An in vitro assessment of titanium functionalized with polysaccharides conjugated with vascular endothelial growth factor for enhanced osseointegration and inhibition of bacterial adhesion

N-acetylcysteine-functionalized coating avoids bacterial adhesion and biofilm formation

N-acetyl cysteine (NAC) is an FDA-approved drug clinically applied on a broad range of pathologies. Further research has been conducted with this drug to benefit from its antimicrobial activity potential. However, NAC has a very short half-life and therefore strategies that accomplish high local concentrations would be beneficial. In this study, covalent immobilization of NAC was performed, in order to obtain long-lasting high local concentration of the drug onto a chitosan(Ch)-derived implant-related coating. For the development of NAC-functionalized Ch films, water-based carbodiimide chemistry was applied to avoid the use of toxic organic solvents. Here we report the optimization steps performed to immobilize NAC onto the surface of pre-prepared Ch coatings, to ensure full exposure of NAC. Surface characterization using ellipsometry, water contact angle measurements and X-ray photoelectron spectroscopy (XPS), demonstrated the success of NAC immobilization at 4 mg/mL. Quartz crystal microbalance with dissipation (QCM-D) demonstrated that surface immobilized NAC decreases protein adsorption to Ch coatings. Biological studies confirmed that immobilized NAC4 avoids methicillin-resistant Staphylococcus aureus adhesion to Ch coating, impairing biofilm formation, without inducing cytotoxic effects. This is particularly interesting towards further developments as a prevention coating.

Bacterial infection microenvironment-responsive enzymatically degradable multilayer films for multifunctional antibacterial properties

The adhesion of bacteria is one of the most important stages in biofilm formation and bacterial infection. Once bacteria have adhered to a biomaterial surface, it is hard to eliminate them, and bacterial growth and infection are inevitable. In the current study, we have designed and constructed enzymatically degradable (hyaluronic acid/chitosan)n-(hyaluronic acid/polylysine)n ((HA/CHI)n-(HA/PLL)n) composite multilayer films via a layer-by-layer self-assembly method. Spectroscopic ellipsometry and scanning electron microscopy cross section measurements showed the exponential growth behavior of (HA/CHI)10-(HA/PLL)10 multilayer films (∼2 μm). The increased secretion of hyaluronidase and chymotrypsin in the bacterial infection microenvironment led to the fast degradation of the outer (PLL/HA)n multilayer films in the first 24 h. Enzymatic degradation of the multilayer films efficiently reduced the adhesion of both Staphylococcus aureus and Escherichia coli (>99%). Bacterial live/dead staining demonstrated the bactericidal action of the remaining bottom (CHI/HA)n multilayer films against the two kinds of bacteria. In vivo subcutaneous tests on New Zealand white rabbits, wound appearance and histopathology analysis showed that the implantation of composite multilayer film-modified PDMS promoted wound healing and the materials demonstrated a self-defense antibacterial effect. The material demonstrated both anti-adhesive and bactericidal properties and could be used to modify biomedical implants.

Backscattered electron imaging and electron backscattered diffraction in the study of bacterial attachment to titanium alloy structure

The application of secondary electron (SE) imaging, backscattered electron imaging (BSE) and electron backscattered diffraction (EBSD) was investigated in this work to study the bacterial adhesion and proliferation on a commercially pure titanium (cp Ti) and a Ti6Al4V alloy (Ti 64) with respect to substrate microstructure and chemical composition. Adherence of Gram-positive Staphylococcus epidermidis 11047 and Streptococcus sanguinis GW2, and Gram-negative Serratia sp. NCIMB 40259 and Escherichia coli 10418 was compared on cp Ti, Ti 64, pure aluminium (Al) and vanadium (V). The substrate microstructure and the bacterial distribution on these metals were characterised using SE, BSE and EBSD imaging. It was observed that titanium alloy-phase structure, grain boundaries and grain orientation did not influence bacterial adherence or proliferation at microscale. Adherence of all four strains was similar on cp Ti and Ti 64 surfaces whilst inhibited on pure Al. This work establishes a nondestructive and straight-forward statistical method to analyse the relationship between microbial distribution and metal alloy structure.

Mussel-inspired chitosan-polyurethane coatings for improving the antifouling and antibacterial properties of polyethersulfone membranes

A straightforward mussel-inspired approach was proposed to construct chitosan-polyurethane coatings and load Ag nanoparticles (AgNPs) to endow polyethersulfone (PES) membranes with dual-antibacterial and antifouling properties. The macromolecule O-carboxymethyl chitosan (CMC) was directly reacted with catechol in the absence of carbodiimide chemistry to form the coating and load AgNPs via in situ reduction; while lysine (Lys) was used as a representative small molecule for comparison. Then, PEG-based polyurethane (PU) was used for constructing Lys-Ag-PU and CMC-Ag-PU composite coatings, which substantially improved the protein antifouling property of the membranes. Furthermore, the CMC-Ag-PU coating exhibited superior broad-spectrum antibacterial property towards E. coli and S. aureus than Lys-Ag-PU coating. Meanwhile, the CMC-Ag-PU coating showed sustained antifouling property against bacteria and could reload AgNPs to be regenerated as antibacterial and antifouling coating. This approach is believed to have potential to fabricate reusable antifouling and antibacterial coatings on materials surfaces for aquatic industries.

Electrochemical deposition of dopamine–hyaluronic acid conjugates for anti-biofouling bioelectrodes

Electrochemical deposition of dopamine-hyaluronic acid conjugates onto electrode surfaces can lead to preserved electrochemical activities and anti-biofouling properties of the electrodes.

Bone tissue response induced by bioactive polymer functionalized Ti6Al4V surfaces: In vitro and in vivo study

Ti6Al4V is commonly used for orthopedic applications. This study was designed to test the potentially added benefit of Ti6Al4V functionalized with a bioactive polymer poly(sodium styrene sulfonate) both in vitro and in vivo. Cell-based assays with MC3T3-E1 osteoblast-like cells were used to measure the cell adhesion strength, cell spreading, focal contact formation, cell differentiation and the mineralization of extracellular matrix on grafted and ungrafted Ti6Al4V discs in combination with FBS and collagen type I. Bone morphogenetic protein-2 (BMP-2) was also included in the cell differentiation assay. Results showed that the grafted surface combined with collagen I gave superior levels in every parameter tested with cell-based assays and was almost equivalent to BMP-2 for cell differentiation. In vivo testing was conducted in rabbits (n=42) with cylinders of grafted and ungrafted Ti6Al4V implanted in defects made to the femoral and lateral condyles and animals that were maintained to 1, 3 and 12months. Hydroxyapatite coated Ti6Al4V cylinders were included as a clinical reference control. Osseointegration was assessed post-mortem using histomorphometric analysis conducted on resin sections of explanted undecalcified bone. Two histomorphometric parameters, that of bone-to-implant contact and the bone area, were analyzed by a trained observer blinded to sample identity. Results showed osseointegration on grafted Ti6Al4V was marginally better than both ungrafted and hydroxyapatite coated Ti6Al4V. Overall, the study found that the grafted Ti6Al4V significantly promoted all aspects of osteogenesis tested in vitro and, although in vivo outcomes were less compelling, histomorphometry showed osseointegration of grafted Ti6Al4V implants was equivalent or better than controls.

Immobilizing bacitracin on titanium for prophylaxis of infections and for improving osteoinductivity: An in vivo study

Bacitracin immobilized on the titanium (Ti) surface significantly improves anti-bacterial activity and biocompatibility in vitro. In the current study, we investigated the biologic performance (bactericidal effect and bone-implant integration) of bacitracin-modified Ti in vivo. A rat osteomyelitis model with femoral medullary cavity placement of Ti rods was employed to analyze the prophylactic effect of bacitracin-modified Ti (Ti-BC). Thirty-six female Sprague Dawley (SD) rats were used to establish the Ti implant-associated infection. The Ti and Ti-BC rods were incubated with and without Staphylococcus aureus to mimic the contaminated Ti rod and were implanted into the medullary cavity of the left femur, and sterile Ti rods were used as the blank control. After 3 weeks, the bone pathology was evaluated using X-ray and micro-computed tomography (micro-CT) analysis. For the investigation of the Ti-BC implant osseointegration in vivo, fifteen SD rats were divided into three groups (N=5), namely Ti, Ti-dopamine immobilized (Ti-DOPA), and Ti-BC. Ti rods were implanted into the left femoral cavity and micro-CT and histological evaluation was conducted after 12 weeks. The in vivo study indicated that Ti-immobilized bacitracin owned the prophylaxis potential for the infection associated with the Ti implants and allowed for the osseointegration. Thus, the multiple biofunctionalized Ti implants could be realized via immobilization of bacitracin, making them promising candidates for preventing the Ti implant-associated infections while retaining the osseointegration effects.

Cellular responses of osteoblast-like cells to 17 elemental metals

Elemental metals have been widely used to alloy metallic orthopedic implants. However, there is still insufficient research data elucidating the cell responses of osteoblastic cells to alloying elemental metals, which impedes the development of new metallic implant materials. In this study, the cellular responses of osteoblast-like cells (SaOS2) to 17 pure alloying elemental metals, that is, titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (Mn), iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), silicon (Si), and tin (Sn) were comparatively investigated in vitro. Cellular responses including intracellular total protein synthesis and collagen content, cell adhesion, cell proliferation, and alkaline phosphatase (ALP) activity on these elemental metals were systematically assessed and compared. It was found that these elemental metals could be categorized into three groups based on the cellular functions on them. Group 1, including Ti, Zr, Hf, Nb, Ta, Cr, Ru, and Si, showed excellent cell proliferation and varied ALP activity for SaOS2 cells. Cells exposed to Group 2, including Mo and Sn, although initially attached and grew, did not proliferate over time. In contrast, Group 3, including V, Mn, Fe, Co, Ni, Cu, and Zn, showed severe cytotoxicity toward SaOS2 cells. It is vital to consider the cell responses to the elemental metals when designing a new metallic implant material and the findings of this study provide insights into the biological performance of the elemental metals. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 148-158, 2017.

From Solution to Biointerface: Graphene Self-Assemblies of Varying Lateral Sizes and Surface Properties for Biofilm Control and Osteodifferentiation

Bringing multifunctional graphene out of solution through facile self-assembly to form 2D surface nanostructures, with control over the lateral size and surface properties, would be an intriguing accomplishment, especially in biomedical fields where biointerfaces with functional diversity are in high demand. Guided by this goal, in this work, we built such graphene-based self-assemblies on orthopedic titanium, attempting to selectively regulate bacterial activities and osteoblastic functions, which are both crucial in bone regeneration. Briefly, large-area graphene oxide (GO) sheets and functionalized reduced GO (rGO) micro-/nanosheets were self-assembled spontaneously and controllably onto solid Ti, through an evaporation-assisted electrostatic assembly process and a mussel-inspired one-pot assembly process, respectively. The resultant layers were characterized in terms of topological structure, chemical composition, hydrophilicity, and protein adsorption properties. The antibacterial efficacies of the assemblies were examined by challenging them with pathogenic Staphylococcus aureus (S. aureus) bacteria that produce biofilms, whereby around 50% antiadhesion effects and considerable antibiofilm activities were observed for both layer types but through dissimilar modes of action. Their cytocompatibility and osteogenic potential were also investigated. Interfaced with MC3T3-E1 cells, the functionalized rGO sheets evoked better cell adhesion and growth than GO sheets, whereas the latter elicited higher osteodifferentiation activity throughout a 28-day in vitro culture. In this work, we showed that it is technically possible to construct graphene interface layers of varying lateral dimensions and surface properties and confirmed the concept of using the obtained assemblies to address the two major challenges facing orthopedic clinics. In addition, we determined fundamental implications for understanding the surface-biology relationship of graphene biomaterials, in efforts to better design and more safely use them for future biomedicine.

Bio-functionalization of biomedical metals

Bio-functionalization means to endow biomaterials with bio-functions so as to make the materials or devices more suitable for biomedical applications. Traditionally, because of the excellent mechanical properties, the biomedical metals have been widely used in clinic. However, the utilized functions are basically supporting or fixation especially for the implantable devices. Nowadays, some new functions, including bioactivity, anti-tumor, anti-microbial, and so on, are introduced to biomedical metals. To realize those bio-functions on the metallic biomedical materials, surface modification is the most commonly used method. Surface modification, including physical and chemical methods, is an effective way to alter the surface morphology and composition of biomaterials. It can endow the biomedical metals with new surface properties while still retain the good mechanical properties of the bulk material. Having analyzed the ways of realizing the bio-functionalization, this article briefly summarized the bio-functionalization concepts of six hot spots in this field. They are bioactivity, bony tissue inducing, anti-microbial, anti-tumor, anticoagulation, and drug loading functions.

Biofunctionalization of titanium with bacitracin immobilization shows potential for anti-bacteria, osteogenesis and reduction of macrophage inflammation

Titanium has been widely used in the orthopedic and dental fields, however, the inert nature of Ti makes it unsuitable for application in promoting bone cell growth，osteogenic differentiation and antibacterial ability. The aims of the current study were to investigate the antimicrobial activity and biofunction of the polypeptide antibiotic bacitracin, and obtain a multi-biofunctional titanium implant by covalently-immobilizing titanium with the bacitracin. The results showed that the bacitracin possessed low minimum inhibitory concentration (MIC) to both Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA), with the non-cytotoxicity concentration up to 500μg/mL to human bone marrow mesenchymal stem cells (hBMSCs), furthermore, the bacitracin could improve the osteogenic differentiation of hBMSCs. The results of Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) indicated that bacitracin had been covalently immobilized on the surface of titanium. Immobilized bacitracin could improve the hydrophilic of immobilized titanium. The results of antimicrobial assay demonstrated that the covalently-immobilized bacitracin also had excellent antimicrobial property, and the bacitracin immobilized titanium could inhibit bacterial adhesion and colonization. The results of cell biology experiments proved that the bacitracin immobilized titanium could improve hBMSCs' adhesion, proliferation and osteogenic differentiation. We also found that the macrophages were difficult to spread or activate on the surface of bacitracin immobilized titanium, and the secretion of inflammatory factors had been inhibited. In conclusion, the novel bacitracin immobilized titanium has multi-biofunctions including outstanding antibacterial properties, excellent cell biology performance, and restraining inflammation, which has exciting application prospect.

Effect of Assembly pH on Polyelectrolyte Multilayer Surface Properties and BMP-2 Release

The effect of solution pH during layer-by-layer assembly of polyelectrolyte multilayer (PEM) coatings on properties relevant to orthopedic implant success was investigated. Bone morphogenetic protein 2 (BMP-2), a potent osteoconductive growth factor, was adsorbed onto the surface of anodized titanium, and PEM coatings prepared from solutions of poly-l-histidine and poly(methacrylic acid) were built on top of the BMP-2. High levels of BMP-2 released over several months were achieved. Approximately 2 μg/cm(2) of BMP-2 were initially adsorbed on the anodized titanium and a pH-dependent release behavior was observed, with more stable coatings assembled at pH = 6-7. Three different diffusion regimes could be determined from the release profiles: an initial burst release, a sustained release regime, and a depletion regime. BMP-2 was shown to maintain bioactivity after release from a PEM and the presence of a PEM was shown to preserve BMP-2 structure. No visible change was observed in surface roughness as the assembly pH was varied, whereas the surface energy decreased for samples prepared at more basic pH. These results indicate that the initial BMP-2 layer affects PEM surface structure, but not the functional groups exposed on the surface.

Reosseointegration Following Regenerative Therapy of Tissue-Engineered Bone in a Canine Model of Experimental Peri-Implantitis

BACKGROUND

Due to the existence of inflammation and limited osteogenesis on the precontaminated implant surface, reosseointegration is difficult to realize by current therapies. Tissue-engineering strategy has been proved quite effective in intractable bone defect situation.

PURPOSE

This study was designed to see whether the adoption of tissue-engineered bone complex of adipose-derived stem cells (ASCs) and bone morphogenetic protein-2 (BMP-2) gene delivery would work efficiently in the correction of experimental peri-implantitis.

METHODS

All premolars in both side of mandibular were removed from six beagle canines three months before implant placement. Typical peri-implantitis were then induced by three month ligature placement. After the implementation of identical anti-bacterial and mechanical debridement therapy, the shaped peri-implant defect were stuffed with four groups of constructs, as A: beta tricalcium phosphate (β-TCP); B: β-TCP with ASCs; C: β-TCP with enhanced green fluorescent protein gene transduced ASCs (AdGFP-ASCs); and D: β-TCP with bone morphogenetic protein-2 gene-modified ASCs (AdBMP-2-ASCs). Systematic radiographic, micro-CT, and histomorphometrical assessments were performed.

RESULTS

After six months of healing, more bone formation and reosseointegration was found around the implant of groups B and C than group A. And group D further promoted the new bone height and reosseointegration percentage. Moreover, sequential fluorescence labeling tells that group D exhibited the quickest and strongest bone formation on the cleaned implant surface during the entire observation period as compared to the other three groups.

CONCLUSIONS

These data demonstrated that tissue engineered bone of ASCs, BMP-2 gene delivery, and β-TCP could exert powerful therapeutic effect on peri-implantitis as expected, which may suggest a feasible way to maintain the stability and masticatory function of dental implant.

Epigallocatechin-3-gallate Protects against Hydrogen Peroxide-Induced Inhibition of Osteogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells

Oxidative stress induces bone loss and osteoporosis, and epigallocatechin-3-gallate (EGCG) may be used to combat these diseases due to its antioxidative property. Herein, oxidative stress in human bone marrow-derived mesenchymal stem cells (BM-MSCs) was induced by H₂O₂, resulting in an adverse effect on their osteogenic differentiation. However, this H₂O₂-induced adverse effect was nullified when the cells were treated with EGCG. In addition, treatment of BM-MSCs with EGCG alone also resulted in the enhancement of osteogenic differentiation of BM-MSCs. After EGCG treatment, expressions of β-catenin and cyclin D1 were upregulated, suggesting that the Wnt pathway was involved in the effects of EGCG on the osteogenic differentiation of BM-MSCs. This was also confirmed by the fact that the Wnt pathway inhibitor, Dickkopf-1 (DKK-1), can nullify the EGCG-induced enhancement effect on BM-MSC's osteogenic differentiation. Hence, our results suggested that EGCG can reduce the effects of oxidative stress on Wnt pathway in osteogenic cells, which supported a potentially promising therapy of bone disorders induced by oxidative stress. Considering its positive effects on BM-MSCs, EGCG may also be beneficial for stem cell-based bone repair.

Strontium (Sr) and silver (Ag) loaded nanotubular structures with combined osteoinductive and antimicrobial activities

Two frequent problems are associated with the titanium surfaces of bone/dental implants: lack of native tissue integration and associated infection. These problems have prompted a significant body of research regarding the modification of these surfaces. The present study describes a hydrothermal treatment for the fabrication of strontium (Sr) and silver (Ag) loaded nanotubular structures with different tube diameters on titanium surfaces. The Sr loading from a Sr(OH)2 solution was regulated by the size of the inner diameter of the titanium nanotubes (NT) (30nm or 80nm, formed at 10V or 40V, respectively). The quantity of Ag was adjusted by immersing the samples in 1.5 or 2.0M AgNO3 solutions. Sr and Ag were released in a controllable and prolonged matter from the NT-Ag.Sr samples, with negligible cytotoxicity. Prominent antibacterial activity was observed due to the release of Ag. Sr incorporation enhanced the initial cell adhesion, migration, and proliferation of preosteoblast MC3T3-E1 cells. Sr release also up-regulated the expression of osteogenic genes and induced mineralization, as suggested by the presence of more mineralized calcium nodules in cells cultured on NT-Ag.Sr surfaces. In vivo experiments showed that the Sr-loaded samples accelerated the formation of new bone in both osteoporosis and bone defect models, as confirmed by X-ray, Micro-CT evaluation, and histomorphometric analysis of rats implanted with NT-Ag.Sr samples. The antibacterial activity and outstanding osteogenic properties of NT-Ag.Sr samples highlight their excellent potential for use in clinical applications.

STATEMENT OF SIGNIFICANCE

Two frequent problems associated with Ti surfaces, widely used in orthopedic and dental arenas, are their lack of native tissue integration and risk of infection. We describe a novel approach for the fabrication of strontium (Sr) and silver (Ag) loaded nanotubular structures on titanium surfaces. A relevant aspect of this work is the demonstration of long-lasting and controllable Ag release, leading to excellent antibacterial and anti-adherent properties against methicillin-resistant Staphylococcus aureus (MRSA), and Gram-negative bacteria such as Escherichia coli. The extended release of Sr accelerates the filling of bone defects by improving the repair of damaged cortical bone and increasing trabecular bone microarchitecture. Our results highlight the potential of Sr and Ag loaded nanotubular structures for use in clinical applications.

Mussel-inspired silver-nanoparticle coating on porous titanium surfaces to promote mineralization

Porous titanium surfaces modified with mussel-inspired silver-nanoparticles for inhibiting bacterial adhesion and promoting mineralization and then improving osteoblast-biocompatibility.

Polysaccharide-based antibiofilm surfaces

Surface treatment by natural or modified polysaccharide polymers is a promising means to fight against implant-associated biofilm infections. The present review focuses on polysaccharide-based coatings that have been proposed over the last ten years to impede biofilm formation on material surfaces exposed to bacterial contamination. Anti-adhesive and bactericidal coatings are considered. Besides classical hydrophilic coatings based on hyaluronic acid and heparin, the promising anti-adhesive properties of the algal polysaccharide ulvan are underlined. Surface functionalization by antimicrobial chitosan and derivatives is extensively surveyed, in particular chitosan association with other polysaccharides in layer-by-layer assemblies to form both anti-adhesive and bactericidal coatings.

STATEMENT OF SIGNIFICANCE

Bacterial contamination of surfaces, leading to biofilm formation, is a major problem in fields as diverse as medicine, first, but also food and cosmetics. Many prophylactic strategies have emerged to try to eliminate or reduce bacterial adhesion and biofilm formation on surfaces of materials exposed to bacterial contamination, in particular implant materials. Polysaccharides are widely distributed in nature. A number of these natural polymers display antibiofilm properties. Hence, surface treatment by natural or modified polysaccharides is a promising means to fight against implant-associated biofilm infections. The present manuscript is an in-depth look at polysaccharide-based antibiofilm surfaces that have been proposed over the last ten years. This review, which is a novelty compared to published literature, will bring well documented and updated information to readers of Acta Biomaterialia.

Surface modifications and Nano-composite coatings to improve the bonding strength of titanium-porcelain

Surface modifications of Ti and nano-composite coatings were employed to simultaneously improve the surface roughness, corrosion resistance and chemical bonding between porclain-Ti. The specimens were studied by field-emission scanning electron microscopy, surface roughness, differential scanning calorimetry, Fourier transform infrared spectroscopy, corrosion resistance and bonding strength tests. The SEM results showed that hybrid structures with micro-stripes, nano-pores and nano-protuberances were prepared by surface modification of Ti, which significantly enhanced the surface roughness and corrosion resistance of Ti. Porous nano-composite coatings were synthesized on Ti anodized with pre-treatment in 40% HF acid. TiO2 nanoparticles were added into the hybrid coating to increase the solid phase content of the sols and avoid the formation of microcracks. With the TiO2 content increasing from 45 wt% to 60 wt%, the quantities of the microcracks on the coating surface gradually decreased. The optimal TiO2 content for the nanocomposite coatings is 60 wt% in this research. Compared to the uncoated group, the bonding strength of the coated groups showed a bonding strength improvement of 23.96%. The cytotoxicity of the 4# coating group was ranked as zero, which corresponds to non-cytotoxicity.

Contribution of fibronectin and vitronectin to the adhesion and morphology of MC3T3-E1 osteoblastic cells to poly(NaSS) grafted Ti6Al4V

This study is focused on understanding the underlying mechanisms involved in the improved in vitro and in vivo responses of osteoblasts on poly(sodium styrene sulfonate) (poly(NaSS)) functionalized Ti6Al4V surfaces. We probed the contribution of cell-adhesive glycoproteins fibronectin (Fn) and vitronectin (Vn) in the initial adhesion of MC3T3-E1 osteoblastic cells to poly(NaSS) functionalized and control Ti6Al4V surfaces. Firstly, culture media containing serum depleted of Fn and Vn (DD) were used to establish the contribution of Fn and Vn in the adhesion and spreading of cells on poly(NaSS) grafted and control surfaces. Compared to ungrafted surfaces, poly(NaSS) grafted surfaces enhanced the levels of cell adhesion, cell spreading and the formation of intracellular actin cytoskeleton and focal contacts in serum treatments where Fn or Vn were present (FBS, DD+Fn, DD+Vn). Cell responses to Fn were more significant than to Vn. Secondly, blocking Fn and Vn integrin receptors using antibodies to α5β1 (Fn) and αvβ1 (Vn) showed that adhesion of cells to poly(NaSS) grafted surfaces principally involved the Fn integrin receptor α5β1. Thirdly, blocking of the heparin and cell-binding regions of Fn molecule (RGD, C-HB, N-HB) showed that grafting with poly(NaSS) altered the conformation of Fn. Together these outcomes explained why the presence of sulfonate (SO3(-)) groups grafted on the Ti6Al4V surface enhanced the early cell adhesion and spreading processes which determine clinical success for applications that require osseointegration.

STATEMENT OF SIGNIFICANCE

This study is devoted to the basic analysis of the mechanism at the origin of the improved in vitro and in vivo osteoblast cell responses exhibited by poly(sodium styrene sulfonate) (poly(NaSS)) functionalized Ti6Al4V surfaces. The aim was to probe the contribution of cell adhesive glycoproteins fibronectin and vitronectin in the initial adhesion of MC3T3-E1 osteoblastic cells to poly(NaSS) functionalized Ti6Al4V surfaces. The outcomes of this research explained why the presence of SO3(-) (sulfonate) groups grafted on the Ti6Al4V surface enhanced the early cell adhesion and spreading processes which determine clinical success for applications that require osseointegration. This work is a step further in the research of poly(NaSS), a very promising bioactive polymer with potential to the orthopedic and dental fields.

Prevention and treatment of Staphylococcus aureus biofilms

S. aureus colonizes both artificial and tissue surfaces in humans causing chronic persistent infections that are difficult to cure. It is a notorious pathogen due to its antibiotic recalcitrance and phenotypic adaptability, both of which are facilitated by its ability to develop biofilms. S. aureus biofilms challenge conventional anti-infective approaches, most notably antibiotic therapy. Therefore there is an unmet need to develop and include parallel approaches that target S. aureus biofilm infections. This review discusses two broad anti-infective strategies: (1) preventative approaches (anti-biofilm surface coatings, the inclusion of biofilm-specific vaccine antigens); and (2) approaches aimed at eradicating established S. aureus biofilms, particularly those associated with implant infections. Advances in understanding the distinct nature of S. aureus biofilm development and pathogenesis have led to growing optimism in S. aureus biofilm targeted anti-infective strategies. Further research is needed however, to see the successful administration and validation of these approaches to the diverse types of infections caused by S. aureus biofilms from multiple clinical strains.

Increased Mesenchymal Stem Cell Response and Decreased Staphylococcus aureus Adhesion on Titania Nanotubes without Pharmaceuticals

Titanium (Ti) implants with enhanced biocompatibility and antibacterial property are highly desirable and characterized by improved success rates. In this study, titania nanotubes (TNTs) with various tube diameters were fabricated on Ti surfaces through electrochemical anodization at 10, 30, and 60 V (denoted as NT10, NT30, and NT60, resp.). Ti was also investigated and used as a control. NT10 with a diameter of 30 nm could promote the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) without noticeable differentiation. NT30 with a diameter of 100 nm could support the adhesion and proliferation of BMSCs and induce osteogenesis. NT60 with a diameter of 200 nm demonstrated the best ability to promote cell spreading and osteogenic differentiation; however, it clearly impaired cell adhesion and proliferation. As the tube diameter increased, bacterial adhesion on the TNTs decreased and reached the lowest value on NT60. Therefore, NT30 without pharmaceuticals could be used to increase mesenchymal stem cell response and decrease Staphylococcus aureus adhesion and thus should be further studied for improving the efficacy of Ti-based orthopedic implants.

Antimicrobial Hyaluronic Acid/Poly(amidoamine) Dendrimer Multilayer on Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) Prepared by a Layer-by-Layer Self-Assembly Method

In this article, we prepared hyaluronic acid/poly(amidoamine) dendrimer (HA/PAMAM) multilayers on a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-4HB)] substrate by a layer-by-layer self-assembly method for antimicrobial biomaterials. The results of ζ potential and quartz crystal microbalance with dissipation (QCM-D) showed that HA/PAMAM multilayers could be formed on the substrate layer by layer. We used QCM-D to show that both the HA outer layer and the PAMAM outer layer exhibited good protein-resistant activity to bovine serum albumin and bacterial antiadhesion activity to Escherichia coli. By a live/dead assay and the colony counting method, we found that the PAMAM outer layer could also exhibit bactericidal activity against E. coli, while the HA outer layer had no bactericidal activity. Both the bacterial antiadhesion activity and the bactericidal activity of the samples could be maintained even after storage in phosphate-buffered saline for up to 14 days. An in vitro MTT assay showed that the multilayers had no cytotoxicity to L929 cells, and HA molecules in the multilayers could improve the biocompatibility of the film.

Dual-function antibacterial surfaces for biomedical applications

Bacterial attachment and the subsequent formation of biofilm on surfaces of synthetic materials pose a serious problem in both human healthcare and industrial applications. In recent decades, considerable attention has been paid to developing antibacterial surfaces to reduce the extent of initial bacterial attachment and thereby to prevent subsequent biofilm formation. Briefly, there are three main types of antibacterial surfaces: bactericidal surfaces, bacteria-resistant surfaces, and bacteria-release surfaces. The strategy adopted to develop each type of surface has inherent advantages and disadvantages; many efforts have been focused on the development of novel antibacterial surfaces with dual functionality. In this review, we highlight the recent progress made in the development of dual-function antibacterial surfaces for biomedical applications. These surfaces are based on the combination of two strategies into one system, which can kill attached bacteria as well as resisting or releasing bacteria. Perspectives on future research directions for the design of dual-function antibacterial surfaces are also provided.

How does the pathophysiological context influence delivery of bone growth factors?

"Orthobiologics" represents an important category of therapeutics for the regeneration of bone defects caused by injuries or diseases, and bone growth factors are a particularly rapidly growing sub-category. Clinical application of bone growth factors has accelerated in the last two decades with the introduction of BMPs into clinical bone repair. Optimal use of growth factor-mediated treatments heavily relies on controlled delivery, which can substantially influence the local growth factor dose, release kinetics, and biological activity. The characteristics of the surrounding environment, or "context", during delivery can dictate growth factor loading efficiency, release and biological activity. This review discusses the influence of the surrounding environment on therapeutic delivery of bone growth factors. We specifically focus on pathophysiological components, including soluble components and cells, and how they can actively influence the therapeutic delivery and perhaps efficacy of bone growth factors.

Biological properties of nanostructured Ti incorporated with Ca, P and Ag by electrochemical method

TiO2 nanotube arrays were synthesized on Ti surface by anodic oxidation. The elements of Ca and P were simultaneously incorporated during nanotubes growth in SBF electrolyte, and then Ag was introduced to nanotube arrays by cathodic deposition, which endowed the good osseointegration and antibacterial property of Ti. The bioactivity of the Ti surface was evaluated by simulated body fluid soaking test. The biocompatibility was investigated by in vitro cell culture test. And the antibacterial effect against Staphylococcus aureus was examined by the bacterial counting method. The results showed that the incorporation of Ca, P and Ag elements had no significant influence on the formation of nanotube arrays on Ti surface during electrochemical treatment. Compared to the polished or nanotubular Ti surface, TiO2 nanotube arrays incorporated with Ca, P and Ag increased the formation of bone-like apatite in simulated body fluid, enhanced cell adhesion and proliferation, and inhibited the bacterial growth. Based on these results, it can be concluded that the nanostructured Ti incorporated with Ca, P and Ag by electrochemical method has promising applications as implant material.

FRET-based dual-emission and pH-responsive nanocarriers for enhanced delivery of protein across intestinal epithelial cell barrier

The oral route is a convenient and commonly employed way for drug delivery. However, therapeutic proteins have poor bioavailability upon oral administration due to the impermeable barrier from intestinal epithelial tight junction (TJ). Moreover, the pH of the small intestine varies among different regions of the intestinal tract where digestion and absorption occur at different levels. In this study, a tunable dual-emitting and pH-responsive nanocarrier that can alter the fluorescent color and emission intensity in response to pH changes and can trigger the opening of intestinal epithelial TJ at different levels were developed from chitosan-N-arginine and poly(γ-glutamic acid)-taurine conjugates. As pH increased from 6.0 to 8.0, the binding affinity of the oppositely charged polyions decreased, whereas the ratio of the intensity of the donor-to-acceptor emission intensity (ID/IA) increased by 27-fold. The fluorescent and pH-responsive nanocarrier was able to monitor the pH change of intestinal environment and to control the release of an anti-angiogenic protein in response to the pH gradient. The nanocarrier triggered the opening of intestinal epithelial TJ and consequently enhanced the permeation of the released protein through the intestinal epithelial barrier model (Caco-2 cell monolayer) to inhibit tube formation of human umbilical vein endothelial cells.

Polymeric nanoarchitectures on Ti-based implants for antibacterial applications

Because of the excellent mechanical properties and good biocompatibility, titanium-based metals are widely used in hard tissue repair, especially load-bearing orthopedic applications. However, bacterial infection and complication during and after surgery often causes failure of the metallic implants. To endow titanium-based implants with antibacterial properties, surface modification is one of the effective strategies. Possessing the unique organic structure composed of molecular and functional groups resembling those of natural organisms, functionalized polymeric nanoarchitectures enhance not only the antibacterial performance but also other biological functions that are difficult to accomplish on many conventional bioinert metallic implants. In this review, recent advance in functionalized polymeric nanoarchitectures and the associated antimicrobial mechanisms are reviewed.

Poly(NaSS) functionalization modulates the conformation of fibronectin and collagen type I to enhance osteoblastic cell attachment onto Ti6Al4V

Functionalization of surfaces with poly(sodium styrenesulfonate) (poly(NaSS)) has recently been found to enhance osteointegration of implantable materials. Radical polymerization of poly(NaSS) on titanium (Ti)-based substrates has been used to improve their long-term performance by preventing fibrosis and consequently implant loosening. However, the influence of the sulfonate groups on the early cell behavior and the associated molecular phenomena remains to be understood. In this work, we used quartz crystal microbalance with dissipation (QCM-D) to elucidate the role of poly(NaSS) in enhancing osteoblastic cell attachment. This was measured by following the cell attachment using the MC3T3-E1 cell line, on fetal bovine serum (FBS) preadsorbed surfaces and on substrates adsorbed with a series of relevant proteins, bovine serum albumin (BSA), fibronectin (Fn), and collagen type I (Col I). Comparison of the performance of poly(NaSS) with other clinically important substrates such as Ti alloy Ti6Al4V, gold, and poly(desamino-tyrosyl-tyrosine ethyl ester carbonate) (poly(DTEc)) indicates poly(NaSS) to be a superior substrate for MC3T3-E1 cells attachment. This attachment was found to be integrin mediated in the presence of Fn and Col I. Antibodies specific to the RGD peptide and the N- and C-terminal HB-binding domains reacted more intensively with Fn adsorbed on poly(NaSS). Fn adapts a conformation favorable to RGD mediated cell attachment when adsorbed onto poly(NaSS).

Characterization of hLF1-11 immobilization onto chitosan ultrathin films, and its effects on antimicrobial activity

hLF1-11 (GRRRRSVQWCA) is an antimicrobial peptide (AMP) with high activity against methicillin-resistant Staphylococcus aureus (MRSA), the most prevalent species in implant-associated infection. In this work, the effect of the surface immobilization on hLF1-11 antimicrobial activity was studied. Immobilization was performed onto chitosan thin films as a model for an implant coating due to its reported osteogenic and antibacterial properties. Chitosan thin films were produced by spin-coating on gold surfaces. hLF1-11 was immobilized onto these films by its C-terminal cysteine in an orientation that exposes the antimicrobial activity-related arginine-rich portion of the peptide. Two levels of exposure (with and without a polyethylene glycol (PEG) spacer) were analyzed. Covalent immobilization was further compared with the AMP physical adsorption onto chitosan films. Surfaces were characterized using ellipsometry, contact angle measurements, atomic force microscopy, infrared and X-ray photoelectron spectroscopies and using a fluorimetric assay for hLF1-11 quantification. Surface antimicrobial activity was assessed through surface adhesion and viability assays using an MRSA (S. aureus ATCC 33591). The incorporation of hLF1-11 increased significantly bacterial adhesion to chitosan films. However, the presence of hLF1-11, namely when immobilized through a PEG spacer, decreased the viability of adherent bacteria with regard to the control surface. These results demonstrated that hLF1-11 after covalent immobilization by its cysteine can maintain activity, particularly if a spacer is applied. However, further studies, exploring the opposite orientation or the same C-terminal orientation, but non-cysteine related, can help to clarify the potential of the hLF1-11 immobilization strategy.

Antibiotic-loaded chitosan hydrogel with superior dual functions: antibacterial efficacy and osteoblastic cell responses

It is critical for the clinical success to take the biological function into consideration when integrating the antibacterial function into the implanted biomaterials. To this aim, we prepared gentamycin sulfate (GS)-loaded carboxymethyl-chitosan (CM-chitosan) hydrogel cross-linked by genipin. The prepared hydrogels not only achieved superb inhibition on bacteria growth and biofilm formation of Staphylococcus aureus but also significantly enhanced the adhesion, proliferation, and differentiation of MC3T3-E1 cells. The observed dual functions were likely based on the intrinsic property of the positive charged chitosan-based hydrogel, which could be modified to selectively disrupt the bacteria wall/membrane and promote cell adhesion and proliferation, as suggested by the membrane permeability study. The genipin concentration played an important role in controlling the degradation time of the chitosan hydrogel and the MC3T3-E1 cell responses. The loading of GS not only significantly increased the antibacterial efficiency but also was beneficial for the osteoblastic cell responses. Overall, the biocompatibility of the prepared chitosan-GS hydrogel could be tuned with both the genipin and GS concentrations, which control the available positive charged sites of chitosan. The results demonstrated that chitosan-GS hydrogel is an effective and simple approach to achieving combined antibacterial efficacy and excellent osteoblastic cell responses, which has great potential in orthopedic applications.

Surface zwitterionization of titanium for a general bio-inert control of plasma proteins, blood cells, tissue cells, and bacteria

Surface coating of antifouling materials on the substrates offers convenient strategies and great opportunities to improve their biocompatibility and functions of host substrates for wide biomedical applications. In this work, we present a general surface zwitterionization strategy to improve surface biocompatibility and antifouling properties of titanium (Ti) by grafting zwitterionic poly(sulfobetaine methacrylate) (polySBMA). This method also demonstrates its general applicability to graft polySBMA onto Ti surface using different anchoring agents of dopamine and silane. The resulting polySBMA grafted from dopamine- (pTi-D-pSBMA) and silane-anchored titanium surfaces (pTi-Si-pSBMA) surfaces exhibit superlow fouling ability to highly resist the adhesions of plasma proteins, platelets, erythrocytes, leukocytes, human fibroblast (HT1080), E. coli, and S. epidermidis. The interfacial properties of the surface-modified Ti surfaces are analyzed and correlated with their antifouling properties. The new method and materials provide a more general, flexible, and robust way to produce an excellent nonfouling surface with adjustable interfacial structures of grafted polymers, which hopefully can be expanded to wider applications based on both the structure and surface superiorities.

Acidic pH resistance of grafted chitosan on dental implant

Over the last decade, access to dental care has increasingly become a service requested by the population, especially in the case of dental implants. However, the major cause of implant failure is an inflammatory disease: peri-implantitis. Currently, the adhesion strength of antibacterial coatings at implant surfaces remains a problem to solve. In order to propose a functionalized implant with a resistant antibacterial coating, a novel method of chitosan immobilization at implant surface has been investigated. Functionalization of the pre-active titanium (Ti) surface was performed using triethoxysilylpropyl succinic anhydride (TESPSA) as a coupling agent which forms a stable double peptide bond with chitosan. The chitosan presence and the chemical resistibility of the coating under acid pH solutions (pH 5 and pH 3) were confirmed by FTIR-ATR and XPS analyses. Furthermore, peel test results showed high adhesive resistance of the TESPSA/chitosan coating at the substrate. Cytocompatibility was evaluated by cell morphology with confocal imaging. Images showed healthy morphology of human gingival fibroblasts (HGF-1). Finally, the reported method for chitosan immobilization on Ti surface via peptide bindings allows for the improvement of its adhesive capacities and resistibility while maintaining its cytocompatibility. Surface functionalization using the TESPSA/chitosan coupling method is noncytotoxic and stable even in drastic environments as found in oral cavity, thus making it a valuable candidate for clinical implantology applications.

Responses of Staphylococcus aureus bacterial cells to nanocrystalline nickel nanostructures

A broad range of human diseases are associated with bacterial infections, often initiated by specific adhesion of a bacterium to the target environment. Despite the significant role of bacterial adhesion in human infectious diseases, details and mechanisms of bacterial adhesion have remained elusive. Herein, we study the physical interactions between Staphylococcus aureus, a type of micro-organism relevant to infections associated with medical implants, and nanocrystalline (nc) nickel nanostructures with various columnar features, including solid core, hollow, x-shaped and c-shaped pillars. Scanning electron microscopy results show the tendency of these bacterial cells to attach to the nickel nanostructures. Moreover, unique single bacterium attachment characteristics were observed on nickel nanostructures with dimensions comparable to the size of a single bacterium.

Enhanced osseointegration and antibacterial action of zinc-loaded titania-nanotube-coated titanium substrates: in vitro and in vivo studies

Poor osseointegration and infection resulting from implants are serious medical issues, and it is not straightforward to manufacture implants that can simultaneously address both of these problems. In this study, we produced coatings containing titania nanotubes (TiO2 -NTs) incorporated with zinc (NT-Zn) on Ti substrates by anodization and hydrothermal treatment. The zinc content was controlled by varying the duration of the hydrothermal treatment. The NT-Zn implants not only exhibited improved bone formation (shown by both in vitro and in vivo studies), which enhances osseointegration between bone and implant, but also inhibited growth of bacteria. The cytotoxicity of locally high concentrations of zinc in the NT-Zn3h specimens observed during in vitro studies was mitigated by the effects of dilution in vivo.

Bacterial and osteoblast behavior on titanium, cobalt-chromium alloy and stainless steel treated with alkali and heat: a comparative study for potential orthopedic applications

HYPOTHESIS

Anatase-modified titanium (Ti) substrates have been found to possess antibacterial properties in the absence of ultraviolet irradiation, but the mechanism is not known. We hypothesize that this is due to the bactericidal effects of reactive oxygen species (ROS) generated by the surface anatase.

EXPERIMENTS

Alkali and heat treatment was used to form anatase on Ti surface. The generation of ROS, and the behavior of bacteria and osteoblasts on the anatase-modified Ti were investigated. Cobalt-chrome (Co-Cr) alloys and stainless steel (SS) were similarly treated with alkali and heat, and their surface properties and effects on bacteria and osteoblasts were compared with the results obtained with Ti.

FINDINGS

The anatase-functionalized Ti substrates demonstrated significant bactericidal effects and promoted apoptosis in osteoblasts, likely a result of ROS generated by the anatase. The alkali and heat-treated Co-Cr and SS substrates also reduced bacterial adhesion but were not bactericidal. This effect is likely due to an increase in hydrophilicity of the surfaces, and no significant ROS were generated by the alkali and heat-treated Co-Cr and SS substrates. The treated Co-Cr and SS substrates did not induce significant apoptosis in osteoblasts, and thus with these properties, they may be promising for orthopedic applications.

PolyNaSS grafting on titanium surfaces enhances osteoblast differentiation and inhibits Staphylococcus aureus adhesion

Titanium surface modifications to simultaneously prevent bacterial adhesion but promote bone-cell functions could be highly beneficial for improving implant osseointegration. In the present in vitro study, the effect of sulfonate groups on titanium surfaces was investigated with respect to both S. aureus adhesion and osteoblast functions pertinent to new bone formation. Commercial pure titanium (cpTi) squares were oxydized (Tiox), grafted with poly(sodium styrene sulfonate) groups (Tigraft) by covalent bonding using radical polymerization, and were characterized by infrared spectroscopy (HATR-FTIR) and colorimetry. Bacterial adhesion study showed that Tigraft exhibited high inhibition of S. aureus adhesion S at levels >90 %, when compared to cpTi (P < 0.05). In contrast osteoblasts adhesion was similar on all three titanium surfaces. While the kinetics of cell proliferation were similar on the three titanium surfaces, Alkaline phosphatase-specific activity of osteoblasts cultured on Tigraft surfaces was twofold higher than that observed on either on Tiox or cpTi surfaces (P < 0.01). More importantly, the amount and the distribution of calcium-containing nodules was different. The total area covered by calcium-containing nodules was 2.2-fold higher on the Tigraft as compared to either Tiox or cpTi surfaces (P < 0.01). These results provide evidence that poly(sodium styrene sulfonate) groups grafting on cpTi simultaneously inhibits bacteria adhesion but promote osteoblast function pertinent to new bone formation. Such modified titanium surfaces offer a promising strategy for preventing biofilm-related infections and enhancing osteointegration of implants in orthopaedic and dental applications.

Assessment of stability of surface anchors for antibacterial coatings and immobilized growth factors on titanium

Titanium (Ti) has been functionalized with biomolecules for biomedical purposes. However, there is very limited information on the stability of such functionalities. Ti surface functionalized with carboxymethyl chitosan (CMCS) and bone morphogenetic protein 2 (BMP-2) has been reported to inhibit bacterial colonization while at the same time enhances osteoblast functions. In this work, three types of anchoring molecules, (3-aminopropyl) triethoxysilane (Silane), dopamine (DA), and polydopamine (PDA), were used for immobilizing the CMCS on Ti. The CMCS-modified surfaces were subjected to 70% ethanol treatment, autoclaving, and prolonged immersion in phosphate buffered saline (PBS). After the treatment procedures, the ability of the CMCS-modified substrates to inhibit colonization by Staphylococcus epidermidis (S. epidermidis) was assessed to evaluate the stability of the immobilized CMCS. The bacterial adhesion assays showed that the CMCS-DA- and CMCS-PDA-modified Ti remained stable after 70% ethanol treatment, autoclaving, and prolonged immersion in PBS, whereas the CMCS-Silane-modified Ti was less stable after autoclaving and prolonged immersion in PBS. The CMCS-DA- and CMCS-PDA-modified Ti substrates were functionalized with BMP-2 and used to support osteoblast growth. Evaluation of alkaline phosphatase (ALP) activity and calcium deposition from osteoblasts cultured on these substrates, which have been treated with 70% ethanol, or subjected to autoclaving, and prolonged immersion in PBS indicated that the immobilized BMP-2 on these surfaces retained its bioactivity.