poly(N-isopropylacrylamide) (PNIPAAm)-grafted poly(dimethylsiloxane) (PDMS) offers an inexpensive, biocompatible, oxygen permeable, and easily microtextured thermo-responsive substrate for producing cell sheets. This study introduces a method of grafting PNIPAAm onto microtextured PDMS that is suitable for generating aligned vascular smooth muscle cell (VSMC) sheets. We examined a wide range of processing parameters in order to identify the conditions that led to acceptable sheet growth and detachment behavior. Substrates grafted under these conditions produced confluent cell sheets that fully detached in less than 10 min after lowering the culture temperature from 37 °C to 20 °C. The grafted layer thickness was determined to be 496±8 nm by atomic force microscopy. Surface characterization by Fourier transform infrared spectroscopy showed a relative grafting yield of 0.488±0.10, defined as the ratio of the PNIPAAm 1647 cm(-1) to the PDMS 2962 cm(-1) absorbance peaks. The water contact angle of the substrates was shown to change from 89.6° to 101.0° at 20 °C and 37 °C, respectively. We also found that cell behavior on PNIPAAm-grafted PDMS was not directly related to surface wettability or relative grafting densities.

Surface design with self-heating smart polymers for on-off switchable traps

We have developed a novel self-heating, temperature-responsive chromatography system for the effective separation of biomolecules. Temperature-responsive poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide), poly(NIPAAm-co-HMAAm), was covalently grafted onto the surface of magnetite/silica composites as 'on-off' switchable surface traps. The lower critical solution temperature (LCST) of the poly(NIPAAm-co-HMAAm)s was controlled from 35 to 55 °C by varying the HMAAm content. Using the heat generated by magnetic particles in an alternating magnetic field (AMF) we were able to induce the hydrophilic to hydrophobic phase separation of the grafted temperature-responsive polymers. To assess the feasibility of the poly(NIPAAm-co-HMAAm)-grafted magnetite/silica particles as the stationary phase for chromatography, we packed the particles into the glass column of a liquid chromatography system and analyzed the elusion profiles for steroids. The retention time for hydrophobic steroids markedly increased in the AMF, because the hydrophobic interaction was enhanced via self-heating of the grafted magnetite/silica particles, and this effect could be controlled by changing the AMF irradiation time. Turning off the AMF shortened the total analysis time for steroids. The proposed system is useful for separating bioactive compounds because their elution profiles can be easily controlled by an AMF.

Induction of cell-cell connections by using in situ laser lithography on a perfluoroalkyl-coated cultivation platform

This article describes a novel laser-directed microfabrication method carried out in aqueous solution for the organization of cell networks on a platform. A femtosecond (fs) laser was applied to a platform culturing PC12, HeLa, or normal human astrocyte (NHA) cells to manipulate them and to facilitate mutual connections. By applying an fs-laser-induced impulsive force, cells were detached from their original location on the plate, and translocated onto microfabricated cell-adhesive domains that were surrounded with a cell-repellent perfluoroalkyl (R(f)) polymer. Then the fs-laser pulse-train was applied to the R(f) polymer surface to modify the cell-repellent surface, and to make cell-adhesive channels of several μm in width between each cell-adhesive domain. PC12 cells elongated along the channels and made contact with others cells. HeLa and NHA cells also migrated along the channels and connected to the other cells. Surface analysis by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed that the R(f) polymer was partially decomposed. The method presented here could contribute not only to the study of developing networks of neuronal, glial, and capillary cells, but also to the quantitative analysis of nerve function.

Application of smart nanostructures in medicine

Smart nanostructures are sensitive to various environmental or biological parameters. They offer great potential for numerous biomedical applications such as monitoring, diagnoses, repair and treatment of human biological systems. The present work introduces smart nanostructures for biomedical applications. In addition to drug delivery, which has been extensively reported and reviewed, increasing interest has been observed in using smart nanostructures to develop various novel techniques of sensing, imaging, tissue engineering, biofabrication, nanodevices and nanorobots for the improvement of healthcare.

Sharp Hydrophilicity Switching and Conformality on Nanostructured Surfaces Prepared via Initiated Chemical Vapor Deposition (iCVD) of a Novel Thermally Responsive Copolymer

A novel thermally responsive copolymer p(NIPAAm-co-DEGDVE) is synthesized using the substrate independent method of iCVD and exhibits a sharp lower critical solution temperature (LCST) transition centered at ≈28.5 ± 0.3 °C determined via quartz crystal microbalance measurements with dissipation monitoring (QCM-D). Swelling with water below the LCST produces a reversible change of ≈3× in film thickness. The layer is conformal on nanostructured surfaces including MWCNT forests and electrospun nanofiber mats. Modified planar substrates exhibit ≈30°change in static contact angle over the LCST, while through conformal coating on nanostructured substrates changes in static contact angle up to 135° are achieved. Additionally, coated surfaces exhibit temperature sensitive BSA adsorption measured by QCM-D and is reversible as shown through fluorescence imaging of a coated electrospun nanofiber mat.

Correlation of cell adhesive behaviors on superhydrophobic, superhydrophilic, and micropatterned superhydrophobic/superhydrophilic surfaces to their surface chemistry

A micropatterned superhydrophobic/superhydrophilic surface was successfully fabricated by plasma CVD and VUV irradiation. Physicochemical properties of the superhydrophobic, superhydrophilic, and superhydrophobic/superhydrophilic surfaces were investigated. The roughness structures on the superhydrophilic surface remained intact compared to those of the superhydrophobic surface. The micropatterned superhydrophobic/superhydrophilic surface was used as a scaffold of cell culture. On the micropatterned surface, the cells attached to the superhydrophilic regions in a highly selective manner, forming circular microarrays of the cells corresponding to the pattern. On the micropatterned surface with pattern distances of 200 microm between superhydrophilic regions, the cells adhered on the superhydrophilic regions and partly extended to the neighboring cells. In contrast, when the pattern distances between the superhydrophilic regions were more than 400 microm, the cells did not extend to the neighboring cells. Cell adhesion behaviors on superhydrophobic and superhydrophilic surfaces were also examined. The cells adhered and proliferated on both superhydrophobic and superhydrophilic surfaces. However, on the superhydrophobic surface, constant contact to facilitate cell division and proliferation was required. On the other hand, the cells easily adhered and proliferated on the superhydrophilic surface immediately after seeding. These differences in cell adhesion behavior induced site-selective cell adhesion on the superhydrophilic regions. Furthermore, protein adsorption behavior that plays an important role in cell adhesion on flat hydrophobic and hydrophilic surface was also examined. The amounts of the protein adsorption on the flat hydrophilic surface were much greater than those on the flat hydrophobic surface.

Design of chemically activated polymer microwells by one-step UV-lithography for stem cell adhesion

A novel method to produce sub-microwalled chemically activated polymer microwells by one-step UV-lithography under ambient conditions which are selectively coated with gelatin is introduced. The dimensions as well as the shape of the resulting polystyrene structures are both tunable merely by the irradiation time through one and the same mask. It is shown that the UV-irradiation initiates three effects at those surface areas which are not covered by the mask: (i) oxidation, (ii) cross-linking, and (iii) degradation of polystyrene. The superposition of those effects results in the formation of microscaled, oxidized polymer wells separated by polymer walls, whereas the polymer walls are formed below the mask structures. Topographical changes induced by the UV-irradiation are investigated by atomic force microscopy after different irradiation times. It is shown by X-ray photoelectron spectroscopy and ellipsometric investigations that the chemical composition of the irradiated areas and the degradation of polystyrene reach an equilibrium state after an irradiation time of 10 min. The lateral distribution of the cross-linked and oxidized and of the nonmodified polystyrene after irradiation was determined by fluorescence microscopy and time-of-flight secondary ion mass spectrometry. After the irradiated samples were treated with gelatin solution, it was found that stem cells selectively attach to the irradiated areas. This is due to the selective immobilization of the gelatin on the irradiated polymer areas, which was proved by X-ray photoelectron spectroscopy experiments.

Fabrication of micropatterns of nanoarrays on a polymeric gel surface

Micro-nano patterns of gold on the surface of poly(ethylene glycol) (PEG) hydrogels were prepared. The approach combines the technique of conventional photolithography (a top-down method for micropatterns), block copolymer micelle nanolithography (a bottom-up method for gold nanopatterns), and a linker-assistant technique to transfer a pattern on a hard surface to a polymeric surface. Hybrid micro-nano patterns on hydrogels were characterized using scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The patterned Au nanoparticles were further modified by a peptide containing arginine-glycine-aspatate (RGD). The cell-adhesion contrast of the patterned hydrogel surface was confirmed by preliminary cell experiments.

The regulation of stem cell differentiation by cell-cell contact on micropatterned material surfaces

Using the material technique recently developed by us, we prepared a micropattern on poly(ethylene glycol) (PEG) hydrogel to keep background resistant to cell adhesion for a long time, which made examination of differentiation of localized stem cells available. Our micropattern designed in this paper prevented or ensured contact between cells adhering in arginine-glycine-aspartic acid (RGD) microdomains, and thus afforded a unique way to study the effects of cell-cell contact on the lineage differentiation of stem cells while ruling out the interference of soluble factors or cell seeding concentration etc. As demonstration, mesenchymal stem cells derived from rats were examined in this study, and both osteogenic and adipogenic differentiations were found to be regulated by cell-cell contact. Isolated cells exhibited less significant differentiation than paired or aggregated cells. For those stem cells in contact, the extent of differentiation was fairly linearly related to the extent of contact characterized by coordination number. Additionally, we revealed the existence of some unknown cues besides gap junction responsible for such effects of cell-cell contact.