Biocompatibility of surface-modified nickel titanium alloys and the effects of their continuous compressive stress on fracture healing

Qiang LI; Yayi XIA; Jicun TANG; Linwei XIN; Qin ZHANG; Wenzhong LIU; Meng WU

ABSTRACT

BACKGROUND:

Several researches have highlighted the selective dissolution of Ni ion from the nickel-titanium (NiTi) alloy during the corrosion process,which can lead to potential damage to human body.Different surface treatments will improve the corrosion resistance of NiTi implants.In modern medicines,it is necessary to analyze the characteristics of surface modified NiTi implants.

OBJECTIVE:

To study the effects of coated and uncoated materials made by elastic nickel-titanium alloy internal fixator on fracture healing and to compare the effects of continuous compressive stress after internal fixator of different types on fracture healing by setting up control group of bone nail internal fixation.DESIGN,TIME AND

SETTING:

A randomized,controlled,animal experiment was performed at the Laboratory of Tissue Engineering,Institute of Orthopedics,Second Hospital Affiliated to Lanzhou University between September 2004 and March 2005.MATERIALSDiamond-like carbon coated and nickel-titanium alloy and uncoated nickel-titanium alloy embracing fixator (type 4H8-40) were provided by Lanzhou Ximai Memory Co.,Ltd.,China.Intramedullary nails (type ZQY-01) were purchased from Tianjin Jinxingda Industries Co.,Ltd.,China.

METHODS:

Thirty Chinchilla rabbits of 4-6 months old were randomly divided into 3 groups (n = 10)diamond-like carbon coated nickel-titanium alloy embracing fixator (group A),uncoated nickel-titanium alloy embracing fixator (group B),and intramedullary fixator (group C).Following anesthesia by injection of 1% sodium pentobarbital (25 mg/kg),transverse fracture models in middle part of the femur were made through a lateral femoral incision and fixed with diamond-like carbon coated nickel-titanium alloy embracing fixator,uncoated nickel-titanium alloy embracing fixator,and intramedullary fixator respectively.MAIN OUTCOME

MEASURES:

The inorganic substance level,osteocalcin,alkaline phosphatase (ALP) and tumor necrosis factor (TNF) expression in callus surrounding fracture site were detected 4 weeks postoperatively.Ni ion level in muscles surrounding fracture site,live tissue,and brain tissue were also detected.

RESULTS:

Inorganic substance level and ALP,osteocalcin,and TNF expression were significantly higher in the groups A and B than in group C (P＜0.05).Ni ion level in the liver tissue,brain tissue,and muscles surrounding the fracture were significantly lower in the groups A and C than in group B (P＜0.05).

CONCLUSION:

Elastic fixation promotes fracture healing.Diamond-like carbon coated nickel-titanium alloy embracing fixator has a better histocompatibility than uncoated group.