Nitric oxide delivery by core/shell superparamagnetic nanoparticle vehicles with enhanced biocompatibility.

We report the synthesis of Fe(3)O(4)/silica core/shell nanoparticles and their functionalization with S-nitrosothiols. These nanoparticles are of immense interest because of their nitric oxide (NO) release capabilities in human alveolar epithelial cells. Moreover, they act as large storage reservoirs of NO that can be targeted magnetically to the specific site with a sustainable release of NO for up to 50 h. Such nanoparticles provide an enhancement of the biocompatibility with released NO while allowing intracellular accumulation ascribed to their small size.

Reduced stress shielding with limited micromotions using a carbon fibre composite biomimetic hip stem: a finite element model.

Total hip arthroplasty (THA) enjoys excellent rates of success in older patients, but younger patients are still at risk of aseptic loosening and bone resorption from stress shielding. One solution to the stress shielding problem is to use a hip stem with mechanical properties matching those of cortical bone. The objective of the present study was to investigate numerically the biomechanical performance of such a biomimetic hip stem based on a hydroxyapatite (HA)-coated carbon fibre composite. A finite element model (FEM) of the biomimetic stem was constructed. Contact elements were studied to model the bone-implant interface in a non-osseointegrated and osseointegrated state in the best way. Three static load cases representing slow walking, stair climbing, and gait in a healthy individual were considered. Stress shielding and bone-implant interface micromotions were evaluated and compared with the results of a similar FEM based on titanium alloy (Ti-6Al-4V). The composite stems allowed for reduced stress shielding when compared with a traditional Ti-6Al-4V stem. Micromotions were slightly higher with the composite stem, but remained below 40 microm on most of the HA-coated surface. It is concluded that a biomimetic composite stem might offer a better compromise between stress shielding and micromotions than the Ti-6Al-4V stem with the same external geometry.

The effect of varying Al2O3 percentage in hydroxyapatite/Al2O3 composite materials: morphological, chemical and cytotoxic evaluation.

Hydroxyapatite (HA) and HA-alumina (HA/Al2O3) composites, with Al2O3 contents of 5, 10, 20, and 30%, were synthesized using a wet precipitation method and sintered at 900 and 1300 degrees C. We investigated the effect of sintering temperature and relative concentration of HA and Al2O3 on the chemical composition, surface morphology, and cytotoxicity of the composite powders. The XRD results show that in the 1300 degrees C composites, HA partially decomposed into CaO which combined with Al2O3 to form different calcium aluminates. For the 900 degrees C composites the CaO phase was not detected, though a Ca/P ratio larger than 1.67 measured by XPS suggests that CaO was present in trace amounts. SEM-EDX analysis indicated that the HA microstructure was affected by the sintering temperature, and this HA is present on the surface of Al2O3 particles. The cytotoxicity of the composites was assessed indirectly using the MTT assay. The short-term effect of leachables was quantified by exposing a L929 mouse fibroblast cell line to the degradation products released by the composites after immersion in the cell culture medium. Degradation products were less toxic to L-929 at lower extract concentrations (10, 50%) than at 100% concentration. Cell viability was also influenced by leachable size.

Accelerated fatigue behavior and mechano-physical characterizations of in vitro physiological simulation of nitinol stents.

In this study, we have provided an experimental evaluation of the fatigue behavior of the nitinol (NiTi) endovascular device (peripheral stent). The accelerated fatigue tests were performed using arterial conditions, which mimicked actual physiological conditions. Natural, rubber latex-tubing materials were used to simulate human arteries. The equipment design and the test parameters used allowed for the simulation of a compliant artery and the application of circumferential forces to the device.The stent compliance values were good indicators for tracking the time evolution of fatigue behavior. Moreover, the analyses of changes on the surface morphology and on the chemical composition were used to establish a relationship between surface characteristics and peripheral stent response during 400 million cycles, which is equivalent to 10 yrs of human life. In order to determine the influence of the accelerated fatigue, an evaluation of both mechanical and surface characteristics was carried out before and after testing using the following tests and methods, respectively: radial hoop testing (RH), scanning electron microscope analysis (SEM), auger electron spectroscopy (AES), atomic absorption spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS). Under these experimental conditions, the studies have shown that after 400 million cycles, the tested stents did not demonstrate any mechanical failure. Moreover, the surface did not undergo any changes in its chemical composition. However, we did observe an increase in roughness and signs of pitting corrosion.

Bioperformance of shape memory alloy single crystals.

Shape memory alloys (SMA) represent a large family of alloys that show unique characteristics. They have been exploited in several fields for diverse applications. For the last 20 years, these alloys and more particularly Ni-Ti alloys have revolutionized the field of metallic biomaterials. Applications in the biomedical area are multiple and these materials improve significantly the quality of the diagnostics, treatments and surgeries. To our knowledge, most devices are made of SMAs in the polycrystalline form. Nevertheless, the single crystal form shows several promising advantages especially concerning its mechanical performances. In this paper we describe the advantages, advances and limits of using different SMA single crystals for biomedical applications, including biocompatibility and corrosion resistance. We also discuss the low response time of classical thermal SMAs as well as the new advances in research on magnetic SMA single crystals.

Surface characterization of Streptococcus mutans biofilms grown on polyethylene and beta-titanium.

In this study, we considered the biofilms as a surface, characterizing them using instruments for surface analyses, environmental microscopy, IR-spectroscopy (ATR-mode) and goniometry of the contact angle. The bacteria that formed the biofilms were grown on two different supports: beta-titanium alloy (beta-Ti) and polyethylene (PE). Environmental microscopy allowed the observation of biofilms in situ and in their hydrated state. On the metallic support, the biofilm quickly adhered and formed a dense structure with micro-colonies, but on the PE a thinner biofilm layer was observed covering a large surface area of the support. IR-spectroscopy is another effective method to detect the biofilm quickly and in situ, without pre-treating the sur-face. Nevertheless, problems with the overlapping of the characteristic bands on the spectra are frequent between the biofilm and PE. Finally, we compared the surface energy (SE) of the supports before and after biofilm formation. Our results indicate that the SE of the supports depends on the sterilization method, and that the SE of the biofilms varies depending on the support and the sterilization method. The biofilm on the beta-Ti had the highest SE, and as mentioned above, microscopic images showed a higher roughness on its surface.

Bioactive hydroxyapatite coatings on polymer composites for orthopedic implants.

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] coatings on polymer composite substrates were investigated for their bioactivity and their physicochemical and mechanical characteristics. HA holds key characteristics for use in orthopedic applications, such as for coating of the femoral stem in a hip replacement device. The plasma-spray technique was used to project HA onto a carbon fiber/polyamide 12 composite substrate. The resulting HA coatings exhibited mechanical adhesion as high as 23 MPa, depending on the surface treatment of the composite substrate. The purpose of this investigation was to evaluate the bioactivity of an HA-coated composite substrate. HA- coated samples have been immersed in simulated body fluid (SBF) and maintained within a shaker bath for periods of 1, 7, 14, 21, and 28 days at 37 degrees C. Scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were performed on the samples before and after immersion into SBF. SBF was analyzed using inductively coupled plasma atomic emission spectrometry for element concentration and evaluation of the solution's purity. SBF conditioning led to the deposition of crystalline HA onto the surface of the coatings. The calcium-to-phosphorous ratios of initial HA coating and of newly deposited HA were respectively 1.72 and 1.65, close to the HA theoretical calcium/phosphorous value of 1.67. Results demonstrated that bioactive HA coatings were produced by plasma spraying, because SBF conditioning induced newly formed HA with high crystallinity. Mechanical adhesion of the HA coatings was not significantly affected upon SBF conditioning.

Protein Corona Formation on Magnetite Nanoparticles: Effects of Culture Medium Composition, and Its Consequences on Superparamagnetic Nanoparticle Cytotoxicity.

The physicochemical properties and potential cytotoxicity of nanoparticles (NPs) are significantly influenced by their inter- action with proteins, which results in corona formation. Here, we have determined whether corona formation, resulting from interactions between superparamagnetic iron oxide nanoparticles (SPIONs) and different cell culture media, may have consequences for driving NP toxic effects. To address this issue, complementary methods were used. The deter- mination of the hydrodynamic size distribution by ζ (zeta) potential measurement indicated that SPIONs were negatively charged under all conditions but that the actual charge was differed with the cell culture medium used. In vitro protein adsorption studies were carried out using the Bradford protein assay and Fourier transform infrared spectroscopy (FTIR). The Bradford assay revealed that the concentration of unadsorbed proteins and other biomolecules decreased when the SPION concentration increased. FTIR showed that the proteins were, indeed, adsorbed onto the NP surface. This was followed by matrix-assisted laser desorption/ionization time-of-flight secondary ion mass spectrometry (MALDI TOF-SIMS), to identify the adsorbed proteins. Ultimately, three different cell viability assays led to the conclusion that the SPIONs were not toxic for all the concentrations used here. In summary, we found that corona formation on the SPIONs depends on the composition of the culture media but has no consequence for nanotoxicity. We have shown that the application of complementary methods has provided novel insights into SPION/protein interactions.

Microscopical investigation of canine anterior cruciate ligament and patellar tendon: collagen fascicle morphology and architecture.

The collagen structure of the canine anterior cruciate ligament (ACL) and patellar tendon (PT) was examined by using light and scanning electron microscopy. The collagen waviness known as a crimping was found to occur in ACL and PT fascicles. This waviness, seen at the periphery of fascicles, is very smooth, and its amplitude seems to decrease from the periphery toward the fascicular center. It appears as a periodic collapse of the fascicle in two dimensions. Two models of the architectural patterns of the ACL and PT wavy fascicles are presented. The constituent collagen fibrils are either parallel or twisted relative to the fascicle axis, giving rise to planar and helical wave patterns, respectively. There is a distinct difference between the ACL and PT collagen structure. The helical wave pattern occurs in both PT and ACL while the planar waveform is found only in the centrally located ACL fascicles. In addition, there is less variability in fascicular size and density over the PT cross-section than in ACL.

Innervation of spinal ligaments of patients with disc herniation. An immunohistochemical study.

The purpose of this work was to demonstrate whether neural elements are present in the spinal ligaments removed from patients with disc herniation. The tissue samples were stained by an immunohistochemical technique using antibodies to neurofilament protein (NFP) subunits as specific markers. Numerous NFP-immunoreactive nerve fibers and free nerve endings were demonstrated within the ligamentous structures. These findings were discussed relative to the low-back pain of disc herniated patients.

Ultrastructure of the human interspinous ligament and ligamentum flavum. A preliminary study.

The ultrastructure of ligamenta flava (LF) and interspinous ligaments (ISL) obtained from four patients who underwent surgery for vertebral fracture (control group) and five patients operated for disc herniation was studied. The fine structure of LF was composed of elastic and elaunin fibers. Small diameter collagen fibrils were found between the elastic system fibers. The ISL was constituted predominantly of collagen fibrils. Elastic fibers were seen in the most ventral part of the ligament. In ISL and LF of the control group, the cells were fibroblastic-like cells. Chondrocytes were present only near their attachment sites. The proteoglycans were demonstrated between the collagen fibrils, and they appeared to form a regular interfibrillar linking. In ligaments obtained from patients with disc herniation, several modifications were found. The fibroblasts transformed into chondrocytic cells, which were surrounded by a pericellular matrix rich in proteoglycan filaments. A few cells that had suffered necrosis were found. Alterations in the collagen-proteoglycans arrangement also were evidenced. The proteoglycan filaments were randomly oriented to the collagen fibrils.

Immunohistochemical study of nerves in lumbar spine ligaments.

An indirect horseradish peroxidase immunohistochemical technique was used to identify neurofilaments protein-immunoreactive fibers in lumbar spine ligaments, from patients who underwent spinal surgery for disc herniation. Histologically, neural elements were abundant in all ligaments examined. In the ligamentum flavum the neurofilaments protein-immunoreactive nerve fibers were located especially close to blood vessels and fat globules. Bundles of nerve fibers were seen in all ligaments specimens except those from the ligamentum flavum. Supraspinous ligament and lumbodorsal fascia show also individual axons and free nerve endings. Contrary to the gold chloride impregnation method, immunohistochemical staining revealed no recognizable sensory corpuscles in these ligaments. This can be explained by the lack of immunoreaction of both the capsule of sensory corpuscles and the perineural sheaths of nerve fibers.

Low-temperature sterilization using gas plasmas: a review of the experiments and an analysis of the inactivation mechanisms.

Utilizing an ionized gas (plasma) to achieve sterilization is an alternative to conventional sterilization means as far as sterilization of heat-sensitive materials and innocuity of sterilizing agents are concerned. The literature on plasma sterilization is reviewed. A major issue of plasma sterilization is the respective roles of UV photons and reactive species such as atomic and radicals. Insight into this matter is obtained by analyzing the survival curves of microorganisms. In contrast to classical sterilization where such plots show a unique straight line, plasma sterilization yields survival diagrams with two or three different linear segments. Three basic mechanisms are involved in the plasma inactivation of microorganisms: (A) direct destruction by UV irradiation of the genetic material of microorganisms; (B) erosion of the microorganisms atom by atom, through intrinsic photodesorption by UV irradiation to form volatile compounds combining atoms intrinsic to the microorganisms; (C) erosion of the microorganisms, atom by atom, through etching to form volatile compounds as a result of slow combustion using oxygen atoms or radicals emanating from the plasma. In some cases, etching is further activated by UV photons, increasing the elimination rate of microorganisms. These mechanisms make plasma sterilization totally different from classical sterilization techniques and suggest its use to inactivate nonconventional infectious agents such as the abnormal prions.

Structure on the capsular ligaments of the facet joints.

Microscopic studies showed that the capsular ligaments were mostly composed of collagenous tissue. The collagen fiber bundles were found to be crimped at right angles to their long axis. The collagen fibrils were connected transversely by proteoglycan filaments which were regularly associated with their periodicity. Among the collagen fiber bundles were varying quantities of elastic fibers and numerous fibroblasts. The highest concentration of elastic fibers was found in the posterior and inferior aspects of the capsular ligaments. These findings are discussed in relation to the mechanical behavior of the capsular ligaments.

Comparison of two methods for reconstruction of the posterior cruciate ligament using a computer based method: quantitative evaluation of laxity, three-dimensional kinematics and ligament deformation measurement in cadaver knees.

The aim of this paper is to present a biomechanical comparison of two different methods for reconstruction of the posterior cruciate ligament in cadaver knees. We used an original computer-based method allowing precise calculation of three-dimensional (3D) knee kinematic parameters as well as the estimation of combined graft deformation (elongation-flexion-torsion). After isolated posterior cruciate ligament (PCL) dissection, double bundle and 'over-the-bottom' methods were performed successively on each knee using synthetic polyester ligaments. The effect of pre-tensioning was tested with the 'over-the-bottom' method. antero-posterior (A-P) and rotational laxity as well as 3D kinematics were recorded and analysed. Our computer based method allowed us to show that both reconstruction methods were equivalent in restoring A-P and rotational laxity as well as kinematic curves. Combined deformation of the prostheses was equivalent for both ligaments.

Computer-based method for the 3-D kinematic analysis of posterior cruciate ligament and postero-lateral corner lesions.

Posterior cruciate ligament (PCL) rupture, whether or not combined with postero-lateral corner (PLC) tears, are more often diagnosed today thanks to improved imaging techniques. However, due to the lack of reliable instrumentation to quantitatively evaluate the knee, much is still unknown about the function of these ligamentous structures. The aim of this paper is to present results on the effect of progressive resection of the PCL and PLC on knee laxity and 3-D knee kinematics. The results show that 3-D movement analysis is important and complements laxity measurements by helping to interpret the complex alteration of knee function.

Computer based method for the three-dimensional kinematic analysis of combined posterior cruciate ligament and postero-lateral complex reconstructions on cadaver knees.

The aim of this study is to evaluate the effect of combined posterior cruciate ligament (PCL) and postero-lateral corner (PLC) reconstruction on laxity and three-dimensional kinematics of cadaver knees. We performed anatomical double bundle PCL reconstruction, and functional one bundle 'over-the-bottom' PCL reconstruction combined with one type of PLC reconstruction, running from the postero-lateral tibia to an isometric point near the lateral epicondyle of the femur. Our results showed that combined reconstruction was necessary to restore rotatory laxity. PLC reconstruction, according to the technique described, invariably created a shift towards internal rotation of the kinematic curves, compared to the intact knee.

The irradiation effect on the initial mechanical properties of meniscal grafts.

In this study, the effect of sterilization was investigated on the mechanical properties of rabbit's meniscal grafts. The processes of freezing and irradiation were carried out and their effects upon the elastic and viscoelastic properties measured using a tensile testing machine and an indentation test. It was found that gamma irradiation, at dosages commonly used for sterilizing grafts, had a significant adverse influence on the elastic and viscous response of the grafts. Freezing led also to a small significant decrease in elastic stiffness but no change in failure strength. It is concluded that irradiation sterilization is unsuitable for clinical use and other techniques should be used whenever possible.

A computer-controlled apparatus for in vitro mechanical stimulation and characterization of ligaments.

A system has been developed to study in vitro the effects of mechanical stimulation on the biomechanical properties of ligaments. The apparatus is based on a ball screw driven by a microcomputer-controlled stepper motor capable of generating 100 Newtons of traction, the resulting force in the tissue is monitored in real-time acquisition by a load cell. It is programmed to perform virtually any kind of mechanical stimulation or biomechanical characterization tests. Preliminary tests on canine anterior cruciate ligaments indicate that this system is adequate for a variety of mechanical stimulations and characterization assays.

Characteristics of porous nickel-titanium alloys for medical applications.

We investigate the behavior of NiTi porous alloys, possessing the property of shape memory, by using different characterization methods XPS, Auger, DSC and SEM. The study mainly focuses on the determination of porosity, surface characteristics and the phase transformation. In the case of porous material the biomechanical compatibility is closely related to the internal structure and porosity distribution. To describe appropriately the influence of the properties of NiTi on the memory shape, two types of materials provided by different sources has been analyzed. Despite the fact that both materials present different pores size, they exhibit an open and interconnected porosity. Our measurements show that the temperature of the inception of the martensite-austenite phase transition occurs at 60 degrees C, which is by 20 degrees C greater than the body temperature. Moreover, we show that the surface characteristics can be greatly influenced by heat treatment. Furthermore, we observe that the R-phase occurs only for one of the used materials after its heat treatment. The correlation between the composition and the other characteristics measured has been found.