In vivo biocompatibility evaluation of nickel-titanium shape memory metal alloy: muscle and perineural tissue responses and encapsule membrane thickness

Feasibility of a Shape-Memory-Alloy-Actuator System for Modular Acetabular Cups

Hip implants have a modular structure which enables patient-specific adaptation but also revision of worn or damaged friction partners without compromising the implant-bone connection. To reduce complications during the extraction of ceramic inlays, this work presents a new approach of a shape-memory-alloy-actuator which enables the loosening of ceramic inlays from acetabular hip cups without ceramic chipping or damaging the metal cup. This technical in vitro study exam-ines two principles of heating currents and hot water for thermal activation of the shape-memory-alloy-actuator to generate a force between the metal cup and the ceramic inlay. Mechanical tests concerning push-in and push-out forces, deformation of the acetabular cup according to international test standards, and force generated by the actuator were generated to prove the feasibility of this new approach to ceramic inlay revision. The required disassembly force for a modular acetabular device achieved an average value of 602 N after static and 713 N after cyclic loading. The actuator can provide a push-out force up to 1951 N. In addition, it is shown that the necessary modifications to the implant modules for the implementation of the shape-memory-actuator-system do not result in any change in the mechanical properties compared to conventional systems.

Nitinol: From historical milestones to functional properties and biomedical applications

Isoatomic NiTi alloy (Nitinol) has become an important biomaterial due to its unique characteristics, including shape memory effect, superelasticity, and high damping. Nitinol has been widely used in the biomedical field, including orthopedics, vascular stents, orthodontics, and other medical devices. However, there have been convicting views about the biocompatibility of Nitinol. Some studies have shown that Nitinol has extremely low cytotoxicity, indicating Nitinol has good biocompatibility. However, some studies have shown that the in-vivo corrosion resistance of Nitinol significantly decreases. This comprehensive paper discusses the historical developments of Nitinol, its biomedical applications, and its specific functional property. These render the suitability of Nitinol for such biomedical applications and provide insights into its in vivo and in vitro biocompatibility in the physiological environment and the antimicrobial strategies that can be applied to enhance its biocompatibility. Although 3D metal printing is still immature and Nitinol medical materials are difficult to be processed, Nitinol biomaterials have excellent potential and commercial value for 3D printing. However, there are still significant problems in the processing of Nitinol and improving its biocompatibility. With the deepening of research and continuous progress in surface modification and coating technology, a series of medical devices made from Nitinol are expected to be released soon.

Smart Compression Therapy Devices for Treatment of Venous Leg Ulcers: A Review

Venous leg ulcers can have significant social and economic impacts, and are generally treated by applying compression to the lower limb, which aids in promoting blood return to the heart. Compression therapies commonly involve the use of passive bandages that suffer from issues associated with incorrect application, and although automated solutions have begun to appear; these are often bulky and hinder mobility. Emerging microtechnologies and new materials enable the development of "smart" compression therapy devices, which are defined as systems that use miniaturized and lightweight actuators and electronics to control the applied pressure. This paper reviews the state of the art in smart compression therapy research. A total of seventeen different devices has been identified, categorized as using one of three actuation mechanisms: pneumatic compression, motor-driven mechanisms, and smart materials (including shape memory alloys, shape memory polymers, and electroactive polymers). The field is still in its relative infancy and further refinements are required to create mass manufacturable compression dressing systems that meet medical, ergonomic, and economic standards. The use of miniaturized actuators has immense potential for the development of smart compression dressings, which will ultimately lead to higher compliance, increased patient comfort, enhanced mobility, and better treatment outcomes.

The role of NiTi shape memory alloys in quality of life improvement through medical advancements: A comprehensive review

The significance of advanced smart materials in recent technological research and advancement is apparent from its extensive use in present day devices and instruments. Of the various smart materials in use today, the fascinating category of shape memory alloys (SMAs) is equipped with the ability to return to a previously memorized shape under certain thermomechanical or magnetic stimuli. The unique property of shape memory effect and superelasticity displayed by these materials along with good biocompatibility and corrosion resistance make them ideal for biomedical applications. The various applications of SMAs in surgical instruments, surgical implants, and assistive and rehabilitative devices have significant effect on the day to day life of people in the present age. Majority of these biomedical devices belong to the orthodontic, orthopedic, or surgical fields. Other remarkable applications of SMAs such as in the production of prostheses and orthoses designed through the biomimetic approach are also highly influential in improving the quality of life. The present paper provides an overview of the various properties of shape memory alloys and their applications in the biomedical field over the years, that have had a significant impact on the realm of medical science.

Biomedical NiTi and β-Ti Alloys: From Composition, Microstructure and Thermo-Mechanics to Application

A comprehensive, bottoms-up characterization of two of the most widely used biomedical Ti-containing alloys, NiTi and β-Ti, was carried out applying a novel combination of neutron diffraction, neutron prompt-gamma activation, surface morphology, thermal analysis and mechanical tests, to relate composition, microstructure and physical-chemical-mechanical properties to unknown processing history. The commercial specimens studied are rectangular (0.43 × 0.64 mm~0.017 × 0.025 inch) wires, in both pre-formed U-shape and straight extended form. Practical performance was quantitatively linked to the influence of alloying elements, microstructure and thermo-mechanical processing. Results demonstrated that the microstructure and phase composition of β-Ti strongly depended on the composition, phase-stabilizing elements in particular, in that the 10.2 wt.% Mo content in Azdent resulted in 41.2% α phase, while Ormco with 11.6 wt.% Mo contained only β phase. Although the existence of α phase is probable in the meta-stable alloy, the α phase has never been quantified before. Further, the phase transformation behavior of NiTi directly arose from the microstructure, whilst being highly influenced by thermo-mechanical history. A strong correlation (r = 0.878) was established between phase transformation temperature and the force levels observed in bending test at body temperature, reconfirming that structure determines performance, while also being highly influenced by thermo-mechanical history. The novel methodology described is evidenced as generating a predictive profile of the eventual biomechanical properties and practical performance of the commercial materials. Overall, the work encompasses a reproducible and comprehensive approach expected to aid in future optimization and rational design of devices of metallic origin.

A Rare Case of Orthograde Retrieval of Extruded Instrument following Periapical Tissue Healing

The ideal retrieval protocol of separated instruments reverts the case to the initial situation prior to the fracture incidence while preserving the tooth hard tissue and the integrity of the supporting structures. When a patient presented for emergency treatment of tooth #37 diagnosed with acute suppurative apical periodontitis, radiographic examination revealed a fractured instrument extruded into the periapex. The treatment options for retrieval were limited to replantation. The initial emergency treatment which consisted of orthograde pus drain, radicular disinfection, and intracanal calcium hydroxide dressing completely resolved patient's symptoms. The follow-up radiographs revealed an interesting finding: gradual shift in the separated fragment position into the radicular space allowing a successful nonsurgical removal of the broken instrument. In conclusion, the reaction of periodontal tissues to an extruded instrument fragment remaining in situ may be favourable; thus, a risk and benefit analysis approach is essential to fractured instrument retrieval.

Functionalization of screw implants with superelastic structured Nitinol anchoring elements

Background

Demographic change is leading to an increase in the number of osteoporotic patients, so a rethink is required in implantology in order to be able to guarantee adequate anchoring stability in the bone. The functional modification of conventional standard screw implants using superelastic, structured Ti6Al4V anchoring elements promises great potential for increasing anchoring stability.

Methods

For this purpose, conventional screw implants were mechanically machined and extended so that structured-superelastic-positionable-Ti6Al4V anchoring elements could be used. The novel implants were investigated with three tests. The setup of the anchoring elements was investigated in CT studies in an artificial bone. In a subsequent simplified handling test, the handling of the functional samples was evaluated under surgical conditions. The anchorage stability compared to standard screw implants was investigated in a final pullout test according to ASTM F543—the international for the standard specification and test methods for metallic medical bone screws.

Results

The functionalization of conventional screw implants with structured superelastic Ti6Al4V anchoring elements is technically realizable. It was demonstrated that the anchoring elements can be set up in the artificial bone without any problems. The anchorage mechanism is easy to handle under operating conditions. The first simplified handling test showed that at the current point of the investigations, the anchoring elements have no negative influence on the surgical procedure (especially under the focus of screw implantation). Compared to conventional standard screws, more mechanical work is required to remove the functional patterns completely from the bone.

Conclusion

In summary, it was shown that conventional standard screw implants can be functionalized with Ti6Al4V-structured NiTi anchoring elements and the new type of screws are suitable for orthopedic and neurosurgical use. A first biomechanical test showed that the anchoring stability could be increased by the anchoring elements.

Chronic nickel (II) exposure induces the stemness properties of cancer cells through repressing isocitrate dehydrogenase (IDH1)

BACKGROUND

Nickel is a component of biomedical alloys that is released during corrosion or friction and causes cytotoxicity, mutation, differentiation or even carcinogenesis in tissues. However, the mechanisms underlying the potential hazards of Nickel-containing alloys implanted in the human body by surgery remain uncertain.

OBJECTIVE

To study the effect of Ni(II) (NiCl_2•6H₂O) on cancer cells.

METHODS

A549 and RKO cells were treated with various concentrations of Ni(II) to determine the effect of Ni(II) on cellular viability using a CCK8 assay. Flow cytometry was performed to analyze the effect of Ni(II) on apoptosis and the cell cycle. Sphere-forming assays were conducted to examine the stemness properties of A549 and RKO cells. Western blotting was to evaluate the expression levels of SOX2, IDH1, HIF-1ɑ and β-catenin. The expression of isocitrate dehydrogenase (IDH1) in rectum adenocarcinoma (READ) was analyzed by Gene Expression Profiling Interactive Analysis (GEPIA). Kaplan-Meier analysis was used to calculate the correlation between survival and IDH1 expression.

RESULTS

Long-term exposure (120 days) to 100 µM Ni(II) significantly repressed cell proliferation, decreased colony formation and arrested the cell cycle at the G₀/G₁ phase. In addition, the stem-like traits of A549 and RKO cells were significantly augmented. Ni(II) also significantly decreased the protein expression of IDH1 and the synthesis rate of NAPDH, which competitively inhibited α-ketoglutarate (α-KG) generation. The downregulation of IDH1 not only promoted β-catenin accumulation in the cell nucleus in a HIF-1ɑ signaling-dependent manner but also induced the expression of the transcription factor SOX2 to maintain the stemness properties of cancer cells. Moreover, IDH1 expression negatively correlated with the clinicopathologic characteristics of READ.

CONCLUSION

These findings demonstrate that chronic and continuous release of Ni(II) to the microenvironment suppresses IDH1 expression and augments the stemness properties of cancer cells via the activation HIF-1ɑ/β-catenin/SOX2 pathway to enhance local tumor recurrence in patients with implanted Nickel-containing alloys at surgical sites.

Key Properties of a Bioactive Ag-SiO2/TiO2 Coating on NiTi Shape Memory Alloy as Necessary at the Development of a New Class of Biomedical Materials

Recent years have seen the dynamic development of methods for functionalizing the surface of implants using biomaterials that can mimic the physical and mechanical nature of native tissue, prevent the formation of bacterial biofilm, promote osteoconduction, and have the ability to sustain cell proliferation. One of the concepts for achieving this goal, which is presented in this work, is to functionalize the surface of NiTi shape memory alloy by an atypical glass-like nanocomposite that consists of SiO2-TiO2 with silver nanoparticles. However, determining the potential medical uses of bio(nano)coating prepared in this way requires an analysis of its surface roughness, tribology, or wettability, especially in the context of the commonly used reference coat-forming hydroxyapatite (HAp). According to our results, the surface roughness ranged between (112 ± 3) nm (Ag-SiO2)-(141 ± 5) nm (HAp), the water contact angle was in the range (74.8 ± 1.6)° (Ag-SiO2)-(70.6 ± 1.2)° (HAp), while the surface free energy was in the range of 45.4 mJ/m2 (Ag-SiO2)-46.8 mJ/m2 (HAp). The adhesive force and friction coefficient were determined to be 1.04 (Ag-SiO2)-1.14 (HAp) and 0.247 ± 0.012 (Ag-SiO2) and 0.397 ± 0.034 (HAp), respectively. The chemical data showed that the release of the metal, mainly Ni from the covered NiTi substrate or Ag from Ag-SiO2 coating had a negligible effect. It was revealed that the NiTi alloy that was coated with Ag-SiO2 did not favor the formation of E. coli or S. aureus biofilm compared to the HAp-coated alloy. Moreover, both approaches to surface functionalization indicated good viability of the normal human dermal fibroblast and osteoblast cells and confirmed the high osteoconductive features of the biomaterial. The similarities of both types of coat-forming materials indicate an excellent potential of the silver-silica composite as a new material for the functionalization of the surface of a biomaterial and the development of a new type of functionalized implants.

Biocompatibility and Biological Corrosion Resistance of Ti-39Nb-6Zr+0.45Al Implant Alloy

Titanium and titanium alloys are promising implant metallic materials because of their high strengths, low elastic moduli, high corrosion resistances, and excellent biocompatibilities. A large difference in elastic modulus between the implant material and bone leads to a stress shielding effect, which increases the probability of implant separation or decrease in the bone density around it. Thus, a lower elastic modulus is required for a better implant metallic material. β titanium has a lower elastic modulus and high strength and can reduce the probability of the stress shielding effect. In this study, the applicability of the Ti–39Nb–6Zr+0.45Al alloy, obtained by adding a small amount of aluminum to the Ti–39Nb–6Zr alloy, as a biomedical implant material was evaluated. The mechanical properties and biocompatibility of the alloy were evaluated. The biocompatibility of Ti–39Nb–6Zr+0.45Al was similar to that of Ti–39Nb–6Zr according to in vitro and in vivo experiments. In addition, the biological corrosion resistances were evaluated through a corrosion test using a 0.9% NaCl solution, which is equivalent to physiological saline. The corrosion resistance was improved by the addition of Al. The yield strength of the Ti–39Nb–6Zr+0.45Al alloy was improved by approximately 20%. The excellent biocompatibility confirmed its feasibility for use as a biomedical implant material.

Biological Cell Investigation of Structured Nitinol Surfaces for the Functionalization of Implants

Expandable implants including shape memory alloy (SMA) elements have great potential to minimize the risk of implant loosening and to increase the primary stability of bone anchoring. Surface structuring of such elements may further improve these properties and support osteointegration and bone healing. In this given study, SMA sheets were processed by deploying additive and removal manufacturing technologies for 3D-printed surgical implants. The additive technology was realized by applying a new laser beam melting technology to print titanium structures on the SMA sheets. The removal step was realized as a standard process with an ultrashort-pulse laser. The morphology, metabolic activity, and mineralization patterns of human bone marrow stromal cells were examined to evaluate the biocompatibility of the new surface structures. It was shown that both surface structures support cell adhesion and the formation of a cytoskeleton. The examination of the metabolic activity of the marrow stromal cells on the samples showed that the number of cells on the laser-structured samples was lower when compared to the 3D-printed ones. The calcium phosphate accumulation, which was used to examine the mineralization of marrow stromal cells, was higher in the laser-structured samples than in the 3D-printed ones. These results indicate that the additive- and laser-structured SAM sheets seem biocompatible and that the macrostructure surface and manufacturing technology may have positive influences on the behavior of the bone formation. The use of the new additive technique and the resulting macrostructures seems to be a promising approach to combine increased anchorage stability with simultaneously enhanced osteointegration.

Corrosion resistance of a Nitinol ocular microstent: Implications on biocompatibility

Nitinol is commonly used in medical implants due to its unique thermomechanical properties of shape memory and superelasticity. Free nickel has the potential to induce biological responses that may be a concern for permanent implants manufactured from nickel-containing alloys. Although there are extensive reports on the effects of surface treatments on corrosion behavior in cardiovascular Nitinol implants, there is a lack of data on corrosion resistance and impact on biocompatibility for ocular implants. Therefore, the objective of this study was to determine localized corrosion and nickel elution resistance of an electropolished Nitinol-based ocular device (Hydrus Microstent, Ivantis, Inc.) intended for patients with primary open angle glaucoma. Pitting corrosion susceptibility was characterized by potentiodynamic polarization testing per ASTM F2129. In addition, nickel ion release was quantified with immersion testing to 63 days. The results indicated high localized corrosion resistance as all samples reached polarization potentials of 800 mV without pitting initiation. Maximum nickel elution rates per device were less than approximately 1.1 ng/device/day after the first day of immersion and reduced to less than 0.1 ng/device/day after 7 days. For a patient with bilateral microstents, these nickel concentrations are ×10,000 lower than previously published tolerable intake levels for systemic toxicity. Overall, these corrosion results are in good agreement with literature values of well processed and biocompatible Nitinol devices indicating adverse systemic biological responses are not expected in vivo.

Surface Analysis of Wire-Electrical-Discharge-Machining-Processed Shape-Memory Alloys

Shape-memory alloys such as nitinol are gaining popularity as advanced materials in the aerospace, medical, and automobile sectors. However, nitinol is a difficult-to-cut material because of its versatile specific properties such as the shape-memory effect, superelasticity, high specific strength, high wear and corrosion resistance, and severe strain hardening. Anunconventional machining process like wire-electrical-discharge-machining (WEDM) can be effectively and efficiently used for the machining of such alloys, although the WEDM-induced surface integrity of nitinol hassignificant impact on material performance. Therefore, this work investigated the surface integrity of WEDM-processed nitinol samples using digital microscopy imaging, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. Three-dimensional analysis of the surfaces was carried out in two different patterns (along the periphery and the vertical plane of the machined surface) andrevealed that surface roughness was maximalat the point where the surface was largely exposed to the WEDM dielectric fluid. To attain the desired surface roughness, appropriate discharge energy is required that, in turn, requires the appropriate parameter settings of the WEDM process. Different SEM image analyses showed a reduction in microcracks and pores, and in globule-density size at optimized parameters. EDX analysis revealed the absence of wire material on the machined surface

Nitinol actuated soft structures towards transnasal drug delivery: a pilot cadaver study

Sudden hearing loss can be treated noninvasively by administering drugs to the middle ear (≈1 ml) via the eustachian tube. The nasopharyngeal cavity requires high dexterity manipulation as it is restricted by the nasal vestibule, and precise drug delivery through the small cavity can allow previously unreachable areas to be reconsidered for localized delivery. Nitinol has shape memory capabilities and can be used for distal actuation accessed from small lumen and a tortuous path. The drug delivery device (DDD) is a soft and needle-sized (2 mm) and comprises of Nitinol, ribbon spring, and a drug delivery tube. By controlling the input voltage to the Nitinol, bending of the device at different angles could be achieved, and the ribbon spring works antagonistically to the Nitinol to revert to the initial position once deactivated. The actuation of the device and its corresponding bending are calculated in vitro and found to have a bending angle ranging between 36.2 and 66.8° for applied voltages of 1.2-2.0 V, with surface temperature of 45.6-154 °C. The DDD is able to actuate 200 cycles with ≈91-76% retention of bending performance, with a temperature increase of ≈8.5-9% when 1.2-2.0 V is applied. Addition of soft insulating material shows ≈34-62% reduction in the surface temperature in the first cycle and ≈37-59% over 200 cycles when actuated at 1.2-2.0 V. The active steering and navigation capabilities of the DDD are demonstrated in simulated environments (based on the eustachian tube dimensions of adult and infant). Preclinical testing in human cadavers is demonstrated and suggests the developed DDD controlled by varying the input voltages for bending, and mechanically varied drug delivery may be a feasible option for localized drug delivery in eustachian tube. Graphical abstract.

Biocompatibility and Clinical Application of Porous TiNi Alloys Made by Self-Propagating High-Temperature Synthesis (SHS)

Porous TiNi alloys fabricated by self-propagating high-temperature synthesis (SHS) are biomaterials designed for medical application in substituting tissue lesions and they were clinically deployed more than 30 years ago. The SHS process, as a very fast and economically justified route of powder metallurgy, has distinctive features which impart special attributes to the resultant implant, facilitating its integration in terms of bio-mechanical/chemical compatibility. On the phenomenological level, the fact of high biocompatibility of porous SHS TiNi (PTN) material in vivo has been recognized and is not in dispute presently, but the rationale is somewhat disputable. The features of the SHS TiNi process led to a multifarious intermetallic Ti4Ni2(O,N,C)-based constituents in the amorphous-nanocrystalline superficial layer which entirely conceals the matrix and enhances the corrosion resistance of the unwrought alloy. In the current article, we briefly explore issues of the high biocompatibility level on which additional studies could be carried out, as well as recent progress and key fields of clinical application, yet allowing innovative solutions.

Potential mechanisms of endothelialisation in individuals implanted with a leadless pacemaker systems: An experimental in vitro study

BACKGROUND

Leadless pacemaker technology is a promising upcoming field in clinical rhythmology. Today, the most commonly used system in the clinical setting is the Micra™ leadless pacemaker system (Medtronic). In autopsies of patients who witnessed non-pacemaker associated death, unexpected ingrowth/encapsulation within the wall of the right ventricle was reported. The occurrence of a complete encapsulation was not expected and the process of endothelialisation remains unclear. We hypothesized, that a local inflammatory response might be the cause of these findings. The aim of our experimental in-vitro study was to investigate the effect of the Micra™ system and its single components on inflammatory processes.

METHODS

For this purpose, whole Micra™ pacemakers were incubated in heparin plasma from 25 healthy volunteers for 48 h at 37 °C. Furthermore, 1 g gold, steel, titanium, tungsten and nitinol wires were incubated in heparin plasma for 48 h at 37 °C as well (n = 10). To detect eventual inflammatory processes, interleukin- (IL) 1β, IL-6, and tumor necrosis factor alpha (TNF-α), the chemokine IL-8 were measured using enzyme-linked immunosorbent assay (ELISA). Additionally, the level of transforming growth factor beta 1 (TGF-β1) and vascular endothelial growth factor (VEGF) were analysed.

RESULTS

ELISA analyses showed that the whole Micra system leads to a significant increase in the inflammatory cytokine IL-6 which correlates with the data gained by the incubation of whole blood with the different wires. In particular, 0.5 g of tungsten showed a significant rise of IL-6 which could also be found for IL-1β and IL-8.

CONCLUSIONS

The in vitro study of the Micra system showed that the material composition led to an onset of inflammatory processes in whole blood. Consequently, one may speculate that the composition of Micra pacemaker may have a local inflammatory, though subclinical, effects in patients implanted with a Micra™ pacemakers.

New Nano-Film Single-Rivet Patent Ductus Arteriosus Occluders: A Prospective, Randomized and Double-blind Study

Nitinol alloy occluders are widely used in the transcatheter intervention treatment of congenital heart diseases like patent ductus arteriosus (PDA). However, nitinol alloy contains high levels of nickel, which can lead to toxic effects in the immune and hematopoietic systems if released in sufficient quantities. A new type of single-rivet occluder coated with nano-film has been developed to limit the release of nickel. In total, 23 patients were recruited and randomly assigned to the experimental group (n=12) with the new nano-film single-rivet occluders or the control group (n=11) with the traditional occluders. One case in the control group was lost to follow-up. The remaining 22 cases were followed up at 24 h, 7 days, 1 month, 3 months, and 6 months after the procedure. There were no statistically significant differences in routine blood test, alanine aminotransferase, creatinine, and troponin between the experimental and control groups. Serum nickel concentration in both two groups increased at 24 h after the procedure, peaked at 1 month, and returned to preoperative levels at 6 months. Serum nickel levels in the experimental group were significantly lower than in the control group at 24 h, 7 days, 1 month, and 3 months after the procedure. These data suggested that the nano-film coating effectively prevented nickel release from the new occluders, and therefore has a preferable safety profile.

Magnetic implants in the tongue for assistive technologies: Tests of migration; oromotor function; and tissue response in miniature pigs

OBJECTIVE

Uncertain biological consequences of titanium-magnet (Ti-mag) tongue implants constrain application of the Tongue Drive System (TDS), a brain-tongue-computer interface for individuals with severe physical impairment. Here we describe oromotor function and tongue tissue response following Ti-Mag implantation and explantation in the miniature pig, an animal model with a tongue similar in size to humans.

DESIGN

A 1.8×6.2mm Ti-mag tracer was implanted into the anterior tongue in five Yucatan minipigs. X-rays were taken immediately and >six days after implantation to evaluate tracer migration. In three minipigs, the tracer was explanted >16days after implantation. Twenty-five days post-explantation, tongue tissue was harvested and processed for histological and immunohistochemical (IHC) markers of healing. In two minipigs tissue markers of healing were evaluated post-mortem following >12days implantation. Drink cycle rate (DCR) was characterized to determine the impact of procedures on oromotor function.

RESULTS

Neither implantation (N=5) nor explantation (N=3) changed DCR. X-rays revealed minimal tracer migration (N=4, 0-4mm). By histology and IHC a robust capsule was present two weeks post-implantation with limited fibrosis. Explantation produced localized fibrosis and limited muscle remodeling.

CONCLUSIONS

These findings suggest the safety of Ti-mag anterior tongue implants for assistive technologies in humans.

Tongue implant for assistive technologies: Test of migration, tissue reactivity and impact on tongue function

OBJECTIVE

The Tongue Drive System (TDS) is a new wearable assistive technology (AT), developed to translate voluntary tongue movements to user-defined computer commands by tracking the position of a titanium-encased magnetic tracer (Ti-Mag) implanted into the tongue. TDS application, however, is constrained by limited information on biological consequence and safety of device implantation into the tongue body. Here we implant a stainless-steel pellet in the rat tongue and assay pellet migration, tongue lick function, and tongue histology to test the safety and biocompatibility of unanchored tongue implants.

DESIGN

Water consumption, weight and lick behavior were measured before and for >24days after implantation of a stainless-steel spherical pellet (0.5mm) into the anterior tongue body of twelve adult male rats. X-rays were obtained weekly to assess pellet migration. Pellet location and tissue reaction to implantation were determined by post-mortem dissection and histology of the anterior tongue.

RESULTS

By dissection pellets were distributed across the transverse plane of the tongue. Measures of water consumption, weight, and lick behavior were unchanged by implantation except for a decrease in consumption immediately post-implantation in some animals. By X-ray, there was no migration of the implant, a finding supported by pellet encapsulation demonstrated histologically. Measures of lick behavior were minimally impacted by implantation.

CONCLUSION

A smooth spherical stainless-steel implant in the anterior tongue of the rat does not migrate, is encapsulated and does not substantially impact lick behavior. These findings support the implantation of small tracers in the anterior tongue in humans for operating wearable assistive technologies.

Biocompatibility and Biostability of Metallic Endovascular Implants: State of the Art and Perspectives

This work was partly supported by the Natural Science and Engineering Research Council (NSERC) of Canada.

More than a million metallic endovascular devices are implanted each year, but the quest for the perfect material continues. The importance of interfacial properties in the overall biocompatibility of metals and alloys has been recognized for a long time. In particular, these properties modulate the hemocompatibility of devices in contact with blood and, in turn, strongly influence implantation outcomes. In this article, the relative properties of metallic materials commonly used in endovascular applications are reviewed. Particular emphasis is given to the corrosion behavior of metallic endovascular materials and the specific surface treatments used in the production processes. Issues relative to corrosion assays will also be reviewed in terms of their relevance to in vivo applications. The potential adverse effects of degradation products with respect to endovascular applications will be described. Finally, this review addresses future perspectives of metallic devices in endovascular procedures in view of the recent promises of antiproliferative strategies that are likely to profoundly modify current procedures.

Surface amorphization of NiTi alloy induced by Ultrasonic Nanocrystal Surface Modification for improved mechanical properties

We report herein the effects of Ultrasonic Nano-crystal Surface Modification (UNSM), a severe surface plastic deformation process, on the microstructure, mechanical (hardness, wear), wettability and biocompatibility properties of NiTi shape memory alloy. Complete surface amorphization of NiTi was achieved by this process, which was confirmed by X-ray diffraction and high-resolution transmission electron microscopy. The wear resistance of the samples after UNSM processing was significantly improved compared with the non-processed samples due to increased surface hardness of the alloy by this process. In addition, cell culture study demonstrated that the biocompatibility of the samples after UNSM processing has not been compromised compared to the non-processed sample. The combination of high wear resistance and good biocompatibility makes UNSM an appealing process for treating alloy-based biomedical devices.

In Vitro and In Vivo Response to Low-Modulus PMMA-Based Bone Cement

The high stiffness of acrylic bone cements has been hypothesized to contribute to the increased number of fractures encountered after vertebroplasty, which has led to the development of low-modulus cements. However, there is no data available on the in vivo biocompatibility of any low-modulus cement. In this study, the in vitro cytotoxicity and in vivo biocompatibility of two types of low-modulus acrylic cements, one modified with castor oil and one with linoleic acid, were evaluated using human osteoblast-like cells and a rodent model, respectively. While the in vitro cytotoxicity appeared somewhat affected by the castor oil and linoleic acid additions, no difference could be found in the in vivo response to these cements in comparison to the base, commercially available cement, in terms of histology and flow cytometry analysis of the presence of immune cells. Furthermore, the in vivo radiopacity of the cements appeared unaltered. While these results are promising, the mechanical behavior of these cements in vivo remains to be investigated.

A Novel Shape Memory Plate Osteosynthesis for Noninvasive Modulation of Fixation Stiffness in a Rabbit Tibia Osteotomy Model

Nickel-titanium shape memory alloy (NiTi-SMA) implants might allow modulating fracture healing, changing their stiffness through alteration of both elastic modulus and cross-sectional shape by employing the shape memory effect (SME). Hypotheses: a novel NiTi-SMA plate stabilizes tibia osteotomies in rabbits. After noninvasive electromagnetic induction heating the alloy exhibits the SME and the plate changes towards higher stiffness (inverse dynamization) resulting in increased fixation stiffness and equal or better bony healing. In 14 rabbits, 1.0 mm tibia osteotomies were fixed with our experimental plate. Animals were randomised for control or induction heating at three weeks postoperatively. Repetitive X-ray imaging and in vivo measurements of bending stiffness were performed. After sacrifice at 8 weeks, macroscopic evaluation, µCT, and post mortem bending tests of the tibiae were carried out. One death and one early implant dislocation occurred. Following electromagnetic induction heating, radiographic and macroscopic changes of the implant proved successful SME activation. All osteotomies healed. In the treatment group, bending stiffness increased over time. Differences between groups were not significant. In conclusion, we demonstrated successful healing of rabbit tibia osteotomies using our novel NiTi-SMA plate. We demonstrated shape-changing SME in-vivo through transcutaneous electromagnetic induction heating. Thus, future orthopaedic implants could be modified without additional surgery.

Transcutaneous electromagnetic induction heating of an intramedullary nickel-titanium shape memory implant

PURPOSE

Inadequate mechanical stimuli are a major cause for nonunions following surgery for femoral and tibial shaft fractures. Adapting fixation rigidity during the course of fracture healing requires additional surgery. Nickel-titanium (NiTi) implants can change shape and rigidity by employing a temperature-dependent shape-memory effect. As a first step in the development of advanced intramedullary (IM) NiTi devices for fracture healing, this study aimed to test the feasibility and safety of transcutaneous electromagnetic induction heating of an IM NiTi implant in a rat model.

METHODS

In 51 rats, NiTi implants were introduced into the left distal femur. Forty-four animals were transferred to an induction coil, and the implant was electromagnetically heated to temperatures between 40° and 60 °C Blood samples were drawn before and four hours after the procedure. Interleukin (IL)-1, IL-4, IL-10, tumour necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) were measured. Animals were sacrificed at three weeks. Histological specimens from the hind leg and liver were retrieved and examined for inflammatory changes, necrosis or corrosion pits.

RESULTS

All animals successfully underwent the surgical procedure. Following transcutaneous induction heating, target temperature was confirmed in 37/44 rats. Postoperative controls showed no signs of undue limitations. Neither cytokine measurements nor histological specimens showed any significant differences between groups. There were no corrosion pits or necrosis.

CONCLUSION

We conclude that electromagnetic induction heating of IM NiTi implants is feasible and safe in a rat femur model. These findings reflect a further step in the development of novel concepts for IM fracture fixation that might lead to better fracture healing, less patient discomfort and less need for surgical interventions.

Histological characteristics of induced membranes in subcutaneous, intramuscular sites and bone defect

BACKGROUND

The induced membrane technique was proposed as a treatment of large segmental bone defects. The influence of the surrounding tissues on its characteristics remains unknown. It is therefore not known which kind of plastic surgery procedure (muscular or facio-cutaneous flap) would optimize bone osteointegration within a bone defect reconstructed using the induced-membrane technique.

HYPOTHESIS

We hypothesized that membrane characteristics could be influenced by the soft-tissue environment either subcutaneous or muscular.

OBJECTIVE

To evaluate the histological characteristics of poly-methylmethacrylate (PMMA) induced membranes in intramuscular, subcutaneous and bony environment (radius defects) at 2 steps: spacer implantation; secondary bone graft and its subsequent osteintegration after spacer removal.

METHODS

PMMA-induced membranes were obtained in the three sites of 15 rabbits. Subsequent new bone formation was studied in the same environments in 24 other rabbits. Six weeks after the initial implantation, PMMA spacers were replaced with iliac autografts. Animals were euthanized at 2, 4, and 8 weeks postoperatively. Tissue samples were harvested and stained with hematoxylin and eosin. The histological characteristics of the membrane (thickness and microvessel density) and the newly-formed bone (cortical thickness) were quantitatively analyzed.

RESULTS

The membranes in the subcutaneous sites developed quicker, were thicker and had the lowest microvessel density (P<0.01). The membranes in the intramuscular sites developed later and were thinner (P<0.01). The membranes in the osseous defects had the greatest microvessel density (P<0.01). After bone grafting, induced membranes became thinner and their microvessel density decreased substantially, but maintained better in osseous site. The newly-formed bone that developed in the radius defects, had the thickest cortices (P<0.01).

CONCLUSIONS

The evolution of membranes induced in the intramuscular and subcutaneous environments was close to that of the bone defect model, although bone formation appeared weaker.

Rods in spinal surgery: a review of the literature

BACKGROUND CONTEXT

Spinal instrumentation has been used for more than five decades. Since the introduction of the Harrington rod in 1962, new rod materials and concepts have been developed. Rigid rod fixation has achieved higher fusion rates than previous methods. Recently, semirigid rod fixation devices have been used for both dynamic stabilization and fusion fixation. Memory rods, which have an interesting ability to return to their pre-bent shape when the temperature increases, are expected to be used for scoliosis correction.

PURPOSE

To review the previous literature regarding biofunctionality and biocompatibility of rods in spinal surgery.

CONCLUSION

The properties of each type of rod need to be taken into consideration when performing spinal instrumentation surgery.

A shape memory stent of poly(ε-caprolactone-co-DL-lactide) copolymer for potential treatment of esophageal stenosis

Biodegradable polymer stent with shape memory effect is expected to be developed in the treatment of esophageal stenosis, most likely due to traditional stents having such shortages as considerable rigidity and nondegradation. A tubular stent with the inner and outer diameters of 28 and 30 mm was manufactured from biodegradable poly(ε-caprolactone-co-DL-lactide) (PCLA) copolymer consisting of ε-caprolactone and DL-lactide at a weight ratio of 10/90. A series of tests were accomplished to investigate its properties including shape memory effects (SMEs), compression property and influence of in vitro degradation of polymer matrix on its shape recovery and dilation force. Significantly, an implantation of the stent into a dog model was performed to evaluate its function for the treatment of esophageal stenosis. The deformed stent needs about 36 s to recover its initial shape in vitro in 37°C warm water. The primary animal experiment in vivo has revealed that the implanted deformed stent could be triggered by body temperature and expectedly returned to a nearly-round shape to support esophageal wall. Therefore, the biodegradable intelligent polymer stent may be great potential to displace the conventional metallic stents for the esophageal stenosis therapy.

Nanometer-thin TiO₂ enhances skeletal muscle cell phenotype and behavior

Background

The independent role of the surface chemistry of titanium in determining its biological properties is yet to be determined. Although titanium implants are often in contact with muscle tissue, the interaction of muscle cells with titanium is largely unknown. This study tested the hypotheses that the surface chemistry of clinically established microroughened titanium surfaces could be controllably varied by coating with a minimally thin layer of TiO₂ (ideally pico-to-nanometer in thickness) without altering the existing topographical and roughness features, and that the change in superficial chemistry of titanium is effective in improving the biological properties of titanium.

Methods and results

Acid-etched microroughened titanium surfaces were coated with TiO₂ using slow-rate sputter deposition of molten TiO₂ nanoparticles. A TiO₂ coating of 300 pm to 6.3 nm increased the surface oxygen on the titanium substrates in a controllable manner, but did not alter the existing microscale architecture and roughness of the substrates. Cells derived from rat skeletal muscles showed increased attachment, spread, adhesion strength, proliferation, gene expression, and collagen production at the initial and early stage of culture on 6.3 nm thick TiO₂-coated microroughened titanium surfaces compared with uncoated titanium surfaces.

Conclusion

Using an exemplary slow-rate sputter deposition technique of molten TiO₂ nanoparticles, this study demonstrated that titanium substrates, even with microscale roughness, can be sufficiently chemically modified to enhance their biological properties without altering the existing microscale morphology. The controllable and exclusive chemical modification technique presented in this study may open a new avenue for surface modifications of titanium-based biomaterials for better cell and tissue affinity and reaction.

Introduction of antibacterial function into biomedical TiNi shape memory alloy by the addition of element Ag

A new kind of biomedical shape memory TiNiAg alloy with antibacterial function was successfully developed in the present study by the introduction of pure Ag precipitates into the TiNi matrix phase. The microstructure, mechanical property, corrosion resistance, ion release behavior in simulated body fluid, cytotoxicity and antibacterial properties were systematically investigated. The typical microstructural feature of TiNiAg alloy at room temperature was tiny pure Ag particles (at submicrometer or micrometer scales with irregular shape) randomly distributed in the TiNi matrix phase. The presence of Ag precipitates was found to result in a slightly higher tensile strength and larger elongation of TiNiAg alloy in comparison with that of TiNi binary alloy. Furthermore, a maximum shape recovery strain of ∼6.4% was obtained with a total prestrain of 7% in the TiNiAg alloy. In electrochemical and immersion tests, TiNiAg alloy presented good corrosion resistance in simulated body fluid, comparable with that of CP Ti and TiNi alloy. The cytotoxicity evaluation revealed that TiNiAg alloy extract induced slight toxicity to cells, but the viability of experimental cells was similar to or higher than that of TiNi alloy extract. In vitro bacterial adhesion study indicated a significantly reduced number of bacteria (S. aureus, S. epidermidis and P. gingivalis) on the TiNiAg alloy plate surface when compared with that on TiNi alloy plate surface, and the corresponding antibacterial mechanism for the TiNiAg alloy is discussed.

Experimental study of the Spider™ patent foramen ovale occluder

AIM

To evaluate the feasibility, safety and efficacy of the Spider™ patent foramen ovale (PFO) occluder for the treatment of PFOs in an animal model.

METHOD

The foramen ovale was punctured to establish an animal model of a PFO. Under fluoroscopic guidance, the PFO was occluded with the Spider PFO occluder. The piglets were electively sacrificed at months 1, 2, 3, 6 and 12 after occlusion for macroscopic and microscopic examination.

RESULTS

PFOs were successfully created and occluded percutaneously in 20 piglets. All piglets recovered from the procedure in good condition and completed follow-up. Macroscopic examination of all hearts showed complete closure of the PFO. The position of each device was correct. All devices were completely covered and embedded in pale and smooth tissue. There was no evidence of interference with adjacent structures of the heart or valves. The occluder was partially covered by endocardium after 1 month, almost completely covered by fresh endocardium after 3 months, and embedded within thick fibrous tissues and fresh vessels after 6 months. The tissue covering both occluder discs demonstrated some infiltration of inflammatory cells, including patches of lymphocyte aggregation. This inflammatory cell reaction diminished with increasing distance from the device. Furthermore, the number of inflammatory cells decreased gradually during follow-up and eventually, at 6-month follow-up, the inflammatory response was no longer visible. The 12-month histological findings did not differ from the 6-month findings.

CONCLUSION

Transcatheter closure of PFO with the Spider PFO occluder is effective and safe in an animal model. These results support further investigation of this device in animals and, if the results are confirmed, in human clinical trials.

Reconstruction of tracheal wall defect with a mesh patch of nickel-titanium shape-memory alloy

OBJECTIVES

We explored the feasibility of reconstructing tracheal wall defects with a mesh patch fashioned from a nickel-titanium shape-memory alloy.

METHODS

A tracheal wall defect was first constructed surgically by resecting the anterior half of the tracheal wall between the second and sixth tracheal rings. The defect was reconstructed in 8 experimental animals by replacing the resected tracheal mucosa and tracheal cartilage with a pedicle skin flap, which was then enclosed in the mesh patch. In 4 control animals, only a pedicle skin flap with strap muscles was used in the reconstruction procedure. The performance of the animals was observed after surgery. At the end of the experiments, the reconstructed segment was harvested for anatomic evaluation.

RESULTS

In the experimental group, 1 animal died 5 days after the operation. Endoscopic and anatomic examination of the 7 animals that survived the observation period showed that the reconstructed trachea was stable, with sufficient airway space for breathing. All 4 control animals died after the operation. After observing successful completion of this operation in animals, we successfully used this method to repair a tracheal wall defect in a human victim of a traffic accident.

CONCLUSIONS

Tracheal defects can be successfully reconstructed by use of a mesh patch of nickel-titanium shape-memory alloy as an extraluminal stent--a method that avoids complications associated with intraluminal stents.

Hydrophilic modification of neural microelectrode arrays based on multi-walled carbon nanotubes

To decrease the impedance of microelectrode arrays, for neuroscience applications we have fabricated and tested MEA based on multi-walled carbon nanotubes. With decreasing physical size of a microelectrode, its impedance increases and charge-transfer capability decreases. To decrease the impedance, the effective surface area of the electrode must generally be increased. We explored the effect of plasma treatment on the surface wettability of MWCNT. With a steam-plasma treatment the surface of MWCNT becomes converted from superhydrophobic to superhydrophilic; this hydrophilic property is attributed to -OH bonding on the surface of MWCNT. We reported the synthesis at 400 °C of MWCNT on nickel-titanium multilayered metal catalysts by thermal chemical vapor deposition. Applying plasma with a power less than 25 W for 10 s improved the electrochemical and biological properties, and circumvented the limitation of the surface reverting to a hydrophobic condition; a hydrophilic state is maintained for at least one month. The MEA was used to record neural signals of a lateral giant cell from an American crayfish. The response amplitude of the action potential was about 275 µV with 1 ms period; the recorded data had a ratio of signal to noise up to 40.12 dB. The improved performance of the electrode makes feasible the separation of neural signals and the recognition of their distinct shapes. With further development the rapid treatment will be useful for long-term recording applications.

Electromagnetic induction heating of an orthopaedic nickel--titanium shape memory device

Shape memory orthopaedic implants made from nickel-titanium (NiTi) might allow the modulation of fracture healing, changing their cross-sectional shape by employing the shape memory effect. We aimed to show the feasibility and safety of contact-free electromagnetic induction heating of NiTi implants in a rat model. A water-cooled generator-oscillator combination was used. Induction characteristics were determined by measuring the temperature increase of a test sample in correlation to generator power and time. In 53 rats, NiTi implants were introduced into the right hind leg. The animals were transferred to the inductor, and the implant was electromagnetically heated to temperatures between 40 and 60°C. Blood samples were drawn before and 4 h after the procedure. IL-1, IL-4, IL-10, TNF-α, and IFN-γ were measured. Animals were euthanized at 3 weeks. Histological specimens from the hind leg and liver were retrieved and examined for inflammatory changes, necrosis, and corrosion pits. Cytokine measurements and histological specimens showed no significant differences among the groups. We concluded that electromagnetic induction heating of orthopedic NiTi implants is feasible and safe in a rat model. This is the first step in the development of new orthopedic implants in which stiffness or rigidity can be modified after implantation to optimize bone-healing.

Fiber-optic nonlinear endomicroscopy with focus scanning by using shape memory alloy actuation

A miniature fiber optic endomicroscope with built-in dynamic focus scanning capability is developed for the first time for 3-D two-photon fluorescence (TPF) imaging of biological samples. Fast 2-D lateral beam scanning is realized by resonantly vibrating a double-clad fiber cantilever with a tubular piezoactuator. Slow axial scanning is achieved by moving the distal end of the imaging probe with an extremely compact electrically driven shape memory alloy (SMA). The 10-mm-long SMA allows 150-μm contractions with a driving voltage varying only from 50 to 100 mV. The response of the SMA contraction with the applied voltage is nonlinear, but repeatable and can be accurately calibrated. Depth-resolved imaging of acriflavine-stained biological tissues and unstained white paper with the endomicroscope is performed, and the results demonstrate the feasibility of 3-D nonlinear optical imaging with the SMA-based scanning fiber-optic endomicroscope.

An in vitro and in vivo investigation of the biological behavior of a ferrimagnetic cement for highly focalized thermotherapy

The cancer treatment by local hyperthermia, using a high frequency electromagnetic field is an extensively studied subject. For this propose it was developed a ferrimagnetic cement (FC) to be injected directly into the tumor. In this study it was determined the FC injectability, its capability to generate heat when placed within a magnetic field and its interaction with a modified simulated body fluid using SEM/EDS and XRD. The FC biological response was assessed by the intramuscular implantation in rats and histological analysis of the surrounding tissues. The results suggest that FC can be injected directly into the tumor, its temperature can be increased when exposed to a magnetic field and the surface of the immersed samples quickly becomes coated with precipitate denoting its ionic change with the surrounding medium. The histological analysis revealed a transient local inflammatory reaction, similar to the control material, only slightly more abundant during the first weeks, with a gradual decrease over the implantation time. Based on these results, we concluded that FC might be useful for highly focalized thermotherapy, with a good potential for clinical use.

Silicon carbide coating of nitinol stents to increase antithrombogenic properties and reduce nickel release

BACKGROUND

The use of stents in the superficial femoral artery is still limited by the number of restenoses. Influencing factors include thrombus formation and smooth muscle cell proliferation as well as motion stress. A reduction of thrombogenicity can be achieved by passive coating with silicon carbide, which induces less thrombus formation due to its semiconducting properties.

METHODS AND MATERIALS

Self-expanding peripheral stents with and without silicon carbide coating were examined in a chandler loop model. Assessed parameters included thrombocyte count, beta-thromboglobulin (TG), thrombin-antithrombin (TAT) III complex, and polymorphonuclear elastase. Nickel release was quantified at Days 1, 3, and 223 using graphite furnace atomic absorption spectrometry. To visualize thrombus formation on the surface, scanning electron microscopy was conducted.

RESULTS

The tests showed a superiority of the coated stents regarding beta-TG (484.0+/-180.2 IU/l vs 2189.1+/-898.9 IU/l) as well as formation of TAT III complex (16.0+/-19.1 microg/l vs 458.3+/-761.0 microg/l). Scanning electron microscopy revealed a nearly absent thrombus formation on the coating. Nickel release was reduced by more than 90% at all time points.

CONCLUSIONS

In the provided in vitro setting, silicon carbide coating applied to self-expanding peripheral stents showed an advantage regarding thrombogenicity. The passive barrier resulted in a limited release of nickel from the alloy itself. These features seem promising for the use in the peripheral vasculature.

Porous NiTi for bone implants: a review

NiTi foams are unique among biocompatible porous metals because of their high recovery strain (due to the shape-memory or superelastic effects) and their low stiffness facilitating integration with bone structures. To optimize NiTi foams for bone implant applications, two key areas are under active study: synthesis of foams with optimal architectures, microstructure and mechanical properties; and tailoring of biological interactions through modifications of pore surfaces. This article reviews recent research on NiTi foams for bone replacement, focusing on three specific topics: (i) surface modifications designed to create bio-inert porous NiTi surfaces with low Ni release and corrosion, as well as bioactive surfaces to enhance and accelerate biological activity; (ii) in vitro and in vivo biocompatibility studies to confirm the long-term safety of porous NiTi implants; and (iii) biological evaluations for specific applications, such as in intervertebral fusion devices and bone tissue scaffolds. Possible future directions for bio-performance and processing studies are discussed that could lead to optimized porous NiTi implants.

Estimation of the strength of adhesion between a thermoresponsive polymer coating and nitinol wire

As polymer coatings become more widely used in the biomedical device industry, both to improve biocompatibility and as coatings for localised drug delivery, quantitative methods to measure the adhesive strength between coatings and substrates become a very important consideration. The aim of this study was to take a method for estimating the interfacial fracture toughness of a film to a flat substrate and apply it to Nitinol wires used in the production of medical devices. An investigation into the affect of surface roughness on the fracture toughness was also conducted. For the present study, a thermoresponsive based Poly (N-isopropylacrylamide) polymer was coated onto nitinol wire substrates and the adhesion strength between the polymer and wire was measured using a nanoindentation technique. Different surface treated nitinol wires, with different surface topography and roughness were used, and the affect of these surface properties on adhesion strength was investigated. Results showed that it was possible to apply the delamination technique to wire samples and obtain fracture toughness values. Results also showed that the surface roughness is an important parameter that can affect the adhesion between a coating and the substrate. It was found that, as the average surface roughness increased so also did the adhesive strength between the coating and wire sample.

In vivo and in vitro response to electrochemically anodized Ti-6Al-4V alloy

Tissues' reactions to metals depend on a variety of properties of the metal, most notably surface structure. Anodizing has been shown to alter the surface properties of metal, thus eliciting a change in the biocompatibility of the metal. In order to evaluate the biocompatibility of unoxidized titanium alloy (Ti-6Al-4V) and anodized titanium alloy samples, the samples were implanted in murine abdominal subcutaneous tissues, and maintained for 2 and 4 weeks. The reaction of the abdominal subcutaneous connective tissues to the samples was then assessed. Fibrous connective tissue capsules were observed around the vicinity of the sample, and these capsules were shown to harbor fibroblasts, fibrocytes, and other cells, including neutrophils, macrophages, and giant multinucleated cells. The average thickness of the fibrous capsules observed around the anodized alloy samples was less than that of the capsules seen around samples of the unoxidized titanium alloy. Blood was obtained from the tails of the experimental mice, and blood cell analyses were conducted in order to assess the levels of leukocytes, red blood cells, and thrombocytes. The blood analysis results of the unoxidized control group and treatment group were all within normal ranges. In addition, the biocompatibility of the titanium alloy samples was evaluated using cell culture techniques. The numbers of MG-63 cells cultured on oxidized samples tended to be greater than those in the controls; however, these increases were not statistically significant. The alkaline phosphatase activity of the sample oxidized at 310 V evidenced significantly higher activity than was observed in the control group. These results indicate that the anodized Ti-6Al-4V alloy will be of considerable utility in biomedical applications.

Covalent functionalization of NiTi surfaces with bioactive peptide amphiphile nanofibers

Surface modification enables the creation of bioactive implants using traditional material substrates without altering the mechanical properties of the bulk material. For applications such as bone plates and stents, it is desirable to modify the surface of metal alloy substrates to facilitate cellular attachment, proliferation, and possibly differentiation. In this work we present a general strategy for altering the surface chemistry of nickel-titanium (NiTi) shape memory alloy in order to covalently attach self-assembled peptide amphiphile (PA) nanofibers with bioactive functions. Bioactivity in the systems studied here includes biological adhesion and proliferation of osteoblast and endothelial cell types. The optimized surface treatment creates a uniform TiO(2) layer with low levels of Ni on the NiTi surface, which is subsequently covered with an aminopropylsilane coating using a novel, lower temperature vapor deposition method. This method produces an aminated surface suitable for covalent attachment of PA molecules containing terminal carboxylic acid groups. The functionalized NiTi surfaces have been characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and atomic force microscopy (AFM). These techniques offer evidence that the treated metal surfaces consist primarily of TiO(2) with very little Ni, and also confirm the presence of the aminopropylsilane overlayer. Self-assembled PA nanofibers presenting the biological peptide adhesion sequence Arg-Gly-Asp-Ser are capable of covalently anchoring to the treated substrate, as demonstrated by spectrofluorimetry and AFM techniques. Cell culture and scanning electron microscopy (SEM) demonstrate cellular adhesion, spreading, and proliferation on these functionalized metal surfaces. Furthermore, these experiments demonstrate that covalent attachment is crucial for creating robust PA nanofiber coatings, leading to confluent cell monolayers.