Hard tissues composed of hydroxyapatite and collagen have evolved in biological and structural features since the dawn of time. The ancient acellular hard tissue, aspidin, was found in agathonae in the Paleozoic age and, at a hundred million years later, this tissue had been transited to be a cellular hard tissue. The hard tissue acquired a function of bone remodeling. The characteristic nanostructure in aspidin has been retained in our bone tissue. Artificial bone including hydroxyapatite ceramics and hydroxyapatite/collagen composites we have developed undergo a similar process of this evolution. Controlling surface and interfacial nanostructures of these materials will play one of great important roles for achieving the next generation of artificial bone that can activate bone physiology and can regenerate bone-marrow tissue. In this paper, we introduce our investigations and industrialization of artificial bones as well as our trial using fish scale collagen toward collagen-based biomaterials from the structural point of view.
Expanded polytetrafluoroethylene (ePTFE) as an artificial dura mater is often associated with cerebrospinal fluid (CSF) leakage after skull base surgeries, because ePTFE is not able to adhere to both fibrin glue and tissue. To improve these critical properties, the surface of ePTFE was modified with ion beam irradiation and the effects of its biocompatibility were investigated. ePTFE sheets were irradiated with Ar+ ions with a fluence of 5×1014 ions/cm2 and an energy of 150 keV. CSF leakage was observed for pristine ePTFE, while CSF leakage did not occur for ion beam irradiated ePTFE that adhered to surrounding tissues. Brain artery aneurysms are frequently treated using microsurgical clipping of the aneurysm neck, endovascular coiling of the aneurysm sac, or balloon occlusion of the parent vessel. For some broad-based aneurysms not suitable for these options, ion implantation was utilized to ePTFE wrapping material for treatment of brain aneurysms. We also studied applications for small diameter vessel anastmosis.
Artificial joint replacement is an effective treatment for patients with severe arthritis whose number has been increasing due to the expansion of the elderly population. In artificial joint replacements with considerably less efficient lubrication, polyethylene (PE) wear leading to osteolysis and aseptic loosening limits the longevity of total hip arthroplasty (THA). As a result, the quality of all artificial joint replacements is becoming increasingly important. In natural synovial joints under physiological conditions, fluid thin-film lubrication by the hydrated intermediate layer (hydration lubrication) of cartilage is known to be essential for the smooth motion of the joints. A surface gel layer of poly (2-methacryloyloxyethyl phosphorylcholine) (MPC) with cartilage-mimicking structures on a cross-linked PE (CLPE) surface, which may realize ideal hydrophilicity and lubricity resembling the physiological joint surface, has been developed for reducing wear. The suggested approaches for bio-mimicking are surely novel in the field of orthopaedic biomaterials science. The cartilage-mimicking, super lubricious surface of the MPC-grafted CLPE could extend longevity of artificial joint replacement.
Here, we describe a comprehensive view of cell sheet engineering that we proposed 15 years ago. Till now, we have succeeded in clinical application of cell sheet engineering to treat human patients. We also discuss the basic problems in the current regenerative medicine and tissue engineering. Finally, we propose a future perspective of cell sheet engineering toward the fundamental achievement of the new therapy.
Radiation is now widely used for clinical diagnosis and therapeutics. On the other hand, radiation influences various tissues represented by immunological and reproductive systems, and is also recognized as one of the cause of carcinogenesis. Such pleiotropic effects of radiation are mediated through generation of damages on DNA molecule, vitally important genetic macromolecule. Among various types of DNA damages, double-strand break (DSB) is considered most critical and, therefore, responsible for biological effects. DSB is repaired mainly through two pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). Understanding of these mechanisms has been greatly deepened in past 20 years and is now providing a promising approach toward cancer therapy. We have studied the mechanisms of NHEJ, focusing especially on the role of phosphorylation and the assembly of machinery therein, which will be introduced below.
Developed blood analysis chips that provide a healthcare check at home are introduced. The electronic blood collection system employing a painless needle is a suitable system as a minimally-invasive technique. To obtain the high sensitivity of blood analysis, the non-specific protein adsorption and cell adhesion should be reduced. Several typed MPC (2-methacryloyloxyethyl phosphorylcholine) polymers with a function of protein adsorption resistance have been developed for the biocompatible materials as a surface modification of microchip. The bio-interface controlled using MPC polymers provides a highly sensitive blood analysis.
Several surface modification techniques are being used to improve the biocompatibility and performance of medical devices. These include the immobilization of bioactive molecules and the incorporation of hydrophilic polymer grafts onto hydrophobic surfaces. This paper describes a unique hemocompatible polymer, lubricious surfaces when wet, and a HIV (Human immunodeficiency virus)-inactivating filter. A new coating material, poly-2-methoxyethylacrylate (PMEA), was developed to improve the biocompatibility of cardiopulmonary bypass circuits. PMEA-coated surfaces suppress the adhesion and denaturation of plasma proteins, and exhibited excellent blood compatibility in widespread clinical use. HIV-inactivating filter was prepared by immobilizing polyethyleneimine onto the surface of polypropylene porous membrane after plasma-induced sequential grafting of PMEA and poly (glycidylacrylate). Lubricity is a desirable property for the surfaces of catheters and guidewires to facilitate insertion and manoeuvrability within blood vessels. Hydrogel-like surfaces were prepared by grafting of poly (N,N-dimethylacrylamide) (PDMAA) and polymer-coatings with reactive PDMAA copolymers, and these showed highly hydrophilic property and excellent lubricious performance.
It is well known that Shuttleworth's equation shows the relation between surface stress and surface tension of the solid. But surface stress is a kind of virtual concept defined to the mathematical surface without thickness, so that the physical meanings of surface stress can not be clear. In this paper, we tried to evaluate surface stress and surface tension of homogeneous isotropic elastic body by using primitive constitutive equation derived from continuum mechanics and thermodynamics of surface. From the results, it was shown that surface stress was the stress caused in the elastic bulk which had infinity small thickness and that surface tension was the function of strain in this elastic bulk.
End-grafted polymer monolayers play an important role in colloidal stabilization, adhesion, and biocompatibility of artificial organs in medicine. There are two main methods to form end-grafting polymer layer:grafting-to and grafting-from methods. Grafting-to method has merit that is easy to conduct and easy to set a homogeneous degree of polymerization. We formed end-grafted polystyrene monolayers by a grafting-to method;a vinyl terminated polystyrene reacted with a H-terminated Si wafer and the polystyrene grafted to it. To clarify surface properties of the grafted polystyrene layer on the grafting density, we controlled it by a reaction temperature;The density could be controlled from 0.09 to 0.20 chains/nm2. At a lower grafting density region, the layer has high surface energy, high layer density, thin thickness, and smooth surface morphology. While at a higher grafting density region, the layer has low surface energy, low layer density, thick thickness, and smooth surface morphology.
We propose a versatile formula that describes action spectra for vibrationally mediated reactions of single molecules with a scanning tunneling microscope. Spectral fitting of the formula to experimental results of CO hopping on Pd(110) and rotation/hopping of propene on Cu(211) enables us to determine the vibrational energy, reaction order, rate constant and effective vibrational broadening. The formula proposed here is general and easy to apply to any vibrationally mediated motion and reaction of single molecules. Quantitative analysis of the spectra provide theoretical background for determining vibrational energy more precisely than conventional manner. The analysis of the spectra are considered plausible because our assignment of vibrational signals follow the propensity rule that was previously proposed.