Sadami Tsutsumi

Study of diopside ceramics for biomaterials.

Diopside was prepared by sintering a powder compact of composition CaO-MgO-2SiO2 at 1300 °C for 2 h. The bending strength of diopside was 300 MPa and the fracture toughness was 3.5 MPa m1/2. It was proved that diopside has no general toxicity in cell culture. Diopside implanted in rabbits came in close contact with the newly grown bone. X-ray microanalysis spectral diagrams show a change of composition across the junction from the diopside to the newly grown bone. High-resolution transmission electron microscopy revealed crystal growth at the interface between diopside and the newly grown bone, and continuity between diopside lattices and those of the new crystals.

ANALYSIS AND PREVENTION OF SPINAL COLUMN DEFORMITY FOLLOWING CERVICAL LAMINECTOMY I : PATHOGENETIC ANALYSIS OF POSTLAMINECTOMY DEFORMITIES

Postlaminectomy deformities were simulated in the cervical or cervicothoracic spine by the use of a displacement incremental method based on finite-element analysis combined with composite material and spanning element theory. The simulation analyses revealed that the primary cause of postlaminectomy deformity was the resection of one or more spinous processes and/or posterior ligaments (ie, ligamenta flava, supraspinous, and interspinous ligaments). After their removal, the tensile stresses that were preoperatively distributed through the posterior ligaments were transferred to the facets. This led to an imbalance of the stresses on the spinal bodies, causing deformity. The gravitational center of the head determined whether the deformity would develop as a kyphosis or increasing lordosis. As the elastic modulus of the soft tissue composites (eg, end plates, ligaments, and facets) increased, a kyphotic deformity changed gradually from swan-neck deformity, to extreme kyphotic deformity with a large curvature, and finally to a straightening deformity. Progressive kyphotic deformity is found only in children.

Impact load transmission of the knee joint-influence of leg alignment and the role of meniscus and articular cartilage

OBJECTIVE The objective of this study was to evaluate load transmission in the cancellous bone of the tibia under static and impact load.BACKGROUND. Abnormal transmission of loads may result in osteoarthritis and fractures. However, the role of the cancellous bone in these processes is not well understood.METHODS. The compressive stresses in the subchondral bone, epiphysis and diaphysis of the tibia of porcine knees were measured under static and impact load using mini-pressure transducers. The tests were performed using a drop-tower type testing machine in neutral, varus and valgus alignments. Tests were repeated after meniscectomy and again after removing the articular cartilage.RESULTS. In the intact knee in all alignments, the highest stress on the medial side was found in the epiphysis, and in the subchondral bone on the lateral side. After meniscectomy, a significant increase was observed in the stress in the subchondral bone on both sides. After the articular cartilage was also removed, the stress in the subchondral bone increased again, but slightly.CONCLUSION. The importance of the meniscus in load transmission is supported by this study. The contribution of the articular cartilage to load transmission is less than that of the meniscus.Relevance. The patterns of static and dynamic load transmission observed in this study correlate with the sites of insufficiency fractures of the medial tibial plateau and traumatic lateral tibial plateau fractures observed clinically. Examination of the load transmission is key to a more complete understanding of the causes of osteoarthritis and tibial plateau fractures.

Crosslinking of Poly(L-lactide) by γ-Irradiation

The radiation crosslinking of poly(L-lactide) (PLLA) was investigated using triallyl isocyanurate (TAIC) as a crosslinking agent. The gel fraction of crosslinked PLLA increased with TAIC concentration and γ-ray dose. Crosslinking of PLLA started at low TAIC contents and low γ-ray dosage. Differential scanning calorimetry and dynamic mechanical thermal analysis revealed that PLLA was completely crosslinked at high weight ratios and high γ-ray doses.

Enhanced wound healing by an epigallocatechin gallate-incorporated collagen sponge in diabetic mice

Epigallocatechin‐3‐O‐gallate (EGCG), the major polyphenolic compound present in green tea, has potent anti‐oxidant and free radical‐scavenging activities. In this study, various concentrations (10, 100, and 1,000 ppm) of EGCG were incorporated into a collagen sponge (CS) in order to investigate its healing effects on full‐thickness wounds created in type 2 diabetic mice. After 14 days, the residual wound size of the mice treated with 10 ppm EGCG‐incorporated collagen sponge (E‐CS) decreased significantly faster than that of the other mice. Moreover, significant increases in the degree of reepithelialization, the thickness of the granulation tissue, and the density of the capillaries were also histologically observed in the wound sites exposed to 10 ppm E‐CS in comparison with the others. Furthermore, 10 ppm E‐CS resulted in significant increases in the immunoreactivity of Ki‐67 (reepithelialization at the wound site), CD31 (formation of blood vessels), and α‐smooth muscle actin (the induction of myofibroblasts across the dermis). These results suggest that a CS incorporated with EGCG at low concentrations can enhance wound healing in diabetic mice by accelerating reepithelialization and angiogenesis as well as improving the cellular reorganization of granulation tissue by triggering the activity of myofibroblasts.

Development of New Nerve Guide Tube for Repair of Long Nerve Defects

A novel nerve guide tube (poly (L-lactic) acid (PLLA)/ polyglycolic acid (PGA)-c-tube) capable of repairing long peripheral nerve injuries in a canine model has been developed. The tube was created by braiding together PLLA and PGA and then coating it with collagen. PLLA was newly added to the formulation to achieve higher sustainability. The tube was compared with a PGA-collagen tube in clinical use since 2002 having the same structure with a collagen coating but composed of PGA alone (PGA-c-tube). When tested for repair of a 40-mm gap in the left peroneal nerve, using PLLA/PGA-c-tube (n = 15), PGA-c-tube (n = 15), and a negative control group where the cut stump was capped using a silicone cap (n = 15), the lumen structure essential for securing the space for nerve regeneration was maintained in PLLA/PGA-c-tube for over 12 months with a higher number of axons both within the tube and at the distal nerve end. Electrophysiological evaluation revealed that the amplitude of compound muscle action potentials and sensory nerve action potentials after nerve regeneration with PLLA/PGA-c-tube were significantly higher. When assessed using magnetic resonance imaging (MRI), the volume of the tibialis anterior (TA) muscle in dogs that had undergone nerve repair using PLLA/PGA-c-tube was approximately 80% that of the positive control at 12 months. Functional analysis conducted by assessing the ankle angle revealed faster recovery in the PLLA/PGA-c-tube group. Better regeneration was achieved using a PLLA/PGA-c-tube that contains the slowly decomposing fiber material, PLLA. This indicates potential for repair of even longer nerve gaps or defects located near joints, and also clinical application.

Somatotopy of corticospinal tract in the internal capsule shown by functional MRI and diffusion tensor images

Using functional MRI and diffusion tensor tractography, we studied the topographical relation of hand and foot fibers of the corticospinal tract within the internal capsule to verify the recent unexpected finding by Holodny et al., who reported that hand fibers are located anterolateral to foot fibers, not anteromedial as is currently believed. The location of hand fibers with respect to foot fibers was anterolateral in four participants, posterolateral in two, and anteromedial in one of seven participants examined. Thus, there was some support for the anterolateral finding of Holodny et al., but interindividual variability was also indicated.

Surface modification of poly(ethylene-co-vinyl alcohol) (EVA). Part I. Introduction of carboxyl groups and immobilization of collagen.

To enhance the surface biocompatibility of poly(ethylene-co-vinyl alcohol) (EVA) and high-density polyethylene (HDPE), carboxyl groups were introduced by ozone exposure. Type I collagen was immobilized onto the surface through polyion complexing. The carboxyl groups on the EVA were characterized by electron spectroscopy for chemical analysis and neutralization. The amounts of the carboxylic group and collagen increased with increases in time and temperature of exposure. Water-soluble fragments were produced by ozone exposure to EVA, and they acted as collagen crosslinkers. The differences in charge distribution of carboxyl groups affected the amount of collagen immobilization. Graft polymerization of acrylic acid was also carried out onto EVA and HDPE surfaces. The amount of collagen immobilized by graft polymerization was much higher than that by ozone exposure despite the introduction of almost the same amounts of carboxylic groups. It was suggested that the negative charge distribution influences the amount of collagen immobilized onto films.

Self-Degradable Bioadhesive

To improve the conventional and commercially-available medical adhesives such as cyanoacrylate, aldehyde-based, and fibrin glue, new bioadhesive has been prepared using medical and food additives as starting materials. Aldehyde groups could be easily introduced in dextran in the presence of sodium periodate in aqueous media, and the extent of the introduction could also be controlled. In vitro degradation speed of the hydrogel prepared by mixing of aldehyded dextran with ε-poly(L-lysine) at 37oC significantly varied by acetic anhydride concentration added to ε-poly(L-lysine) from < 5h to > 5 weeks. Bonding strength of the glue was 4 times higher than that of commercial fibrin glue and almost no cytotoxicity was observed, suggesting the development of novel self-degradable bioadhesive.

Biomechanical Aspects of the Development of Aseptic Necrosis of the Femoral Head

SummaryWith the advancement of computer technology it has been possible to determine stress distribution in bone by the finite-element method (FEM), for a pathomechanical analysis of aseptic necrosis of the femoral head. Development of aseptic necrosis of the femoral head has been considered to be coincident with ischemic changes in the bone. However, the area of necrosis in the femoral head does not correspond to vascular distribution. We speculated that not only biological, but also biomechanical factors might play an important role in the development of femoral head necrosis. A two-dimensional finite-element model, with 801 elements and 454 nodes, was constructed to mimic the hip joint. Conditions for the disease were simulated on the assumption that concentrated areas of high stress cause changes in the biomechanical properties of bone, according to Wolffs law, such as necrosis or sclerosis. Results of the simulation correlated well with clinical findings. Biomechanical factors should be considered, not only to prevent the collapse of bone structure but also to limit the spread of bone necrosis in the early phase of the disease.ZusammenfassungMit dem Fortschritt der Computertechnologie ist es möglich geworden, Knochenstressverteilung durch die begrenzte Elementmethode zu bestimmen für eine pathomechanische Analyse der aseptischen Oberschenkelkopfnekrose. Es wurde bisher angenommen, daß die Entwicklung einer aseptischen Oberschenkelkopfnekrose mit einer ischämischen Knochenalteration zusammentreffe. Die Nekrosenzone im Oberschenkelkopf entspricht jedoch nicht seiner Gefäßverteilung. Wir sind davon ausgegangen, daß nicht nur biologische, sondern auch biomechanische Faktoren bei der Entwicklung der Oberschenkelkopfnekrose eine wichtige Rolle spielen könnten. Ein zweidimensionales begrenztes Elementmodell, mit 801 Elementen und 454 Knoten, wurde dem Hüftgelenk nachgebaut. In der Annahme, daß mit starken Stressen konzentriert belastete Bereiche nach Wolffs Gesetz biologische Knochenalterationen wie z. B. Nekrose oder Sklerose verursachen, wurden Krankheitsbedingungen nachgebildet. Die Ergebnisse dieser Nachahmung entsprechen sehr gut den klinischen Befunden. Nicht nur um den Kollaps im Knochenbau zu verhindern, sondern auch um die Verbreitung von Knochennekrose in der frühen Phase der Krankheit zu begrenzen, sollen biomechanische Faktoren berücksichtigt werden.