Nanostructured coatings by adhesion of phosphonated polystyrene particles onto titanium surface for implant material applications

Analytical Techniques for the Characterization of Bioactive Coatings for Orthopaedic Implants

The development of bioactive coatings for orthopedic implants has been of great interest in recent years in order to achieve both early- and long-term osseointegration. Numerous bioactive materials have been investigated for this purpose, along with loading coatings with therapeutic agents (active compounds) that are released into the surrounding media in a controlled manner after surgery. This review initially focuses on the importance and usefulness of characterization techniques for bioactive coatings, allowing the detailed evaluation of coating properties and further improvements. Various advanced analytical techniques that have been used to characterize the structure, interactions, and morphology of the designed bioactive coatings are comprehensively described by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 3D tomography, quartz crystal microbalance (QCM), coating adhesion, and contact angle (CA) measurements. Secondly, the design of controlled-release systems, the determination of drug release kinetics, and recent advances in drug release from bioactive coatings are addressed as the evaluation thereof is crucial for improving the synthesis parameters in designing optimal bioactive coatings.

PEGylating poly(p-phenylene vinylene)-based bioimaging nanoprobes

HYPOTHESIS

Conjugated polymer nanoparticles (CNPs) have attracted considerable attention within bioimaging due to their excellent optical properties and biocompatibility. However, unspecific adsorption of proteins hampers their effective use as advanced bioimaging probes. Controlled methodologies made possible tailor-made functional poly(p-phenylene vinylene), enabling one-pot synthesis of CNPs containing functional surface groups. Hence, it should be feasible to PEGylate these CNPs to tune the uptake by cell lines representative for the brain without imparting their optical properties.

EXPERIMENTS

CNPs consisting of the statistical copolymer 2-(5'-methoxycarbonylpentyloxy)-5-methoxy-1,4-phenylenevinylene and poly(2-methoxy-5-(3',7'-dimethoxyoctyloxy)-1,4-phenylenevinylene) were fabricated by miniemulsion solvent evaporation technique. Surface carboxylic acid groups were used to covalently attach amine-terminated polyethylene glycol (PEG) of different molecular weights. We investigated the effect of grafting CNPs with PEG chains on their intrinsic optical properties, protein adsorption behavior and uptake by representative brain cell lines.

FINDINGS

PEGylation did not affect the optical properties and biocompatibility of our CNPs. Moreover, a significant decrease in protein corona formation and unspecific uptake in central nervous system cell lines, depending on PEG chain length, was observed. This is the first report indicating that PEGylation does not affect the CNPs role as excellent bioimaging tools and can be adapted to tune biological interactions with brain cells.

Molecular Dynamics Insights into Water-Parylene C Interface: Relevance of Oxygen Plasma Treatment for Biocompatibility

Solid-water interfaces play a vital role in biomaterials science because they provide a natural playground for most biochemical reactions and physiological processes. In the study, fully atomistic molecular dynamics simulations were performed to investigate interactions between water molecules and several surfaces modeling for unmodified and modified parylene C surfaces. The introduction of -OH, -CHO, and -COOH to the surface and alterations in their coverage significantly influence the energetics of interactions between water molecules and the polymer surface. The theoretical studies were complemented with experimental measurements of contact angle, surface free energy, and imaging of osteoblast cells adhesion. Both MD simulations and experiments demonstrate that the optimal interface, in terms of biocompatibility, is obtained when 60% of native -Cl groups of parylene C surface is exchanged for -OH groups. By exploring idealized models of bare and functionalized parylene C, we obtained a unique insight into molecular interactions at the water-polymer interface. The calculated values of interaction energy components (electrostatic and dispersive) correspond well with the experimentally determined values of surface free energy components (polar and dispersive), revealing their optimal ratio for cells adhesion. The results are discussed in the context of controllable tuning and functionalization of implant polymeric coating toward improved biocompatibility.

Polydopamine-functionalized polymer particles as templates for mineralization of hydroxyapatite: biomimetic and in vitro bioactivity

Polydopamine-assisted biomimetic mineralization was presented to fabricate hydroxyapatite-based, organic–inorganic hybrid materials with excellent biocompatibility.

Phosphonic Acid-Functionalized Polyurethane Dispersions with Improved Adhesion Properties

A facile route to phosphorus-functionalized polyurethane dispersions (P-PUDs) with improved adhesion properties is presented. (Bis)phosphonic acid moieties serve as adhesion promoting sites that are covalently attached via an end-capping reaction to isocyanate-reactive polyurethane particles under aqueous conditions. The synthetic approach circumvents solubility issues, offers great flexibility in terms of polyurethane composition, and allows for the synthesis of semicrystalline systems with thermomechanical response due to reversible physical cross-linking. Differential scanning calorimetry (DSC) is used to investigate the effect of functionalization on the semicrystallinity. The end-capping conversion was determined via inductively-coupled plasma optical emission spectroscopy (ICP-OES) and was surprisingly found to be almost independent of the stoichiometry of reaction, suggesting an adsorption-dominated process. Particle charge detection (PCD) experiments reveal that a dense surface coverage of phosphonic acid groups can be attained and that, at high functionalization degrees, the phosphonic adhesion moieties are partially dragged inside the colloidal P-PUD particle. Quartz crystal microbalance with dissipation (QCMD) investigations conducted with hydroxyapatite (HAP) and stainless steel sensors as model surfaces show a greatly enhanced affinity of the aqueous P-PUDs and furthermore indicate polymer chain rearrangements and autonomous film formation under wet conditions. Due to their facile synthesis, significantly improved adhesion, and variable film properties, P-PUD systems such as the one described here are believed to be of great interest for multiple applications, e.g., adhesives, paints, anticorrosion, or dentistry.

Bioactivity response of Ta1-xOx coatings deposited by reactive DC magnetron sputtering

The use of dental implants is sometimes accompanied by failure due to periimplantitis disease and subsequently poor esthetics when soft-hard tissue margin recedes. As a consequence, further research is needed for developing new bioactive surfaces able to enhance the osseous growth. Tantalum (Ta) is a promising material for dental implants since, comparing with titanium (Ti), it is bioactive and has an interesting chemistry which promotes the osseointegration. Another promising approach for implantology is the development of implants with oxidized surfaces since bone progenitor cells interact with the oxide layer forming a diffusion zone due to its ability to bind with calcium which promotes a stronger bond. In the present report Ta-based coatings were deposited by reactive DC magnetron sputtering onto Ti CP substrates in an Ar+O2 atmosphere. In order to assess the osteoconductive response of the studied materials, contact angle and in vitro tests of the samples immersed in Simulated Body Fluid (SBF) were performed. Structural results showed that oxide phases where achieved with larger amounts of oxygen (70 at.% O). More compact and smooth coatings were deposited by increasing the oxygen content. The as-deposited Ta coating presented the most hydrophobic character (100°); with increasing oxygen amount contact angles progressively diminished, down to the lowest measured value, 63°. The higher wettability is also accompanied by an increase on the surface energy. Bioactivity tests demonstrated that highest O-content coating, in good agreement with wettability and surface energy values, showed an increased affinity for apatite adhesion, with higher Ca/P ratio formation, when compared to the bare Ti substrates.

Poly(vinylphosphonic acid) (PVPA) on titanium alloy acting as effective cartilage-like superlubricity coatings

Poly(vinylphosphonic acid) (PVPA) is a type of hydrophilic polymer that can be used in surface modifications. In our study, PVPA coatings were formed on the surfaces of titanium alloy (Ti6Al4V) using a simple and novel method to achieve efficient lubrication at friction interfaces. The composition and 3D skeletal structure of the PVPA coatings were confirmed by X-ray photoelectron spectroscopy (XPS), focused ion beam/scanning electron microscopy (FIB/SEM), and solid-state nuclear magnetic resonance (NMR). The PVPA-modified Ti6Al4V/polytetrafluoroethylene (PTFE) interface shows a superlow friction coefficient (approximately 0.006) for at least 8 h under a contact pressure of 44.2 MPa (initial pressure), which means it falls into the superlubricity regime. Moreover, wear on the surfaces of both the Ti6Al4V and PTFE after the tribological experiment is superlow. It is proposed that the 3D skeletal structure of the PVPA coating and fluid-like manner at friction interfaces owing to the fast exchange of water molecules are the main factors accounting for the superlow friction and wear. The PVPA-modified Ti6Al4V has the potential uses in artificial cervical discs.

Wetting behavior of ionic liquid on mesoporous titanium dioxide surface by atomic force microscopy

Ionic liquids based on 1-butyl-3-methylimidazolium hexafluoro-phosphate (ILs [Bmim][PF6]) has been employed to wet the mesoporous and dense titanium dioxide (TiO2) films. It has been found from atomic force microscopy (AFM) analysis that ILs [Bmim][PF6] can form a wetting phase on mesoporous TiO2 films, but nonwetting and sphere shaped droplets on dense films. AFM topography, phase images, and adhesion measurements suggest a remarkable dependence of wetting ILs [Bmim][PF6] films on the TiO2 porous geometry. On mesoporous TiO2 films, the adhesive force of ILs [Bmim][PF6] reaches at 40 nN, but only 4 nN on dense TiO2 films. The weak interacting ILs [Bmim][PF6] on dense TiO2 films forms rounded liquid spheres (contact angle as 40°), which helps to reduce friction locally but not on the whole surface. The stronger adhesive force on mesoporous TiO2 films makes ILs [Bmim][PF6] adhere to the surface tightly (contact angle as 5°), and this feature remains after five months. The stable spreading ILs [Bmim][PF6] films provide low friction coefficient (0.0025), large wetting areas, and short CO2 diffusion distance on the whole mesoporous TiO2 surface, avoiding the significant decelerating effect through equilibrium limitations to enable CO2 capture rate up to 1.6 and 10 times faster than that on dense TiO2 and pure ILs, respectively. And importantly, ILs wetted on mesoporous TiO2 shorten the time reaching to the maximum adsorption rate (2.8 min), faster than that on mesoporous TiO2 (6.1 min), and dense TiO2 (11.2 min). This work provides an important guidance for the improvement of the efficiency of CO2 capture, gas separation, and the lubrication of micro/nanoelectromechanical systems (M/NEMs).

UV-induced functionalization of poly(divinylbenzene) nanoparticlesvia efficient [2 + 2]-photocycloadditions

A facile postmodification strategy for the surface functionalization of nanoparticles is presented based on [2 + 2] photoconjugation with particles made from miniemulsion polymerization of divinylbenzene.

Simple physical approach to reducing frictional and adhesive forces on a TiO2 surface via creating heterogeneous nanopores

A simple physical strategy to reduce the frictional and adhesive forces on TiO(2) films was proposed by constructing mesoporous TiO(2) films with heterogeneously distributed nanopores on the film surfaces. In comparison, TiO(2) films with densely packed nanoparticles were also prepared. The crystal structure and morphology of the films were characterized with Raman spectroscopy, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). It was found that the TiO(2)(B) phase exists in the mesoporuos TiO(2) films but not in the densely packed films. The existence of TiO(2)(B) plays a significant role in creating and maintaining the nanopores in the mesoporous TiO(2) films. The frictional and adhesive forces were measured on both films using AFM. The mesoporous films exhibit two typical adhesion forces of around 3 and 12 nN in the force distribution profile whereas the densely packed films show only one around 12 nN. The frictional coefficients were 2.6 × 10(-3) and 6.7 × 10(-2) for the mesoporous and densely packed TiO(2) films, respectively. A model based on the atomic structures of a thin film of water molecules adsorbed on TiO(2) surfaces leading to hydrophobic effects was proposed to understand the lower frictional and adhesive forces observed on the mesoporous TiO(2) films. This simple physical approach to reducing the frictional and adhesive forces on TiO(2) films could have broad applications to a variety of surface coatings.

Functionalized polystyrene nanoparticles trigger human dendritic cell maturation resulting in enhanced CD4+ T cell activation

Nanoparticles (NP) represent a promising tool for biomedical applications. Here, sulfonate- and phosphonate-functionalized polystyrene NP are analyzed for their interaction with human monocyte-derived dendritic cells (DC). Immature dendritic cells (iDC) display a higher time- and dose-dependent uptake of functionalized polystyrene NP compared to mature dendritic cells (mDC). Notably, NP induce an enhanced maturation of iDC but not of mDC (upregulation of stimulatory molecules and cytokines). NP-triggered maturation results in a significantly enhanced T cell stimulatory capacity (increased CD4(+) T cell proliferation and IFN-γ production), indicating a shift to a pronounced Th1 response. Immunomodulatory properties of NP may be a useful strategy for strengthening the efficacy of NP-based approaches in immunotherapy.

Nanoparticles and their potential for application in bone

Biomaterials are commonly applied in regenerative therapy and tissue engineering in bone, and have been substantially refined in recent years. Thereby, research approaches focus more and more on nanoparticles, which have great potential for a variety of applications. Generally, nanoparticles interact distinctively with bone cells and tissue, depending on their composition, size, and shape. Therefore, detailed analyses of nanoparticle effects on cellular functions have been performed to select the most suitable candidates for supporting bone regeneration. This review will highlight potential nanoparticle applications in bone, focusing on cell labeling as well as drug and gene delivery. Labeling, eg, of mesenchymal stem cells, which display exceptional regenerative potential, makes monitoring and evaluation of cell therapy approaches possible. By including bioactive molecules in nanoparticles, locally and temporally controlled support of tissue regeneration is feasible, eg, to directly influence osteoblast differentiation or excessive osteoclast behavior. In addition, the delivery of genetic material with nanoparticulate carriers offers the possibility of overcoming certain disadvantages of standard protein delivery approaches, such as aggregation in the bloodstream during systemic therapy. Moreover, nanoparticles are already clinically applied in cancer treatment. Thus, corresponding efforts could lead to new therapeutic strategies to improve bone regeneration or to treat bone disorders.

Design, synthesis, and miniemulsion polymerization of new phosphonate surfmers and application studies of the resulting nanoparticles as model systems for biomimetic mineralization and cellular uptake

Heterophase polymerizations have gained increasing attention in the past decades, especially as the decoration and functionalization of the particle surface for further applications gets more and more into focus. One promising approach for the functionalization exclusively on the particle surface is the use of surfmers (surfactant and monomer). Herein, we present the synthesis of a new family of surfmers and their use for decorating nanoparticles with phosphonate groups through miniemulsion polymerization. Furthermore the synthesis of a dye-labeled functional surfmer provided an elegant manner to evaluate and get deeper insights about its copolymerization. Additionally, potential applications of the synthesized particles in biological studies as well as their use as template for biomimetic mineralization are presented.