Nano-scale surface morphology, wettability and osteoblast adhesion on nitrogen plasma-implanted NiTi shape memory alloy

Plasma immersion ion implantation (PIII) is an effective method to increase the corrosion resistance and inhibit nickel release from orthopedic NiTi shape memory alloy. Nitrogen was plasma-implanted into NiTi using different pulsing frequencies to investigate the effects on the nano-scale surface morphology, structure, wettability, as well as biocompatibility. X-ray photoelectron spectroscopy (XPS) results show that the implantation depth of nitrogen increases with higher pulsing frequencies. Atomic force microscopy (AFM) discloses that the nano-scale surface roughness increases and surface features are changed from islands to spiky cones with higher pulsing frequencies. This variation in the nano surface structures leads to different surface free energy (SFE) monitored by contact angle measurements. The adhesion, spreading, and proliferation of osteoblasts on the implanted NiTi surface are assessed by cell culture tests. Our results indicate that the nano-scale surface morphology that is altered by the implantation frequencies impacts the surface free energy and wettability of the NiTi surfaces, and in turn affects the osteoblast adhesion behavior.

Extracellular matrix stability of primary mammalian chondrocytes and intervertebral disc cells cultured in alginate-based microbead hydrogels

Three-dimensional alginate constructs are widely used as carrier systems for transplantable cells. In the present study, we evaluated the chondrogenic matrix stability of primary rat chondrocytes and intervertebral disc (IVD) cells cultured in three different alginate-based microbead matrices to determine the influence of microenvironment on the cellular and metabolic behaviors of chondrogenic cells confined in alginate microbeads. Cells entrapped in calcium, strontium, or barium ion gelled microbeads were monitored with the live/dead dual fluorescent cell viability assay kit and the 1,9-dimethylmethylene blue (DMB) assay designed to evaluate sulfated glycosaminoglycan (s-GAG) production. Expression of chondrogenic extracellular matrix (ECM) synthesis was further evaluated by semiquantitative RT-PCR of sox9, type II collagen, and aggrecan mRNAs. Results indicate that Ca and Sr alginate maintained significantly higher population of living cells compared to Ba alginate (p < 0.05). Production of s-GAG was similarly higher in Ca and Sr alginate microbead cultures compared to Ba alginate microbeads. Although there was no significant difference between strontium and calcium up to day 14 of culture, Sr alginate showed remarkably improved cellular and metabolic activities on long-term cultures, with chondrocytes expressing as much as 31% and 44% greater s-GAG compared to calcium and barium constructs, respectively, while IVD cells expressed 63% and 74% greater s-GAG compared to calcium and barium constructs, respectively, on day 28. These findings indicate that Sr alginate represent a significant improvement over Ca- and Ba alginate microbeads for the maintenance of chondrogenic phenotype of primary chondrocytes and IVD cells.

Approach-related complications of open versus thoracoscopic anterior exposures of the thoracic spine

This article reviews the approach-related complications of open versus thoracoscopic anterior exposures of the thoracic spine and suggests possible ways to avoid them.

A biomimetic hierarchical scaffold: natural growth of nanotitanates on three-dimensional microporous Ti-based metals

Nanophase materials are promising alternative implant materials in tissue engineering. Here we report for the first time the large-scale direct growth of nanostructured bioactive titanates on three-dimensional (3D) microporous Ti-based metal (NiTi and Ti) scaffolds via a facile low temperature hydrothermal treatment. The nanostructured titanates show characteristics of 1D nanobelts/nanowires on a nanoskeleton layer. Besides resembling cancelous bone structure on the micro/macroscale, the 1D nanostructured titanate on the exposed surface is similar to the lowest level of hierarchical organization of collagen and hydroxyapatite. The resulting surface displays superhydrophilicity and favors deposition of hydroxyapatite and accelerates cell attachment and proliferation. The remarkable simplicity of this process makes it widely accessible as an enabling technique for applications from engineering materials treatment including energy-absorption materials and pollution-treatment materials to biotechnology.

In vitro chondrogenic differentiation of human mesenchymal stem cells in collagen microspheres: influence of cell seeding density and collagen concentration

Given the inadequacies of existing repair strategies for cartilage injuries, tissue engineering approach using biomaterials and stem cells offers new hope for better treatments. Recently, we have fabricated injectable collagen-human mesenchymal stem cell (hMSC) microspheres using microencapsulation. Apart from providing a protective matrix for cell delivery, the collagen microspheres may also act as a bio-mimetic matrix facilitating the functional remodeling of hMSCs. In this study, whether the encapsulated hMSCs can be pre-differentiated into chondrogenic phenotype prior to implantation has been investigated. The effects of cell seeding density and collagen concentration on the chondrogenic differentiation potential of hMSCs have been studied. An in vivo implantation study has also been conducted. Fabrication of cartilage-like tissue micro-masses was demonstrated by positive immunohistochemical staining for cartilage-specific extracellular matrix components including type II collagen and aggrecan. The meshwork of collagen fibers was remodeled into a highly ordered microstructure, characterized by thick and parallel bundles, upon differentiation. Higher cell seeding density and higher collagen concentration favored the chondrogenic differentiation of hMSCs, yielding increased matrix production and mechanical strength of the micro-masses. These micro-masses were also demonstrated to integrate well with the host tissue in NOD/SCID mice.

Osteogenic behavior of alginate encapsulated bone marrow stromal cells: an in vitro study

Sodium alginate is a useful polymer for the encapsulation and immobilization of a variety of cells in tissue engineering because it is biocompatible, biodegradable and easy to process into injectable microbeads. Despite these properties, little is known of the efficacy of calcium cross-linked alginate gel beads as a biodegradable scaffold for osteogenic cell proliferation and differentiation. In this study, we investigated the ability of rabbit derived bone marrow cells (BMCs) to proliferate and differentiate in alginate microbeads and compared them with BMCs cultured in poly-L-lysine (PLL) coated microbeads and on conventional 2D plastic surfaces. Results show that levels of proliferation and differentiation in microbeads and on tissue culture plastics were comparable. Cell proliferation in microbeads however diminished after fortification with a coating layer of PLL. Maximum cell numbers observed were, 3.32 x 10(5) +/- 1.72 x 103; 3.11 x 10(5) +/- 1.52 x 10(3) and 3.28 x 10(5) +/- 1.21 x 10(3 ) for the uncoated, PLL coated and plastic surface groups respectively. Alkaline phosphatase and protein expressions reflected the stage of cell differentiation. We conclude that calcium cross-linked alginate microbeads can act as a scaffold for BMC proliferation and osteogenic differentiation and has potential for use as 3D degradable scaffold.

Right hip adduction deficit and adolescent idiopathic scoliosis

PURPOSE

To determine whether right hip adduction deficit is associated with adolescent idiopathic scoliosis.

METHODS

102 adolescents (mean age, 14 years) with idiopathic scoliosis were prospectively studied. Their spinal curve pattern (according to Lenke's classification), curve severity (by Cobb's angle), and hip adduction ranges of both sides were recorded. Additional factors that may affect hip adduction range including the preferred leg during standing, the presence of hip flexor tightness, and the side of the dominant leg were also assessed.

RESULTS

The mean Cobb's angle was 27 degrees. The difference in hip adduction range between the right and left hips was 5 degrees (p<0.05). Of 102 patients, 64 had an adduction range deficit of the right hip, 4 of the left hip, and 34 had no difference. Patients with >10 degrees of right hip adduction deficit were associated with a higher proportion of left leg dominance than those with less than or equal to 10 degrees of right hip adduction deficit (18% vs 4%).

CONCLUSION

Left leg dominance may play a role in right hip adduction deficit and scoliosis.

Characteristics and mechanical properties of acrylolpamidronate-treated strontium containing bioactive bone cement

The aim of the present study was to determine the influence of surface treatment on the mechanical properties of strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement. Previously we developed an injectable bioactive cement (SrHAC) system composed of Sr-HA powders and bisphenol A diglycidylether dimethacrylate (Bis-GMA). In this study, the Sr-HA powder was subjected to surface treatment using acrylolpamidronate, a bisphosphonate derivative, which has a polymerizable group, to improve the interface between inorganic filler and organic matrix by binding Sr-HA and copolymerizing into the matrix. After surface treatment, the compression strength, bending strength, and stiffness of the resulting composites were defined by using a material testing machine (MTS) according to ISO 5833. The fracture surface of the bone cement specimen was observed with a scanning electron microscope. Invitro cytotoxicity of surface-treated SrHAC was also studied using a tetrazolium-based cell viability assay (MTS/pms) on human osteoblast-like cells, the SaOS-2 cell line. Cells were seeded at a density of 10(4)/mL and allowed to grow in an incubator for 48 h at 37 degrees C. Results indicated that after surface treatment, the compression strength and stiffness significantly improved by 22.68 and 14.51%, respectively. The bending strength and stiffness of the bioactive bone cement also showed 19.06 and 8.91% improvements via three-point bending test. The fracture surface micromorphology after compression and bending revealed that the bonding between the resin to surface-treated filler considerably improved. The cell viability indicated that the treated particles were nontoxic and did not inhibit cell growth. This study demonstrated a new surface chemistry route to enhance the covalent bonds between inorganic fillers and polymer matrix for improving the mechanical properties of bone cement. This method not only improves the overall mechanical performance but also increases osteoblastic activity.

Effect of weight-bearing on bone-bonding behavior of strontium-containing hydroxyapatite bone cement

The purpose of this study was to investigate and compare the chemical composition and nanomechanical properties at the bone-cement interface under non-weight-bearing and weight-bearing conditions, in order to understand the effect of weight-bearing on the bone-bonding behavior of strontium-containing hydroxyapatite (Sr-HA) cement. In one group, Sr-HA cement was injected into rabbit ilium (under non-weight-bearing conditions). Unilateral hip replacement was performed with Sr-HA cement (under weight-bearing conditions) in the other group. Six months later, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis and nanoindentation tests were conducted on the interfaces between cancellous bone and the Sr-HA cement. The nanoindentation results revealed two different transitional behaviors under different conditions. nder weight-bearing conditions, both the Young modulus and hardness at the interface were considerably higher than those at either the Sr-HA cement or cancellous bone. On the contrary, under non-weight-bearing conditions, both the Young modulus and hardness values at the interface were lower than those at the cancellous bone, but were higher than the Sr-HA cement. In addition, EDX results showed that the calcium and phosphorus contents at the interface under weight-bearing conditions were considerably higher than those under non-weight-bearing conditions. The differences in chemical composition and nanomechanical properties at the cement-bone interface under two different conditions indicate that weight-bearing produces significant effects on the bone-bonding behavior of the Sr-HA cement.

Surface mechanical properties, corrosion resistance, and cytocompatibility of nitrogen plasma-implanted nickel-titanium alloys: a comparative study with commonly used medical grade materials

Stainless steel and titanium alloys are the most common metallic orthopedic materials. Recently, nickel-titanium (NiTi) shape memory alloys have attracted much attention due to their shape memory effect and super-elasticity. However, this alloy consists of equal amounts of nickel and titanium, and nickel is a well known sensitizer to cause allergy or other deleterious effects in living tissues. Nickel ion leaching is correspondingly worse if the surface corrosion resistance deteriorates. We have therefore modified the NiTi surface by nitrogen plasma immersion ion implantation (PIII). The surface chemistry and corrosion resistance of the implanted samples were studied and compared with those of the untreated NiTi alloys, stainless steel, and Ti-6Al-4V alloy serving as controls. Immersion tests were carried out to investigate the extent of nickel leaching under simulated human body conditions and cytocompatibility tests were conducted using enhanced green fluorescent protein mice osteoblasts. The X-ray photoelectron spectroscopy results reveal that a thin titanium nitride (TiN) layer with higher hardness is formed on the surface after nitrogen PIII. The corrosion resistance of the implanted sample is also superior to that of the untreated NiTi and stainless steel and comparable to that of titanium alloy. The release of nickel ions is significantly reduced compared with the untreated NiTi. The sample with surface TiN exhibits the highest amount of cell proliferation whereas stainless steel fares the worst. Compared with coatings, the plasma-implanted structure does not delaminate as easily and nitrogen PIII is a viable way to improve the properties of NiTi orthopedic implants.

Photochemical cross-linking for collagen-based scaffolds: a study on optical properties, mechanical properties, stability, and hematocompatibility

Collagen presents an attractive biomaterial for tissue engineering because of its excellent biocompatibility and negligible immunogenicity. However, some intrinsic features related to the mechanical stability and thrombogenicity limit its applications in orthopedic and vascular tissue engineering. Photochemical cross-linking is an emerging technique able to stabilize tissue grafts and improve the physicochemical properties of collagen-based structures. However, other important properties of collagen-based structures and the effect of processing parameters on these properties have not been explored. In this study, we aim to investigate the dose dependence of tensile and swelling properties on two parameters, namely, laser energy fluence and rose Bengal photosensitizer concentration. We also study the compression properties using cyclic compression test, long-term stability using subcutaneous implantation, and hematocompatibility using platelets adhesion test, of cross-linked collagen structures. Moreover, because limited optical penetration in turbid media is the major obstacle for light-based techniques, we also characterize the optical properties, which partially determine the effective optical penetration depth in collagen gel samples, during photochemical cross-linking. Laser energy fluence and rose Bengal concentration are important parameters affecting the cross-linking efficiency, which was characterized as the mechanical and the swelling properties, in a dose-dependent manner. Under the experimental conditions in this study, the peak fluence was 12.5 J/cm2 and the minimal rose Bengal concentration for effective cross-linking was >0.00008% (0.786 micromol). Photochemical cross-linking also enhanced the compression strength and long-term stability of collagen structures without compromising the tissue compatibility. Furthermore, photochemical cross-linking reduced platelet adhesion and abolished fibrin mesh formation, thereby improving the hematocompatibility of collagen structures. These results suggest the feasibility of using the photochemically cross-linked collagen structures for orthopedic and vascular tissue engineering. Finally, the effective optical penetration depth in collagen gel samples is wavelength and rose Bengal concentration dependent, and was approximately 12 mm at 514 nm at 0.001% (9.825 micromol), the rose Bengal concentration mostly used in this study.

Nickel release behavior, cytocompatibility, and superelasticity of oxidized porous single-phase NiTi

Porous NiTi shape memory alloys are one of the promising biomaterials for surgical implants because of their unique shape memory effects and porous structure with open pores. However, the complex surface morphology and larger area of porous NiTi compared to dense NiTi make it more vulnerable from the viewpoint of release of nickel, which can cause deleterious effects in the human body. It is also more difficult to modify the exposed surfaces of a porous structure using conventional surface modification technologies. In this work, oxidation in conjunction with postreaction heat treatment was used to modify the surfaces of porous single-phase NiTi prepared by capsule-free hot isostatic pressing to mitigate Ni leaching and enhance the surface properties. Differential scanning calorimetry thermal analysis, uniaxial compression tests, inductively-coupled plasma mass spectrometry, and cell cultures reveal that porous NiTi alloys oxidized at 450 degrees C for 1 h have an austenite transition temperature below 37 degrees C, excellent superelasticity, lower nickel release, and no cytotoxicity.

Preliminary clinical outcomes of percutaneous kyphoplasty with Sky-bone expander

BACKGROUND

Percutaneous kyphoplasty (PKP) using balloon expander has been proved to be effective in the treatment of painful vertebral compression fractures. Recently, Sky-bone expander, an alternative bone expander for PKP has been developed. The purpose of this study was to show our preliminary clinical outcomes of PKP with Sky-bone expander.

METHODS

PKP with Sky-bone expander was performed in 25 patients (30 vertebrae). The operation time, bleeding volume, cement volume injected were recorded. The pain and functional activities of the patients before and after the operation were compared using Wilcoxon signed-rank test. The cement distribution in the vertebrae, vertebral height restoration, and kyphosis correction after the procedure were evaluated by radiography. The pre- and post-operative absolute values of the vertebral height and kyphotic angle were compared by paired-sample t test. All the patients were followed up by telephone or clinic consulting after being discharged from our hospital.

RESULTS

The procedure was performed successfully in all the patients. Bipedicular injection was used in 2 of the patients, and unipedicular injection was made in the others. The operation time ranged from 25 to 120 minutes (45 minutes per vertebra on average). The average bleeding volume was about 20 ml. Polymethylmethacrylate 1.5-5.0 ml (mean, (3.15+/-0.78) ml) was injected through each pedicle into all the patients except one, who received calcium sulphate 3.5 ml instead. The patients were followed up for 12-15 months (13.5 months on average). The mean visual analogue scale (VAS) score, Oswestry Disability Index, anterior, midline, and posterior vertebral height, and kyphotic angle of the patients were improved significantly at the end of the follow-up compared with those before the operation. (2.5+/-1.3, 35.1%, (20.94+/-6.15) mm, (20.26+/-4.59) mm, (26.72+/-3.49) mm, and 8.2 degrees vs. 8.5+/-1.9, 61.2%, (19.11+/-6.72) mm, (15.88+/-5.73) mm, (25.78+/-3.67) mm, and 17.3 degrees; all P<0.05). The cement distribution with unipedicular injection was mostly limited within the injection site in the vertebral body. Cement extravasation was seen at ten levels (33.3%).

CONCLUSIONS

PKP with Sky-bone expander is an effective and relatively safe alternative to the PKP using balloon expander. It can relieve pain, improve physical function, and restore the height of the collapsed vertebrae, but the cement extravasation is unsolved.

Chemical composition, crystal size and lattice structural changes after incorporation of strontium into biomimetic apatite

Recently, strontium (Sr) as ranelate compound has become increasingly popular in the treatment of osteoporosis. However, the lattice structure of bone crystal after Sr incorporation is yet to be extensively reported. In this study, we synthesized strontium-substituted hydroxyapatite (Sr-HA) with different Sr content (0.3%, 1.5% and 15% Sr-HA in mole ratio) to simulate bone crystals incorporated with Sr. The changes in chemical composition and lattice structure of apetite after synthetic incorporation of Sr were evaluated to gain insight into bone crystal changes after incorporation of Sr. X-ray diffraction (XRD) patterns revealed that 0.3% and 1.5% Sr-HA exhibited single phase spectrum, which was similar to that of HA. However, 15% Sr-HA induced the incorporation of HPO4(2-) and more CO3(2-), the crystallinity reduced dramatically. Transmission electron microscopy (TEM) images showed that the crystal length and width of 0.3% and 1.5% Sr-HA increased slightly. Meanwhile, the length and width distribution were broadened and the aspect ratio decreased from 10.68+/-4.00 to 7.28+/-2.80. The crystal size and crystallinity of 15% Sr-HA dropped rapidly, which may suggest that the fundamental crystal structure is changed. The findings from this work indicate that current clinical dosage which usually results in Sr incorporation of below 1.5% may not change chemical composition and lattice structure of bone, while it will broaden the bone crystal size distribution and strengthen the bone.

Visualization of lumbar muscle contraction synergy using surface electromyography (sEMG) streaming topography

Because of the difficulty in analysis and interpretation of surface electromyography (sEMG), the specific muscle contraction synergy associated with low back pain continues to be debated. Streaming topography is a novel method of continuously visualizing the distribution of sEMG signals during dynamic motion to provide a more comprehensive examination and subsequent insight into the synergy of muscle recruitment pattern. The purpose of this study was to assess the feasibility of streaming topography as a diagnostic tool. Ten healthy subjects were recruited to establish the normal pattern of lumbar muscle activity. An array of surface EMG electrodes was applied to the low back region and recorded during forward bending. The root mean square (RMS) of the sEMG signals were calculated as a function of both position and time to produce streaming topographical videos of the muscle activity in the lumbar region. In addition, a preliminary clinical study was carried out with 3 LBP patients. In normal subjects, RMS streaming topography was consistent, reproducible, and reliable. In clinical observation, the RMS streaming topography of LBP patients was obviously different from that of normal subjects. Some of LBP patients showed an asymmetric distribution during symmetric action. Streaming topography provides a dynamic analysis of lumbar muscle activities and illustrates the synergy of muscle contractions, which may be useful to improve physiotherapy management of LBP.

Phenotypic and population differences in the association between CILP and lumbar disc disease

BACKGROUND

Lumbar disc disease (LDD) is one of the leading causes of disability in the working-age population. A functional single-nucleotide polymorphism (SNP), +1184T-->C, in exon 8 of the cartilage intermediate layer protein gene (CILP) was recently identified as a risk factor for LDD in the Japanese population (odds ratio (OR) 1.61, 95% CI 1.31 to 1.98), with implications for impaired transforming growth factorbeta1 signalling.

AIM

To validate this finding in two different ethnic cohorts with LDD.

METHODS

This SNP and flanking SNPs were analysed in 243 Finnish patients with symptoms of LDD and 259 controls, and in 348 Chinese subjects with MRI-defined LDD and 343 controls.

RESULTS AND CONCLUSION

The results showed no evidence of association in the Finnish (OR = 1.35, 95% CI 0.97 to 1.87; p = 0.14) or the Chinese (OR = 1.05, 95% CI 0.77 to 1.43; p = 0.71) samples, suggesting that cartilage intermediate layer protein gene is not a major risk factor for symptoms of LDD in Caucasians or in the general population that included individuals with or without symptoms.

Surface characteristics, biocompatibility, and mechanical properties of nickel-titanium plasma-implanted with nitrogen at different implantation voltages

NiTi shape memory alloy is one of the promising orthopedic materials due to the unique shape memory effect and superelasticity. However, the large amount of Ni in the alloy may cause allergic reactions and toxic effects thereby limiting its applications. In this work, the surface of NiTi alloy was modified by nitrogen plasma immersion ion implantation (N-PIII) at various voltages. The materials were characterized by X-ray photoelectron spectroscopy (XPS). The topography and roughness before and after N-PIII were measured by atomic force microscope. The effects of the modified surfaces on nickel release and cytotoxicity were assessed by immersion tests and cell cultures. The XPS results reveal that near-surface Ni concentration is significantly reduced by PIII and the surface TiN layer suppresses nickel release and favors osteoblast proliferation, especially for samples implanted at higher voltages. The surfaces produced at higher voltages of 30 and 40 kV show better adhesion ability to osteoblasts compared to the unimplanted and 20 kV PIII samples. The effects of heating during PIII on the phase transformation behavior and cyclic deformation response of the materials were investigated by differential scanning calorimetry and three-point bending tests. Our results show that N-PIII conducted using the proper conditions improves the biocompatibility and mechanical properties of the NiTi alloy significantly.

In vitro evaluation of alginate encapsulated adipose-tissue stromal cells for use as injectable bone graft substitute

This study aims to investigate the survival and osteogenic behavior of murine-derived adipose-tissue stromal cells (ATSCs) encapsulated in alginate microcapsules thereby instigating further studies in this cell delivery strategy for in vivo osteogenesis. Cell viability was quantified using a tetrazolium-based assay and osteogenic differentiation was evaluated by both alkaline-phosphatase (ALP) histochemistry and osteocalcin mRNA analysis. Following microencapsulation, cell numbers increased from 3.9 x 10(3) on day 1 to 7.8 x 10(3) on day 7 and maintained excellent viability in the course of 21-day culture. ALP was 6.9, 5.5, and 3.2 times higher than monolayer cultures on days 7, 14, and 21, respectively. In addition, osteocalcin mRNA was detectable in encapsulated cultures earlier (day 14) than monolayer cultures. We conclude that alginate microcapsules can act as three-dimensional matrix for ATSC proliferation and has potential for use as injectable, biodegradable scaffold in bone tissue engineering.

The feasibility of repositioning ability as a tool for ergonomic evaluation: effects of chair back inclination and fatigue on head repositioning

Poor posture has been suggested as one of the main factors contributing to the high prevalence of neck pain in video display unit (VDU) users, but no clear association between pain and any particular resting neck posture has been found. Postural awareness of the neck, as indicated by the repositioning accuracy, may therefore be an appropriate measure and potentially useful assessment tool. The objective of this study is to examine whether posture and fatigue affect the head repositioning ability in typical VDU usage. A group of 20 healthy participants reproduced a normal comfortable posture for forward, upright and backward chair back inclinations in random order both before and after fatigue of the upper trapezius muscles. Ten repetitions of the posture were recorded for 2 s each, and the angular and translational deviations from the original head position were measured with regard to the external environment (head in space repositioning) and with regard to the trunk (head on trunk repositioning). Analysis by repeated measures ANOVA showed significant effects and interactions of fatigue and chair back inclination on the repositioning errors in the sagittal plane, which typically showed systematic trends towards certain postures rather than random errors around a mean position. While further work is required to examine the ergonomic impact of impaired repositioning ability, head repositioning is sensitive to ergonomic factors such as seating configuration and fatigue, and may therefore be a useful tool for evaluation of static working postures.

Surface characteristics, mechanical properties, and cytocompatibility of oxygen plasma-implanted porous nickel titanium shape memory alloy

Good surface properties and biocompatibility are crucial to porous NiTi shape memory alloys (SMA) used in medical implants, as possible nickel release from porous NiTi may cause deleterious effects in the human body. In this work, oxygen plasma immersion ion implantation (O-PIII) was used to reduce the amount of nickel leached from porous NiTi alloys with a porosity of 42% prepared by capsule-free hot isostatic pressing. The mechanical properties, surface properties, and biocompatibility were studied by compression tests, X-ray photoelectron spectroscopy (XPS), and cell culturing. The O-PIII porous NiTi SMAs have good mechanical properties and excellent superelasticity, and the amount of nickel leached from the O-PIII porous NiTi is much less than that from the untreated samples. XPS results indicate that a nickel-depleted surface layer predominantly composed of TiO(2) is produced by O-PIII and acts as a barrier against out-diffusion of nickel. The cell culturing tests reveal that both the O-PIII and untreated porous NiTi alloys have good biocompatibility.

Carbon plasma immersion ion implantation of nickel–titanium shape memory alloys

Nickel-titanium (NiTi) shape memory alloys possess super-elasticity in addition to the well-known shape memory effect and are potentially suitable for orthopedic implants. However, a critical concern is the release of harmful Ni ions from the implants into the living tissues. We propose to enhance the corrosion resistance and other surface and biological properties of NiTi using carbon plasma immersion ion implantation and deposition (PIII&D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII&D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Our tribological tests show that the treated surfaces are mechanically more superior and cytotoxicity tests reveal that both sets of plasma-treated samples favor adhesion and proliferation of osteoblasts.

Investigation of nickel suppression and cytocompatibility of surface-treated nickel-titanium shape memory alloys by using plasma immersion ion implantation

Nickel-titanium (NiTi) shape memory alloys are increasingly being used in orthopedic applications. However, there is a concern that Ni is harmful to the human body. We have recently investigated the use of nitrogen, or oxygen plasma immersion ion implantation to mitigate this deleterious effect. Our results reveal that the near-surface Ni concentration in all the treated samples is significantly suppressed. In addition, our in vitro tests show that the plasma-treated surfaces are cytologically compatible allowing the attachment and proliferation of osteoblasts. Among the two types of samples, the best biological effects are found on the samples with nitrogen implantation.

Effect of segmental artery ligation on the blood supply of the thoracic spinal cord during anterior spinal surgery: a quantitative histomorphological fresh cadaver study

STUDY DESIGN

Human cadaver quantitative morphometric analysis of the blood vessels in the spinal cord after ligation of segmental arteries.

OBJECTIVES

To investigate the effect of ligation of segmental arteries on the quantity and density of the blood vessels in the spinal cord.

SUMMARY OF BACKGROUND DATA

Ligation of segmental arteries is often used in the anterior approach for correction scoliosis. However, whether or not segmental artery ligation is liable to deny the spinal cord an adequate blood supply, thus leading to paraplegia, still remains controversial.

METHODS

Eleven fresh cadavers were divided into control, unilateral, and bilateral groups. For the unilateral and bilateral groups, 5 segmental vertebral arteries (T7-T11) were ligated unilaterally and bilaterally, respectively. Then, the number and density of blood vessels at different levels in the 3 groups were measured.

RESULTS

Compared to that of the corresponding level in the control group, the number of blood vessels at T5 to L1 all decreased in the ligation groups. And significant differences were found at T8 (82.80 +/- 16.36), T10 (77.80 +/- 19.80), and T11 (99.20 +/- 14.85) levels, compared to those of the corresponding levels in the control group: T8 (175.80 +/- 8. 31), T9 (176.40 +/- 32. 33), T10 (171.40 +/- 9. 73), and T11 (189.20 +/- 15. 92). Further decrease was found at each corresponding level in the bilateral group, and significant differences were found at T8 (65.80 +/- 15.55), T9 (24.80 +/- 13.43), T10 (0), T11 (0), and T12 (0) levels. Similar results were obtained with regard to the density of blood vessels. Significant differences were found at T11 (1.246 +/- 0.112) and L1 (1.349 +/- 0.109) in the unilateral group, and T9 (0.260 +/- 0.088), T10 (0), T11 (0), T12 (0), and L1 (0.147 +/- 0.117) in the bilateral group compared to those of the corresponding levels in the control group: T9 (1.810 +/- 0.202), T10 (1.833 +/- 0.175), T11 (2.308 +/- 0.335), T12 (2.510 +/- 0.617), and L1 (2.193 +/- 0.033).

CONCLUSIONS

This study suggests that the more levels the ligation encompasses, the higher the risk of spinal cord damage. Therefore, caution should be taken when several segmental arteries are to be ligated in the clinical setting. What is more, bilateral ligation, which is worse than unilateral ligation, can lead to a significant decrease in the number and density of blood vessels of the spinal.

Investigation of nickel suppression and cytocompatibility of surface-treated nickel-titanium shape memory alloys by using plasma immersion ion implantation

Nickel-titanium (NiTi) shape memory alloys are increasingly being used in orthopedic applications. However, there is a concern that Ni is harmful to the human body. We have recently investigated the use of nitrogen, or oxygen plasma immersion ion implantation to mitigate this deleterious effect. Our results reveal that the near-surface Ni concentration in all the treated samples is significantly suppressed. In addition, our in vitro tests show that the plasma-treated surfaces are cytologically compatible allowing the attachment and proliferation of osteoblasts. Among the two types of samples, the best biological effects are found on the samples with nitrogen implantation.

Corrosion resistance, surface mechanical properties, and cytocompatibility of plasma immersion ion implantation-treated nickel-titanium shape memory alloys

Nickel-titanium shape memory alloys are promising materials in orthopedic applications because of their unique properties. However, for prolonged use in a human body, deterioration of the corrosion resistance of the materials becomes a critical issue because of the increasing possibility of deleterious ions released from the substrate to living tissues. We have investigated the use of nitrogen, acetylene, and oxygen plasma immersion ion implantation (PIII) to improve the corrosion resistance and mechanical properties of the materials. Our results reveal that the corrosion resistance and mechanical properties such as hardness and elastic modulus are significantly enhanced after surface treatment. The release of nickel is drastically reduced as compared with the untreated control. In addition, our in vitro tests show that the plasma-treated surfaces are well tolerated by osteoblasts. Among the three types of samples, the best biological effects are observed on the nitrogen PIII samples.

Strengthening mechanisms of bone bonding to crystalline hydroxyapatite in vivo

The formation and strengthening mechanisms of bone bonding of crystalline hydroxyapatite (HA) has been investigated using high-resolution transmission electron microscope (HRTEM) and energy-dispersive X-ray (EDX) analysis. A series of results were obtained: (i) a layer of amorphous HA, which has almost the same chemistry as the implanted HA, was formed on the surface of crystalline HA particles prior to dissolution; (ii) at 3 months a bone-like tissue formed a bonding zone between mature bone and the HA implant, composed of nanocrystalline and amorphous apatite; and (iii) at 6 months, mature bone was in direct contact with HA particles, and collagen fibres were perpendicularly inserted into the surface layer of implanted HA crystals. Findings (i) and (ii) indicated the following dissolution-precipitation process. (i) The crystalline HA transforms into amorphous HA; (ii) the amorphous HA dissolves into the surrounding solution, resulting in over-saturation; and (iii) the nanocrystallites are precipitated from the over-saturated solution in the presence of collagen fibres. A preliminary analysis indicated several conclusions: (i) the transition from crystalline to amorphous HA might be the controlling step in the bone bonding of crystalline HA; (ii) biological interdigitation (or incorporation) of collagen fibres with HA and chemical bonding of a apatite layer were both necessary to strengthen and toughen a bone bond, not only for the bonding between bone and HA at 6 months, but also for the bonding zone at 3 months, which would otherwise be very fragile due to the inherited brittleness of polycrystalline ceramics; and (iii) perpendicular interdigitation is an effective way for collagen fibres to impart their unique combination of flexibility and strength to the interface which they are keying.

In vivo cancellous bone remodeling on a strontium-containing hydroxyapatite (sr-HA) bioactive cement

The purpose of this study was to investigate the in vivo bone response to the strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into the cancellous bone. Sr-HA cement was injected into the iliac crest of rabbits for 1, 3, and 6 months. Active bone formation and remodeling were observed after 1 month. Newly formed bone was observed to grow onto the bone cement after 3 months. Thick osteoid layer with osteoblasts formed along the bone and guided over the bone cement surface reflected the stimulating effect of Sr-HA. From scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thick layer of 70 microm in width, and fusion of Sr-HA with the bone was observed. Blood vessels were found developing in remodeling sites. The affinity of bone on Sr-HA cement was increased from 73.55 +/- 3.50% after 3 months up to 85.15 +/- 2.74% after 6 months (p < 0.01). In contrast to Sr-HA cement, poly(methyl methacrylate) (PMMA) bone cement was neither osteoconductive nor bioresorbable. Results show that the Sr-HA cement is biocompatible and osteoconductive, which is suitable for use in treating osteoporotic vertebral fractures.

A prospective comparison of the coronal deformity correction in thoracic scoliosis using four different instrumentations and the fulcrum-bending radiograph

STUDY DESIGN

A prospective study on comparing coronal deformity correction in thoracic scoliosis using four different instrumentations.

OBJECTIVES

To compare the ability of four different instrumentation systems in correcting thoracic scoliosis based on the curve flexibility as reviewed by the fulcrum-bending radiograph.

SUMMARY OF BACKGROUND DATA

The fulcrum-bending radiograph has been shown to be able to accurately reflect the flexibility of thoracic curves, and the fulcrum bending correction index (FBCI) predicts the amount of correction achieved by current surgical techniques. By recruiting curves of known flexibility, the efficacy of the different instrumentations in correcting coronal deformity can be truly compared.

METHODS

A consecutive series of 127 patients with idiopathic scoliosis were treated by one of four implants: CD-Horizon (CD-H), Moss Miami (MM), TSRH, and ISOLA. All surgeries were performed by the same group of surgeons using the respective recommended techniques. FBCI was used to compare the correction achieved by these implants.

RESULTS

The mean FBCI/correction rate was 101.0%/57.9% in the TSRH group, 103.5%/58.5% in ISOLA, 109.1%/67.6% in CD-H, and 100.2%/62.7% in the MM group. The correction rate was significantly (P < 0.05) higher in the CD-H group than those in the TSRH and ISOLA groups, while the differences in the FBCI between the four implants were not statistically significant.

CONCLUSIONS

When curve flexibility is taken into account, despite differences in material and design of four commonly used instrumentations, their ability to correct thoracic scoliosis is the same. Future studies describing surgical correction results should be based on the FBCI.

Spinal flexibility increase after chymopapain injection is dose dependent: a possible alternative to anterior release in scoliosis

STUDY DESIGN

Experimental animal study.

OBJECTIVES

To investigate whether the increase in spinal flexibility after chymopapain injection is dose dependent and determine the "optimal" dosage of chymopapain to increase spinal flexibility in a rabbit model.

SUMMARY OF BACKGROUND DATA

Spinal instability after chymopapain injection may result in severe back pain. However, this undesired mechanical effect in treating disc herniation may provide a safe minimally invasive approach for anterior spinal release in scoliosis correction.

METHODS

A total of 138 lumbar intervertebral discs from 46 New Zealand white rabbits were randomly injected with chymopapain at 6.25, 12.5, 25, 50, 75, and 100 picokatals (pKats)/0.05 mL/disc. The rabbits were killed 1 week after the injection, and the lateral bending stiffness of the spinal segments without posterior elements was determined.

RESULTS

The lateral bending spinal stiffness showed no significant change after injection of 6.25 and 12.5 pKats/0.05 mL/disc but reduced significantly following chymopapain injection of 25, 50, 75, and 100 pKats (all P < 0.05 by post hoc least significant difference tests). While the lateral bending stiffness was lowest at the 100-pKats dose, there were no significant differences between the four higher dosages.

CONCLUSION

The reduction in the lateral bending spinal stiffness after chymopapain injection is dose dependent, and an optimal dosage for spinal release existed; doses greater than the optimal dosage did not result in further significant decrease in lateral bending spinal stiffness.

Surface treatment of injectable strontium-containing bioactive bone cement for vertebroplasty

A novel injectable bioactive bone-bonding cement (SrHAC) composed of strontium-containing hydroxyapatite (Sr-HA) as the inorganic filler and bisphenol A diglycidylether dimethacrylate (Bis-GMA) as the organic matrix for vertebroplasty was developed previously. In this study, the Sr-HA powders were surface treated with methyl methacrylate (MMA) to improve the interface integration of the two phases. After surface treatment, the compression strength and Young's modulus, which were tested after immersion in distilled water at 37 degrees C for 24 h according to ISO 5833, were increased by 68.65 % (p <.001) and 31.02% (p <.001), respectively. The bending strength and bending stiffness of the bioactive bone cement were significantly improved by 54.44% (p <.001) and 83.90% (p <.001). In addition, the handling property of the cement was also enhanced. In vitro biomechanical testing showed that the stiffness of the fractured spine recovered to 82.5% (p <.01) of the intact condition after cementation with surface-treated SrHAC. The failure load of the spine cemented with original and MMA-treated SrHAC improved by 14.25% (p <.05) and 46.91% (p <.05) in comparison with the fractured spines. Results from this study revealed that the MMA-treated SrHAC has a better mechanical effect for orthopedic applications.

Ultrastructural study of mineralization of a strontium-containing hydroxyapatite (Sr-HA) cementin vivo

The purpose of this study was to investigate the mineralization leading to osseointegration of strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into cancellous bone in vivo. Sr-HA cement was injected into the ilium of rabbits for 1, 3, and 6 months. The bone mineralization area was found to be largest at 3 months, then at 1 month, and smallest at 6 months (p < 0.01) measured with tetracycline labeling. Osseointegration of Sr-HA cement was achieved at 3 months as observed by scanning electron microscopy. A high calcium and phosphorus area was observed at the interface of bone-Sr-HA cement determined by energy-dispersive X-ray analysis. Transmission electron microscopy gave evidence of the mechanism of bone formation. Dissolution of Sr-HA into debris by the bone remodeling process was thought to increase the concentration of calcium and phosphorus at the interface of bone-Sr-HA cement and stimulate bone formation. Crystalline Sr-HA formed an amorphous layer and dissolved into the surrounding solution, then apatite crystallites were precipitated and formed new bone at 3 months. This young bone then becomes mature bone, which bonds tightly to the Sr-HA cement with collagen fibers inserted perpendicularly after 6 months.

Controllable porosity hydroxyapatite ceramics as spine cage: fabrication and properties evaluation

A procedure was designed to prepare porosity-graded hydroxyapatite (HA) ceramics simulating the bimodal structure of natural bone, which could be used to build a cage that would promote the reconstruction of the anterior column after vertebrectomy or corpectomy in tumor and trauma surgery. HA ceramics with controllable pore size distribution and porosity were developed by using chitosan and Poly(vinyl alcohol) (PVA) as the pore-forming agents. HA ceramics with worthwhile properties such as a wide range of volume porosity (10-50%) and pore size (nanometer to 400 microm) can be obtained from this method, which allows the fabrication of HA ceramics with desirable porous characteristics simulating the bimodal natural bone architecture expected to provide advantages for bony fusion in the intervertebral foramina. When coated with chitosan-gelatin network, the bending strength of the porous HA ceramics significantly improved. The polymer network coated porous HA have potential application in the construction of cages for spinal operations.

Gene therapy for new bone formation using adeno-associated viral bone morphogenetic protein-2 vectors

Previous reports have suggested that bone morphogenetic protein (BMP) gene therapy could be applied for in vivo bone regeneration. However, these studies were conducted either using immunodeficient animals because of immunogenicity of adenovirus vectors, or using ex vivo gene transfer technique, which is much more difficult to handle. Adeno-associated virus (AAV) is a replication-defective virus without any association with immunogenicity and human disease. This study was conducted to investigate whether orthotopic new bone formation could be induced by in vivo gene therapy using AAV-based BMP2 vectors. To test the feasibility of this approach, we constructed an AAV vector carrying human BMP2 gene. Mouse myoblast cells (C2C12) transduced with this vector could produce and secrete biologically active BMP2 protein and induce osteogenic activity, which was confirmed by ELISA and alkaline phosphatase activity assay. For in vivo study, AAV-BMP2 vectors were directly injected into the hindlimb muscle of immunocompetent Sprague-Dawley rats. Significant new bone under X-ray films could be detected as early as 3 weeks postinjection. The ossification tissue was further examined by histological and immunohistochemical analysis. This study is, to our knowledge, the first to establish the feasibility of AAV-based BMP2 gene therapy for endochondral ossification in immunocompetent animals.