Nanoparticles based on novel amphiphilic polyaspartamide copolymers

In this article, the synthesis of two amphiphilic polyaspartamide copolymers, useful to obtain polymeric nanoparticles without using surfactants or stabilizing agents, is described. These copolymers were obtained starting from α,β-poly-(N-2-hydroxyethyl)-dl-aspartamide (PHEA) by following a novel synthetic strategy. In particular, PHEA and its pegylated derivative (PHEA-PEG₂₀₀₀) were functionalized with poly(lactic acid) (PLA) through 1,1′-carbonyldiimidazole (CDI) activation to obtain PHEA–PLA and PHEA-PEG₂₀₀₀–PLA graft copolymers, respectively. These copolymers were properly purified and characterized by ¹H-NMR, FT-IR, and Size Exclusion Chromatography (SEC) analyses, which confirmed that derivatization reactions occurred. Nanoparticles were obtained from PHEA–PLA and PHEA-PEG₂₀₀₀–PLA graft copolymers by using the high pressure homogenization-solvent evaporation method, avoiding the use of surfactants or stabilizing agents. Polymeric nanoparticles were characterized by dimensional analysis, before and after freeze-drying process, and Scanning Electron Microscopy (SEM). Zeta potential measurements and X-ray Photoelectron Spectroscopy (XPS) analysis demonstrated the presence of PEG and/or PHEA onto the PHEA-PEG₂₀₀₀–PLA and PHEA–PLA nanoparticle surface, respectively.     

Polyaspartamide–Polylactide Graft Copolymers with Tunable Properties for the Realization of Fluorescent Nanoparticles for Imaging

Here, the synthesis and the characterization of novel amphiphilic graft copolymers with tunable properties, useful in obtaining polymeric fluorescent nanoparticles for application in imaging, are described. These copolymers are obtained by chemical conjugation of rhodamine B (RhB) moieties, polylactic acid (PLA), and O‐(2‐aminoethyl)‐O′‐methyl poly(ethylene glycol) (PEG) on α,β‐poly(N‐2‐hydroxyethyl)‐d,l ‐aspartamide (PHEA). In particular, PHEA is first functionalized with RhB to obtain PHEA–RhB with a derivatization degree in RhB (DD_RhB) equal to 0.55 mol%. By varying the reaction conditions, different amounts of PLA are grafted on PHEA–RhB to obtain PHEA‐RhB‐PLA with DD_PLA equal to 1.9, 4.0, and 6.2 mol%. Then, PEG chains are grafted on PHEA‐RhB‐PLA derivatives to obtain PHEA‐RhB‐PLA‐PEG graft copolymers. The preparation of polymeric fluorescent nanoparticles with tunable properties and spherical shape is described by using PHEA‐RhB‐PLA‐PEG with DD in PLA and PEG equal to 4.0 and 4.9 mol%, by following easily scaling up processes, such as emulsion‐solvent evaporation and high pressure homogenization (HPH)‐solvent evaporation techniques.

     

Development of New Targeted Inulin Complex Nanoaggregates for siRNA Delivery in Antitumor Therapy

Here, a novel strategy of formulating efficient polymeric carriers based on the already described INU-IMI-DETA for gene material whose structural, functional, and biological properties can be modulated and improved was successfully investigated. In particular, two novel derivatives of INU-IMI-DETA graft copolymer were synthesized by chemical functionalisation with epidermal growth factor (EGF) or polyethylenglycol (PEG), named INU-IMI-DETA-EGF and INU-IMI-DETA-PEG, respectively, in order to improve the performance of already described “inulin complex nanoaggregates” (ICONs). The latter were thus prepared by appropriately mixing the two copolymers, by varying each component from 0 to 100 wt% on the total mixture, named EP-ICONs. It was seen that the ability of the INU-IMI-DETA-EGF/INU-IMI-DETA-PEG polymeric mixture to complex siGL3 increases with the increase in the EGF-based component in the EP-ICONs and, for each sample, with the increase in the copolymer:siRNA weight ratio (R). On the other hand, the susceptibility of loaded siRNA towards RNase decreases with the increase in the pegylated component in the polymeric mixture. At all R values, the average size and the zeta potential values are suitable for escaping from the RES system and suitable for prolonged intravenous circulation. By means of biological characterisation, it was shown that MCF-7 cells are able to internalize mainly the siRNA-loaded into EGF-decorated complexes, with a significant difference from ICONs, confirming its targeting function. The targeting effect of EGF on EP-ICONs was further demonstrated by a competitive cell uptake study, i.e., after cell pre-treatment with EGF. Finally, it was shown that the complexes containing both EGF and PEG are capable of promoting the internalisation and therefore the transfection of siSUR, a siRNA acting against surviving mRNA, and to increase the sensitivity to an anticancer agent, such as doxorubicin.     

New biodegradable hydrogels based on a photo-cross-linkable polyaspartamide and poly(ethylene glycol) derivatives. Release studies of an anticancer drug

 The functionalization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) with glycidyl methacrylate (GMA) gives rise to a water-soluble photosensitive copolymer PHEA-GMA (PHG). Aqueous solutions of PHG alone or in combination with various concentrations of poly(ethylene glycol) dimethacrylate or poly(ethylene glycol) diacrylate (PEGDA) have been exposed to a source of UV rays at 313 nm in order to obtain polymeric networks. All samples have been prepared both as water-swellable microparticles and as gel systems. Microparticles have been characterised by Fourier transform IR spectrophotometry, dimensional analysis and swelling measurements in aqueous media mimicking biological fluids. In vitro chemical and enzymatic hydrolysis studies showed that all the prepared samples undergo a partial degradation at pH 1, 7.4 and 10 as well as after incubation with enzymes such as esterase. The effect of the cross-linking density on the rheological behavior of gel systems has also been investigated. PHG/PEGDA hydrogel is able to incorporate, during UV-irradiation, 5-fluorouracil (5-FU), chosen as a model drug, and to release it in simulated biological fluids, as confirmed by in vitro drug release studies at pH 1 and 7.4. PHG/PEGDA gel containing 5-FU is able to release this drug in a prolonged way, more slowly than a commercial ointment, as confirmed by in vitro studies at pH 5.5 and 7.4 using a Franz diffusion cell system and a synthetic membrane. Received: 3 October 2000 Accepted: 13 December 2000     

Synthesis and characterisation of novel chemical conjugates based on α,β-polyaspartylhydrazide and β-cyclodextrins

A new family of supramolecular systems based on a synthetic polyaminoacid and cyclic oligosaccharides such as β-cyclodextrins (β-CDs) was synthesised. The pharmaceutical potential of these systems arises from the proper combination between the complexing properties of cyclodextrins and the particular pharmacokinetic profile that can be obtained by using macromolecular conjugates with a biocompatible backbone. Five supramolecular conjugates were synthesised by using α,β-polyaspartylhydrazide (PAHy) as a polymeric component and various amounts of two β-CD derivatives. In particular, by reaction of PAHy with β-CD monoaldehyde, samples named as A₁, A₂ and A₃, bearing, respectively, 4.0, 7.5 and 10.7 mol% of β-CDs were obtained. The reaction of PAHy with 6-[aminoethyl(4′-carboxybutanamide)]-β-CD afforded samples named as B₁ and B₂, bearing, respectively, 1.8 and 2.6 mol% of β-CDs linked to the polymer. The occurrence of the conjugation reactions as well as the evaluation of the amount of oligosaccharides conjugated to the polymeric backbone were confirmed by FT-IR, ¹H NMR, DSC, SEC analyses and viscosimetric measurements. Molecular weight values obtained by SEC analysis were in good agreement with the theoretical increase of molecular weight of PAHy due to the β-CD moieties linked to the polymeric backbone. Fluorescence studies on the conjugate A₃ evidenced an interaction of a probe molecule with β-CDs linked to PAHy greater than that found with β-CDs alone and even in both cases the formation of a 1:1 host-guest complex occurs.     

Optimizing source and receiver placement in multistatic sonar networks to monitor fixed targets

Multistatic sonar networks consisting of non-collocated sources and receivers are a promising development in sonar systems, but they present distinct mathematical challenges compared to the monostatic case in which each source is collocated with a receiver. This paper is the first to consider the optimal placement of both sources and receivers to monitor a given set of target locations. Prior publications have only considered optimal placement of one type of sensor, given a fixed placement of the other type. We first develop two integer linear programs capable of optimally placing both sources and receivers within a discrete set of locations. Although these models are capable of placing both sources and receivers to any degree of optimality desired by the user, their computation times may be unacceptably long for some applications. To address this issue, we then develop a two-step heuristic process, Adapt-LOC, that quickly selects positions for both sources and receivers, but with no guarantee of optimality. Based on this, we also create an iterative approach, Iter-LOC, which leads to a locally optimal placement of both sources and receivers, at the cost of larger computation times relative to Adapt-LOC. Finally, we perform computational experiments demonstrating that the newly developed algorithms constitute a powerful portfolio of tools, enabling the user to slect an appropriate level of solution quality, given the available time to perform computations. Our experiments include three real-world case studies.     

Centred TVD schemes for hyperbolic conservation laws

New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented.     

A nanoparticulate drug-delivery system for rivastigmine: physico-chemical and in vitro biological characterization

The preparation and characterization of surface-PEGylated polymeric nanoparticles are described. These systems were obtained by UV irradiation of PHM and PHM-PEG(2000) as an inverse microemulsion, using an aqueous solution of the PHM/PHM-PEG(2000) copolymer mixture as the internal phase and triacetin saturated with water as the external phase, and characterized by dimensional analysis, zeta-potential measurements and XPS. in vitro biological tests demonstrated their cell compatibility and their ability to escape from phagocytosis. Rivastigmine was encapsulated into the nanoparticle structure and drug-release profiles from loaded samples were investigated in PBS at pH = 7.4 and human plasma.