Danyal A. Siddiqui

Dicationic imidazolium-based ionic liquids: a new strategy for non-toxic and antimicrobial materials

New dicationic imidazolium-based ionic liquids (ILs) were synthesized, characterized and tested in regards to cytotoxicity and antimicrobial activity. Insertion of a new cationic head and use of organic anions increased the biocompatibility of the ILs developed. IC50 (concentration necessary to inhibit 50% of enzymatic activity) values obtained were considerably higher than those described for monocationic ILs, which indicates an improvement in cytocompatibility. Antimicrobial activity against bacterial species of clinical relevance in wounds and the oral environment was tested. The results showed that ILs were effective in inhibiting bacterial growth even below the minimum inhibitory concentration (MIC). It was observed that structural features that confer higher hydrophobicity to ILs decreased both the IC50 and MIC simultaneously. However, it was possible to establish an equilibrium between those two effects, which gives the safe range of concentrations that ILs can be employed. The results demonstrated that the dicationic-imidazolium-based ILs synthesized may constitute a potent strategy for applications requiring non-toxic materials exhibiting antimicrobial activity.

Ionic Liquid Coatings for Titanium Surfaces: Effect of IL Structure on Coating Profile

Dicationic imidazolium-based ionic liquids (ILs) having bis(trifluoromethylsulfonyl)imide (NTf2) and amino acid-based (methionine and phenylalanine) anionic moieties were synthesized and used to coat titanium surfaces using a dip-coating technique. Dicationic moieties with varying alkyl chains (8 and 10 carbons) and anions with distinct characteristics were selected to understand the influence of IL structural features on deposition profile. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used in this study to help elucidate intermolecular interactions within ILs as well as between ILs and TiO2 surfaces and to investigate IL coating morphology. Charge concentration on IL moieties, as well as the presence of functional groups that can interact via hydrogen bond, such as carboxylate and amino groups, were observed to influence the deposition profile. ILs containing amino acids as the anionic moiety were observed to interact strongly with TiO2, which resulted in more pronounced changes in Ti 2p binding energy. The higher hydrophobicity of the IL having NTf2 as the anionic moiety resulted in higher adhesion strength between the IL coating and TiO2.

Evaluation of mammalian and bacterial cell activity on titanium surface coated with dicationic imidazolium-based ionic liquids

This work presents a new strategy to protect titanium surfaces against bacterial colonization and biofilm formation using dicationic imidazolium-based ionic liquid coatings. Ionic liquids (ILs) were designed as multi-functional coatings and their compatibility with human gingival fibroblasts (HGF-1) and pre-osteoblast (MC3T3-E1) cells was investigated. Results demonstrated that IL coatings were stable and present on titanium surfaces after 7 days of immersion and showed that using phenylalanine as the anionic moiety allowed for cell proliferation and differentiation on titanium surface while also providing strong antimicrobial and anti-biofilm activity against bacterial strains relevant to the oral environment (Streptococcus sp.). Strains such as Streptococcus mutans, S. sanguinis, S salivarius, S. gordonii and S. uberis are known to colonize the surface of dental implants in the early stages after implantation (early colonizers), compromising the success of these devices. The “race for the surface” between cells and bacteria was established by correlating results obtained from cell proliferation (epithelial and osteoblast) and differentiation (osteoblast) studies with that of antimicrobial activity against early bacterial colonizers.

Improvement of tribological and anti-corrosive performance of titanium surfaces coated with dicationic imidazolium-based ionic liquids

In this work, dicationic imidazolium-based ionic liquids (ILs) with amino acid anionic moieties were employed as coatings for commercially pure titanium (Ti) surfaces. Coated and non-coated samples were tested with regard to their anti-corrosive and lubricant properties. Phosphate buffer saline (PBS), artificial saliva, and 50/50 PBS–saliva (v/v) were used as electrolytes during electrochemical testing and as control lubricants for Ti samples during tribological testing. Samples coated with ILs possessing longer alkyl chains in their spacer group and more hydrophobic anionic moieties, such as phenylalanine, demonstrated superior anti-corrosive and lubricant behavior. Protection against corrosion was reflected in lower corrosion current (Icorr) and corrosion rate values as well as independently measured higher polarization resistance values. Immersion medium was also observed to influence the corrosion behavior of samples. Control Ti exhibited increased susceptibility to corrosion in more acidic environments (artificial saliva) while the opposite trend was observed for IL-coated Ti samples. Enhanced lubrication was verified by a significant reduction in the coefficient of friction and total wear volume loss of IL-coated samples in comparison to control Ti.

Detoxification of Titanium Implant Surfaces: Evaluation of Surface Morphology and Bone-Forming Cell Compatibility

Peri-implantitis is one of the major clinical conditions associated with dental implant failure. Adhesion of bacterial biofilm is considered as the primary etiological factor for this condition. A commonly used therapeutic method for surgical removal of adhered biofilm is mechanical debridement, which may cause detrimental effects on the implant surface. Post-treatment, implants are expected to re-osseointegrate with bone tissue, providing mechanical stability. However, it is important to understand that both bacterial adhesion and detoxification procedures can affect the titanium surface, which is vital for growth of bone-forming cells, osteoblasts. The goal of this study was to evaluate the synergistic effect of bacterial adhesion and detoxification treatment method on subsequent bone cell growth on implant surface. Polished titanium specimens underwent bacterial contamination and debridement/detoxification treatment with acidic and neutral chemicals to model a treatment for a peri-implantitis-infected dental implant. Subsequently, bone cell activity and surface morphology were evaluated using standard cell viability/differentiation assays, scanning electron and optical microscopies, respectively. The synergistic activity of bacterial contamination and detoxification with acidic chemicals generally lowered cell viability and proliferation rates. This suggested higher toxicity of titanium surfaces imparted by detoxification methods on osteoblasts. Electrochemical testing corroborated visual signs of corrosion attack and revealed that immersion-treated specimens had higher corrosion resistance than their corresponding rubbing-treated counterparts, excluding saline. Overall, surface damage induced by detoxification methods must be considered when selecting the most appropriate therapy to increase the probability of re-osseointegration of titanium substrates.

Investigation of the Corrosive Effects of Dental Cements on Titanium

Biocompatibility, strength, and corrosion resistance make titanium the material of choice for dental implants and abutment components. In cemented implant restorations, dental cement is used to provide retention of the crown to the abutment and to create access to the implant. Reported problems in the literature associated with dental cement cite inflammation, and in some cases peri-implantitis, due to its residual presence in subgingival tissues. It has been recently suggested that particular components of dental cement may play a role in promoting corrosion while in contact with titanium surfaces. The goal of this study was to understand the electrochemical behavior of commercially pure titanium (cpTi) in contact with various commercially available dental cements. Open-circuit potential, linear polarization resistance, and corrosion rates were measured for cpTi disks cemented with resin, eugenol, zinc phosphate, and bioceramic cements. Results determined that the bioceramic cement investigated induced significantly lower polarization resistance values and a higher corrosion rate relative to noncemented cpTi. Resin, eugenol, and zinc phosphate cements exhibited corrosion behavior between that of control and bioceramic-cemented cpTi. Overall, fluoride-containing cements were observed to increase the corrosion rate of cpTi.

Dicationic Imidazolium-Based Ionic Liquid Coatings on Zirconia Surfaces: Physico-Chemical and Biological Characterization

In the present work, dicationic imidazolium-based ionic liquids (ILs) were investigated as multi-functional coatings on a zirconia (ZrO2) surface to prevent biofilm formation and enhance the wear performance of zirconia while maintaining the material’s compatibility with host cells. ILs containing phenylalanine and methionine were synthesized and deposited on zirconia. Intermolecular interactions driving IL deposition on zirconia were studied using X-ray photoelectron spectroscopy (XPS). Anti-biofilm activity and cell compatibility were evaluated in vitro after one and seven days, and wear performance was tested using a pin-on-disk apparatus. ILs were observed to form strong hydrogen bonds with zirconia. IL containing phenylalanine formed a stable film on the surface after one and seven days in phosphate-buffered saline (PBS) and artificial saliva and showed excellent anti-biofilm properties against Streptococcus salivarius and Streptococcus sanguinis. Compatibility with gingival fibroblasts and pre-osteoblasts was maintained, and conditions for growth and differentiation were preserved. A significantly lower coefficient of friction and wear volume loss were observed for IL-coated surfaces as compared to non-coated substrates. Overall, zirconia is an emerging alternative to titanium in dental implants systems, and this study provides additional evidence of the materials’ behavior and IL coatings as a potential surface treatment technology for improvement of its properties.