High-manganese and nitrogen stabilized austenitic stainless steel (Fe-18Cr-22Mn-0.65N): a material with a bright future for orthopedic implant devices.

The rationale behind the success of nickel free or with extremely low nickel austenitic high manganese and nitrogen stabilized stainless steels is adverse influences of nickel ion on human body. Replacement of nickel by nitrogen and manganese provides a stable microstructure and facilitates better biocompatibility in respect of the conventional 316L austenitic stainless steel (316L SS). In this investigation, biocompatibility of the high-manganese and nitrogen stabilized (Fe-18Cr-22Mn-0.65N) austenitic stainless steel was studied and found highly promising.In vitrocell culture and cell proliferation (MTT) assays were performed on this stainless steel and assessed in respect of the 316L SS. Both the steels exhibited similar cell growth behavior. Furthermore, an enhancement was observed in cell proliferation on the Fe-18Cr-22Mn-0.65N SS after surface modification by ultrasonic shot peening (USP). The mean percent proliferation of the MG-63 cells increased from ≈88% for Un-USP to 98% and 105% for USP 3-2 and USP 2-2 samples, respectively for 5 d of incubation. Interestingly,in vivoanimal study performed in rabbits for 3 and 6 weeks showed callus formation and sign of union without any allergic reaction.

Effect of ultrasonic shot peening duration on microstructure, corrosion behavior and cell response of cp-Ti.

Surface mechanical attrition treatment (SMAT) of metallic biomaterials has gained significant importance due to its ability to develop nano structure in the surface region. In the present study, the microstructural changes and corrosion behavior of the commercially pure titanium (cp-Ti), following different durations of ultrasonic shot peening (USSP) has been investigated. cp-Ti was shot peened for different durations from 0 to 120 s and the treated samples were examined for microstructural changes in the surface region, cell viability and corrosion behavior. Cell viability was considerably increased after USSP for 60-120 s, exhibiting maximum for the 90 s of USSP. The passivation tendency was also improved with peening duration up to 90 s, however, it declined for longer duration of USSP. The beneficial effects of USSP may be attributed to nano structuring in the surface region and development of higher positive potentials at the USSP treated surface. Transmission Electron Microscope (TEM) examination of the USSPed surface revealed dislocation entanglement and substructure. Also, higher surface volta potential was observed over the USSPed sample exhibiting better cell proliferation. The present work is corollary to previous work of the group and mainly discusses the role of USSP duration, as a process parameter, on the cell viability and corrosion resistance of cp-Ti.

Optimization of USSP duration for enhanced corrosion resistance of AA7075.

This investigation was carried out following our earlier work on the effect of ultrasonic shot peening (USSP) on corrosion resistance of the 7075 aluminium alloy in 3.5 wt% NaCl solution to optimize the duration of USSP. The samples not treated with USSP and different samples treated with USSP were subjected to potentiodynamic polarization and electrochemical impedance spectroscopy. Among the specimens USSP treated from 5 to 30 s, the one USSP treated for 15 s (USSP 15) was found to exhibit highest corrosion potential (Ecorr) and lowest corrosion current density (icorr). Corrosion products were characterized by Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). Scanning Kelvin Probe Force Microscopy (SKPFM) was used to measure the surface free potential. The enhanced corrosion resistance of the USSP 15 sample was found to be due to combined effect of surface nanostructure of the matrix, homogeneity and refinement of second phase precipitates. There was enhancement in formation of adherent passive layer in the USSP15 specimen.

Effect of Ultraviolet Irradiation on the Osseointegration of a Titanium Alloy with Bone.

INTRODUCTION: Attempt has been made to analyze the potential of titanium (Ti) alloy for osteointegration by the effect of surface photo functionalization in different aspects as follows: in Ringer's solution, in vitro cell growth, and in vivo study on rabbit. The present study was aimed to investigate the influence of ultraviolet (UV) light on surface topography, corrosion behavior, and bioactivity of indigenously manufactured samples of Ti alloy mini-implant. MATERIALS AND METHODS: The study includes surface modification of Ti samples by UV treatment, corrosion testing of the specimens using Potentiostat (GAMRY System), qualitative examination of modified surface topography using scanning electron microscope, and cellular viability test on Ti alloy surface (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide ASSAY). To find the effect of UV light on implant bone integration, biochemical test was performed on the femur of rabbits. RESULTS AND DISCUSSION: Corrosion resistance of untreated Ti alloy in Ringer's solution was found to be less, whereas corrosion rate was more. Corrosion resistance of UV-treated samples was found to increase significantly, thereby lowering the corrosion rate. Cell growth in UV-treated specimen was observed to be higher than that in untreated samples. It is important to mention that cell growth was significantly enhanced on samples which were UV treated for longer duration of time. CONCLUSIONS: There was a marked improvement in cell growth on UV-treated Ti alloy samples. Hence, it is expected that it would enhance the process of osseointegration of Ti with bone. Another important finding obtained was that the removal torque values of UV-treated implants were higher than that of untreated implants. The overall result reveals that UV treatment of implants does help us in speeding up the osseointegration process.

Enhanced osteoblast proliferation and corrosion resistance of commercially pure titanium through surface nanostructuring by ultrasonic shot peening and stress relieving.

This investigation was carried out to study the effect of a novel process of surface modification, surface nanostructuring by ultrasonic shot peening, on osteoblast proliferation and corrosion behavior of commercially pure titanium (c p-Ti) in simulated body fluid. A mechanically polished disc of c p-Ti was subjected to ultrasonic shot peening with stainless steel balls to create nanostructure at the surface. A nanostructure (<20 nm) with inhomogeneous distribution was revealed by atomic force and scanning electron microscopy. There was an increase of approximately 10% in cell proliferation, but there was drastic fall in corrosion resistance. Corrosion rate was increased by 327% in the shot peened condition. In order to examine the role of residual stresses associated with the shot peened surface on these aspects, a part of the shot peened specimen was annealed at 400°C for 1 hour. A marked influence of annealing treatment was observed on surface structure, cell proliferation, and corrosion resistance. Surface nanostructure was much more prominent, with increased number density and sharper grain boundaries; cell proliferation was enhanced to approximately 50% and corrosion rate was reduced by 86.2% and 41% as compared with that of the shot peened and the as received conditions, respectively. The highly significant improvement in cell proliferation, resulting from annealing of the shot peened specimen, was attributed to increased volume fraction of stabilized nanostructure, stress recovery, and crystallization of the oxide film. Increase in corrosion resistance from annealing of shot peened material was related to more effective passivation. Thus, the surface of c p-Ti, modified by this novel process, possessed a unique quality of enhancing cell proliferation as well as the corrosion resistance and could be highly effective in reducing treatment time of patients adopting dental and orthopedic implants of titanium and its alloys.

In vitro comparison of resistance to implant failure in unstable trochanteric fractures fixed with intramedullary single screw versus double screw device.

BACKGROUND: The purpose of this study was to compare the resistance of intramedullary single screw device (Gamma nail) and double screw device proximal femoral nail (PFN) in unstable trochanteric fractures in terms of the number of cycles sustained, subsidence and implant failure in an axial loading test in cadaveric femora. MATERIALS AND METHODS: The study was conducted on 18 dry cadaveric femoral specimens, 9 of these were implanted with a Gamma nail and 9 with PFN. There was no significant difference found in average dual energy X-ray absorptiometry value between both groups. The construct was made unstable (AO type 31A3.3) by removing a standard sized posteromedial wedge. These were tested on a cyclic physiological loading machine at 1 cycle/s with a load of 200 kg. The test was observed for 50,000 loading cycles or until implant failure, whichever occurred earlier. Peak displacements were measured and analysis was done to determine construct stiffness and gap micromotion in axial loading. RESULT: It was observed that there was statistically significant difference in terms of displacement at the fracture gap and overall construct stiffness of specimens of both groups. PFN construct group showed a mean subsidence of 1.02 mm and Gamma nail construct group showed mean subsidence of 2.36 mm after cycling. The average stiffness of Gamma nail group was 62.8 ± 8.4 N/mm which was significantly lower than average stiffness of the PFN group (80.4 ± 5.9 N/mm) (P = 0.03). In fatigue testing, 1 out of 9 PFN bone construct failed, while 5 of 9 Gamma nail bone construct failed. CONCLUSION: When considering micromotion (subsidence) and incidence of implant/screw failure, double screw device (PFN) had statistically significant lower micromotion across the fracture gap with axial compression and lower incidence of implant failure. Hence, double screw device (PFN) construct had higher stability compared to single screw device (GN) in an unstable trochanteric fracture femur model.

Biomechanical analysis of distal femoral fracture fixation: dynamic condylar screw versus locked compression plate.

BACKGROUND: This human cadaveric study i ntroduces a laboratory model to establish and compare the fixation stability of the distal femoral locking plate (DFLP) and dynamic condylar screw (DCS) in distal femoral fracture fixation. MATERIALS AND METHODS: The study was conducted on 16 fresh cadaveric femoral specimens, 8 implanted with the DCS and the other 8 with the DFLP. The construct was made unstable by removing a standard-sized medial wedge with a 1-cm base (gap osteotomy) beginning 6 cm proximal to the lateral joint line in the distal metaphyseal region with loss of the medial buttress. Each specimen underwent axial and torsional stiffness testing along with cyclic axial loading to failure. The mean DEXA value for the DFLP group was 0.82 g/cm(2) and in the DCS group was 0.79 g/cm(2). RESULTS: Axial stiffness in the DFLP group was significantly higher than in the DCS group, but no significant difference was found in torsional stiffness between the groups. A significant difference was found in the load-to-failure results between the groups. Plastic and total deformation was significantly higher in constructs in the DCS group than in those in the DFLP group. Total energy absorbed before construct failure was also significantly higher in the DFLP group than in the DCS group. CONCLUSIONS: The DFLP construct proved stronger than the DCS in both axial stiffness and cyclic loading, but similar in torsional stiffness in biomechanical testing in a simulated A3 distal femoral fracture.

Bone cement based nanohybrid as a super biomaterial for bone healing.

A novel nanohybrid based on bone cement has been developed which is capable of healing fractured bone in 30 days, one-third of the time required for the natural healing process. Nanohybrids of bone cement based on poly(methyl methacrylate) (PMMA), currently used as a grouting material in joint replacement surgery, were prepared by simple mixing with organically modified layered silicates of varying chemical compositions. The temperature arising from exothermic polymerization in one of the nanohybrids is 12 °C lower than that in pure bone cement, thus circumventing the reported cell necrosis that occurs during implantation with pure bone cement. The thermal stability and mechanical superiority of this nanohybrid were verified in terms of its higher degradation temperature, better stiffness, superior toughness, and significantly higher fatigue resistance compared with pure bone cement; these properties make it appropriate for use as an implant material. The biocompatibility and bioactivity of the nanohybrid were confirmed using cell adhesion, cell viability, and fluorescence imaging studies. Osteoconductivity and bone bonding properties were monitored in vivo in rabbits through radiographic imaging and histopathological studies of growing bone and muscle near the surgery site. The observed dissimilarity of the properties of two different nanoclays used as fillers were visualized through interactions measured using spectroscopic techniques. Studies of the influence of different elements on bioactivity showed a higher efficiency for the nanoclay containing greater amounts of iron.

Pullout strength of misplaced pedicle screws in the thoracic and lumbar vertebrae - A cadaveric study.

BACKGROUND: The objective of this cadaveric study was to analyze the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of lower thoracic and lumbar pedicle screws. We also investigated the effect of bone mineral density (BMD), diameter of pedicle screws, and the region of spine on the pullout strength of pedicle screws. MATERIALS AND METHODS: Sixty fresh human cadaveric vertebrae (D10-L2) were harvested. Dual-energy X-ray absorptiometry (DEXA) scan of vertebrae was done for BMD. Titanium pedicle screws of different diameters (5.2 and 6.2 mm) were inserted in the thoracic and lumbar segments after dividing the specimens into three groups: a) standard pedicle screw (no cortical perforation); b) screw with medial cortical perforation; and c) screw with lateral cortical perforation. Finally, pullout load of pedicle screws was recorded using INSTRON Universal Testing Machine. RESULTS: Compared with standard placement, medially misplaced screws had 9.4% greater mean pullout strength and laterally misplaced screws had 47.3% lesser mean pullout strength. The pullout strength of the 6.2 mm pedicle screws was 33% greater than that of the 5.2 mm pedicle screws. The pullout load of pedicle screws in lumbar vertebra was 13.9% greater than that in the thoracic vertebra (P = 0.105), but it was not statistically significant. There was no significant difference between pullout loads of vertebra with different BMD (P = 0.901). CONCLUSION: The mean pullout strength was less with lateral misplaced pedicle screws while medial misplaced pedicle screw had more pullout strength. The pullout load of 6.2 mm screws was greater than that of 5.2 mm pedicle screws. No significant correlation was found between bone mineral densities and the pullout strength of vertebra. Similarly, the pullout load of screw placed in thoracic and lumbar vertebrae was not significantly different.

Layered double hydroxide induced advancement in joint prosthesis using bone cement: the effect of metal substitution.

Poly(methyl methacrylate) based bone cement and its nanocomposites with layered double hydroxide (LDH) have been developed with greater mechanical strength and biocompatibility as a grouting material for total joint arthroplasty. Bivalent magnesium has been replaced with trivalent aluminium with various mole ratios, keeping the layered pattern of the LDH intact, to cater for the effect of varying substitution on the property enhancement of the nanocomposites. The intercalation of polymer inside the LDH layers makes them disordered and mechanically stiffer and tougher by more than 100%. The thermal stability of bone cement has increased by more than 30 °C in the presence of 1 wt% of nanoLDH, homogenously distributed in the bone cement matrix by creating an inorganic thermal barrier out of the LDH dispersion. The improvement in the properties of the nanocomposites has been explained in terms of the strong interaction between nanoLDH and polymer. The superior bioactivity and biocompatibility of the nanocomposites, as compared to pure bone cement, has been established through hemolysis assay, cell adhesion, MTT assay and cell proliferation using fluorescence imaging. The developed nanocomposites have been used as a grouting material and significant improvements have been achieved in fatigue behaviour with gradual increment of Al substitution in the Mg : Al mole ratio in nanoLDH, demonstrating the real use of the material in the biomedical area. In vivo experiments on rabbits clearly revealed the superior efficacy of bone cement nanocomposites, over pure bone cement and a blank.

Biomechanical comparison of dynamic condylar screw and locking compression plate fixation in unstable distal femoral fractures: An in vitro study.

BACKGROUND: Distal femur fractures are difficult to manage and the selection of implant for internal fixation remains controversial. The objective of this study is to establish the relative strength of fixation of a distal femoral locking plate (DFLP) compared with the dynamic condylar screw (DCS) in the distal femur fractures. MATERIALS AND METHODS: Study was conducted on 16 freshly harvested cadaveric distal femoral specimens, eight implanted with DCS and other eight with DFLP. The construct was made unstable by removing a standard sized medial wedge of 1 cm base (gap-osteotomy) beginning 6 cm proximal to the lateral joint line in distal metaphyseal region with the loss of medial buttress. Fatigue test was conducted under load control mode at the frequency of I Hz. Specimens were subjected to cyclic loading of 2 kN, under observation for 50,000 cycles or until failure/cutout, which ever occurred earlier. RESULTS: In DFLP group, there was no implant failure and the average number of cycles sustained was 50,000. Six out of eight specimens completed 50,000 cycles and two failed in DCS group. The average number of cycles sustained by DCS was 46150. Though the bone quality as assessed by dual energy X-ray absorptiometry DEXA was comparable in both DFLP and DCS group (P = 0.06), none failed in DFLP group and subsidence was 1.02 ± 0.34 mm (range: 0.60-1.32 mm), which was significantly 43% lower (P = 0.006) than subsidence in DCS group (1.82 ± 0.58; range: 1.20-3.08 mm). The average stiffness of DCS group was 52.8 ± 4.2 N/mm, which was significantly lower than average stiffness of locked condylar plate group (71.2 ± 5.1 N/mm) (P = 0.02). CONCLUSIONS: DFLP fixation of the distal femur fractures resulted in stronger construct than the DCS fixation in both cyclic loading and ultimate strength in biomechanical testing of a simulated A3 distal femur fracture.

Comparison of cutout resistance of dynamic condylar screw and proximal femoral nail in reverse oblique trochanteric fractures: A biomechanical study.

BACKGROUND: Reverse oblique trochanteric fracture of femur is a distinct fracture pattern. 95° Dynamic condylar screw (DCS) and proximal femoral nail (PFN) are currently the most commonly used implants for its fixation. This study aims to biomechanically compare the cutout resistance as well as modes of failure of DCS and PFN in reverse oblique trochanteric fractures. MATERIALS AND METHODS: Sixteen freshly harvested cadaveric proximal femoral specimens were randomly assigned to three mean bone mineral density matched groups, eight of which were implanted with 95° DCS and the other eight with PFN. The constructs were made unstable to resemble a reverse oblique trochanteric fracture by removing a standard size posteromedial wedge. These constructs were subjected to computer controlled cyclic compressive loading with 200 kg at a frequency of 1 cycle/second (1 Hz) and end points of both the groups were analyzed. RESULTS: The bending moment of the PFN group was approximately 50% less than that of the DCS group (P<0.0001). The PFN group resisted more number of cycles than the DCS group (P=0.03) and showed lesser number of component failures as compared with the DCS group (P=0.003). CONCLUSIONS: The PFN is biomechanically superior to DCS for the fixation of reverse oblique trochanteric fractures of femur.

Bone cement/layered double hydroxide nanocomposites as potential biomaterials for joint implant.

Poly(methyl methacrylate)-based bone cement and layered double hydroxide (LDH) nanocomposites have been used as a grouting material for total joint arthroplasty. Few weight percentage of nanoLDH was uniformly dispersed in the bone cement matrix to have adequate interaction with matrix polymer. Mechanical strength, stiffness, toughness, and fatigue resistance of the nanocomposites are found to be higher than that of pure bone cement. Nanocomposites are thermally stable as compared to pristine bone cement. Direct mixing of the nanoLDH without any organic solvent makes these nanocomposites biocompatible. Biocompatibility was evaluated and compared with that of commercial bone cement by measuring hydrophilic nature, hemolysis assay, thrombosis assay, and deposition of apatite in simulated body fluid immersion. Finally, the viability of human osteoblast cells on the above developed nanocomposites was testified for actual biocompatibility. The experiment showed better cell growth in nanocomposites as compared to pure bone cement. Thus, these nanocomposites are found to be better grouting material than bone cement.

Effect of simvastatin on fracture healing--an experimental study.

Left femur was osteotomized and fixed with K wire in 21 rabbits. One group was fed simvastatin (120 mg/kg body wt/day) orally, whereas another group without medication served as control. Both groups were assessed radiologically, morphologically, histologically and biomechanically at 4, 8 and 12 weeks. An analysis of various parameters of study showed that simvastatin treated group had improved bone healing at 4 and 8 weeks of follow up, however, the difference was not significant statistically at 12 weeks. So it is concluded that Simvastatin favourably hastened the process of fracture healing in the rabbits at earlier phases.