Coatings of Cyclodextrin/Citric-Acid Biopolymer as Drug Delivery Systems: A Review

In the early 2000s, a method for cross-linking cyclodextrins (CDs) with citric acid (CTR) was developed. This method was nontoxic, environmentally friendly, and inexpensive compared to the others previously proposed in the literature. Since then, the CD/CTR biopolymers have been widely used as a coating on implants and other materials for biomedical applications. The present review aims to cover the chemical properties of CDs, the synthesis routes of CD/CTR, and their applications as drug-delivery systems when coated on different substrates. Likewise, the molecules released and other pharmaceutical aspects involved are addressed. Moreover, the different methods of pretreatment applied on the substrates before the in situ polymerization of CD/CTR are also reviewed as a key element in the final functionality. This process is not trivial because it depends on the surface chemistry, geometry, and physical properties of the material to be coated. The biocompatibility of the polymer was also highlighted. Finally, the mechanisms of release generated in the CD/CTR coatings were analyzed, including the mathematical model of Korsmeyer-Peppas, which has been dominantly used to explain the release kinetics of drug-delivery systems based on these biopolymers. The flexibility of CD/CTR to host a wide variety of drugs, of the in situ polymerization to integrate with diverse implantable materials, and the controllable release kinetics provide a set of advantages, thereby ensuring a wide range of future uses.

Nonthermal Plasma Treatment Improves Uniformity and Adherence of Cyclodextrin-Based Coatings on Hydrophobic Polymer Substrates

Low surface energy substrates, which include many plastics and polymers, present challenges toward achieving uniform, adherent coatings, thus limiting intended coating function. These inert materials are common in various applications due to favorable bulk, despite suboptimal surface, properties. The ability to functionally coat low surface energy substrates holds broad value for uses across medicine and industry. Cyclodextrin-based materials represent an emerging, widely useful class of coatings, which have previously been explored for numerous purposes involving sustained release, enhanced sorption, and reversible reuse thereof. In this study, substrate exposure to nonthermal plasma was explored as a novel means to improve uniformity and adherence of cyclodextrin-based polyurethane coatings upon unreceptive polypropylene substrates. Plasma effects on substrates were investigated using contact angle goniometry and X-ray photoelectron spectroscopy (XPS). Plasma impact on coating uniformity was assessed through visualization directly and microscopically. Plasma effects on coating adhesion and bonding were studied with mechanical lap-shear testing and XPS, respectively. Substrate surface wettability and oxygen content increased with plasma exposure, and these modifications were associated with improved coating uniformity, adhesion, and interfacial covalent bonding. Findings demonstrate utility of, and elucidate mechanisms behind, plasma-based surface activation for improving coating uniformity, adherence, and performance on inert polymeric substrates.

Magnetic β-Cyclodextrin Nanosponges for Potential Application in the Removal of the Neonicotinoid Dinotefuran from Wastewater

This article describes the use of β-cyclodextrin-based carbonate nanosponges (NSs) decorated with superparamagnetic Fe₃O₄ nanoparticles to study and investigate the potential removal of dinotefuran (DTF) from wastewater. The NS-DTF inclusion compound was characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), UV-visible spectroscopy (UV-VIS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray powder diffraction (XRPD) and proton nuclear magnetic resonance (¹H-NMR). The adsorption efficiency of NSs was evaluated as function of different contact times. The results confirmed that the NSs have a favourable sorption capacity for the chosen guest, as the polymers exhibited a maximum adsorption of 4.53 × 10⁻³ mmol/g for DTF. We also found that magnetic NSs show good reusability as they maintain their efficiency after eight adsorption and desorption cycles. Our studies and characterization by means of SEM, TEM, EDS, vibrating sample magnetometer (VSM) and UV-VIS also show that NSs with magnetic properties are excellent tools for insecticide removal from aqueous environments.

Removal of Aromatic Chlorinated Pesticides from Aqueous Solution Using β-Cyclodextrin Polymers Decorated with Fe₃O₄ Nanoparticles

This article describes the sorption properties of cyclodextrin polymers (nanosponges; NS) with the pesticides 4-chlorophenoxyacetic acid (4-CPA) and 2,3,4,6-tetrachlorophenol (TCF), including an evaluation of its efficiency and a comparison with other materials, such as granulated activated carbon (GAC). NS-pesticide complexes were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray powder diffraction (XRPD), proton nuclear magnetic resonance (¹H-NMR), UV–VIS, and thermogravimetric analysis (TGA). This confirms the interactions of the guests with nanosponges and shows that the polymers have favorable sorption capacities for chlorinated aromatic guests. Our studies also show that the inclusion complex is predominantly favored for NS/CPA rather than those formed between TCF and NS due to the size of the adsorbate and steric effects. Sorption studies carried with repeated cycles demonstrate that NS polymers could be an improved technology for pollutant removal from aquatic environments, as they are very efficient and reusable materials. Our experiments and characterization by SEM, EDS, UV–VIS, and magnetization saturation (VSM) also show that NS is an optimal substrate for the deposition of magnetite nanoparticles, thus improving the usefulness and properties of the polymer, as the nanosponges could be retrieved from aqueous solution with a neodymium magnet without losing its efficiency as a pesticide sorbent.

Removal of volatile organic compounds using amphiphilic cyclodextrin-coated polypropylene

Polypropylene nonwovens were functionalised using a self-assembled, amphiphilic cyclodextrin coating and the potential for water purification by removal of pollutants was studied. As benzene is one of the problematic compounds in the Water Framework Directive, six volatile organic compounds (benzene and five benzene-based substances) were chosen as model compounds. The compounds were tested as a mixture in order to provide a more realistic situation since the wastewater will be a complex mixture containing multiple pollutants. The volatile organic compounds are known to form stable inclusion complexes with cyclodextrins. Six different amphiphilic cyclodextrin derivatives were synthesised in order to elucidate whether or not the uptake abilities of the coating depend on the structure of the derivative. Headspace gas chromatography was used for quantification of the uptake exploiting the volatile nature of benzene and its derivatives. The capacity was shown to increase beyond the expected stoichiometries of guest-host complexes with ratios of up to 16:1.

Surface modification of electrospun polyester nanofibers with cyclodextrin polymer for the removal of phenanthrene from aqueous solution

Surface modified electrospun polyester (PET) nanofibers with cyclodextrin polymer (CDP) were produced (PET/CDP). CDP formation onto electrospun PET nanofibers was achieved by polymerization between citric acid (CTR, crosslinking agent) and cyclodextrin (CD). Three different types of native CD (α-CD, β-CD and γ-CD) were used to form CDP. Water-insoluble crosslinked CDP coating was permanently adhered onto the PET nanofibers. SEM imaging indicated that the nanofibrous structure of PET mats was preserved after CDP surface modification process. PET/CDP nanofibers have shown rougher/irregular surface and larger fiber diameter when compared to untreated PET nanofibers. The surface analyses of PET/CDP nanofibers by XPS elucidated that CDP was present on the fiber surface. DMA analyses revealed the enhanced mechanical properties for PET/CDP where PET/CDP nanofibers have shown higher storage modulus and higher glass transition temperature compared to untreated PET nanofibers. The surface area of the PET/CDP nanofibers investigated by BET measurements showed slight decrease due to the presence of CDP coating compared to pristine PET nanofibers. Yet, it was observed that PET/CDP nanofibers were more efficient for the removal of phenanthrene as a model polycyclic aromatic hydrocarbon (PAH) from aqueous solution when compared to pristine PET nanofibers. Our findings suggested that PET/CDP nanofibers can be a very good candidate as a filter material for water purification and waste treatment owing to their very large surface area as well as inclusion complexation capability of surface associated CDP.

Sorption of Aromatic Compounds with Copolymer Sorbent Materials Containing β-Cyclodextrin

Urethane copolymer sorbent materials that incorporate β-cyclodextrin (CD) have been prepared and their sorption properties with chlorinated aromatic compounds (i.e., pentachlorophenol, 2,4-dichlorophenol and 2,4-dichlorophenoxy acetic acid) have been evaluated. The sorption properties of granular activated carbon (GAC) were similarly compared in aqueous solution at variable pH conditions. The sorbents displayed variable BET surface areas as follows: MDI-X copolymers (< 10¹ m²/g), CDI-X copolymers (< 10¹ m²/g), and granular activated carbon (GAC ~10³ m²/g). The sorption capacities for the copolymers sorbents are listed in descending order, as follows: GAC > CDI-3 copolymer ≈ MDI-3 copolymer. The sorption capacity for the aromatic adsorbates with each sorbent are listed in descending order, as follows: 2,4-dichlorophenol > 2,4-dichlorophenoxy acetic acid > pentachlorophenol. In general, the differences in the sorption properties of the copolymer sorbents with the chlorinated organics were related to the following factors: (i) surface area of the sorbent; (ii) CD content and accessibility; and (iii) and the chemical nature of the sorbent material.

Comparative study of polymer containing beta-cyclodextrin and -COOH for adsorption toward aniline, 1-naphthylamine and methylene blue

Three different polymers P1, P2 and P3 (P1 containing both beta-CD and -COOH, P2 containing beta-CD and P3 containing -COOH) were synthesized and applied to adsorption toward aniline, 1-naphthylamine and methylene blue. The concentrations (C) before and after adsorption were determined and the adsorption capacities (q) of P1, P2 and P3 were calculated. The maximum adsorption capacities (q(max)) toward aniline: q(max) (P1)=104 micromol g(-1), q(max) (P2)=14.9 micromol g(-1) and q(max) (P3)=53.1 micromol g(-1); toward 1-naphthylamine: q(max) (P1)=184 micromol g(-1), q(max) (P2)=53.8 micromol g(-1) and q(max) (P3)=125 micromol g(-1); toward methylene blue: q(max) (P1)=200 micromol g(-1), q(max) (P2)=12.7 micromol g(-1) and q(max) (P3)=215 micromol g(-1). P1 exhibited remarkable adsorption toward all the three adsorbates. P2 was almost equal to P1 in adsorption toward methylene blue, but was less efficient than P1 in adsorption toward aniline and 1-naphthylamine. P3 also exhibited considerable adsorption toward aniline and 1-naphthylamine, but was inefficient toward methylene blue. P1 was obtained from nontoxic materials and through environment friendly procedures, so it was potentially an efficient and green adsorbent for water purification.

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.

Vascular prostheses with controlled release of antibiotics

Vascular prostheses were functionalised with the aim to obtain a slow release of antibiotics in order to reduce postoperative infections. The original process that we present in this paper is based on the use of a family of cage molecules named cyclodextrins (CD). These compounds have the ability to form reversible inclusion complexes with drugs such as antibiotics. The aim of this work was to graft CD onto the prosthesis, so that an antibiotic can be bound on it by this inclusion phenomenon, and then be progressively released over a prolonged period by a complex dissociation mechanism. This paper presents the first part of this research program and concerns mainly the study of the functionalization parameters. It presents surface characterization results of the modified prostheses. The PET prostheses were immersed into a solution containing a cross linking agent, cyclodextrins (beta-CD, gamma-CD, HP-beta-CD and HP-gamma-CD) and a catalyst and were padded. Grafting occurred by the mean of a thermofixation step at a temperature comprised between 140 and 180 degrees C. It was observed that the support was permanently modified when the CD polymer that coated the fibres resisted to the final washing process. Grafting rates of 12 wt% in CD polymer could be reached. It was also observed that the fibre coating reaction induced an increase of the permeability of the grafts.