Evaluation of toxicity and biocompatibility of a novel Mg-Nd-Gd-Sr alloy in the osteoblastic cell

BACKGROUND

We investigated the toxicity and biocompatibility of a novel Mg-3Nd-1Gd-0.3Sr-0.2Zn-0.4Zr (abbreviated to Mg-Nd-Gd-Sr) alloy in the osteoblastic cell line MC3T3-E1 as osteoblasts play an important role in bone repair and remodeling.

METHODS

We used cytotoxicity tests and apoptosis to investigate the effects of the Mg-Nd-Gd-Sr alloy on osteoblastic cells. Cell bioactivity, cell adhesion, cell proliferation, mineralization, ALP activity, and expression of BMP-2 and OPG by osteoblastic cells were also used to investigate the biocompatibility of Mg-Nd-Gd-Sr alloy.

RESULTS

The results showed that the Mg-Nd-Gd-Sr alloy had no obvious cytotoxicity, and did not induce apoptosis to MC3T3-E1 cells. Compared with the control group, the number of adherent cells within 12 h was increased significantly in each experimental group (P < 0.05); the OD value of MC3T3-E1 cells was increased significantly in each experimental group on days 1 and 3 of culture (P < 0.05); the number of mineralized nodules formed in each experimental group was significantly increased (P < 0.05), and ALP activity was significantly increased in each experimental group (P < 0.05). RT-PCR results showed that the mRNA expression of BMP-2 and OPG was significantly higher in each experimental group compared with the control group (P < 0.05). Western blotting showed that the Mg-Nd-Gd-Sr alloy extract significantly increased the protein expression of BMP-2 and OPG compared with the control group (P < 0.05).

CONCLUSIONS

Our data indicated that the novel Mg-Nd-Gd-Sr-Zn-Zr alloy had no obvious cytotoxic effects, and did not cause apoptosis to MC3T3-E1 cells; meanwhile it promoted cell adhesion, cell proliferation, mineralization, and ALP activity of osteoblasts. During this process, there was an increase in the expressions of BMP-2 and OPG mRNAs and proteins.

In Situ Upregulating Heat Shock Protein 70 via Gastric Nano-Heaters for the Interference of Helicobacter pylori Infection

Taking inspiration from the mechanism of Helicobacter pylori infection can lead to innovative antibacterial ways to fight antibiotics resistance. Herein, a gastric nano-heater iron-cobalt alloy shielded with graphitic shells (FeCo@G) is developed to interfere with H. pylori infection under an alternating magnetic field. FeCo@G shows a high and stable specific loss power (SLP = 534.1 W g^-1) in the acidic environment and provides efficient magnetothermal stimulation in the stomach. Such stimulation upregulates the cytoprotective heat shock protein 70 (HSP70) in gastric epithelial cells, which antagonizes the infection of H. pylori. This finding is further supported by the transcriptomic analysis verifying the upregulation of HSP70 in the stomach. Moreover, the nano-heater shows a high inhibition rate of H. pylori in vivo with good biocompatibility; 95% of FeCo@G is excreted from the mouse's gastrointestinal tract within 12 h. In summary, FeCo@G allows magnetothermal therapy to be used in harsh gastric environments, providing an approach for the therapy against H. pylori.

In vitro and in vivo assessment of the effect of biodegradable magnesium alloys on osteogenesis

Magnesium (Mg) and some of its alloys are considered promising biodegradable metallic biomaterials for bone implant applications. The osteogenesis effect of Mg alloys is widely reported; however, the underlying mechanisms are still not clear. In this study, pure Mg, Mg-3Zn, and Mg-2Zn-1Mn were prepared, and their degradation behavior, biocompatibility, and osteogenesis effect were systematically assessed both in vitro and in vivo. Primary rat bone marrow-derived mesenchymal stem cells (BMSCs) were used to evaluate the biocompatibility of the prepared Mg alloys, and a rat femur fracture model was used to assess the stimulating effect of these alloys on bone-tissue formation. Mg-2Zn-1Mn showed higher corrosion resistance and more stable degradation behavior than pure Mg and Mg-3Zn. Extracts of the three materials showed significant stimulating effects on osteogenic differentiation of BMSCs along with non-cytotoxicity. Implantation of Mg-2Zn-1Mn wires into the femur of rats demonstrated superior histocompatibility, stable degradation, and notable promotion of osteogenesis without systemic toxicity. Moreover, the results of both in vitro and in vivo assessments demonstrated that bone morphogenetic proteins and fibroblast growth factor receptors are involved in the stimulating effect of Mg alloys. STATEMENT OF SIGNIFICANCE: This work reports the degradation behavior, biocompatibility, and osteogenic effect of pure Mg and Mg-3Zn and Mg-2Zn-1Mn alloys in both in vitro and in vivo conditions. Mg-2Zn-1Mn showed higher corrosion resistance and more stable degradation behavior than pure Mg and Mg-3Zn. The extracts of the three materials showed a significant stimulating effect on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs) along with non-cytotoxicity. Mg-2Zn-1Mn wires implanted into the femur of rats showed good histocompatibility, stable degradation, and notable promotion of osteogenesis without systemic toxicity. The results of the present study suggest that bone morphogenetic proteins (BMPs) and fibroblast growth factor receptors (FGFRs) are involved in the stimulating effect of Mg alloys on osteogenesis.

NiTi Alloys Exposure Alters miR-124 Expression in Physiological and Osteoarthritic Osteoblasts

PURPOSE OF THE STUDY Nitinol (NiTi) is a biomaterial widely used in medicine based on super-elastic and shape memory properties. miR-124 has a key role in inflammatory process, osteoblasts differentiation, and mineralization. The aim of study was evaluating the differences in gene expression of miR-124 of human physiological osteoblasts (HOB) and human osteoarthritic osteoblasts (OSBA) as a response to NiTi alloy in different heat treatments. MATERIAL AND METHODS The cells were cultivated with NiTi discs with/without addition of bacterial lipopolysaccharide (LPS) for 72 hours. MicroRNAs were isolated, underwent reverse transcription and were analyzed by RT-PCR. RESULTS As a response to LPS, HOB overexpressed miR-124, while in OSBA expression change did not occur. Overexpression was also observed in both cell lines as a response to hydrogen and helium treated NiTi discs. HOB expressed significantly higher amount of miR-124 than OSBA as a response to hydrogen treatment of NiTi discs. In addition, hydrogen treatment caused significantly higher expression in HOB than LPS. The combination of NiTi disc and LPS treatment in HOB didn't cause any expression changes. Comparing to LPS-only treatment, the expression in HOB with combination of LPS and alloy was significantly lower. In OSBA, the expression was increased by the combination of LPS and hydrogen disc, in case of helium disc, the expression was decreased. CONCLUSIONS In conclusion, human physiological and osteoarthritic osteoblasts respond to NiTi alloy with both surface (hydrogen and helium atmosphere) treatment by overexpression of miR-124. The effect of LPS as inflammatory modulator suggests the presence of an "anti-inflammatory preconditioning" in osteoarthritic osteoblasts, as physiological osteoblasts overexpression was significantly higher. Key words: nitinol, osteoblast, miR-124, lipopolysaccharide.

Surface Roughness of Titanium Orthopedic Implants Alters the Biological Phenotype of Human Mesenchymal Stromal Cells

Metal orthopedic implants are largely biocompatible and generally achieve long-term structural fixation. However, some orthopedic implants may loosen over time even in the absence of infection. In vivo fixation failure is multifactorial, but the fundamental biological defect is cellular dysfunction at the host-implant interface. Strategies to reduce the risk of short- and long-term loosening include surface modifications, implant metal alloy type, and adjuvant substances such as polymethylmethacrylate cement. Surface modifications (e.g., increased surface rugosity) can increase osseointegration and biological ingrowth of orthopedic implants. However, the localized responses of cells to implant surface modifications need to be better characterized. As an in vitro model for investigating cellular responses to metallic orthopedic implants, we cultured mesenchymal stromal/stem cells on clinical-grade titanium disks (Ti6Al4V) that differed in surface roughness as high (porous structured), medium (grit blasted), and low (bead blasted). Topological characterization of clinically relevant titanium (Ti) materials combined with differential mRNA expression analyses (RNA-seq and real-time quantitative polymerase chain reaction) revealed alterations to the biological phenotype of cells cultured on titanium structures that favor early extracellular matrix production and observable responses to oxidative stress and heavy metal stress. These results provide a descriptive model for the interpretation of cellular responses at the interface between native host tissues and three-dimensionally printed modular orthopedic implants, and will guide future studies aimed at increasing the long-term retention of such materials after total joint arthroplasty. Impact statement Using an in vitro model of implant-to-cell interactions by culturing mesenchymal stromal cells (MSCs) on clinically relevant titanium materials of varying topological roughness, we identified mRNA expression patterns consistent with early extracellular matrix (ECM) production and responses to oxidative/heavy metal stress. Implants with high surface roughness may delay the differentiation and ECM formation of MSCs and alter the expression of genes sensitive to reactive oxygen species and protein kinases. In combination with ongoing animal studies, these results will guide future studies aimed at increasing the long-term retention of widely used titanium materials after total joint arthroplasty.

In vitro and in vivo degradation assessment and preventive measures of biodegradable Mg alloys for biomedical applications

Magnesium (Mg) and its alloys have been widely explored as a potential biodegradable implant material. However, the fast degradation of Mg-based alloys under physiological environment has hindered their widespread use for implant applications till date. The present review focuses on in vitro and in vivo degradation of biodegradable Mg alloys, and preventive measures for biomedical applications. Initially, the corrosion assessment approaches to predict the degradation behavior of Mg alloys are discussed along with the measures to control rapid corrosion. Furthermore, this review attempts to explore the correlation between in vitro and in vivo corrosion behavior of different Mg alloys. It was found that the corrosion depends on experimental conditions, materials and the results of different assessment procedures hardly matches with each other. It has been demonstrated the corrosion rate of magnesium can be tailored by alloying elements, surface treatments and heat treatments. Various researches also studied different biocompatible coatings such as dicalcium phosphate dihydrate (DCPD), β-tricalcium phosphate (β-TCP), hydroxyapatite (HA), polycaprolactone (PCL), polylactic acid (PLA), and so on, on Mg alloys to suppress rapid degradation and examine their influence on new bone regeneration as well. This review shows the need for a standard method of corrosion assessment to predict the in vivo corrosion rate based on in vitro data, and thus reducing the in vivo experimentation.

Tissue responses after implantation of biodegradable Mg alloys evaluated by multimodality 3D micro-bioimaging in vivo

The local response of tissue triggered by implantation of degradable magnesium-based implant materials was investigated in vivo in a murine model. Pins (5.0 mm length by 0.5 mm diameter) made of Mg, Mg-10Gd, and Ti were implanted in the leg muscle tissue of C57Bl/6N mice (n = 6). Implantation was generally well tolerated as documented by only a mild short term increase in a multidimensional scoring index. Lack of difference between the groups indicated that the response was systemic and surgery related rather than material dependent. Longitudinal in vivo monitoring utilizing micro-computed tomography over 42 days demonstrated the highest and most heterogeneous degradation for Mg-10Gd. Elemental imaging of the explants by micro X-ray fluorescence spectrometry showed a dense calcium-phosphate-containing degradation layer. In order to monitor resulting surgery induced and/or implant material associated local cell stress, sphingomyelin based liposomes containing indocyanine green were administered. An initial increase in fluorescent signals (3-7 days after implantation) indicating cell stress at the site of the implantation was measured by in vivo fluorescent molecular tomography. The signal decreased until the 42nd day for all materials. These findings demonstrate that Mg based implants are well tolerated causing only mild and short term adverse reactions.

Metabolic Fingerprinting on Synthetic Alloys for Medulloblastoma Diagnosis and Radiotherapy Evaluation

Diagnostics is the key in screening and treatment of cancer. As an emerging tool in precision medicine, metabolic analysis detects end products of pathways, and thus is more distal than proteomic/genetic analysis. However, metabolic analysis is far from ideal in clinical diagnosis due to the sample complexity and metabolite abundance in patient specimens. A further challenge is real-time and accurate tracking of treatment effect, e.g., radiotherapy. Here, Pd-Au synthetic alloys are reported for mass-spectrometry-based metabolic fingerprinting and analysis, toward medulloblastoma diagnosis and radiotherapy evaluation. A core-shell structure is designed using magnetic core particles to support Pd-Au alloys on the surface. Optimized synthetic alloys enhance the laser desorption/ionization efficacy and achieve direct detection of 100 nL of biofluids in seconds. Medulloblastoma patients are differentiated from healthy controls with average diagnostic sensitivity of 94.0%, specificity of 85.7%, and accuracy of 89.9%, by machine learning of metabolic fingerprinting. Furthermore, the radiotherapy process of patients is monitored and a preliminary panel of serum metabolite biomarkers is identified with gradual changes. This work will lead to the application-driven development of novel materials with tailored structural design and establishment of new protocols for precision medicine in near future.

Evaluation of a Porous Bioabsorbable Interbody Mg-Zn Alloy Cage in a Goat Cervical Spine Model

PURPOSE

Bioabsorbable Mg-based implants were previously assessed due to their intrinsic advantages, but Mg-based cage related research is limited. The specific blood supply and stress of the intervertebral environment can affect the function of Mg-based implants. The objective of this study was to investigate the performance of a bioabsorbable Mg-Zn alloy cage in anterior cervical discectomy and fusion (ACDF) and evaluate the control of degradation of the Mg-Zn cage surface modified by microarc oxidation (MAO) technology containing Si under an intervertebral microenvironment.

METHODS

Twenty-four goats were divided into four groups according to the experimental period and all underwent ACDF at C2-3 and C4-5 with porous Mg-Zn cage covered with a MAO/Si-containing coating in one intervertebral space and with autologous iliac bone in another space. After 3, 6, 12, or 24 weeks after operation, the cervical spine specimens were harvested to evaluate the biocompatibility, fusion status, and degradation conditions using blood analysis, radiology, biomechanical testing, histology, and micro-CT.

RESULTS

The Mg-Zn cages showed ideal biocompatibility and biomechanical characterization; however, the fusion state, as evaluated with radiology and histology, was not acceptable. Modified by the MAO/Si-containing coating, the degradation rate of the Mg-Zn cages was controllable but slower than expected.

CONCLUSION

MAO/Si-containing coating Mg-Zn alloy cages demonstrated excessive control of degradation and fusion failure after 24 weeks postoperatively. We conclude that further studies should be designed to improve the using of Mg-based materials at the intervertebral space.

Transgenic zebrafish model for quantification and visualization of tissue toxicity caused by alloying elements in newly developed biodegradable metal

The cytotoxicity of alloying elements in newly developed biodegradable metals can be assessed through relatively low-cost and rapid in vitro studies using different cell types. However, such approaches have limitations; as such, additional investigations in small mammalian models are required that recapitulate the physiological environment. In this study, we established a zebrafish (Danio rerio) model for cytotoxicity evaluations that combines the physiological aspects of an animal model with the speed and simplicity of a cell-based assay. The model was used to assess the cytotoxicity of five common alloying elements in biodegradable implant materials. Conventional in vitro testing using heart, liver, and endothelial cell lines performed in parallel with zebrafish studies revealed statistically significant differences in toxicity (up to 100-fold), along with distinct changes in the morphology of the heart, liver, and blood vessels that were undetectable in cell cultures. These results indicate that our zebrafish model is a useful alternative to mammalian systems for accurately and rapidly evaluating the in vivo toxicity of newly developed metallic materials.

Dual modulation of bone formation and resorption with zoledronic acid-loaded biodegradable magnesium alloy implants improves osteoporotic fracture healing: An in vitro and in vivo study

Osteoporotic fracture (OPF) remains a major clinical challenge for skeletal regeneration. Impaired osteogenesis and excessive remodeling result in prolonged and poor quality of fracture healing. To augment bone formation and inhibit excessive resorption simultaneously, we constructed a biodegradable magnesium-based implant integrated with the anti-catabolic drug zoledronic acid (ZA); this implant exhibits controllable, sustained release of magnesium degradation products and ZA in vitro. The extracts greatly stimulate the osteogenic differentiation of rat-bone marrow-derived mesenchymal stem cells (rBMSCs), while osteoclastogenesis is inhibited by ZA. Implantation of intramedullary nails to fix femur fracture in ovariectomy-induced osteoporotic rats for up to 12 weeks demonstrates magnesium implants alone can enhance OPF repair through promoting callus formation compared to conventional stainless steel, while the combinatory treatment with local ZA release from implant coating further increases bone regeneration rate and callus size, remarkably improves bone quality and mechanical strength and suppresses osteoclasts and bone remodeling, due to the synergistic effect of both agents. The slow and uniform degradation of the implant ensures a steady decrease in bending force, which meets clinical requirements. In summary, biodegradable magnesium-based implants can locally co-deliver magnesium degradation products and zoledronic acid in a controlled manner, and can be superior alternatives for the reconstruction of osteoporosis-related fracture.

STATEMENT OF SIGNIFICANCE

Management of osteoporotic fracture has posed a major challenge in orthopedics, as the imbalance between diminished osteogenesis and excessive bone remodeling often leads to delayed and compromised fracture repair. Among various efforts expended on augmenting osteoporotic fracture healing, herein we reported a new strategy by engineering and utilizing a biodegradable magnesium-based implant integrated with local drug delivery, specifically, zoledronic acid (ZA)-loaded polylactic acid/brushite bilayer coating on a biodegradable Mg-Nd-Zn-Zr alloy (denoted as Mg/ZA/CaP), aiming to combine the favorable properties of Mg and zoledronic acid for simultaneous modulation of bone formation and bone resorption. In vitro and in vivo studies demonstrated its superior treatment efficacy along with adequate degradation. It stimulated new bone formation while suppressing remodeling, ascribed to the local release of magnesium degradation products and zoledronic acid. To our knowledge, the enhanced fracture repair capability of Mg-based implants was for the first time demonstrated in an osteoporotic fracture animal model. This innovative biodegradable Mg-based orthopedic implant presents great potential as a superior alternative to current internal fixation devices for treating osteoporotic fracture.

Investigation on Composition, Mechanical Properties, and Corrosion Resistance of Mg-0.5Ca-X(Sr, Zr, Sn) Biological Alloy

Four nontoxic biological alloys, Mg-0.5Ca-1Sr-4Zr (Alloy 1), Mg-0.5Ca-1Sr-1.5Zr (Alloy 2), Mg-0.5Ca-3Sr-1.5Zr (Alloy 3), and Mg-0.5Ca-1Sr-0.5Sn (Alloy 4), were prepared by vacuum smelting, gravity casting, and hot rolling. The composition and microstructure of the alloys were investigated by optical microscope, X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion spectroscopy (EDS). The mechanical properties and corrosion behaviors of the alloys in Hank's solution were studied. Results showed that a large amount of fine and uniformly distributed second-phase particles (Zr, Mg₁₇Sr₂, and CaMgSn) was observed in four alloys obtained after rolling and alloying. The segregation of Zr in alloys was observed in EDS image, and chemical analysis showed that there was macrosegregation of the elements in the alloys. Furthermore, Mg₁₇Sr₂ phases in the Mg-0.5Ca-1Sr-0.5Sn alloy homogenized the distribution of CaMgZn phases. The comprehensive mechanical properties of four newly designed rolled alloys were much higher than those of pure Mg, and the compressive strength of the alloys was more than twice as high as that of pure magnesium. The Mg-0.5Ca-1Sr-0.5Sn alloy released the least hydrogen in Hank's solution, which was lower than that of pure magnesium. Electrochemical test results in Hank's solution further showed that the Mg-0.5Ca-1Sr-0.5Sn alloy had delayed corrosion and lowest I_corr which was 25% of that of pure magnesium. Biological experiments results showed that the Mg-0.5Ca-1Sr-0.5Sn alloy had better biocompatibility and optimal potential for bone substitute material.

AuPt Alloy Nanostructures with Tunable Composition and Enzyme-like Activities for Colorimetric Detection of Bisulfide

Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS- on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS- and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS- than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis.

Carbon Nanotubes Filled with Different Ferromagnetic Alloys Affect the Growth and Development of Rice Seedlings by Changing the C:N Ratio and Plant Hormones Concentrations

The aim of this study was to investigate the phytotoxicity of thin-walled carbon nanotubes (CNTs) to rice (Oryza sativa L.) seedlings. Three different CNTs, including hollow multi-walled carbon nanotubes (MWCNTs), Fe-filled carbon nanotubes (Fe-CNTs), and Fe-Co-filled carbon nanotubes (FeCo-CNTs), were evaluated. The CNTs significantly inhibited rice growth by decreasing the concentrations of endogenous plant hormones. The carbon to nitrogen ratio (C:N ratio) significantly increased in rice roots after treatments with CNTs, and all three types of CNTs had the same effects on the C:N ratio. Interestingly, the increase in the C:N ratio in roots was largely because of decreased N content, indicating that the CNTs significantly decreased N assimilation. Analyses of the Fe and Co contents in plant tissues, transmission electron microscope (TEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis proved that the CNTs could penetrate the cell wall and the cell membrane, and then enter the root cells. According to the author's knowledge, this is the first time to study the relationship between carbon nanotubes and carbon nitrogen ratio and plant hormones.

Peri-implant tissue response and biodegradation performance of a Mg-1.0Ca-0.5Sr alloy in rat tibia

Biodegradable magnesium (Mg) alloys combine the advantages of traditional metallic implants and biodegradable polymers, having high strength, low density, and a stiffness ideal for bone fracture fixation. A recently developed Mg-Ca-Sr alloy potentially possesses advantageous characteristics over other Mg alloys, such as slower degradation rates and minimal toxicity. In this study, the biocompatibility of this Mg-Ca-Sr alloy was investigated in a rat pin-placement model. Cylindrical pins were inserted in the proximal tibial metaphyses in pre-drilled holes orthogonal to the tibial axis. Implant and bone morphologies were investigated using μCT at 1, 3, and 6 weeks after implant placement. At the same time points, the surrounding tissue was evaluated using H&E, TRAP and Goldner's trichrome staining. Although gas bubbles were observed around the degrading implant at early time points, the bone remained intact with no evidence of microfracture. Principle findings also include new bone formation in the area of the implant, suggesting that the alloy is a promising candidate for biodegradable orthopedic implants.

Shape and site dependent in vivo degradation of Mg-Zn pins in rabbit femoral condyle

A type of specially designed pin model of Mg-Zn alloy was implanted into the full thickness of lesions of New Zealand rabbits’ femoral condyles. The recovery progress, outer surface healing and in vivo degradation were characterized by various methods including radiographs, Micro-CT scan with surface rendering, SEM (scanning electron microscope) with EDX (Energy Dispersive X-ray analysis) and so on. The in vivo results suggested that a few but not sufficient bridges for holding force were formed between the bone and the implant if there was a preexisting gap between them. The rapid degradation of the implantation in the condyle would result in the appearance of cavities. Morphological evaluation of the specially designed pins indicated that the cusp was the most vulnerable part during degradation. Furthermore, different implantation sites with distinct components and biological functions can lead to different degradation rates of Mg-Zn alloy. The rate of Mg-Zn alloy decreases in the following order: implantation into soft tissue, less trabecular bone, more trabecular bone, and cortical bone. Because of the complexities of in vivo degradation, it is necessary for the design of biomedical Mg-Zn devices to take into consideration the implantation sites used in clinics.

Bioaccessibility of metals in alloys: evaluation of three surrogate biofluids

Bioaccessibility in vitro tests measure the solubility of materials in surrogate biofluids. However, the lack of uniform methods and the effects of variable test parameters on material solubility limit interpretation. One aim of this study was to measure and compare bioaccessibility of selected economically important alloys and metals in surrogate physiologically based biofluids representing oral, inhalation and dermal exposures. A second aim was to experimentally test different biofluid formulations and residence times in vitro. A third aim was evaluation of dissolution behavior of alloys with in vitro lung and dermal biofluid surrogates. This study evaluated the bioaccessibility of sixteen elements in six alloys and 3 elemental/metal powders. We found that the alloys/metals, the chemical properties of the surrogate fluid, and residence time all had major impacts on metal solubility. The large variability of bioaccessibility indicates the relevancy of assessing alloys as toxicologically distinct relative to individual metals.

Nanophasic biodegradation enhances the durability and biocompatibility of magnesium alloys for the next-generation vascular stents

Biodegradable metal alloys emerge as a new class of biomaterials for tissue engineering and medical devices such as cardiovascular stents. Deploying biodegradable materials to fabricate stents not only obviates a second surgical intervention for implant removal but also circumvents the long-term foreign body effect of permanent implants. However, these materials for stents suffer from an un-controlled degradation rate, acute toxic responses, and rapid structural failure presumably due to a non-uniform, fast corrosion process. Here we report that highly uniform, nanophasic degradation is achieved in a new Mg alloy with unique interstitial alloying composition as the nominal formula Mg-2.5Nd-0.2Zn-0.4Zr (wt%, hereafter, denoted as JDBM). This material exhibits highly homogeneous nanophasic biodegradation patterns as compared to other biodegradable metal alloy materials. Consequently it has significantly reduced degradation rate determined by electrochemical characterization. The in vitro cytotoxicity test using human vascular endothelial cells indicates excellent biocompatibility and potentially minimal toxic effect on arterial vessel walls. Finally, we fabricated a cardiovascular stent using JDBM and performed in vivo long-term assessment via implantation of this stent in an animal model. The results confirmed the reduced degradation rate in vivo, excellent tissue compatibility and long-term structural and mechanical durability. Thus, this new Mg-alloy with highly uniform nanophasic biodegradation represents a major breakthrough in the field and a promising material for manufacturing the next generation biodegradable vascular stents.

[In vivo experimental study on MAO-ZK60 magnesium alloy bio-safety and degradation]

OBJECTIVE

To investigate the tissue toxicity and degradation of ZK60 magnesium alloy with micro-arc oxidation coatings (MAO-ZK60), in order to discuss the possibility of its potential application for orthopedic implantation.

METHODS

Eighteen Sprague-Dawley rats were randomized equally to three groups of A, B, C. MAO-ZK60 sticks were implanted in the femoral condyles of rats in group A (experimental group). Sticks of ZK60 magnesium alloy without any surface treatment (ZK60) were implanted in the femoral condyles of rats in group B (control group). The poly L-lactic acid (PLLA) sticks were implanted in the femoral condyles of rats in group C (control group). The changes of blood bio-chemical indexes of different groups were observed and compared. All the rats were sacrificed at 12 weeks and histological observation of liver and kidney were carried out to evaluate the hepatic and renal toxicity. Micro-CT was used to evaluate the degradation of the implants and to observe the bone-implant interface. GEHC MicroView software was operated to calculate the volume variation of magnesium alloy.

RESULTS

There was no apparent biochemical index change with time in each group, and there was no significant change among each group. No significant pathology change of liver and kidney was detected among three groups. By using a micro-CT, a gap was found on the bone-implant interface at 4 weeks after implantation in group A, which decreased gradually at 8 weeks after implantation and continued to decrease at 12 weeks after implantation. A good combination between bone and implant formed at 12 weeks after implantation. Group A has less change of volume with time than group B (P < 0.05).

CONCLUSION

ZK60 magnesium alloy with micro-arc oxidation coatings is safe in vivo. It has higher corrosion resistance than ZK60 magnesium alloy without any surface treatment.

In vitro degradation of four magnesium-zinc-strontium alloys and their cytocompatibility with human embryonic stem cells

Magnesium alloys have attracted great interest for medical applications due to their unique biodegradable capability and desirable mechanical properties. When designed for medical applications, these alloys must have suitable degradation properties, i.e., their degradation rate should not exceed the rate at which the degradation products can be excreted from the body. Cellular responses and tissue integration around the Mg-based implants are critical for clinical success. Four magnesium-zinc-strontium (ZSr41) alloys were developed in this study. The degradation properties of the ZSr41 alloys and their cytocompatibility were studied using an in vitro human embryonic stem cell (hESC) model due to the greater sensitivity of hESCs to known toxicants which allows to potentially detect toxicological effects of new biomaterials at an early stage. Four distinct ZSr41 alloys with 4 wt% zinc and a series of strontium compositions (0.15, 0.5, 1, and 1.5 wt% Sr) were produced through metallurgical processing. Their degradation was characterized by measuring total mass loss of samples and pH change in the cell culture media. The concentration of Mg ions released from ZSr41 alloy into the cell culture media was analyzed using inductively coupled plasma atomic emission spectroscopy. Surface microstructure and composition before and after culturing with hESCs were characterized using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Pure Mg was used as a control during cell culture studies. Results indicated that the Mg-Zn-Sr alloy with 0.15 wt% Sr provided slower degradation and improved cytocompatibility as compared with pure Mg control.

[Progress of in vivo study on degradable magnesium alloys application as bone-implant materials]

OBJECTIVE

To review the progress of in vivo study on degradable magnesium alloys application as bone-implant materials.

METHODS

Recent literature was extensively reviewed and summarized, concerning the in vivo study on degradable magnesium alloys as orthopaedic implants.

RESULTS

Magnesium alloys possess a natural ability to degrade via corrosion in vivo, which is promising candidate material for orthopaedic medical device applications. A great progress has been made to improve in vivo performance and integration with bone tissue. However, the degradation mechanism of magnesium-based materials in the physiological environment and long-term effect on body are not available. The modulation of the corrosion rate of magnesium alloys must also be accomplished.

CONCLUSION

Magnesium alloys have the potential to serve as degradable implants for orthopaedic applications, but a great deal of further investigation is still necessary.

In vivo assessment of the host reactions to the biodegradation of the two novel magnesium alloys ZEK100 and AX30 in an animal model

BACKGROUND

Most studies on biodegradable magnesium implants published recently use magnesium-calcium-alloys or magnesium-aluminum-rare earth-alloys.However, since rare earths are a mixture of elements and their toxicity is unclear, a reduced content of rare earths is favorable. The present study assesses the in vivo biocompatibility of two new magnesium alloys which have a reduced content (ZEK100) or contain no rare earths at all (AX30).

METHODS

24 rabbits were randomized into 4 groups (AX30 or ZEK100, 3 or 6 months, respectively) and cylindrical pins were inserted in their tibiae. To assess the biodegradation μCT scans and histological examinations were performed.

RESULTS

The μCT scans showed that until month three ZEK100 degrades faster than AX30, but this difference is leveled out after 6 months. Histology revealed that both materials induce adverse host reactions and high numbers of osteoclasts in the recipient bone. The mineral apposition rates of both materials groups were high.

CONCLUSIONS

Both alloys display favorable degradation characteristics, but they induce adverse host reactions, namely an osteoclast-driven resorption of bone and a subsequent periosteal formation of new bone. Therefore, the biocompatibility of ZEK100 and AX30 is questionable and further studies, which should focus on the interactions on cellular level, are needed.

Calcium phosphate coatings on magnesium alloys for biomedical applications: a review

Magnesium has been suggested as a revolutionary biodegradable metal for use as an orthopaedic material. As a biocompatible and degradable metal, it has several advantages over the permanent metallic materials currently in use, including eliminating the effects of stress shielding, improving biocompatibility concerns in vivo and improving degradation properties, removing the requirement of a second surgery for implant removal. The rapid degradation of magnesium, however, is a double-edged sword as it is necessary to control the corrosion rates of the materials to match the rates of bone healing. In response, calcium phosphate coatings have been suggested as a means to control these corrosion rates. The potential calcium phosphate phases and their coating techniques on substrates are numerous and can provide several different properties for different applications. The reactivity and low melting point of magnesium, however, require specific parameters for calcium phosphate coatings to be successful. Within this review, an overview of the different calcium phosphate phases, their properties and their behaviour in vitro and in vivo has been provided, followed by the current coating techniques used for calcium phosphates that may be or may have been adapted for magnesium substrates.

Effects of thermal treatments on protein adsorption of Co-Cr-Mo ASTM-F75 alloys

Post-manufacturing thermal treatments are commonly employed in the production of hip replacements to reduce shrinkage voids which can occur in cast components. Several studies have investigated the consequences of these treatments upon the alloy microstructure and tribological properties but none have determined if there are any biological ramifications. In this study the adsorption of proteins from foetal bovine serum (FBS) on three Co-Cr-Mo ASTM-F75 alloy samples with different metallurgical histories, has been studied as a function of protein concentration. Adsorption isotherms have been plotted using the surface concentration of nitrogen as a diagnostic of protein uptake as measured by X-ray photoelectron spectroscopy. The data was a good fit to the Langmuir adsorption isotherm up to the concentration at which critical protein saturation occurred. Differences in protein adsorption on each alloy have been observed. This suggests that development of the tissue/implant interface, although similar, may differ between as-cast (AC) and heat treated samples.

In vivo biocompatibility and degradation behavior of Mg alloy coated by calcium phosphate in a rabbit model

This study is conducted to investigate the biocompatibility and biodegradation behavior of calcium phosphate-coated Mg alloy in vivo. Calcium phosphate (Ca-P) was coated on the Mg alloy (AZ31) by a chemical process. Samples of Ca-P coated rods, the naked alloy rods, and degradable polymer as controls were implanted into the thighbone of rabbits to investigate the bone response at the early stage. The reduction in implant volume was determined by micro-computed tomography and three-dimensional reconstruction of the remaining Mg alloy segmented from the bone matrix. It was observed that the biodegradation rate of naked Mg implant is faster than that of the coated ones. The bone-implant interface was characterized in sections by scanning electron microscopy with energy-dispersive spectroscopy. Biodegradation or reaction layer was formed on the surface of Mg alloy implants and direct contact with the surrounding bone. The layer was mainly composed of Ca, P, O, and Mg. After 8 weeks of post-operation, paraffin sections were generated for histomorphologic analysis; 100% implants were fixed and no inflammation was observed. Histological analysis showed that new bone tissue is formed around the Mg implants, and no fibrous capsule was found. Blood examination showed that the biodegradation of the Mg implant caused little change to blood composition. Ca-P coating on Mg alloy substrate might be an effective method to reduce the biodegradation rate of Mg alloy in vivo and improve the surface bioactivity of Mg alloy implants.

In vitro evaluation of human osteoblast adhesion to a thermally oxidized gamma-TiAl intermetallic alloy of composition Ti-48Al-2Cr-2Nb (at.%)

Ti-48Al-2Cr-2Nb (at.%) (gamma-TiAl), a gamma titanium aluminide alloy originally designed for aerospace applications, appears to have excellent potential as implant material. Thermal treatment of gamma-TiAl renders this alloy extremely corrosion resistant in vitro, which could improve its biocompatibility. In this study, the surface oxides produced by thermal oxidation (at 500 degrees C, and at 800 degrees C for 1 h in air) on gamma-TiAl were characterized by X-ray photoelectron spectroscopy (XPS). hFOB 1.19 cell adhesion on thermally oxidized gamma-TiAl was examined in vitro by a hexosaminidase assay, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) after 1, 7 and 14 days. Ti-6Al-4V surfaces were used for comparison. Hexosaminidase assay data and CLSM analysis of focal contacts and cytoskeleton organization showed no differences in cell attachment on autoclaved and both heat-treated gamma-TiAl surfaces at the different time points. SEM images showed well organized multi-layers of differentiated cells adhered on thermally oxidized gamma-TiAl surfaces at day 14. Unexpectedly, thermally oxidized Ti-6Al-4V surfaces oxidized at 800 degrees C exhibited cytotoxic effects on hFOB 1.19 cells. Our results indicate that thermal oxidation of gamma-TiAl seems to be a promising method to generate highly corrosion resistant and biocompatible surfaces for implant applications.

[Research on bioactivity of magnesium and its alloys]

Magnesium is an essential microelement which is not harmful to human body. As a light-weight metal with properties similar to natural bone, magnesium material possesses the characteristics of its degradability, little biotoxicity, as well as its regulatory strength and controllable degradation-speed. After the tissue has healed sufficiently, the burden of a second surgical procedure can be avoided. Therefore, there is need of investigation on the possible use of magnesium and its alloys as medical biomaterials, and the study of its bioactivity is the foundation of further application. This article reviews the bioactivity of magnesium and its alloys.

[Development of biodegradable magnesium-based biomaterials]

Magnesium is a macroelement which is indispensable to human bodies. As a lightweight metal with high specific strength and favorable biocompatibility, magnesium and its alloys have been introduced in the field of biomedical materials research and have a broad application prospect. It is possible to develop new type of biodegradable medical magnesium alloys by use of the poor corrosion resistance of magnesium. Bioabsorbable magnesium stents implanted in vivo could mechanically support the vessel in a short term, effectly prevent the acute coronary occlusion and in-stent restenosis, and then be gradully biodegraded and completely absorbed in a long term. Osteoconductive bioactivity in magnesium-based alloys could promote the apposition growth of bone tissue. This paper reviews the progress of magnesium and its alloys applied in bone tissue and cardiovascular stents, and the prospect of the future research of magnesium-based biomaterials is discussed.

Analysis of the effects of surface treatments on nickel release from nitinol wires and their impact on candidate gene expression in endothelial cells

Nitinol has many applications in the medical device industry, however the large amount of nickel, a known allergen and carcinogen remains a serious concern. Studies have already shown that nickel ions induce the differential expression of a range of genes, including cell adhesion molecules. This study sought to determine the level of nickel ions released from nitinol wires that had been surface treated by etching and mechanically polishing or etching and pickling compared to untreated wires and determine the biological impact of the wires on human umbilical vein endothelial cells (HUVECs) at the transcriptional level by real-time PCR. The four different wire types were incubated in media and the amount of nickel eluted after 24, 48 and 72 h was determined. HUVECs were then cultured and incubated with the four different wire types for 24 h. Cells were harvested, RNA isolated and real-time PCR was carried out to measure the expression levels of ICAM-1, VCAM-1 and E-selectin, three known inflammatory mediators, compared to control cells. E-selectin, a marker of endothelial cell injury and activation was found to be significantly up-regulated in cells incubated with wires that released the highest amount of nickel ions. Nickel ions are released from nitinol wires with certain surface characteristics and these ions have a biological effect on HUVECs in vitro.

Titanium particles that have undergone phagocytosis by macrophages lose the ability to activate other macrophages

Titanium particles derived from the wear of the orthopaedic implant surfaces can activate macrophages to secrete cytokines and stimulate osteoclastic bone resorption, causing osteolysis around orthopaedic implants. However, what happens to the titanium particles after being phagocytosed by macrophages is not known. We prepared titanium particles (as received, clean, and LPS-coated), and exposed them to macrophages in culture. Free particles were washed away after 24 h and the intracellular particles were kept in culture for additional 48 h until being harvested by lysing the cells. Particles that had been cell treated or noncell treated were examined by scanning electronic microscopy to analyze the shape, size, and concentration of the particles. The cell treated and noncell treated particles were exposed to macrophages in culture with a particle to cell ratio of 300:1. After 18 h, the levels of TNF-alpha in culture medium and the viability of the cells were examined. Clean particles did not stimulate TNF-alpha secretion by macrophages, while LPS-coated particles dramatically increased that response. Phagocytosis by macrophages did not change the shape and size of the particles, but depleted the ability of the particles to stimulate TNF-alpha secretion by macrophages. This indicates that macrophages are capable of rendering titanium particles inactive without degrading the particles, possibly by altering the surface chemistry of the particles.

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.

[Pharmacodynamics of China-made rapamycin-polylactide-co-glycolide peripheral arterial eluting stent membrane: in vitro experiment]

OBJECTIVE

To evaluate the property and drug releasing pattern of the China-made rapamycin-polylactide-co-glycolide (PLGA) peripheral arterial eluting stent membrane.

METHODS

Rapamycin was put into PLGA so as to made rapamycin-PLGA complex. Twelve nickel-titanium self-expanding stents were dipped into the complex to make drug-eluting stents. Somatotype microscope was used to observe the macro-form of the surface of the eluting membrane, and atom force microscope was used to analyzing the three-dimensional appearance and surface roughness of the membrane. The stents were put into fluid with platelets to observe the form of platelets blood compatibility by scanning electron microscopy. The extra degradation of the coating layer, by putting the stents into a simulation system of internal environment. High efficacy liquid chromatography was used to study the pharmacokinetics of the stents. Standard curve and stimulative curve, and drug release curve of multiple stents were drawn and analyzed.

RESULTS

The membranes of all 12 stents had smooth surfaces and regular thickness and no membrane falling-off was observed. The platelets on the surfaces of the stents were inactivated and the number of the platelets adhering to the surfaces of the stents were reduced obviously in comparison with the blank control. PLGA degraded by 20% within 2 weeks and then the degradation speed accelerated until complete degradation occurred within 6 weeks, and the drug releasing lasted more than 50 days. The percentage of accumulative drug release was 11.02% in 24 hours, 41.23% in 9 days, and 79.44% in 30 days.

CONCLUSION

Smooth and even, and capable of controlling the drug release, rapamycin-PLGA peripheral arterial eluting stent membrane coating has the potential clinical value in preventing in-stent stenosis.

Bone formation at the surface of low modulus Ti-7.5Mo implants in rabbit femur

The biocompatibility of the Ti-7.5Mo alloy was examined, because the alloy has a high-strength/modulus ratio and thus is a potential candidate for orthopedic applications. Cell viability assay using 3T3 cells revealed that the Ti-7.5Mo did not induce apparent cell death, when the cells were grown on disks made of the alloy or incubated with the alloy-conditioned medium at 37 or 72 degrees C for 24-72h. The Ti-6Al-4V alloy was used as a control and did not cause apparent cell death either. Moreover, pins of 6mm long and 2mm in diameter of Ti-7.5Mo and Ti-6Al-4V were implanted into the left and right rabbit femurs, respectively, for 6, 12 and 26 weeks. New bone tissue grew to surround the pins, which spanned cortical and marrow regions, as shown by toluidine blue-stained bone sections of the three time points. Strikingly, the amount of new bone encircling the Ti-7.5Mo implant was approximate two-folds of that at Ti-6Al-4V by 26 weeks post-implantation. This facilitation of bone formation could be associated with the unique properties, such as a low modulus and the composition of Mo, of the Ti-7.5Mo.

Study on hemocompatibility and corrosion behavior of ion implanted TiNi shape memory alloy and Co-based alloys

Biomedical TiNi shape memory alloy and Co-based alloys were ion implanted, and corrosion resistance and hemocompatibility of these had been investigated with electrochemical method, dynamic clotting time, and hemolysis rate tests. The results indicated that the electrochemical stability and anodic polarization behavior of the materials were improved significantly after ion implantation. When TiNi, Co-based alloys were implanted Mo + C and Ti + C, respectively, the corrosion potentials were enhanced more than 200 mV, passive current densities decreased, and passive ranges were broadened. Dynamic clotting time of the ion implanted substances was prolonged and hemolysis rate decreased. All the results pointed out that corrosion resistance and hemocompatibility of the alloys were improved by ion implantation, and effects of dual implantation was better than that of C single implantation. X-ray diffraction analysis of the alloys after dual implantation revealed that TiC, Mo(2)C, Mo(9)Ti(4), and Mo appeared on the surface of TiNi alloy, and CoC(x), Co(3)Ti, TiC, and TiO on the surface of Co-based alloys. These phases dispersing on the alloy surface formed amorphous film, prevented dissolving of alloy elements and improved the corrosion resistance and hemocompatibility of the alloys.

Gene expression by human monocytes from peripheral blood in response to exposure to metals

With increasing life expectancy and active lifestyles, the longevity of arthroplasties has become an important problem in orthopaedic surgery and will remain so until novel approaches to joint preservation have been developed. The sensitivity of the recipient to the metal alloys may be one of the factors limiting the lifespan of implants. In the present study, the response of human monocytes from peripheral blood to an exposure to metal ions was investigated, using the method of real-time polymerase chain reaction (PCR)-based low-density arrays. Upon stimulation with bivalent (Co2+ and Ni2+) and trivalent (Ti3+) cations and with the calcium antagonist LaCl3, the strength of the elicited monocytic response was in the order of Co2+ > or = Ni2+ > Ti3+ > or = LaCl3. The transcriptional regulation of the majority of genes affected by the exposure of monocytes to Co2+ and Ni2+ was similar. Some genes critically involved in the processes of inflammation and bone resorption, however, were found to be differentially regulated by these bivalent cations. The data demonstrate that monocytic gene expression is adapted in response to metal ions and that this response is, in part, specific for the individual metals. It is suggested that metal alloys used in arthroplasties may affect the extent of inflammation and bone resorption in the peri-implant tissues in dependence of their chemical composition.

Osteoblast adhesion and matrix mineralization on sol–gel-derived titanium oxide

The biological events occurring at the bone-implant interface are influenced by the topography, chemistry and wettability of the implant surface. The surface properties of titanium alloy prepared by either surface sol-gel processing (SSP), or by passivation with nitric acid, were investigated systematically using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and contact angle metrology. The bioreactivity of the substrates was assessed by evaluating MC3T3-E1 osteoblastic cell adhesion, as well as by in vitro formation of mineralized matrix. Surface analysis of sol-gel-derived oxide on Ti6Al4V substrates showed a predominantly titanium dioxide (TiO(2)) composition with abundant hydroxyl groups. The surface was highly wettable, rougher and more porous compared to that of the passivated substrate. Significantly more cells adhered to the sol-gel-coated surface, as compared with passivated surfaces, at 1 and 24h following cell seeding, and a markedly greater number of mineralized nodules were observed on sol-gel coatings. Collectively our results show that the surface properties of titanium alloy can be modified by SSP to enhance the bioreactivity of this biomaterial.

Magnesium and its alloys as orthopedic biomaterials: A review

As a lightweight metal with mechanical properties similar to natural bone, a natural ionic presence with significant functional roles in biological systems, and in vivo degradation via corrosion in the electrolytic environment of the body, magnesium-based implants have the potential to serve as biocompatible, osteoconductive, degradable implants for load-bearing applications. This review explores the properties, biological performance, challenges and future directions of magnesium-based biomaterials.

Influence of Nitinol wire surface treatment on oxide thickness and composition and its subsequent effect on corrosion resistance and nickel ion release

Medical implants and devices are now used successfully in surgical procedures on a daily basis. Alloys of nickel and titanium, and in particular Nitinol are of special interest in the medical device industry, because of their shape memory and superelastic properties. The corrosion behavior of nitinol in the body is also of critical importance because of the known toxicological effects of nickel. The stability of a NiTi alloy in the physiological environment is dependant primarily on the properties of the mostly TiO(2) oxide layer that is present on the surface. For the present study, a range of nitinol wires have been prepared using different drawing processes and a range of surface preparation procedures. It is clear from the results obtained that the wire samples with very thick oxides also contain a high nickel content in the oxide layer. The untreated samples with the thicker oxides show the lowest pitting potential values and greater nickel release in both long and short-term experiments. It was also found that after long-term immersion tests breakdown potentials increased for samples that exhibited lower values initially. From these results it would appear that surface treatment is essential for the optimum bioperformance of nitinol.

A Model System to Assess Key Vascular Responses to Biomaterials

PURPOSE

To establish a reproducible laboratory test to evaluate prospective vascular biomaterials with respect to their thromboinflammatory properties by examining fibrinogen, platelet, and monocyte binding. Endothelial migration onto these surfaces was used as an index of vascular healing.

METHODS

To evaluate biomaterials for potential thrombogenicity and inflammation, binding assays of radiolabeled human fibrinogen, platelets, and monocytes were performed on standard pieces of vascular biomaterials, including metals and polymeric and ceramic-coated materials. Using an established in vitro endothelial cell migration model, the relative migration rate of cultured human aortic endothelial cells onto these vascular biomaterials was measured and compared. The fibrinogen, platelet, and monocyte binding results were combined along with the migration results to create an overall score of biocompatibility.

RESULTS

A significant direct relation of platelet and monocyte binding to the amount of adsorbed fibrinogen was observed. In contrast, migration rates of cultured human aortic endothelial cells onto the same biomaterial surfaces were found to be inversely related the amount of bound fibrinogen. Among the materials tested, stainless steel received the highest score of biocompatibility, while turbostratic carbon scored the lowest.

CONCLUSIONS

Fibrinogen, platelet, and monocyte binding levels, as well as endothelial migration rates onto vascular material surfaces, provide a basis for evaluating thrombogenicity, inflammatory potential, and endothelialization in the laboratory prior to in vivo testing.

Gene expression clustering using self-organizing maps: analysis of the macrophage response to particulate biomaterials

The most common cause of total joint replacement failure is peri-implant bone loss causing pain and prosthesis loosening. This process, known as osteolysis or aseptic loosening, is characterized by macrophage phagocytosis of particulate implant wear debris. In an incompletely defined step, particulate biomaterial debris induces macrophages to release a variety of inflammatory mediators and signaling proteins that lead to bone loss. In an in vitro model of this process, we used microarray technology and data analysis techniques, including the use of self-organizing maps (SOMs), to understand the mRNA gene expression changes occurring in macrophages exposed to clinically relevant particles of ultra-high molecular weight polyethylene and TiAlV alloy. Earlier studies have been limited by technology that only allowed analysis of a few genes at a time, but the microarray techniques used in this paper generate the quantitative analysis of over a thousand genes simultaneously. Our microarray analysis utilized an SOM clustering to elucidate general patterns in the data, lists of top up- and down-regulated genes for each time point and genes with differential expression under different biomaterial exposures. The expression levels of the majority of genes (>95%) did not vary over time or with exposure to different biomaterials, but a few important genes, such as TNF-alpha, IL-1beta, IL-6, and MIP1alpha, proved to be highly regulated in response to biomaterial exposure. We also uncovered a novel set of genes, which not only validates and logically extends the current model of the pathogenesis of osteolysis and aseptic loosening, but also provides new targets for further research and therapeutics.

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.

Biocompatibility and strength properties of nitinol shape memory alloy suture in rabbit tendon

Nitinol (NiTi) is a promising new tendon suture material with good strength, easy handling and good super-elastic properties. NiTi sutures were implanted for biocompatibility testing into the right medial gastrocnemius tendon in 15 rabbits for 2, 6 and 12 weeks. Additional sutures were implanted in subcutaneous tissue for strength measurements in order to determine the effect of implantation on strength properties of NiTi suture material. Braided polyester sutures (Ethibond) of approximately the same diameter were used as control. Encapsulating membrane formation around the sutures was minimal in the case of both materials. The breaking load of NiTi was significantly greater compared to braided polyester. Implantation did not affect the strength properties of either material.

Corrosion behavior of nitinol wires in body fluid environments

In this study, breakdown potentials were measured for unpolished and mechanically polished nitinol wires in simulated body fluids. These wires are similar to those used in the manufacture of stents. Considerable scatter was observed in the results indicating a variable surface state. After appropriate heat treatments, the measured breakdown values were lower but more reproducible for the mechanically polished samples. Significantly higher breakdown potentials were observed for cross-section wire samples. Some wires were tested in human blood and the breakdown values were higher than in Ringer and 0.9% NaCl solutions. Energy dispersive X-ray analysis of the surface layers indicated that oxide thickening occurred after heat treatments. Dynamic secondary ion mass spectroscopy also revealed thickened surface oxides on the wires. The oxide was predominantly made up of TiO(2) with a very thin layer of NiO at the outer surface. Galvanic corrosion tests were performed on nitinol wires coupled with gold, elgiloy/phynox, and stainless steel. Nitinol was found to be anodic in all cases yet the currents measured were small. In tests in which nitinol-gold couples were immersed in 0.9% NaCl for periods up to 12 months, only very small amounts of nickel (in the part per billion range) were released into solution and scanning electron microscopy examination revealed no corrosion.

Characterization of implant materials in fetal bovine serum and sodium sulfate by electrochemical impedance spectroscopy. II. Coarsely sandblasted samples

Electrochemical impedance spectroscopy is used to investigate the corrosion resistance of coarsely sandblasted implant alloys, commercially pure titanium, Ti6Al4V, Ti6Al7Nb, and CoCrMo in 0.1M sodium sulfate and fetal bovine serum. Coarsely sandblasted samples have a heterogeneous surface constituted by a large number of protrusions and recessions. Impedance spectra collected in sodium sulfate present two time constants (maxima in the phase-angle of the bode plot) associated with the total surface and with the tips, respectively. In bovine serum, the two maxima in the impedance spectra cannot be distinguished because of the formation of an adsorption layer of organic molecules, which causes a decrease in the values of both the total and tips' capacitances as well as an increase in the polarization resistance. Ti6Al4V and Ti6Al7Nb show the highest corrosion rate both in serum and in sodium sulfate. Based on the capacitance values obtained in sodium sulfate, the real surface area of the coarsely sandblasted electrodes has been estimated relative to mechanically polished surfaces. The values of the effective electrode area correlate with the mechanical properties of the samples: in fact, the softest electrode (commercially pure titanium) shows the largest effective electrode area, whereas the hardest material (CoCrMo alloy) shows the smallest surface area.

Biocorrosion of magnesium alloys: a new principle in cardiovascular implant technology?

OBJECTIVES

To develop and test a new concept of the degradation kinetics of newly developed coronary stents consisting of magnesium alloys.

METHODS

Design of a coronary stent prototype consisting of the non-commercial magnesium based alloy AE21 (containing 2% aluminium and 1% rare earths) with an expected 50% loss of mass within six months. Eleven domestic pigs underwent coronary implantation of 20 stents (overstretch injury).

RESULTS

No stent caused major problems during implantation or showed signs of initial breakage in the histological evaluation. There were no thromboembolic events. Quantitative angiography at follow up showed a significant (p < 0.01) 40% loss of perfused lumen diameter between days 10 and 35, corresponding to neointima formation seen on histological analysis, and a 25% re-enlargement (p < 0.05) between days 35 and 56 caused by vascular remodelling (based on intravascular ultrasound) resulting from the loss of mechanical integrity of the stent. Inflammation (p < 0.001) and neointimal plaque area (p < 0.05) depended significantly on injury score. Planimetric degradation correlated with time (r = 0.67, p < 0.01).

CONCLUSION

Vascular implants consisting of magnesium alloy degradable by biocorrosion seem to be a realistic alternative to permanent implants.

Investigation of endotoxin adsorption with polyether polymer alloy dialysis membranes

Endotoxin (ET) in the dialysate is known to be adsorbed by dialysis membranes made of polyether polymer alloy (PEPA) and polymethylmethacrylate (PMMA). In the present study, the effect of polyvinylpyrrolidone (PVP) localization of the PEPA dialysis membrane on the adsorption of ET was investigated. The compounding of PVP in the PEPA membrane was changed, and hydrophobic membrane in both blood side and dialysate side, and hydrophilic membrane in only the blood side were used. Adsorption was evaluated by filling the contaminated dialysate inside and outside the membrane after priming with physiological saline, and determining the ET concentration in the blood side and dialysate side of dialysis membrane during the 240 min period from the start of filling the contaminated dialysate. With the PEPA membranes investigated, ET was significantly adsorbed to the hydrophobic side and was not adsorbed to the blood side of hydrophilic type membrane. These results suggest that in addition to electrostatic action attributable to the compounding of hydrophilic agent PVP to the dialysis membrane, the distribution of PVP that was compounded and the potential of the membrane itself may cause differences in adsorption of ET.

Accumulation of a black material around some titanium coupling posts

PURPOSE

To report 5 patients with a black material accumulating in the conjunctiva around the titanium peg and sleeve systems.

METHODS

Retrospective small case series. The clinical features of 5 patients were reviewed. Histopathologic analysis was performed on specimens from 3 patients. Neutron activation analysis was performed on 1 sample.

RESULTS

Five asymptomatic patients with black material accumulating in the conjunctiva at the conjunctival-titanium peg interface were evaluated. All patients had a hydroxyapatite-coated titanium sleeve with a titanium peg in position. Histopathologic analysis performed on specimens from 3 patients revealed a mixed inflammatory cell infiltrate with focal areas of a black, foreign-appearing material showing birefringence under polarized light that was predominantly intracytoplasmic. This black material did not respond to bleaching, and in 2 patients, it showed positive staining for iron (Perls method). The material from one patient was evaluated by neutron activation analysis and was found to contain titanium, aluminum, and vanadium. In 18 to 48 months of follow-up, the presence of the material did not appear to be associated with any problems.

CONCLUSIONS

The presence of a black substance accumulating in the conjunctiva around some titanium coupling posts is uncommon and appears to be without any consequence in 18 to 48 months of follow-up. Our analysis revealed this substance to be consistent with titanium alloy (Ti-6Al-4V).

Evaluation of the TiMo12Zr6Fe2 alloy for orthopaedic implants: in vitro biocompatibility study by using primary human fibroblasts and osteoblasts

To reveal the biocompatibility of TiMo12Zr6Fe2 (TMZF), a new titanium alloy used since 1998 for orthopaedic prosthesis, we compared the behavior of primary human fibroblasts and osteoblasts grown on TMZF discs or on plastic tissue culture dishes, a widely used material specifically treated by the manufacturer to enhance cell growth. Proliferation, differentiation. RNA and collagen type I expression level of human cells were carried out. The analysis were performed over a period of 96 h. Fibroblasts behaved at the same way on the two different supports after 48 h, their number increased after 96 h when cells were grown on the alloy. Osteoblasts adhered and proliferated on the alloy discs as well as on plastic. RNA expression level was not affected. Interestingly, cell number at each time point was higher for fibroblasts than for osteoblasts. The RNA expression level was higher for the osteoblasts. Both cell types cultured on the alloy revealed an increase in the amount of type I collagen and a similar electrophoretic pattern was found for collagen produced by fibroblasts and osteoblasts grown on either supports. These results indicate good biocompatibility of the TMZF alloy, which allowed adhesion and proliferation of both the examined cell types and suggest that TMZF is a promising material for orthopaedic implants.

Relating nickel-induced tissue inflammation to nickel release in vivo

Nickel has a number of adverse biological effects that have made the use of nickel in biomedical implants controversial. Yet information about the distribution of nickel in tissues around nickel-containing implants is scarce. The purpose of the current study was to use a laser ablation technique, combined with inductively coupled mass spectroscopy, to assess the spatial distribution of nickel around nickel-containing implants in vivo. Polyethylene, pure nickel wire, or a nickel-containing alloy (Ni-Cr) were implanted subcutaneously into rats for 7 days. The tissues were analyzed for Ni content and inflammation at 1-mm intervals up to 5 mm away from the implants. The sham surgery sites and the polyethylene caused mild to moderate inflammation 1-2 mm from the implant site with no detectable nickel in the tissue. The nickel wire caused severe inflammation up to 5 mm away from the implant site with necrosis for 1 mm around the implant. Nickel concentrations reached 48 microg/g near the implants, falling exponentially to undetectable levels at 3-4 mm from the implants. The Ni-Cr wire caused inflammation equivalent to polyethylene, with less than 4 microg/g of nickel present in the tissue for 1-2 mm around the implants. The current study showed that the laser-ablation technique was well suited for the analysis of soft tissues for metal-ion content, and that the nickel distribution in tissues correlated well with overt tissue inflammation.