All-in-one trifunctional strategy: A cell adhesive, bacteriostatic and bactericidal coating for titanium implants

Surface (bio)-functionalization of metallic materials: How to cope with real interfaces?

Metallic materials are an important class of biomaterials used in various medical devices, owing to a suitable combination of their mechanical properties. The (bio)-functionalization of their surfaces is frequently performed for biocompatibility requirements, as it offers a powerful way to control their interaction with biological systems. This is particularly important when physicochemical processes and biological events, mainly involving proteins and cells, are initiated at the host-material interface. This review addresses the state of "real interfaces" in the context of (bio)-functionalization of metallic materials, and the necessity to cope with it to avoid frequent improper evaluation of the procedure used. This issue is, indeed, well-recognized but often neglected and emerges from three main issues: (i) ubiquity of surface contamination with organic compounds, (ii) reactivity of metallic surfaces in biological medium, and (iii) discrepancy in (bio)-functionalization procedures between expectations and reality. These disturb the assessment of the strategies adopted for surface modifications and limit the possibilities to provide guidelines for their improvements. For this purpose, X-ray photoelectrons spectroscopy (XPS) comes to the rescue. Based on significant progresses made in methodological developments, and through a large amount of data compiled to generate statistically meaningful information, and to insure selectivity, precision and accuracy, the state of "real interfaces" is explored in depth, while looking after the two main constituents: (i) the bio-organic adlayer, in which the discrimination between the compounds of interest (anchoring molecules, coupling agents, proteins, etc) and organic contaminants can be made, and (ii) the metallic surface, which undergoes dynamic processes due to their reactivity. Moreover, through one of the widespread (bio)-functionalization strategy, given as a case study, a particular attention is devoted to describe the state of the interface at different stages (composition, depth distribution of contaminants and (bio)compounds of interest) and the mode of protein retention. It is highlighted, in particular, that the occurrence or improvement of bioactivity does not demonstrate that the chemical schemes worked in reality. These aspects are particularly essential to make progress on the way to choose the suitable (bio)-functionalization strategy and to provide guidelines to improve its efficiency.

Polyimide biocomposites coated with tantalum pentoxide for stimulation of cell compatibility and enhancement of biointegration for orthopedic implant

Orthopedic implants are an important tool in the treatment of musculoskeletal conditions and helped many patients to improve their quality of life. Various inorganic-organic biocomposites have been broadly investigated particularly in the area of load-bearing orthopedic/dental applications. Polyimide (PI) is a promising organic material and shows excellent mechanical properties, biocompatibility, bio-stability, and its elastic modulus is similar to human bone but it lacks bioactivity, which is very important for cell adhesion and ultimately for bone regeneration. In this research, tantalum pentoxide (Ta2O5) coating was prepared on the surface of PI by polydopamine (PDA) bonding. The results showed that Ta2O5 was evenly coated on the surface of PI, and with the concentration of Ta2O5 in the PDA suspension increased, the content of Ta2O5 particles on the surface of PI increased significantly. In addition, the Ta2O5 coating significantly increased the roughness and hydrophilicity of the PI matrix. Cell experiments showed that PI surface coating Ta2O5 could promote the proliferation, adhesion, and osteogenic differentiation of bone marrow-derived stromal cells (BMSCs). The results demonstrated that fabricating Ta2O5 coating on the surface of PI through PDA bonding could improve the biocompatibility as well as bioactivity of PI, and increase the application potential of PI in the field of bone repair materials.

Research progress of biomimetic materials in oral medicine

Biomimetic materials are able to mimic the structure and functional properties of native tissues especially natural oral tissues. They have attracted growing attention for their potential to achieve configurable and functional reconstruction in oral medicine. Though tremendous progress has been made regarding biomimetic materials, significant challenges still remain in terms of controversy on the mechanism of tooth tissue regeneration, lack of options for manufacturing such materials and insufficiency of in vivo experimental tests in related fields. In this review, the biomimetic materials used in oral medicine are summarized systematically, including tooth defect, tooth loss, periodontal diseases and maxillofacial bone defect. Various theoretical foundations of biomimetic materials research are reviewed, introducing the current and pertinent results. The benefits and limitations of these materials are summed up at the same time. Finally, challenges and potential of this field are discussed. This review provides the framework and support for further research in addition to giving a generally novel and fundamental basis for the utilization of biomimetic materials in the future.

Titanium Boston keratoprosthesis with corneal cell adhesive and bactericidal dual coating

The Boston keratoprosthesis (BKPro) is a medical device used to restore vision in complicated cases of corneal blindness. This device is composed by a front plate of polymethylmethacrylate (PMMA) and a backplate usually made of titanium (Ti). Ti is an excellent biomaterial with numerous applications, although there are not many studies that address its interaction with ocular cells. In this regard, despite the good retention rates of the BKPro, two main complications compromise patients' vision and the viability of the prosthesis: imperfect adhesion of the corneal tissue to the upside of the backplate and infections. Thus, in this work, two topographies (smooth and rough) were generated on Ti samples and tested with or without functionalization with a dual peptide platform. This molecule consists of a branched structure that links two peptide moieties to address the main complications associated with BKPro: the well-known RGD peptide in its cyclic version (cRGD) as cell pro-adherent motif and the first 11 residues of lactoferrin (LF1-11) as antibacterial motif. Samples were physicochemically characterized, and their biological response was evaluated in vitro with human corneal keratocytes (HCKs) and against the gram-negative bacterial strain Pseudomonas aeruginosa. The physicochemical characterization allowed to verify the functionalization in a qualitative and quantitative manner. A higher amount of peptide was anchored to the rough surfaces. The studies performed using HCKs showed increased long-term proliferation on the functionalized samples. Gene expression was affected by topography and peptide functionalization. Roughness promoted α-smooth muscle actin (α-SMA) overexpression, and the coating notably increased the expression of extracellular matrix components (ECM). Such changes may favour the development of unwanted fibrosis, and thus, corneal haze. In contrast, the combination of the coating with a rough topography decreased the expression of α-SMA and ECM components, which would be desirable for the long-term success of the prosthesis. Regarding the antibacterial activity, the functionalized smooth and rough surfaces promoted the death of bacteria, as well as a perturbation in their wall definition and cellular morphology. Bacterial killing values were 58 % for smooth functionalised and 68 % for rough functionalised samples. In summary, this study suggests that the use of the dual peptide platform with cRGD and LF1-11 could be a good strategy to improve the in vitro and in vivo performance of the rough topography used in the commercial BKPro.

Comparison of the Antibacterial Effect of Silver Nanoparticles and a Multifunctional Antimicrobial Peptide on Titanium Surface

Titanium implantation success may be compromised by Staphylococcus aureus surface colonization and posterior infection. To avoid this issue, different strategies have been investigated to promote an antibacterial character to titanium. In this work, two antibacterial agents (silver nanoparticles and a multifunctional antimicrobial peptide) were used to coat titanium surfaces. The modulation of the nanoparticle (≈32.1 ± 9.4 nm) density on titanium could be optimized, and a sequential functionalization with both agents was achieved through a two-step functionalization method by means of surface silanization. The antibacterial character of the coating agents was assessed individually as well as combined. The results have shown that a reduction in bacteria after 4 h of incubation can be achieved on all the coated surfaces. After 24 h of incubation, however, the individual antimicrobial peptide coating was more effective than the silver nanoparticles or their combination against Staphylococcus aureus. All tested coatings were non-cytotoxic for eukaryotic cells.

Polymers showing intrinsic antimicrobial activity

Pathogenic microorganisms are considered to a major threat to human health, impinging on multiple sectors including hospitals, dentistry, food storage and packaging, and water contamination. Due to the increasing levels of antimicrobial resistance shown by pathogens, often caused by long-term abuse or overuse of traditional antimicrobial drugs, new approaches and solutions are necessary. In this area, antimicrobial polymers are a viable solution to combat a variety of pathogens in a number of contexts. Indeed, polymers with intrinsic antimicrobial activities have long been an intriguing research area, in part, due to their widespread natural abundance in materials such as chitin, chitosan, carrageen, pectin, and the fact that they can be tethered to surfaces without losing their antimicrobial activities. In addition, since the discovery of the strong antimicrobial activity of some synthetic polymers, much work has focused on revealing the most effective structural elements that give rise to optimal antimicrobial properties. This has often been synthesis targeted, with the generation of either new polymers or the modification of natural antimicrobial polymers with the addition of antimicrobial enhancing modalities such as quaternary ammonium or guanidinium groups. In this review, the growing number of polymers showing intrinsic antimicrobial properties from the past decade are highlighted in terms of synthesis; often based on post-synthesis modification and their utilization. This includes as surface coatings, for example on medical devices, such as intravascular catheters, orthopaedic implants and contact lenses, or directly as antibacterial agents (specifically as eye drops). Surface functionalisation with inherently antimicrobial polymers is highlighted and has been achieved via various techniques, including surface-bound initiators allowing RAFT or ATRP surface-based polymerization, or via physical immobilization such as by layer-by-layer techniques. This article also covers the mechanistic modes of action of intrinsic antimicrobial polymers against bacteria, viruses, or fungi.

Recent Advances in the Control of Clinically Important Biofilms

Biofilms are complex structures formed by bacteria, fungi, or even viruses on biotic and abiotic surfaces, and they can be found in almost any part of the human body. The prevalence of biofilm-associated diseases has increased in recent years, mainly because of the frequent use of indwelling medical devices that create opportunities for clinically important bacteria and fungi to form biofilms either on the device or on the neighboring tissues. As a result of their resistance to antibiotics and host immunity factors, biofilms have been associated with the development or persistence of several clinically important diseases. The inability to completely eradicate biofilms drastically increases the burden of disease on both the patient and the healthcare system. Therefore, it is crucial to develop innovative ways to tackle the growth and development of biofilms. This review focuses on dental- and implant-associated biofilm infections, their prevalence in humans, and potential therapeutic intervention strategies, including the recent advances in pharmacology and biomedical engineering. It lists current strategies used to control the formation of clinically important biofilms, including novel antibiotics and their carriers, antiseptics and disinfectants, small molecule anti-biofilm agents, surface treatment strategies, and nanostructure functionalization, as well as multifunctional coatings particularly suitable for providing antibacterial effects to the surface of implants, to treat either dental- or implant-related bacterial infections.

Dental Materials for Oral Microbiota Dysbiosis: An Update

The balance or dysbiosis of the microbial community is a major factor in maintaining human health or causing disease. The unique microenvironment of the oral cavity provides optimal conditions for colonization and proliferation of microbiota, regulated through complex biological signaling systems and interactions with the host. Once the oral microbiota is out of balance, microorganisms produce virulence factors and metabolites, which will cause dental caries, periodontal disease, etc. Microbial metabolism and host immune response change the local microenvironment in turn and further promote the excessive proliferation of dominant microbes in dysbiosis. As the product of interdisciplinary development of materials science, stomatology, and biomedical engineering, oral biomaterials are playing an increasingly important role in regulating the balance of the oral microbiome and treating oral diseases. In this perspective, we discuss the mechanisms underlying the pathogenesis of oral microbiota dysbiosis and introduce emerging materials focusing on oral microbiota dysbiosis in recent years, including inorganic materials, organic materials, and some biomolecules. In addition, the limitations of the current study and possible research trends are also summarized. It is hoped that this review can provide reference and enlightenment for subsequent research on effective treatment strategies for diseases related to oral microbiota dysbiosis.

Graphene oxide and mineralized collagen-functionalized dental implant abutment with effective soft tissue seal and romotely repeatable photodisinfection

Grasping the boundary of antibacterial function may be better for the sealing of soft tissue around dental implant abutment. Inspired by ‘overdone is worse than undone’, we prepared a sandwich-structured dental implant coating on the percutaneous part using graphene oxide (GO) wrapped under mineralized collagen. Our unique coating structure ensured the high photothermal conversion capability and good photothermal stability of GO. The prepared coating not only achieved suitable inhibition on colonizing bacteria growth of Streptococcus sanguinis, Fusobacterium nucleatum and Porphyromonas gingivalis but also disrupted the wall/membrane permeability of free bacteria. Further enhancements on the antibacterial property were generally observed through the additional incorporation of dimethylaminododecyl methacrylate. Additionally, the coating with sandwich structure significantly enhanced the adhesion, cytoskeleton organization and proliferation of human gingival fibroblasts, which was effective to improve soft tissue sealing. Furthermore, cell viability was preserved when cells and bacteria were cultivated in the same environment by a coculture assay. This was attributed to the sandwich structure and mineralized collagen as the outmost layer, which would protect tissue cells from photothermal therapy and GO, as well as accelerate the recovery of cell activity. Overall, the coating design would provide a useful alternative method for dental implant abutment surface modification and functionalization.

Influence of Bone-Level Dental Implants Placement and of Cortical Thickness on Osseointegration: In Silico and In Vivo Analyses

The purpose of this research is to study the biomechanical response of dental implants in bone-level type locations, 0.5 mm above and below the bone level. In addition, the influence of the thickness of the cortical bone on osseointegration is determined due to the mechanical loads transfer from the dental implant to the cortical and trabecular bone. The thicknesses studied were 1.5 mm and 2.5 mm. Numerical simulations were performed using a finite element method (FEM)-based model. In order to verify the FEM model, the in silico results were compared with the results obtained from a histological analysis performed in an in vivo study with 30 New Zealand rabbits. FEM was performed using a computerized 3D model of bone-level dental implants inserted in the lower jawbone with an applied axial load of 100 N. The analysis was performed using different distances from the bone level and different thicknesses of cortical bone. The interface area of bone growth was evaluated by analyzing the bone–implant contact (BIC), region of interest (ROI) and total bone area (BAT) parameters obtained through an in vivo histological process and analyzed by scanning electron microscopy (SEM). Bone-level implants were inserted in the rabbit tibiae, with two implants placed per tibia. These parameters were evaluated after three or six weeks of implantation. FEM studies showed that placements 0.5 mm below the bone level presented lower values of stress distribution compared to the other studied placements. The lower levels of mechanical stress were then correlated with the in vivo studies, showing that this position presented the highest BIC value after three or six weeks of implantation. In this placement, vertical bone growth could be observed up the bone level. The smallest thickness of the study showed a better transfer of mechanical loads, which leads to a better osseointegration. In silico and in vivo results both concluded that the implants placed 0.5 mm below the cortical bone and with lower thicknesses presented the best biomechanical and histological behavior in terms of new bone formation, enhanced mechanical stability and optimum osseointegration.

Multifunctional Coatings of Titanium Implants Toward Promoting Osseointegration and Preventing Infection: Recent Developments

Titanium and its alloys are dominant material for orthopedic/dental implants due to their stable chemical properties and good biocompatibility. However, aseptic loosening and peri-implant infection remain problems that may lead to implant removal eventually. The ideal orthopedic implant should possess both osteogenic and antibacterial properties and do proper assistance to in situ inflammatory cells for anti-microbe and tissue repair. Recent advances in surface modification have provided various strategies to procure the harmonious relationship between implant and its microenvironment. In this review, we provide an overview of the latest strategies to endow titanium implants with bio-function and anti-infection properties. We state the methods they use to preparing these efficient surfaces and offer further insight into the interaction between these devices and the local biological environment. Finally, we discuss the unmet needs and current challenges in the development of ideal materials for bone implantation.

Microbial Biofilm Decontamination on Dental Implant Surfaces: A Mini Review

Introduction

After insertion into the bone, implants osseointegrate, which is required for their long-term success. However, inflammation and infection around the implants may lead to implant failure leading to peri-implantitis and loss of supporting bone, which may eventually lead to failure of implant. Surface chemistry of the implant and lack of cleanliness on the part of the patient are related to peri-implantitis. The only way to get rid of this infection is decontamination of dental implants.

Objective

This systematic review intended to study decontamination of microbial biofilm methods on titanium implant surfaces used in dentistry.

Methods

The electronic databases Springer Link, Science Direct, and PubMed were explored from their inception until December 2020 to identify relevant studies. Studies included had to evaluate the efficiency of new strategies either to prevent formation of biofilm or to treat matured biofilm on dental implant surfaces.

Results and Discussion

In this systematic review, 17 different groups of decontamination methods were summarized from 116 studies. The decontamination methods included coating materials, mechanical cleaning, laser treatment, photodynamic therapy, air polishing, anodizing treatment, radiation, sonication, thermal treatment, ultrasound treatment, chemical treatment, electrochemical treatment, antimicrobial drugs, argon treatment, and probiotics.

Conclusion

The findings suggest that most of the decontamination methods were effective in preventing the formation of biofilm and in decontaminating established biofilm on dental implants. This narrative review provides a summary of methods for future research in the development of new dental implants and decontamination techniques.

3D printing of hierarchical porous biomimetic hydroxyapatite scaffolds: Adding concavities to the convex filaments

Porosity plays a key role on the osteogenic performance of bone scaffolds. Direct Ink Writing (DIW) allows the design of customized synthetic bone grafts with patient-specific architecture and controlled macroporosity. Being an extrusion-based technique, the scaffolds obtained are formed by arrays of cylindrical filaments, and therefore have convex surfaces. This may represent a serious limitation, as the role of surface curvature and more specifically the stimulating role of concave surfaces in osteoinduction and bone growth has been recently highlighted. Hence the need to design strategies that allow the introduction of concave pores in DIW scaffolds. In the current study, we propose to add gelatin microspheres as a sacrificial material in a self-setting calcium phosphate ink. Neither the phase transformation responsible for the hardening of the scaffold nor the formation of characteristic network of needle-like hydroxyapatite crystals was affected by the addition of gelatin microspheres. The partial dissolution of the gelatin resulted in the creation of spherical pores throughout the filaments and exposed on the surface, increasing filament porosity from 0.2 % to 67.9 %. Moreover, the presence of retained gelatin proved to have a significant effect on the mechanical properties, reducing the strength but simultaneously giving the scaffolds an elastic behavior, despite the high content of ceramic as a continuous phase. Notwithstanding the inherent difficulty of in vitro cultures with this highly reactive material an enhancement of MG-63 cell proliferation, as well as better spreading of hMSCs was recorded on the developed scaffolds. STATEMENT OF SIGNIFICANCE: Recent studies have stressed the role that concave surfaces play in tissue regeneration and, more specifically, in osteoinduction and osteogenesis. Direct ink writing enables the production of patient-specific bone grafts with controlled architecture. However, besides many advantages, it has the serious limitation that the surfaces obtained are convex. In this article, for the first time we develop a strategy to introduce concave pores in the printed filaments of biomimetic hydroxyapatite by incorporation and partial dissolution of gelatin microspheres. The retention of part of the gelatin results in a more elastic behavior compared to the brittleness of hydroxyapatite scaffolds, while the needle-shaped nanostructure of biomimetic hydroxyapatite is maintained and gelatin-coated concave pores on the surface of the filaments enhance cell spreading.

New trends in the development of multifunctional peptides to functionalize biomaterials

Improving cell-material interactions is a major goal in tissue engineering. In this regard, functionalization of biomaterials with cell instructive molecules from the extracellular matrix stands out as a powerful strategy to enhance their bioactivity and achieve optimal tissue integration. However, current functionalization strategies, like the use of native full-length proteins, are associated with drawbacks, thus urging the need of developing new methodologies. In this regard, the use of synthetic peptides encompassing specific bioactive regions of proteins represents a promising alternative. In particular, the combination of peptide sequences with complementary or synergistic effects makes it possible to address more than one biological target at the biomaterial surface. In this review, an overview of the main strategies using peptides to install multifunctionality on biomaterials is presented, mostly focusing on the combination of the RGD motif with other peptides sequences. The evolution of these approaches, starting from simple methods, like using peptide mixtures, to more advanced systems of peptide presentation, with very well defined chemical properties, are explained. For each system of peptide's presentation, three main aspects of multifunctionality-improving receptor selectivity, mimicking the extracellular matrix and preventing bacterial colonization while improving cell adhesion-are highlighted.

Surface engineering of biomaterials in orthopedic and dental implants: Strategies to improve osteointegration, bacteriostatic and bactericidal activities

BACKGROUND

The success of biomedical implants in orthopedic and dental applications is usually limited due to insufficient bone-implant integration, and implant-related infections. Biointerfaces are critical in regulating their interactions and the desirable performance of biomaterials in biological environment. Surface engineering has been widely studied to realize better control of the interface interaction to further enhance the desired behavior of biomaterials.

PURPOSE AND SCOPE

This review aims to investigate surface coating strategies in hard tissue applications to address insufficient osteointegration and implant-related infection problems.

SUMMARY

We first focused on surface coatings to enhance the osteointegration and biocompatibility of implants by emphasizing calcium phosphate-related, nanoscale TiO₂ -related, bioactive tantalum-based and biomolecules incorporated coatings. Different coating strategies such as plasma spraying, biomimetic deposition, electrochemical anodization and LENS are discussed. We then discussed techniques to construct anti-adhesive and bactericidal surface while emphasizing multifunctional surface coating techniques that combine potential osteointegration and antibacterial activities. The effects of nanotopography via TiO₂ coatings on antibacterial performance are interesting and included. A smart bacteria-responsive titanium dioxide nanotubes coating is also attractive and elaborated.

CONCLUSION

Developing multifunctional surface coatings combining osteogenesis and antimicrobial activity is the current trend. Surface engineering methods are usually combined to obtain hierarchical multiscale surface structures with better biofunctionalization outcomes.

One-Step Liquid Phase Polymerization of HEMA by Atmospheric-Pressure Plasma Discharges for Ti Dental Implants

Dental implants can fail due to various factors, in which bad tissue integration is believed to have a significant role. Specific properties of the implant surface, such as its chemistry and roughness, are of paramount importance to address specific cell responses, such as the adsorption of proteins, as well as the adhesion and differentiation of cells, which are suitable for biomaterial and tissue engineering. In this study, an acrylate-containing coating was produced on titanium surfaces through the atmospheric pressure plasma treatment of a liquid precursor, 2-hydroxyethyl methacrylate. A hydrophilic coating was obtained, showing retention of the monomer chemistry as assessed by FTIR analysis and XPS. Enhanced fibroblast adhesion and decreased Staphylococcus aureus and Escherichia coli adhesion were recorded, showing that this is a suitable method to produce biocompatible coatings with a reduced bacterial adhesion.

New developments in anti-biofilm intervention towards effective management of orthopedic device related infections (ODRI's)

Orthopedic device related infections (ODRI's) represent a difficult to treat situation owing to their biofilm based nature. Biofilm infections once established are difficult to eradicate even with an aggressive treatment regimen due to their recalcitrance towards antibiotics and immune attack. The involvement of antibiotic resistant pathogens as the etiological agent further worsens the overall clinical picture, pressing on the need to look into alternative treatment strategies. The present review highlightes the microbiological challenges associated with treatment of ODRI's due to biofilm formation on the implant surface. Further, it details the newer anti-infective modalities that work either by preventing biofilm formation and/or through effective disruption of the mature biofilms formed on the medical implant. The study, therefore aims to provide a comprehensive insight into the newer anti-biofilm interventions (non-antibiotic approaches) and a better understanding of their mechanism of action essential for improved management of orthopedic implant infections.

Chemically Diverse Multifunctional Peptide Platforms with Antimicrobial and Cell Adhesive Properties

Bacterial infections and incomplete biomaterial integration are major problems that can lead to the failure of medical implants. However, simultaneously addressing these two issues remains a challenge. Here, we present a chemical peptide library based on a multifunctional platform containing the antimicrobial peptide LF1-11 and the cell-adhesive motif RGD. The scaffolds were customized with catechol groups to ensure straightforward functionalization of the implant surface, and linkers of different length to assess the effect of peptide accessibility on the biological response. The peptidic platforms significantly improved the adhesion of mesenchymal stem cells and showed antimicrobial effects against Staphylococcus aureus. Of note is that peptides bearing spacers that were too long displayed the lowest efficiency. Subsequently, we designed a platform replacing linear RGD by cyclic RGD; this further enhanced eukaryotic cell adhesion while retaining excellent antimicrobial properties, thus being a suitable candidate for tissue engineering applications.

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Biological Effects of Titanium Surface Charge with a Focus on Protein Adsorption

The effect of changes in surface charge on the biological properties of implants is not clear. The objective of this study was to evaluate the biological properties of the surface of titanium sheets with different charges due to different treatment methods. Titanium sheets were sandblasted with large grit and underwent acid etching before being subsequently divided into the following groups: SLA, no further treatment; SLA-Ca²⁺, immersed in 1% CaCl₂ solution; SLA-NaCl, immersed in saline; and SLA-Ca²⁺-NaCl, immersed in 1% CaCl₂ solution followed by saline. Surface characteristics were evaluated using field-emission scanning electron microscopy with energy-dispersive spectrometry, surface profilometry, and contact angle assays. Additionally, we used a ζ-potential analyzer to directly measure the electrostatic charge on the different group surfaces. The effect of changes in the Ti surface on biological processes after different treatments was determined by analyzing fibronectin adsorption, osteoblast-like MG63 cell adhesion and proliferation, and the expression of osteogenesis-related genes. Compared to the SLA surface, the other three groups contained corresponding trace elements because they were soaked in different liquids; the contact angles of the three groups were not significantly different, but they were significantly smaller than that of the SLA group; and there was no change in the surface topography or roughness. Furthermore, the SLA-Ca²⁺ group had a significantly reduced negative charge compared to that of the other three groups. There were no differences between the SLA-NaCl and SLA-Ca²⁺-NaCl groups in terms of negative charge, and the SLA group surface carried the most negative charge. Fibronectin adsorption capacity and cytological performance testing further showed that the SLA-Ca²⁺ group had the most significant change, followed by the SLA-NaCl and SLA-Ca²⁺-NaCl groups; the SLA group had significantly lower capacity and performance than the other three groups. These results suggest that the surface charge of the titanium sheet changed when immersed in different liquids and that this treatment enhanced biocompatibility by reducing the electrostatic repulsion between biomaterials and biomolecules.

Electrophoretic deposition of polymers and proteins for biomedical applications

This review is focused on new electrophoretic deposition (EPD) mechanisms for deposition biomacromolecules, such as biopolymers, proteins and enzymes. Among the rich literature sources of EPD of biopolymers, proteins and enzymes for biomedical applications we selected papers describing new fundamental deposition mechanisms. Such deposition mechanisms are of critical importance for further development of EPD method and its emerging biomedical applications. Our goal is to emphasize innovative ideas which have enriched colloid and interface science of EPD during recent years. We describe various mechanisms of cathodic and anodic EPD of charged biopolymers. Special attention is focused on in-situ chemical modification of biopolymers and crosslinking techniques. Recent innovations in the development of natural and biocompatible charged surfactants and film forming agents are outlined. Among the important advances in this area are the applications of bile acids and salts for EPD of neutral polymers. Such innovations allowed for the successful EPD of various electrically neutral functional polymers for biomedical applications. Particularly important are biosurfactant-polymer interactions, which facilitate dissolution, dispersion, charging, electrophoretic transport and deposit formation. Recent advances in EPD mechanisms addressed the problem of EPD of proteins and enzymes related to their charge reversal at the electrode surface. Conceptually new methods are described, which are based on the use of biopolymer complexes with metal ions, proteins, enzymes and other biomolecules. This review describes new developments in co-deposition of biomacromolecules and future trends in the development of new EPD mechanisms and strategies for biomedical applications.

Two-in-one strategy: a remineralizing and anti-adhesive coating against demineralized enamel

Tooth enamel is prone to be attacked by injurious factors, leading to a de/remineralization imbalance. To repair demineralized enamel and prevent pulp inflammation caused by biofilm accumulation, measures are needed to promote remineralization and inhibit bacterial adhesion on the tooth surface. An innovative material, poly (aspartic acid)-polyethylene glycol (PASP-PEG), was designed and synthesized to construct a mineralizing and anti-adhesive surface that could be applied to repair demineralized enamel. A cytotoxicity assay revealed the low cytotoxicity of synthesized PASP-PEG. Adsorption results demonstrated that PASP-PEG possesses a high binding affinity to the hydroxyapatite (HA)/tooth surface. In vitro experiments and scanning electron microscopy (SEM) demonstrated a strong capacity of PASP-PEG to induce in situ remineralization and direct the oriented growth of apatite nanocrystals. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD) and Vickers hardness tests demonstrated that minerals induced by PASP-PEG were consistent with healthy enamel in Ca/P ratio, crystal form and surface micro-hardness. Contact angle tests and bacterial adhesion experiments demonstrated that PASP-PEG yielded a strong anti-adhesive effect. In summary, PASP-PEG could achieve dual effects for enamel repair and anti-adhesion of bacteria, thereby widening its application in enamel repair.

Surface Immobilization Chemistry of a Laminin-Derived Peptide Affects Keratinocyte Activity

Many chemical routes have been proposed to immobilize peptides on biomedical device surfaces, and in particular, on dental implants to prevent peri-implantitis. While a number of factors affect peptide immobilization quality, an easily controllable factor is the chemistry used to immobilize peptides. These factors affect peptide chemoselectivity, orientation, etc., and ultimately control biological activity. Using many different physical and chemical routes for peptide coatings, previous research has intensely focused on immobilizing antimicrobial elements on dental implants to reduce infection rates. Alternatively, our strategy here is different and focused on promoting formation of a long-lasting biological seal between the soft tissue and the implant surface through transmembrane, cell adhesion structures called hemidesmosomes. For that purpose, we used a laminin-derived call adhesion peptide. However, the effect of different immobilization chemistries on cell adhesion peptide activity is vastly unexplored but likely critical. Here, we compared the physiochemical properties and biological responses of a hemidesmosome promoting peptide immobilized using silanization and copper-free click chemistry as a model system for cell adhesion peptides. Successful immobilization was confirmed with water contact angle and X-ray photoelectron spectroscopy. Peptide coatings were retained through 73 days of incubation in artificial saliva. Interestingly, the non-chemoselective immobilization route, silanization, resulted in significantly higher proliferation and hemidesmosome formation in oral keratinocytes compared to chemoselective click chemistry. Our results highlight that the most effective immobilization chemistry for optimal peptide activity is dependent on the specific system (substrate/peptide/cell/biological activity) under study. Overall, a better understanding of the effects immobilization chemistries have on cell adhesion peptide activity may lead to more efficacious coatings for biomedical devices.

Polyethylene Glycol Pulsed Electrodeposition for the Development of Antifouling Coatings on Titanium

Titanium dental implants are widely used for the replacement of damaged teeth. However, bacterial infections at the interface between soft tissues and the implant can impair the functionality of the device and lead to failure. In this work, the preparation of an antifouling coating of polyethylene glycol (PEG) on titanium by pulsed electrodeposition was investigated in order to reduce Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) adhesion while maintaining human fibroblast adhesion. Different pulsed conditions were prepared and characterized by contact angle, Focused Ion Beam (FIB), Fourier Transformed Infrared Spectroscopy in the Attenuated Total Reflectance mode (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). XPS tested fibronectin adsorption. S. aureus, E. coli and human fibroblast adhesion was tested in vitro in both mono and co-culture settings. Physicochemical characterization proved useful for confirming the presence of PEG and evaluating the efficiency of the coating methods. Fibronectin adsorption decreased for all of the conditions, but an adsorption of 20% when compared to titanium was maintained, which supported fibroblast adhesion on the surfaces. In contrast, S. aureus and E. coli attachment on coated surfaces decreased up to 90% vs. control titanium. Co-culture studies with the two bacterial strains and human fibroblasts showed the efficacy of the coatings to allow for eukaryotic cell adhesion, even in the presence of pre-adhered bacteria.

Influence of the electrostatic condition of the titanium surface on bacterial adhesion: A systematic review

STATEMENT OF PROBLEM

Infection of a dental implant is undesirable and decreases the success rate of the dental prosthesis; however, systematic reviews on the issue are lacking.

PURPOSE

The purpose of this systematic review was to evaluate studies that dealt with inherent factors or those applied to the titanium surface or alloys to provide an antimicrobial action.

MATERIAL AND METHODS

SCOPUS, PubMed/Medline, Web of Science, EMBASE, and Science Direct databases were searched and manual searches made between June and July 2019 using the keywords "titanium," "surface," "implants," "photoelectron spectroscopy," and "fourier transform infrared spectroscopy." The criteria included in vitro studies evaluating the titanium surface and describing hydrophobicity, surface crystalline phase, nanotopography, surface charges, and their relationship with bacteria and/or osseointegration.

RESULTS

A comprehensive search identified 767 articles that were selected by the title and/or abstract as per the inclusion criteria. Of the 58 studies selected for full reading, 7 were used for this systematic review. Another 6 studies were added by further research, resulting in 13 articles, all in vitro studies. As the selected studies had a high heterogeneity that precluded any statistical analysis of the data, a descriptive analysis of these topics was performed: hydrophilicity, surface crystalline phase, nanotopography, and surface charges.

CONCLUSIONS

The articles analyzed in this systematic review suggest that hydrophilicity, crystalline phase, surface topography, and surface titanium charge, when altered, may provide an antimicrobial surface. However, the strategy used resulted in heterogeneous articles, making it impossible to demonstrate the unique effect of the electrostatic surface of titanium or titanium alloy used for implants and its effect on bacterial control.

Antibacterial Properties of Triethoxysilylpropyl Succinic Anhydride Silane (TESPSA) on Titanium Dental Implants

Infections related to dental implants are a common complication that can ultimately lead to implant failure, and thereby carries significant health and economic costs. In order to ward off these infections, this paper explores the immobilization of triethoxysilylpropyl succinic anhydride (TESPSA, TSP) silane onto dental implants, and the interaction of two distinct monospecies biofilms and an oral plaque with the coated titanium samples. To this end, titanium disks from prior machining were first activated by a NaOH treatment and further functionalized with TESPSA silane. A porous sodium titanate surface was observed by scanning electron microscopy and X-ray photoelectron spectroscopy analyses confirmed the presence of TESPSA on the titanium samples (8.4% for Ti-N-TSP). Furthermore, a lactate dehydrogenase assay concluded that TESPSA did not have a negative effect on the viability of human fibroblasts. Importantly, the in vitro effect of modified surfaces against Streptococcus sanguinis, Lactobacillus salivarius and oral plaque were studied using a viable bacterial adhesion assay. A significant reduction was achieved in all cases but, as expected, with different effectiveness against simple mono-species biofilm (ratio dead/live of 0.4) and complete oral biofilm (ratio dead/live of 0.6). Nevertheless, this approach holds a great potential to provide dental implants with antimicrobial properties.

Proteins, peptides and peptidomimetics as active agents in implant surface functionalization

The recent impact of implants on improving the human life quality has been enormous. During the past two decades we witnessed major advancements in both material and structural development of implants. They were driven mainly by the increasing patients' demand and the need to address the major issues that come along with the initially underestimated complexity of the bone-implant interface. While both, the materials and design of implants reached a certain, balanced state, recent years brought a shift in focus towards the bone-implant interface as the weakest link in the increasing implant long-term usability. As a result, several approaches were developed. They aimed at influencing and enhancing the implant osseointegration and its proper behavior when under load and stress. With this review, we would like to discuss the recent advancements in the field of implant surface modifications, emphasizing the importance of chemical methods, focusing on proteins, peptides and peptidomimetics as promising agents for titanium surface coatings.

Biocompatible Organic Coatings Based on Bisphosphonic Acid RGD-Derivatives for PEO-Modified Titanium Implants

Currently, significant attention is attracted to the problem of the development of the specific architecture and composition of the surface layer in order to control the biocompatibility of implants made of titanium and its alloys. The titanium surface properties can be tuned both by creating an inorganic sublayer with the desired morphology and by organic top coating contributing to bioactivity. In this work, we developed a composite biologically active coatings based on hybrid molecules obtained by chemical cross-linking of amino acid bisphosphonates with a linear tripeptide RGD, in combination with inorganic porous sublayer created on titanium by plasma electrolytic oxidation (PEO). After the addition of organic molecules, the PEO coated surface gets nobler, but corrosion currents increase. In vitro studies on proliferation and viability of fibroblasts, mesenchymal stem cells and osteoblast-like cells showed the significant dependence of the molecule bioactivity on the structure of bisphosphonate anchor and the linker. Several RGD-modified bisphosphonates of β-alanine, γ-aminobutyric and ε-aminocaproic acids with BMPS or SMCC linkers can be recommended as promising candidates for further in vivo research.

UV Light Assisted Coating Method of Polyphenol Caffeic Acid and Mediated Immobilization of Metallic Silver Particles for Antibacterial Implant Surface Modification

Titanium implants are extensively used in biomedical applications due to their excellent biocompatibility, corrosion resistance, and superb mechanical stability. In this work, we present the use of polycaffeic acid (PCA) to immobilize metallic silver on the surface of titanium materials to prevent implant bacterial infection. Caffeic acid is a plant-derived phenolic compound, rich in catechol moieties and it can form functional coatings using alkaline buffers and with UV irradiation. This combination can trigger oxidative polymerization and deposition on the surface of metallic substrates. Using PCA can also give advantages in bone implants in decreasing inflammation by decelerating macrophage and osteoclast activity. Here, chemical and physical properties were investigated using FE-SEM, EDS, XPS, AFM, and contact angle. The in vitro biocompatibility and antibacterial studies show that PCA with metallic silver can inhibit bacterial growth, and proliferation of MC-3T3 cells was observed. Therefore, our results suggest that the introduced approach can be considered as a potential method for functional implant coating application in the orthopedic field.

Electrochemical Strategies for Titanium Implant Polymeric Coatings: The Why and How

Among the several strategies aimed at polymeric coatings deposition on titanium (Ti) and its alloys, metals commonly used in orthopaedic and orthodontic prosthesis, electrochemical approaches have gained growing interest, thanks to their high versatility. In this review, we will present two main electrochemical procedures to obtain stable, low cost and reliable polymeric coatings: electrochemical polymerization and electrophoretic deposition. Distinction should be made between bioinert films—having mainly the purpose of hindering corrosive processes of the underlying metal—and bioactive films—capable of improving biological compatibility, avoiding inflammation or implant-associated infection processes, and so forth. However, very often, these two objectives have been pursued and achieved contemporaneously. Indeed, the ideal coating is a system in which anti-corrosion, anti-infection and osseointegration can be obtained simultaneously. The ultimate goal of all these coatings is the better control of properties and processes occurring at the titanium interface, with a special emphasis on the cell-coating interactions. Finally, advantages and drawbacks of these electrochemical strategies have been highlighted in the concluding remarks.

A Dual Molecular Biointerface Combining RGD and KRSR Sequences Improves Osteoblastic Functions by Synergizing Integrin and Cell-Membrane Proteoglycan Binding

Synergizing integrin and cell-membrane heparan sulfate proteoglycan signaling on biomaterials through peptidic sequences is known to have beneficial effects in the attachment and behavior of osteoblasts; however, controlling the exact amount and ratio of peptides tethered on a surface is challenging. Here, we present a dual molecular-based biointerface combining integrin (RGD) and heparin (KRSR)-binding peptides in a chemically controlled fashion. To this end, a tailor-made synthetic platform (PLATF) was designed and synthesized by solid-phase methodologies. The PLATF and the control linear peptides (RGD or KRSR) were covalently bound to titanium via silanization. Physicochemical characterization by means of contact angle, Raman spectroscopy and XPS proved the successful and stable grafting of the molecules. The biological potential of the biointerfaces was measured with osteoblastic (Saos-2) cells both at short and long incubation periods. Biomolecule grafting (either the PLATF, RGD or KRSR) statistically improved (p < 0.05) cell attachment, spreading, proliferation and mineralization, compared to control titanium. Moreover, the molecular PLATF biointerface synergistically enhanced mineralization (p < 0.05) of Saos-2 cells compared to RGD or KRSR alone. These results indicate that dual-function coatings may serve to improve the bioactivity of medical implants by mimicking synergistic receptor binding.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Resisting Bacteria and Attracting Cells: Spontaneous Formation of a Bifunctional Peptide-Based Coating by On-Surface Assembly Approach

Due to extension of life expectancy, millions of people suffer nowadays from bone and dental malfunctions that can only be treated by different types of implants. However, these implants tend to fail due to bacterial infection and lack of integration with the remaining tissue. Here, we demonstrate a new concept in which we use specifically designed peptides, in a "Lego-like" manner to endow multiple preprogrammed functions. We developed a bifunctional peptide-based coating that simultaneously rejects the adhesion of infecting bacteria and attracts cells that build the new connecting tissue. The peptide design contains fluorinated phenylalanine that mediates the self-assembly of the peptide into a coating that resists bacterial adhesion. It also includes an Arg-Gly-Asp (RGD) motif that attracts mammalian cells. The whole compound is attached to the surface using a third unit, the amino acid 3,4-dihydroxyphenylalanine (DOPA). This novel, yet very simple approach is significantly advantageous for practical use and synthesis. More importantly, this peptide design can serve as a general platform for generating functional coatings.

Dose-response effect of chlorhexidine on a multispecies oral biofilm formed on pure titanium and on a titanium-zirconium alloy

This study aimed to test the dose-response effect of chlorhexidine on multispecies biofilms formed on commercially pure titanium (cpTi) and titanium-zirconium (TiZr) alloy. Biofilms were formed on cpTi and TiZr discs and treated two times per day with five different chlorhexidine concentrations (0.12, 0.20, 0.50, 1, 2%). The biofilms were collected for microbiological, biochemical and microscopic analyses. The significance of differences among groups was evaluated by linear regression, ANOVA, Bonferroni and Tukey tests. The mean number of colony-forming units decreased as the chlorhexidine concentration increased for both cpTi and TiZr (p < 0.05). The maximum effect was observed with the 0.5% concentration. Confocal microscopy images suggested an increase in the number of dead bacterial cells with increased chlorhexidine concentration. The biofilm pH increased after chlorhexidine exposure (p < 0.05). Chlorhexidine showed an antimicrobial dose-response effect in controlling biofilm on cpTi and TiZr. 0.5% chlorhexidine can be used to achieve the maximum antimicrobial effect on both materials.

Antimicrobial Peptides: Powerful Biorecognition Elements to Detect Bacteria in Biosensing Technologies

Bacterial infections represent a serious threat in modern medicine. In particular, biofilm treatment in clinical settings is challenging, as biofilms are very resistant to conventional antibiotic therapy and may spread infecting other tissues. To address this problem, biosensing technologies are emerging as a powerful solution to detect and identify bacterial pathogens at the very early stages of the infection, thus allowing rapid and effective treatments before biofilms are formed. Biosensors typically consist of two main parts, a biorecognition moiety that interacts with the target (i.e., bacteria) and a platform that transduces such interaction into a measurable signal. This review will focus on the development of impedimetric biosensors using antimicrobial peptides (AMPs) as biorecognition elements. AMPs belong to the innate immune system of living organisms and are very effective in interacting with bacterial membranes. They offer unique advantages compared to other classical bioreceptor molecules such as enzymes or antibodies. Moreover, impedance-based sensors allow the development of label-free, rapid, sensitive, specific and cost-effective sensing platforms. In summary, AMPs and impedimetric transducers combine excellent properties to produce robust biosensors for the early detection of bacterial infections.