Potential risks of using cement-augmented screws for spinal fusion in patients with low bone quality.

BACKGROUND CONTEXT: Dramatic increases in the average life expectancy have led to increases in the variety of degenerative changes and deformities observed in the aging spine. The elderly population can present challenges for spine surgeons, not only because of increased comorbidities, but also because of the quality of their bones. Pedicle screws are the implants used most commonly in spinal surgery for fixation, but their efficacy depends directly on bone quality. Although polymethyl methacrylate (PMMA)-augmented screws represent an alternative for patients with osteoporotic vertebrae, their use has raised some concerns because of the possible association between cement leakages (CLs) and other morbidities. PURPOSE: To analyze potential complications related to the use of cement-augmented screws for spinal fusion and to investigate the effectiveness of using these screws in the treatment of patients with low bone quality. STUDY DESIGN: A retrospective single-center study. PATIENT SAMPLE: This study included 313 consecutive patients who underwent spinal fusion using a total of 1,780 cement-augmented screws. METHODS AND OUTCOME MEASURES: We analyzed potential complications related to the use of cement-augmented screws, including CL, vascular injury, infection, screw extraction problems, revision surgery, and instrument failure. There are no financial conflicts of interest to report. RESULTS: A total of 1,043 vertebrae were instrumented. Cement leakage was observed in 650 vertebrae (62.3%). There were no major clinical complications related to CL, but two patients (0.6%) had radicular pain related to CL at the S1 foramina. Of the 13 patients (4.1%) who developed deep infections requiring surgical debridement, two with chronic infections had possible spondylitis that required instrument removal. All patients responded well to antibiotic therapy. Revision surgery was performed in 56 patients (17.9%), most of whom had long construction. A total of 180 screws were removed as a result of revision. There were no problems with screw extraction. CONCLUSIONS: These results demonstrate the efficacy and safety of cement-augmented screws for the treatment of patients with low bone mineral density.

Hybrid titania-aminosilane platforms evaluated with human mesenchymal stem cells.

The properties of hybrid aminopropyltriethoxysilane-tetraisopropylorthotitanate (APTS-TIPT) platforms prepared by a sol-gel route have been explored, and their biocompatibility was assayed after culture of human mesenchymal stem cells (hMSCs). The organic content of this material was observed to be preferably surface-oriented as indicated by microanalytical techniques. Furthermore, the surface showed characteristic amino-silane bands when explored by Raman spectroscopy as well as indications of silane and titanate condensation. Surface activity of the amino groups was probed by ultraviolet-visible spectroscopy imine derivatization and chemical force spectroscopy, showing a pH-dependent surface charge-induced potential. hMSCs cultured onto these surfaces showed relevant differences with respect to their behavior on gelatin-coated glass plates. Even if with a lower proliferative rate than controls, the cells develop long cytosolic prolongations in osteogenic differentiation medium, thus, supporting the idea of an APTS-TIPT stimulated process.

One step processing of aminofunctionalized gate oxides.

A plasma discharge process has been developed that allows the growth of biosensor gate oxides with adapted surface properties for the direct application of biomolecular immobilization cascades. The process involves an accurate selection of processing conditions, mainly, low temperature evaporation of (3-aminopropyl)triethoxysilane (APTS) and dynamic power and flow conditions. Room temperature evaporation of APTS was achieved by designing a vessel with an internal capillary network. The initial high power (100 W) plasma conditions were replaced by milder molecular fragmentation (50 W, 25 W) in a pure Ar discharge. Under these conditions the thin SiO(2) layers presented graded properties with a denser layer at the Si (100) interface and a hybrid organic-inorganic structure at the surface. The chemistry of the films was analysed by Fourier transformed infrared spectroscopy (FTIR) and Rutherford backscattering spectroscopy combined with elastic recoil detection analysis (RBS, ERDA), which confirmed the presence of the SiO(2) and organic phases. Contact angle measurements indicate the higher contribution of the basic polar component to the surface free energy. Furthermore, the higher affinity of the surface towards biomolecular immobilization was confirmed by fluorescence microscopy. Finally, penetration of nitrobenzaldehyde was obtained by application of a molecular permeation method evaluated by UV-vis spectroscopy onto fused silica substrates.

Textured hydroxyapatite interface onto biomedical titanium-based coatings.

Hydroxyapatite (HAP) bioceramic coatings grown onto titanium-nitride (TiN) buffer layers by the aerosol-gel procedure present interfaces with a preferred growth orientation. These coatings were crystallized at 800 degrees C and subsequently etched to ease the study of the interface by Auger electron spectroscopy depth profiling. Ion beam milling was applied to cross-section samples to analyze the interface structures using transmission electron microscopy. At the interface, the HAP crystals showed a <002> orientation. It was shown by Auger electron spectroscopy depth profiling that O atoms diffuse into the nitride interlayer, indicating that the formation of O channels in the HAP structure is the driving force inducing the textured film. The outstanding biocompatible properties of both the materials and properties of their interface suggest that HAP/TiN structures are particularly well suited for endoprosthetic applications.

Microstructural study of aerosol-gel derived hydroxyapatite coatings.

Highly porous aerosol-gel derived hydroxyapatite (HAP) coatings have been prepared from calcium nitrate and phosphoric acid based sols. Precursor solutions were prepared by filtering the suspension formed during the ultrasonic slurring of the reactants mixture. The coatings deposited on Si wafers were studied after sintering at different temperatures by using Fourier transform infrared spectroscopy, X-ray diffraction, energy disperse microanalysis and scanning electron microscopy. The composition, structure and morphology of the coatings sintered at 650 degrees C were found to fit highly porous HAP. That is considered of great relevance since the deposition parameters are compatible with the processing of bioactive coatings on load bearing metallic substrates.

Testing biomaterials by the in-situ evaluation of cell response.

In this work, we describe a technique for the in-situ observation of cells adhered on opaque biomaterial surfaces. The visualisation of the morphology of cells adhered onto a surface allows to derive nuclear apoptotic signs or even the existence of organisation between groups of these cells. The technique is based on the use of an auto-immune reaction combined with a fluorescent agent that allows a direct inspection of the cell behaviour. The versatility of the technique is demonstrated by presenting several examples with different cultured cells (human chondrosarcome cells (CSRCs) and pluripotential mesenchymal stem cells (MSCs) from bone marrow) seeded over two different Ti-based surfaces (TiO(2) and TiN, respectively). These in-vitro observations are compared with the behaviour of the same cells on bare TiAlV alloy. From our results it is concluded that both TiO(2) and TiN surfaces show enhanced biological responses.

Mechanical and in vitro testing of aerosol-gel deposited titania coatings for biocompatible applications.

The biocompatible properties of sol-gel litania have increased the interest in the mechanical properties of this material in the form of functional coatings for prosthetic applications. In the present work. titania coatings with thicknesses of 1 microm have been prepared using the aerosol gel process. The main objective has been to evaluate the mechanical properties of the coatings and to prove their in-vitro biocompatibility. For this purpose, the hardness and Young's modulus of the coatings were measured by nanoindentation with loads in the 6-30 mN range. A continuous increase of these magnitudes was observed for the coatings treated at increasing sintering temperatures (150-800 degrees C). The hardness and the Young's modulus ranged between 15.8-19.5 GPa and 142-186 GPa, respectively. This behaviour has been confirmed by measurements of the plastic energy of deformation in 10 mN full loading unloading tests and by determination of the mean indentation creep under 30 mN loads. The films were additionally characterised by XRD. FTIR and ellipsometry to study the chemical and structural changes produced by sintering. Biocompatibility tests are very conclusive. Cells seeded on aerosol-gel titania coatings grow while adhered onto the surface. These coatings are thus of potential interest for the enhancement of the properties of prosthetic TiAlV alloys.

Development of human mesenchymal stem cells on DC sputtered titanium nitride thin films.

The biocompatible properties of titanium nitride (TiN) have opened a new field of applications for this material. In the present work, TiN coatings with thicknesses around 1 microm have been prepared by DC magnetron sputtering. The aim has been to evaluate the adherence, growth and proliferation of human pluripotent mesenchymal stem cells (hMSCs) on the surface of TiN films with contrasted structural, electrical, and mechanical properties. For this purpose, the films were characterized by X-ray diffraction, scanning electron microscopy, sheet resistance measurements, and nanoindentation. Biological tests show that hMSCs adhere and proliferate onto TiN surfaces. The combination of the mechanical, electrical, and biological responses suggest that TiN coatings present appropriate properties to induce the in vitro stimulated differentiation of hMSCs. This possibility gives an added value to TiN based biomaterial coatings.

Electrodeposition of hydroxyapatite coatings in basic conditions.

Hydroxyapatite films have been grown in this work by an electrodeposition method involving both physical and chemical processes and presenting several differences with respect to other reported works. Description of the coating formation is based on the evolution of current through the sample placed as positive electrode in the basic electrolyte. The characterisation of hydroxyapatite films is of special importance since the bioactive properties related to HAP have been directly identified with its specific composition (Ca/P ratio) and crystalline structure. This characterisation has been traditionally fulfilled by the use of XRD, FTIR and SEM. Results of a further characterisation of the coatings by TEM and SFM, additional to the analysis by XRD, FTIR and SEM, are presented. Interpretation and comparison of our results with those obtained by other electrodeposition methods lead to arguments in favour of a deposition produced directly from ionic species.