Mario Casolaro

An insulin-releasing system that is responsive to glucose

Abstract A membrane system consisting of poly(acrylic acid)-grafted porous cellulose film and glucose oxidase was synthesized for insulin delivery in response to glucose concentration. The principle of this system is based on the conformational change of the graft chains in response to pH. At neutral pH in the absence of glucose, the carboxylate groups of poly(acrylic acid) grafts were negatively charged. Repulsion between negative charges made the polymer chains extend and closed the pores of the membrane. Glucose oxidase catalyzed the oxidation of glucose to gluconic acid which, in turn, protonated the carboxylate groups on the graft membrane. A reduced electrostatic repulsion between the poly(acrylic acid) side chains made the graft chains coil-like and opened the pores of the membrane to insulin.

Biohydrogels with magnetic nanoparticles as crosslinker: characteristics and potential use for controlled antitumor drug-delivery.

Hybrid magnetic hydrogels are of interest for applications in biomedical science as controlled drug-delivery systems. We have developed a strategy to obtain novel hybrid hydrogels with magnetic nanoparticles (NPs) of CoFe(2)O(3) and Fe(3)O(4) as crosslinker agents of carboxymethylcellulose (CMC) or hyaluronic acid (HYAL) polymers and we have tested these systems for controlled doxorubicin release. The magnetic NPs are functionalized with (3-aminopropyl)trimethoxysilane (APTMS) in order to introduce amino groups on the surface. The amino coating is determined and quantified by standard Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy methods, and by cyclic voltammetry, a novel approach that permits us to look at the solution properties of the functionalized NPs. The gel formation involves the creation of an amide bond between the carboxylic groups of CMC or HYAL and the amine groups of functionalized NPs, which work as crosslinking agents of the polymer chains. The hybrid hydrogels are chemically and morphologically characterized. The rheological and the water uptake properties of the hydrogels are also investigated. Under the application of an alternating magnetic field, the CMC-HYAL hybrid hydrogel previously loaded with doxorubicin shows a drug release greater than that showed by the CMC-HYAL hydrogel crosslinked with 1,3-diaminopropane. In conclusion, the presence of magnetic NPs makes the synthesized hybrid hydrogels suitable for application as a drug-delivery system by means of alternating magnetic fields.

Cisplatin/Hydrogel Complex In Cancer Therapy

Hydrogels containing alpha-amino acid residues (L-phenylalanine, L-histidine) were used to complex the chemotherapeutic agent cisplatin. The release of the drug in phosphate buffer solution showed an initial burst effect, followed by a near zero-order release phase over the seven days of reported period. Unlike the nonreleasing pattern of the hydrogel poly(N-acryloyl-L-phenylalanine-co-N-isopropylacrylamide) (CP2), the homopolymer poly(N-acryloyl-L-phenylalanine) (P9) hydrogel showed a released amount of cisplatin loaded from a water/DMSO mixture that was three times greater than that loaded from simple water. The hydrogel P9 formed with cisplatinum(II) complex species of well-defined stoichiometry; the drug species was released by a chemically controlled process. The Pt(II)/L (L is the monomeric unit of the polymer) stoichiometric molar ratio of 0.5, corresponding to two close carboxylate groups per Pt(II), was found by the viscometric data on the soluble polymer analogue. The platinum species released from cisplatin-loaded (from water) hydrogel retained its cytotoxic activity toward Me665/2/21 human melanoma cell line, in the same manner shown by the native cisplatin. On the contrary, the platinum species released from cisplatin-loaded (from water/DMSO) hydrogel was devoid of any cytotoxic effect.

Polyelectrolyte Hydrogel Platforms for the Delivery of Antidepressant Drugs

Some vinyl hydrogels containing α-amino acid residues (l-phenylalanine, l-valine) were used as polyelectrolyte platforms for the evaluation of the controlled release of two antidepressants (paroxetine and duloxetine). The closer acidity constant (pKa) values of the two drugs show a closer release profile in physiological phosphate buffered saline (PBS) buffer (pH 7.40) and for long periods of time. The great electrostatic interaction forces between the COO− group of the hydrogel and the protonated secondary amino nitrogen of the drug are the main factor improving the release kinetics; this release was found to be slower compared to that of two structurally related drugs bearing the tertiary amino nitrogen atom (citalopram and trazodone). Moreover, at the lower value of pH 4.60, paroxetine showed a flatter release profile from the hydrogel containing the l-phenylalanine residues that, after six days, is half of that shown by duloxetine. Further effects due to steric and hydrophobic interactions may contribute to the different release profile. A further stimulation with alternating magnetic fields (AMF) of low frequency (20 kHz/50 W) enhanced the release of the drug at pH 7.40 from the hydrogel containing magnetic nanoparticles. Both AMF and PBS solution at pH 7.40 were used to trigger the ‘on-demand’ pulsatile paroxetine release from the nanocomposite hydrogel.

Pulsed release of antidepressants from nanocomposite hydrogels

The pulsed release of three antidepressants (paroxetine, duloxetine, vortioxetine), loaded on two vinyl hydrogels bearing uf061-amino acid residues (L-phenylalanine, L-valine) and embedded magnetic nanoparticles, was evaluated in different buffer solutions of purposely chosen pHs (2.9, 4.6, and 7.4). At low pH values the release of the drug was always small for a long period of days, and it underwent a sudden increase when a solution of pH 7.4 was maintained for a short period of hours. The releasing increase becomes much higher as greater was the residence time of the solution in contact with the hydrogel. The application of an alternating magnetic field (AMF) further increases the amount of drug released during the pH pulses. These different release variations were related to a different and reversible ability to swell of the hydrogel. The mechanism behind the process was mainly due to the different acid/base behaviour of the free carboxyl groups. Correspondence to: Mario Casolaro, Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Via Aldo Moro 2, Siena 53100, Italy, Tel.: +39-0577-234388; E-mail: mario.casolaro@unisi.it

Antibacterial Properties of Silver Nanoparticles Embedded on Polyelectrolyte Hydrogels Based on α-Amino Acid Residues

Polyelectrolyte hydrogels bearing l-phenylalanine (PHE), l-valine (AVA), and l-histidine (Hist) residues were used as scaffolds for the formation of silver nanoparticles by reduction of Ag+ ions with NaBH4. The interaction with the metal ion allowed a prompt collapse of the swollen hydrogel, due to the neutralization reaction of basic groups present on the polymer. The imidazole nitrogen of the hydrogel with Hist demonstrated greater complexing capacity with the Ag+ ion compared to the hydrogels with carboxyl groups. The subsequent reduction to metallic silver allowed for the restoration of the hydrogel’s degree of swelling to the starting value. Transmission electron microscopy (TEM) and spectroscopic analyses showed, respectively, a uniform distribution of the 15 nm spherical silver nanoparticles embedded on the hydrogel and peak optical properties around a wavelength of 400 nm due to the surface plasmonic effect. Unlike native hydrogels, the composite hydrogels containing silver nanoparticles showed good antibacterial activity as gram+/gram− bactericides, and higher antifungal activity against S. cerevisiae.

CHAPTER 20:Multiple Stimuli-responsive Hydrogels Based on α-Amino Acid Residues for Drug Delivery

Vinyl hydrogels containing α-amino-acid (l-valine, l-phenylalanine, l-histidine) residues are endowed with unique stimulus-responsive properties and undergo large changes in swelling degree as a function of temperature, pH and ionic strength conditions or the intensity of an electric field. These biocompatible smart hydrogels exhibit single or multiple stimuli-responsiveness potentially useful for biomedical applications, including controlled drug delivery, bioengineering or tissue engineering. This chapter focuses on recent developments and future trends of the α-amino-acid-based hydrogels as drug- (cisplatin, temsirolimus, pilocarpine) delivery systems for cancer and glaucoma therapy, and as platforms for lithium ion delivery to the brain for bipolar disorder management.