Development of sustained antimicrobial-release systems using poly(2-hydroxyethyl methacrylate)/trimethylolpropane trimethacrylate hydrogels

Applications of Hydrogels in Drug Delivery for Oral and Maxillofacial Diseases

Oral and maxillofacial diseases have an important impact on local function, facial appearance, and general health. As a multifunctional platform, hydrogels are widely used in the biomedical field due to their excellent physicochemical properties. In recent years, a large number of studies have been conducted to adapt hydrogels to the complex oral and maxillofacial environment by modulating their pore size, swelling, degradability, stimulus-response properties, etc. Meanwhile, many studies have attempted to use hydrogels as drug delivery carriers to load drugs, cytokines, and stem cells for antibacterial, anticancer, and tissue regeneration applications in oral and maxillofacial regions. This paper reviews the application and research progress of hydrogel-based drug delivery systems in the treatment of oral and maxillofacial diseases such as caries, endodontic diseases, periodontal diseases, maxillofacial bone diseases, mucosal diseases, oral cancer, etc. The characteristics and applications of hydrogels and drug-delivery systems employed for the treatment of different diseases are discussed in order to provide a reference for further research on hydrogel drug-delivery systems in the future.

Incorporation of chlorhexidine in self-adhesive resin cements

The aim of this study was to evaluate the maximum amount of chlorhexidine (CHX) that could be incorporated to self-adhesive resin cements to add antibacterial effect without affecting the physical properties. The CHX was incorporated into a commercial self-adhesive resin cement at mass fractions of 0.5-15 wt%, and the CHX-release profile, antibacterial effect, flexural and bond strengths of experimental cements were evaluated. Increasing the CHX content from 5 to 15 wt% resulted in a higher released concentration of CHX. In agar diffusion tests, experimental cements containing 5, 10, and 15 wt% CHX produced inhibition zones against oral bacteria. In flexural strength and shear bond strength to dentin, no significant reduction was observed with the incorporation of 5 wt% CHX. This in vitro study suggests that the addition of 5 wt% CHX yielded an antibacterial self-adhesive cement and had no adverse effect on the flexural and shear bond strengths.

Antimicrobial PEGtides: A Modular Poly(ethylene glycol)-Based Peptidomimetic Approach to Combat Bacteria

Despite their high potency, the widespread implementation of natural antimicrobial peptides is still challenging due to their low scalability and high hemolytic activities. Herein, we address these issues by employing a modular approach to mimic the key amino acid residues present in antimicrobial peptides, such as lysine, leucine, and serine, but on the highly biocompatible poly(ethylene glycol) (PEG) backbone. A series of these PEG-based peptides (PEGtides) were developed using functional epoxide monomers, corresponding to each key amino acid, with several possessing highly potent bactericidal activities and controlled selectivities, with respect to their hemolytic behavior. The critical role of the composition and the structure of the PEGtides in their selectivities was further supported by coarse-grained molecular dynamic simulations. This modular approach is anticipated to provide the design principles necessary for the future development of antimicrobial polymers.

Development of endodontic sealers containing antimicrobial-loaded polymer particles with long-term antibacterial effects

OBJECTIVE

The objective of this study is to prepare new dental resins with a long-lasting antimicrobial activity. Specifically, this study evaluates an approach for controlling infection in root canals using sealers containing polyhydroxyethyl methacrylate trimethylolpropane trimethacrylate (polyHEMA/TMPT) particles loaded with cetylpyridinium chloride (CPC). In addition, the physical properties of sealers containing CPC-loaded polyHEMA/TMPT particles (CLP) are determined.

METHODS

PolyHEMA/TMPT particles with 10 (10%-CLP) and 25wt.% CPC (25%-CLP) with different particle sizes were fabricated and incorporated in HEMA-based sealers. CPC-release profiles were evaluated over 14 days of immersion in water, followed by 14 days of storage and 14 days of water immersion. The antibacterial activity of these sealers against Enterococcus faecalis in dentinal tubules was assessed using a root-canal-infection model. Their sealing abilities were evaluated by fluid filtration and physical properties were tested according to the ISO 6876 standard. The long-term antibacterial activity of the cured sealer containing 25%-CLP (∼21μm particle diameter) was re-assessed after 1 year of storage.

RESULTS

After 28 days of immersion, 25%-CLP exhibited a higher and sustained CPC release unlike 10%-CLP. Residual bacteria in root dentinal tubules were eradicated by obturation with 25%-CLP-containing sealers. The incorporation of 25%-CLP (∼21μm) had no adverse effects on the sealing ability and physical properties of the sealer and resulted in long-term antibacterial activity.

SIGNIFICANCE

The incorporation of CPC-loaded particles in HEMA resins yielded endodontic sealers with long-term bactericidal activity against E. faecalis in root canals. These sealers can potentially be used to prevent recurrent apical periodontitis.

Antibacterial activities and mineral induction abilities of proprietary MTA cements

Mineral trioxide aggregate (MTA) cements are used in direct pulp capping and many other applications, and several types of these products have been commercialized. The aim of this study was to examine the antibacterial effects and mineral induction abilities of three conventional MTA cements and one resin-modified MTA cement. Agar diffusion tests revealed that, after setting, all four cements exhibited little antibacterial effects against Enterococcus faecalis and Streptococcus mutans, with no significant differences among the materials. After 24 h, E. faecalis and S. mutans suspensions incubated in the presence of each cement did not exhibit reduced numbers of viable bacteria, compared with those same bacterial suspensions incubated without any cement; this indicated that none of the cements inhibited bacterial growth. Furthermore, the resin-modified MTA cement exhibited lower mineral induction ability, compared with that of the three conventional MTA cements.

Acidity-induced release of zinc ion from BioUnionTM filler and its inhibitory effects against Streptococcus mutans

BioUnion filler incorporated into restorative/coating materials is a new bio-functional glass powder. The most unique function of BioUnion filler is its ability to release Zn²⁺ in acidic environments. In this study, the ion release profile of BioUnion filler under acidic conditions and its antibacterial effects against Streptococcus mutans were evaluated. The concentrations of Zn²⁺ released from BioUnion fillers into acetic acids were greater than those released into water. S. mutans inhibition by BioUnion fillers was greater with sucrose than without sucrose, reflecting a decrease in suspension pH in response to the addition of sucrose. Exposure to acids increased Zn²⁺ release from BioUnion fillers, and the fillers after repeated exposure to acids demonstrated inhibitory effects against S. mutans. These findings suggest that BioUnion filler accelerated the release of Zn²⁺ under acidic conditions, which induced bactericidal/inhibitory effects against S. mutans.

Cutting-edge filler technologies to release bio-active components for restorative and preventive dentistry

Advancements in materials used for restorative and preventive treatment is being directed toward "bio-active" functionality. Incorporation of filler particles that release active components is a popular method to create bio-active materials, and many approaches are available to develop fillers with the ability to release components that provide "bio-protective" or "bio-promoting" properties; e.g. metal/calcium phosphate nanoparticles, multiple ion-releasing glass fillers, and non-biodegradable polymer particles. In this review paper, recent developments in cutting-edge filler technologies to release bio-active components are addressed and summarized according to their usefulness and functions, including control of bacterial infection, tooth strengthening, and promotion of tissue regeneration.

Rechargeable anti-microbial adhesive formulation containing cetylpyridinium chloride montmorillonite

Long-term anti-bacterial effect is a desired ability of any dental material in combating tooth caries as one of the most common and widespread persistent diseases today. Among several cationic quaternary ammonium compounds with antiseptic properties, cetylpyridinium chloride (CPC) is often used in mouthrinses and toothpastes. In this study, we incorporated CPC in a soft phyllosilicate mineral (clay), referred to as montmorillonite (Mont), to enable gradual CPC release with rechargeability. Besides measuring CPC release and recharge, we examined the anti-bacterial effect, cytotoxicity and bonding effectiveness of five experimental adhesive formulations, prepared by adding 1 and 3 wt% CPC_Mont, 3 wt% Mont (without CPC), and 1 and 3 wt% CPC (without Mont) to the commercial adhesive Clearfil S³ Bond ND Quick ('C-S³B'; Kuraray Noritake). Strong inhibition of Streptococcus mutans biofilm formation by CPC_Mont adhesives was confirmed by optical density and SEM. CPC release from CPC_Mont adhesives was higher and lasted longer than from CPC adhesives, while CPC_Mont adhesives could also be recharged with CPC upon immersion in 2 wt% CPC. In conclusion, CPC_Mont technology rendered adhesives anti-bacterial properties with recharge ability, this without reducing its bonding potential, neither increasing its cytotoxicity. STATEMENT OF SIGNIFICANCE: Dental caries is one of the most prevalent chronic diseases in the population worldwide and is the major cause of tooth loss. In this study, we developed cetylpyridinium chloride (CPC) loaded montmorillonite (CPC-Mont) with a long-term antibacterial efficacy to prevent caries. CPC is an antibacterial agent approved by FDA, used as an OTC drug and contained in oral hygiene aids. CPC-Mont was incorporated in a dental adhesive to gradually release CPC. CPC_Mont technology rendered adhesives anti-bacterial properties with rechargeability, this without reducing its bonding potential, neither increasing its cytotoxicity.

Hydrogels Based Drug Delivery Synthesis, Characterization and Administration

Hydrogels represent 3D polymeric networks specially designed for various medical applications. Due to their porous structure, they are able to swollen and to entrap large amounts of therapeutic agents and other molecules. In addition, their biocompatibility and biodegradability properties, together with a controlled release profile, make hydrogels a potential drug delivery system. In vivo studies have demonstrated their effectiveness as curing platforms for various diseases and affections. In addition, the results of the clinical trials are very encouraging and promising for the use of hydrogels as future target therapy strategies.

Sulindac encapsulation and release from functional poly(HEMA) microparticles prepared in supercritical carbon dioxide

Sulindac loaded poly(HEMA) cross-linked microparticles were synthesized via one-pot free-radical dispersion polymerisation in supercritical carbon dioxide (scCO₂) in presence of photocleavable diblock stabilisers based on polyethylene oxide (PEO) and poly(heptadecafluorodecyl acrylate) (PFDA) bearing a o-nitrobenzyl photosensitive junction (hv) (PEO-hv-PFDA), and ethylene glycol dimethacrylate (EGDMA) as cross-linker. Poly(HEMA) cross-linked microparticles either empty or sulindac loaded were obtained with well-defined spherical morphology with the sizes between 250 and 350 nm. Additionally, upon UV-photolysis the stabiliser on the surface was cleaved which permits to microparticles to be redispersed in water leading to water swollen microgels about 2.1-3.6 µm. Moreover, the release behaviour from obtained microgels indicated the sustained release of sulindac over 10 days. Besides, the surface modification after UV-photolysis was studied and proved that the particles can be functionalised with further chemistries.

Revisiting Current Photoactive Materials for Antimicrobial Photodynamic Therapy

Microbial infection is a severe concern, requiring the use of significant amounts of antimicrobials/biocides, not only in the hospital setting, but also in other environments. The increasing use of antimicrobial drugs and the rapid adaptability of microorganisms to these agents, have contributed to a sharp increase of antimicrobial resistance. It is obvious that the development of new strategies to combat planktonic and biofilm-embedded microorganisms is required. Photodynamic inactivation (PDI) is being recognized as an effective method to inactivate a broad spectrum of microorganisms, including those resistant to conventional antimicrobials. In the last few years, the development and biological assessment of new photosensitizers for PDI were accompanied by their immobilization in different supports having in mind the extension of the photodynamic principle to new applications, such as the disinfection of blood, water, and surfaces. In this review, we intended to cover a significant amount of recent work considering a diversity of photosensitizers and supports to achieve an effective photoinactivation. Special attention is devoted to the chemistry behind the preparation of the photomaterials by recurring to extensive examples, illustrating the design strategies. Additionally, we highlighted the biological challenges of each formulation expecting that the compiled information could motivate the development of other effective photoactive materials.

Recent Progress in Polymer Research to Tackle Infections and Antimicrobial Resistance

Global health is increasingly being threatened by the rapid emergence of drug-resistant microbes. The ability of these microbes to form biofilms has further exacerbated the scenario leading to notorious infections that are almost impossible to treat. For addressing this clinical threat, various antimicrobial polymers, polymer-based antimicrobial hydrogels and polymer-coated antimicrobial surfaces have been developed in the recent past. This review aims to discuss such polymer-based antimicrobial strategies with a focus on their current advancement in the field. Antimicrobial polymers, whose designs are inspired from antimicrobial peptides (AMPs), are described with an emphasis on structure-activity analysis. Additionally, antibiofilm activity and in vivo efficacy are delineated to elucidate the real potential of these antimicrobial polymers as possible therapeutics. Antimicrobial hydrogels, prepared from either inherently antimicrobial polymers or biocide-loaded into polymer-derived hydrogel matrix, are elaborated followed by various strategies to engineer polymer-coated antimicrobial surfaces. In the end, the current challenges are accentuated along with future directions for further expansion of the field toward tackling infections and antimicrobial resistance.

Influence of polymerization properties of 4-META/MMA-based resin on the activity of fibroblast growth factor-2

Dental adhesive resins based on 4-methacryloxyethyl trimellitate anhydride (4-META)/methyl methacrylate (MMA) have been utilized for root-end filling and the bonding of fractured roots. To increase the success rate of these treatments, it would be beneficial to promote the healing of surrounding tissue by applying growth factors. In this study, the influences of the polymerization properties of 4-META/MMA-based resins on the activity of fibroblast growth factor-2 (FGF-2) were evaluated in vitro. The temperature increase caused by the heat generation during polymerization of the 4-META/MMA-based resin was insufficient to change the structure and function of FGF-2. Unpolymerized monomers released from the cured 4-META/MMA-based resin had no negative influences on the ability of FGF-2 to promote the proliferation of osteoblast-like cells. These findings suggest that it is possible to use FGF-2 in combination with 4-META/MMA-based resins.

Automation of antimicrobial activity screening

Manual and automated methods were compared for routine screening of compounds for antimicrobial activity. Automation generally accelerated assays and required less user intervention while producing comparable results. Automated protocols were validated for planktonic, biofilm, and agar cultures of the oral microbe Streptococcus mutans that is commonly associated with tooth decay. Toxicity assays for the known antimicrobial compound cetylpyridinium chloride (CPC) were validated against planktonic, biofilm forming, and 24 h biofilm culture conditions, and several commonly reported toxicity/antimicrobial activity measures were evaluated: the 50 % inhibitory concentration (IC50), the minimum inhibitory concentration (MIC), and the minimum bactericidal concentration (MBC). Using automated methods, three halide salts of cetylpyridinium (CPC, CPB, CPI) were rapidly screened with no detectable effect of the counter ion on antimicrobial activity.

Evolution of resistance to cationic biocides in Streptococcus mutans and Enterococcus faecalis

OBJECTIVES

The aim of this study was to investigate whether Streptococcus mutans and Enterococcus faecalis develop resistance to the cationic biocides chlorhexidine (CHX), cetylpyridinium chloride (CPC), and 12-methacryloyloxydodecylpyridinium bromide (MDPB).

METHODS

The minimum inhibitory concentrations (MICs) of CHX, CPC, and MDPB were assessed after repeated exposure of S. mutans and E. faecalis to these biocides. Cell-surface hydrophobicity and protein expression profiles of bacterial cells were examined to elucidate possible resistance mechanisms.

RESULTS

The MIC of CHX against E. faecalis showed constant increases up to 10 passages. No changes in the MICs of CPC and MDPB against E. faecalis were observed. The MICs of CHX, CPC, and MDPB against S. mutans did not increase. The surface hydrophobicity of E. faecalis significantly increased with increasing exposure to CHX and CPC. However, changes in protein expression profiles were only found in CHX-adapted E. faecalis, as evidenced by the emergence of a novel, approximately 19-kDa band following sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

CONCLUSIONS

While E. faecalis and S. mutans did not exhibit increased resistance to CPC or MDPB, repeated exposure of E. faecalis to CHX led to resistance. It is likely that the acquisition of resistance is related to an altered protein composition.

CLINICAL SIGNIFICANCE

Alkyl pyridinium compounds, such as CPC and MDPB, could have a lower risk to cause adaptation of E. faecalis, which is advantageous compared with CHX.