Effects of surface wettability and contact time on protein adhesion to biomaterial surfaces

In vitro hemocompatibility on thin ceramic and hydrogel films deposited on polymer substrate performed in arterial flow conditions

Hydrogel coatings were stabilized by titanium carbonitride a-C:H:Ti:N buffer layers deposited directly onto the polyurethane (PU) substrate beneath a final hydrogel coating. Coatings of a-C:H:Ti:N were deposited using a hybrid method of pulsed laser deposition (PLD) and magnetron sputtering (MS) under high vacuum conditions. The influence of the buffer a-C:H:Ti:N layer on the hydrogel coating was analysed by means of a multi-scale microstructure study. Mechanical tests were performed at an indentation load of 5 mN using Berkovich indenter geometry. Haemocompatible analyses were performed in vitro using a blood flow simulator. The blood-material interaction was analysed under dynamic conditions. The coating fabrication procedure improved the coating stability due to the deposition of the amorphous titanium carbonitride buffer layer.

Interactions of liposomes with dental restorative materials

The in vitro adsorption and retention of liposomes onto four common types of dental restorative materials (conventional and silorane-based resin composites as well as conventional and resin-modified glass ionomer cements (GIC)) have been investigated due to their potential use in the oral cavity. Uncoated liposomes (positively and negatively charged) and pectin (low- and high-methoxylated) coated liposomes were prepared and characterized in terms of particle size and zeta potential. The adsorption of liposomes was performed by immersion, quantified by fluorescence detection, and visualized by fluorescence imaging and atomic force microscopy. Positive liposomes demonstrated the highest adsorption on all four types of materials likely due to their attractive surface charge. They also retained well (minimum 40% after 60 min) on both conventional resin composite and GIC even when exposed to simulated salivary flow. Although an intermediate initial level of adsorption was found for the pectin coated liposomes, at least 70% high methoxylated-pectin coated liposomes still remained on the conventional resin composite after 60 min flow exposure. This indicates significant contribution of hydrophobic interactions in the prolonged binding of liposomes to resin composites. Based on these results, the present paper suggests two new possible applications of liposomes in the preservation of dental restorations.

Collagen/elastin hydrogels cross-linked by squaric acid

Hydrogels based on collagen and elastin are very valuable materials for medicine and tissue engineering. They are biocompatible; however their mechanical properties and resistance for enzymatic degradation need to be improved by cross-linking. Up to this point many reagents have been tested but more secure reactants are still sought. Squaric acid (SqAc), 3,4-dihydroxy 3-cyclobutene 1,2-dione, is a strong, cyclic acid, which reacts easily with amine groups. The properties of hydrogels based on collagen/elastin mixtures (95/5, 90/10) containing 5%, 10% and 20% of SqAc and neutralized via dialysis against deionized water were tested. Cross-linked, 3-D, transparent hydrogels were created. The cross-linked materials are stiffer and more resistant to enzymatic degradation than those that are unmodified. The pore size, swelling ability and surface polarity are reduced due to 5% and 10% of SqAc addition. At the same time, the cellular response is not significantly affected by the cross-linking. Therefore, squaric acid would be regarded as a safe, effective cross-linking agent.

Shaping Nanoparticles with Hydrophilic Compositions and Hydrophobic Properties as Nanocarriers for Antibiotic Delivery

Inspired by the lotus effect in nature, surface roughness engineering has led to novel materials and applications in many fields. Despite the rapid progress in superhydrophobic and superoleophobic materials, this concept of Mother Nature's choice is yet to be applied in the design of advanced nanocarriers for drug delivery. Pioneering work has emerged in the development of nanoparticles with rough surfaces for gene delivery; however, the preparation of nanoparticles with hydrophilic compositions but with enhanced hydrophobic property at the nanoscale level employing surface topology engineering remains a challenge. Herein we report for the first time the unique properties of mesoporous hollow silica (MHS) nanospheres with controlled surface roughness. Compared to MHS with a smooth surface, rough mesoporous hollow silica (RMHS) nanoparticles with the same hydrophilic composition show unusual hydrophobicity, leading to higher adsorption of a range of hydrophobic molecules and controlled release of hydrophilic molecules. RMHS loaded with vancomycin exhibits an enhanced antibacterial effect. Our strategy provides a new pathway in the design of novel nanocarriers for diverse bioapplications.

Cytocompatibility of Si-incorporated TiO2 nanopores films

Si-incorporated TiO2 nanopores films were prepared by anodization and silicon plasma immersion ion implantation. The microstructure and phase composition of the films were investigated by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The hydrophilicity of the films was evaluated using water contact angle measurement and MG63 cells were cultured on the films to investigate the cytocompatibility. The results showed that the concentration and depth of silicon on the Si-incorporated TiO2 nanopores films increased with the duration time of implantation. Both the as-annealed and Si-incorporated nanopores films exhibited good hydrophilicity and cytocompatibility, while the TiO2 nanopores films implanted silicon for 1.0h showed higher proliferation rate and vitality of MG63 cells than others, indicating a great potential application for titanium implants.

Surface properties of nanocrystalline TiO2 coatings in relation to the in vitro plasma protein adsorption

This study reports on the selective adsorption of whole plasma proteins on hydrothermally (HT) grown TiO2-anatase coatings and its dependence on the three main surface properties: surface charge, wettability and roughness. The influence of the photo-activation of TiO2 by UV irradiation was also evaluated. Even though the protein adhesion onto Ti-based substrates was only moderate, better adsorption of any protein (at pH = 7.4) occurred for the most negatively charged and hydrophobic substrate (Ti non-treated) and for the most nanorough and hydrophilic surface (HT Ti3), indicating that the mutual action of the surface characteristics is responsible for the attraction and adhesion of the proteins. The HT coatings showed a higher adsorption of certain proteins (albumin 'passivation' layer, apolipoproteins, vitamin D-binding protein, ceruloplasmin, α-2-HS-glycoprotein) and higher ratios of albumin to fibrinogen and albumin to immunoglobulin γ-chains. The UV pre-irradiation affected the surface properties and strongly reduced the adsorption of the proteins. These results provide in-depth knowledge about the characterization of nanocrystalline TiO2 coatings for body implants and provide a basis for future studies on the hemocompatibility and biocompatibility of such surfaces.

The in vitro and in vivo performance of a strontium-containing coating on the low-modulus Ti35Nb2Ta3Zr alloy formed by micro-arc oxidation

The β-titanium alloy is thought to be a promising alloy using as orthopedic or dental implants owing to its characteristics, which contains low elastic modulus, high corrosion resistance and well biocompatibility. Our previous study has reported that a new β-titanium alloy Ti35Nb2Ta3Zr showed low modulus close to human bone, equal tissue compatibility to a traditional implant alloy Ti6Al4V. In this study, micro-arc oxidation (MAO) was applied on the Ti35Nb2Ta3Zr alloy to enhance its surface characteristics and biocompatibility and osseointegration ability. Two different coatings were formed, TiO2 doped with calcium-phosphate coating (Ca-P) and calcium-phosphate-strontium coating (Ca-P-Sr). Then we evaluated the effects of the MAO coatings on the Ti35Nb2Ta3Zr alloy through in vitro and in vivo tests. As to the characteristics of the coatings, the morphology, chemical composition, surface roughness and contact angle of MAO coatings were tested by scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, and video contact-angle measurement system respectively. Besides, we performed MTT assay, ALP test and cell morphology-adhesion test on materials to evaluate the MAOed coating materials' biocompatibility in vitro. The in vivo experiment was performed through rabbit model. Alloys were implanted into rabbits' femur shafts, then we performed micro-CT, histological and sequential fluorescent labeling analysis to evaluate implants' osseointegration ability in vivo. Finally, the Ca-P specimens and Ca-P-Sr specimens exhibited a significant enhancement in surface roughness, hydrophilicity, cell proliferation, cell adhesion. More new bone was found around the Ca-P-Sr coated alloy than Ca-P coated alloy and Ti35Nb2Ta3Zr alloy. In conclusion, the MAO treatment improved in vitro and in vivo performance of Ti35Nb2Ta3Zr alloy. The Ca-P-Sr coating may be a promising modified surface formed by MAO for the novel β-titanium alloy Ti35Nb2Ta3Zr.

Antithrombogenic Properties of Amphiphilic Block Copolymer Coatings: Evaluation of Hemocompatibility Using Whole Blood

Antithrombogenicity is one of the most critical properties required for materials used in biomedical devices, particularly in devices that contact blood. The antithrombogenicity of surfaces coated with amphiphilic block copolymers composed of hydrophobic poly(2-methoxyethyl acrylate) (M) and hydrophilic poly(N,N-dimethylacrylamide) (D) segments was investigated using plasma protein and whole blood with regard to protein adsorption, thrombus formation, platelet activation, and clotting kinetics. Three types of block copolymers and a random copolymer were synthesized using one-pot reversible addition-fragmentation chain-transfer (RAFT) polymerization under conditions of high yield and high molecular weight. Triblock and 4-arm block copolymers with MDM and (MD)₄ architecture, respectively, showed good adhesion to both organic and inorganic substrates, including polyvinyl chloride (PVC) tubes, and the resulting coated surfaces showed superior protein repellency and hemocompatibility compared to the diblock or random copolymer coatings and noncoated control. In a Chandler-loop method with whole blood, PVC tubes coated with MDM and (MD)₄ showed improved thromboresistance and adsorption resistance to blood-derived proteins. This high hemocompatibility was also confirmed with human whole blood by thrombelastography (suppression of blood-clotting behavior in both intrinsic and extrinsic coagulation pathways) and platelet function analyses (significant reductions in the aggregation activity of platelets under two types of stimulation). The antithrombogenicity has been discussed based on the structural analyses of the MDM-coated surface. The results of this study will enable the development of more effective biomedical and analytical devices with excellent antithrombogenic characteristics by using a simple and environmentally friendly approach.

Effect of SiC interlayer between Ti6Al4V alloy and hydroxyapatite films

Bioactive coatings are frequently used to improve the osseointegration of the metallic implants used in dentistry or orthopaedics. Among different types of bioactive coatings, hydroxyapatite (Ca10(PO4)6(OH)2) is one of the most extensively used due to its chemical similarities to the components of bones and teeth. In this article, production and characterization of hydroxyapatite films deposited on Ti6Al4V alloy prepared by magnetron sputtering were reported. Besides, SiC was deposited on substrate surface to study the interlayer effect. Obtained coatings were annealed at 600 °C for 30 and 120 min in a mixed atmosphere of N2 + H2O vapours with the heating rate of 12 °C min−1. The effects of SiC interlayer and heat treatment parameters on the structural, mechanical and corrosion properties were investigated. After heat treatment process, the crystalline hydroxyapatite was obtained. Additionally, cell viability tests were performed. The results show that the presence of the SiC interlayer contributes a decrease in surface roughness and improves the mechanical properties and corrosion performance of the hydroxyapatite coatings. Biological properties were not affected by the presence of the SiC interlayer.

Wettability studies of topologically distinct titanium surfaces

Biomedical implants made of titanium-based materials are expected to have certain essential features including high bone-to-implant contact and optimum osteointegration, which are often influenced by the surface topography and physicochemical properties of titanium surfaces. The surface structure in the nanoscale regime is presumed to alter/facilitate the protein binding, cell adhesion and proliferation, thereby reducing post-operative complications with increased lifespan of biomedical implants. The novelty of our TiO2 nanostructures lies mainly in the high level control over their morphology and roughness by mere compositional change and optimisation of the experimental parameters. The present work focuses on the wetting behaviour of various nanostructured titanium surfaces towards water. Kinetics of contact area of water droplet on macroscopically flat, nanoporous and nanotubular titanium surface topologies was monitored under similar evaporation conditions. The contact area of the water droplet on hydrophobic titanium planar surface (foil) was found to decrease during evaporation, whereas the contact area of the droplet on hydrophobic nanorough titanium surfaces practically remained unaffected until the complete evaporation. This demonstrates that the surface morphology and roughness at the nanoscale level substantially affect the titanium dioxide surface-water droplet interaction, opposing to previous observations for microscale structured surfaces. The difference in surface topographic nanofeatures of nanostructured titanium surfaces could be correlated not only with the time-dependency of the contact area, but also with time-dependency of the contact angle and electrochemical properties of these surfaces.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Facilely tuning the bioactivity of an orthopedic implant surface based on nanostructured polypyrrole/glycosaminoglycans

The wettability of nanostructured polypyrrole/glycosaminoglycans can be controlled in situ by electrical stimulus to tune the bioactivity of implants.

Effects of different functional groups on metastatic behavior of SPC-A-1/human lung cancer cells in self-assembled monolayers

Self-assembled monolayers terminated with different functional groups were used to explore their effects on the metastatic behaviors of human lung cancer cells (SPC-A-1) in vitro. The addition of –SH group has potential applications for lung cancer metastasis therapy.

Physical and biological activities of newly designed, macro-pore-structure-controlled 3D fibrous poly(ε-caprolactone)/hydroxyapatite composite scaffolds

A 3D fibrous scaffold using an electrohydrodynamic jet process supplemented with in vitro mineralization to obtain a hydroxyapatite layer in simulated body fluid was fabricated.

Formation and oxygen diffusion barrier properties of fish gelatin/natural sodium montmorillonite clay self-assembled multilayers onto the biopolyester surface

In order to expand the application of bio-derived polymers it is imperative that the issues related to their poor gas barrier properties be addressed.

Immobilization of nattokinase-loaded red blood cells on the surface of superhydrophobic polypropylene targeting fibrinolytic performance

A superhydrophobic polypropylene (PP) platform with fibrinolytic ability was fabricated by capturing and releasing nattokinase (NK)-encapsulating red blood cells (RBCs).

Proteins, platelets, and blood coagulation at biomaterial interfaces

Blood coagulation and platelet adhesion remain major impediments to the use of biomaterials in implantable medical devices. There is still significant controversy and question in the field regarding the role that surfaces play in this process. This manuscript addresses this topic area and reports on state of the art in the field. Particular emphasis is placed on the subject of surface engineering and surface measurements that allow for control and observation of surface-mediated biological responses in blood and test solutions. Appropriate use of surface texturing and chemical patterning methodologies allow for reduction of both blood coagulation and platelet adhesion, and new methods of surface interrogation at high resolution allow for measurement of the relevant biological factors.

Reversibly controlling preferential protein adsorption on bone implants by using an applied weak potential as a switch

A facile method is needed to control the protein adsorption onto biomaterials, such as, bone implants. Herein we doped taurocholic acid (TCA), an amphiphilic biomolecule, into an array of 1D nano-architectured polypyrrole (NAPPy) on the implants. Doping TCA enabled the implant surface to show reversible wettability between 152° (superhydrophobic, switch-on state) and 55° (hydrophilic, switch-off state) in response to periodically switching two weak electrical potentials (+0.50 and -0.80 V as a switch-on and switch-off potential, respectively). The potential-switchable reversible wettability, arising from the potential-tunable orientation of the hydrophobic and hydrophilic face of TCA, led to potential-switchable preferential adsorption of proteins as well as cell adhesion and spreading. This potential-switchable strategy may open up a new avenue to control the biological activities on the implant surface.

High-performance scaffolds on titanium surfaces: osteoblast differentiation and mineralization promoted by a globular fibrinogen layer through cell-autonomous BMP signaling

Titanium has been widely used as a dental implant material. However, it takes several months for the implant body to bind with the jawbone. To develop new bioactive modification on titanium surfaces to achieve full osseointegration expeditiously, we used fibrinogen and fibronectin as bioactive scaffolds on the titanium plate, which are common extracellular matrix (ECM) proteins. We analyzed the features of the surface of ECM-modified titanium plates by atomic force microscopy and Fourier transform infrared spectrophotometry. We also evaluated the effect of ECM modification on promoting the differentiation and mineralization of osteoblasts on these surfaces. Fibrinogen had excellent adsorption on titanium surfaces even at low concentrations, due to the binding ability of fibrinogen via its RGD motif. The surface was composed of a fibrinogen monolayer, in which the ratio of β-sheets was decreased. Osteoblast proliferation on ECM-modified titanium surface was significantly promoted compared with titanium alone. Calcification on the modified surface was also accelerated. These ECM-promoting effects correlated with increased expression of bone morphogenetic proteins (BMPs) by the osteoblasts themselves and were inhibited by Noggin, a BMP inhibitor. These results suggest that the fibrinogen monolayer-modified titanium surface is recognized as bioactive scaffolds and promotes bone formation, resulting in the acceleration of osseointegration.

Laser surface modification of AZ31B Mg alloy for bio-wettability

Magnesium alloys are the potential degradable materials for load-bearing implant application due to their comparable mechanical properties to human bone, excellent bioactivity, and in vivo non-toxicity. However, for a successful load-bearing implant, the surface of bio-implant must allow protein absorption and layer formation under physiological environment that can assist the cell/osteoblast growth. In this regard, surface wettability of bio-implant plays a key role to dictate the quantity of protein absorption. In light of this, the main objective of the present study was to produce favorable bio-wettability condition of AZ31B Mg alloy bio-implant surface via laser surface modification technique under various laser processing conditions. In the present efforts, the influence of laser surface modification on AZ31B Mg alloy surface on resultant bio-wettability was investigated via contact-angle measurements and the co-relationships among microstructure (grain size), surface roughness, surface energy, and surface chemical composition were established. In addition, the laser surface modification technique was simulated by computational (thermal) model to facilitate the prediction of temperature and its resultant cooling/solidification rates under various laser processing conditions for correlating with their corresponding composition and phase evolution. These predicted thermal properties were later used to correlate with the corresponding microstructure, chemical composition, and phase evolution via experimental analyses (X-ray diffractometer, scanning electron microscope, energy-dispersive spectroscopy).

Barnacle larvae exploring surfaces with variable hydrophilicity: influence of morphology and adhesion of "footprint" proteins by AFM

Interaction forces of adhesive proteins employed by cyprid larvae of Amphibalanus amphitrite for temporary attachment during surface exploration in marine fouling were studied by AFM force spectroscopy using chemically modified, reactive colloidal probes. The proteins were covalently attached to the surfaces of the probes by incubation in the protein deposits (footprints) left behind at the surface by the cyprids. This covalent coupling enabled robust and reproducible probing of adhesion of the attachment proteins to model surfaces with variable hydrophilicity. Three model monolayer surfaces were designed and prepared that exhibited different wettabilities derived from variations in the monolayer chemical composition. The morphology and size of cyprid protein deposits was imaged by AFM. The deposits showed larger area of spreading on more hydrophobic surfaces, whereas the overall volume of the secreted proteins exhibited no significant variation. Notable difference in adhesion forces was found among the surfaces by force spectroscopy, with substantially higher values measured on the hydrophobic surface (21 ± 2 nN) than that measured on the more hydrophilic surface (7.2 ± 1 nN). The same surfaces were also tested in laboratory essays. Rather surprisingly, no significant differences were found in values of fractional cyprid settlement among the surfaces studied, indicating that variations of surface wettability and adhesion strength of settlement proteins may be insufficient to explain settlement trends.

MRI-compatible Nb-60Ta-2Zr alloy used for vascular stents: haemocompatibility and its correlation with protein adsorption

Nb-60Ta-2Zr is a newly developed MRI-compatible alloy used for vascular stents. In this work, its haemocompatibility was investigated, including platelet adhesion (lactate dehydrogenase activity), platelet activation (P-selectin expression), coagulation and haemolysis. For comparison, parallel assessments for these factors were performed for the niobium, tantalum, 316L stainless steel (316L SS) and L605 Co-Cr alloy (L605). In addition, albumin and fibrinogen were selected to examine the correlation of protein adsorption with platelet adhesion and metal surface properties. The propensity for platelet adhesion and activation on the Nb-60Ta-2Zr alloy was at nearly the same level as that for Nb and Ta but was slightly less than those of 316L SS and L605. The mitigated platelet adhesion and activation of the Nb-60Ta-2Zr alloy is associated with its decreased adsorption of fibrinogen. The Nb-60Ta-2Zr alloy has a longer clotting time and exhibits significantly superior thromboresistance than 316L SS and L605. Moreover, the haemolysis rate of the Nb-60Ta-2Zr alloy satisfies the bio-safety requirement of the ISO 10993-4 standard. The favourable haemocompatiblity of the Nb-60Ta-2Zr alloy provides evidence of its good biocompatibility and of its suitability as a candidate stent material.

An extremely simple method for fabricating 3D protein microarrays with an anti-fouling background and high protein capacity

Protein microarrays have become vital tools for various applications in biomedicine and bio-analysis during the past decade. The intense requirements for a lower detection limit and industrialization in this area have resulted in a persistent pursuit to fabricate protein microarrays with a low background and high signal intensity via simple methods. Here, we report on an extremely simple strategy to create three-dimensional (3D) protein microarrays with an anti-fouling background and a high protein capacity by photo-induced surface sequential controlled/living graft polymerization developed in our lab. According to this strategy, "dormant" groups of isopropyl thioxanthone semipinacol (ITXSP) were first introduced to a polymeric substrate through ultraviolet (UV)-induced surface abstraction of hydrogen, followed by a coupling reaction. Under visible light irradiation, the ITXSP groups were photolyzed to initiate surface living graft polymerization of poly(ethylene glycol) methyl methacrylate (PEGMMA), thus introducing PEG brushes to the substrate to generate a full anti-fouling background. Due to the living nature of this graft polymerization, there were still ITXSP groups on the chain ends of the PEG brushes. Therefore, by in situ secondary living graft cross-linking copolymerization of glycidyl methacrylate (GMA) and polyethylene glycol diacrylate (PEGDA), we could finally plant height-controllable cylinder microarrays of a 3D PEG network containing reactive epoxy groups onto the PEG brushes. Through a commonly used reaction of amine and epoxy groups, the proteins could readily be covalently immobilized onto the microarrays. This delicate design aims to overcome two universal limitations in protein microarrays: a full anti-fouling background can effectively eliminate noise caused by non-specific absorption and a 3D reactive network provides a larger protein-loading capacity to improve signal intensity. The results of non-specific protein absorption tests demonstrated that the introduction of PEG brushes greatly improved the anti-fouling properties of the pristine low-density polyethylene (LDPE), for which the absorption to bovine serum albumin was reduced by 83.3%. Moreover, the 3D protein microarrays exhibited a higher protein capacity than the controls to which were attached the same protein on PGMA brushes and monolayer epoxy functional groups. The 3D protein microarrays were used to test the immunoglobulin G (IgG) concentration in human serum, suggesting that they could be used for biomedical diagnosis, which indicates that more potential bio-applications could be developed for these protein microarrays in the future.

SYNTHESIS AND CHARACTERISATION OF ELECTROSPUN CHITOSAN MEMBRANES REINFORCED BY HALLOYSITE NANOTUBES

We report on the electrospinning method to synthesize and characterise chitosan membranes reinforced by halloysite nanotubes (HNTs). The synthesis process addressed two levels of HNTs concentration, i.e., 2 and 5 wt.%. Tensile testing was carried out to determine the strength (σ), strain (ε) at σ and elastic modulus (E) of the membranes. Tensile test data revealed that the membranes reinforced with 5 wt.% HNTs yielded the highest E (0.153 ± 0.02 GPa) and strength (22.53 ± 8.57 MPa). Electron micrographs of the fractured surfaces showed uniform dispersions of HNTs in the chitosan matrix. Infrared spectra indicated interactions between chitosan and inner and outer surfaces of HNTs. Thermogravimetric analysis demonstrated an increase in thermal stability with the addition of HNTs. Membranes immersed in simulated body fluid system for 28 days revealed the formation of dense apatite blocks with the addition of HNTs. Surface roughness increased with the addition of HNTs resulted a rise in degree of contact angle.

The effect of terminal sterilization on structural and biophysical properties of a decellularized collagen-based scaffold; implications for stem cell adhesion

Terminal sterilization induces physical and chemical changes in the extracellular matrix (ECM) of ex vivo-derived biomaterials due to their aggressive mechanism of action. Prior studies have focused on how sterilization affects the mechanical integrity of tissue-based biomaterials but have rarely characterized effects on early cellular interaction, which is indicative of the biological response. Using a model fibrocartilage disc scaffold, these investigations compare the effect of three common sterilization methods [peracetic acid (PAA), gamma irradiation (GI), and ethylene oxide (EtO)] on a range of material properties and characterized early cellular interactions. GI and EtO produced unfavorable structural damage that contributed to inferior cell adhesion. Conversely, exposure to PAA resulted in limited structural alterations while inducing chemical modifications that favored cell attachment. Results suggest that the sterilization approach can be selected to modulate biomaterial properties to favor cellular adhesion and has relevance in tissue engineering and regenerative medicine applications. Furthermore, the study of cellular interactions with modified biomaterials in vitro provides information of how materials may react in subsequent clinical applications.

Evaluation of biocompatibility using in vitro methods: interpretation and limitations

The in vitro biocompatibility of novel materials has to be proven before a material can be used as component of a medical device. This must be done in cell culture tests according to internationally recognized standard protocols. Subsequently, preclinical and clinical tests must be performed to verify the safety of the new material and device. The present chapter focuses on the first step, the in vitro testing according to ISO 10993-5, and critically discusses its limited significance. Alternative strategies and a brief overview of activities to improve the current in vitro tests are presented in the concluding section.

Fabrication and magnetic testing of a poly-L-lactide biocomposite incorporating magnetite nanoparticles

Polylactic acid (PLA)-based composite has been widely used in tissue engineering. To modify the material’s properties, inorganic substances have been used to form nanoparticle-PLA composites. The aim of this study is to develop a novel magnetic biodegradable composite. Nanoscale magnetite (Fe3O4) was incorporated into a poly-L-lactide (PLLA) matrix with proportions of 0%, 5%, 10%, and 15% (w/w). Injection molding was carried out to produce the nano-magnetite-PLLA composite samples. X-ray diffraction (XRD), differential scanning calorimetry (DSC), superconducting quantum device (SQUID), and three-point bending were performed to test the physical properties of the magnetite-PLLA composite. The results showed that the magnetite-PLLA composite exhibited typical ferromagnetic hysteresis loops. The addition of nanoscale magnetite significantly increased the magnetic flux density of the PLLA composite. These results suggest that the magnetite-PLLA composite has the potential to be used for future applications in tissue engineering.

Bacterial cellulose and hyaluronic acid hybrid membranes: Production and characterization

In this study, the effect of the addition of hyaluronic acid (HA) on bacterial cellulose (BC) production, under static conditions was evaluated in terms of the properties of the resulting BC hybrid membranes. HA was added to the fermentation process in three distinct time points: first day (BC-T0), third day (BC-T3) and sixth day (BC-T6). Analyses of FT-IR and CP/MAS (13)C NMR confirmed the presence of HA in bacterial cellulose membranes. The crystal structure, crystallinity index (Ic) surface roughness, thermal stability and hybrophobic/hydrophilic character changed. Membranes with higher roughness were produced with HA added on the first and third day of fermentation process. The surface energy of BC/HA membranes was calculated and more hydrophilic membranes were produced by the addition of HA on the third and sixth day, also resulting in more thermally stable materials. The results demonstrate that bacterial cellulose/hyaluronic acid hybrid membranes can be produced in situ and suggest that HA interacts with the sub-elementary bacterial cellulose fibrils, changing the properties of the membranes. The study and understanding of the factors that affect those properties are of utmost importance for the safe and efficient use of BC as biomaterials in numerous applications, specifically in the biological field.

Advances in biocompatibility and physico-chemical characterization of microspheres for cell encapsulation

Cell encapsulation has already shown its high potential and holds the promise for future cell therapies to enter the clinics as a large scale treatment option for various types of diseases. The advancement in cell biology towards this goal has to be complemented with functional biomaterials suitable for cell encapsulation. This cannot be achieved without understanding the close correlation between cell performance and properties of microspheres. The ongoing challenges in the field of cell encapsulation require a critical view on techniques and approaches currently utilized to characterize microspheres. This review deals with both principal subjects of microspheres characterization in the cell encapsulation field: physico-chemical characterization and biocompatibility. The up-to-day knowledge is summarized and discussed with the focus to identify missing knowledge and uncertainties, and to propose the mandatory next steps in characterization of microspheres for cell encapsulation. The primary conclusion of this review is that further success in development of microspheres for cell therapies cannot be accomplished without careful selection of characterization techniques, which are employed in conjunction with biological tests.

Biomaterials in co-culture systems: towards optimizing tissue integration and cell signaling within scaffolds

Most natural tissues consist of multi-cellular systems made up of two or more cell types. However, some of these tissues may not regenerate themselves following tissue injury or disease without some form of intervention, such as from the use of tissue engineered constructs. Recent studies have increasingly used co-cultures in tissue engineering applications as these systems better model the natural tissues, both physically and biologically. This review aims to identify the challenges of using co-culture systems and to highlight different approaches with respect to the use of biomaterials in the use of such systems. The application of co-culture systems to stimulate a desired biological response and examples of studies within particular tissue engineering disciplines are summarized. A description of different analytical co-culture systems is also discussed and the role of biomaterials in the future of co-culture research are elaborated on. Understanding the complex cell-cell and cell-biomaterial interactions involved in co-culture systems will ultimately lead the field towards biomaterial concepts and designs with specific biochemical, electrical, and mechanical characteristics that are tailored towards the needs of distinct co-culture systems.

Role of nanostructured gold surfaces on monocyte activation and Staphylococcus epidermidis biofilm formation

The role of material surface properties in the direct interaction with bacteria and the indirect route via host defense cells is not fully understood. Recently, it was suggested that nanostructured implant surfaces possess antimicrobial properties. In the current study, the adhesion and biofilm formation of Staphylococcus epidermidis and human monocyte adhesion and activation were studied separately and in coculture in different in vitro models using smooth gold and well-defined nanostructured gold surfaces. Two polystyrene surfaces were used as controls in the monocyte experiments. Fluorescent viability staining demonstrated a reduction in the viability of S. epidermidis close to the nanostructured gold surface, whereas the smooth gold correlated with more live biofilm. The results were supported by scanning electron microscopy observations, showing higher biofilm tower formations and more mature biofilms on smooth gold compared with nanostructured gold. Unstimulated monocytes on the different substrates demonstrated low activation, reduced gene expression of pro- and anti-inflammatory cytokines, and low cytokine secretion. In contrast, stimulation with opsonized zymosan or opsonized live S. epidermidis for 1 hour significantly increased the production of reactive oxygen species, the gene expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-10, as well as the secretion of TNF-α, demonstrating the ability of the cells to elicit a response and actively phagocytose prey. In addition, cells cultured on the smooth gold and the nanostructured gold displayed a different adhesion pattern and a more rapid oxidative burst than those cultured on polystyrene upon stimulation. We conclude that S. epidermidis decreased its viability initially when adhering to nanostructured surfaces compared with smooth gold surfaces, especially in the bacterial cell layers closest to the surface. In contrast, material surface properties neither strongly promoted nor attenuated the activity of monocytes when exposed to zymosan particles or S. epidermidis.

Bioactivation of calcium deficient hydroxyapatite with foamed gelatin gel. A new injectable self-setting bone analogue

An alternative approach to bone repair for less invasive surgical techniques, involves the development of biomaterials directly injectable into the injury sites and able to replicate a spatially organized platform with features of bone tissue. Here, the preparation and characterization of an innovative injectable bone analogue made of calcium deficient hydroxyapatite and foamed gelatin is presented. The biopolymer features and the cement self-setting reaction were investigated by rheological analysis. The porous architecture, the evolution of surface morphology and the grains dimension were analyzed with electron microscopy (SEM/ESEM/TEM). The physico-chemical properties were characterized by X-ray diffraction and FTIR analysis. Moreover, an injection test was carried out to prove the positive effect of gelatin on the flow ensuing that cement is fully injectable. The cement mechanical properties are adequate to function as temporary substrate for bone tissue regeneration. Furthermore, MG63 cells and bone marrow-derived human mesenchymal stem cells (hMSCs) were able to migrate and proliferate inside the pores, and hMSCs differentiated to the osteoblastic phenotype. The results are paving the way for an injectable bone substitute with properties that mimic natural bone tissue allowing the successful use as bone filler for craniofacial and orthopedic reconstructions in regenerative medicine.

Specific ultraviolet-C irradiation energy for functionalization of titanium surface to increase osteoblastic cellular attachment

Purpose

The objective of this in vitro study was to examine the influence of the total energy of ultraviolet-C preirradiation on the number and morphology of osteoblastic cells attached to turned or acid-etched titanium surfaces, and physicochemical properties of the surface.

Materials and methods

Rat bone marrow-derived osteoblasts were incubated with turned or acid-etched titanium disks preirradiated with ultraviolet-C at 1 or 3 mW/cm2, resulting in total energies of 10, 100, 250, 400, 500, 600, 750, or 1000 J/cm2. Osteoblast attachment to the surface was evaluated using the WST-1 assay. Physicochemical changes of the titanium were evaluated by measuring water wettability and X-ray photoelectron spectroscopy analysis.

Results

Number of attached cells was greater on turned or acid-etched surface preirradiated with 500 or 750 J/cm2 of 3 mW/cm2 ultraviolet-C than on the nonirradiated surface, respectively. However, the further irradiation energy did not increase the numbers on both types of the surfaces. These phenomena were also seen on the surfaces preirradiated at different ultraviolet-C intensities. Ultraviolet-C irradiation induced superhydrophilicity on both types of surface even with the less irradiation energy. The amount of carbon on ultraviolet-C preirradiated titanium surfaces decreased gradually with an increase in the total irradiation energy.

Conclusion

Specific ultraviolet-C energy used to irradiate turned or acid-etched surfaces increased the number of osteoblastic cells attached to each of the surface. This was canceled by overirradiation, despite maintenance of both the acquired superhydrophilicity and the accompanying reduction in carbon on each surface.

Strong adhesion and cohesion of chitosan in aqueous solutions

Chitosan, a load-bearing biomacromolecule found in the exoskeletons of crustaceans and insects, is a promising biopolymer for the replacement of synthetic plastic compounds. Here, surface interactions mediated by chitosan in aqueous solutions, including the effects of pH and contact time, were investigated using a surface forces apparatus (SFA). Chitosan films showed an adhesion to mica for all tested pH ranges (3.0-8.5), achieving a maximum value at pH 3.0 after a contact time of 1 h (Wad ~ 6.4 mJ/m(2)). We also found weak or no cohesion between two opposing chitosan layers on mica in aqueous buffer until the critical contact time for maximum adhesion (chitosan-mica) was reached. Strong cohesion (Wco ~ 8.5 mJ/m(2)) between the films was measured with increasing contact times up to 1 h at pH 3.0, which is equivalent to ~60% of the strongest, previously reported, mussel underwater adhesion. Such time-dependent adhesion properties are most likely related to molecular or molecular group reorientations and interdigitations. At high pH (8.5), the solubility of chitosan changes drastically, causing the chitosan-chitosan (cohesion) interaction to be repulsive at all separation distances and contact times. The strong contact time and pH-dependent chitosan-chitosan cohesion and adhesion properties provide new insight into the development of chitosan-based load-bearing materials.