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Features of OSTEOTRANS™ System
• High strength: Possesses excellent bending strength higher than human cortical bone.
• Bioactivity: Possesses osteoconductivity so that bone bonding is promoted.
• Bone bonding capability : Directly binds with surrounding normal bone without intervening fibrous tissues.
• Stable fixation ability : Positive initial fixation is obtained by binding with surrounding bone.
• Biocompatibility/Safety : Is entirely composed of materials with proven track records as safe biomaterials and shows good biocompatibility throughout bioresorption process.
• Bioresorbability : Degrades and is totally resorbed more rapidly than conventional PLLA only devices.
• Radiopacity: Changes in the condition of devices with time can be observed postoperatively in X-ray images , if an incidence angle is selected correctly.
Strengths
  • Possesses high mechanical strengths and moduli superior to those of osteosynthesis devices consisting of PLLA-only or PL/DLLA.
  • Possesses an initial bending strength higher than that of human cortical bone.
  • Possesses toughness without easily breaking off.
  • Maintains a bending strength equal to that of human cortical bone for about 6 months in vivo.
Temporal changes in the bending strength and
molecular weight of OSTEOTRANS™-OT (in vitro testing)
(measured in a 3.2 mm diameter cylindrical specimen at 37°C in PBS)
(Y.Shikinami, et al., Biomaterials,20,859-877,1999)
Composition and Structure of OSTEOTRANS System
A SEM image showing u-HA particles homogeneously dispersed in PLLA
OSTEOTRANS is bioactive and totally resorbable osteosynthetic bone fixation device, consisting of composite materials of bioactive, bioresorbable unsintered hydroxyapatite (u-HA; Ca/P=1.69 (mol.ratio), Carbonate ion=3.8 mol%, having fine particles (average size; 3-5 µm) of 30 wt% in screws and 40 wt% in plates) combined with poly L-lactide (PLLA), which has been reinforced using a unique compression forging process. The u-HA fine particles are uniformly distributed throughout the composite materials, partially exposing on the surface (the white dots visible in the photograph on the right).
Characteristics of u-HA particles
Hydroxyapatite is a bioactive bioceramics having faculties for bone augmentation and substitution and is categorized in non-resorbable, surface bioactive group, which is produced by calcined or sintered at high temperatures. The u-HA belongs to an inorganic compound which is entirely uncalcined and unsintered, and is a raw material of HA ceramic and has same chemical composition as natural bone. In contrast to the non-resorbable hard HA fine particles, soft u-HA particle is composed of low crystalline resorbable HA, of which physical irritation to act on surrounding tissue is extremely mild, and is gradually resorbed and finally disappeared. The u-HA also has superior bioactivity, enabling good bone conductivity and bone bonding capability, as well as providing excellent biocompatibility and safety throughout total resorption.
OSTEOTRANS Bioactivity
OSTEOTRANS is bioactive and has the feature of osteoconductivity and osteobinding ability. Early after surgery, small trabecular bone formation occurs peripheral to an OSTEOTRANS round rod and gradually surrounds the outside of the rod (lower left photograph).The surrounding bone directly binds to the u-HA particles that are exposed at the surface of the rod(arrow in lower right photograph). This condition is maintained for a long period, during which time the rod is resorbed as the PLLA matrix extremely degrades and the composite breaks down. After continued osteoconduction, the composite is also replaced with new bone as the PLLA is totally resorbed.
Contact microradiogram of u-HA/PLLA rod after 25W.
I:u-HA/PLLA rod, B:bone, Arrow:direct bone contact/bone ingrowth position
(T.Furukawa et al., J Biomed Mater Res,50,410-419,2000)
Degradation/Resorption Characteristics
1. Degradation rate
Once the device has been implanted in the bone, PLLA in the OSTEOTRANS starts to hydrolyze with body fluids. The decrease over time in molecular weight indicates the extent to which the product has degraded to the small molecules of PLLA. The molecular weight of PLLA in OSTEOTRANS decreases faster than the PLLA in PLLA-only device, because hydrolytic reaction in the OSTEOTRANS occurs homogeneously throughout the device body as the following explanation.
2. Degradation behavior
When the OSTEOTRANS device has been implanted in the bone, body fluids enter into it via the interface between u-HA particles and PLLA matrices, and reach the center of the device in a short time. Hence, uniform hydrolysis occurs throughout the thin PLLA matrices in the composite device (left photograph-A). This results in the steady release of small amounts of debris as the materials degrade, which does not provoke adverse tissue responses in vivo. In contrast, a PLLA-only device degrades initially from the surface that comes into contact with body fluids; the degradation then spreads gradually and unevenly towards the center (right photograph-B). This can be demonstrated by the variable decreases in molecular weight between the surface and the inner region in PLLA-only devices.Uneven PLLA fragments released at irregular time intervals may induce some physical irritation to surrounding tissues, although the occurrence of inflammation responses is rare.
(A) (B)
Macroscopical change in morphology of lateral and cross-sectional area of OSTEOTRANS(A) and PLLA-only (B) devices after 44 weeks in PBS at 37°C.
(Y.Shikinami et al., Biomaterials,20,859-877,1999)
3. Resorption process
Resorption action differs depending on the shape, size, and implantation site of the device. However, a few years after implantation, u-HA fine particles are released, together with debris of reduced-molecular weight PLLA. The size of the device is thus gradually diminished as it disintegrated. At the same time, the osteoconductivity of u-HA promotes the growth of new bone in the region, which starts to repair the hole made for the implantation. Total replacement of the hole with new bone takes place when PLLA matrices have been completely absorbed and the device has entirely collapsed and fragmented remaining few unabsorbed u-HA fine particles, as shown in following figure.
Morphological changes in u-HA30 /40 rods
in the distal femoral condyle of rabbit
(Y.Shikinami, et al., Biomaterials,26,5542-5551,2005)
4. Total replacement
An example for total resorption and complete bone replacement is demonstrated in the next figures.
A 4-6 year period is appropriate, but not too late, in light of the phagocytic abilities of living tissues and the longevity of human life. In addition, the steady release of small amounts of debris is particularly important in cases when several large devices are used in combination to treat relatively narrow areas.
Cross sectional morphological change of u-HA30/40 rods over time in the distal femoral condyle of rabbit.