Novel cell patterning using microheater-controlled thermoresponsive plasma films

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.

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.

REVERSIBLE THERMOSENSITIVE GLUE FOR RETINAL IMPLANTS

PURPOSE

To determine in vitro effects of a plasma polymerized N-isopropyl acrylamide (pNIPAM) coating for thermally controllable adhesion to retinal tissue.

METHODS

Polyimide (50 microm), parylene C [poly(monochloro-p-xylylene)] (20 microm), and poly(dimethyl siloxane) (PDMS) (200 microm) coated with pNIPAM were used as implant materials to test retinal adhesion in enucleated pig eyes. Following preparation of the implant materials (n = 5) and retina, the authors held the implants over the retinal tissue at 22 degrees C and gradually increased the temperature of the water bath within 15 minutes. While increasing the temperature the authors monitored the adhesion with the retina and pNIPAM coated implant. The authors measured the adhesive force by a traction test using a suture attached to the implant and a strain gauge. Then the authors checked the reversibility of the adhesion by lowering the temperature of the water bath.

RESULTS

There was no retinal adhesion at room temperature (22 degrees C). The adhesion developed strongly within 60 seconds after reaching the critical temperature (>or=32 degrees C). This adhesion was persistent when the authors applied tractional forces of 98 mN and 148 mN between 32 and 38 degrees C. When the authors lowered the temperature back to 22 degrees C by irrigation with cold BSS, the implants detached from the retinal surface without using any tractional force.

CONCLUSION

pNIPAM provides effective in vitro retinal adhesion between 32 and 38 degrees C and this adhesion is completely reversible by lowering the temperature of the physiologic medium.

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.

Micromechanical control of cell-cell interactions

The development and function of living tissues depends largely on interactions between cells that can vary in both time and space; however, temporal control of cell-cell interaction is experimentally challenging. By using a micromachined silicon substrate with moving parts, we demonstrate the dynamic regulation of cell-cell interactions via direct manipulation of adherent cells with micrometer-scale precision. We thereby achieve mechanical control of both tissue composition and spatial organization. As a case study, we demonstrate the utility of this tool in deconstructing the dynamics of intercellular communication between hepatocytes and supportive stromal cells in coculture. Our findings indicate that the maintenance of the hepatocellular phenotype by stroma requires direct contact for a limited time ( approximately hours) followed by a sustained soluble signal that has an effective range of <400 microm. This platform enables investigation of dynamic cell-cell interaction in a multitude of applications, spanning embryogenesis, homeostasis, and pathogenic processes.

Engineering tissues for in vitro applications

Engineered tissues can be employed for studies on the fundamental mechanisms of embryology and adult physiology and for investigating the evolution of disease processes. They also provide platforms to evaluate the behavior of new chemical entities in drug development. The recent development of three specific technologies has greatly facilitated the engineering of tissues for in vitro applications: the microfabrication tools that serve to both define the cellular microenvironment and enable parallelization of cell-based assays; synthetic, tunable hydrogels to create three-dimensional microenvironments; and bioreactors to control nutrient transport and fluid shear stress. Furthermore, convergence of these tools is providing investigators with the opportunity to construct and study tissues in vitro with unprecedented levels of sophistication.

Heterotypic cell interactions on a dually patterned surface

It is worth investigating heterotypic cell-cell interactions by mimicking their in vivo structures and environment. In the present study, physiological cellular response and behavior of hepatocytes and endothelial cells were investigated by controlling their contact periphery in a new co-culture system. Rat primary hepatocytes and bovine endothelial cells were co-cultured on a dually patterned surface. Hepatic physiological functions such as albumin secretion and ammonium metabolism were enhanced by increasing heterotypic cell-cell interactions in a patterned co-culture. Furthermore, enhanced hepatic functions through heterotypic interactions are effective within a limited area apart from endothelial cells as evidenced by immunofluorescence staining of hepatic intracellular albumin, indicating that heterotypic interactions act in a paracrine manner. Thus, heterotypic cell communications that play indispensable roles in increasing hepatic physiological functions should be obtained with an increasing periphery of two-cell domains. These findings are important for the reconstruction of complex tissues such as liver and pancreas.

Switchable surface traps for injectable bead-based chromatography in PDMS microfluidic channels

We report here a reversible microchannel surface capture system for stimuli-responsive grafted bioanalytical beads. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto polydimethylsiloxane (PDMS) surfaces by a UV-mediated graft polymerization from a photoinitiator that was preadsorbed in the channel wall. The surface grafting density and resulting switchable hydrophilic/hydrophobic properties were controlled by varying the photo-illumination times and/or the initiator concentration. At limiting PNIPAAm-graft densities, the surfaces demonstrated minimal contact angles of 35 degrees below the lower critical solution temperature (LCST) and maximal contact angles of 82 degrees above it. These contact angles could be varied depending on the graft density. The surface grafts are spatially limited to the photo-illuminated region to define where the trap is constructed. The surface traps capture PNIPAAm-grafted nanobeads uniformly above the LCST and facilitate their rapid release as the temperature is reversed to below the LCST. This dual surface trap and injectable chromatography system could be useful in many applications, such as affinity separations, immunoassays, and enzyme bioprocesses, by providing for the controlled capture and release of chromatography beads.

Immobilization and enzymatic activity of glucose oxidase on polystyrene surface modified with ozone aeration and UV irradiation in distilled water and/or aqueous ammonia solution

Adsorption condition and enzymatic activity of glucose oxidase (GOD) on polystyrene (PS) film surfaces modified with ozone aeration and UV irradiation (O3/UV) treatment were investigated. The total amount of GOD immobilized on the PS film modified with the O3/UV treatment in distilled water (PS-W film) was approximately twice as large as that on the film treated in an aqueous ammonia solution (PS-A film), whereas the specific activity of GOD on the PS-A film was four times higher than that on the PS-W film. In contrast, no enzymatic activity of GOD on the non-treated PS film was observed because of irreversible denaturation of the adsorbed GOD. We therefore conclude that the PS films modified by the O3/UV treatment in the aqueous media are effective in immobilizing GOD.

Polypeptide multilayer films

Research on polypeptide multilayer films, coatings, and microcapsules is located at the intersection of several disciplines: synthetic polymer chemistry and physics, biomaterials science, and nanoscale engineering. The past few years have witnessed considerable growth in each of these areas. Unexplored territory has been found at the borders, and new possibilities for technology development are taking form from technological advances in polypeptide production, sequencing of the human genome, and the nature of peptides themselves. Most envisioned applications of polypeptide multilayers have a biomedical bent. Prospects seem no less positive, however, in fields ranging from food technology to environmental science. This review of the present state of polypeptide multilayer film research covers key points of polypeptides as materials, means of polymer production and film preparation, film characterization methods, focal points of current research in basic science, and the outlook for a few specific applications. In addition, it discusses how the study of polypeptide multilayer films could help to clarify the physical basis of assembly and stability of polyelectrolyte multilayers, and mention is made of similarities to protein folding studies.

Surface engineering approaches to micropattern surfaces for cell-based assays

The ability to produce patterns of single or multiple cells through precise surface engineering of cell culture substrates has promoted the development of cellular bioassays that provide entirely new insights into the factors that control cell adhesion to material surfaces, cell proliferation, differentiation and molecular signaling pathways. The ability to control shape and spreading of attached cells and cell-cell contacts through the form and dimension of the cell-adhesive patches with high precision is important. Commitment of stem cells to different specific lineages depends strongly on cell shape, implying that controlled microenvironments through engineered surfaces may not only be a valuable approach towards fundamental cell-biological studies, but also of great importance for the design of cell culture substrates for tissue engineering. Furthermore, cell patterning is an important tool for organizing cells on transducers for cell-based sensing and cell-based drug discovery concepts. From a material engineering standpoint, patterning approaches have greatly profited by combining microfabrication technologies, such as photolithography, with biochemical functionalization to present to the cells biological cues in spatially controlled regions where the background is rendered non-adhesive ("non-fouling") by suitable chemical modification. The focus of this review is on the surface engineering aspects of biologically motivated micropatterning of two-dimensional (flat) surfaces with the aim to provide an introductory overview and critical assessment of the many techniques described in the literature. In particular, the importance of non-fouling surface chemistries, the combination of hard and soft lithography with molecular assembly techniques as well as a number of less well known, but useful patterning approaches, including direct cell writing, are discussed.

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.

Cell Engineering Biointerface Focusing on Cytocompatibility Using Phospholipid Polymer with an Isomeric Oligo(lactic acid) Segment

Initial contact between a biological environment and a biomaterial ultimately decides the in vivo performance. Therefore, the fabrication of a delicate biointerface is important because it can be utilized as a platform for novel biomaterials. For the preparation of advanced biomedical devices such as biochips, nanoparticles, and cell engineering devices, the surface properties may be modified by the design of polymeric biomaterials. Anomalous phospholipid polymers with an isomeric oligo(lactic acid) segment were designed and evaluated as a biointerface. The phospholipid polymer containing 2-methacryloyloxyethyl phosphorylcholine was easily copolymerized with isomeric oligo(lactic acid) macromonomers, and the obtained polymer could easily form thin coating membranes as biointerfaces. The oligo(lactic acid) involves three kinds of isomers: dl-, d-, and l-forms. The favorable characteristic on the surface provides regulation of cell-material interactions on the biointerface. The oligo(lactic acid) segment could form hydrophobic domains, which were considered to be located on the interface, to enhance protein adsorption and cell adhesion. The most favorable characteristics on the biointerface were dual functions of cytocompatibility by the phospholipid polymer and cell adhesion property by the oligo(lactic acid) segment. In this study, we focused on the biological responses such as protein adsorption and cell adhesion by change in the oligo(lactic acid) component. The cell viability on the confluent stage was evaluated in terms of metabolic activity.

Biomaterials: where we have been and where we are going

Since its inception just over a half century ago, the field of biomaterials has seen a consistent growth with a steady introduction of new ideas and productive branches. This review describes where we have been, the state of the art today, and where we might be in 10 or 20 years. Herein, we highlight some of the latest advancements in biomaterials that aim to control biological responses and ultimately heal. This new generation of biomaterials includes surface modification of materials to overcome nonspecific protein adsorption in vivo, precision immobilization of signaling groups on surfaces, development of synthetic materials with controlled properties for drug and cell carriers, biologically inspired materials that mimic natural processes, and design of sophisticated three-dimensional (3-D) architectures to produce well-defined patterns for diagnostics, e.g., biological microelectromechanical systems (bioMEMs), and tissue engineering.