Multilayer coatings on biomaterials for control of MG-63 osteoblast adhesion and growth

Anti-marine biofouling adhesion performance and mechanism of PDMS fouling-release coating containing PS-PEG hydrogel

Polystyrene microspheres compounded with polyethylene glycol-based hydrogel (PS-PEG)/polydimethylsiloxane (PDMS) coatings were prepared using the physical blending method. The chemical structure, surface and interface properties, interlayer adhesion, and tensile properties were tested in this paper. Furthermore, the antifouling performance was evaluated through bovine serum albumin fluorescent protein adsorption testing, marine bacteria adhesion testing, and benthic diatom adhesion testing. The results showed that the coating performance was best when 20 wt% PS-PEG hydrogel was added. Its surface energy was only 19.21 mJ/m2, the maximum breaking strength was 1.24 MPa, the maximum elongation rate was 675 %, the elastic modulus was 2.53 MPa, and the anti-stripping rate was 100 %. In addition, the coating with added 20 wt% PS-PEG hydrogel bacterial adherence rate was 5.36 % and 2.45 % after rinsing and washing, respectively, and the removal rate was 54.29 %. In the benthic diatom adhesion test, the chlorophyll concentration a-value was only 0.0017 mg/L after washing with added 20 wt% hydrogel, and the protein desorption rate was 84.19 % higher than PDMS in the fluorescent protein adsorption test. This coating has the 'low adhesion' and 'desorption' characteristics in the three growth stages of biofouling. Meanwhile, the low surface energy of the silicone is stable, and the hydrogel also dynamically migrates to the surface to gradually form a hydration layer, both are synergistic. When 20 wt% PS-PEG hydrogel was added, the coating demonstrated excellent antifouling performance due to its high hydration layer, low surface energy, high elasticity, and high interlayer adhesion. This research is expected to contribute to the practical applications of hydrogel coatings in marine antifouling.

Polyelectrolyte-Coated Mesoporous Bioactive Glasses via Layer-by-Layer Deposition for Sustained Co-Delivery of Therapeutic Ions and Drugs

In the field of bone regeneration, considerable attention has been addressed towards the use of mesoporous bioactive glasses (MBGs), as multifunctional therapeutic platforms for advanced medical devices. In fact, their extremely high exposed surface area and pore volume allow to load and the release of several drugs, while their framework can be enriched with specific therapeutic ions allowing to boost the tissue regeneration. However, due to the open and easily accessible mesopore structure of MBG, the release of the incorporated therapeutic molecules shows an initial burst effect leading to unsuitable release kinetics. Hence, a still open challenge in the design of drug delivery systems based on MBGs is the control of their release behavior. In this work, Layer-by-layer (LbL) deposition of polyelectrolyte multi-layers was exploited as a powerful and versatile technique for coating the surface of Cu-substituted MBG nanoparticles with innovative multifunctional drug delivery systems for co-releasing of therapeutic copper ions (exerting pro-angiogenic and anti-bacterial effects) and an anti-inflammatory drug (ibuprofen). Two different routes were investigated: in the first strategy, chitosan and alginate were assembled by forming the multi-layered surface, and, successively, ibuprofen was loaded by incipient wetness impregnation, while in the second approach, alginate was replaced by ibuprofen, introduced as polyelectrolyte layer. Zeta-potential, TGA and FT-IR spectroscopy were measured after the addition of each polyelectrolyte layer, confirming the occurrence of the stepwise deposition. In addition, the in vitro bioactivity and the ability to modulate the release of the cargo were evaluated. The polyelectrolyte coated-MBGs were proved to retain the peculiar ability to induce hydroxyapatite formation after 7 days of soaking in Simulated Body Fluid. Both copper ions and ibuprofen were co-released over time, showing a sustained release profile up to 14 days and 24 h, respectively, with a significantly lower burst release compared to the bare MBG particles.

The Anchorage of Bone Cells onto an Yttria-Stabilized Zirconia Surface with Mild Nano-Micro Curved Profiles

The high biocompatibility, good mechanical properties, and perfect esthetics of ceramic dental materials motivate investigation into their suitability as an endosseous implant. Osseointegration at the interface between bone and implant surface, which is a criterion for dental implant success, is dependent on surface chemistry and topography. We found out earlier that osteoblasts on sharp-edged micro-topographies revealed an impaired cell phenotype and function and the cells attempted to phagocytize these spiky elevations in vitro. Therefore, micro-structured implants used in dental surgery should avoid any spiky topography on their surface. The sandblasted, acid-etched, and heat-treated yttria-stabilized zirconia (cer.face^®14) surface was characterized by scanning electron microscopy and energy dispersive X-ray. In vitro studies with human MG-63 osteoblasts focused on cell attachment and intracellular stress level. The cer.face 14 surface featured a landscape with nano-micro hills that was most sinusoidal-shaped. The mildly curved profile proved to be a suitable material for cell anchorage. MG-63 cells on cer.face 14 showed a very low reactive oxygen species (ROS) generation similar to that on the extracellular matrix protein collagen I (Col). Intracellular adenosine triphosphate (ATP) levels were comparable to Col. Ceramic cer.face 14, with its sinusoidal-shaped surface structure, facilitates cell anchorage and prevents cell stress.

Switchable and Obedient Interfacial Properties That Grant New Biomedical Applications

Toward imitating the natural smartness and responsivity of biological systems, surface interfacial properties are considered to be responsive and tunable if they show a reactive behavior to an environmental stimulus. This is still quite different from many contemporary biomaterials that lack responsiveness to interact with blood and different body tissues in a physiological manner. Meanwhile it is possible to even go one step further from responsiveness to dual-mode switchability and explore "switchable" or "reversible" responses of synthetic materials. We understand "switchable biomaterials" as materials undergoing a stepwise, structural transformation coupled with considerable changes of interfacial and other surface properties as a response to a stimulus. Therewith, a survey on stimuli-induced dynamic changes of charge, wettability, stiffness, topography, porosity, and thickness/swelling is presented here, as potentially powerful new technologies especially for future biomaterial development. Since living cells constantly sense their environment through a variety of surface receptors and other mechanisms, these obedient interfacial properties were particularly discussed regarding their advantageous multifunctionality for protein adsorption and cell adhesion signaling, which may alter in time and with environmental conditions.

Effect of Polyelectrolyte Multilayers Assembled on Ordered Nanostructures on Adhesion of Human Fibroblasts

Nanosphere lithography (NSL) and the layer-by-layer (LbL) technique are combined here for the first time to design a flexible system to achieve nanotopographical control of cell adhesion. NSL is used to generate regular patterns of tetrahedral gold nanodots of different size and distance. Besides the change in topography, LbL is used to generate a polyelectrolyte multilayer (PEM) system consisting of heparin (HEP) and poly(ethylene imine) (PEI) on top of the gold dots. The localized formation of PEM on gold dots is achieved by prior passivation of the surrounding silicon or glass surface. Properties of PEM are changed by adjusting the pH value of HEP solution to either acidic or alkaline values. Studies with human dermal fibroblasts (HDF) reveal that cells spread to a higher extent on PEM formed at pH 5.0 in dependence on the structure dimension. Further, filopodia formation is highly increased in cells on nanostructures exhibiting HEP as a terminal layer. The new system offers a great potential to guide stem cell differentiation in the future owing to its high degree of chemical and topographical heterogeneity.

Polyelectrolyte multilayers generated in a microfluidic device with pH gradients direct adhesion and movement of cells

In this study, multilayers from polyethylene imine, heparin and chitosan are prepared at three different pH values of 5, 7 and 9. Water contact angle and quartz microbalance measurements show that resulting multilayers differ in terms of wetting behaviour, layer mass and mechanical properties. The multilayer is then formed within a gradient generation microfluidic (μFL) device. Polyethylene imine or heparin solutions of pH 5 are introduced into one inlet and the same solutions but at pH 9 into another inlet of the μFL device. The pH gradient established during the multilayer formation can be visualized inside the microchamber by pH sensitive fluorophores and confocal laser scanning microscopy. From this setup it is expected that properties of multilayers displayed at distinct pH values can be realised in a gradient manner inside the μFL device. Behaviour of the osteoblast cell line MG-63 seeded and cultured on top of multilayers created inside the μFL device support this hypothesis. It is observed that more cells adhere and spread on multilayers build-up at the basic side of the μFL channel, while those cells on top of multilayers built at pH 5 are fewer and smaller. These results are consistent with the behaviour of MG-63 cells seeded on multilayers formed at discrete pH values. It is particularly interesting to see that cells start to migrate from multilayers built at pH 5 to those built at pH 9 during 6 h of culture. Overall, the presented multilayer formation setup applying pH gradients leads to surfaces that promote migration of cells.

Fabrication and characterization of sol-gel derived 45S5 Bioglass®-ceramic scaffolds

Although Bioglass® has existed for nearly half a century its ability to trigger bone formation and tuneable degradability is vastly superior to other bioceramics, such as SiO(2)-CaO bioactive glasses. The sol-gel process of producing glass foams is well established for SiO(2)-CaO compositions, but not yet established for 45S5 composites containing Na(2)O. In this work the sol-gel derived 45S5 Bioglass® has for the first time been foamed into highly porous three-dimensional scaffolds using a surfactant, combined with vigorous mechanical stirring and subsequent sintering at 1000°C for 2 h. It was found that the mechanical strength of the sintered sol-gel derived Bioglass® scaffolds was significantly improved, attributable to the small fraction of material on the pore walls. More importantly, the compressive strength of the three-dimensional scaffolds produced by this surfactant foaming method could be predicted using Gibson and Ashby's closed cell model of porous networks. A comparative experiment revealed that ion release from the sol-gel derived Bioglass® foams was faster than that of counterparts produced by the replication technique. In vitro evaluation using osteoblast-like cells demonstrated that the sol-gel derived 45S5 Bioglass foams supported the proliferation of viable cell populations on the surface of the scaffolds, although few cells were observed to migrate into the virtually closed pores within the foams. Further work should be focused on modifications of the reaction conditions or alternative foaming techniques to improve pore interconnection.

Controlling Fibroblast Adhesion with Ph Modified Polyelectrolyte Multilayers

Tissue cells need to adhere to a biomaterial surface to promote their growth and differentiation and, thus, foster the integration of implants. As a result, surface features and their modification play an important role in biomedical applications. In this study, the layer-by-layer (LbL) technique was used to design self-assembled polyelectrolyte multilayer (PEM) coatings of polyethyleneimine (PEI) and heparin (HEP) on glass, which will control the adhesion of primary human dermal fibroblasts in a model system. The study showed that, among other surface features, the wettability of surfaces can be controlled by changing the conditions during multilayer self-assembly. Here, the pH value of the HEP solution was adjusted to acidic or alkaline values for terminal layers, which also led to a change in multilayer growth. Further, the study revealed that plain terminal layers were rather cytophobic. Upon pre-adsorption of fibronectin (FN), a clear effect on cell adhesion and morphology in dependence on the pH setup was evident. Proliferation studies clearly showed that terminal layers, which impaired cell adhesion, also inhibited growth of human fibroblasts under serum-conditions. On the other hand, on layers with pronounced cell adhesion an elevated cell growth was also observed. As a result, HEP terminated multilayers are interesting for applications requiring cell repellent properties, whereas PEI terminated multilayers could be used to promote cell adhesion and growth on implant surfaces.

Synergistic effect of polyelectrolyte multilayers and osteogenic growth medium on differentiation of human mesenchymal stem cells

Layer-by-layer assembly of biogenic polyelectrolytes (PEL) was carried out on the surface of poly (L-lactide) to generate polyelectrolyte multilayers (PEM) that foster osteogenic differentiation of human mesenchymal stem cell (hMSC). Gelatin (GEL), hyaluronic acid (HA) and heparin (HEP) were chosen as polyanions, while chitosan (CHI) was employed as polycation. Multilayer formation was monitored by surface plasmon resonance and water contact angle measurements showing that layer formation process and surface wetting properties depended on the type of polyanions. While HEP as strong PEL led to thicker and more hydrophilic PEM, layer mass was lower for weak polyanions GEL and HA. Short-term adhesion studies with hMSC showed strong adhesion and spreading of cells on PEM composed of GEL/CHI and low spreading, motile phenotype and aggregation of hMSC on HEP/CHI or HA/CHI. Long term studies over three weeks were carried out to follow growth and differentiation of hMSC on the PEM. Weak osteogenic differentiation of hMSC was observed on GEL/CHI if cells were cultured in normal medium while no osteogenic phenotypes were observed on HEP/CHI or HA/CHI. When cells were cultured in osteogenic differentiation medium, however, PEM composed of HEP/CHI or HA/CHI promoted differentiation of hMSC towards osteoblasts, while PEM composed of GEL/CHI failed to do so. Overall, the composition of PEMs can be used as additional tool to control osteogenic differentiation of hMSC.

Self-assembled chitosan/heparin multilayer film as a novel template for in situ synthesis of silver nanoparticles

Chitosan and heparin multilayer films were successfully constructed via layer-by-layer self assembly. These films were used as a polymeric template to synthesize silver nanoparticles. The silver concentration and nanoparticle size can be simply controlled by the assembly pH and loading pH, as demonstrated by UV-visible spectroscopy, transmission electron microscopy and atomic absorbance spectroscopy. The pH tunable uncompensated charge density within the multilayer films is believed to have great effect on the loading of silver ions, and then control the size and amount of silver nanoparticles within multilayer films. The antibacterial experiment shows that the silver nanoparticle-loaded chitosan/heparin multilayer films exhibit greatly enhanced antibacterial performance compared to the chitosan/heparin multilayer films without silver nanoparticles. In addition, the strong antibacterial property of silver nanoparticle-loaded films can last more than 1 month. Our method of in situ synthesis of metal nanoparticles in biocompatible multilayer films might provide great potential to design biofunctional nanocomposite films.

pH-dependent modulation of fibroblast adhesion on multilayers composed of poly(ethylene imine) and heparin

Adhesion of tissue cells is a prerequisite for their growth and differentiation but prevents also apoptosis. Here the layer-by-layer technique (LbL) was used to design multilayer structures of poly(ethylene imine) (PEI) and heparin (HEP) on glass as model biomaterial to control the adhesion of primary human dermal fibroblasts. Distinct surface features like wettability, charge and lateral structures were controlled by changing the pH value of the HEP solution during multilayer assembly to acidic, neutral or alkaline values. While plain terminal layers were rather cytophobic, the pre-adsorption of serum or fibronectin (FN) caused a distinct change in cell morphology in dependence on the pH setup. The effect of serum was more prominent on PEI layers probably due to their positive surface charge, whereas the effect of FN was more pronounced on HEP terminated multilayers possibly due to its ability to bind FN specifically. Those layers which hampered cell adhesion also inhibited growth of human fibroblasts under serum conditions. Conversely, on layers where cell adhesion was increased also an elevated growth and, thus, metabolic activity was observed.