Titanium scaffolds fabricated by Direct Ink Writing and functionalized with dual-action coatings with osteoinductive and antibacterial properties

The stress shielding, a result of the stiffness mismatch between titanium and bone, the lack of bioactivity and the infections are the main cause of the implants failure. In this work, porous titanium structures (between 50 and 70%) were produced by direct ink writing, using a new Ti ink formulation. A water and thermal treatment was optimized to ensure the complete elimination of the binder before the sintering process. The samples were sintered in high vacuum at 1150 ºC.The stiffness and compressive strength were similar to those of cancellous bone. The functionalization of the scaffold surface with a thermochemical treatment that incorporates Ga ions resulted in Ga-containing calcium titanate layer that generate homogeneous apatite layer in simulated body fluid. The Ga3+ release promote the antibacterial effect against gram positive strains. SaOS-2 cells adhered and proliferated on the Ga-doped Ti surfaces; its presence contributes to cell differentiation and increases the mineralization. © European Powder Metallurgy Association (EPMA)Postprint (published version

Blocking methods to prevent non-specific adhesion of mesenchymal stem cells to titanium and evaluate the efficiency of surface functionalization: albumin vs poly(ethylene glycol) coating

Premio SIBB 2014Surface modification of biocompatible materials with biologically-active molecules is a well-known strategy to enhance the osteointegration of implantable devices. In order to evaluate the efficiency of these treatments, an in vitro study of cell behavior on the modified surface is usually carried out. A key point to evaluate the efficacy of this strategy is to avoid non specific protein adsorption by creating a non-fouling background. This blocking step ensures that the observed response of cells can be exclusively ascribed to the modification treatment applied. Several techniques are available to create this neutral background. Thus, the aim of this study is to compare two different blocking methods, namely adsorption of albumin from bovine serum (BSA) and grafting of small polyethylene glycol (PEG) chains to titanium, which is the gold standard metal for orthopedics and dentistry. To this end, titanium surfaces were coated with a recently synthesized cell adhesive peptide-based molecule and subjected to a blocking procedure with either BSA or PEG.  Non-functionalized titanium samples were also blocked and used as controls. The biological response of human mesenchymal stem cells was evaluated by measuring the number of attached cells and studying the degree of cell spreading on the substrate. Both aspects of cell behavior are not affected significantly by the blocking method: cells adhere and spread significantly more on the functionalized samples, regardless of the blocking method used. This confirms that the surface feature that defines cell response is the presence/absence of the biomolecule, and not the anti-fouling layer. These results, together with the reduction of variability of results observed in presence of a blocking layer, demonstrate the efficacy and necessity of blocking the surface. PEG grafting is demonstrated as effective as BSA coating in reducing non-specific interactions and not hindering the effect of the biomolecule. However, taken into account the numerous advantages of a synthetic and customizable polymer chain over a complex natural protein, PEG blocking stands out as a very good alternative to albumin adsorption.Peer ReviewedAward-winnin

Modification of the titanium backplate of the BKPro by electrodeposition

The Boston keratoprosthesis (BKPro) is the most widely used artificial cornea in the world for the treatment of corneal blindness in patients who are not candidates for conventional keratoplasty. Despite excellent retention rates and good vision restoration, implant viability is affected by two main complications: infection and visual loss due to retroprosthetic membrane (RPM) formation [1]. In previous work the electrodeposition technique has been shown to be efficient to functionalize titanium with silver [2]. In this work the electrodeposition technique was used to modify the BKPro titanium backplate. The aim was to confer antibacterial properties to decrease the infection rates. For this, the experimental conditions have been optimized to adjust the number of cycles, voltage, and type of applied pulse. The obtained surfaces have been characterized physiochemically by means of X-ray photoelectron spectroscopy (XPS), contact angle measurements, profilometer, and scanning electron microscopy (SEM). Adhesion and cytotoxicity were studied in human fibroblasts using the MTT assay. The effect on bacterial strains that cause ocular infections (Pseudomonas aeruginosa and Staphylococcus epidermidis) was measured by a 2-hour adhesion test. The results of SEM and XPS corroborate the presence of silver particles in the titanium samples. Cytotoxicity has not been observed. The studied treatments decrease adhesion of epidermidis and aeruginosa by 78% and almost 63%, respectively

Antibacterial PHAs coating for titanium implants

Biomaterial-associated infection is a serious complication of modern implantation surgery. Thus, the improvement of implant surfaces is required to avoid the first stage for biofilm formation, bacterial adhesion. The current research addresses this issue by developing drug delivery systems (DDS) consisting of antibiotic-loaded polyhydroxyalkanoates (PHAs) coatings on titanium implants. Dip-coating technique was used to achieve optimal coatings with biodegradable biopolyesters, polyhydroxybutyrate (PHB) and its copolymer, polyhydroxybutyrate-co-hydroxyvalerate (PHBV). The coatings were completely characterized (wettability, topography, thickness and roughness), and studies of drug delivery, toxicity, antibacterial effect, and cell adhesion were performed. For both of biopolymers, surfaces were partially covered with 1 and 3 immersions, while with 6, they were completely covered. Although both antibiotic-loaded biopolymer coatings assure the protection against bacteria populations, PHBV coatings are closer to the desired release profile; its faster degradation provides for a greater and more stable drug release for a given period of time compared to PHB coatings. The use of coatings with different drug concentration per layer results in more controlled and homogeneous releases. The DDS designed not only assure to avoid the first stage of bacterial adhesion, but also their proliferation and biofilm formation, since the coatings degrade with time under physiological conditions, guaranteeing a prolonged drug release.Preprin

Antimicrobial PHAs coatings for solid and porous tantalum implants

Biomaterial-associated infections (BAI) are the major cause of failure of indwelling medical devices. The risk of BAI can end dramatically in the surgical removal of the affected device. Therefore, a major effort must be undertaken to guarantee the permanence of the implant. In this regard, we have developed antimicrobial coatings for tantalum (Ta) implants, using polyhydroxyalkanoates (PHAs) as matrices for carrying an active principle. The dip-coating technique was successfully used for covering solid Ta discs. An original PHA emulsion flow process was developed for the coating of porous Ta structures, specially for the inner surfaces. The complete characterization of the biopolymer coatings, their antibacterial properties, toxicity and biointegration were analyzed. Thus, non-toxic, well-biointegrated homogeneous biopolymer coatings were attained, which showed antibacterial properties. By using biodegradable PHAs, the resulting drug delivery system assured the protection of Ta against bacterial infections for a period of time.Peer ReviewedPostprint (author's final draft

Guiding fibroblast activation using an RGD-mutated heparin binding II fragment of fibronectin for gingival titanium integration

The formation of a biological seal around the neck of titanium (Ti) implants is critical for ensuring integration at the gingival site and for preventing bacterialcolonization that may lead to periimplantitis. This process is guided byactivated fibroblasts, named myofibroblasts, which secrete extracellularmatrix (ECM) proteins and ECM-degrading enzymes resolving the wound.However, in some cases, Ti is not able to attract and activate fibroblasts to asufficient extent, which may compromise the success of the implant.Fibronectin (FN) is an ECM component found in wounds that is able to guidesoft tissue healing through the adhesion of cells and attraction of growthfactors (GFs). However, clinical use of FN functionalized Ti implants isproblematic because FN is difficult to obtain, and is sensitive to degradation.Herein, functionalizing Ti with a modified recombinant heparin binding II(HBII) domain of FN, mutated to include an Arg-Gly-Asp (RGD) sequence forpromoting both fibroblast adhesion and GF attraction, is aimed at. TheHBII-RGD domain is able to stimulate fibroblast adhesion, spreading,proliferation, migration, and activation to a greater extent than the nativeHBII, reaching values closer to those of full-length FN suggesting that itmight induce the formation of a biological sealing.Peer ReviewedPostprint (published version

Mejora de la resistencia al desgaste de titanio y sus aleaciones utilizados para prótesis articulares

Se han estudiado los endurecimientos superficiales que se producen en la aleación Ti 6Al 4V, mediante los procesos de anodización electroquímica y mediante diferentes tratamientos térmicos a distintas microestructuras de dicha aleación, así como los procesos de nitruración mediante difusión gaseosa.. Los resultados de la combinación de la anodización y los tratamientos térmicos producen endurecimientos superiores a 1000 HV lo que mejorará la resistencia al desgaste de estas aleaciones en sus aplicaciones para prótesis articulares. Mejores resultados ofrecen los valores de nitruración que pueden alcanzar las 1400 unidades Vickers

Mechanical and microstructural characterization of new nickel-free low modulus beta-type titanium wires during thermomechanical treatments

NiTi alloy is the only practical shape memory alloy (SMA) in biomedical use because of its excellent mechanical stability and functionality. However, it is estimated that between 4.5% and 28.5% of the population are hypersensitive to nickel metal, with a higher prevalence in females. Therefore, developing nickel-free low modulus beta-type titanium alloys showing shape memory or super elastic behavior would have a great interest in the biomaterials field. Homogeneous 127 mu m diameter Ti25Hf21Nb wires were produced and compared to straight annealed Ti-50.8 at% Ni (Nitinol) and 90% cold-drawn 316L wires. Microstructural changes taking place during the heat treatment of cold-worked Ti25Hf21Nb wires were investigated. Large plastic deformation during wire drawing and subsequent annealing led to nano-crystallization and amorphization which may contribute to the observed superelasticity. Mechanical properties were characterized using cyclic uniaxial tension and rotary beam fatigue test modes. A modulus of elasticity of less than 60 GPa and axial recoverable strain of greater than 3% were observed with stress hysteresis resembling a reversible stress-induced martensitic transformation at higher temperatures. The new Ti25Hf21Nb alloy is an important candidate for developing Ni-free SMAs in the future. (C) 2015 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author's final draft