Antibacterial Calcium Phosphate Coatings for Biomedical Applications Fabricated via Micro-Arc Oxidation.

A promising method for improving the functional properties of calcium-phosphate coatings is the incorporation of various antibacterial additives into their structure. The microbial contamination of a superficial wound is inevitable, even if the rules of asepsis and antisepsis are optimally applied. One of the main problems is that bacteria often become resistant to antibiotics over time. However, this does not apply to certain elements, chemical compounds and drugs with antimicrobial properties. In this study, the fabrication and properties of zinc-containing calcium-phosphate coatings that were formed via micro-arc oxidation from three different electrolyte solutions are investigated. The first electrolyte is based on calcium oxide, the second on hydroxyapatite and the third on calcium acetate. By adding zinc oxide to the three electrolyte solutions, antibacterial properties of the coatings are achieved. Although the same amount of zinc oxide has been added to each electrolyte solution, the zinc concentration in the coatings obtained vary greatly. Furthermore, this study investigates the morphology, structure and chemical composition of the coatings. The antibacterial properties of the zinc-containing coatings were tested toward three strains of bacteria-Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. Coatings of calcium acetate and zinc oxide contained the highest amount of zinc and displayed the highest zinc release. Moreover, coatings containing hydroxyapatite and zinc oxide show the highest antibacterial activity toward Pseudomonas aeruginosa, and coatings containing calcium acetate and zinc oxide show the highest antibacterial activities toward Staphylococcus aureus and methicillin-resistant Staphylococcus aureus.

Transition Metal-Decorated Mg12O12 Nanoclusters as Biosensors and Efficient Drug Carriers for the Metformin Anticancer Drug.

Drug carriers have been designed and investigated remarkably due to their effective use in the modern medication process. In this study, the decoration of the Mg12O12 nanocluster has been done with transition metals (Ni and Zn) for effective adsorption of metformin (anticancer drug). Decoration of Ni and Zn on a nanocluster allows two geometries, and similarly, the adsorption of metformin also provides two geometries. Density functional theory and time-dependent density functional theory have been employed at the B3LYP with 6-311G(d,p) level. The decoration of Ni and Zn offers good attachment and detachment of the drug, which is observed from their good adsorption energy values. Further, the reduction in the energy band gap is noted in the metformin-adsorbed nanocluster, which allows high charge transfer from a lower energy level to a high energy level. The drug carrier systems show an efficient working mechanism in a water solvent with the visible-light absorption range. Natural bonding orbital and dipole moment values suggested that the adsorption of the metformin causes charge separation in these systems. Moreover, low values of chemical softness with a high electrophilic index recommended that these systems are naturally stable with the least reactivity. Thus, we offer novel kinds of Ni- and Zn-decorated Mg12O12 nanoclusters as efficient carriers for metformin and also recommend them to experimentalists for the future development of drug carriers.

Surface Modification of Additively Fabricated Titanium-Based Implants by Means of Bioactive Micro-Arc Oxidation Coatings for Bone Replacement.

In this work, the micro-arc oxidation method is used to fabricate surface-modified complex-structured titanium implant coatings to improve biocompatibility. Depending on the utilized electrolyte solution and micro-arc oxidation process parameters, three different types of coatings (one of them-oxide, another two-calcium phosphates) were obtained, differing in their coating thickness, crystallite phase composition and, thus, with a significantly different biocompatibility. An analytical approach based on X-ray computed tomography utilizing software-aided coating recognition is employed in this work to reveal their structural uniformity. Electrochemical studies prove that the coatings exhibit varying levels of corrosion protection. In vitro and in vivo experiments of the three different micro-arc oxidation coatings prove high biocompatibility towards adult stem cells (investigation of cell adhesion, proliferation and osteogenic differentiation), as well as in vivo biocompatibility (including histological analysis). These results demonstrate superior biological properties compared to unmodified titanium surfaces. The ratio of calcium and phosphorus in coatings, as well as their phase composition, have a great influence on the biological response of the coatings.

Biodegradable magnesium fuel-based Janus micromotors with surfactant induced motion direction reversal.

The speed and motion directionality of bubble-propelled micromotors is dependent on bubble lifetime, bubble formation frequency and bubble stabilization. Absence and presence of bubble stabilizing agents should significantly influence speed and propulsion pattern of a micromotor, especially for fast-diffusing molecules like hydrogen. This study demonstrates a fully biodegradable Janus structured micromotor, propelled by hydrogen bubbles generated by the chemical reaction between hydrochloric acid and magnesium. Six different concentrations of hydrochloric acid and five different concentrations of the surfactant Triton X-100 were tested, which also cover the critical micelle concentration at a pH corresponding to an empty stomach. The Janus micromotor reverses its propulsion direction depending on the availability and concentration of a surfactant. Upon surfactant-free condition, the Janus micromotor is propelled by bubble cavitation, causing the micromotor to be pulled at high speed for short time intervals into the direction of the imploding bubble and thus backwards. In case of available surfactant above the critical micelle concentration, the Janus micromotor is pushed forward by the generated bubbles, which emerge at high frequency and form a bubble trail. The finding of the propulsion direction reversal effect demonstrates the importance to investigate the motion properties of artificial micromotors in a variety of different environments prior to application, especially with surfactants, since biological media often contain large amounts of surface-active components.

Nitrogen-doped titanium dioxide films fabricated via magnetron sputtering for vascular stent biocompatibility improvement.

Nowadays, vascular stents are commonly used to treat cardiovascular diseases. This article focuses on the influence of nitrogen doping of titanium dioxide thin films, utilized for coating metallic stents to improve their biological properties and biocompatibility. The hereby-investigated titanium oxide thin films are fabricated by magnetron sputtering in a reactive gas atmosphere consisting of argon and oxygen in the first case and argon, nitrogen and oxygen in the second case. Control of the nitrogen and oxygen gas flow rates, and hence their mixing ratios, allows adjustment of the nitrogen-doping level within the titanium dioxide thin films. A correlation of the thin film internal structure on the in vitro behavior of human mesenchymal stem cells derived from adipose tissue is hereby demonstrated. Different nitrogen doping levels affect the surface energy, the wettability, the cell adhesion and thus the cellular proliferation on top of the thin films. The surface colonization of cells on titanium dioxide thin films decreases up to a nitrogen-doping level of âˆ¼ 3.75 at.%, which is associated with a decreasing polar component of the surface energy. For non-doped titanium dioxide thin films, a weak chondrogenesis of adult human adipose-derived mesenchymal stem cells with lower chondrogenic differentiation compared to glass is observed. An increasing nitrogen-doping level leads to linear increase in the chondrogenic differentiation rate, which is comparable to the control value of uncoated glass. Other investigated differentiated cell types do not display this behavior.

Stimuli-Responsive Microarray Films for Real-Time Sensing of Surrounding Media, Temperature, and Solution Properties via Diffraction Patterns.

Stimuli-responsive polymers have attracted increasing attention over the years due to their ability to alter physiochemical properties upon external stimuli. However, many stimuli-responsive polymer-based sensors require specialized and expensive equipment, which limits their applications. Here an inexpensive and portable sensing platform of novel microarray films made of stimuli-responsive polymers is introduced for the real-time sensing of various environmental changes. When illuminated by laser light, microarray films generate diffraction patterns that can reflect and magnify variations of the periodical microstructure induced by surrounding invisible parameters in real time. Stimuli-responsive polyelectrolyte complexes are structured into micropillar arrays to monitor the pH variation and the presence of calcium ions based on reversible swelling/shrinking behaviors of the polymers. A pH hysteretic effect of the selected polyelectrolyte pair is determined and explained. Furthermore, polycaprolactone microchamber arrays are fabricated and display a thermal-driven structural change, which is exploited for photonic threshold temperature detection. Experimentally observed diffraction patterns are additionally compared with rigorous coupled-wave analysis simulations that prove that induced diffraction pattern alterations are solely caused by geometrical microstructure changes. Microarray-based diffraction patterns are a novel sensing platform with versatile sensing capabilities that will likely pave the way for the use of microarray structures as photonic sensors.

Laser-triggered drug release from polymeric 3-D micro-structured films via optical fibers.

Photosensitive polymeric three-dimensional microstructured film (PTMF) is a new type of patterned polymeric films functionalized with an array of sealed hollow 3D containers. The microstructured system with enclosed chemicals provides a tool for the even distribution of biologically active substances on a given surface that can be deposited on medical implants or used as a cells substrate. In this work, we proposed a way for photothermally activating and releasing encapsulated substances at picogram amounts from the PTMF surface in different environments using laser radiation delivered with a multimode optical fiber. The photosensitive PTMFs were prepared by the layer-by-layer (LbL) assembly from alternatively charged polyelectrolytes followed by covering with a layer of hydrophobic polylactic acid (PLA) and a layer of gold nanoparticles (AuNPs). Moreover, the typical photothermal cargo release amounts were determined on the surface of the PTMF for a range of laser powers delivered to films placed in the air, deionized (DI) water, and 1% agarose gel. The agarose gel was used as a soft tissue model for developing a technique for the laser activation of PTMFs deep in tissues using optical waveguides. The number of PTMF chambers activated by a near-infrared (NIR) laser beam was evaluated as the function of optical parameters.

Microchamber arrays made of biodegradable polymers for enzymatic release of small hydrophilic cargos.

The encapsulation of small hydrophilic molecules and response to specific biological triggers in a controlled manner have become two of the significant challenges in biomedical research, in particular in the field of localized drug delivery and biosensing. This work reports the fabrication of free-standing microchamber array films made of biodegradable polymers for the encapsulation and enzymatically triggered release of small hydrophilic molecules. Polycaprolactone (PCL) microchamber arrays were demonstrated to fully biodegrade within 5 hours of exposure to lipase from Pseudomonas cepacia (lipase PS) at a concentration of 0.5 mg ml-1, with lower concentrations producing correspondingly longer degradation times. The gradual process of deterioration was real-time monitored utilising laser Fraunhofer diffraction patterns. Additionally, a small hydrophilic molecule, 5(6)-carboxyfluorescein (CF), was loaded into the PCL microchamber arrays in a dry state; however, the substantial permeability of the PCL film led to leakage of the dye molecules. Consequently, polylactic acid (PLA) was blended with PCL to reduce its permeability, enabling blended PCL-PLA (1 : 2 ratio correspondingly) microchamber arrays to trap the small hydrophilic molecule CF. PCL-PLA (1 : 2) microchamber arrays hold potential for controlled release under the catalysis of lipase within 26 hours. Additionally, it is calculated that approximately 11 pg of CF dye crystals was loaded into individual microchambers of 10 µm size, indicating that the microchamber array films could yield a highly efficient encapsulation.

pH dependent degradation properties of lactide based 3D microchamber arrays for sustained cargo release.

Encapsulation of small water soluble molecules is important in a large variety of applications, ranging from medical substance releasing implants in the field of medicine over release of catalytically active substances in the field of chemical processing to anti-corrosion agents in industry. In this work polylactic acid (PLA) based hollow-structured microchamber (MC) arrays are fabricated via one-step dip coating of a silicone rubber stamp into PLA solution. These PLA MCs are able to retain small water soluble molecules (Rhodamine B) stably entrapped within aqueous environments. It is shown, that degradation of PLA MCs strongly depends on environmental conditions like surrounding pH and follows first order degradation kinetics. This pH dependent PLA MC degradation can be utilized to control the release kinetics of encapsulated cargo.

Alginate Microparticle Arrays as Self-Polishing Bio-Fouling Release Coatings.

Biofouling is a severe problem of any water borne structure. Since the ban of tin-organic compounds and expected bans of other poisonous chemical formulations in the near future, replacement of these compounds are sought. This study investigates antibiofouling properties of micro- and nanostructured alginate layer films. Alginate is a natural product from brown algae and was in this study electro-sprayed and crosslinked with divalent calcium and copper ions to produce homogeneous micro- and nanoparticles. These calcium- and copper-alginate particles were assembled into micro- and nanostructured layer films and the antifouling properties of these low elastic modulus, hydrophilic, biodegradable system were evaluated with the microalgae chlorella. Comparison with pristine glass slides, smooth copper- and calcium alginate bulk films was performed. The comparison shows less biofouling for smooth bulk films compared to micro-nanostructured alginate, while all alginate systems are less bio-fouled on long timescales compared to pristine glass.

Magnetically-guided hydrogel capsule motors produced via ultrasound assisted hydrodynamic electrospray ionization jetting.

Hydrogel capsules are a potential candidate for drug delivery and an interesting alternative to polyelectrolyte multilayer capsules which are under investigation since 20 years. Recently introduced polyelectrolyte complex capsules produced by spraying are non-biodegradable and not biocompatible, which limits their practical application, while biodegradable alginate capsules require complex coaxial electrospray ionization jetting. In this work, biodegradable alginate capsules cross-linked by calcium are successfully produced by hydrodynamic electrospray ionization jetting with the assistance of low frequency ultrasound. The size and shape of most capsules show significant differences with respect to different spraying distance, spraying mode, electrode shape and spraying concentration. Capsules in the shape of vase, mushrooms and spheres were successfully produced. Average capsule size can be adjusted from 10 µm to 2 mm. These capsules are used to encapsulate a model drug. Encapsulated paramagnetic particles enable defined directional motion under the propulsion of a rotating magnetic field, while model drugs can be released by ultrasound.

Polylactic acid sealed polyelectrolyte complex microcontainers for controlled encapsulation and NIR-Laser based release of cargo.

Surface mediated drug delivery is important for a large variety of applications, especially in medicine to control cell growth, prevent blood platelet activation on implants or for self-disinfecting devices (e.g. catheters). In industrial applications, controlled release of substances from surfaces is needed in a broad range of applications from anti-corrosion systems to anti-biofouling. Polyelectrolyte multilayers (PEM) based microcontainers (MCs) require several days production time, while MCs composed out of polylactic acid (PLA) are entirely hydrophobic, offering no functionality. We hereby present an approach to fabricate PLA coated synthetic as well as biopolymer based biodegradable polyelectrolyte complex MCs able to encapsulate small hydrophilic cargo within less than one hour. The chambers facilitate laser controlled release of cargo within submerged conditions.

Magnetically-propelled hydrogel particle motors produced by ultrasound assisted hydrodynamic electrospray ionization jetting.

One of the most promising future applications of hydrogels is drug delivery. The hydrogels act as a biomedical cargo model to reach the target and release drugs to cure diseases. This application requires no side effects of the hydrogel and the ability to pass through porous media (e.g. membranes, interstitial tissue etc.) with nanoscaled channels. At the same time, the hydrogel must be mass-producible in an economic way. In this work, we show that hydrodynamic electrospray ionization jetting combined with ultrasound can fulfill these high requirements. This method can produce mucoadhesive micro-/nano-particles, which are small enough to pass through the gastrointestinal epithelium. The average size of the produced particles is exactly predictable by controlling the spraying distance, spraying mode, alginate concentration, ultrasound bath frequency and counter electrode shape. These micro-/nano-particles are loaded with biocompatible magnetite nanoparticles, and propelled by a rotating magnetic field between 5 to 20 m T and a frequency from 1 Hz to 100 Hz. These rotating micro-/nano-particle motors perform directional motion in solution, offering a promising possibility for magnetically controlled drug delivery.

Elastic to Plastic Deformation in Uniaxially Stressed Polylelectrolyte Multilayer Films.

Polyelectrolyte multilayer (PEM) are thin polymeric films produced by alternating adsorption of positively and negatively charged polyelectrolytes (PE) on a substrate. These films are considered drug delivery agents as well as coating material for implants, due to their antibiofouling and biologically benign properties. For these reasons the film mechanical properties as well as response to mechanical stress are important measurement parameters. Especially intriguing is the correlation of the mechanical properties of PEM on macroscopic level with the structure of PEM on molecular level, which is addressed here for the first time. This study investigates PEM from PDADMA/PSS produced by spraying technique with neutron and X-ray reflectometry. Reflectometry technique provides precise information on thickness and density (i.e., electron density or scattering length density, respectively), and, this way, allows to conclude on changes in film composition. Thus, neutron and X-ray reflectometry technique is suitable to investigate the overall and the internal transformations, which PEM films might undergo upon exposure to mechanical load. During uniaxial elongation two regimes of PEM-deformation can be observed: An elastic regime at small elongations (below ca. 0.2%), which is characterized by a reversible change of film thickness, and a plastic regime with a permanent change above this limit. Both regimes have in common, that the mechanical load induces an increase of the film thickness, which is accompanied by an uptake of water from the surrounding atmosphere. The strain causes a molecular rearrangement within the PEM-structure of stratified layers, which, even in elastic regime, is permanent, although the thickness change remains reversible.

In-situ NIR-laser mediated bioactive substance delivery to single cell for EGFP expression based on biocompatible microchamber-arrays.

Controlled drug delivery and gene expression is required for a large variety of applications including cancer therapy, wound healing, cell migration, cell modification, cell-analysis, reproductive and regenerative medicine. Controlled delivery of precise amounts of drugs to a single cell is especially interesting for cell and tissue engineering as well as therapeutics and has until now required the application of micro-pipettes, precisely placed dispersed drug delivery vehicles, or injections close to or into the cell. Here we present surface bound micro-chamber arrays able to store small hydrophilic molecules for prolonged times in subaqueous conditions supporting spatiotemporal near infrared laser mediated release. The micro-chambers (MCs) are composed of biocompatible and biodegradable polylactic acid (PLA). Biocompatible gold nanoparticles are employed as light harvesting agents to facilitate photothermal MC opening. The degree of photothermal heating is determined by numerical simulations utilizing optical properties of the MC, and confirmed by Brownian motion measurements of laser-irradiated micro-particles exhibiting similar optical properties like the MCs. The amount of bioactive small molecular cargo (doxycycline) from local release is determined by fluorescence spectroscopy and gene expression in isolated C2C12 cells via enhanced green fluorescent protein (EGFP) biosynthesis.

Hydrodynamic electrospray ionization jetting of calcium alginate particles: effect of spray-mode, spraying distance and concentration.

Hydrodynamic electrospray ionization jetting was applied for generating and characterizing calcium cross-linked alginate microparticles. These microparticles show different diameters and aspect ratios for three electrospray modes (dripping, conejet and multijet modes), four spraying distances (5, 10, 15 and 20 cm), and six spraying concentrations. Comparing the three different electrospray modes, we found that the conejet mode results in the smallest particle diameters, lowest aspect ratio and smallest variations over the parameter space mentioned above. For all spraying modes, the resultant particle diameters become independent of the spraying distance at a sprayed solute concentration ≥ 2.5%. The aspect ratio of microparticles varies significantly for different spraying modes and distances. An increasing aspect ratio of all spray modes was determined for sodium alginate spraying concentrations ≤ 1.5% and spraying distances of 20 cm; this phenomenon can be explained with the chain ejection effect. This systematic investigation offers a basic database for industrial applications of hydrodynamic electrospray ionization.

Polylactic acid nano- and microchamber arrays for encapsulation of small hydrophilic molecules featuring drug release via high intensity focused ultrasound.

Long term encapsulation combined with spatiotemporal release for a precisely defined quantity of small hydrophilic molecules on demand remains a challenge in various fields ranging from medical drug delivery, controlled release of catalysts to industrial anti-corrosion systems. Free-standing individually sealed polylactic acid (PLA) nano- and microchamber arrays were produced by one-step dip-coating a PDMS stamp into PLA solution for 5 s followed by drying under ambient conditions. The wall thickness of these hydrophobic nano-microchambers is tunable from 150 nm to 7 µm by varying the PLA solution concentration. Furthermore, small hydrophilic molecules were successfully in situ precipitated within individual microchambers in the course of solvent evaporation after sonicating the PLA@PDMS stamp to remove air-bubbles and to load the active substance containing solvent. The cargo capacity of single chambers was determined to be in the range of several picograms, while it amounts to several micrograms per cm2. Two different methods for sealing chambers were compared: microcontact printing versus dip-coating whereby microcontact printing onto a flat PLA sheet allows for entrapment of micro-air-bubbles enabling microchambers with both ultrasound responsiveness and reduced permeability. Cargo release triggered by external high intensity focused ultrasound (HIFU) stimuli is demonstrated by experiment and compared with numerical simulations.

Polylactic Acid Sealed Polyelectrolyte Multilayer Microchambers for Entrapment of Salts and Small Hydrophilic Molecules Precipitates.

Efficient depot systems for entrapment and storage of small water-soluble molecules are of high demand for wide variety of applications ranging from implant based drug delivery in medicine and catalysis in chemical processes to anticorrosive systems in industry where surface-mediated active component delivery is required on a time and site specific manner. This work reports the fabrication of individually sealed hollow-structured polyelectrolyte multilayer (PEM) microchamber arrays based on layer-by-layer self-assembly as scaffolds and microcontact printing. These PEM chambers are composed out of biocompatible polyelectrolytes and sealed by a monolayer of hydrophobic biocompatible and biodegradable polylactic acid (PLA). Coating the chambers with hydrophobic PLA allows for entrapment of a microair-bubble in each chamber that seals and hence drastically reduces the PEM permeability. PLA@PEM microchambers are proven to enable prolonged subaqueous storage of small hydrophilic salts and molecules such as crystalline NaCl, doxicycline, and fluorescent dye rhodamine B. The presented microchambers are able to entrap air bubbles and demonstrate a novel strategy for entrapment, storage, and protection of micropackaged water-soluble substances in precipitated form. These chambers allow triggered release as demonstrated by ultrasound responsiveness of the chambers. Low-frequency ultrasound exposure is utilized for microchamber opening and payload release.

Forecastable and Guidable Bubble-Propelled Microplate Motors for Cell Transport.

Cell transport is important to renew body functions and organs with stem cells, or to attack cancer cells with immune cells. The main hindrances of this method are the lack of understanding of cell motion as well as proper transport systems. In this publication, bubble-propelled polyelectrolyte microplates are used for controlled transport and guidance of HeLa cells. Cells survive attachment on the microplates and up to 22 min in 5% hydrogen peroxide solution. They can be guided by a magnetic field whereby increased friction of cells attached to microplates decreases the speed by 90% compared to pristine microplates. The motion direction of the cell-motor system is easier to predict due to the cell being opposite to the bubbles.

Polybenzoxazole Nanofiber-Reinforced Moisture-Responsive Soft Actuators.

Hydromorphic biological systems, such as morning glory flowers, pinecones, and awns, have inspired researchers to design moisture-sensitive soft actuators capable of directly converting the change of moisture into motion or mechanical work. Here, we report a moisture-sensitive poly(p-phenylene benzobisoxazole) nanofiber (PBONF)-reinforced carbon nanotube/poly(vinyl alcohol) (CNT/PVA) bilayer soft actuator with fine performance on conductivity and mechanical properties. The embedded PBONFs not only assist CNTs to form a continuous, conductive film, but also enhance the mechanical performance of the actuators. The PBONF-reinforced CNT/PVA bilayer actuators can unsymmetrically adsorb and desorb water, resulting in a reversible deformation. More importantly, the actuators show a pronounced increase of conductivity due to the deformation induced by the moisture change, which allows the integration of a moisture-sensitive actuator and a humidity sensor. Upon changing the environmental humidity, the actuators can respond by the deformation for shielding and report the humidity change in a visual manner, which has been demonstrated by a tweezer and a curtain. Such nanofiber-reinforced bilayer actuators with the sensing capability should hold considerable promise for the applications such as soft robots, sensors, intelligent switches, integrated devices, and material storage.