Introducing a semi-coated model to investigate antibacterial effects of biocompatible polymers on titanium surfaces

Cell Type-Specific Adhesion and Migration on Laser-Structured Opaque Surfaces

Cytocompatibility is essential for implant approval. However, initial in vitro screenings mainly include the quantity of adherent immortalized cells and cytotoxicity. Other vital parameters, such as cell migration and an in-depth understanding of the interaction between native tissue cells and implant surfaces, are rarely considered. We investigated different laser-fabricated spike structures using primary and immortalized cell lines of fibroblasts and osteoblasts and included quantification of the cell area, aspect ratio, and focal adhesions. Furthermore, we examined the three-dimensional cell interactions with spike topographies and developed a tailored migration assay for long-term monitoring on opaque materials. While fibroblasts and osteoblasts on small spikes retained their normal morphology, cells on medium and large spikes sank into the structures, affecting the composition of the cytoskeleton and thereby changing cell shape. Up to 14 days, migration appeared stronger on small spikes, probably as a consequence of adequate focal adhesion formation and an intact cytoskeleton, whereas human primary cells revealed differences in comparison to immortalized cell lines. The use of primary cells, analysis of the cell-implant structure interaction as well as cell migration might strengthen the evaluation of cytocompatibility and thereby improve the validity regarding the putative in vivo performance of implant material.

Titanium coating: introducing an antibacterial and bioactive chitosan-alginate film on titanium by spin coating

Coating of titanium (Ti) implants with biocompatible polymers were performed to improve bone healing. In this study, pure Ti implants were coated via chitosan and alginate by spin coating method at 1000, 4000, and 8000 rpm. The coating layer was cross-linked by calcium chloride. Their chemical structures were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) evaluations. The morphology of the created coating was observed by scanning electron microscopy (SEM), and the best uniformity was observed in the prepared coating at 8000 rpm (6093× g) spinal speed. The adhesion strength of the coating layer on the substrate was evaluated by the adhesion pull-off test. Also, the best adhesion strength was achieved at an 8000 rpm (6093× g) coating rate. Bioactivity of the chitosan-alginate coating on Ti sheets was evaluated by soaking the samples in a simulated body fluid (SBF) solution. The apatite formation on prepared Ti sheets was investigated by SEM, XRD, and energy dispersive X-ray spectroscopy (EDS). A higher mineralization appeared on coated samples compared with pure Ti. The antibacterial behavior of the implants was analyzed by bacterial counting against Escherichia coli. The presence of chitosan and alginate on the Ti sheets resulted in a better antibacterial effect. In-vitro experiments, with L929 fibroblast cells, confirmed the biocompatibility of the implants. Coating the Ti implants with chitosan and alginate improved biomineralization and biological behavior of the implant especially at the spinal speed of 8000 rpm (6093× g). These implants can support osteoblast cell adhesion and facilitate bone regeneration.

Can Dental Cement Composition Affect Dental Implant Success?

Cement-retained restorations on dental implants are a well-established method to replace missing teeth. However, undetected residual cement left during crown cementation procedures encourages microorganism growth, and it has been identified as a risk factor for peri-implant disease. Currently, there is no official guidance for dental cement selection, and the increasing variety of available compositions intensifies the complexity of the clinicians' decision process. The present study aimed to evaluate the in vitro host and bacterial cellular response to four different commercial dental cements as well as their effects on cement surface morphology. Disk specimens (n = 3) of bioceramic, zinc phosphate, resin-modified glass ionomer, and resin cements were exposed to host (murine pre-osteoblasts, human gingival fibroblasts, and undifferentiated human macrophages) and oral bacterial (Streptococcus mutans, Streptococcus salivarius, Streptococcus sanguinis, and Aggregatibacter actinomycetemcomitans) cells. Results indicated that oral bacteria degraded the cement surface, but bacterial viability was not significantly affected by the presence of dental cement. Conversely, the biocompatibility and morphology of host cells were severely impacted by the cement composition. Only the bioceramic cement achieved >70% viability for all cell lines investigated. Within the limitations of this study, the results indicated the importance of considering the biological interactions of a dental cement composition during selection as it played a significant role in the host cellular response and the degree of surface degradation due to bacterial attack.

Liquid-Infused Structured Titanium Surfaces: Antiadhesive Mechanism to Repel Streptococcus oralis Biofilms

To combat implant-associated infections, there is a need for novel materials which effectively inhibit bacterial biofilm formation. In the present study, the antiadhesive properties of titanium surface functionalization based on the "slippery liquid-infused porous surfaces" (SLIPS) principle were demonstrated and the underlying mechanism was analyzed. The immobilized liquid layer was stable over 13 days of continuous flow in an oral flow chamber system. With increasing flow rates, the surface exhibited a significant reduction in attached biofilm of both the oral initial colonizer  Streptococcus oralis and an oral multispecies biofilm composed of S. oralis, Actinomyces naeslundii, Veillonella dispar, and Porphyromonas gingivalis. Using single cell force spectroscopy, reduced S. oralis adhesion forces on the lubricant layer could be measured. Gene expression patterns in biofilms on SLIPS, on control surfaces, and expression patterns of planktonic cultures were also compared. For this purpose, the genome of S. oralis strain ATCC 9811 was sequenced using PacBio Sequel technology. Even though biofilm cells showed clear changes in gene expression compared to planktonic cells, no differences could be detected between bacteria on SLIPS and on control surfaces. Therefore, it can be concluded that the ability of liquid-infused titanium to repel S. oralis biofilms is mainly due to weakened bacterial adhesion to the underlying liquid interface.

Time resolved 3D live-cell imaging on implants

It is estimated that two million new dental implants are inserted worldwide each year. Innovative implant materials are developed in order to minimize the risk of peri-implant inflammations. The broad range of material testing is conducted using standard 2D, terminal, and invasive methods. The methods that have been applied are not sufficient to monitor the whole implant surface and temporal progress. Therefore, we built a 3D peri-implant model using a cylindrical implant colonized by human gingival fibroblasts. In order to monitor the cell response over time, a non-toxic LIVE/DEAD staining was established and applied to the new 3D model. Our LIVE/DEAD staining method in combination with the time resolved 3D visualization using Scanning Laser Optical Tomography (SLOT), allowed us to monitor the cell death path along the implant in the 3D peri-implant model. The differentiation of living and dead gingival fibroblasts in response to toxicity was effectively supported by the LIVE/DEAD staining. Furthermore, it was possible to visualize the whole cell-colonized implant in 3D and up to 63 hours. This new methodology offers the opportunity to record the long-term cell response on external stress factors, along the dental implant and thus to evaluate the performance of novel materials/surfaces.

Development of Laser-Structured Liquid-Infused Titanium with Strong Biofilm-Repellent Properties

Medical implants are commonly used in modern medicine but still harbor the risk of microbial infections caused by bacterial biofilms. As their retrospective treatment is difficult, there is a need for biomedical materials that inhibit bacterial colonization from the start without using antibacterial agents, as these can promote resistance development. The promising concept of slippery liquid-infused porous surfaces (SLIPS) possesses enormous potential for this purpose. In the present study, this principle was applied to titanium, a common material in implantology, and its biofilm-repellent properties were demonstrated. To simplify prospective approval of the medical device and to avoid chemical contamination, surface structuring was performed by ultrashort pulsed laser ablation. Four different structures (hierarchical micro- and nanosized spikes, microsized grooves, nanosized ripples, and unstructured surfaces) and five infusing perfluoropolyethers of different viscosities were screened; the best results were obtained with the biomimetic, hierarchical spike structure combined with lubricants of medium viscosities (20-60 cSt at 37 °C, 143 AZ, and GPL 104). The surfaces exhibited extremely low contact angle hysteresis, as is typical for liquid-infused materials and a reliable 100-fold reduction of human oral pathogen Streptococcus oralis biofilms. This characteristic was maintained after exposure to shear forces and gravity. The titanium SLIPS also inhibited adherence of human fibroblasts and osteoblasts. Toxicity tests supported the explanation that solely the surface's repellent properties are responsible for the vigorous prevention of the adhesion of bacteria and cells. This use of physically structured and liquid-infused titanium to avoid bioadhesion should support the prevention of bacterial implant-associated infections without the use of antibacterial agents.

Recent Advances in Antimicrobial Polymers: A Mini-Review

Human safety and well-being is threatened by microbes causing numerous infectious diseases resulting in a large number of deaths every year. Despite substantial progress in antimicrobial drugs, many infectious diseases remain difficult to treat. Antimicrobial polymers offer a promising antimicrobial strategy for fighting pathogens and have received considerable attention in both academic and industrial research. This mini-review presents the advances made in antimicrobial polymers since 2013. Antimicrobial mechanisms exhibiting either passive or active action and polymer material types containing bound or leaching antimicrobials are introduced. This article also addresses the applications of these antimicrobial polymers in the medical, food, and textile industries.

Influence of quaternization of ammonium on antibacterial activity and cytocompatibility of thin copolymer layers on titanium

Antimicrobial coatings are able to improve the osseointegration of dental implants. Copolymers are promising materials for such applications due to their combined properties of two different monomers. To investigate the influence of different monomer mixtures, we have been synthesized copolymers of dimethyl (methacryloxyethyl) phosphonate (DMMEP) and dipicolyl aminoethyl methacrylate in different compositions and have them characterized to obtain the r-parameters. Some of the copolymers with different compositions have also been alkylated with 1-bromohexane, resulting in quaternized ammonium groups. The copolymers have been deposited onto titanium surfaces resulting in ultrathin, covalently bound layers. These layers have been characterized by water contact angle measurements and ellipsometry. The influence of quaternary ammonium groups on antibacterial properties and cytocompatibility was studied: Activity against bacteria was tested with a gram positive Staphylococcus aureus strain. Cytocompatibility was tested with a modified LDH assay after 24 and 72 h to investigate adhesion and proliferation of human fibroblast cells on modified surfaces. The copolymer with the highest content of DMMEP showed a good reduction of S. aureus and in the alkylated version a very good reduction of about 95%. On the other hand, poor cytocompatibility is observed. However, our results show that this trend cannot be generalized for this copolymer system.

Effectiveness of Hypochlorous Acid to Reduce the Biofilms on Titanium Alloy Surfaces in Vitro

Chemotherapeutic agents have been used as an adjunct to mechanical debridement for peri-implantitis treatment. The present in vitro study evaluated and compared the effectiveness of hypochlorous acid (HOCl), sodium hypochlorite (NaOCl), and chlorhexidine (CHX) at eliminating Gram-negative (E. coli and P. gingivalis) and Gram-positive (E. faecalis and S. sanguinis) bacteria. The effect of irrigating volume and exposure time on the antimicrobial efficacy of HOCl was evaluated, and a durability analysis was completed. Live/dead staining, morphology observation, alamarBlue assay, and lipopolysaccharide (LPS) detection were examined on grit-blasted and biofilm-contaminated titanium alloy discs after treatment with the three chemotherapeutic agents. The results indicated that HOCl exhibited better antibacterial efficacy with increasing irrigating volumes. HOCl achieved greater antibacterial efficacy as treatment time was increased. A decrease in antimicrobial effectiveness was observed when HOCl was unsealed and left in contact with the air. All the irrigants showed antibacterial activity and killed the majority of bacteria on the titanium alloy surfaces of biofilm-contaminated implants. Moreover, HOCl significantly lowered the LPS concentration of P. gingivalis when compared with NaOCl and CHX. Thus, a HOCl antiseptic may be effective for cleaning biofilm-contaminated implant surfaces.

Quantifying implant-associated biofilms: Comparison of microscopic, microbiologic and biochemical methods

Biofilm-associated infections pose severe problems in modern implant medicine. Screening for new implant materials with antibacterial properties requires reliable quantification of colonizing bacteria. There are many different methods to quantify biofilms on solid surfaces in vitro, employing different (bio-)chemical/microbiological reference parameters. It is therefore difficult to compare studies with different quantification techniques. Here, we have evaluated commonly used microscopic, microbiologic and biochemical methods to quantify bacterial biofilms, in order to clarify their comparability and applicability. Two bacterial species frequently involved in biofilm-associated infections, Staphylococcus aureus and Aggregatibacter actinomycetemcomitans, were used as model organisms; their initial adhesion and biofilm formation on titanium and on antibacterial copper were analyzed using the following methods: LIVE/DEAD fluorescence staining and confocal laser-scanning microscopy, ultrasonic or a newly developed enzymatic detachment followed by standard plate counting (CFU method), a resazurin-based assay, the BacTiter-Glo™ assay and crystal violet staining. The methods differed greatly in complexity, reliability and the applicability to initial adhesion and biofilm formation. To screen biofilm formation on a multitude of surfaces, the resazurin-based and the BacTiterGlo™ assay are well suited. LIVE/DEAD staining and confocal laser-scanning microscopy can be applied for a more detailed analysis of both, initial adhesion and biofilm formation. When using the CFU method for screening purposes, the introduced enzymatic detachment procedure is to be favored over ultrasonic detachment. There is not one single method, which is suitable for all purposes. The appropriate biofilm quantification method has to be chosen on the basis of the specific scientific question.

Reduced bacterial adhesion on titanium surfaces micro-structured by ultra-short pulsed laser ablation

Implant-associated infections still pose serious problems in modern medicine. The development of fabrication processes to generate functional surfaces, which inhibit bacterial attachment, is of major importance. Sharklet™-like as well as grooves and grid micro-structures having similar dimensions were fabricated on the common implant material titanium by ultra-short pulsed laser ablation. Investigations on the biofilm formation of

Disinfection of titanium dioxide nanotubes using super-oxidized water decrease bacterial viability without disrupting osteoblast behavior

Amorphous titanium dioxide (TiO2) nanotubes (NTs) on Ti6Al4V alloy were synthesized by anodization using a commercially available super-oxidized water (SOW). The NT surfaces were sterilized by ultraviolet (UV) irradiation and disinfected using SOW. The adhesion and cellular morphology of pig periosteal osteoblast (PPO) cells and the behavior of Staphylococcus aureus (S. aureus) cultured on the sterilized and disinfected surfaces were investigated. A non-anodized Ti6Al4V disc sterilized by UV irradiation (without SOW) was used as control. The results of this study reveal that the adhesion, morphology and filopodia development of PPO cells in NTs are dramatically improved, suggesting that SOW cleaning may not disrupt the benefits obtained by NTs. Significantly decreased bacterial viability in NTs after cleaning with SOW and comparing with non-cleaned NTs was seen. The results suggest that UV and SOW could be a recommendable method for implant sterilization and disinfection without altering osteoblast behavior while decreasing bacterial viability.