Dental Implants with Anti-Biofilm Properties: A Pilot Study for Developing a New Sericin-Based Coating

Surface characteristics of additively manufactured CoCr and Ti6Al4V dental alloys: The effects of carbon and gold thin film coatings, and alkali-heat treatment

This study investigates the impact of surface modifications on additively manufactured CoCr and Ti6Al4V dental alloys, focusing on surface properties. Thin film carbon (C) and gold (Au) coatings, as well as alkali-heat treatment, were applied to the high- and low-polished specimens. Scanning electron microscopy (SEM) showed that thin film coatings retained the underlying surface topography, while the alkali-heat treatment induced distinct morphological changes. Energy-dispersive x-ray spectroscopy (EDS) analysis revealed that C-coating enriched surfaces with C, and Au-coating introduced detectable amounts of Au. Nevertheless, signs of coating delamination were observed in the high-polished specimens. Alkali-heat treatment led to the formation of a sodium titanate layer on Ti6Al4V surfaces, confirmed by sodium presence and Fourier transform infrared spectroscopy (FTIR) results showing carbonate bands. Surface roughness measurements with atomic force microscopy (AFM) showed that C-coating increased surface roughness in both high- and low-polished alloys. Au-coating slightly increased roughness, except for low-polished Au-coated Ti6Al4V, where a decrease in roughness was observed compared to low-polished bare Ti6Al4V, likely due to surface defects present in the latter resulting from the additive manufacturing process. Alkali-heat treatment led to a pronounced increase in roughness for both alloys, particularly for Ti6Al4V. Both thin film coatings decreased the water contact angles in all specimens in varying magnitudes, indicating an increase in wettability. However, the alkali-heat treatment caused a substantial decrease in contact angles, resulting in a highly hydrophilic state for Ti6Al4V. These findings underscore the substantial impact of surface modifications on additively manufactured dental alloys, potentially influencing their clinical performance. RESEARCH HIGHLIGHTS: Thin film coatings and chemical/heat treatment modify the surface properties of additively manufactured dental alloys. The surfaces of the alloys get rougher and more hydrophilic after alkali-heat treatment. Thin gold coatings exhibit potential adhesion challenges.

Layer-by-Layer Coatings of Collagen-Hyaluronic acid Loaded with an Antibacterial Manuka Honey Bioactive Compound to Fight Metallic Implant Infections

Implant-associated severe infections can result in catastrophic implant failures; thus, advanced antibacterial coatings are needed to combat infections. This study focuses on harnessing nature-inspired self-assembly of extracellular matrix (ECM)-like coatings on Ti alloy with a combination of jellyfish-derived collagen (J-COLL) and hyaluronic acid (HA) using our customized automated hybrid layer-by-layer apparatus. To improve the anti-infection efficacy of coatings, we have incorporated a natural antibacterial agent methylglyoxal (MGO, a Manuka honey compound) in optimized multilayer coatings. The obtainment of MGO-loaded multilayer coatings was successfully assessed by profilometry, contact angle, attenuated total reflectance (ATR)-Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. In vitro degradation confirmed the controlled release activity of MGO with a range of concentrations from 0.90 to 2.38 mM up to 21 days. A bacterial cell culture study using Escherichia coli (E. coli) and Staphylococcus epidermidis (S. epidermidis) confirmed that the MGO incorporated within layers 7 and 9 had a favorable effect on preventing bacterial growth and colonization on their surfaces. An in vitro cytocompatibility study confirmed that MGO agents included in the layers did not affect or reduce the cellular functionalities of L929 fibroblasts. In addition, MGO-loaded layers with Immortalized Mesenchymal Stem Cells (Y201 TERT-hMSCs) were found to favor the growth and differentiation of Y201 cells and promote calcium nodule formation. Overall, these surface coatings are promising candidates for delivering antimicrobial activity with bone-inducing functions for future bone tissue engineering applications.

A comprehensive review of recent advances in silk sericin: Extraction approaches, structure, biochemical characterization, and biomedical applications

Silks are natural polymers that have been widely used for centuries. Silk consists of a filament core protein, termed fibroin, and a glue-like coating substance formed of sericin (SER) proteins. This protein is extracted from the silkworm cocoons (particularly Bombyx mori) and is mainly composed of amino acids like glycine, serine, aspartic acid, and threonine. Silk SER can be obtained using numerous methods, including enzymatic extraction, high-temperature, autoclaving, ethanol precipitation, cross-linking, and utilizing acidic, alkali, or neutral aqueous solutions. Given the versatility and outstanding properties of SER, it is widely fabricated to produce sponges, films, and hydrogels for further use in diverse biomedical applications. Hence, many authors reported that SER benefits cell proliferation, tissue engineering, and skin tissue restoration thanks to its moisturizing features, antioxidant and anti-inflammatory properties, and mitogenic effect on mammalian cells. Remarkably, SER is used in drug delivery depending on its chemical reactivity and pH-responsiveness. These unique features of SER enhance the bioactivity of drugs, facilitating the fabrication of biomedical materials at nano- and microscales, hydrogels, and conjugated molecules. This review thoroughly outlines the extraction techniques, biological properties, and respective biomedical applications of SER.

Characterization of a New Silk Sericin-Based Hydrogel for Water Retention in Soil

Hydrogel-type absorbent materials are currently a technological alternative for improving water retention in the soil and reducing nutrient loss by leaching and evaporation. This study aimed to evaluate the application of a new hydrogel based on silk sericin (SS) as a water retention material in soil. The morphology of the hydrogel was characterized using Scanning Electron Microscopy (SEM), and its impact on moisture retention in sandy loam soil (SLS) under different levels of matric pressure (MP) was evaluated. Additionally, water content data were collected over time for both SLS and SLS with hydrogel (SLS + H), and the data were used to fit predictive models. The results indicate that the hydrogel had a porous morphology that promoted water retention and soil release. Under a MP of 0.3 bar, the use of the hydrogel increased water retention by 44.70% with respect to that of SLS. The predictive models developed were adequately adjusted to the behavior of the moisture data over time and evidenced the incidence of the absorbent material on the dynamics of the moisture content in the soil. Therefore, these models could be useful for facilitating subsequent simulations or for designing automatic soil moisture control systems oriented to smart farming.

Silk proteins in reconstructive surgery: Do they possess an inherent antibacterial activity? A systematic review

The field of reconstructive surgery encompasses a wide range of surgical procedures and regenerative approaches to treat various tissue types. Every surgical procedure is associated with the risk of surgical site infections, which are not only a financial burden but also increase patient morbidity. The surgical armamentarium in this area are biomaterials, particularly natural, biodegradable, biocompatible polymers, including the silk proteins fibroin (SF) and sericin (SS). Silk is known to be derived from silkworms and is mainly composed of 60-80% fibroin, which provides the structural form, and 15-35% sericin, which acts as a glue-like substance for the SF threads. Silk proteins possess most of the desired properties for biomedical applications, including biocompatibility, biodegradability, minimal immunogenicity, and tunable biomechanical behaviour. In an effort to alleviate or even prevent infections associated with the use of biomaterials in surgery, antibacterial/antimicrobial properties have been investigated in numerous studies. In this systematic review, the following question was addressed: Do silk proteins, SF and SS, possess an intrinsic antibacterial property and how could these materials be tailored to achieve such a property?

Silk sericin as building blocks of bioactive materials for advanced therapeutics

Silk sericin is a class of protein biopolymers produced by silkworms. Increasing attention has been paid to silk sericin for biomedical applications in the last decade, not only because of its excellent biocompatibility and biodegradability but also due to the pharmacological activities stemming from its unique amino acid compositions. In this review, the biological properties of silk sericin, including curing specific diseases and promoting tissue regeneration, as well as underlying mechanisms are summarized. We consider the antioxidant activity of silk sericin as a fundamental property, which could account for partial biological activities, despite the exact mechanisms of silk sericin's effect remaining unknown. Based on the reactive groups on silk sericin, approaches of bottom-up fabrication of silk sericin-based biomaterials are highlighted, including non-covalent interactions and chemical reactions (reduction, crosslinking, bioconjugation, and polymerization). We then briefly present the cutting-edge advances of silk sericin-based biomaterials applied in tissue engineering and drug delivery. The challenges of silk sericin-based biomaterials are proposed. With more bioactivities and underlying mechanisms of silk sericin uncovered, it is going to boost the therapeutic potential of silk sericin-based biomaterials.

Metabolic Conditions and Peri-Implantitis

Dental implants to replace lost teeth are a common dentistry practice nowadays. Titanium dental implants display a high success rate and improved safety profile. Nevertheless, there is an increasing peri-implantitis (PI), an inflammatory disease associated with polymicrobial infection that adversely affects the hard and soft tissues around the implant. The present review highlights the contribution of different metabolic conditions to PI. The considerations of both local and systemic metabolic conditions are crucial for planning successful dental implant procedures and during the treatment course of PI. Un- or undertreated PI can lead to permanent jaw bone suffering and dental implant losses. The common mediators of PI are inflammation and oxidative stress, which are also the key mediators of most systemic metabolic disorders. Chronic periodontitis, low-grade tissue inflammation, and increased oxidative stress raise the incidence of PI and the underlying systemic metabolic conditions, such as obesity, diabetes mellitus, or harmful lifestyle factors (cigarette smoking, etc.). Using dental biomaterials with antimicrobial effects could partly solve the problem of pathogenic microbial contamination and local inflammation. With local dentistry considering factors, including oral microbiota and implant quality control, the inclusion of the underlying systemic metabolic conditions into the pre-procedure planning and during the treatment course should improve the chances of successful outcomes.

New Ceramic Multi-Unit Dental Abutments with an Antimicrobial Glassy Coating

The choice of suitable materials and new designs in oral implantology and the subsequent enhancement of the characteristics of the dental implant developed is an important research topic with wide scope. The present work aims to develop a new multifunctional zirconia-ceria/alumina (Ce-TZP/Al₂O₃) composite with an antimicrobial glass-based coating to be used in multi-unit abutments compatible with commercially available Ti implants for peri-implantitis prevention. An airbrush spraying technique was effectively applied to coat the sintered ceramic composite starting from a glass powder suspension. This deposition technique was appropriate for obtaining continuous antimicrobial glass-based coatings with homogenous thickness (~35 µm) on ceramic dental implant components. The dental implant systems with the antimicrobial glassy coating were subjected to a mechanical integrity test following ISO 14801 to determine their long-term stability. The tested implant-coating structure seems to be stable under in vitro conditions with ultimate applied forces exceeding the maximum physiological occlusal loading force. This paper also presents a pilot clinical case report that shows peri-implant tissue around the mechanically stable glass coating with no signs of inflammation 1 year after implant insertion. This result is a preliminary probe of the durability and biological tolerance of the glassy material by the gingiva, as well as the antimicrobial effect on the peri-implant microbiota displayed by the coating.

Three interfaces of the dental implant system and their clinical effects on hard and soft tissues

Anatomically, the human tooth has structures both embedded within and forming part of the exterior surface of the human body. When a tooth is lost, it is often replaced by a dental implant, to facilitate the chewing of food and for esthetic purposes. For successful substitution of the lost tooth, hard tissue should be integrated into the implant surface. The microtopography and chemistry of the implant surface have been explored with the aim of enhancing osseointegration. Additionally, clinical implant success is dependent on ensuring that a barrier, comprising strong gingival attachment to an abutment, does not allow the infiltration of oral bacteria into the bone-integrated surface. Epithelial and connective tissue cells respond to the abutment surface, depending on its surface characteristics and the materials from which it is made. In particular, the biomechanics of the implant-abutment connection structure (i.e., the biomechanics of the interface between implant and abutment surfaces, and the screw mechanics of the implant-abutment assembly) are critical for both the soft tissue seal and hard tissue integration. Herein, we discuss the clinical importance of these three interfaces: bone-implant, gingiva-abutment, and implant-abutment.

Polydopamine-Assisted Surface Modification of Ti-6Al-4V Alloy with Anti-Biofilm Activity for Dental Implantology Applications

Coating the surfaces of implantable materials with various active principles to ensure inhibition of microbial adhesion, is a solution to reduce infections associated with dental implant. The aim of the study was to optimize the polydopamine films coating on the Ti-6Al-6V alloy surface in order to obtain a maximum of antimicrobial/antibiofilm efficacy and reduced cytotoxicity. Surface characterization was performed by evaluating the morphology (SEM, AFM) and structures (Solid-state 13C NMR and EPR). Antimicrobial activity was assessed by logarithmic reduction of CFU/mL, and the antibiofilm activity by reducing the adhesion of Escherichia coli, Staphylococcus aureus, and Candida albicans strains. The release of NO was observed especially for C. albicans strain, which confirms the results obtained for microbial adhesion. Among the PDA coatings, for 0.45:0.88 (KMnO4:dopamine) molar ratio the optimal compromise was obtained in terms of antimicrobial activity and cytotoxicity, while the 0.1:1.5 ratio (KMnO4:dopamine) led to higher NO release and implicitly the reduction of the adhesion capacities only for C. albicans, being slightly cytotoxic but with moderate release of LDH. The proposed materials can be used to reduce the adhesion of yeast to the implantable material and thus inhibit the formation of microbial biofilms.

Counter-Acting Candida albicans-Staphylococcus aureus Mixed Biofilm on Titanium Implants Using Microbial Biosurfactants

This study aimed to grow a fungal-bacterial mixed biofilm on medical-grade titanium and assess the ability of the biosurfactant R89 (R89BS) coating to inhibit biofilm formation. Coated titanium discs (TDs) were obtained by physical absorption of R89BS. Candida albicans-Staphylococcus aureus biofilm on TDs was grown in Yeast Nitrogen Base, supplemented with dextrose and fetal bovine serum, renewing growth medium every 24 h and incubating at 37 °C under agitation. The anti-biofilm activity was evaluated by quantifying total biomass, microbial metabolic activity and microbial viability at 24, 48, and 72 h on coated and uncoated TDs. Scanning electron microscopy was used to evaluate biofilm architecture. R89BS cytotoxicity on human primary osteoblasts was assayed on solutions at concentrations from 0 to 200 μg/mL and using eluates from coated TDs. Mixed biofilm was significantly inhibited by R89BS coating, with similar effects on biofilm biomass, cell metabolic activity and cell viability. A biofilm inhibition >90% was observed at 24 h. A lower but significant inhibition was still present at 48 h of incubation. Viability tests on primary osteoblasts showed no cytotoxicity of coated TDs. R89BS coating was effective in reducing C. albicans-S. aureus mixed biofilm on titanium surfaces and is a promising strategy to prevent dental implants microbial colonization.

Oral prosthetic microbiology: aspects related to the oral microbiome, surface properties, and strategies for controlling biofilms

The oral cavity is an environment that allows for the development of complex ecosystems; the placement of prosthetic devices as a consequence of partial or total tooth loss may alter the diversity of microbial communities. Biofilms on the surface of materials used in dental prostheses can promote important changes in the mechanic and aesthetic properties of the material itself and may cause local and systemic diseases for the prosthetic wearer. This review presents the main features of the oral microbiome associated with complete or partial dentures and dental implants. The main diseases associated with microbial colonization of prosthetic surfaces, factors that may affect biofilm formation on prosthetic materials, as well as novel alternative therapies aiming to reduce biofilm formation and/or to eradicate biofilms formed on these materials are also explored.

Effect of biofilm formation on implant abutments with an anti-bacterial coating: A pre-clinical in vivo study

OBJECTIVES

To analyse the long-term effect of plaque formation on implant abutments with an antibacterial coating and the ensuing host response in peri-implant tissues.

MATERIALS AND METHODS

Four implants were installed in each mandibular premolar region following tooth extraction in six dogs. Three months later, two test abutments with a titanium-bismuth-gallium (Ti-Bi-Ga) coating and two control titanium abutments were connected to the implants on each side of the mandible. After 2 months, ligatures were placed around the implants in one side of the mandible and plaque formation was allowed until the end of the experiment. The ligatures were removed after 4 weeks. Radiographs and microbiological samples were obtained from each implant site during the plaque formation period. Biopsies were obtained 8 months after abutment connection and prepared for histological analysis.

RESULTS

The analysis did not reveal any statistically significant differences in bone loss, bacterial growth and size of inflammatory lesions between implant units with and without the Ti-Bi-Ga coating. Implant sites exposed to the short period of ligature-induced breakdown demonstrated more pronounced bone loss and bacterial growth than non-ligature sites.

CONCLUSIONS

It is suggested that a Ti-Bi-Ga coating does not prevent biofilm formation on the implant device and does not influence the ensuing host response in the adjacent peri-implant mucosa.

Rhamnolipid coating reduces microbial biofilm formation on titanium implants: an in vitro study

Background

Peri-implant mucositis and peri-implantitis are biofilm-related diseases causing major concern in oral implantology, requiring complex anti-infective procedures or implant removal. Microbial biosurfactants emerged as new anti-biofilm agents for coating implantable devices preserving biocompatibility. This study aimed to assess the efficacy of rhamnolipid biosurfactant R89 (R89BS) to reduce Staphylococcus aureus and Staphylococcus epidermidis biofilm formation on titanium.

Methods

R89BS was physically adsorbed on titanium discs (TDs). Cytotoxicity of coated TDs was evaluated on normal lung fibroblasts (MRC5) using a lactate dehydrogenase assay. The ability of coated TDs to inhibit biofilm formation was evaluated by quantifying biofilm biomass and cell metabolic activity, at different time-points, with respect to uncoated controls. A qualitative analysis of sessile bacteria was also performed by scanning electron microscopy.

Results

R89BS-coated discs showed no cytotoxic effects. TDs coated with 4 mg/mL R89BS inhibited the biofilm biomass of S. aureus by 99%, 47% and 7% and of S. epidermidis by 54%, 29%, and 10% at 24, 48 and 72 h respectively. A significant reduction of the biofilm metabolic activity was also documented. The same coating applied on three commercial implant surfaces resulted in a biomass inhibition higher than 90% for S. aureus, and up to 78% for S. epidermidis at 24 h.

Conclusions

R89BS-coating was effective in reducing Staphylococcus biofilm formation at the titanium implant surface. The anti-biofilm action can be obtained on several different commercially available implant surfaces, independently of their surface morphology.

Inhibitory Effects of Lipopeptides and Glycolipids on C. albicans-Staphylococcus spp. Dual-Species Biofilms

Microbial biofilms strongly resist host immune responses and antimicrobial treatments and are frequently responsible for chronic infections in peri-implant tissues. Biosurfactants (BSs) have recently gained prominence as a new generation of anti-adhesive and antimicrobial agents with great biocompatibility and were recently suggested for coating implantable materials in order to improve their anti-biofilm properties. In this study, the anti-biofilm activity of lipopeptide AC7BS, rhamnolipid R89BS, and sophorolipid SL18 was evaluated against clinically relevant fungal/bacterial dual-species biofilms (Candida albicans, Staphylococcus aureus, Staphylococcus epidermidis) through quantitative and qualitative in vitro tests. C. albicans-S. aureus and C. albicans-S. epidermidis cultures were able to produce a dense biofilm on the surface of the polystyrene plates and on medical-grade silicone discs. All tested BSs demonstrated an effective inhibitory activity against dual-species biofilms formation in terms of total biomass, cell metabolic activity, microstructural architecture, and cell viability, up to 72 h on both these surfaces. In co-incubation conditions, in which BSs were tested in soluble form, rhamnolipid R89BS (0.05 mg/ml) was the most effective among the tested BSs against the formation of both dual-species biofilms, reducing on average 94 and 95% of biofilm biomass and metabolic activity at 72 h of incubation, respectively. Similarly, rhamnolipid R89BS silicone surface coating proved to be the most effective in inhibiting the formation of both dual-species biofilms, with average reductions of 93 and 90%, respectively. Scanning electron microscopy observations showed areas of treated surfaces that were free of microbial cells or in which thinner and less structured biofilms were present, compared to controls. The obtained results endorse the idea that coating of implant surfaces with BSs may be a promising strategy for the prevention of C. albicans-Staphylococcus spp. colonization on medical devices, and can potentially contribute to the reduction of the high economic efforts undertaken by healthcare systems for the treatment of these complex fungal-bacterial infections.

Polyetheretherketone and Its Composites for Bone Replacement and Regeneration

In this article, recent advances in the development, preparation, biocompatibility and mechanical properties of polyetheretherketone (PEEK) and its composites for hard and soft tissue engineering are reviewed. PEEK has been widely employed for fabricating spinal fusions due to its radiolucency, chemical stability and superior sterilization resistance at high temperatures. PEEK can also be tailored into patient-specific implants for treating orbital and craniofacial defects in combination with additive manufacturing process. However, PEEK is bioinert, lacking osseointegration after implantation. Accordingly, several approaches including surface roughening, thin film coating technology, and addition of bioactive hydroxyapatite (HA) micro-/nanofillers have been adopted to improve osseointegration performance. The elastic modulus of PEEK is 3.7-4.0 GPa, being considerably lower than that of human cortical bone ranging from 7-30 GPa. Thus, PEEK is not stiff enough to sustain applied stress in load-bearing orthopedic implants. Therefore, HA micro-/nanofillers, continuous and discontinuous carbon fibers are incorporated into PEEK for enhancing its stiffness for load-bearing applications. Among these, carbon fibers are more effective than HA micro-/nanofillers in providing additional stiffness and load-bearing capabilities. In particular, the tensile properties of PEEK composite with 30wt% short carbon fibers resemble those of cortical bone. Hydrophobic PEEK shows no degradation behavior, thus hampering its use for making porous bone scaffolds. PEEK can be blended with hydrophilic polymers such as polyglycolic acid and polyvinyl alcohol to produce biodegradable scaffolds for bone tissue engineering applications.

Biological Responses to the Transitional Area of Dental Implants: Material- and Structure-Dependent Responses of Peri-Implant Tissue to Abutments

The stability of peri-implant tissue is essential for the long-term success of dental implants. Although various types of implant connections are used, little is known about the effects of the physical mechanisms of dental implants on the stability of peri-implant tissue. This review summarizes the relevant literature to establish guidelines regarding the effects of connection type between abutments and implants in soft and hard tissues. Soft tissue seals can affect soft tissue around implants. In external connections, micromobility between the abutment and the hex component of the implant, resulting from machining tolerance, can destroy the soft tissue seal, potentially leading to microbial invasion. Internal friction connection implants induce strain on the surrounding bone via implant wall expansion that translates into masticatory force. This strain is advantageous because it increases the amount and quality of peri-implant bone. The comparison of internal and external connections, the two most commonly used connection types, reveals that internal friction has a positive influence on both soft and hard tissues.

Medical-Grade Silicone Coated with Rhamnolipid R89 Is Effective against Staphylococcus spp. Biofilms

Staphylococcus aureus and Staphylococcus epidermidis are considered two of the most important pathogens, and their biofilms frequently cause device-associated infections. Microbial biosurfactants recently emerged as a new generation of anti-adhesive and anti-biofilm agents for coating implantable devices to preserve biocompatibility. In this study, R89 biosurfactant (R89BS) was evaluated as an anti-biofilm coating on medical-grade silicone. R89BS is composed of homologues of the mono- (75%) and di-rhamnolipid (25%) families, as evidenced by mass spectrometry analysis. The antimicrobial activity against Staphylococcus spp. planktonic and sessile cells was evaluated by microdilution and metabolic activity assays. R89BS inhibited S. aureus and S. epidermidis growth with minimal inhibitory concentrations (MIC₉₉) of 0.06 and 0.12 mg/mL, respectively and dispersed their pre-formed biofilms up to 93%. Silicone elastomeric discs (SEDs) coated by R89BS simple adsorption significantly counteracted Staphylococcus spp. biofilm formation, in terms of both built-up biomass (up to 60% inhibition at 72 h) and cell metabolic activity (up to 68% inhibition at 72 h). SEM analysis revealed significant inhibition of the amount of biofilm-covered surface. No cytotoxic effect on eukaryotic cells was detected at concentrations up to 0.2 mg/mL. R89BS-coated SEDs satisfy biocompatibility requirements for leaching products. Results indicate that rhamnolipid coatings are effective anti-biofilm treatments and represent a promising strategy for the prevention of infection associated with implantable devices.