Properties of eight methacrylated beta-cyclodextrin composite formulations

Cyclodextrins as Multi-Functional Ingredients in Dentistry

Cyclodextrins are present in a variety of oral hygiene compositions. The present work describes the role of cyclodextrins in several toothpastes and mouthwashes that are already available in the market, as well as their prospective use in other applications as investigated in studies in the literature. Moreover, cyclodextrins are under study for the development of materials used in various techniques of dental repair, such as fillings, cements and binders therein. Their role in each of the innovative materials is presented. Finally, the prospect of the use of cyclodextrin-based delivery systems for the oral cavity is introduced, with a focus on new cyclodextrin molecules with dual action as bone-targeting agents and osteogenic drugs, and on new cross-linked cyclodextrin particles with a high drug loading and sustained drug delivery profile for the treatment of diseases that require prolonged action, such as periodontitis. In conclusion, cyclodextrins are herein demonstrated to act as versatile and multi-action ingredients with a broad range of applications in dentistry.

Recent advances and developments in composite dental restorative materials

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization-induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors. Fortunately, these materials have been the focus of a great deal of research in recent years with the goal of improving restoration performance by changing the initiation system, monomers, and fillers and their coupling agents, and by developing novel polymerization strategies. Here, we review the general characteristics of the polymerization reaction and recent approaches that have been taken to improve composite restorative performance.

Solventless visible light-curable coating: I. Critical formulation and processing parameters

Film coating is generally accomplished by spraying polymers dissolved in solvents onto a cascading bed of tablets. The limitations associated with the use of solvents (both aqueous and organic) can be overcome by the use of solventless coating technologies. In this proposed solventless photocurable film coating system, each layer of coating onto the pellets (non-pareil beads) was formed using liquid photocurable monomer, powdered pore-forming agents, photosensitizers and photoinitiators in a mini-coating pan and later cured by visible light. Yield, coating efficiency, variation in color, diameter and roundness were determined for each batch to evaluate process efficiency and coating quality. It was found that the ratio (S/L ratio) of the amount of solid (S) pore-forming agent to volume of liquid (L) monomer, particle size and type of the pore-forming agent, concentration of initiator, and total exposure (light intensity x exposure time) of light were critical formulation and processing parameters for the process. Using lactose as a pore-forming agent, an optimum ratio of pore-forming agent to photocurable polymer was 1.8-3.0 to achieve good process efficiency and uniformity. The ratio was sensitive to particle size and type of pore-forming agent.

Soft contact lenses functionalized with pendant cyclodextrins for controlled drug delivery

The aim of this work was to develop acrylic hydrogels with high proportions of cyclodextrins maintaining the mechanical properties and the biocompatibility of the starting hydrogels, but notably improving their ability to load drugs and to control their release rate. Poly(hydroxyethylmethacrylate) hydrogels were prepared by copolymerization with glycidyl methacrylate (GMA) at various proportions and then beta-cyclodextrin (betaCD) was grafted to the network by reaction with the glycidyl groups under mild conditions. This led to networks in which the betaCDs form no part of the structural chains but they are hanging on 2-3 ether bonds through the hydroxyl groups. The pendant betaCDs did not modify the light transmittance, glass transition temperature, swelling degree, viscoelasticity, oxygen permeability, or surface contact angle of the hydrogels, but decreased their friction coefficient by 50% and improved diclofenac loading by 1300% and enhanced drug affinity 15-fold. The hydrogels were able to prevent drug leakage to a common conservation liquid for soft contact lenses (SCLs) and to sustain drug delivery in lacrimal fluid for two weeks. To summarize, the hydrogels with pendant betaCDs are particularly useful for the development of cytocompatible medicated implants or biomedical devices, such as drug-loaded SCLs.

Poly(hydroxyethyl methacrylate-co-methacrylated-beta-cyclodextrin) hydrogels: synthesis, cytocompatibility, mechanical properties and drug loading/release properties

Copolymerization of hydroxyethyl methacrylate (HEMA) with a methacrylated-derivative of beta-cyclodextrin (beta-CD) was evaluated as a way to obtain hydrogels with tunable mechanical and drug loading and release properties, particularly for preparing medicated soft contact lenses. A fully methacrylated beta-CD monomer was synthesized and added to the HEMA and cross-linker solution at concentrations ranging from 0.042 to 0.333 g ml(-1) (i.e. 0.23-1.82 mol.%). Thermal polymerization led to transparent hydrogels with a degree of conversion above 74%, which showed a high cytocompatibility and did not induce macrophage response. The greater the content in methacrylated beta-CD was, the higher the glass transition temperature, the lower the degree of swelling and free water proportion, and the greater the storage and loss moduli of the swollen disks. These findings are directly related to the increase in the degree of cross-linking caused by the methacrylated beta-CD. Loading studies were carried out with hydrocortisone and acetazolamide, both able to form complexes with CDs in water and in lacrimal fluid. Hydrocortisone loading progressively decreased as the content in methacrylated beta-CD rose due to a decrease in the volume of aqueous phase of the hydrogel. Acetazolamide loading showed a maximum for an intermediate content in beta-CD (0.125-0.167 g ml(-1)) owing to a balance between complexation with beta-CD and hydrogel mesh size. The hydrogels sustained drug delivery for several days, the acetazolamide release rate being dependent on the beta-CD content. An adequate selection of the content in beta-CD enables pHEMA-co-beta-CD hydrogels suitable for specific biomedical applications to be obtained.

Rheological properties of flowable resin composites and pit and fissure sealants

OBJECTIVES

The purpose of this research was to determine the viscoelastic properties of commercially available flowable resin composites and resin-based pit and fissure sealants. The weight percentage of filler particles and the morphology of the filler particles were also investigated.

METHODS

Eight flowable resin composites (Admira Flow, Filtek Flow, FlowLine, Grandio Flow, Point-4 Flowable, Revolution Formula 2, Tetric Flow and X-Flow) and four pit and fissure sealants (Clinpro, Delton FS+, Estiseal F and Guardian Seal) were tested. Rheological measurements were performed using a dynamic oscillation rheometer. The filler weight content was determined by thermogravimetric analysis (TGA) and the morphology of the particles was investigated by scanning-electron microscopy (SEM).

RESULTS

Flowable resin composites are non-Newtonian, shear-thinning materials. As the shear rate increased, the complex viscosity decreased drastically. They all showed elasticity even at the lowest frequencies. They also all showed thixotropy. Pit and fissure sealants are non-Newtonian, very low-viscosity fluids. No correlation was found between the rheological properties and the filler weight content or the particles' shape.

SIGNIFICANCE

Huge differences are observed in the viscosity and flow characteristics of flowable resin composites that can have a potential influence on their clinical behavior during handling and thus on their clinical indications. Pit and fissure sealants show very different rheological properties from one another.

Polymerization shrinkage and hygroscopic expansion of contemporary posterior resin-based filling materials—A comparative study

OBJECTIVES

To investigate the polymerization shrinkage and hygroscopic expansion of contemporary posterior resin-based filling materials.

METHODS

The densities of SureFil (SU), CeramXMono (CM), Clearfil AP-X (CF), Solitaire 2 (SO), TetricEvoCeram (TE), and Filtek P60 (FT) were measured using the Archimedes' principle prior to and 15min after curing for 20, 40 and 60s and after 1h, 24h, 7 d, and 30 d storage at 37 degrees C in water. Volumetric changes (DeltaV) in percent after polymerization and after each storage period in water were calculated from the changes of densities. Water sorption and solubility were determined after 30 d for all specimens and their curing times. Two-way ANOVA was calculated for shrinkage and repeated measures ANOVA was calculated for hygroscopic expansion (p<0.05).

RESULTS

DeltaV depended on filler load but not on curing time (SU approximately -2.0%, CM approximately -2.6%, CF approximately -2.1%, SO approximately -3.3%, TE approximately -1.7%, FT approximately -1.8%). Hygroscopic expansion depended on water sorption and solubility. Except for SU, all materials showed DeltaV approximately +1% after water storage.

CONCLUSION

Polymerization shrinkage depended on the type of resin-based filling material but not on curing time. Shrinkage was not compensated by hygroscopic expansion.

Solventless pharmaceutical coating processes: a review

Coatings are an essential part in the formulation of pharmaceutical dosage form to achieve superior aesthetic quality (e.g., color, texture, mouth feel, and taste masking), physical and chemical protection for the drugs in the dosage forms, and modification of drug release characteristics. Most film coatings are applied as aqueous- or organic-based polymer solutions. Both organic and aqueous film coating bring their own disadvantages. Solventless coating technologies can overcome many of the disadvantages associated with the use of solvents (e.g., solvent exposure, solvent disposal, and residual solvent in product) in pharmaceutical coating. Solventless processing reduces the overall cost by eliminating the tedious and expensive processes of solvent disposal/treatment. In addition, it can significantly reduce the processing time because there is no drying/evaporation step. These environment-friendly processes are performed without any heat in most cases (except hot-melt coating) and thus can provide an alternative technology to coat temperature-sensitive drugs. This review discusses and compares six solventless coating methods - compression coating, hot-melt coating, supercritical fluid spray coating, electrostatic coating, dry powder coating, and photocurable coating - that can be used to coat the pharmaceutical dosage forms.

Monomer conversion and hardness of novel dental cements based on ethyl cyanoacrylate

OBJECTIVES

The aim of this work was to study the setting of two novel dental cements: (i) a 'hybrid' cement, incorporating an ethyl cyanoacrylate into a glass-ionomer cement (ECGIC) formulation and (ii) an ethyl cyanoacrylate/hydroxyapatite composite cement (ECHC). The mechanical role of the cyanoacrylate and its curing within the cements have been discussed.

METHODS

The setting of the cements was characterised using Vickers indentation hardness and near-infrared (near-IR) spectroscopy.

RESULTS

The cyanoacrylate component of ECGIC was 100% cured approximately 10min after the initial cement mixing. The ECGIC continued to increase in hardness after the cyanoacrylate component was fully cured. This proved that the fully polymerised network of cyanoacrylate did not prevent the acid-base reactions of the GIC components from continuing. The Vickers hardness number of ECGIC at 18 weeks was approximately 105. The curing of the cyanoacrylate within ECHC was much slower and was still not complete (98%) 18 weeks after the initial cement mixing. The hardness of the ECHC was shown to be correlated with the extent of cyanoacrylate cure. The Vickers hardness number of ECHC at 18 weeks was approximately 21. The primary reasons for the overall lower hardness of ECHC in comparison to ECGIC were the lower powder:liquid ratio and the softer filler type.

SIGNIFICANCE

Careful consideration is needed when incorporating cyanoacrylates into dental cements, as speed of cure and hardness are particularly important.

Influence of different light curing units on the cytotoxicity of various dental composites

OBJECTIVES

To evaluate the dependence of the toxicity of various dental composites on the use of high- and low-power light curing units (LCUs).

METHODS

The composites Filtek Z 250, Durafill VS, Solitaire 2 and Grandio were polymerized using different light densities from three LCUs, namely Heliolux II, Swiss Master Light (SML) and a prototype LED. The toxicity of polymerized samples was tested by exposing them to the cell culture medium up to 28 days. The extracts of the composites were collected daily and used for incubation in human gingival fibroblasts cultures.

RESULTS

Slow, low-intensity curing using the LED or the Heliolux II showed similar characteristics for all four composites, regarding the cell viability rate of human gingival fibroblasts. After 1 day of storage suboptimal results could be observed for the SML/Durafill and optimal results for SML/Grandio combination (approximately 100% cell viability). In addition, the composite Solitaire the SML yielded significantly better results than the other LCUs (cell viability, p < or = 0.001: SML 60.5%, Heliolux 44.5%, LED 44.2%). Furthermore, the combination of the SML with Z 250 composite showed, after the first day and up to day 28, statistically significantly higher cell viability rates than the combination with the LED or Heliolux II.

SIGNIFICANCE

This study shows that the combination of a high power LCU with some composites positively influences the HGF cell viability effected by the investigated composite extracts. Moreover, there is further indication that a reduction of composite toxicity is possible if the curing mode is adapted to the used composite.

New Cyclodextrin Hydrogels Cross-Linked with Diglycidylethers with a High Drug Loading and Controlled Release Ability

PURPOSE

The goal of the study is to develop new hydrogels based on cyclodextrins cross-linked with ethyleneglycol diglycidylether (EGDE) under mild conditions, to be used as carriers of amphiphilic drugs. Also, it aims to characterize the cross-linking and the drug loading and release processes.

METHODS

The cross-linking of hydroxypropyl-beta-cyclodextrin (HPbetaCD) with EGDE, in the absence or presence of hydroxypropylmethylcellulose (HPMC) Methocel K4M, was optimized applying oscillatory rheometry and Fourier transform infrared. Hydrogels were characterized regarding swelling in water, ability to load diclofenac, and release after different drying treatments.

RESULTS

Solutions of HPbetaCD (14.28%), without or with HPMC (0.2-1.0%), provided firm and transparent hydrogels after cross-linking with EGDE (14.28%), in which around two thirds of the OH groups were cross-linked. The incorporation of HPMC progressively reduced the gel time and the swelling degree of hydrogels. HPbetaCD hydrogels efficiently loaded diclofenac and sustained the release for several hours. The presence of HPMC slowed the release from swollen hydrogels, but promoted it from hydrogels dried before the loading and also before the release.

CONCLUSIONS

HPbetaCD hydrogels with good mechanical properties and tunable loading and release ability can be obtained by direct cross-linking with EGDE.

Acrylic/cyclodextrin hydrogels with enhanced drug loading and sustained release capability

The influence of the proportion of acrylamidomethyl-gamma-cyclodextrin (gamma-CD-NMA) on loading and release of the hydrophobic triamcinolone acetonide (TA) and the hydrophilic propranolol (PR) by acrylic acid hydrogels was evaluated. gamma-CD-NMA was synthesized by condensation of gamma-cyclodextrin (gamma-CD) with N-(hydroxymethyl) acrylamide. Hydrogels were prepared with gamma-CD-NMA and sodium acrylate (3 M or 4 M), using N,N'-methylen(bisacrylamide) (BIS) as cross-linker, by free radical polymerization into glass moulds of 2 mm wide and were cut as discs (10 mm diameter). gamma-CD-NMA did not modify the pH-dependent swelling of the hydrogels, but significantly increased the swelling degree in the 40:60 ethanol:water, medium in which TA can be dissolved. Hydrogels prepared with gamma-CD-NMA above 5% (w/w of total monomers) showed a remarkably higher capacity to load TA, e.g., 33 mg/g dry hydrogel versus 0.6 mg/g dry hydrogel without gamma-CD-NMA. This is explained by the formation of 1:1 inclusion complexes of TA with gamma-CD mers that overcomes the lack of interactions with the acrylic groups of the network. The release of TA in water, 0.1 N HCl, or pH 6.8 phosphate buffer was sustained for at least 24 h, whatever the pH and the composition of the medium used. In contrast, loading of PR from the water solutions was greater for hydrogels prepared with 3 M acrylate than with 4 M acrylate, irrespective to their content in gamma-CD-NMA, and in less than 2 h ca. 80% PR was released. The lower affinity of PR for the gamma-CD cavities, compared to the strong intensity of the electrostatic interactions with the acrylic acid groups, explains why the incorporation of gamma-CD-NMA did not increased the loading and control release capacity of the hydrogels of this hydrophilic drug. In summary, the copolymerisation of CD with acrylic monomers can provide highly hydrophilic pH-sensitive networks which load large amounts of hydrophobic drugs and release them in a sustained way.

Shear bond strength of experimental methacrylated beta-cyclodextrin-based formulations

Previous studies have shown that methacrylated beta-cyclodextrins (MCDs) can be used as comonomers in resin-based dental composites. These MCDs by virtue of having several polymerizable methacrylate groups and hydrophilic hydroxyl groups, may also promote bonding of dental composites to dentin. This study evaluated MCDs as adhesive comonomers, and optimized comonomer and polymerization initiator concentrations for maximum shear bond strength (SBS). Experimental MCD-based bonding formulations in acetone were prepared by mixing 33 mass fraction % MCDs with (10, 20, 30, 40, or 50) mass fraction % of 2-hydroxyethyl methacrylate (HEMA). The MCD/HEMA-based solutions were activated with varied amounts of camphorquinone (CQ) and ethyl 4-dimethylamino benzoate (4E). Samples for SBS were prepared by bonding a composite resin to acid-etched dentin surfaces of extracted human molars with the experimental bonding solutions. The specimens were immersed in 37 degrees C water for 24 h and bond strengths were determined in shear mode. With increasing HEMA concentration, the SBS values of MCD-bonding solutions increased to 16 MPa at a composition of 33% MCD, 30% HEMA, and 37% acetone by mass. Also, SBS values of MCD-bonding solutions varied as a function of the CQ and 4E concentrations and passed through a maximum SBS at 21 MPa, which was comparable to that of a commercial control. This preliminary study indicated that nonacidic MCD monomers could be used as an adhesion-promoting comonomer. Additional modification of MCDs having both polymerizable groups and anionic ligand groups, e.g., polymerizable acidic cyclodextrin derivatives should increase the SBS even further.