Biomaterials approaches to combating oral biofilms and dental disease

Effects of a new chlorhexidine varnish on Streptococcus mutans biofilm formation in vitro

Background

Local sustained-release drug delivery systems increase the substantivity of drugs in the oral environment and subsequently enhance their therapeutic effects. This study sought to compare the effects of two commercially available varnishes and one experimental chlorhexidine (CHX) varnish on formation of Streptococcus mutans biofilm. The solubility rates of the varnishes were evaluated as well.

Methods

Standard acrylic discs were fabricated and divided into groups based on the varnish applied to the disc surfaces, namely, V-varnish, Pascal, and experimental CHX varnish. The effects of the varnishes on S. mutans biofilm were assessed after 48 h. Bacterial growth on the discs was evaluated by colony count and scanning electron microscopy (SEM). Solubility was assessed by immersing the samples in phosphate buffered saline and recording their weight changes at different times. The data were analyzed using one-way ANOVA.

Results

In the Pascal and experimental varnish groups, the total number of bacteria did not differ from that in the negative control group. The SEM findings confirmed the aforementioned results. Solubility varied significantly among the materials. V-varnish was detached from the surfaces after 2 days. No significant weight change was noted in the experimental varnish group at 14 days, while Pascal varnish showed gradual weight loss from the 5th day to the 10th day and had a plateau thereafter.

Conclusions

Biofilm formation was inhibited by the Pascal and experimental varnishes but not by the V-varnish. The highest acceptable rate of solubility was observed in the Pascal samples.

Superhydrophobic and White Light-Activated Bactericidal Surface through a Simple Coating

Bacterial adhesion and proliferation on surfaces are a challenge in medical and industrial fields. Here, a simple one-step technique is reported to fabricate self-cleaning and bactericidal surfaces. White, blue, and violet paints were produced using titanium dioxide nanoparticles, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, crystal violet, toluidine Blue O, and ethanol solution. All of the painted surfaces showed superhydrophobicity in air, and even after hexadecane oil contamination, they retained water repellency and self-cleaning properties. In an assay of bacterial adhesion, significant reductions (>99.8%) in the number of adherent bacteria were observed for all the painted surfaces. In bactericidal tests, the painted surfaces not only demonstrated bactericidal activity against Staphylococcus aureus and Escherichia coli in the dark but also induced very potent photosensitization (>4.4 log reduction in the number of viable bacteria on the violet painted surface) under white light illumination. The technique that we developed here is general and can be used on a wide range of substrates such as paper, glass, polymers, and others.

Covalent immobilization of hLf1-11 peptide on a titanium surface reduces bacterial adhesion and biofilm formation

Bacterial infection represents a major cause of implant failure in dentistry. A common approach to overcoming this issue and treating peri-implant infection consists in the use of antibiotics. However, the rise of multidrug-resistant bacteria poses serious concerns to this strategy. A promising alternative is the use of antimicrobial peptides due to their broad-spectrum activity against bacteria and reduced bacterial resistance responses. The aim of the present study was to determine the in vitro antibacterial activity of the human lactoferrin-derived peptide hLf1-11 anchored to titanium surfaces. To this end, titanium samples were functionalized with the hLf1-11 peptide either by silanization methods or physical adsorption. X-ray photoelectron spectroscopy analyses confirmed the successful covalent attachment of the hLf1-11 peptide onto titanium surfaces. Lactate dehydrogenase assay determined that hLf1-11 peptide did not affect fibroblast viability. An outstanding reduction in the adhesion and early stages of biofilm formation of Streptococcus sanguinis and Lactobacillus salivarius was observed on the biofunctionalized surfaces compared to control non-treated samples. Furthermore, samples coated with the hLf1-11 peptide inhibited the early stages of bacterial growth. Thus, this strategy holds great potential to develop antimicrobial biomaterials for dental applications.

Quorum sensing in biofilms--how to destroy the bacterial citadels or their cohesion/power?

Biofilms or microbial communities formed by adherent and cohesive cells on cellular or inert substrata (like medical devices), are involved in ≈ 60% of all infections and characterized by moderate intensity symptoms, chronic evolution and resistance to antibiotics. Biofilms' pathogenicity, even of those formed by opportunistic microorganisms, is amplified by two major biofilm characteristics: 1) the increased resistance to antimicrobials; 2) the protection of cells against the host's defence mechanisms. The studies at the molecular level shown that the biofilms formation is controlled by cell-to-cell signalling mechanisms and the gene regulation during biofilm growth is due to the accumulation of signal molecules. In this regard, quorum sensing mechanism (QS) is defined as a cell-density dependent bacterial intercellular communication, involved in gene expression (e.g. virulence genes for exoenzymes, exopolysaccharides) and the consequent changed behaviour of biofilm's cells, including the resistance to stress conditions; this resistance is different of well known antibioresistance, being named phenotypical resistance or tolerance. Considering the differences in physiology and susceptibility to antibiotics of biofilm embedded bacteria, as well as their increased power against the host defence responses, there are necessary new strategies for prevention and therapy of biofilm associated infections. The dental plaque is a typical example of biofilm, involved in the ethiology of cariogenesis and periodontal diseases associated with local chronic inflammation and cytokines production. The genetical and phenotypical versatility of the biofilm's cells represent a challenge for discovering new methods of treatment and prevention of biofilm associated infections. A novel class of antibiofilm and antipathogenic therapeutics which are interfering with a new target - the QS pathway, not based on growth inhibition and called QS inhibitors, natural, with different origins or artificial, are now developing as an alternative to antibiotherapy.

[Replacement of infected knee and hip endoprostheses]

Infections occur in 0.5-5% of cases after implantation of an endoprosthesis and represent one of the most severe complications of artificial joint replacements. Approximately 300,000 primary implantations for hip and knee prostheses are carried out in Germany annually with a corresponding number of early and late infections. This means that approximately 4,000-6,000 cases are to be expected annually. Periprosthetic infections normally lead to a significant loss of function and quality of life for patients and the complex remediation is costly. Therefore, preventive measures, such as perioperative prophylaxis with antibiotics, maintaining highly sterile conditions during operations and an expedient selection of patients are of substantial importance. The basic principles of an adequate restoration include identification of the pathogen, local eradication of the infection mostly after removal of the prosthesis, pathogen-oriented systemic and local antibiotic therapy and finally re-implantation of the revision prosthesis under infection-free conditions. The standard procedure for revision surgery is a two-phase replacement with maintenance of an infection-free interval before renewal of the prosthesis. The use of single-phase or multi-phase strategies, as well as the selection of cemented or cement-free revision, varies between centers as a definitive evaluation is not yet available.The most important parameters for successful treatment of periprosthetic infections have been identified as the earliest possible diagnosis, radical surgical cleansing with an adequate antibiotic therapy and successful restoration has been reported in approximately 80% of cases. Because of the complex therapy regime, treatment in specialized centers is generally recommended especially under the aspect of a demanding patient monitoring.

Principles of demineralization: modern strategies for the isolation of organic frameworks. Part II. Decalcification

This is the second paper on principles of demineralization. The initial paper is dedicated to the common definitions and the history of demineralization. In present work we review the principles and mechanisms of decalcification, i.e., removing the mineral Ca-containing compounds (phosphates and carbonates) from the organic matrix in its two main aspects: natural and artificial. Natural chemical erosion of biominerals (cavitation of biogenic calcareous substrata by bacteria, fungi, algae, foraminifera, sponges, polychaetes, and mollusks) is driven by production of mineral and organic acids, acidic polysaccharides, and enzymes (cabonic anhydrase, alkaline and phosphoprotein phosphataes, and H(+)-ATPase). Examples of artifical decalcification includes demineralization of bone, dentin and enamel, and skeletal formations of corals and crustacean. The mechanism and kinetics of Ca-containing biomineral dissolution is analyzed within the framework of (i) diffusion-reaction theory; (ii) surface-reaction controlled, morphology-based theories, and (iii) phenomenological surface coordination models. The application of surface complexation model for describing and predicting the effect of organic ligands on calcium and magnesium dissolution kinetics is also described. Use of the electron microscopy-based methods for observation and visualization of the decalcification phenomenon is discussed.

Medical biofilms

For more than two decades, Biotechnology and Bioengineering has documented research focused on natural and engineered microbial biofilms within aquatic and subterranean ecosystems, wastewater and waste-gas treatment systems, marine vessels and structures, and industrial bioprocesses. Compared to suspended culture systems, intentionally engineered biofilms are heterogeneous reaction systems that can increase reactor productivity, system stability, and provide inherent cell:product separation. Unwanted biofilms can create enormous increases in fluid frictional resistances, unacceptable reductions in heat transfer efficiency, product contamination, enhanced material deterioration, and accelerated corrosion. Missing from B&B has been an equivalent research dialogue regarding the basic molecular microbiology, immunology, and biotechnological aspects of medical biofilms. Presented here are the current problems related to medical biofilms; current concepts of biofilm formation, persistence, and interactions with the host immune system; and emerging technologies for controlling medical biofilms.