Gaio Paradossi

Poly(vinyl alcohol) as versatile biomaterial for potential biomedical applications

In this paper, we present some new case examples where the chemical versatility of poly (vinyl alcohol) (PVA) can be used for potential biomedical applications. PVA, the polymeric material used for designing new nanostructured devices, is water soluble, biocompatible and has excellent physical properties. We point out the possibility of obtaining wall-to-wall chemical hydrogels as well as microgels without diminishing the biocompatibility available in the starting PVA material. Injectability is another important factor to take into account in controlled drug delivery for gene therapy. In this respect, in this paper, established and more innovative methods are prospected in order to obtain particles with dimensions suitable for these applications.

Novel PVA-based hydrogel microparticles for doxorubicin delivery.

Micro- and nanoparticles are considered suitable drug delivery systems for their unique features, such as a large surface to volume ratio, and for the possibility to tune their size and hydrophobicity. A polymer/polymer/water emulsion method was used for producing a chemically cross-linked hydrogel made of poly(vinyl alcohol) and of poly(methacrylate) moieties. Mesoscopic investigation of the microparticles was accomplished by laser scanning confocal microscopy. Dynamics of confined water within the gel meshes was studied by quasi-elastic incoherent neutron scattering. Succinoylation of these particles allowed an efficient loading with a maximum doxorubicin payload of about 50% (w/w) of dry microparticles. To evaluate the potentials of such a microdevice for drug delivery, LoVo colon cancer cells have been exposed to doxorubicin loaded microparticles to study the in vitro efficiency of the payload release and the consequent cytotoxic effect.

Temperature-sensitive poly(vinyl alcohol)/poly(methacrylate-co-N-isopropyl acrylamide) microgels for doxorubicin delivery

Microgels based on poly(vinyl alcohol), PVA, grafted with methacrylate side chains, MA, incorporating N-isopropylacrylamide, NiPAAm, monomer, were prepared by water-in-water emulsion polymerization method. These systems exhibit a spherical shape and a volume-phase transition, that is, shrinking, below physiological temperature. The behavior of these microgels were studied with respect to their average size and size distribution, swelling, and release properties. It was observed that the stirring speed is a key parameter for controlling the amount of incorporated NiPAAm, the particle size and the sharpness of the volume-phase transition. The volume-phase transition temperature, VPPT, of the microgels was evaluated around 38 and 34 degrees C for microgels with a NiPAAm/methacrylate molar ratio of 0.8 and 2.4, respectively. Water uptake increased with the amount of NiPAAm monomer present in the polymer network. In vitro biocompatibility of microgels was assessed with respect to NIH3T3 mouse fibroblasts. O-Succinoylated microgels were loaded with doxorubicin by exploiting the favorable electrostatic interaction between negatively charged microgel surface and positively charged doxorubicin. The drug release was influenced by the microgels surface/volume ratio. At physiological temperatures, above the VPTT exhibited by these systems, the release was enhanced by the specific area increase. This study provides the background for the design of an injectable device suitable for the controlled delivery of doxorubicin based on the volume-phase transition of microgels.

Magnetite Nanoparticles Can Be Coupled to Microbubbles to Support Multimodal Imaging

Microbubbles (MBs) are commonly used as injectable ultrasound contrast agent (UCA) in modern ultrasonography. Polymer-shelled UCAs present additional potentialities with respect to marketed lipid-shelled UCAs. They are more robust; that is, they have longer shelf and circulation life, and surface modifications are quite easily accomplished to obtain enhanced targeting and local drug delivery. The next generation of UCAs will be required to support not only ultrasound-based imaging methods but also other complementary diagnostic approaches such as magnetic resonance imaging or computer tomography. This work addresses the features of MBs that could function as contrast agents for both ultrasound and magnetic resonance imaging. The results indicate that the introduction of iron oxide nanoparticles (SPIONs) in the poly(vinyl alcohol) shell or on the external surface of the MBs does not greatly decrease the echogenicity of the host MBs compared with the unmodified one. The presence of SPIONs provides enough magnetic susceptibility to the MBs to accomplish good detectability both in vitro and in vivo. The distribution of SPIONs on the shell and their aggregation state seem to be key factors for the optimization of the transverse relaxation rate.

Polymer Shelled Microparticles for a Targeted Doxorubicin Delivery in Cancer Therapy

Targeting is a main feature supporting any controlled drug delivery modality. Recently we developed poly(vinyl alcohol), PVA, based microbubbles as a potential new ultrasound contrast agent featuring an efficient ultrasound backscattering and a good shelf stability. The chemical versatility of the polymeric surface of this device offers a vast variety of coupling modalities useful for coating and specific targeting. We have designed a conjugation strategy on PVA shelled microbubbles to enable the localization and the drug delivery on tumor cells by modifying the surface of this polymeric ultrasound contrast agent (UCA) with oxidized hyaluronic acid (HAox). After the conversion of the microbubbles into microcapsules, the kinetics of the release of doxorubicin, a well-known antitumor drug, from uncoated and HAox-coated PVA microbubbles and microcapsules was investigated. Cytocompatibility and bioadhesive properties of the HA-modified microparticles were then tested on the HT-29 tumor cell line. Cytotoxicity to HT-29 tumor cells of microcapsules after loading with doxorubicin was studied, evidencing the efficacy of the HAox coating for the delivery of the drug to cells. These features are a prerequisite for a theranostic, that is, diagnostic and therapeutic, use of polymer-based UCAs.

Characterization of acoustic properties of PVA-shelled ultrasound contrast agents : linear properties (Part I)

This work examines the linear acoustic behavior of ultrasound contrast agents made of three types of poly (vinyl alcohol) (PVA) shelled microbubbles manufactured at different pH and temperature conditions. Backscattered power, attenuation coefficient and phase velocity of ultrasonic waves propagating through suspensions of PVA contrast agents were measured at temperature values ranging between 24 degrees C and 37 degrees C in a frequency range from 3 MHz to 13 MHz. Enhancement of the backscattered power higher than 20 dB and displaying a weak dependence on temperature was observed. Attenuation and phase velocity, on the other hand, showed higher sensitivity to temperature variations. A modified version of the Church model, which accounts for the dispersion of the dynamic modulus of the PVA shells, was developed to simultaneously fit the attenuation and phase velocity data at 24 degrees C. The frequency dependence of the storage modulus was found to be that of semiflexible polymeric networks. On the other hand, the frequency dependence of the dynamic loss modulus suggests that additional mechanisms, which may be related to the finite dimensions of the shell and/or to its inhomogeneity, may play a significant role in the dissipation of the acoustic energy. For the microbubbles of interest, this model predicts frequency dependent resonance frequency higher than 100 MHz.

New hydrogels based on carbohydrate and on carbohydrate-synthetic polymer networks

Abstract Novel synthetic routes recently explored in our laboratories in order to obtain crosslinked polymeric samples, comprising either chitosan or gellan as polysaccharidic components, are outlined. The former networks, in which different crosslinking partners have been used (i.e. oxidized cyclodextrin and telechelic poly(vinylalcohol)), can bear fixed positive charges while the latter are anionic. Zwitterionic networks formed by the template polymerization of acrylic acid onto chitosan with concomitant crosslinking (bisacrylamide) have also been prepared. Procedures adopted are simple and, once optimized, may lead to biocompatible hydrogels, with easily tunable physical properties, of potential interest in the biomedical area.

Targeted doxorubicin delivery by chitosan-galactosylated modified polymer microbubbles to hepatocarcinoma cells

Targeted drug delivery is a main issue in cancer treatment. Taking advantage of recently developed polyvinyl alcohol (PVA)-based microbubbles, which are characterized by chemical versatility of the polymeric surface thereby allowing coating with different ligands, we set up a strategy for the targeted delivery of the anticancer agent doxorubicin to hepatocarcinoma cells. Such microbubbles are exceptionally efficient ultrasound scatterers and thus represent also an option as potential ultrasound contrast agents. Moreover, the oscillation of microbubbles induced by ultrasound could contribute to favor the release of drugs allocated on shell. Specifically, PVA-based microbubbles were reacted with a galactosylated chitosan complex and loaded with doxorubicin to enable the localization and drug delivery to HepG2 hepatocarcinoma cells overexpressing asialoglycoprotein receptors. We demonstrated selectivity and greater bioadhesive properties of the functionalized microbubbles for tumor cells than to normal fibroblasts, which were influenced by the degree of galactosylation. The presence of galactosylated chitosan did not modify the rate of doxorubicin release from microbubbles, whichwas almost complete within 48h. Cellular uptake of doxorubicin loaded on functionalized microbubbles was higher in HepG2 than in normal fibroblasts, which do not over express the asialoglycoprotein receptors. In addition, doxorubicin loaded onto functionalized microbubbles fully retained its cytotoxic activity. Cells were also irradiated with ultrasound, immediately after exposure to microbubbles. An early enhancement of doxorubicin release and cellular drug uptake associated to a concomitant increase in cytotoxicity was observed in HepG2 cells. Overall, results of the study indicate that galactosylated chitosan microbubbles represent promising devices for the targeted delivery of antitumor agents to liver cancer cells.

Targeting tumor cells through chitosan-folate modified microcapsules loaded with camptothecin.

Poly(vinyl alcohol) microcapsules have been tailored as carriers to deliver camptothecin, an anticancer drug poorly soluble in water. The capsules have been reacted with a chitosan--folate complex in order to selectively target cancer cells overexpressing the folic acid receptor. Microcapsules decorated with the chitosan--folate complex have been characterized in their uptake and release of camptothecin, following the absorption band at λ = 370 nm diagnostic of the drug molecule. The selectivity of chitosan-folate microcapsules in targeting cancer cells has been demonstrated by fluorescence microscopy using HeLa cells, overexpressing the folate receptor and NIH3t3 fibroblasts as a negative control. The chitosan--folate microcapsules loaded with camptothecin significantly reduce the proliferation of HeLa tumor cells, while they have a negligible effect on fibroblasts. This work demonstrates that the chitosan--folate microcapsules represent a promising system to selectively target hydrophobic drugs, such as camptothecin, to tumor cells.

Copper complexes immobilized to chitosan.

Polymeric ligands, such as 2-substituted pentanedioic acid (2), 2-substituted propanoic acid (3), and deoxylactit-1-yl (4) derivatives of chitosan (1), were used to prepare copper complexes that are widely soluble in aqueous solution. EPR results (100 K) show that all association complexes basically have a tetragonal symmetry. Visible CD spectra suggest, however, that the order of increasing departure from this geometry is Cu-(1) approximately Cu-(3) less than Cu-(2) less than or equal to Cu-(4), the lack of sterically constraining side-chains in (1) and (3) allowing a more symmetric arrangement of ligands around the central metal ion. Results on the catalytic activity of the association complexes for air oxidation of catechol derivatives are also presented.