Melting and crystallization behaviors of biodegradable polymers enzymatically coalesced from their cyclodextrin inclusion complexes

Inclusion complexed (IC) and coalesced biodegradable poly(epsilon-caprolactone) (PCL), poly(L-lactic acid) (PLLA), and their diblock copolymer (PCL-b-PLLA) were achieved by forming ICs between host alpha-cyclodextrin(alpha-CD) and guest PCL, PLLA, and PCL-b-PLLA, followed by removing the alpha-CD host with an amylase enzyme. FTIR spectra of the coalesced polymers reveal that the host alpha-CD can be completely removed, without polymer degradation, by treatment with an amylase enzyme. The melting and crystallization behavior of these CD-IC treated polymers, which are crystallizable, biodegradable, and bioabsorbable, are investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. Results show that coalescence increased the crystallinities of the homopolymers but decreased that of the diblock copolymer. The Avrami exponent (n), derived from both isothermal and nonisothermal crystallization models for homo-PCL and -PLLA and the PCL and PLLA blocks in the diblock copolymer samples coalesced from their ICs, is close to 4, indicating homogeneous crystallization, whereas crystallization of the blocks in the as-synthesized diblock copolymer yields an Avrami exponent around 3, indicating heterogeneous crystallization. All of these results demonstrate that the PCL and PLLA homopolymers and blocks in the IC-coalesced samples are more readily and homogeneously crystallized than those in the as-synthesized samples or their physical blend, even though the level of crystallinity in the IC-coalesced diblock copolymer is significantly lower. Moreover, unlike the as-synthesized diblock copolymer, the crystallization of PCL and PLLA blocks in the IC-coalesced diblock copolymer are not influenced by their covalent connection.     

Kinetically controlled nanostructure formation in self-assembled globular protein-polymer diblock copolymers

Aqueous processing of globular protein-polymer diblock copolymers into solid-state materials and subsequent solvent annealing enables kinetic and thermodynamic control of nanostructure formation to produce block copolymer morphologies that maintain a high degree of protein fold and function. When model diblock copolymers composed of mCherry-b-poly(N-isopropylacrylamide) are used, orthogonal control over solubility of the protein block through changes in pH and the polymer block through changes in temperature is demonstrated during casting and solvent annealing. Hexagonal cylinders, perforated lamellae, lamellae, or hexagonal and disordered micellar phases are observed, depending on the coil fraction of the block copolymer and the kinetic pathway used for self-assembly. Good solvents for the polymer block produce ordered structures reminiscent of coil-coil diblock copolymers, while an unfavorable solvent results in kinetically trapped micellar structures. Decreasing solvent quality for the protein improves long-range ordering, suggesting that the strength of protein interactions influences nanostructure formation. Subsequent solvent annealing results in evolution of the nanostructures, with the best ordering and the highest protein function observed when annealing in a good solvent for both blocks. While protein secondary structure was found to be almost entirely preserved for all processing pathways, UV-vis spectroscopy of solid-state films indicates that using a good solvent for the protein block enables up to 70% of the protein to be retained in its functional form.     

In vitro and in vivo release of albumin using a biodegradable MPEG-PCL diblock copolymer as an in situ gel-forming carrier

An MPEG-PCL diblock copolymer was synthesized as an in situ gel carrier, and its phase transition behavior in aqueous solutions was examined. For comparison, aqueous solutions of Pluronic F-127, a widely used injectable gel-forming solution, were also studied. Both MPEG-PCL copolymer and Pluronic aqueous solutions were sols at room temperature. As the temperature was increased above room temperature, the diblock copolymer and Pluronic solutions underwent a sol-to-gel phase transition, which manifested as an increase in viscosity indicative of the formation of a gel. All of the copolymer solutions became gels at body temperature, although the gel viscosity increased with the increasing concentration of the MPEG-PCL diblock copolymer in the solution. In in vitro experiments, in which the gels were exposed to PBS, the MPEG-PCL gels maintained their structural integrity for more than 28 days, whereas the Pluronic gel disappeared within 2 days. The same results were observed when the polymer solutions were subcutaneously injected into rats. The MPEG-PCL gels maintained their structural integrity longer than 30 days, while the Pluronic gel could not be observed after 2 days. The ability of the gels as drug carriers was studied by measuring the release of fluorescein isothiocyanate-labeled bovine serum albumin (BSA-FITC) from MPEG-PCL diblock copolymer gels in vitro as well as in vivo. In vitro, BSA release was sustained above 20 days, with a greater release at lower diblock copolymer concentration; by contrast, Pluronic gels exhibited almost complete release of BSA-FITC within 1 day. When the BSA-FITC-loaded diblock copolymer and Pluronic solutions were subcutaneously injected into rats, they immediately transformed into a gel. In vivo, sustained release of BSA-FITC over 30 days was observed from the MPEG-PCL gel, whereas BSA-FITC release from the Pluronic gel ceased within 3 days. Collectively, the present findings show that MPEG-PCL diblock copolymer solutions are thermo-responsive and maintain their structural integrity under physiological conditions, indicating that they are suitable for use as injectable drug carriers.     

"Schizophrenic" micellization associated with coil-to-helix transitions based on polypeptide hybrid double hydrophilic rod-coil diblock copolymer

A polypeptide hybrid double hydrophilic diblock copolymer (DHBC), poly( N-isopropylacrylamide)- b-poly( l-glutamic acid) (PNIPAM- b-PLGA), was synthesized via the ring-opening polymerization of gamma-benzyl- l-glutamate N-carboxyanhydride (BLG-NCA) using monoamino-terminated PNIPAM as the macroinitiator, followed by deprotection of benzyl groups under alkaline conditions. Containing a thermoresponsive PNIPAM block and a pH-responsive PLGA block, the obtained polypeptide hybrid diblock copolymer molecularly dissolves in aqueous solution at alkaline pH and room temperature but supramolecularly self-assembles into PNIPAM-core micelles at alkaline pH and elevated temperatures and PLGA-core micelles at acidic pH and room temperature accompanied with coil-to-helix transition of the PLGA sequence. The pH- and thermoresponsive "schizophrenic" micellization behavior of PNIPAM- b-PLGA diblock copolymer has been investigated by (1)H NMR, optical transmittance, fluorescence probe measurement, transmission electron microscopy (TEM), dynamic and static laser light scattering (LLS), and circular dichroism (CD) spectroscopy. Moreover, the micellization process was investigated employing stopped-flow light scattering technique. The pH-induced micelle growth of PNIPAM- b-PLGA in aqueous solution exhibits drastically different kinetics compared to that of conventional pH-responsive DHBCs, probably due to the stabilization effects exerted by the formed alpha-helix secondary structures within the PLGA core at low pH. Exhibiting "schizophrenic" micellization, the polypeptide sequence of PNIPAM- b-PLGA can either locate within micelle cores or stabilizing coronas. The incorporation of polypeptide block into DHBCs can endow them with structural versatility, tunable spatial arrangement of chain segments within self-assembled nanostructures, and broader applications in the field of biomedicines.     

Synthesis and characterization of RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) triblock copolymer

Advances in tissue engineering require biofunctional scaffolds that can provide not only physical support for cells but also chemical and biological cues needed in forming functional tissues. To achieve this goal, a novel RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) (PEG-PLA-PGL/RGD) was synthesized in four steps (1) to prepare diblock copolymer PEG-PLA-OH and to convert its -OH end group into -NH(2) (to obtain PEG-PLA-NH(2)), (2) to prepare triblock copolymer PEG-PLA-PBGL by ring-opening polymerization of NCA (N-carboxyanhydride) derived from benzyl glutamate with diblock copolymer PEG-PLA-NH(2) as macroinitiator, (3) to remove the protective benzyl groups by catalytic hydrogenation of PEG-PLA-PBGL to obtain PEG-PLA-PGL, and (4) to react RGD (arginine-glycine-(aspartic amide)) with the carboxyl groups of the PEG-PLA-PGL. The structures of PEG-PLA-PGL/RGD and its precursors were confirmed by (1)H NMR, FT-IR, amino acid analysis, and XPS analysis. Addition of 5 wt % PEG-PLA-PGL/RGD into a PLGA matrix significantly improved the surface wettability of the blend films and the adhesion and proliferation behavior of human chondrocytes and 3T3 cells on the blend films. Therefore, the novel RGD-grafted triblock copolymer is expected to find application in cell or tissue engineering.     

Interaction of nonionic PEO-PPO diblock copolymers with lipid bilayers

The relationship between the molecular architecture of a series of poly(ethylene oxide)-b-poly(propylene oxide) (PEO-PPO) diblock copolymers and the nature of their interactions with lipid bilayers has been studied using small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC). The number of molecular repeat units in the hydrophobic PPO block has been found to be a critical determinant of the nature of diblock copolymer-lipid bilayer association. For dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-based biomembrane structures, polymers whose PPO chain length approximates that of the acyl chains of the lipid bilayer yield highly ordered, expanded lamellar structures consistent with well-integrated (into the lipid bilayer) PPO blocks. Shorter diblock copolymers produce mixed lamellar and nonlamellar mesophases. The thermotropic phase behavior of the polymer-doped membrane systems is highly influenced by the presence and molecular architecture of the diblock copolymer, as evidenced by shifting of the main phase transition to higher temperatures, broadening of the main transition, and the appearance of other features. Studies of temperature-induced changes in the mesophase structure for compositions prepared with well-integrated PEO-PPO polymers indicate that they undergo reversible changes to a nonlamellar structure as the temperature is lowered. Increasing either the number of repeat units in the PEO block or the polymer concentration promotes a greater degree of structural ordering.     

Diblock glycopolymers promote colloidal stability of polyplexes and effective pDNA and siRNA delivery under physiological salt and serum conditions

A series of glycopolymers composed of 2-deoxy-2-methacrylamido glucopyranose (MAG) and the primary amine-containing N-(2-aminoethyl) methacrylamide (AEMA) were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. The colloidal stability of the polyplexes formed with three diblock glycopolymers and pDNA was assessed using dynamic light scattering, and the polyplexes were found to be stable against aggregation in the presence of salt and serum over the 4 h time period studied. Delivery experiments were performed in vitro to examine the cellular uptake, transfection efficiency, and cytotoxicity of the glycopolymer/pDNA polyplexes in cultured HeLa cells and the diblock copolymer with the shortest AEMA block was found to be the most effective. Additionally, the ability of the diblock glycopolymers to deliver siRNA to U-87 (glioblastoma) cells was screened, and the diblock copolymer with the longest AEMA block was found to have gene knockdown efficacy similar to Lipofectamine 2000.     

Polyolefin matrixes with permanent antibacterial activity: preparation, antibacterial activity, and action mode of the active species

Poly[2-(tert-butylamino)ethyl methacrylate] (PTBAEMA) belongs to a novel class of water-insoluble biocides. Dispersion of a poly(ethylene-co-butylene)-b-poly[2-(tert-butylamino)ethyl methacrylate] diblock copolymer (PEB-b-PTBAEMA) within low-density polyethylene (LDPE) imparts antimicrobial properties to the polyolefin as assessed by the viable cell counting method against Escherichia coli (E. coli). This diblock copolymer has been synthesized by atom transfer radical polymerization (ATRP) with a poly(ethylene-co-butylene) (PEB) oligomer end-capped by an activated bromide as a macroinitiator for the polymerization of 2-(tert-butylamino)ethyl methacrylate (TBAEMA). Morphological changes of E. coli bacteria in contact with modified LDPE have been observed by transmission and scanning electron microscopy and indicate that the diblock copolymer is bactericide rather than bacteriostatic. Finally, the action mode of the PEB-b-PTBAEMA copolymer more likely relies on the displacement of the Ca(2+) and/or Mg(2+) ions of the outer membrane of the bacteria, which is disorganized and finally disrupted.     

Synthesis, characterization, and bioavailability of mannosylated shell cross-linked nanoparticles

Saccharide-functionalized shell cross-linked (SCK) polymer micelles designed as polyvalent nanoscaffolds for selective interactions with receptors on Gram negative bacteria were constructed from mixed micelles composed of poly(acrylic acid-b-methyl acrylate) and mannosylated poly(acrylic acid-b-methyl acrylate). The mannose unit was conjugated to the hydrophilic chain terminus of the amphiphilic diblock copolymer precursor, from which the SCK nanoparticles were derived, by the growth of the diblock copolymer from a mannoside functionalized atom transfer radical polymerization (ATRP) initiator. Mixed micelle formation between the amphiphilic diblock copolymer and mannosylated amphiphilic diblock copolymer was followed by condensation-based cross-linking between the acrylic acid residues present in the periphery of the polymer micelles to afford SCK nanoparticles. SCKs presenting variable numbers of mannose functionalities were prepared from mixed micelles of controlled stoichiometric ratios of mannosylated and nonmannosylated diblock copolymers. The polymer micelles and SCKs were characterized by dynamic light scattering (DLS), electrophoretic light scattering, atomic force microscopy (AFM), transmission electron microscopy (TEM), and analytical ultracentrifugation (AU). Surface availability and bioactivity of the mannose units were evaluated by interactions of the nanostructures with the model lectin Concanavalin A via DLS studies, with red blood cells (rabbit) via agglutination inhibition assays and with bacterial cells (E. coli) via TEM imaging.     

Novel preparation method for poly(L-lactide)-based block copolymers: extended chain crystallites as a solid-state macro-coinitiator

A novel synthetic method for poly(L-lactide) (PLLA)-based diblock copolymers was developed by the use of PLLA extended chain crystallites (or crystalline residues) as a solid-state macro-coinitiator. In this study, we showed one example, i.e., a synthesis of diblock copolymer composed of a crystalline PLLA chain and an amorphous poly(DL-lactide) chain by ring-opening polymerization of DL-lactide initiated with stannous octoate (i.e., tin(II) 2-ethylhexanoate) in the presence of PLLA extended chain crystallites. The PLLA extended chain crystallites were prepared by hydrolytic degradation of crystallized PLLA films at 97 degrees C for 70 h. The chains inside the extended chain crystallites are expected to be protected from transesterfication reaction. Gel permeation chromatography, polarimetry, 1H NMR spectroscopy, wide-angle X-ray scattering, and differential scanning calorimetry revealed that the diblock copolymer poly(L-lactide-block-DL-lactide) was successfully prepared without significant transesterification.     

Computer simulation of polymer and biopolymer self-assembly for drug delivery

Molecular simulation is an emerging tool to bridge relevant time- and length-scales in self-assembly and interfacial processes in soft matter and biological systems. In this review, we highlight mesoscale and coarse-grained molecular dynamics simulation techniques as applied to poly(ethylene oxide)-based diblock copolymer self-assembly. Moreover, we review recent progress pertaining to diblock copolymer and biopolymer self-assembly, stability, and finally, interactions of hydrophobic drugs with polymer membranes. We expect that these computational investigations should provide a useful complement to experimental studies that address open questions in the field of polymeric drug delivery.     

Pressure effects in confined nanophases

In this article, we review how pressure effects in pores affect both the physics of the confined fluid and the properties of the host porous material. Molecular simulations in which high-pressure effects were observed are first discussed; we will see how the strong dependence on bulk phase pressure of the freezing temperature of a fluid confined in nanopores can be explained by important variations of the pressure within the pore. We then discuss recent works in which direct calculations of the pressure tensor of fluids confined in pores provide evidence for large pressure enhancements. Finally, practical applications of these pressure effects in which gas adsorption in microporous solids (pore size < 2 nm) was found to enhance their mechanical properties by increasing the elastic modulus by a factor 4 are discussed.     

Biocompatible and biodegradable polymersome encapsulated hemoglobin: a potential oxygen carrier

This work describes the development of polymersome-encapsulated hemoglobin (PEH) self-assembled from biodegradable and biocompatible amphiphilic diblock copolymers composed of poly(ethylene oxide) (PEO), poly(caprolactone) (PCL), and poly(lactide) (PLA). In the amphiphilic diblock, PEO functions as the hydrophilic block, while either PCL or PLA can function as the hydrophobic block. PEO, PCL, and PLA are biocompatible polymers, while the last two polymers are biodegradable. PEH dispersions were prepared by extrusion through 100 nm pore radii polycarbonate membranes. In this work, the encapsulation efficiency of human and bovine hemoglobin (hHb and bHb) in polymersomes was adjusted by varying the initial concentration of Hb. This approach yielded Hb loading capacities that were comparable to values in the literature that supported the successful resuscitation of hamsters experiencing hemorrhagic shock. Moreover, the Hb loading capacities of PEHs in this study can also be tailored simply by controlling the diblock copolymer concentration. In this study, typical Hb/diblock copolymer weight ratios ranged 1.2-1.5, with initial Hb concentrations less than 100 mg/mL. The size distribution, Hb encapsulation efficiency, oxygen affinity (P 50), cooperativity coefficient (n), and methemoglobin (metHb) level of these novel PEH dispersions were consistent with values required for efficient oxygen delivery in the systemic circulation. Taken together, our results demonstrate the development of novel PEH dispersions that are both biocompatible and biodegradable. These novel dispersions show very good promise as therapeutic oxygen carriers.     

Mixed stimuli-responsive magnetic and gold nanoparticle system for rapid purification, enrichment, and detection of biomarkers

A new diagnostic system for the enrichment and detection of protein biomarkers from human plasma is presented. Gold nanoparticles (AuNPs) were surface-modified with a diblock copolymer synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The diblock copolymer contained a thermally responsive poly(N-isopropylacrylamide) (pNIPAAm) block, a cationic amine-containing block, and a semi-telechelic PEG?-biotin end group. When a mixed suspension of 23 nm pNIPAAm-modified AuNPs was heated with pNIPAAm-coated 10 nm iron oxide magnetic nanoparticles (mNPs) in human plasma, the thermally responsive pNIPAAm directed the formation of mixed AuNP/mNP aggregates that could be separated efficiently with a magnet. Model studies showed that this mixed nanoparticle system could efficiently purify and strongly enrich the model biomarker protein streptavidin in spiked human plasma. A 10 ng/mL streptavidin sample was mixed with the biotinylated pNIPAAm-modified AuNPs and magnetically separated in the mixed nanoparticle system with pNIPAAm mNPs. The aggregates were concentrated into a 50-fold smaller fluid volume at room temperature where the gold nanoparticle reagent redissolved with the streptavidin target still bound. The concentrated gold-labeled streptavidin could be subsequently analyzed directly using lateral flow immunochromatography. This rapid capture and enrichment module thus utilizes the mixed stimuli-responsive nanoparticle system to achieve concentration of a gold-labeled biomarker that can be directly analyzed using lateral flow or other rapid diagnostic strategies.     

Monomolecular assembly of siRNA and poly(ethylene glycol)-peptide copolymers

In this work, we design and investigate the complex formation of highly uniform monomolecular siRNA complexes utilizing block copolymers consisting of a cationic peptide moiety covalently bound to a poly(ethylene glycol) (PEG) moiety. The aim of the study was to design a shielded siRNA construct containing a single siRNA molecule to achieve a sterically stabilized complex with enhanced diffusive properties in macromolecular networks. Using a 14 lysine-PEG (K14-PEG) linear diblock copolymer, formation of monomolecular siRNA complexes with a stoichiometric 1:3 grafting density of siRNA to PEG is realized. Alternatively, similar PEGylated monomolecular siRNA particles are achieved through complexation with a graft copolymer consisting of six cationic peptide side chains bound to a PEG backbone. The hydrodynamic radii of the resulting complexes as measured by fluorescence correlation spectroscopy (FCS) were found to be in good agreement with theoretical predictions using polymer brush scaling theory of a PEG decorated rodlike molecule. It is furthermore demonstrated that the PEG coating of the siRNA-PEG complexes can be rendered biodegradable through the use of a pH-sensitive hydrazone or a reducible disulfide bond linker between the K14 and the PEG blocks. To model transport under in vivo conditions, diffusion of these PEGylated siRNA complexes is studied in various charged and uncharged matrix materials. In PEG solutions, the diffusion coefficient of the siRNA complex is observed to decrease with increasing polymer concentration, in agreement with theory of probe diffusion in semidilute solutions. In charged networks, the behavior is considerably more complex. FCS measurements in fibrin gels indicate complete dissociation of the diblock copolymer from the complex, while transport in collagen solutions results in particle aggregation.     

Spin-on end-functional diblock copolymers for quantitative DNA immobilization

We demonstrate a simple means to covalently bond DNA to both hard (i.e., glass and silicon wafers) and soft (i.e., polymeric) substrates that provides quantitative and precise control of the DNA areal density. The approach is based on spin coating an alkyne-end-functional diblock copolymer, alpha-alkyne-omega-Br-poly( tBA- b-MMA), that self-assembles on both types of substrates as an ordered monolayer and thereby directs alkyne groups to the surface. Azido-functionalized DNA is covalently linked to the alkyne functionalized substrates by means of a "click" reaction between azide and alkyne groups. The density of immobilized DNA can be quantitatively controlled by varying the parameters used for spin-coating the copolymer film, that is, solution concentration and rotational speed, or by varying the copolymer molecular weight. We find the yield of the DNA coupling reaction to be dependent on the nature of the polymer underlying the reactive alkyne functional groups, being higher for more hydrophilic polymers.     

Synthesis and micellization of amphiphilic brush-coil block copolymer based on poly(epsilon-caprolactone) and PEGylated polyphosphoester

A novel biodegradable amphiphilic brush-coil block copolymer consisting of poly(epsilon-caprolactone) and PEGylated polyphosphoester was synthesized by ring opening polymerization. The composition and structure of the copolymer were characterized by 1H NMR, 13C NMR, and FT-IR, and the molecular weight and molecular weight distribution were analyzed by gel permeation chromatograph (GPC) measurements to confirm the diblock structure. These amphiphilic copolymers formed micellar structures in water, and the critical micelle concentrations (CMCs) were around 10(-3) mg/mL, which was determined using pyrene as a fluorescence probe. Transmission electron microscopy (TEM) images showed that the micelles took an approximately spherical shape with core-shell structure, which was further demonstrated by laser light scattering (LLS) technique. The degradation behavior of the polymeric micelle was also investigated in the presence of Pseudomonas lipase and characterized by GPC measurement. Such polymer micelles from brush-coil block copolymers are expected to have wide utility in the field of drug delivery.     

Mechanism of Sodium Storage in Hard Carbon: An X‐Ray Scattering Analysis

Hard carbon is a standard anode material for Na‐ion batteries. However, its low crystallinity and diverse microstructures make obtaining a full understanding of the sodium storage mechanism challenging. Here, the results of a systematic ex situ small and wide angle X‐ray scattering study of a series of nanostructured hard carbons, which reveal clear evidence of sodium storage in the graphene–graphene interlayers and nanopores, are presented. Particularly, an emergence of a broad peak around q ≈ 2.0–2.1 Å^?1 in the low voltage region is suggested to be an indicator that sodium is densely confined in the nanopores. Thus, classical X‐ray scattering techniques are demonstrated to be effective in elucidating the overall reaction scheme of Na insertion into hard carbon.     

DNA Strands Attached Inside Single Conical Nanopores: Ionic Pore Characteristics and Insight into DNA Biophysics

Single nanopores attract a great deal of scientific interest as a basis for biosensors and as a system to study the interactions and behavior of molecules in a confined volume. Tuning the geometry and surface chemistry of nanopores helps create devices that control transport of ions and molecules in solution. Here, we present single conically shaped nanopores whose narrow opening of 8 or 12 nm is modified with single-stranded DNA molecules. We find that the DNA occludes the narrow opening of nanopores and that the blockade extent decreases with the ionic strength of the background electrolyte. The results are explained by the ionic strength dependence of the persistence length of DNA. At low KCl concentrations (10 mM) the molecules assume an extended and rigid conformation, thereby blocking the pore lumen and reducing the flow of ionic current to a greater extent than compacted DNA at high salt concentrations. Attaching flexible polymers to the pore walls hence creates a system with tunable opening diameters in order to regulate transport of both neutral and charged species.     

Design of polypeptide-functionalized polystyrene microspheres

In this contribution, the principle of spontaneous surface segregation has been applied for the preparation of polypeptide-functionalized polystyrene microspheres. For that purpose, an amphiphilic diblock copolymer was introduced in the mixture styrene/divinylbenzene and polymerized using AIBN as initiator. During the polymerization, cross-linked particles were obtained in which the diblock copolymer was encapsulated. The amphiphilic diblock copolymers used throughout this study contain a hydrophilic polypeptide segment, either poly(L-lysine) or poly(L-glutamic acid) and a hydrophobic polystyrene block. After 4 h of polymerization, rather monodisperse particles with sizes of approximately 3-4 microm were obtained. Upon annealing in hot water, the hydrophilic polypeptides migrate to the interface, hence, either positively charged or neutral particles were obtained when poly(L-lysine) is revealed at the surface and exposed to acidic or basic pH, respectively. On the opposite, negatively charged particles were achieved in basic pH water by using poly(L-glutamic acid) as additive. The surface chemical composition was modified by changing the environment of the particles. Thus, exposure in toluene provoked a surface rearrangement, and due to its affinity, the polystyrene block reorients toward the interface.