Tissue engineering is one newly emerging biomedical form to assist the regeneration and repairing of body tissue or to substitute the biological functions of damaged organs by making use of living cells. However, the tissue regeneration cannot always be achieved only by giving the cells of high proliferation and differentiation potential to a body defect. To this end, it is key to artificially create a site suitable for regeneration induction at the body defect. This can be achieved by taking advantage of an artificial scaffold for cell proliferation and differentiation, growth factors, and their combinations. Tissue engineering involves the technology and methodology to assist the creation of site to induce the regeneration of tissue and organ by use of various biomaterials. Growth factor is often required to promote tissue regeneration while it can also induce angiogenesis which is effective in angiogenic therapy for ischemic disease or the supply of oxygen and nutrients to the cells transplanted for organ substitution. However, the biological effects cannot be always expected without the drug delivery system (DDS) of growth factor. This paper overviews recent research prospective of tissue engineering and emphasizes significance role of biomaterials in tissue engineering.

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Because archaeal lipids are considered to be chemically and physically stable, it is of great interest to utilize these lipids as biotechnological materials. We have developed and proposed modeled archaeal diether-type (phytanyl-chained) glycolipids, a series of 1, 3-di-O-phytanyl-2-O- (β-maltooligoglycosyl) glycerols. This review discusses basic membrane properties of the proposed glycolipids, i.e., membrane-formability, intermembrane interaction, proton permeability, and intramembrane environment; subsequently usefulness of these membranes as reconstitution matrices for energy-conversion membrane proteins by employing such as labile oxygen-evolving photosystem 2. The characteristics of the proposed glycolipids are expected to lead to a new class of artificial membrane matrices for basic science such as glycobiology as well as for biotechnological applications.

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Biological and biophysical understanding of cellular functions and machinery will provide a variety of insights into design and synthesis of materials and devices. For instance, shielding of the cell surface can block some of cellular recognition processes and is a useful technique to protect cells and tissues against the harmful substances. By using water-soluble and nonionic polymers having a lipophilic anchor group at one end, polymer chains were attached to a cell surface through the hydrophobic interaction. Alternatively, polymer chains could be chemically linked to membrane proteins or saccharides. Furthermore, cell modification could be carried out using polymer chains with affinities such as RGD-integrin. In all the cases, activation of modified cells was suppressed when they met with relatively large materials such as a tissue culture dish and a micrometer-sized latex particle. Another cell surface engineering is associated with the signal transduction through cell membrane receptors. In signaling process, the signaling appears to emerge from the dynamic motions such as clustering and patterning of distribution of proteins and other molecules in the membrane. Neutrophils were coupled to thermosensitive polymer chains with cell-adhesive RGD peptides. The cells became activated when the temperature was raised. This modification makes it possible to induce the specific activation by clustering of receptors through the polymer association. Nanoparticles can be prepared by the interchain aggregation or the chemical cross-linking of polymer chains. We developed a novel drug delivery system for apoptosis induction by a “smart” polymer vehicle possessing thermo-sensitivity and bioaffinity. The polymeric nanoparticles incorporating an apoptotic inducer, dol-p, were added to a human promonocytic leukemia U937 cell suspension at 37°C. By lowering temperature to 25°C, cells underwent apoptosis in the presence of Ca²⁺. This technique would allow cells to possess the ability to induce apoptosis in response to stimuli such as temperature. Such engineered cells would be expected for the gene therapy, the cytomedical therapy, and the tissue engineering.

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Apolipoprotein (apo) A-I and E are exchangeable proteins in plasma and play key roles in lipoprotein metabolism. Association of apoA-I and E with lipid is required for their functions; apoA-I functions as an acceptor of cell membrane cholesterol and apoE serves as a high-affinity ligand for cell surface receptors. To better understand apolipoprotein-lipid interactions on cell membranes and lipoprotein surfaces, thermodynamic approach using isothermal titration calorimetry, fluorescence measurements using fluorescent phospholipid analogue, and natural abundance ¹³C NMR method were employed. ApoA-I binding to lipid membrane was found to be superficial and binding capacity was modulated by the degree of separation between the carbonyl groups at the surface. Cholesterol increased the head group space of phospholipids so as to allow more apoA-I to bind to the membrane surface, suggesting the interaction of apoA-I with cholesterol-enriched membrane domains. ApoE binds to the lipoprotein surface through the 10-kDa C-terminal domain that has a high-affinity for lipid. Our results showed that apoE bound to the spherical particles can adopt two distinct conformations with the N-terminal four-helix bundle either open or closed, suggesting that lipoprotein-associated apoE displays variable receptor binding activity depending upon the surface structure. Cholesterol may be the key component regulating such a conformational change of apoE on the lipoprotein surface.

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In order to improve the large membrane resistance of symmetric conventional porous glass membrane in microfiltration, new asymmetric type of porous glass membrane was prepared by use of two kinds of NaO-CaO-Al₂O₃-B₂O₃-ZrO₂-SiO₂ glass with different growth rate of phase separation, and was characterized for separative membrane.
Growth rate of separated phase from the primary glass composition decreased with increasing content of Al₂O₃. Therefore, Al₂O₃-rich glass and Al₂O₃-poor glass were laminated in two layers to be formed into a tube. The primary glass tube was thermal-treated to cause the phase separation, and the separated phase was leached out with an acid. Both skin layer and support layer of the asymmetric porous glass membrane had the uniformly controlled pore size. Skin layer with 15 μm in thickness was formed inside the membrane.
The pure water flux through the asymmetric porous glass membrane were much higher about 10 times of that through conventional symmetric porous glass membrane, because of decreasing of membrane resistance. The flux in crossflow microfiltration of acrylic resin suspension were much higher about 2 times of those through symmetric membrane. High permeability of the asymmetric porous glass membrane was confirmed through these measurements.

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Bovine brain sphingomyelin was converted to ceramide by sphingomyelinase in order to mimic the sphingomyelin cycle. By observing hydration process of dimyristoylphosphatidylcholine (DMPC) including the sphingomyelin or the ceramide under an optical microscope, the effect of conversion on membrane structure was examined morphologically. Sphingomyelin in DMPC did not affect the shape of myelin formation, but ceramide changed the shape to thinner tube. This suggests that ceramide should be a non-bilayer forming lipid. Phase transition behavior of phosphatidylcholines (dipalmitoylphosphatidylcholine, DPPC and dielaidoylphosphoatidycholine, DEPC) containing various contents of sphingomyelin or ceramide was investigated by fluorescent anisotropy measurement of diphenylhexatriene (DPH). The temperature dependence of anisotropy was differentiated by temperature, which gave a similar profile to differential scanning calorimetric (DSC) thermogram. Phosphatidylcholines containing ceramide gave two peaks. This result suggests that ceramide molecules are immiscible with phosphatidylcholine molecules while sphingomyelin molecules are miscible.

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The automatic adsorption apparatuses (BELSORP-mini, BELSORP-18plus, BELSORP BG) have been developed in order to measure adsorption isotherms for single gas and binary mixed gases. In BELSORP-mini, the new methods of measuring the dead volume (V_d) and saturation vapor pressure (P⁰) are adopted; namely, both of V_d and P⁰ are measured at each point of the adsorption isotherm of nitrogen gas at 77 K. As a result, the reliability of the N₂ isotherm increases. In BELSORP-18plus, the adsorption of vapor on the inner-wall of the apparatus is taken into account in determination of the isotherm of vapor. In BELSORP BG, a combination of gravimetry and volumetry is adopted in determination of the isotherms for binary mixed gases. The adsorption data obtained from both methods make it possible to determine the individual isotherm of each constituent gas without chemical analysis.

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