Biomedical subjects

Stefano Leporatti

Publications and source records attributed to Stefano Leporatti.

5 recordsLinked to original sources

PubMed2005

Elasticity and adhesion of resting and lipopolysaccharide-stimulated macrophages.

Colloidal Force Microscopy was employed to study the viscoelastic and adhesive properties of macrophages upon stimulation with lipopolysaccharide (LPS). Force vs. distance measurements were performed. The adhesion of LPS-stimulated cells (separation force=37+/-3 nN) was almost twice as high as that of resting macrophages (16+/-1 nN). Upon retraction pulling of membrane tethers was observed. Tether lengths and forces at which rupture take place did not depend on stimulation. The reduced Young's modulus K, a measure of cytoskeleton elasticity, was three times lower than that of the control. The data show that LPS has profound effects on cytomechanical and adhesion properties of macrophages.

Cell Adhesion↗

PubMed2005

Interaction forces between cellulose microspheres and ultrathin cellulose films monitored by colloidal probe microscopy-effect of wet strength agents.

Colloidal probe microscopy was employed to study forces between cellulose surfaces upon addition of a series of cationic copolymers in aqueous solution, as model compounds for wet strength agents. The content of quaternary ammonium groups and primary amines was systematically varied in the cationic polymers, to distinguish between the importance of electrostatical and H-bonding effects. Cellulose microspheres were glued at the apex of tipless microfabricated cantilevers and used as colloidal probes. Ultra thin cellulose films and cellulose fibres were employed as model surfaces. The cellulose films of a thickness of about 5 nm were spin-coated from cellulose solution onto silicon substrates. The root-mean-square-roughness (RMS) was 0.3-0.8 nm. The cationic model polymers were compared to Servamine, a polymer employed as standard wet strength resin in papermaking industries. Force versus separation measurements showed a detailed picture of adhesion and contact breaking. Relatively strong adhesion of the order of 0.3 mJ/m(2) was observed with Servamine within a range of approximately 10 nm. At larger distances weak bond breaking and elastic chain pulling were identified. When approaching the surface one to two small jump-in's possibly related to strong binding of Servamine and subsequent attraction could be found in the case of Servamine. In contrast, all the model copolymers showed only a weak adhesion of 8-30 micro/m(2), i.e., an order of magnitude less than that of Servamine and subsequent elastic rupture domains. The contour length, persistence length and characteristic rupture distances were calculated by means of applying the WLC model. Measurements against cellulose fibres obtained from the production process proved the relevance of the model systems.

Amines↗

PubMed2003

Swelling and shrinking of polyelectrolyte microcapsules in response to changes in temperature and ionic strength.

Swelling and shrinking of polyelectrolyte microcapsules consisting of poly(styrene sulfonate, sodium salt) (PSS) and poly(diallyldimethyl ammonium) chloride (PDADMAC) multilayers have been observed in response to temperature and electrolyte exposure, respectively. Heat-induced capsule swelling and capsule wall volume reduction were observed by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). On the other hand, pronounced shrinking in diameter induced by exposure to an electrolyte was observed in parallel to increases in the thickness of the capsule wall. The estimated wall volume was reduced to two thirds of the control for the salt-exposed capsules and one half for the salt-exposed and simultaneously annealed capsules. This reduction in volume was supposedly mainly caused by the compression of the capsule wall due to the ionic screening from the electrolyte. The highly porous microstructure of the multilayers and loosely bound PSS/PDADMAC complex are thought to be responsible for the structure of the PSS/PDADMAC capsules being easily modulated upon annealing and salt-exposure.

Journal Article↗

PubMed2002

Precipitation of inorganic salts inside hollow micrometer-sized polyelectrolyte shells.

Hollow polymer shells formed by layer-by-layer adsorption of oppositely charged polyelectrolytes onto micrometer-sized colloidal particles with subsequent decomposition of the colloidal core were employed as a model system for the study of inorganic crystallization reactions in restricted volumes. The size-selective permeability of shells is used for spatially controlling the precipitation of inorganic salts CaCO3 and BaCO3 into the shell interior. Outside the shells the precipitation was suppressed by the polymers, which are unable to penetrate the shell wall. The precipitates were studied by scanning electron microscopy and atomic force microscopy. The fundamental and applied aspects of research on spatially confined synthesis of inorganic particles are under discussion.

Journal Article↗

PubMedDate not supplied

Protamine assembled in multilayers on colloidal particles can be exchanged and released.

Biocomposite thin films assembled on colloidal particles by means of layer-by-layer adsorption have been suggested as drug carriers and diagnostic devices. Protamine (PRM)/dextransulfate (DXS) and protamine/bovine serum albumine (BSA) multilayers were fabricated on colloidal silica and subsequently investigated by means of fluorescence activated cell sorting (FACS) and microelectrophoresis. Fluorescein labeled polyelectrolytes were embedded at different positions in the multilayers as a marker for layer growth. FACS showed that PRM and DXS formed regular growing stable multilayers, yet adsorbed PRM can be nevertheless exchanged with PRM in solution during layer formation and also after the multilayer formation has been completed. Up to 90% of the PRM pool was available for exchange. PRM together with BSA as demonstrated by SFM did not form multilayers under the applied conditions although the zeta-potential, commonly used as an indicator for stepwise adsorption, observed characteristic alternations. The capability of bound PRM to exchange with PRM in solution is attributed to its relatively small size. The demonstrated exchange may have importance in designing multilayers with smart release features. Furthermore, FACS proved to be a rather suitable means to quantify the aggregation behavior during coating and washing. Singulets, doublets, triplets, and aggregates of higher order could be clearly resolved. The aggregation of particles coated with PRM/DXS layers was higher than that of silica particles coated with PAH/PSS layers. In the first case about 50% of all recorded events are attributed to aggregats, while the PAH/PSS coating produced only about 10% aggregates.

Adsorption↗