Recent progress in biomedical applications of Pluronic (PF127): Pharmaceutical perspectives

Most of the administered anti-cancer drugs are hydrophobic in nature and are known to have poor water solubility, short residence time, rapid clearance from the body and systemic side effects. Polymeric-based targeted particulate carrier system has shown to directly deliver the encapsulated anti-cancer drug to the desired site of action and prevent the interaction of encapsulated drug with the normal cells. Pluronic F127 (PF127) has been widely investigated for its broad-range of therodiagnostic applications in biomedical and pharmaceutical sciences, but rapid dissolution in the physiological fluids, short residence time, rapid clearance, and weak mechanical strength are the main shortcomings that are associated with PF127 and have recently been overcome by making various modifications in the structure of PF127 notably through preparation of PF127-based mixed polymeric micelles, PF127-conjugated nanoparticles and PF127-based hydrophobically modified thermogels. In this article, we have briefly discussed the recent studies that have been conducted on various anti-cancer drugs using PF127 as nano-carrier modified with other copolymers and/or conjugated with magnetic nanoparticles. The key findings of these studies demonstrated that the modified form of PF127 can significantly increase the stability of incorporated hydrophobic drugs with enhanced in vitro cytotoxicity and cellular uptake of anti-cancer drugs. Moreover, the modified form of PF127 has also shown its therapeutic potentials as therodiagnostics in various types of tumors and cancers. Hence, it can be concluded that the modified form of PF127 exhibits significant therodiagnostic effects with increased tumor-specific delivery of anti-cancer drugs having minimal toxic effects as compared to PF127 alone and/or other copolymers.

Thermosensitive hydrogels of poly(methyl vinyl ether-co-maleic anhydride) - Pluronic(®) F127 copolymers for controlled protein release

Thermosensitive hydrogels are of a great interest due to their many biomedical and pharmaceutical applications. In this study, we synthesized a new series of random poly (methyl vinyl ether-co-maleic anhydride) (Gantrez(®) AN, GZ) and Pluronic(®) F127 (PF127) copolymers (GZ-PF127), that formed thermosensitive hydrogels whose gelation temperature and mechanical properties could be controlled by the molar ratio of GZ and PF127 polymers and the copolymer concentration in water. Gelation temperatures tended to decrease when the GZm/PF127 ratio increased. Thus, at a fixed GZm/PF127 value, sol-gel temperatures decreased at higher copolymer concentrations. Moreover, these hydrogels controlled the release of proteins such as bovine serum albumin (BSA) and recombinant recombinant kinetoplastid membrane protein of Leishmania (rKMP-11) more than the PF127 system. Toxicity studies carried out in J774.2 macrophages showed that cell viability was higher than 80%. Finally, histopathological analysis revealed that subcutaneous administration of low volumes of these hydrogels elicited a tolerable inflammatory response that could be useful to induce immune responses against the protein cargo in the development of vaccine adjuvants.

Preparation and characterization of PEG-PPG-PEG copolymer/pregelatinized starch blends for use as resorbable bone hemostatic wax

In this study, polymer blends between PEG-PPG-PEG copolymer mixtures and pregelatinized starch at various compositions ranging from 0 to 3 % by weight were prepared and evaluated for potential use as novel resorbable bone hemostatic wax. It was found that the prepared samples had sufficient smearability for use as a bone wax. An addition of pregelatinized starch increased the hardness, smoothness and consistency of the texture while decreasing the adherence to glove. Thermal analysis indicated that the heat of fusion slightly decreased with increasing pregelatinized starch content. Compressive stiffness tended to decrease with increasing starch content for concentrations lower than 20 %, but re-increased at higher starch levels. In contrast, adherence deformation increased initially, but then decreased with increasing starch content. This behavior was related to the dependence of softening or reinforcing effect on the level of starch concentration in the samples. Adherence load and energy decreased with the addition of pregelatinized starch implying the decrease in adhesiveness of the samples. Furthermore, increasing the pregelatized starch amount also increased the liquid sealing duration of the samples at both 23 and 37 °C. Cytotoxicity tests against osteoblasts using a MTT assay revealed that the all the prepared samples and their raw materials did not show any cytotoxic potential. Formulations containing pregelatinized starch content between 20 and 30 % were found to show optimized performance.

Temperature-sensitive polymers for drug delivery

The ability to undergo rapid changes in response to subtle environmental cues make stimuli- responsive materials attractive candidates for minimally invasive, targeted and personalized drug delivery applications. This special report aims to highlight and provide a brief description of several of the significant natural and synthetic temperature-responsive materials that have clinical relevance for drug delivery applications. This report examines the advantages and disadvantages of natural versus synthetic materials and outlines various scaffold architectures that can be utilized with temperature-sensitive drug delivery materials. The authors provide a commentary on the current state of the field and provide their insight into future expectations for temperature-sensitive drug delivery, emphasizing the importance of the emergence of dual and multiresponsive systems capable of responding precisely to an expanding set of stimuli, thereby allowing the development of disease-specific drug delivery vehicles.

Topical treatment of the buccal mucosa and wounded skin in rats with a triamcinolone acetonide-loaded hydrogel prepared using an electron beam

In this study, a triamcinolone acetonide-loaded hydrogel was prepared by electron beam irradiation and evaluated for use as a buccal mucoadhesive drug delivery system. A poloxamer was modified to have vinyl end groups for preparation of the hydrogel via an irradiation cross-linking reaction. Carbopol was introduced to improve the mucoadhesive properties of the hydrogel. The in vitro release of triamcinolone acetonide from the hydrogel was examined at 37 °C. To investigate the topical therapeutic effect of triamcinolone acetonide on wounded rat skin and buccal mucosa, the appearance and histological changes were evaluated for 15 days after treatment with saline, triamcinolone acetonide solution, triamcinolone acetonide hydrogel, and blank hydrogel, respectively. Triamcinolone acetonide was released constantly from the gel formulation at 37 °C and reach 100% at about 48 h. After 15 days, in the skin of the group treated with the triamcinolone acetonide-loaded hydrogel, the wound was almost completely free of crust and a number of skin appendages, including hair follicles, had formed at the margins of the tissue. Moreover, the inflammatory response in the buccal mucosa was milder than that in the other groups, and the wound surface was completely covered with regenerating, hyperkeratotic, thickened epithelial cells. Our results indicate that the triamcinolone-acetonide hydrogel showed sustained drug release behavior, while causing no significant histopathological changes in buccal and skin tissues. Therefore, this hydrogel system may be a powerful means of drug delivery for buccal administration with controlled release and no tissue irritation.

New directions in thermoresponsive polymers

Interest in thermoresponsive polymers has steadily grown over many decades, and a great deal of work has been dedicated to developing temperature sensitive macromolecules that can be crafted into new smart materials. However, the overwhelming majority of previously reported temperature-responsive polymers are based on poly(N-isopropylacrylamide) (PNIPAM), despite the fact that a wide range of other thermoresponsive polymers have demonstrated similar promise for the preparation of adaptive materials. Herein, we aim to highlight recent results that involve thermoresponsive systems that have not yet been as fully considered. Many of these (co)polymers represent clear opportunities for advancements in emerging biomedical and materials fields due to their increased biocompatibility and tuneable response. By highlighting recent examples of newly developed thermoresponsive polymer systems, we hope to promote the development of new generations of smart materials.

Enhanced brain targeting of curcumin by intranasal administration of a thermosensitive poloxamer hydrogel

OBJECTIVES

The aim of this study was to develop a curcumin intranasal thermosensitive hydrogel and to improve its brain targeting efficiency.

METHODS

The hydrogel gelation temperature, gelation time, drug release and mucociliary toxicity characteristics as well as the nose-to-brain transport in the rat model were evaluated.

KEY FINDINGS

The developed nasal hydrogel, composed of Pluronic F127 and Poloxamer 188, had shorter gelation time, longer mucociliary transport time and produced prolonged curcumin retention in the rat nasal cavity at body temperature. The hydrogel release mechanism was diffusion-controlled drug release, evaluated by the dialysis membrane method, but dissolution-controlled release when evaluated by the membraneless method. A mucociliary toxicity study revealed that the hydrogel maintained nasal mucosal integrity until 14 days after application. The drug-targeting efficiencies for the drug in the cerebrum, cerebellum, hippocampus and olfactory bulb after intranasal administration of the curcumin hydrogel were 1.82, 2.05, 2.07 and 1.51 times that after intravenous administration of the curcumin solution injection, respectively, indicating that the hydrogel significantly increased the distribution of curcumin into the rat brain tissue, especially into the cerebellum and hippocampus.

CONCLUSIONS

A thermosensitive curcumin nasal gel was developed with favourable gelation, release properties, biological safety and enhanced brain-uptake efficiency.

Control over hygroscopic growth of saline aqueous aerosol using Pluronic polymer additives

The hygroscopic properties of an aerosol originating from a nebulizer solution can affect the extent of peripheral deposition within the respiratory tract, which in turn affects drug efficacy of drugs delivered to the lungs. Thus, the ability to tailor the degree and rate of hygroscopic growth of an aerosol produced by a nebulizer through modification of the formulation would serve to improve drug efficacy through targeted lung deposition. In this study, the kinetic and thermodynamic hygroscopic properties of sodium chloride aerosol mixed with commercially available Pluronic polymers, specifically F77 and F127, are reported using three complementary single aerosol analysis techniques, specifically aerosol optical tweezers, a double ring electrodynamic balance and a concentric cylinder electrodynamic balance. The F77 polymer is shown to have a predictable effect on the hygroscopic properties of the aerosol: the ability of the droplet to uptake water from the air depends on the solute weight percent of sodium chloride present in a linear dose dependant manner. Unlike the smaller F77, a non-linear relationship was observed for the larger molecular weight F127 polymer, with significant suppression of hygroscopic growth (>50% by mass) for solution aerosol containing even only 1 wt% of the polymer and 99 wt% sodium chloride. The suppression of growth is shown to be consistent with the formation of mixed phase aerosol particles containing hydrophilic inorganic rich domains and hydrophobic polymer rich domains that sequester some of the inorganic component, with the two phases responding to changes in relative humidity independently. This independence of coupling with the gas phase is apparent in both the equilibrium state and the kinetics of water evaporation/condensation. By starting with a saline nebulizer solution with a concentration of F127 ∼10(-2)mM, a 12% reduction in the radius of all aerosol produced at a relative humidity (RH) of 84% is possible. The difference in diameter is RH dependent, and may be much greater at higher humidities. These findings suggest that the addition of μM concentrations of larger Pluronic polymers to nebulizer formulations may greatly reduce the size of aerosols produced.

Understanding the interaction of block copolymers with DMPC lipid bilayer using coarse-grained molecular dynamics simulations

In this paper, we present a computational model of the adsorption and percolation mechanism of poloxamers (poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymers) across a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayer. A coarse-grained model was used to cope with the long time scale of the percolation process. The simulations have provided details of the interaction mechanism of Pluronics with lipid bilayer. In particular, the results have shown that polymer chains containing a PPO block with a length comparable to the DMPC bilayer thickness, such as P85, tends to percolate across the lipid bilayer. On the contrary, Pluronics with a shorter PPO chain, such as L64 and F38, insert partially into the membrane with the PPO block part while the PEO blocks remain in water on one side of the lipid bilayer. The percolation of the polymers into the lipid tail groups reduces the membrane thickness and increases the area per lipid. These effects are more evident for P85 than L64 or F38. Our findings are qualitatively in good agreement with published small-angle X-ray scattering experiments that have evidenced a thinning effect of Pluronics on the lipid bilayer as well as the role of the length of the PPO block on the permeation process of the polymer through the lipid bilayer. Our theoretical results complement the experimental data with a detailed structural and dynamic model of poloxamers at the interface and inside the lipid bilayer.

Nature of interactions between PEO-PPO-PEO triblock copolymers and lipid membranes: (I) effect of polymer hydrophobicity on its ability to protect liposomes from peroxidation

PEO-PPO-PEO triblock copolymers have opposing effects on lipid membrane integrity: they can behave either as membrane sealants or as membrane permeabilizers. To gain insights into their biomembrane activities, the fundamental interactions between a series of PEO-based polymers and phospholipid vesicles were investigated. Specifically, the effect of copolymer hydrophobicity on its ability to prevent liposomes from peroxidation was evaluated, and partitioning free energy and coefficient involved in the interactions were derived. Our results show that the high degree of hydrophilicity is a key feature of the copolymers that can effectively protect liposomes from peroxidation and the protective effect of the copolymers stems from their adsorption at the membrane surface without penetrating into the bilayer core. The origin of this protective effect induced by polymer absorption is attributed to the retardation of membrane hydration dynamics, which is further illustrated in the accompanying study on dynamic nuclear polarization (DNP)-derived hydration dynamics (Cheng, C.-Y.; Wang, J.-Y.; Kausik, R.; Lee, K. Y. C.; Han S. Biomacromolecules, 2012, DOI: 10.1021/bm300848c).

Poly(alkylene oxide) copolymers for nucleic acid delivery

The advancement of gene-based therapeutics to the clinic is limited by the ability to deliver physiologically relevant doses of nucleic acids to target tissues safely and effectively. Over the last couple of decades, researchers have successfully employed polymer and lipid based nanoassemblies to deliver nucleic acids for the treatment of a variety of diseases. Results of phase I/II clinical studies to evaluate the efficacy and biosafety of these gene delivery vehicles have been encouraging, which has promoted the design of more efficient and biocompatible systems. Research has focused on designing carriers to achieve biocompatibility, stability in the circulatory system, biodistribution to target the disease site, and intracellular delivery, all of which enhance the resulting therapeutic effect. The family of poly(alkylene oxide) (PAO) polymers includes random, block, and branched structures, among which the ABA type triblocks copolymers of ethylene oxide (EO) and propylene oxide (PO) (commercially known as Pluronic) have received the greatest consideration. In this Account, we highlight examples of polycation-PAO conjugates, liposome-PAO formulations, and PAO micelles for nucleic acid delivery. Among the various polymer design considerations, which include molecular weight of polymer, molecular weight of blocks, and length of blocks, the overall hydrophobic-lipophilic balance (HLB) is a critical parameter in defining the behavior of the polymer conjugates for gene delivery. We discuss the effects of varying this parameter in the context of improving gene delivery processes, such as serum stability and association with cell membranes. Other innovative macromolecular modifications discussed in this category include our work to enhance the serum stability and efficiency of lipoplexes using PAO graft copolymers, the development of a PAO gel-based carrier for sustained and stimuli responsive delivery, and the development of biodegradable PAO-based amphiphilic block copolymers.

Formulation and characterization of poloxamine-based hydrogels as tissue sealants

In situ cross linkable polyethylene glycol (PEG)-based polymers play an increasing role in surgical practice as sealants that provide a barrier to fluid/gas leakage and adhesion formation. This study investigated the gelation behavior and physical properties of hydrogels formed from homogeneous and blended solutions of two acrylated poloxamines (Tetronics® T1107 and T904) of various molecular weights and hydrophilic/lipophilic balances relative to a PEG control. Hydrogels were formed by reverse thermal gelation at physiological temperature (T1107-containing formulations) and covalent crosslinking by Michael-type addition with dithiothreitol. All poloxamine-based hydrogels exhibited thermosensitive behavior and achieved significantly reduced swelling, increased tensile properties and increased tissue bond strength relative to the PEG hydrogel at physiological temperature. Swelling and tensile properties of all poloxamine-based hydrogels were significantly greater at 37°C relative to 4°C, suggesting that their improved physical properties derive from cooperative crosslinking by both noncovalent and covalent mechanisms. Poloxamine-based hydrogels were cytocompatible and underwent hydrolytic degradation over 2-5weeks, depending on their T1107/T904 composition. In conclusion, select poloxamine-based hydrogels possess a number of properties potentially beneficial to tissue sealant applications, including a substantial increase in viscosity between room/physiological temperatures, resistance to cell adhesion and maintenance of a stable volume during equilibration.

Nanocomposite thermogel for controlled release of small proteins

A nanocomposite thermogel composed of Pluronic®-based multiblock copolymer and laponite nanoclay was developed to sustain delivery of low-molecular-weight proteins. The rapid release of low-molecular-weight proteins from multiblock copolymer thermogels has been a problem for sustained delivery but was solved by using nanocomposite thermogel. Lysozyme (Mw = 14,700), a relatively low-molecular-weight protein, was successfully loaded into and released from nanocomposite thermogel. In addition, interactions among multiblock copolymer, laponite, and lysozyme were studied in terms of gelation, micellization, particle size, and zeta potential. Critical micellization temperatures and sol–gel transition temperatures of multiblock copolymer solutions were lowered with laponite addition. Positively charged lysozyme was adsorbed onto anionic surface of laponite, which increased with an increase in the lysozyme concentration. Particle size and zeta potential of the laponite–lysozyme complex were also dependent on the lysozyme concentration. The nanocomposite thermogel sustained lysozyme release to 40 days, whereas lysozyme release from multiblock copolymer thermogel lasted for only 18 days. The structural stability of released lysozyme was confirmed by circular dichroism spectroscopy and differential scanning calorimetry.

Development of hydrogels and biomimetic regulators as tissue engineering scaffolds

This paper reviews major research and development issues relating to hydrogels as scaffolds for tissue engineering, the article starts with a brief introduction of tissue engineering and hydrogels as extracellular matrix mimics, followed by a description of the various types of hydrogels and preparation methods, before a discussion of the physical and chemical properties that are important to their application. There follows a short comment on the trends of future research and development. Throughout the discussion there is an emphasis on the genetic understanding of bone tissue engineering application.

Cell survival and proliferation after encapsulation in a chemically modified Pluronic(R) F127 hydrogel

Pluronic® F127 is a biocompatible, injectable, and thermoresponsive polymer with promising biomedical applications. In this study, a chemically modified form, i.e., Pluronic ALA-L with tailored degradation rate, was tested as an encapsulation vehicle for osteoblastic cells. UV cross-linking of the modified polymer results in a stable hydrogel with a slower degradation rate. Toxicological screening showed no adverse effects of the modified Pluronic ALA-L on the cell viability. Moreover, high viability of embedded cells in the cross-linked Pluronic ALA-L was observed with life/death fluorescent staining during a 7-day-culture period. Cells were also cultured on macroporous, cross-linked gelatin microbeads, called CultiSpher-S® carriers, and encapsulated into the modified cross-linked hydrogel. Also, in this situation, good cell proliferation and migration could be observed in vitro. Preliminary in vivo tests have shown the formation of new bone starting from the injected pre-loaded CultiSpher-S® carriers.

Transport of biological molecules in surfactant-alginate composite hydrogels

Obstructed transport of biological molecules can result in improper release of pharmaceuticals or biologics from biomedical devices. Recent studies have shown that nonionic surfactants, such as Pluronic® F68 (F68), positively alter biomaterial properties such as mesh size and microcapsule diameter. To further understand the effect of F68 (incorporated at concentrations well above the critical micelle concentration (CMC)) in traditional biomaterials, the transport properties of BSA and riboflavin were investigated in F68-alginate composite hydrogels, formed by both internal and external cross-linking with divalent cations. Results indicate that small molecule transport (represented by riboflavin) was not significantly hindered by F68 in homogeneously (internally) cross-linked hydrogels (up to an 11% decrease in loading capacity and 14% increase in effective diffusion coefficient, D(eff)), while protein transport in homogeneously cross-linked hydrogels (represented by BSA) was significantly affected (up to a 43% decrease in loading capacity and 40% increase in D(eff)). For inhomogeneously cross-linked hydrogels (externally cross-linked by CaCl(2) or BaCl(2)), the D(eff) increased up to 50 and 83% for small molecules and proteins, respectively. Variation in the alginate gelation method was shown to affect transport through measurable changes in swelling ratio (30% decrease) and observable changes in cross-linking structure as well as up to a 3.6- and 11.8-fold difference in D(eff) for riboflavin and BSA, respectively. Aside from the expected significant changes due to the cross-linking method utilized, protein transport properties were altered due to mesh size restrictions (10-25 nm estimated by mechanical properties) and BSA-F68 interaction (DLS). Taken as a whole, these results show that incorporation of a nonionic surfactant at concentrations above the CMC can affect device functionality by impeding the transport of large biological molecules.

Thermosensitive polymeric micelles for targeted drug delivery

Thermosensitive polymers are characterized by temperature-dependent aqueous solution properties. Below their lower critical solution temperature they are in an expanded state and fully dissolved, while above it they are dehydrated and insoluble. This has been exploited for the development of polymeric micelles that can be formed or destabilized depending on the solution temperature. Many micelle forming thermosensitive polymers have been described in literature, among which poly(N-isopropylacrylamide) (pNIPAAm), Pluronics (triblock copolymers of polypropylene oxide middle block flanked by two polyethylene oxide blocks) and poly(hydroxypropyl methacrylamide-lactate) (p(HPMAm-Lacn)) are the most frequently studied and some drug-loaded formulations based on thermosensitive polymers have reached clinical trials. The first generation of micelles composed of thermosensitive polymers was based on mere hydrophobic interactions between polymer blocks, while more recently shell or core crosslinking was introduced, in order to improve their stability in the circulation after intravenous administration and therefore, the accumulation of their depot in diseased areas. Various formulations of drug-loaded micelles based on thermosensitive polymers have shown promising results in vitro, as well as in vivo. This review gives an overview of the most important recent developments regarding the design and synthesis of various types of thermosensitve polymers for drug delivery.

Enzyme-mediated cross-linking of Pluronic copolymer micelles for injectable and in situ forming hydrogels

A new class of injectable and erodible hydrogels exhibiting highly robust gel strength at body temperature was fabricated by enzyme-mediated cross-linking between Pluronic copolymer micelles. Tyramine-conjugated Pluronic F-127 tri-block copolymers at two terminal ends of polyethylene oxide (PEO) side chains were synthesized and utilized to form self-assembled micelles in aqueous solution. Tyrosinase was employed to convert tyramine-conjugated micelles to highly reactive catechol conjugated micelles that could further cross-link individual Pluronic copolymer micelles to form a highly stable gel structure. The enzyme cross-linked Pluronic hydrogels showed far lower critical gelation concentration, concomitantly showing enhanced gel strength compared to unmodified Pluronic copolymer hydrogels, suitable for sustained delivery of bioactive agents. Rheological studies demonstrated that the enzyme cross-linked hydrogels exhibited a fast and reversible sol-gel transition in response to temperature while maintaining sufficient mechanical strength at the gel state. In situ formed hydrogels were eroded gradually, releasing FITC-labeled dextran in an erosion-controlled manner. Moreover, they showed tissue-adhesive properties due to the presence of unreacted catechol groups in the gel structure. Enzyme cross-linked Pluronic hydrogels could be potentially used for delivery applications of drugs and cells.

Injectable thermally responsive mucoadhesive gel for sustained protein delivery

Poloxamer thermoresponsive gels are widely explored in controlled drug delivery. Nevertheless, these gels possess inadequate mechanical properties, poor bioadhesiveness, and high permeability to water. To overcome these issues, we blended mucoadhesive hyaluronic acid (HA) with poloxamer analogs. This study aimed to investigate the features affecting the microscopic properties of the gels, which determine their macroscopic properties and capability to control/sustain protein release. Results showed that HA hampers water-poloxamer interactions, thus, strongly influencing physicochemical properties of poloxamer gels. This leads to gels with improved mechanical properties in which the diffusion kinetics of macromolecular active molecules are drastically slowed down. Poloxamer-HA gels can sustain the delivery of proteins, such as insulin, and may allow the modulation of its release kinetics by modifying HA content within the gels in the administration sites in which the active molecule release mechanism is mainly governed by its diffusion.

Structural characterization of nonionic mixed micelles formed by C12EO6 surfactant and P123 triblock copolymer

A structural characterization of mixed micelles formed in aqueous solution by the PEO-PPO-PEO triblock copolymer P123 and the nonionic surfactant C(12)EO(6) was carried out using various techniques, including ultralow shear viscosimetry, depolarized dynamic light scattering (VH-DLS), depolarized static light scattering (VH-SLS), and small-angle X-ray scattering (SAXS). The sphere-to-rod transition of the mixed micelles was studied in a diluted regime (P123 concentrations ranging from 0.5 to 10 wt %) at C(12)EO(6)/P123 molar ratios of 2.2, 3.2, 6.0, and 11 as well as for the pure C(12)EO(6). The data from VH-SLS and viscosimetry displayed a sharp increase in the intensity and viscosity, respectively, at the sphere-to-rod transition, and the results from the two methods were in accordance. In both techniques, an increased transition temperature with increasing content of C(12)EO(6) (in the molar ratio regime from 2.2 to 11) was observed. SAXS was used as the main technique, and a thorough structural characterization was performed, where indirect Fourier transformation (IFT) and generalized indirect Fourier transformation (GIFT) were employed in the analysis procedure of the SAXS data. The p(r) functions obtained from the IFT (employed at low P123 concentrations, i.e., 1.0 and 2.0 wt %) and GIFT (employed above 2.0 wt %) analyses revealed increased inhomogeneities in the mixed micelles when the molar ratio was increased. This suggested that the C(12)EO(6) organized themselves at the interface between the PPO core and the PEO corona of the P123 micelles, with the C(12) alkyl chain stretching into the hydrophobic core and the EO(6) part residing in the hydrophilic corona. The structure factor parameters obtained with GIFT for a molar ratio of 2.2 at a P123 concentration of 5.0 wt % showed radius values smaller than what was estimated from the p(r) functions. This was explained by an interpenetration of the PEO chains from one mixed micelle into a neighboring one. VH-DLS was performed on the mixed micelles at a temperature 3 degrees C above the transition temperature and at a molar ratio of 2.2. From the analyzed data, the average length L of the rods was estimated to be 102 nm.

Pluronics' influence on pseudomonad biofilm and phenazine production

Colonization of roots by Pseudomonas chlororaphis O6 (PcO6) involves root surface coverage through surface motility and biofilm formation. Root colonization and the production of antifungal phenazines are important in the ability of the bacterium to protect plants against pathogens. In this in vitro study we report that both biofilm formation and phenazine production are differentially influenced by nutrition and the presence of polyethylene oxide/polypropylene oxide triblock copolymer surfactants (Pluronics). Such surfactants are used for many purposes including agricultural formulations. Four Pluronics differing in molecular weight and in hydrophobic/hydrophilic proportions had distinct effects on biofilm formation and secondary metabolite production, although each increased surface motility, termed swarming, to a similar extent. These findings show that Pluronics had specific metabolic impacts on the bacterium, where both up- and downregulation was achieved depending on the medium and the Pluronic composition. In environmental and agricultural settings, Pluronics may have unanticipated effects on soil microorganisms, while in bioprocessing these effects may be leveraged to regulate metabolite yield.

An In Situ Gel-Forming Heparin-Conjugated PLGA-PEG-PLGA Copolymer

Novel heparin-conjugated PLGA-PEG-PLGA hydrogels were prepared via Michael-type addition between thiolated heparin and PLGA-PEG-PLGA diacrylate. The thiolated heparin (HP-SH) was conjugated with thiolacid dihydrazide followed by reduction. The structure and the thiol determination of obtained HP-SH were characterized by 1H NMR and the Ellman method. Anticoagulant activity and pK a of the HP-SH were determined by aPTT test and UV absorbance measurement which were 79.3% and 10.5, respectively. The PLGA-PEG-PLGA diacrylate was synthesized by bulk ring-opening polymerization of D,L-lactide (DLLA) and glycolide (GA) with PEG and stannous 2-ethylhexanoate, followed by the acrylation of the terminal groups. HP—SH was then conjugated to PLGA-PEG-PLGA diacrylate by Michael addition. Phase diagrams of the hydrogels were obtained by vial tilting; the release of heparin from the hydrogels exhibited temperature dependent sol—gel transition behavior. These in situ-forming heparin-conjugated hydrogels are novel as injectable and tissue-compatible scaffold formation, thermo-sensitivity, and growth factor binding.