Polyglobalide-Based Porous Networks Containing Poly(ethylene glycol) Structures Prepared by Photoinitiated Thiol-Ene Coupling.

The high interest in polymers from natural resources prompted us to investigate the use of enzymatically synthesized polyglobalide (PGL) in the preparation of polymer networks with potential applications as biomaterials for drug delivery devices. Polymer networks were obtained under mild conditions by photoinitiated thiol-ene coupling between PGL and a poly(ethylene glycol- co-thiomalate) (PEG-SH) copolymer obtained by polycondensation. The obtained polymer networks were thoroughly characterized by Raman spectroscopy, scanning electron microscopy, titration of thiol groups and elemental analysis. Our study took into consideration the synthesis parameters for the polymer networks, such as the total polymer concentration and the SH/C=C functionality molar ratio. Swelling in both THF and water was assessed, and the potential of the materials for drug delivery was determined. The scanning electron microscopy images showed that the prepared polymer networks may have different morphologies ranging from homogeneous polymer materials to macroporous structures. Additionally, the prepared materials were found to be suitable from a cytotoxicity point of view, enabling their application as biomaterials for drug delivery devices.

Scaffolds Based on Collagen, Hyaluronan and Sericin with Potential Applications as Controlled Drug Delivery System.

Natural proteins have been extensively studied as matrices for tissue engineering, due to their excellent biocompatibility and biological properties associated with increasing cell proliferation. By generating complex materials, cell and tissue functions can be tailored to obtain a specific direction, according to the medical needs. The aim of this paper was to obtain scaffolds based on collagen, hyaluronan and sericin, with morphology and physical-chemical properties adequate for controlled drug delivery systems. In this aim various tests were performed: in vitro swelling and degradation studies, Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electronic Microscopy (SEM) and thermogravimetric analysis. Loading and releasing of ibuprofen is also discussed. The results indicate that scaffolds based on collagen, hyaluronan and sericin have a porous structure, strength and stability adequate for skin tissue engineering. The obtained scaffolds swell, degrade and have controlled drug release properties in simulated biological fluids.

Microparticulated systems based on chitosan and poly(vinyl alcohol) with potential ophthalmic applications.

Spherical microparticles for encapsulation of drugs for the treatment of diseases, with a diameter ranging between 2 and 4 µm, were obtained by double crosslinking (ionic and covalent) of chitosan and poly(vinyl alcohol) blend in a water-in-oil emulsion. Microparticles characterisation was carried out in terms of structural, morphological and swelling properties in aqueous media. The presence of chitosan in particles composition confers them a pH-sensitive character. Toxicity and hemocompatibility tests prove the biocompatible character of microparticles. The pilocarpine loading capacity is high as well as the release efficiency which increases up to 72 and 82% after 6 h. The obtained results recommend the microparticles as sustained release drug carriers for the treatment of eye diseases.

Histological findings for the absorption of small and large liposomes - the basis of future drug delivery and contrast media systems.

BACKGROUND AND OBJECTIVES: The purpose of our study was to obtain and characterize carrier systems in different sizes that can affect oral absorption, since the mechanisms of liposome absorption are not yet fully understood. From stomach to the small intestine, liposomes can be gradually destroyed. Understanding the factors that affect oral absorption leads to developing safe and effective nanosystems to improve the oral delivery of therapeutics. MATERIALS AND METHODS: We determined the efficiency of the absorption of small and large liposomes at the level of gingival mucosa, heart, liver, testicles, kidneys, and lungs, using frozen-section fluorescence microscopy, on rat tissues after liposomes administration. A number of 36 male rats were divided in four groups: control groups, A and C, consisted of six rats each and did not receive liposomes; two other groups, B and D, were the experimental ones, and consisted of 12 male rats each. The animals received small liposomes (75-76 nm) and large liposomes (80-87 nm), respectively, administered either by endogastric tube or intraperitoneal injection. After 24 hours, the animals were sacrificed, and we harvested the organs. We performed frozen sections and analyzed them with fluorescence microscopy. RESULTS: The frozen sections obtained from all organs revealed a higher absorption level of small liposomes in the testicles, liver, and gum, while the large liposomes had a greater affinity for the liver, with variations dependent on the route of administration. CONCLUSIONS: Frozen-section fluorescence microscopy is a reliable technique for visualization of liposome absorption. Based on the size of these nanosystems, we revealed significant absorption for small liposomes in testicles, liver, heart, and gum, and for large liposomes mainly in the liver, compared with the control groups. The study advocates for the usage of liposomes for medical purposes, based on their absorption proprieties.

Chitosan grafted-poly(ethylene glycol) methacrylate nanoparticles as carrier for controlled release of bevacizumab.

The aim of the present study is to obtain, for the first time, polymeric nanocarriers based on the chitosan grafted-poly(ethylene glycol) methacrylate derivative. The strategy involves the use of chitosan grafted-poly(ethylene glycol) methacrylate with high solubility in water, obtained via Michael addition, in order to prepare potentially non-toxic micro/nanoparticles (MNPs). By modifying chitosan, its solubility in aqueous media was improved. Micro/nanoparticles-based chitosan grafted-poly(ethylene glycol) methacrylate were obtained under mild condition, with good and controlled swelling properties in acetate buffer solution (ABS) and phosphate buffer solution (PBS). The technique selected for the preparation of the MNPs was a double crosslinking (ionic and covalent) process in reverse emulsion which provide the mechanical stability of the polymeric nanocarrier. The chitosan derivative and MNPs were thoroughly characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM). The Scanning Electron Microscopy photographs revealed that prepared MNPs have different diameters depending on the used stirring rate and polymer concentration. Nanoparticles potential as drug delivery system was analyzed by loading bevacizumab (BEV) a full-length monoclonal antibody. Also, the prepared particles were found suitable from the cytotoxicity and hemocompatibility point of view enabling their potential use as delivery system for the treatment of posterior segment of the eye conditions.

Release of liposome-encapsulated calcein from liposome entrapping gelatin-carboxymethylcellulose films: a presentation of different possibilities.

Liposome entrapment in films consisting of gelatin (GEL) or GEL/sodium carboxymethylcellulose (NaCMC) mixtures, as a method to alter drug release kinetics from polymeric films and/or incorporate sensitive bioactive molecules in solid films, was investigated. Bulk or thin complex (liposome trapping) films were formed by crosslinking (with glutaraldehyde) solutions of GEL or GEL/NaCMC in presence of calcein-encapsulating or rhodamine-labeled liposomes (Rho-Lip). Rho-Lip were observed by confocal microscopy to be homogenously distributed in the films. Calcein release from films was evaluated for periods up to 25 d, and it was found that several possibilities, concerning the release of the liposome-encapsulated molecule from the films, are offered; (i) Release can be sustained, if large liposomes are entrapped in the films. In this case the liposome-encapsulated molecules are released from the films only after they have been released from the vesicles, and the release can be controlled by modifying the film composition, the network density and/or the film geometry. (ii) Intact small unilamellar liposomes (SUV) can be released from the polymeric films depending on their swelling degree. The later can be controlled by modulating the film composition and amount of crosslinker. Film composition also affects the integrity of the film-entrapped liposomes during the crosslinking process, possibly due its effect on the density of the polymeric network of the film.

Rheological study of in-situ crosslinkable hydrogels based on hyaluronanic acid, collagen and sericin.

The elaboration of chemically crosslinked hydrogels based on collagen (C), hyaluronanic acid (HA) and sericin (S) with different polymer ratios was investigated by in-situ rheology. This reaction was performed via amide or ester bond reaction activated by carbodiimide, in pure water. Prior to molecule crosslinking, the rheological behaviour of the biopolymers (alone or in mixture) was characterized in a semi-dilute concentration regime. Both flow and dynamic measurements showed that uncrosslinked collagen alone appears to be rather elastic with yield stress properties, whereas uncrosslinked HA alone appears to be rather shear thinning and viscoelastic in agreement with entangled polymer behaviour. Sericin exhibited Newtonian low viscosity behaviour according to its very low molar mass. Before crosslinking, HA exhibited viscoelastic behaviour at concentrations above the critical entangled concentration (C*) in the mixtures, thus HA shows promise as a matrix for future crosslinked networks, whereas sericin did not significantly modify the rheology. During the reaction, followed by rheology, the kinetics were slower for pure HA systems compared with the mixtures (i.e., with added collagen and/or to a lesser extent sericin). At the same time, the final network of hydrogels (i.e., the elastic modulus) was more structured in the mixture based systems. This result is explained by ester bonds (the only possibility for pure HA systems), which are less favourable and reactive than amide bonds (possible with sericin and collagen). The presence of collagen in the HA matrix reinforced the hydrogel network. SEM studies confirmed the structure of the hydrogels, and in vitro degradability was globally consistent with the effect of the selected enzyme according to the hydrogel composition. All the elaborated hydrogels were non-cytotoxic in vitro.

INTRAOCULAR BIODISTRIBUTION OF INTRAVITREAL INJECTED FLUORESCENT DEXAMETHASONE-CHITOSAN NANOPARTICLES IN RABBIT EYES.

AIM: To evaluate intraocular biodistribution of fluorescent nanoparticles composed of dexamethasone bound to chitosan after intravitreal administration in rabbit eyes. MATERIAL AND METHODS: The chitosan and gelatin based nanoparticles were synthetized using a reverse emulsion-double crosslinking technique (ionic and covalent) and then dexamethasone was bound. Two units of 1% suspension of these nanoparticles in saline solution were injected intravitreally into rabbit eyes. The histologic sections obtained at 72 hours were analyzed by confocal microscopy. RESULTS: The chitosan-fluorescein conjugate bound to dexamethasone was present in all ocular tissues at 72 hours. The nanoparticles were present in the retina and lens in a larger amount than in the other ocular tissues. CONCLUSIONS: The reverse emulsion-double crosslinking technique was efficient in synthesizing a biocompatible polymeric nanosystem. The in vivo study of intraocular biodistribution of fluorescein-marked nanoparticles capable of binding dexamethasone revealed their affinity for the retina and lens after intravitreal administration.

Nanotechnology approaches for pain therapy through transdermal drug delivery.

The paper focuses on the advances in the field of pain treatment by transdermal delivery of specific drugs. Starting from a short description of the skin barrier, the pharmacodynamics and pharmacokinetics including absorption, distribution, action mechanism, metabolism and toxicity, aspects related to the use of pain therapy drugs are further discussed. Most recent results on topical anesthetic agents as well as the methods proved to overcome the skin barrier and to provide efficient delivery of the drug are also discussed. The present review is proposing to summarize the recent literature on the pharmacotherapeutic principles of local anesthetics and non-steroidal anti-inflammatory drugs, generally used to alleviate pain but also the drugs as nanoformulations with potential applications in transdermal delivery. A special attention is given to efficient formulations meant for transdermal penetration enhancement of anesthetics where the drug is encapsulated into macrocyclic molecules (cyclodextrins, cyclodextrin derivatives), liposomes or polymer nanoparticles and hydrogels.

Intraocular biodistribution of intravitreal injected chitosan/gelatin nanoparticles.

The aim of this study was to evaluate intraocular biodistribution of a fluorescent polymeric nanosystem composed of chitosan and gelatin after intravitreal administration in rat eyes. The nanoparticles based on chitosan and gelatin were synthesized using a reverse emulsion-double cross-linking technique (ionic and covalent) and their structural characteristics are presented. Two units of 1% suspension of fluorescein-labeled nanoparticles in saline solution were injected intravitreal in rat eyes. The histological cross-sections obtained at 24 and 72 hours were analyzed by confocal microscopy and compared to a similar number of control cross-sections. The scanning electron microscopy of the nanoparticles obtained by double cross-linking in reverse emulsion technique revealed spherical, smooth, highly porous particles with no tendency to form aggregates. The chitosan-fluorescein conjugate was present in all the ocular tissues both at 24 and at 72 hours. The nanoparticles were present in the retina in a larger quantity and persisted longer than in the other ocular tissues. They were mainly fixed paravascular. The double cross-linking in reverse emulsion technique was efficient in synthesizing a biocompatible polymeric nanosystem. The in vivo study of intraocular biodistribution of fluorescein-labeled nanoparticles revealed their affinity for the retina after intravitreal administration.

Modulated release from liposomes entrapped in chitosan/gelatin hydrogels.

The paper describes the preparation of chitosan/gelatin hydrogels, obtained by double crosslinking with glutaraldehyde and sodium sulphate/sodium tripolyphosphate that may be used as matrices for the inclusion of drug loaded liposomes composed of phosphatidylcholine. The main objective was to create a protective layer to stabilize the liposomal surface and to prolong/control the release of drugs from such systems. Therefore, complex systems capable of prolonged drug release and controlled release kinetics were obtained. Samples consisting of different chitosan/gelatin ratios and type/amount of ionic crosslinker have been prepared and characterized. The present study shows that calcein (used as a model hydrophilic drug) release from polymeric hydrogels has been retarded from several days to weeks after calcein inclusion in small unilamellar vesicles (SUVs) and multilamellar vesicles (MLVs) entrapped subsequently in hydrogels with variable composition. The calcein release kinetics of complex systems were compared to simple systems (control hydrogels) and important changes were observed thus proving that the mechanism of the process increases in complexity. Also, it is demonstrated that liposomes' stability can be greatly improved by inclusion in polymeric matrices. Multilamellar liposomes showed a better release behaviour, which indicates that these calcein loaded vesicles remained intact to some extent after release from the matrix, due to their improved stability provided by the multiple layers. When small unilamellar liposomes were tested, calcein have been released from hydrogels predominantly in a free form (due to their unilamellarity related instability even inside the hydrogel) but in a sustained and controllable manner. The main applications of the systems obtained are in the area of drug release for tissue engineering/tissue repair (topical administration of drugs for wound therapy - burns, for example). Hydrogels capable of delivering drugs over prolonged periods of time represent a step forward in wound management and many diseases that request long term and sustained delivery of drugs. These hydrogels could be used as tissue replacement or injectable depot systems in many high risk diseases including cancer.

Double crosslinked interpenetrated network in nanoparticle form for drug targeting--preparation, characterization and biodistribution studies.

The development of polymer nanosystems able to target and control/sustain the drug delivery is still considered an important desideratum in pharmaceutical research. The present study reports the preparation of nanoparticles based on chitosan and gelatin, using a reverse emulsion-double crosslinking (ionic followed by covalent one) technique. The nanoparticles structural and morphological characteristics (diameter and size distribution), their swelling capacity in aqueous media of different pH (4 and 7.4) and their ability to include and release poorly water-soluble drugs were seen to be influenced by the composition of the polymer mixture and by the surfactants concentration. Also, nanoparticles biodistribution after intraperitoneal or intravenous administration was evaluated by polymer marking with fluorescein. Particles ability to penetrate different organs (liver, heart, lungs, and less brain, gums, testicles) was increased when injected intravenously.

Covalent and ionic co-cross-linking--an original way to prepare chitosan-gelatin hydrogels for biomedical applications.

The first goal of this work was to develop a method for obtaining interpenetrating gelatin (G)-chitosan (CS) networks prepared by double cross-linking (covalent followed by ionic) that exhibit hydrogel character. The second goal was to modulate their properties as a function of the preparation parameters by using neural network models. This study was therefore carried out by experiment and simulation. The covalent cross-linking resulted from the reaction between the carbonyl groups of glutaraldehyde with amino groups belonging to both polymers; the ionic cross-linking is based on the interaction between tripolyphosphate anions and protonated amine groups (ammonium ions) of the polymers. The total cross-linking density (indirectly assessed by estimating the water swelling capacity) and the ability to include hydrosoluble bioactive principles are influenced by the following process parameters: the CS/G ratio, the amount of ionic cross-linker, and the ionic cross-linking time. The prepared hydrogels were characterized with respect to their structural, morphological, and some physical properties. The hydrogels ability to load high amounts of water-soluble drugs indicates their potential use as carriers for biologically active principles in the human body. A neural network methodology was applied to model the swelling degree and caffeine loading/release capacity depending on reaction conditions; in addition, applying this method, the optimal preparation conditions have been determined, targeting pre-established values for swelling degree or maximum caffeine value. The accuracy of the results obtained through this technique proves that the neural networks are suitable tools for modeling cross-linking processes taking place complex nonlinear polymers.

[New tendencies in controlled drug release--liposomes entrapped in polymer matrices]. / Noi tendinte in eliberarea controlata de medicamente--lipozomi imobilizati în matrici polimere.

Liposomes entrapment in different forms of polymers represents in the last few years a method to modify the drug release kinetics in order to attend the specificity of this phenomenon. This will result generally in complex systems in which liposomes are dispersed in polymer matrices like gels, hydrogels and microparticles. As a consequence the drug release will be influenced by both polymer matrix and small carrier entrapped in. The researchers are trying to control the release of drug from such solid complex system by modulating not only the vesicle properties but also those of polymer support. This kind of system is necessary also for the cases when time stable liposomes are desired, being already well known that the major drawback of this type of carrier is the stability in time and in different physiologic conditions.