NiTi superelastic orthodontic archwires with polyamide coating.

Twenty orthodontic archwires with 55.2% Ni and 44.8% Ti (% weight) were subjected to a dipping treatment to coat the NiTi surface by a polyamide polymer. It has been selected a Polyamide 11 due to its remarkable long lasting performance. The transformation temperatures as well as the transformation stresses of the NiTi alloy were determined in order to know whether the coating process can alter its properties. The adhesive wear tests have been demonstrated that the wear rates as well as the dynamic friction coefficients µ of polymer coated wires are much lower than metallic wires. The corrosion studies have shown that the use of this polymer, as coating, seals the NiTi surface to prevent corrosion and the release of nickel ions. The average decrease of Ni ions release due to this coating is around 85%.

Friction coefficients and wear rates of different orthodontic archwires in artificial saliva.

The aim of this paper is to analyze the influence of the nature of the orthodontic archwires on the friction coefficient and wear rate against materials used commonly as brackets (Ti-6Al-4V and 316L Stainless Steel). The materials selected as orthodontic archwires were ASI304 stainless steel, NiTi, Ti, TiMo and NiTiCu. The array archwire's materials selected presented very similar roughness but different hardness. Materials were chosen from lower and higher hardness degrees than that of the brackets. Wear tests were carried out at in artificial saliva at 37 °C. Results show a linear relationship between the hardness of the materials and the friction coefficients. The material that showed lower wear rate was the ASI304 stainless steel. To prevent wear, the wire and the brackets have high hardness values and in the same order of magnitude.

Control of stem cell response and bone growth on biomaterials by fully non-peptidic integrin selective ligands.

In this communication we report that anchoring αvß3 or α5ß1 integrin-selective RGD peptidomimetics to titanium efficiently tunes mesenchymal stem cell response in vitro and bone growth in rat calvarial defects. Our results demonstrate that this molecular chemistry-derived approach could be successful to engineer instructive coatings for orthopedic applications.

Acceleration of apatite nucleation on microrough bioactive titanium for bone-replacing implants.

The viability of a new two-step method for obtaining bioactive microrough titanium surfaces for bone replacing implants has been evaluated. The method consists of (1) Grit blasting on titanium surface to roughen it; and (2) Thermo-chemical treating to obtain a bioactive surface with bone-bonding ability by means of nucleating and growing an apatite layer on the treated surface of the metal. The aim of this work is to evaluate the effect of surface roughness and chemical composition of the grit-blasting particles on the ability of the surfaces of nucleating and growing a homogeneous apatite layer. The determination and kinetics of the nucleation and growing of the apatite layer on the surfaces has mainly been studied with environmental scanning electron microscopy (ESEM) and grazing-incidence X-ray diffractometry. The results show that Al(2)O(3)-blasted and thermochemically-treated titanium surfaces accelerates nucleation of the apatite, whereas SiC-blasted and thermochemically-treated titanium surfaces inhibits apatite nucleation, compared with the well studied polished and thermochemically-treated titanium surfaces. The acceleration of the apatite nucleation on the Al(2)O(3)-blasted microrough titanium surfaces is because concave parts of the microroughness that are obtained during grit blasting provides to the rough and bioactive surfaces with a chemical- and electrostatic-favored situation for apatite nucleation. This consists of a high density of surface negative charges (also assisted by the nanoroughness of the surface obtained after the thermochemical treatment) and an increased concentration of the Ca(2+)-ions of the fluid, which have a limited mobility at the bottom of the concave parts.

Improved surgical mesh integration into the rat abdominal wall with arginine administration.

Prosthetic meshes are used as the standard of care in abdominal wall hernia repair. However, hernia recurrences and side effects remain unsolved problems. The demand by health care providers for increasingly efficient and cost-effective surgery encourages the development of newer strategies to improve devices and outcomes. Here, we evaluated whether l-arginine administration was able to ameliorate long-term polypropylene prostheses incorporation into the abdominal wall of Sprague-Dawley rats. Meshes were placed on-lay and continuous l-arginine was administered. In vivo biocompatibility was studied at 7, 25 and 30 days post-implantation. Effectively, l-arginine administration in combination with mesh triggered subtle changes in ECM composition that impinged on critical biochemical and structural features. Lastly, tensile strength augmented and stiffness decreased over the control condition. This could help to restructure the mechanical load transfer from the implant to the brittle surrounding tissues, i.e., impact load and fatigue load associated with mechanical tensions could be distributed between the mesh and the restored tissue in a more balanced manner, and ultimately help to reduce the incidence of loosening, recurrences, and local wound complications. Since the newly formed tissue is more mechanically stable, this approach could eventually be introduced to human hernia repair.

Tuning Mesenchymal Stem Cell Response onto Titanium-Niobium-Hafnium Alloy by Recombinant Fibronectin Fragments.

Since metallic biomaterials used for bone replacement possess low bioactivity, the use of cell adhesive moieties is a common strategy to improve cellular response onto these surfaces. In recent years, the use of recombinant proteins has emerged as an alternative to native proteins and short peptides owing to the fact that they retain the biological potency of native proteins, while improving their stability. In the present study, we investigated the biological effect of two different recombinant fragments of fibronectin, spanning the 8-10th and 12-14th type III repeats, covalently attached to a new TiNbHf alloy using APTES silanization. The fragments were studied separately and mixed at different concentrations and compared to a linear RGD, a cyclic RGD and the full-length fibronectin protein. Cell culture studies using rat mesenchymal stem cells demonstrated that low to medium concentrations (30% and 50%) of type III 8-10th fragment mixed with type III 12-14th fragment stimulated cell spreading and proliferation compared to RGD peptides and the fragments separately. On the other hand, type III 12-14th fragment alone or mixed at low volume percentages ≤50% with type III 8-10th fragment increased alkaline phosphatase levels compared to the other molecules. These results are significant for the understanding of the role of fibronectin recombinant fragments in cell responses and thus to design bioactive coatings for biomedical applications.

Study on the use of 3-aminopropyltriethoxysilane and 3-chloropropyltriethoxysilane to surface biochemical modification of a novel low elastic modulus Ti-Nb-Hf alloy.

A biocompatible new titanium alloy Ti-16Hf-25Nb with low elastic modulus (45 GPa) and the use of short bioadhesive peptides derived from the extracellular matrix have been studied. In terms of cell adhesion, a comparative study with mixtures of short peptides as RGD (Arg-Gly-Asp)/PHSRN (Pro-His-Ser-Arg-Asn) and RGD (Arg-Gly-Asp)/FHRRIKA (Phe-His-Arg-Arg-Ile-Lys-Ala) have been carried out with rat mesenchymal cells. The effect of these mixtures of short peptides have already been studied but there are no comparative studies between them. Despite the wide variety of silane precursors available for surface modification in pure titanium, the majority of studies have used aminosilanes, in particular 3-minopropyltriethoxysilane (APTES). Nevertheless, the 3-chloropropyltriethoxysilane (CPTES) is, recently, proposed by other authors. Unlike APTES, CPTES does not require an activation step and offers the potential to directly bind the nucleophilic groups present on the biomolecule (e.g., amines or thiols). Since the chemical surface composition of this new alloy could be different to that pure titanium, both organosilanes have been compared and characterized by means of a complete surface characterization using contact angle goniometry and X-ray photoelectron spectroscopy.

Mechanical and physicochemical characterization along with biological interactions of a new Ti25Nb21Hf alloy for bone tissue engineering.

Nowadays, one of the main challenges in metal implants for bone substitution is the achievement of an elastic modulus close to that of human cortical bone as well as to provide an adequate interaction with the surrounding tissue avoiding in vivo foreign body reaction. From this perspective, a new Ti-based alloy has been developed with Nb and Hf as alloying elements which are known as non-toxic and with good corrosion properties. The microstructure, mechanical behaviour and the physicochemical properties of this novel titanium alloy have been studied. Relationship of surface chemistry and surface electric charge with protein adsorption and cell adhesion has been evaluated due to its role for understanding the mechanism of biological interactions with tissues. The Ti25Nb21Hf alloy presented a lower elastic modulus than commercial alloys with a superior ultimate strength and yield strength than CP-Ti and very close to Ti6Al4V. It also exhibited good corrosion resistance. Furthermore, the results revealed that it had no cytotoxic effect on rat mesenchymal stem cells and allowed protein adsorption and cell adhesion. The experimental results make this alloy a promising material for bone substitution or for biomedical devices.

Bioactive compounds immobilized on Ti and TiNbHf: AFM-based investigations of biofunctionalization efficiency and cell adhesion.

Implant materials require optimal biointegration, including strong and stable cell-material interactions from the early stages of implantation. Ti-based alloys with low elastic modulus are attracting a lot of interest for avoiding stress shielding, but their osseointegration potential is still very low. In this study, we report on how cell adhesion is influenced by linear RGD, cyclic RGD, and recombinant fibronectin fragment III8-10 coated on titanium versus a novel low-modulus TiNbHf alloy. The bioactive molecules were either physisorbed or covalently coupled to the substrates and their conformation on the surfaces was investigated with atomic force microscopy (AFM). The influence of the different bioactive coatings on the adhesion of rat mesenchymal stem cells was evaluated using cell culture assays and quantitatively analyzed at the single cell level by AFM-based single-cell force spectroscopy. Our results show that bioactive moieties, particularly fibronectin fragment III8-10, improve cell adhesion on titanium and TiNbHf and that the covalent tethering of such molecules provides the most promising strategy to biofunctionalize these materials. Therefore, the use of recombinant protein fragments is of high importance for improving the osseointegration potential of implant materials.

Applications of environmental scanning electron microscopy (ESEM) in biomaterials field.

Various tasks were undertaken in our laboratory where environmental scanning electron microscopy (ESEM) has been of particular interest within the biomaterials field. The possibility of observing wet samples, as well as the fact that sample preparation is minimal, has improved shorter time scales and lower costs in microscopy. Minimal preparation has also reduced the possibility of introducing artifacts. Examples like cell cultures used for pit resorption assays, calcium phosphate deposition processes, and dissolution of phosphate glasses used as biomaterials are presented. Finally, a servohydraulic testing machine designed for mechanical testing in situ in ESEM has allowed the study of shape memory alloys for orthodontic applications or the behavior of different adhesives used in odontology.

A radiopaque polymeric matrix for acrylic bone cements.

As part of the search for an alternative to inorganic radiopaque agents, this work studies the possibility of modifying bone cement formulations by incorporating a radiopaque monomer, that is, 4-iodophenol methacrylate (IPMA), in the liquid phase. The monomer was synthesized in the laboratory, and cements were prepared by the standard method. The influence on the different cement characteristics of various monomer concentrations was studied. It was seen that the setting time decreased as the percentage of monomer increased. The radiopacity attained in the 15 vol.% IPMA formulations was about the same as that for a cement containing 10 wt.% barium sulphate. Dynamic and static mechanical properties were measured. The materials did not show significant differences in the glass transition temperature. However, static mechanical properties showed enhanced compressive strength, tensile strength, and elastic modulus with respect to conventional cements formulated with barium sulphate. Histological studies showed a good response of muscular tissue to implanted specimens.

Wear behaviour of the pair Ti-6Al-4V-UHMWPE of acrylic bone cements containing different radiopaque agents.

The objective of this study was to improve the wear behaviour of acrylic bone cements by substituting the conventional inorganic radiopaque agents (BaSO(4), ZrO(2)) for different iodinated radiopaque monomers which can co-polymerize with the methyl methacrylate monomer, MMA. To this aim, the wear behaviour of the pair Ti-6Al-4V-UHMWPE (ultra high molecular weight polyethylene) was studied in the absence and in the presence of cement particles (the third body).

Propagation of fatigue cracks in acrylic bone cements containing different radiopaque agents.

In this work three iodine-containing monomers were proposed as new radiopaque agents for acrylic bone cements. In previous studies the addition of iodine-containing methacrylate monomers provided a statistically significant increase in tensile stress, fracture toughness and ductility, with respect to the barium sulphate (BaSO4)-containing cement. However, since fatigue resistance is one of the main properties required to ensure a good long-term performance of permanent prostheses, it is important to compare the fatigue properties of these new bone cement formulations with the radiolucent and BaSO4-containing bone cements. Because the acrylic cements have initial cracks, fatigue crack propagation studies were performed. It can be observed that these acrylic cements followed the Paris-Erdogan model. The results showed that the addition of some organic radiopacifiers (DISMA, TIBMA) increased the fatigue crack propagation resistance as compared to the radiolucent cement, being similar to the BaSO4-containing cement. The radiolucent cement showed a low crack propagation resistance.

A study of the abrasive resistance of metal alloys with applications in dental prosthetic fixators.

Wear is one of the main surface failure mechanisms in materials and it will play a leading role in substitutive dental biomaterials. The aim of the present study is to compare the abrasive wear of different metallic materials used in dental applications. The results show that the abrasive wear of alloys based on precious metals such as Pt, Pd, Au and Ag is higher than for Ti and Ti based alloys. The alloy with the highest wear resistance is the Co-Cr which exhibits as well the highest hardness and Young's modulus. Since the method corresponds to a well-established abrasive wear standard, the behaviour of the different materials can be easily compared.

A study of load cycling in a NiTi shape memory alloy with pseudoelastic behaviour used in dental prosthetic fixators.

NiTi alloy used in dental prosthetic fixators shows pseudoelastic behaviour and exhibits a great potential in dental and orthopaedic applications where constant correcting loads are required. In order to use such materials in dental prosthetic fixators, where the device is cyclically deformed, it is necessary to investigate the effect of the cyclic straining upon the transformation stresses and temperatures of the material. The aim of this work is to study the load cycling of a pseudoelastic NiTi shape memory alloy to be applied in the making of dental prosthetic fixators.

Cyclic deformation fatigue behaviour of Ti6Al4V thermochemically nitrided for articular prostheses.

Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes the use of titanium and Ti6Al4V difficult in some biomedical applications, for example, articulating components of prostheses. To overcome this limitation, nitriding has been investigated as a surface-hardening method for titanium. Although nitriding greatly improves the wear resistance, this method reduces the fatigue strength. Low cycle fatigue performance in air of nitrided Ti6Al4V at different deformation amplitudes has been studied. Results show a reduction of low cycle fatigue life of up to 10% compared to the non-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment. (Journal of Applied Biomaterial & Biomechanics 2003; 1: 43-7).

Partially resorbable acrylic bone cements based on self-curing acrylic/phosphate glass formulations.

Partially resorbable self-curing cements based on poly(methyl methacrylate)/phosphate glasses were prepared by mixing methyl methacrylate monomer with poly(methyl methacrylate) powder in different proportions (20-60 wt-%) of phosphate glass (BV11) in the system 44.5-P2 O5 , 44.5-CaO, 11-Na2 O (mol-%). The curing of these formulations showed a reduction of 10 degrees C in the maximum temperature and an increase of 10 minutes in the setting time although the content of residual monomer in the cured materials was unaltered. The presence of the inorganic particles did not significantly change the glass transition temperature of the cement. Static mechanical properties were evaluated in compression. The compressive yield strength of PM-MA/BV11 cements were in the range 110-118 MPa, superior to those of the control for dry specimens. When the test was conducted with wet specimens, a decrease in strength was observed due to the dissolution of the glasses in the medium, but the composites prepared with 20 or 40 wt-% BV11 had the compressive yield strengths required by the international standard for acrylic bone cements (ISO 5833). The dynamic mechanical properties of the formulation containing 60 wt-% BV11 and the corresponding control were evaluated through a fatigue crack propagation test. The results showed that both formulations followed a Paris-Erdogan model in the stable crack propagation, with no significant differences in the value of the exponent m of the mentioned law. Finally, the presence of the phosphate glasses in the acrylic composite did not change the wear damage of the pair UHMWPE/Ti6Al4V produced by the PMMA formulations. (Journal of Applied Biomaterials & Biomechanics 2003; 1: 48-57).

[Pure prostatic leiomyoma]. / Leiomioma prostático puro.

We present a case of pure prostatic leiomyoma, benign and rare entity, diagnosed in a patient with prostatism. We review the published papers about this disease and the different subjects about etiology, clinic, histopathology, diagnosis and treatment.

[Urinary continence after radial prostatectomy. Prognostic factors and recovery time]. / Continencia urinaria tras prostatectomía radical. Factores pronósticos y tiempo de recuperación.

OBJECTIVES: To assess the urinary continence after radical prostatectomy and its evolution over time. To analyse possible prognosis factors. MATERIAL AND METHODS: We have reviewed 101 patients that have undergone radical prostatectomy. We define "continent patient" as that one who doesn't require any type of urinary protection. By means of Kaplan-Meier method, we evaluate the recovery of continence along time. We analyze potential conditional factors (age, stage, surgery technique, surgery experience,...). The statistical tools used are: chi-square, Fisher, Cox regression, T-test and Kaplan-Meier. RESULTS: Median monitoring time: 27.33 months. 80% are continent patients, 48.7% of which reach maximum continence before the 3rd, month is due and 17.5% after the 6 months (2.5% between 9-12 months). Their probability of becoming "continents" during the first 4 months es 0.4692. patients under 70 years old recover continence before those who are over 70 years old (medians: 3.51 months and 5.67 months respectively, p = 0.0211). CONCLUSIONS: The recovery of continence takes place progressively and a 17.5% of patients reach plain recovery in the 6-12 months period after surgery. The evaluation of the surgery treatment to correct incontinence should consider the possibility of "spontaneous" recovery in a 2.5% of patients in the 9-12 months period after surgery. Age affects negatively the recovery time; it is significantly less for patients under 70.

[Leiomyosarcoma of the urinary bladder]. / Leiomiosarcoma de vejiga urinaria.

We report a case of bladder leiomyosarcoma treated at our department. We review the published papers about this entity. We emphasize the low incidence of that pathology and the lack of consensus about treatment.