Bioactive Coatings on Titanium: A Review on Hydroxylation, Self-Assembled Monolayers (SAMs) and Surface Modification Strategies

Titanium (Ti) and its alloys have been demonstrated over the last decades to play an important role as inert materials in the field of orthopedic and dental implants. Nevertheless, with the widespread use of Ti, implant-associated rejection issues have arisen. To overcome these problems, antibacterial properties, fast and adequate osseointegration and long-term stability are essential features. Indeed, surface modification is currently presented as a versatile strategy for developing Ti coatings with all these challenging requirements and achieve a successful performance of the implant. Numerous approaches have been investigated to obtain stable and well-organized Ti coatings that promote the tailoring of surface chemical functionalization regardless of the geometry and shape of the implant. However, among all the approaches available in the literature to functionalize the Ti surface, a promising strategy is the combination of surface pre-activation treatments typically followed by the development of intermediate anchoring layers (self-assembled monolayers, SAMs) that serve as the supporting linkage of a final active layer. Therefore, this paper aims to review the latest approaches in the biomedical area to obtain bioactive coatings onto Ti surfaces with a special focus on (i) the most employed methods for Ti surface hydroxylation, (ii) SAMs-mediated active coatings development, and (iii) the latest advances in active agent immobilization and polymeric coatings for controlled release on Ti surfaces.This research was funding by Basque Government (ELKARTEK program, HAZITEK program–IMABI exp number ZE-2019/00012), Department of Development and Infrastructures of the Basque Country, University of the Basque Country UPV/EHU (GIU 207075), Ministry of Economy, Industry and Competitiveness (grant MAT2017-89553-P) and i+Med S. Coop

Use of graphene as protection film in biological environments

Corrosion of metal in biomedical devices could cause serious health problems to patients. Currently ceramics coating materials used in metal implants can reduce corrosion to some extent with limitations. Here we proposed graphene as a biocompatible protective film for metal potentially for biomedical application. We confirmed graphene effectively inhibits Cu surface from corrosion in different biological aqueous environments. Results from cell viability tests suggested that graphene greatly eliminates the toxicity of Cu by inhibiting corrosion and reducing the concentration of Cu(2+) ions produced. We demonstrated that additional thiol derivatives assembled on graphene coated Cu surface can prominently enhance durability of sole graphene protection limited by the defects in graphene film. We also demonstrated that graphene coating reduced the immune response to metal in a clinical setting for the first time through the lymphocyte transformation test. Finally, an animal experiment showed the effective protection of graphene to Cu under in vivo condition. Our results open up the potential for using graphene coating to protect metal surface in biomedical application

Self-assembled monolayers of alendronate on Ti6Al4V alloy surfaces enhance osteogenesis in mesenchymal stem cells

Phosphonates have emerged as an alternative for functionalization of titanium surfaces by the formation of homogeneous self-assembled monolayers (SAMs) via Ti-O-P linkages. This study presents results from an investigation of the modification of Ti6Al4V alloy by chemisorption of osseoinductive alendronate using a simple, effective and clean methodology. The modified surfaces showed a tailored topography and surface chemistry as determined by SEM microscopy and RAMAN spectroscopy. X-ray photoelectron spectroscopy revealed that an effective mode of bonding is created between the metal oxide surface and the phosphate residue of alendronate, leading to formation of homogenous drug distribution along the surface. In-vitro studies showed that alendronate SAMs induce differentiation of hMSC to a bone cell phenotype and promote bone formation on modified surfaces. Here we show that this novel method for the preparation of functional coatings on titanium-based medical devices provides osseoinductive bioactive molecules to promote enhanced integration at the site of implantation

A comprehensive review of techniques for biofunctionalization of titanium

A number of surface modification techniques using immobilization of biofunctional molecules of Titanium (Ti) for dental implants as well as surface properties of Ti and Ti alloys have been developed. The method using passive surface oxide film on titanium takes advantage of the fact that the surface film on Ti consists mainly of amorphous or low-crystalline and non-stoichiometric TiO2. In another method, the reconstruction of passive films, calcium phosphate naturally forms on Ti and its alloys, which is characteristic of Ti. A third method uses the surface active hydroxyl group. The oxide surface immediately reacts with water molecules and hydroxyl groups are formed. The hydroxyl groups dissociate in aqueous solutions and show acidic and basic properties. Several additional methods are also possible, including surface modification techniques, immobilization of poly(ethylene glycol), and immobilization of biomolecules such as bone morphogenetic protein, peptide, collagen, hydrogel, and gelatin

A New Insight into Coating’s Formation Mechanism Between TiO2 and Alendronate on Titanium Dental Implant

Organophosphorus compounds, like bisphosphonates, drugs for treatment and prevention of bone diseases, have been successfully applied in recent years as bioactive and osseoinductive coatings on dental implants. An integrated experimental-theoretical approach was utilized in this study to clarify the mechanism of bisphosphonate-based coating formation on dental implant surfaces. Experimental validation of the alendronate coating formation on the titanium dental implant surface was carried out by X-ray photoelectron spectroscopy and contact angle measurements. Detailed theoretical simulations of all probable molecular implant surface/alendronate interactions were performed employing quantum chemical calculations at the density functional theory level. The calculated Gibbs free energies of (TiO2)10–alendronate interaction indicate a more spontaneous exergonic process when alendronate molecules interact directly with the titanium surface via two strong bonds, Ti–N and Ti–O, through simultaneous participation common to both phosphonate and amine branches. Additionally, the stability of the alendronate-modified implant during 7 day-immersion in a simulated saliva solution has been investigated by using electrochemical impedance spectroscopy. The alendronate coating was stable during immersion in the artificial saliva solution and acted as an additional barrier on the implant with overall resistivity, R ~ 5.9 MΩ cm2

Fabrication of bioactive osteogenic controlled-release systems, cellular platforms, and cellular capsules using layer -by -layer nanoassembly

There is an ever-increasing awareness that the field of tissue engineering offers many potential solutions to clinical problems. While advances along these lines have been made, the design and implementation of an off the shelf tissue is yet to be realized. Thus, the objectives of this work were largely aimed at the design and fabrication of biocompatible, bioactive structures which could be integrated into existing biomaterial products. The electrostatic layer-by-layer (LbL) self-assembly technique was used to incorporate biologically relevant molecules within controlled release systems, cell culture platforms, and 3-D cellular capsules. Two delivery systems were investigated to determine the release of a model drug, dexamethasone (DEX). In the first system, nanothin polyelectrolyte (PE) layers were applied to the micronized drug crystals as a diffusion barrier. In the second system, DEX was physically entrapped within calcium alginate microspheres which were further modified with PE layers. The fabrication of cell culture platforms functionalized with nanothin layers of PEs, TiO2 nanoparticles, and the growth factor TGFβ1 was achieved through ultrasonic nebulization. Finally, individual cellular capsules were fabricated by elaborating the LbL process on mesenchymal stem cell and human dermal fibroblast templates. Materials characterization and cell culture testing were performed as preliminary indicators of potential cytotoxicity. Release of the drug DEX was enhanced when directly templated with polyelectrolyte layers while DEX entrapment within polyelectrolyte-modified alginate microspheres reduced drug release by a factor of three. An encouraging result of in vitro cell culture assessment was the distinct change in fibrochondrocyte morphology when compared with positive and negative controls. An ultrasonic nebulizer produced 14-layered cell culture substrates containing DEX, TiO2 nanoparticles, and the growth factor TGFβ1. In comparison with traditionally dipped substrates, layer fabrication was expedited six-fold. Moreover, the positioning of TGFβ1 within the layer architecture modulated cell behavior. For example, incorporation of the growth factor as a terminal layer produced visible cellular extensions associated with enhanced adhesion of human dermal fibroblasts (HDFs) to the substrates. The final application of LbL was for production of nanothin cellular capsules. Layer fabrication onto both HDFs and mouse mesenchymal stem cells (MSCs) was demonstrated with acceptable cell tolerances although cell viability is likely affected by layer composition and encapsulation time. The major findings of this work not only demonstrated the feasibility of the technologies, but also their ability to influence cellular behavior by exposure to specific layer chemistries and architectures. The results are extremely promising for both further fundamental research, as well as translation into products. A major obstacle is determining optimal parameters necessary to yield a given cell response. Moreover, cost effectiveness must be addressed before clinical implementation of these systems is realized. Undoubtedly, the work here provides an underpinning for the development of additional capsules, microspheres, and substrates which could ultimately be integrated to create novel, biocompatible, heterogeneous assemblies

Inflammatory responses to biomaterials : Interaction between leukocytes and self-assembled monolayers

Tese de mestrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 199

Implant surface physicochemistry affects keratinocyte hemidesmosome formation

Previous studies have shown hydrophilic/hydrophobic implant surfaces stimulate/hinder osseointegration. An analogous concept was applied here using common biological functional groups on a model surface to promote oral keratinocytes (OKs) proliferation and hemidesmosomes (HD) to extend implant lifespans through increased soft tissue attachment. However, it is unclear what physicochemistry stimulates HDs. Thus, common biological functional groups (NH2 , OH, and CH3 ) were functionalized on glass using silanization. Non-functionalized plasma-cleaned glass and H silanization were controls. Surface modifications were confirmed with X-ray photoelectron spectroscopy and water contact angle. The amount of bovine serum albumin (BSA) and fibrinogen, and BSA thickness, were assessed to understand how adsorbed protein properties were influenced by physicochemistry and may influence HDs. OKs proliferation was measured, and HDs were quantified with immunofluorescence for collagen XVII and integrin β4. Plasma-cleaned surfaces were the most hydrophilic group overall, while CH3 was the most hydrophobic and OH was the most hydrophilic among functionalized groups. Modification with the OH chemical group showed the highest OKs proliferation and HD expression. The OKs response on OH surfaces appeared to not correlate to the amount or thickness of adsorbed model proteins. These results reveal relevant surface physicochemical features to favor HDs and improve implant soft tissue attachment.© 2023 The Authors. Journal of Biomedical Materials Research Part A published by Wiley Periodicals LLC

Anchoring of Aminophosphonates on Titanium Oxide for Biomolecular Coupling

Aminophosphonates were chosen for a first step functionalization of TiO2 grown on titanium, as they possess a phosphonate group on one end, that can be exploited for coupling with the oxide surface, and an amino group on the other end to enable further functionalization of the surface. The deposition of aminophosphonates with different chain lengths (6 and 12 methylenes) was investigated. Oxygen plasma treatment proved useful in increasing the number of 12OH groups at the TiO2 surface, thus helping to anchor the aminophosphonates. By combining different surface-sensitive experimental techniques, we found the existence of a discontinuous monolayer where the molecules are covalently coupled to the TiO2 surface. For the molecules with longer chains, we find evidence of their covalent coupling to the surface through Ti\u2013O\u2013P bond formation, of the exposure of the amino groups at the outer surface, and of an increase in the order of the layer upon thermal annealing

Anti-microbial self-assembling click monolayers utilizing silver nanoparticles for indwelling medical devices

The objective of this study was to synthesize and characterize antimicrobial, silver nanoparticles based self-assembling monolayer coatings, for use on chronic indwelling medical devices. The coatings are comprised of novel biomass mediated silver nano particles (SNP) that are biocompatible, highly concentrated, highly pure, cost-effective, polydispersed and compatible for use with existing chronic indwelling medical devices. The HPC SNPs were functionalized with an azide functional group and covalently bound to titanium substrates via ¨Dclick¡¬ chemistry