Yusuke Yoshihara

Bone bonding strength of diamond-structured porous titanium-alloy implants manufactured using the electron beam-melting technique

The present study examined the bone bonding strength of diamond-structured porous titanium-alloy (Porous-Ti-alloy) manufactured using the electron beam-melting technique in comparison with fiber mesh-coated or rough-surfaced implants. Cylindrical implants with four different pore sizes (500, 640, 800, and 1000μm) of Porous-Ti-alloy, titanium fiber mesh (FM), and surfaces roughened by titanium arc spray (Ti-spray) were implanted into the distal femur of rabbits. Bone bonding strength and histological bone ingrowth were evaluated at 4 and 12weeks after implantation. The bone bonding strength of Porous-Ti-alloy implants (640μm pore size) increased over time from 541.4N at 4weeks to 704.6N at 12weeks and was comparable to that of FM and Ti-spray implants at both weeks. No breakage of the porous structure after mechanical testing was found with Porous-Ti-alloy implants. Histological bone ingrowth that increased with implantation time occurred along the inner structure of Porous-Ti-alloy implants. There was no difference in bone ingrowth in Porous-Ti-alloy implants with pore sizes among 500, 640, and 800μm; however, less bone ingrowth was observed with the 1000μm pore size. These results indicated Porous-Ti-alloy implants with pore size under 800μm provided biologically active and mechanically stable surface for implant fixation to bone, and had potential advantages for weight bearing orthopedic implants such as acetabular cups.

Repairing of Osteochondral Defects in Joint Using Beta-TCP/ Carboxymethyl Chitin Composite

Beta-tricalcium phosphate/carboxymethyl chitin composites [TCP/CMCh] of various ratios of TCP granules and CMCh were made and their mechanical properties, handling properties and repair performance for bone defects and for osteochondral defects were investigated. Water pooling ratio of CMCh was approximately 40 times the weight itself. TCP/CMCh of a higher TCP ratio had higher stress at 50%-strain. The stress at 50%-strain of TCP/CMCh with 0, 2.5, 5.0, 7.5, 10 TCP ratios was 0.12, 0.51, 1.08, 1.46, 1.67 (MPa, n=5), respectively. The TCP/CMCh with 5.0 TCP ratios had the best total scores in handling tests. The bone repair rate of TCP/CMCh was TCP ratio 2.5< Blank= TCP ratio 7.5< TCP ratio 5.0. In the implantation test for osteochondral defects, TCP/CMCh was completely absorbed at four weeks after surgery. Regeneration of the articular cartilage was seen with TCP/CMCh and HA/CMCh but not with TCP granules, which remained eight weeks after implantation. The regenerated articular cartilage had remained 32 weeks after implantation. In conclusion, it was demonstrated that this TCP/CMCh composite was a promising material for repairing osteochondral defects.

Carboxymethyl-chitin promotes chondrogenesis by inducing the production of growth factors from immune cells.

Many techniques have been tested for their ability to restore cartilage defects, but several problems still remain in the complete healing of injured cartilage. In our previous study, we found that a carboxymethyl-chitin/beta-tricalcium phosphate (CM-chitin/beta-TCP) composite induced cartilage regeneration in the osteochondral defects of rabbits in vivo. We also found that CM-chitin stimulated peritoneal exudate cells (PEC) in mice and induced several kinds of inflammatory cytokines and transforming growth factor beta-1 (TGF-beta1). In this study, we examined whether CM-chitin is responsible for the induction of chondrogenesis via the production of TGF-beta1 in vitro. The murine pluripotent cell line C3H10T1/2 was maintained as a micromass culture in conditioned medium prepared from PEC stimulated with and without CM-chitin. CM-chitin-conditioned medium induced RNA expression of the chondrogenic-factor Sox9 and the matrix proteins aggrecan, Col2a1, and Comp. Their expression levels were decreased in the presence of anti-TGF-beta1 antibody. The micromass tissues cultured in CM-chitin conditioned medium at day 21 were clearly stained by Toluidine blue or Alcian blue (histological staining) and collagen II antibody (immunohistological staining), showing the expression of acidic glycosaminoglycan and type II collagen. Similar results were observed in micromass tissue stimulated with TGF-beta1 as a positive control. However, no chondrogenesis occurred when CM-chitin was added directly to a C3H10T1/2 cell culture. These results indicated that CM-chitin is a potent inducer of chondrogenesis via the induction of TGF-beta1 in immune cells.

Bone formation using β-tricalcium phosphate/carboxymethyl-chitin composite scaffold in rat calvarial defects

OBJECTIVE The aim of the present study was to evaluate the effects of β-tricalcium phosphate/carboxymethyl-chitin material (β-TCP/CM-chitin) on bone formation in rat calvarial defects. STUDY DESIGN Eighteen animals surgically received 2 calvarial defects (5 mm) bilaterally in each parietal bone. β-TCP/CM-chitin was implanted in one side of each defect, and the contralateral side of the defect was left empty as a control. The animals were humanely killed at 4, 8, and 12 weeks after surgery for histologic evaluation. RESULTS New bone formation in the β-TCP/CM-chitin group was significantly greater than that in the control group throughout the healing periods (P < .05). β-TCP/CM-chitin was remarkably resorbed 12 weeks after surgery. CONCLUSIONS These results indicate that β-TCP/CM-chitin is useful as a scaffold for bone formation.