Jacqueline Forcada

Temperature-sensitive nanogels: poly(N-vinylcaprolactam) versus poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinylcaprolactam) (PVCL) are temperature-responsive polymers which show a lower critical solution temperature (LCST) around 32 °C in aqueous solutions. Nanogels based on these temperature sensitive polymers swell at low temperatures and collapse at high ones, showing a volume phase transition temperature (VPTT) near physiological temperature. This unique behavior makes these nanogels attractive for biotechnological applications. PNIPAM is the building block of a huge amount of nanogels reported in the literature. However, PVCL is especially interesting due to the fact that it is very stable against hydrolysis and biocompatible. In this mini-review, various synthesis procedures together with the functionalization of different PNIPAM- and PVCL-based nanogels are revised and compared.

Gel swelling theories: the classical formalism and recent approaches

In this work, the classical theory of polymer/polyelectrolyte gel swelling is reviewed. This formalism is easy to understand and has been widely applied to gels and microgel particles. Nevertheless, its limitations and obscure aspects should be known before use. The case of temperature-sensitive gels is discussed in some detail because it deserves particular clarification. The application to experimental swelling data (of both gels and microgels) is also reviewed. In this way, strengths and weaknesses of this approach can be elucidated. Moreover, other formalisms are also outlined. Many of them are inspired by the classical one. Their improvements are briefly commented in this case. Others are based on different grounds.

Cationic polymer nanoparticles and nanogels: from synthesis to biotechnological applications.

Biotechnological Applications Jose Ramos,† Jacqueline Forcada,*,† and Roque Hidalgo-Alvarez*,‡ †POLYMAT, Bionanoparticles Group, Departamento de Química Aplicada, UFI 11/56, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, Apdo. 1072, 20080 Donostia-San Sebastiań, Spain ‡Grupo de Física de Fluidos y Biocoloides, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain

Soft nanoparticles (thermo-responsive nanogels and bicelles) with biotechnological applications: from synthesis to simulation through colloidal characterization

The use of nanotechnology in biotechnological applications has attracted tremendous attention from researchers. Currently many nanomaterials, such as soft nanoparticles, are under investigation and development for their use in biomedicine. Among soft nanoparticles, polymeric gels in the nanometre range, known as nanogel particles, have received considerable attention. Nanogel particles, which are formed by polymeric chains loosely cross-linked to form a three-dimensional network, swell by a thermodynamically good solvent but do not dissolve in it. Nanogels are composed of hydrophilic polymers capable of undergoing reversible volume-phase transitions in response to environmental stimuli. Among them, temperature-sensitive nanogels showing a volume phase transition temperature (VPTT) near physiological temperature have been investigated in detail. Nanogels based on biocompatible and temperature-sensitive polymers having a lower critical solution temperature (LCST) around 32 °C in aqueous solutions swell at low temperatures and collapse at high ones. This unique behavior makes these nanogels attractive for pharmaceutical, therapeutical, and biomedical applications. In this review, different synthesis strategies to produce this type of nanogels in dispersed media are revised. Special attention is paid to poly(N-vinylcaprolactam) (PVCL)-based nanogels due to their proven biocompatibility. On the other hand, an extensive review on the characteristics, preparation, and physicochemical properties of another type of soft nanoparticles, which are the bicelles, is presented. The different morphologies obtained depending on experimental conditions such as temperature, lipid concentration, and long- and short-chain phospholipids molar ratio are revised, emphasizing on an important property of bicelles: their alignment in the presence of a magnetic field, and presenting the most important applications of bicelles as membrane models in diverse conformational studies of proteins and membrane peptides, together with the possibilities of administration of such vesicles by systemic routes. A key challenge for the characterization of both soft nanoparticles (nanogels and bicelles) involves the elucidation of their colloidal properties. In this work, some colloidal features of these nanoparticles such as their size, electric double layer or the internal structure and motions of their chains are analyzed. In addition, an overview on the previous and current understanding of the methods and techniques employed in this colloidal characterization is presented, mainly from an experimental point of view. Finally, the most recent results on polyelectrolyte gels and bicelles obtained from computer simulations are also briefly commented. Concerning polyelectrolyte gels, this review is mainly focused on the most important feature of these systems, their large capacity of swelling, which has been explored by simulation in the last decade.

Computer simulations of thermo-sensitive microgels: quantitative comparison with experimental swelling data.

In this work, a quantitative comparison between experimental swelling data of thermo-sensitive microgels and computer simulation results obtained from a coarse-grained model of polyelectrolyte network and the primitive model of electrolyte is carried out. Polymer-polymer hydrophobic forces are considered in the model through a solvent-mediated interaction potential whose depth increases with temperature. The qualitative agreement between simulation and experiment is very good. In particular, our simulations predict a gradual shrinkage with temperature, which is actually observed for the microgels studied in this survey. In addition, the model can explain the swelling behavior for different contents of ionizable groups without requiring changes in the hydrophobic parameters. Our work also reveals that the abruptness of the shrinkage of charged gels is considerably conditioned by the number of monomeric units per chain. The swelling data are also analyzed with the Flory-Rhener theory, confirming some limitations of this classical formalism.

Surfactant-Free Miniemulsion Polymerization as a Simple Synthetic Route to a Successful Encapsulation of Magnetite Nanoparticles

Due to the existing interest in new hybrid particles in the colloidal range based on both magnetic and polymeric materials for applications in biotechnological fields, this work is focused on the preparation of magnetic polymer nanoparticles (MPNPs) by a single-step miniemulsion process developed to achieve better control of the morphology of the magnetic nanocomposite particles. MPNPs are prepared by surfactant-free miniemulsion polymerization using styrene (St) as a monomer, hexadecane (HD) as a hydrophobe, and potassium persulfate (KPS) as an initiator in the presence of oleic acid (OA)-modified magnetite nanoparticles. The effect of the type of cross-linker used [divinylbenzene (DVB) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP)] together with the effect of the amount of an aid stabilizer (dextran) on size, particle size distribution (PSD), and morphology of the hybrid nanoparticles synthesized is analyzed in detail. The mixture of different surface modifiers produces hybrid nanocolloids with various morphologies: from a typical core-shell composed by a magnetite core surrounded by a polymer shell to a homogeneously distributed morphology where the magnetite is uniformly distributed throughout the entire nanocomposite.

Acetal-functionalized polymer particles useful for immunoassays

The synthesis of core-shell type polystyrene monodisperse particles with surface acetal groups was carried out by a two-step emulsion polymerization process. In a first step, the core was synthesized by batch emulsion polymerization of styrene (St), and in the second step, the shell was polymerized by batch emulsion terpolymerization of styrene, methacrylic acid (MAA), and methacrylamidoacetaldehyde dimethyl acetal (MAAMA), using the seed obtained previously. With the aim of analyzing the effect of the thickness of the shell, the pH of the reaction medium and the weight ratio of the termonomers to prepare the shell, on the amount of the functionalized groups, several core-shell type latex particles were synthesized by two-step emulsion polymerization in a batch reactor. The latexes were characterized by TEM and conductimetric titration to obtain the particle size distribution and the amount of carboxyl and acetal groups on the surface, respectively. Looking for the applicability of the synthesized latexes in immunoassays, IgG a-CRP rabbit antibody was covalently bonded to the surface of the particles synthesized in neutral medium. The complex latex-protein was immunologically active against the CRP antigen.

Synthesis of core-shell type polystyrene monodisperse particles with chloromethyl groups

The synthesis of core-shell type polystyrene monodisperse particles with surface chloromethyl groups was carried out by a two-step emulsion polymerization process at different reaction temperatures. In a first step, the core was synthesized at 90 °C by means of batch emulsion polymerization of styrene (St), and in the second step, the shell was polymerized by batch emulsion copolymerization of St and chloromethylstyrene (CMS) using the seed obtained previously. With the aim of optimizing the production of these core-shell type polystyrene monodisperse particles with surface chloromethyl groups, the reaction temperature in the second step, the purification or not of the functionalized monomer (CMS), the amount and type of the redox initiator system used, and the type of addition of the initiator system to the reactor were studied.

Synthesis of new enzymatically degradable thermo-responsive nanogels

Two new families of thermo-responsive and enzymatically degradable nanogels were synthesized by batch emulsion polymerization of N-vinylcaprolactam (VCL) with dextran methacrylates (Dex-MA) with different degrees of substitution (DS). The first family was prepared using different amounts of Dex-MA with high DS forming highly cross-linked nanogel particles with the typical thermal behavior of PVCL-based nanogels: below the volume phase transition temperature (VPTT) nanogel particles were swollen and above it they were collapsed. After their enzymatic degradation with dextranase, nanogel particles swelled due to the cleavage of some glucopyranosyl bonds of dextran, but preserved their identity. On the other hand, the second family was prepared using different amounts of Dex-MA with low DS forming slightly cross-linked nanogel particles with an anomalous thermal behavior. Surprisingly, above the VPTT of the nanogel particles monodisperse interparticle reversible aggregates were formed. In addition, after their enzymatic degradation, a release of reducing sugars together with an intense de-swelling due to the fragmentation of the nanogel structure was observed. Both nanogel families could be suitable for drug delivery in tissues or organs where dextranase is present.

Covalent coupling of antibodies to aldehyde groups on polymer carriers

The aim of the present work is to prepare and characterize a functionalized latex with acetal groups on the surface and to obtain the covalent coupling of an a-CRP IgG protein. The acetal latex was synthesized by means of a core-shell emulsion polymerization in a batch reactor. The core was a seed of polystyrene and the shell was obtained by terpolymerization of styrene, methacrylic acid and methacryloylacetaldehyde di(n.methyl)acetal. The latex was characterized by TEM and conductimetric and potentiometric titration, in order to obtain the particle size distribution and the amount of carboxyl and acetal groups on the surface, respectively. Several latex-protein particles with the IgG physically or chemically bound to the surface were obtained by modifying the incubation conditions. In the covalent coupling experiments of the IgG, the protein physically adsorbed was removed by redispersion of the complexes in the presence of a non-ionic surfactant (Tween 20). The latex-protein complexes were characterized from the electrokinetic point of view with the aim to determine the isoelectric point of the complexes and to detect any difference in the electric state of the protein when these molecules are physically or chemically coupled to the surface. The final part of this work was to study the immunoreactivity of several latex-IgG complexes at several experimental conditions. By measuring the change in the turbidity after the addition of CRP antigen into the dispersion, it was possible to compare the immunoreactivity results when the protein is physically or chemically bound to the surface, and to study the effect of the presence of a surfactant in the reaction medium.