As an effective adhesive with surgical applications, we designed a chitosan molecule that can be photocrosslinked by ultraviolet (UV) light irradiation, thus forming a hydrogel. This photocrosslinkable chitosan showed strong ability and potential use as a new tissue adhesive in surgical application. The purpose of this work was to evaluate the effectiveness of the photocrosslinkable chitosan as a delivery system for agents (for example: FGF-2 and paclitaxel) and as a submucosal injection agent for endoscopic mucosal resection (EMR). Application of FGF-2-incorporated photocrosslinkable chitosan hydrogel induced wound contraction and accelerated wound closure in healing-impaired diabetic mice. In the experiment for EMR, the photocrosslinkable chitosan showed the ability to keep the mucosa elevated sufficiently for a prolonged period of time, and reduced bleeding in rats. In the experiment using paclitaxel which is an anti-cancer agent, application of paclitaxel-incorporated photocrosslinlkable chitosan hydrogel inhibited tumor growth in mice. This photocrosslikable chitosan have abilities to be a delivery system for agents and as a submucosal injection agent for EMR. Thus, use of laser for UV irradiation develops this hydrogel application.

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Recently among the biophotonis and laser medicine increased attention has been given to the revolutionary advances in molecular and tissue engineering, and nanotechnology as a new field. Many areas of laser medicine are expected to benefit from these kinds of emerging technology and take route to the innovative and high-performance clinical technology .

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Cell adhesion to synthetic materials is crucially important in the various aspects of their biomedical and biotechnological applications. To understand cell behavior on materials, we employed self-assembled monolayers (SAM) of alkanethiols presenting a variety of functional groups as model surfaces, a surface plasmon resonance (SPR) method to determine protein adsorption, and total internal reflection fluorescence microscope (TIRFM) to see cell adhesion process. When SAM was brought into contact with a biological fluid containing cells, proteins immediately adsorbed on the SAM surfaces, and then cell adhesion occurred. Cell adhesion on the materials was determined by the quantity, composition, and conformation of adsorbed proteins. We believe that the three methods, SAM, SPR and TIRFM are very useful methods for future more detail studies on cell-material interactions.

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A single cell manipulator with PC-controlled laser, which is named as BioCyber, that controls individual cells, was developed by combining laser trapping, laser cutting, and micro-fluidic systems. Arrangement, fusion and screening of individual living cells was demonstrated by leading 1064 nm infrared and 355 nm ultraviolet lasers to an inverted microscope to trap and cut individual cells, respectively. PC-controlled trapping laser beam arranged 5 polymer microparticles, which are used as a model of an animal cell, within a few min and geometrical arrangement of the particles could be kept by scanning the trapping laser beam during the cell movement. As one of the applications of BioCyber, we demonstrated laser-assistant cell fusion that the microparticles as a model of egg and body cells were aligned by the laser manipulation and fused by electric pulse or ultraviolet laser pulse. Furthermore, individual animal cells were screened by irradiating 355 nm ultraviolet laser, by which needless cells were destroyed. A negative screening of the cells in a micro chamber with diameter of 1 mm was achieved within 2 hrs by scanning the ultraviolet laser beam with galvanic mirror and the PC-controlled sample stage.

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There is a demand in the field of regenerative medicine for measurement technology that enables functions of engineered tissue to be determined non-invasively. For meeting this demand, we previously proposed a method for determination of the viscoelasticity of tissue based on photoacoustic measurements. The relaxation times, which were calculated as the time at which amplitude of the photoacoustic waves decreased by a factor of 1/e, gave the intrinsic relaxation parameters (η/G) of tissue, where η is viscosity and G is elasticity. In this study, the scheme of photoacoustic measurement was improved for in vivo application. The measurement scheme was changed from a transmittance mode to a reflectance mode in which an optical fiber was coaxially arranged with a piezoelectric transducer. It was verified the usefulness of the photoacoustic measurement method for evaluation of the viscoelastic properties of actual engineered tissue when the relaxation times of engineered cartilage were measured by the photoacoustic method with various cultured periods. The photoacoustic measurement method enabled the assessment of the cartilage viscoelasticity both in vitro and in vivo, which were revealed in the process of regeneration of a full-thickness defect in rabbit articular cartilage using allografted tissue-engineered cartilage.

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