Lung UltrasouNd Guided surfactant therapy in preterm infants: an international multicenter randomized control trial (LUNG study)

BACKGROUND

The management of respiratory distress syndrome (RDS) in premature newborns is based on different types of non-invasive respiratory support and on surfactant replacement therapy (SRT) to avoid mechanical ventilation as it may eventually result in lung damage. European guidelines currently recommend SRT only when the fraction of inspired oxygen (FiO2) exceeds 0.30. The literature describes that early SRT decreases the risk of bronchopulmonary dysplasia (BPD) and mortality. Lung ultrasound score (LUS) in preterm infants affected by RDS has proven to be able to predict the need for SRT and different single-center studies have shown that LUS may increase the proportion of infants that received early SRT. Therefore, the aim of this study is to determine if the use of LUS as a decision tool for SRT in preterm infants affected by RDS allows for the reduction of the incidence of BPD or death in the study group.

METHODS/DESIGN

In this study, 668 spontaneously-breathing preterm infants, born at 25+0 to 29+6 weeks' gestation, in nasal continuous positive airway pressure (nCPAP) will be randomized to receive SRT only when the FiO2 cut-off exceeds 0.3 (control group) or if the LUS score is higher than 8 or the FiO2 requirements exceed 0.3 (study group) (334 infants per arm). The primary outcome will be the difference in proportion of infants with BPD or death in the study group managed compared to the control group.

DISCUSSION

Based on previous published studies, it seems that LUS may decrease the time to administer surfactant therapy. It is known that early surfactant administration decreases BPD and mortality. Therefore, there is rationale for hypothesizing a reduction in BPD or death in the group of patients in which the decision to administer exogenous surfactant is based on lung ultrasound scores.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT05198375 . Registered on 20 January 2022.

Failure of early non-invasive ventilation in preterm infants with respiratory distress syndrome in current care practice in Spanish level-III neonatal intensive care units - a prospective observational study

Introduction

Despite advances in respiratory distress syndrome (RDS) management over the past decade, non-invasive ventilation (NIV) failure is frequent and associated with adverse outcomes. There are insufficient data on the failure of different NIV strategies currently used in clinical practice in preterm infants.

Methods

This was a prospective, multicenter, observational study of very preterm infants [gestational age (GA) <32 weeks] admitted to the neonatal intensive care unit for RDS that required NIV from the first 30 min after birth. The primary outcome was the incidence of NIV failure, defined as the need for mechanical ventilation for <72 h of life. Secondary outcomes were risk factors associated with NIV failure and complication rates.

Results

The study included 173 preterm infants with a median GA of 28 (IQR 27-30) weeks and a median birth weight of 1,100 (IQR 800-1,333) g. The incidence of NIV failure was 15.6%. In the multivariate analysis, lower GA (OR, 0.728; 95% CI, 0.576-0.920) independently increased the risk of NIV failure. Compared to NIV success, NIV failure was associated with higher rates of unfavorable outcomes, including pneumothorax, intraventricular hemorrhage, periventricular leukomalacia, pulmonary hemorrhage, and a combined outcome of moderate-to-severe bronchopulmonary dysplasia or death.

Conclusion

NIV failure occurred in 15.6% of the preterm neonates and was associated with adverse outcomes. The use of LISA and newer NIV modalities most likely accounts for the reduced failure rate. Gestational age remains the best predictor of NIV failure and is more reliable than the fraction of inspired oxygen during the first hour of life.

Microparticle-embedded fibroin/alginate beads for prolonged local release of simvastatin hydroxyacid to mesenchymal stem cells

In the present work, we propose silk fibroin/alginate (SF/Alg) beads embedding simvastatin-loaded biodegradable microparticles as a versatile platform capable of tuning SVA release and in so doing osteogenic effects. In a first part of the study, microparticles of poly(lactic-co-glycolic) acid incorporating simvastatin either as lactone (SVL) or as hydroxyacid form (SVA) were prepared by spray-drying. While SVA-loaded microparticles released the drug in three days, long-term release of SVA could be obtained from SVL-loaded microparticles. In this latter case, SVL was promptly transformed to the osteogenic active SVA during release. When tested on mesenchymal stem cells, a time- and dose-dependent effect of SVL-loaded microparticles on cell proliferation and alkaline phosphatase (ALP) activity was found. Thereafter, SVL-loaded microparticles were embedded in SF/Alg beads to limit the initial simvastatin burst and to achieve easier implantation as well. Microparticle-embedded beads showed no cytotoxicity while ALP activity increased. If correctly exploited, the developed system may be suitable as osteogenic polymer scaffolds releasing correct amount of the drug locally for long time-frames.

Dually sensitive dextran-based micelles for methotrexate delivery

Temperature and pH-sensitive micelles prepared from dextran grafted with poly(N-isopropylacrylamide) (PNIPAAm)/polyethylene glycol methyl ether (PEGMA) with/without 2-aminoethylmethacrylate (2-AEM) were evaluated as methotrexate delivery systems.

Low viscosity-PLGA scaffolds by compressed CO2foaming for growth factor delivery

Foaming technology using supercritical and compressed fluids has emerged as a promising solution in regenerative medicine for manufacturing porous polymeric scaffolds.

Bioinspired superamphiphobic surfaces as a tool for polymer- and solvent-independent preparation of drug-loaded spherical particles

Superamphiphobic surfaces were evaluated as a tool to prepare spherical particles from polymers and solvents of very diverse nature, under mild conditions and with 100% drug encapsulation yield. Different from bioinspired superhydrophobic surfaces suitable only for aqueous dispersions, the superamphiphobic platforms allowed the formation of spherical droplets when solvents of any polarity were deposited onto them. Spherical poly(d,l-lactide-co-glycolide) (PLGA) particles were synthesized by placing drops of PLGA/ciprofloxacin suspensions in dioxane on a superamphiphobic surface followed by solvent evaporation. The particles prepared covering a wide range of PLGA/ciprofloxacin weight ratios delivered a 20% dose in the first 24h and then sustained the release of the remaining drug for more than 1month. The particles, both freshly prepared and after being 26days in the release medium, showed efficiency against different types of microorganisms. The developed polymer- and solvent-independent approach could be useful for microencapsulation with very high efficiency of active substances of varied nature into size-tunable particles for a wide range of applications in an affordable and cost-effective manner.

Bone regeneration induced by an in situ gel-forming poloxamine, bone morphogenetic protein-2 system

The aim of this study was to confirm previously shown, in vitro osteogenic induction by the Tetronics T908 and T1307 in a critical-size, rat calvaria defect. In vivo, the osteogenic activity of the hydrogels was comparable to in vitro, but less pronounced. However, similar to in vitro, the system was strongly potentiated by incorporating 6.5 microg of bone morphogenetic protein-2 in solution or pre-encapsulated in poly(lactic-co-glycolic) acid microspheres. These two systems extended the in vivo release of bone morphogenetic protein-2, determined with 125I- bone morphogenetic protein-2, for one and two additional weeks, respectively, time enough to fill approximately 40% and 90% of the defect with well-organized bone. Furthermore, the structural characteristics of Tetronic hydrogels together with their biocompatibility, injectability, and adaptability to multiple defect sizes and shapes suggest their role as new, potential bone morphogenetic protein-2 delivery, low-cost scaffolds for minor as well as critical bone defects.

Free and copolymerized γ-cyclodextrins regulate the performance of dexamethasone-loaded dextran microspheres for bone regeneration

Incorporation of γ-cyclodextrins (γ-CD), as free entities or structural monomers (acrylamidomethyl-γ-cyclodextrin, γ-CD–NMA), into dextran-methacrylate (dextran-MA) photopolymerized spheres modifies the loading and release of an osteogenic agent.

Cytocompatibility and P-glycoprotein inhibition of block copolymers: structure-activity relationship

Amphiphilic polymeric micelles greatly improve the solubilization and sustained release of hydrophobic drugs and provide a protective environment for the cargo molecules in aqueous media, which favors lower drug administration doses, reduces adverse side effects, and increases blood circulation times and passive targeting to specific cells. These capabilities depend, among other variables, on the structure and composition of the polymer chains. Composition and, in particular, block length have been shown to play an important role in the modification of cellular responses such as drug internalization processes or transduction pathways when polymeric unimer/micelles are in close contact with cells. Here we present a detailed study about the role copolymer structure and composition play on cell viability and cellular response of several cell lines. To do that, more than 30 structurally related copolymers with diblock and triblock architectures containing different hydrophobic blocks and poly(ethylene oxide) as the common hydrophilic unit have been analyzed regarding cytocompatibility and potential as "active" cell response modifiers by testing their influence on the P-gp pump efflux mechanism responsible of multidrug resistance in cancerous cells. An empirical threshold for cell viability could be established at a copolymer EO/POeffective value above ca. 1.5 for copolymers with triblock structure, whereas no empirical rule could be observed for diblocks. Moreover, some of the tested copolymers (e.g., BO12EO227BO12 and EO57PO46EO57 that notably increased and C16EO455C16 that decreased the P-gp ATPase activity) were observed to act as efficient inhibitors of the P-gp efflux pump promoting an enhanced doxorubicin (DOXO) accumulation inside multidrug resistant (MDR) NCI-ADR-RES cells.

Drug/Medical Device Combination Products with Stimuli-responsive Eluting Surface

Drug-eluting medical devices are designed to improve the primary function of the device and at the same time offer local release of drugs which otherwise might find it difficult to reach the insertion/implantation site. The incorporation of the drug enables the tuning of the host/microbial responses to the device and the management of device-related complications. On the other hand, the medical device acts as platform for the delivery of the drug for a prolonged period of time just at the site where it is needed and, consequently, the efficacy and the safety of the treatment, as well as its cost-effectiveness are improved. This chapter begins with an introduction to the combination products and then focuses on the techniques available (compounding, impregnation, coating, grafting of the drug or of polymers that interact with it) to endow medical devices with the ability to host drugs/biological products and to regulate their release. Furthermore, the methods for surface modification with stimuli-responsive polymers or networks are analyzed in detail and the performance of the modified materials as drug-delivery systems is discussed. A wide range of chemical-, irradiation- and plasma-based techniques for grafting of brushes and networks that are sensitive to changes in temperature, pH, light, ionic strength or concentration of certain biomarkers, from a variety of substrate materials, is currently available. Although in vivo tests are still limited, such a surface functionalization of medical devices has already been shown useful for the release on-demand of drugs and biological products, being switchable on/off as a function of the progression of certain physiological or pathological events (e.g. healing, body integration, biofouling or biofilm formation). Improved knowledge of the interactions among the medical device, the functionalized surface, the drug and the body are expected to pave the way to the design of drug-eluting medical devices with optimized and novel performances.

From Drug Dosage Forms to Intelligent Drug-delivery Systems: a Change of Paradigm

The design of new drug-delivery systems (DDSs) able to regulate the moment and the rate at which the release should take place, and even to target the drug to specific tissues and cell compartments, has opened novel perspectives to improve the efficacy and safety of the therapeutic treatments. Ideally, the drug should only have access to its site of action and the release should follow the evolution of the disease or of certain biorhythms. The advances in the DDSs field are possible because of a better knowledge of the physiological functions and barriers to the drug access to the action site, but also due to the possibility of having “active” excipients that provide novel features. The joint work in a wide range of disciplines, comprising materials science, biomedical engineering and pharmaceutical technology, prompts the design and development of materials (lipids, polymers, hybrids) that can act as sensors of physiological parameters or external variables, and as actuators able to trigger or tune the release process. Such smart excipients lead to an advanced generation of DDSs designed as intelligent or stimuli-responsive. This chapter provides an overview of how the progress in DDSs is intimately linked to the evolution of the excipients, understood as a specific category of biomaterials. The phase transitions, the stimuli that can trigger them and the mechanisms behind the performance of the intelligent DDSs are analyzed as a whole, to serve as an introduction to the topics that are comprehensively discussed in the subsequent chapters of the book. A look to the future is also provided.

Molecularly Imprinted Hydrogels for Affinity-controlled and Stimuli-responsive Drug Delivery

The performance of smart or intelligent hydrogels as drug-delivery systems (DDSs) can be notably improved if the network is endowed with high-affinity receptors for the therapeutic molecule. Conventional molecular imprinting technology aims to create tailored binding pockets (artificial receptors) in the structure of rigid polymers by means of a template polymerization, in which the target molecules themselves induce a specific arrangement of the functional monomers during polymer synthesis. Adaptation of this technology to hydrogel synthesis implicates the optimization of the imprinting pocket to be able to recover the high-affinity conformation when distorted by swelling or after the action of a stimulus. This chapter analyzes the implementation of the molecular imprinting technology to the synthesis of both non-responsive and responsive loosely cross-linked hydrogels, and provides recent examples of the suitability of the imprinted networks to attain affinity-controlled, activation-controlled or stimuli-triggered drug and protein release.

Doxorubicin-loaded micelles of reverse poly(butylene oxide)-poly(ethylene oxide)-poly(butylene oxide) block copolymers as efficient "active" chemotherapeutic agents

Five reverse poly(butylene oxide)-poly(ethylene oxide)-poly(butylene oxide) block copolymers, BOnEOmBOn, with BO ranging from 8 to 21 units and EO from 90 to 411 were synthesized and evaluated as efficient chemotherapeutic drug delivery nanocarriers and inhibitors of the P-glycoprotein (P-gp) efflux pump in a multidrug resistant (MDR) cell line. The copolymers were obtained by reverse polymerization of poly(butylene oxide), which avoids transfer reaction and widening of the EO block distribution, commonly found in commercial poly(ethylene oxide)-poly(propylene oxide) block copolymers (poloxamers). BOnEOmBOn copolymers formed spherical micelles of 10-40 nm diameter at lower concentrations (one order of magnitude) than those of equivalent poloxamers. The influence of copolymer block lengths and BO/EO ratios on the solubilization capacity and protective environment for doxorubicin (DOXO) was investigated. Micelles showed drug loading capacity ranging from ca. 0.04% to 1.5%, more than 150 times the aqueous solubility of DOXO, and protected the cargo from hydrolysis for more than a month due to their greater colloidal stability in solution. Drug release profiles at various pHs, and the cytocompatibility and cytotoxicity of the DOXO-loaded micelles were assessed in vitro. DOXO loaded in the polymeric micelles accumulated more slowly inside the cells than free DOXO due to its sustained release. All copolymers were found to be cytocompatible, with viability extents larger than 95%. In addition, the cytotoxicity of DOXO-loaded micelles was higher than that observed for free drug solutions in a MDR ovarian NCI-ADR-RES cell line which overexpressed P-gp. The inhibition of the P-gp efflux pump by some BOnEOmBOn copolymers, similar to that measured for the common P-gp inhibitor verapamil, favored the retention of DOXO inside the cell increasing its cytotoxic activity. Therefore, poly(butylene oxide)-poly(ethylene oxide) block copolymers offer interesting features as cell response modifiers to complement their role as efficient nanocarriers for cancer chemotherapy.

Structural properties of biodegradable polyesters and rheological behaviour of their dispersions and films

This paper focuses on the dependence of the rheological properties of PLA-PEG and PLGA dispersions and films on the polymer structural properties, in order to obtain useful information to predict and explain the performance of polyester films as drug-delivery systems. In this study, one PLA-PEG and three PLGA polymers of different molecular mass were synthesized and characterized by NMR, GPC, DSC and TGA-FT-IR. To characterize the viscoelastic behaviour of concentrated solutions in dichloromethane and of the films obtained by a solvent-casting technique, oscillatory shear rheometry was used. The polymer dispersions showed a characteristic Newtonian viscous behaviour, but with different consistency index depending on the nature of the polymer. Freshly prepared, PLGA and PLA-PEG films had elastic modulus (G') greater than viscous modulus (G"). The decrease in both moduli caused by an increase in temperature from 25 to 37 degrees C was especially marked for the polymers with T(g) below or around 25 degrees C (PLGA 27 kDa and PLA-PEG 27 kDa). After being immersed in pH 7.4 aqueous solution for one week, PLGA films showed a significant increase in both G' and G", due to the promotion of polymer-polymer interactions in a non-solvent medium. In contrast, the PLA-PEG film became softer and more hydrated, due to the amphiphilic character of the polymer. The water taken up by the film acted as a plasticizer and induced the softening of the system. These results suggest that the presence of PEG chains exerts a strong influence on the mechanical properties of polyesters films and, possibly, the performance as coating or matrices of drug-delivery systems.

Estradiol sustained release from high affinity cyclodextrin hydrogels

Hydrogels for loading estradiol and controlling its release were prepared cross-linking various cyclodextrins with ethyleneglycol diglycidylether. To select the more adequate cyclodextrins, estradiol solubility diagrams in water with beta-cyclodextrin (betaCD), methyl-beta-cyclodextrin (MbetaCD), hydroxypropyl-beta-cyclodextrin (HPbetaCD), and sulfobutyl-beta-cyclodextrin (SBbetaCD) were made in absence and presence of hydroxypropyl methylcellulose (HPMC) applying or not autoclaving. Although all cyclodextrins showed enough complexation capability, the low solubility of betaCD and the high anionic character of SBbetaCD hindered the cross-linking process, and these cyclodextrins were discarded for preparing hydrogels. Hydrogels prepared with MbetaCD (20%, 25%) or HPbetaCD (20%, 25%, and 30%), with or without HPMC 0.25%, absorbed 4-10 times their weight in water and loaded up to 24 mg estradiol per gram, which is 500 times greater than the amount of drug that can be dissolved in their aqueous phase. Positive linear correlation was found between the stability constant and the network/water partition coefficients of drug. The hydrogels sustained the release up to one week; the affinity of estradiol for the cyclodextrin units controlling the process, as shown by the negative correlation with the release rate constants. These results highlight the potential of cyclodextrin complexation for the development of hydrogels useful in loading hydrophobic drugs and controlling their release.

Drug solubilization and delivery from cyclodextrin-Pluronic aggregates

Colloidal systems based on Pluronic F127 (PF127) and hydroxypropyl-beta-cyclodextrin (HPbetaCD) have been characterized with a view to their potential use as delivery systems of hydrophobic drugs. Complexation of PF127 and HPbetaCD was evaluated by surface tension measurements, 1H-NMR spectroscopy and transmission electron microscopy. The critical micellar concentration, CMC, at 25 degrees C of PF127 (0.39 mM in pH 5.8 and 7.4 phosphate buffers, and 0.59 mM in pH 4.5 acetic/acetate and lactic/lactate buffers) was shifted to higher values by the addition of 38.17 mM HPbetaCD (CMC(app) = 1.18 mM). This is related to the threading of HPbetaCD onto the PF127 chains, as confirmed by 1H NMR experiments. HPbetaCD at this concentration notably raised the sol-gel transition temperature; the minimum PF127 concentration required for providing gelling systems in physiological environments being 13.4 mM. Both HPbetaCD and PF127 by themselves are able to notably increase the solubility of sertaconazole (SN). At HPbetaCD concentrations below 80 mM, an additive effect of both components on SN solubility was observed. At greater HPbetaCD concentrations, a non-additive increase occurred, which is related to the complexation of some PF127 unimers with HPbetaCD molecules, decreasing the total number of micelles and HPbetaCD cavities available for interacting with SN. The 13.4 mM PF127/38.17 mM HPbetaCD system, able to increase up to 100 times the SN solubility in pH5.8 phosphate buffer, showed temperature-dependent drug diffusion coefficients, able to control the release for one week at 37 degrees C.

Preparation of chitosan beads by simultaneous cross-linking/insolubilisation in basic pH

A one-step procedure to prepare chitosan beads by simultaneous cross-linking with glutaraldehyde and insolubilisation in 1.5 M NaOH solution has been developed. The optimisation of the procedure was carried out by monitoring the evolution of the loss and storage moduli of chitosan solutions (1.5% (w/v), in acetic acid 0.2 M) in the presence of different proportions of glutaraldehyde. Increasing the chitosan molecular weight, glutaraldehyde concentration and/or process temperature from 20 to 37 degrees C, a reduction of time to reach the gel point was observed. The diameter of freshly prepared swollen beads was 3.2+/-0.4 mm and, after drying 0.48+/-0.18 mm. Swollen or previously dried beads were loaded with metronidazole by immersion in 0.1% (w/v), drug solution in a phosphate buffer pH 7.5, purified water, 0.2 M acetic acid or 0.1 M HCl. Beads synthesised at 37 degrees C experimented faster swelling than the ones prepared at 20 degrees C and even disintegrated in acetic acid. The amounts of metronidazole loaded (ranging from 1 to 286 mg/g dried beads) increased with swelling capacity of beads. The release studies carried out in 0.1 M HCl indicated that, regardless of the medium used to load the beads, all of them released the dose in less than 30 min. In summary, applying this one-step procedure and choosing the adequate glutaraldehyde proportion, it is possible to obtain particles of chitosan cross-linked with itself, which exhibit pH-sensitive swelling and which are able to release all the drug quickly into an acidic environment such as the stomach. The results obtained also highlight the importance of the pH of the medium for modulating the amount of drug loaded (it is remarkably greater at lower pHs) and the influence of temperature at which the beads are prepared on their tendency to disintegrate.

Glass transitions and viscoelastic properties of carbopol and noveon compacts

Glass transitions of five varieties of Carbopol (acrylic acid polymers cross-linked with allyl sucrose or allyl pentaerythritol) and two varieties of Noveon (calcium salts of acrylic acid polymer cross-linked with divinylglycol) differing in cross-linking density and nature and content in residual solvents, were analysed (as compressed probes) by differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry (MTDSC), and oscillatory rheometry. All carbopol compacts showed a main glass transition, at a temperature between 130 and 140 degrees C, Tg, independently of their cross-linking degree and molecular weight. Additionally two batches of Carbopol 971P, which had greater contents in residual solvents, also presented a secondary transition at 65-70 degrees C. Sorption of water during storage of carbopol compacts at different relative humidity environments caused the Tg to strongly decrease. Compacts stored at 97.5% relative humidity have Tg below 0 degrees C and behave, at room temperature, as flexible hydrogels. The Gordon-Taylor/Kelley-Bueche equation only fit the dependence of Tg on water content well for carbopol compacts containing less than 15% water. The plasticizing effect of water was clearly evidenced in the considerable decrease in the storage and loss moduli of the compacts. Although the energy associated to the glass transitions of carbopol polymers, 0.40-0.50 Jg(-1) degrees C(-1), is high enough to be clearly detected by DSC, in some cases the evaporation of residual solvents may make it difficult to observe the Tg. This inconvenience is overcome using MTDSC or oscillatory rheometry. The decrease in Tg of carbopol caused by water sorption when compacts were stored at 97.5% R.H. explains why their loss (G") and storage (G') moduli at room temperature decreased four orders of magnitude. In contrast, in noveon varieties, calcium ions act as ionic cross-linkers of the carboxylic groups, providing rigid networks with much higher Tg, and storage and loss moduli. This explains that despite sorbing similar amounts of water to carbopol, the changes on the mechanical properties of noveon compacts were much less important (i.e., G' and G" decreased up to one order of magnitude).

Rheological properties of PLGA film-based implants: correlation with polymer degradation and SPf66 antimalaric synthetic peptide release

This paper reports on the rheological properties of poly(D,L-lactic-co-glycolic acid) polymers (PLGA) dispersions used to form films and of the implants prepared by compression of SPf66 antimalaric peptide between several films, before application and during drug release. 25% PLGA (M(w)=48,000Da) dispersions in dichloromethane showed viscous Newtonian behaviour, being easy flowing and adaptable to the moulds. Evolution of viscoelastic properties, polymer molecular weight, and SPf66 release pattern from the implants immersed in various media was evaluated. Oscillatory shear test showed that freshly prepared implants have an elastic modulus, G', greater than the viscous modulus, G", being both practically independent of angular frequency. After 6 weeks immersion in a pH 7.4 phosphate buffer, G' and G" increased in almost one order of magnitude, despite of a significant polymer degradation. Polymer molecular weight decreased slowly during the first 10 days of immersion (a similar pattern was obtained at pHs 2 and 7.4) and then the degradation process accelerated (degradation index on day 7 equals to 0.89, and on day 14 equals to 16.5). SPf66 release profile followed a pattern similar to that of the polymer degradation index. These observations are explained in terms of changes in polymer structure and conformation that happen in the implant.

Influence of cationic cellulose structure on its interactions with sodium dodecylsulfate: implications on the properties of the aqueous dispersions and hydrogels

The interactions of sodium dodecylsulfate (SDS) with the aqueous dispersions and the chemically cross-linked hydrogels of two cationic hydroxyethylcelluloses, polyquaternium-4 (PQ-4) and polyquaternium-10 (PQ-10), commonly used in cosmetics and in topical drug delivery devices, were analyzed. This surfactant was chosen not only for its interest as excipient, but also as a model of the amphiphilic behavior shown by many drugs. In aqueous dispersions, the interaction process was studied through transmittance, surface tension, fluorescence, microcalorimetry titration, viscosity and oscillatory rheometry measurements. The ammonium/sulfate groups ratios at the critical aggregation concentration (0.05% SDS) were 2.61 for PQ-4 and 4.02 for PQ-10; while at the saturation concentration (0.25% SDS), these ratios decreased to 0.52 and 0.80, respectively. The binding process, through ionic and hydrophobic interactions, was strongly exothermic in both water and aqueous NaCl 0.9% solution, which indicates that the salt did not modify the interaction. PQ-4/SDS dispersions had, for all SDS concentrations, higher viscous (G") and, especially, elastic (G') moduli than the polymer solution. The maxima in G' and G" (four orders of magnitude greater than PQ-4 only solutions) were observed at the SDS concentrations in which the ammonium/sulfate groups ratio is close to 1. PQ-10/SDS dispersions behaved very differently and, near the neutralization point, the precipitation of the system caused G" to decrease abruptly, and G' to disappear. The contrasting behavior of the two cationic celluloses may be attributed to their structural differences; PQ-4 has less ammonium groups, in small chains grafted to the cellulose backbone, and more free hydroxyethyl substituents than PQ-10. Therefore, although the neutralization of charges causes the formation of a neutral polyampholyte, the presence of the free hydrophilic hydroxyethyl groups in PQ-4 avoids the precipitation of the aggregates and contributes to the establishment of a three-dimensional network. In contrast, in PQ-10, the ammonium groups are directly bonded to the hydroxyethyl substituents and, in the aggregation process, they may be included in the polyampholyte complex, contributing to the precipitation. This different behavior was easily seen in the surfactant-induced shrinking of the hydrogels around the charges neutralization. Although the SDS binding isotherms were very similar, PQ-10 hydrogels decreased their volume up to 20 times at the neutralization point, while PQ-4 hydrogels reduced their initial volume only three times under the same conditions. These results suggest that the phase transitions of the hydrogels may be used as quick predictors of the behavior of the polymer dispersions.

Poly(acrylic acid) microgels (carbopol 934)/surfactant interactions in aqueous media. Part I: nonionic surfactants

The interaction between Tween 80 and Pluronic F-127 with carbopol in water was studied as a function of surfactant concentration. 0.25% carbopol microgels dispersions showed a continuous decrease in transmittance, viscosity and conductivity when surfactant concentration ranged from 0.01-0.02% to 0.50% Tween 80 or from 0.03-0.06% to 0.30% Pluronic F-127. These limit values can be considered as the critical association concentration and the saturation binding concentration, respectively. In this concentration range, a strong rise in pH (from 3.18 to 3.50) suggested that surfactant-polymer binding occurred mainly through a stoichiometric hydrogen-bonding interaction between the oxyethylene and carboxylic groups. In the presence of carbopol, the concentration of Tween 80 at the air/water interface decreases as the surfactant is adsorbed onto the polymer and drawn into the bulk solution. In contrast, the interaction with the polymer seems to change the conformation of the expanded chains of Pluronic F-127, making it easier for more molecules of surfactant to be at the interface and increasing the thickness of the interfacial surfactant layer. Fluorescence probes indicated that the carbopol network presents a more apolar medium than pure water, and the differences in the hydrophile-lipophile balance (HLB) of each surfactant were responsible for the lower I(I)/I(III) values obtained with Tween 80/carbopol systems. Microcalorimetry titration data made it possible to conclude that Tween 80/carbopol interaction, at 298K, is an enthalpy-driven process due to stabilization of Tween 80 units inside the polymer network. In contrast, Pluronic F-127/carbopol association (endothermic process) occurs owing to a gain in entropy when polymer-surfactant interaction allows the restoration of free water hydrogen-bonding structure, resembling the micellization process.

Poly(acrylic acid) microgels (carbopol 934)/surfactant interactions in aqueous media. Part II: Ionic surfactants

The interaction of sodium dodecylsulfate (SDS) or benzalkonium chloride (BkCl) with carbopol microgels (0.25% (w/w)) in water was studied through pH, trasmittance, viscosity, surface tension, conductivity, fluorescence, oil solubilization, and microcalorimetry measurements. In the case of the anionic surfactant, enthalpy-driven hydrophobic absorption of SDS into carbopol microgels began when SDS concentration reached 0.05-0.08% and ended around 0.6%. These concentrations were estimated as the critical aggregation (cac) and saturation binding concentration, respectively. The hydrophobic absorption of the surfactant accompanied by its counter-ion caused carbopol microgels to swell and promoted the occurrence of bridges among several carbopol microgels. As a consequence, the consistency of the dispersions increased significantly. Above binding saturation, further addition of SDS produced a shielding effect among the anionic charges of carbopol and its dehydration, which was shown as a decrease in the viscosity of the dispersions. At low shear rates, the dispersions behaved as pseudoplastic owing to orientation of carbopol/SDS aggregates in the flow direction. Increasing shear rates caused the inter-microgel bridges to break, the water layer surrounding them to diminish, and the system to show a shear-thickening behavior. In contrast, carbopol/BkCl aggregates showed shear-thickening flow in the whole range of shear rates analyzed. Electrostatic interactions between BkCl and carbopol carboxylic groups release protons to the medium and decrease the internal osmotic pressure of the microgels. This may favor the establishment of hydrophobic interactions among surfactant tails, and induces carbopol microgels to collapse. The cac was approximately 0.01% BkCl. Saturation binding occurred at 0.3-0.5%, indicating that only 25-40mol% carboxylic groups were neutralized with BkCl. The shrinking of carbopol microgels as BkCl is absorbed prevents additional surfactant molecules from interacting with the remaining carboxylic groups. Microcalorimetry assays revealed that the aggregation process occurred with a strong gain in enthalpy.

Effect of microcrystalline cellulose grade and process variables on pellets prepared by extrusion-spheronization

This study evaluated the effects of spheronizer load and speed on the size, circularity, microporosity, compressibility, and friability of pellets prepared by extrusion-spheronization of wet microcrystalline cellulose (MCC) masses with a water content shown by mixer torque rheometry to ensure maximum consistency. Two MCC grades with different mean particle size were used. Both gave pellets with good particle size, sphericity, and compressibility, under a wide range of spheronization conditions. Modification of pellet properties of interest (including size and porosity) was possible by adjustment of spheronization conditions and MCC grade; in particular, pellet porosity was greater with MCC of larger particle size.

Rheological evaluation of the interactions between cationic celluloses and Carbopol 974P in water

This paper reports on the influence of the structural properties of two cationic hydroxyethylecelluloses, polyquaternium-4 (PQ-4; 1.13-1.27% N) and polyquaternium-10 (PQ-10; 1.88-1.95% N), on the rheological behavior of their dispersions and of the dispersions of their blends with Carbopol 974P (60.9% COOH) in water. Dynamic shear oscillation measurements showed that the rheological behavior of 1 and 2% (w/w) cellulose polymers was mainly viscous. Flow curves of PQ-10 dispersions presented a higher consistency and pseudoplasticity than PQ-4 dispersions, in which the thixotropy was higher. Structural features, such as type and distribution of substituents and molecular weight, explain why they behave different. The presence of 0.00125-0.02% Carbopol in diluted cationic cellulose (0.01-0.08%) dispersions produced an important decrease in viscosity, due to a strong associative process via an electrostatic interaction phenomenon. Similar results were obtained when sodium acetate was added instead of Carbopol. In contrast, in the concentrated range (1% cellulose polymer), the viscous (G") and especially the elastic (G') moduli of the dispersions increased monotonically with Carbopol concentration (0.010-0.125%) and became physical gels, except in the proximity of the neutralization of the ammonium groups (0.07% Carbopol for PQ-4, and 0.1% Carbopol for PQ-10) in which G" and G' decreased. The concentrated dispersions showed pH-sensitivity when the Carbopol added was around or above the neutralization point. In dispersions with this composition, consistency increased dramatically when pH changed from 4.5 to 7.4. This property can open a wide range of applications, especially in the pharmaceutical field to prepare gelling in situ systems.

Incorporation of small quantities of surfactants as a way to improve the rheological and diffusional behavior of carbopol gels

This paper analyzes the effects of Tween 80, Pluronic F-127, sodium dodecylsulfate (SDS), and benzalkonium chloride on the macro and microviscosity of Carbopol 934NF (0.25-0.50 g/dl) pharmaceutical gels. Carbopol/surfactant interactions, which were reflected in changes in the intrinsic viscosity of the polymer and in shifts of IR spectra bands of films, considerably modified the rheological properties of the gel (flow and oscillatory rheometry) and the diffusion coefficients of polystyrene particles (dynamic light scattering, DLS). At pH 4, any surfactant at a concentration of 0.01 g/dl promoted interpolymer connections producing an open three-dimensional network with maximum viscous and elastic moduli, which does not disturb the diffusive movement of polystyrene particles. An increase in non-ionic surfactant (0.05-0.50 g/dl) gradually decreased viscosity and elasticity since there were more surfactant molecules to surround each carbopol particle, forming intrapolymeric micelles and breaking the interpolymer connections. This macroscopic effect is, however, not reflected in a decrease but in an increase in microviscosity (estimated by DLS) owing to the formation of larger carbopol/surfactant aggregates and free micelles that contribute significantly to the obstruction of the diffusional path. Both ionic surfactants decreased macroviscosity owing to ionic aggregation (benzalkonium chloride) or increase in ionic strength (mainly SDS), while the repercussion on the diffusion of polystyrene particles was dramatically different, and was hindered (due to the carbopol/surfactant aggregates) or enhanced (due to the shrinking of carbopol microgels), respectively. At pH 7.4, the ionization of the carboxylic groups produced an expansion of the polymer chains accompanied by a huge increase in viscosity and elasticity and a decrease in diffusion coefficients in comparison with those obtained at pH 4. The effects of the surfactants were similar to those observed at pH 4 but less intense. Chloramphenicol release studies (Franz-Chien cells) revealed that 0.01 g/dl surfactant did not affect the diffusion while a change in pH dramatically altered the process. The results show that by choosing the appropriate proportion of the most suitable surfactant, it is possible to modulate the flow behavior, elastic properties, and diffusional microenvironment of carbopol gels, without losing the pH-dependent gelling ability, which could improve the suitability of carbopol gels for drug delivery through different routes.

Extrusion-Spheronization of blends of carbopol 934 and microcrystalline cellulose

We evaluated the effects of several process variables on the pharmaceutical and drug release properties of extrusion-spheronization pellets of blends of Carbopol 934 and microcrystalline cellulose (MCC) containing a high proportion of Carbopol. The model drug was theophylline. Rheological monitoring during mixing was by mixer torque rheometry. Carbopol:MCC blends wetted with a CaCl2 solution showed different rheological behavior compared to blends with a high proportion of MCC wetted with water only. In contrast to previous suggestions, the optimal wetting point for extrusion did not coincide with the point of peak torque, but occurred just beyond this point, at much lower torque. The influence of process variables on blend properties was investigated with a three-variable factorial design (Carbopol:MCC ratio, wetting liquid proportion, CaCl2:Carbopol ratio), and the influence of process variables on pellet properties with a four-variable design (the variables listed plus extrusion screen hole diameter). Blend torque values were strongly influenced by CaCl2 proportion, while mean pellet diameter was influenced by Carbopol:MCC ratio. Mean pellet diameter also differed depending on whether the pellets contained theophylline. The observed among-formulation differences in theophylline release kinetics were largely explained by differences in pellet size and theophylline hydration state. Compaction of pellets to form tablets markedly modified the drug release profile, making it biphasic.

Interactions between hydroxypropylcelluloses and vapour/liquid water

Understanding of the uptake of water vapour or liquid water by cellulose-based polymers is important because of the influence of these processes on many of the biologically or technologically relevant properties of these polymers. In this work we studied these processes in the cases of twelve hydroxypropylcelluloses with low or medium-high degrees of substitution (L-HPCs and HPCs, respectively), characterization of which showed significant differences in structural and physical parameters (substitution pattern, crystallinity, particle size, specific surface area, and intraparticular porosity). Water vapour sorption-desorption isotherms determined to characterize the uptake of water vapour were fitted well by the Young-Nelson model, the optimized parameters of which indicated that at all relative humidities the capacity to bind water vapour as a surface monolayer is greater for HPCs than L-HPCs, but the capacity to absorb water vapour internally is greater for L-HPCs than HPCs. Guggenheim-Anderson-deBoer (GAB) models fitted the sorption-desorption isotherms less well. Differential scanning calorimetry (DSC) experiments showed all sorbed water vapour to be held as non-freezing water. Isoperibol microcalorimetry experiments carried out to investigate interactions with liquid water showed enthalpies of hydration/dissolution of between -62.86 and -71.35 J g(-1) for L-HPCs and between -82.95 and -99.80 J g(-1) for HPCs, and DSC showed average numbers of non-freezing water molecules per polymer repeat unit of 2.65-4.19 for L-HPCs and 18.10-22.42 for HPCs. DSC characterization of the kinetics of the water uptake by 10 mg compacts obtained by direct compression of hydroxypropylcelluloses showed faster uptake by L-HPC compacts than by HPC compacts, among which there were significant differences in capacity for diffusive uptake. The explanations of the above differences in terms of the different substituent contents, particle sizes and porosities of the HPCs is supported by multiple linear regression analyses.

Interactions between liposomes and hydroxypropylmethylcellulose

The characteristics of the adsorption process of hydroxypropylmethylcellulose (HPMC) of molecular weight 35400 Da and nominal viscosity 100 cps onto liposomes prepared with different egg lecithin-cholesterol molar ratios were examined. Adsorption isotherms were constructed and analysed to investigate the mechanisms implicated in the incorporation of the polymer to the interface. Only the isotherms obtained with cholesterol-free liposomes were fitted with Langmuir model. When cholesterol is present in the composition they present a sigmoidal slope. The mechanism of adsorption depends on liposome composition being the main force that drives polymer adsorption of hydrophobic nature. The apparent volumes of HPMC indicate that the conformation of the adsorbed macromolecules depends on liposome composition. Hydration enthalpy values show that adsorbed polymers do not give more hydrophilic systems after freeze-drying as expected with the hydrophilic characteristics of the HPMC.

A comparison of cellactose with two ad hoc processed lactose-cellulose blends as direct compression excipients

Three processed lactose-cellulose blends of similar composition, particle size and true density were compared as direct compression excipients: one was prepared by dry granulation, one by extrusion-spheronization, and the commercial product Cellactose. Differences among their flow properties depended solely on their different sphericities. Unlike those of the other blends, Cellactose particles exhibited numerous macropores. The mean yield pressures of all three blends were similar to those of direct compression lactoses. Cellactose tablets prepared at a punch pressure that largely eliminated macropores (pores >1 microm) had better mechanical properties but much poorer disintegration than tablets of the other blends prepared at the same punch pressure. However, the tensile strength and disintegration time of Cellactose tablets both fell rapidly as macropore volume was increased by reducing punch pressure, while the enthalpy of wetting/dissolution rose. The strength and water-resistance of well-compacted Cellactose tablets is attributed to the spatial distribution of lactose and cellulose in Cellactose particles, rather than to beta-lactose content or extra-particular structural features.

Evaluation of low-substituted hydroxypropylcelluloses (L-HPCs) as filler-binders for direct compression

The aims of this study were to assess the potential value of low-substituted hydroxypropylcelluloses (L-HPCs) as excipients of direct compression, and to investigate relationships between the chemical and physical properties of the polymers and (a) the powder rheological behavior and (b) drug release profiles from direct compressed tablets elaborated with (1:1) theophylline:L-HPC mixtures. Experiments were performed with five L-HPC varieties of different nominal particle sizes and degree of substitution. The products were characterized with regard to the moisture content, density, IR and Raman spectroscopy, hydroxypropyloxy content, heat of hydration, particle size, specific surface and porosity, and important differences were found in relation with all these properties. The differences in specific surface principally determine the flow and compaction properties of the powders, and the mechanical and microstructural properties of the tablets. The control of the hydroxypropyloxy content and the particle size of the L-HPCs allow the theophylline release profile to be regulated.

The stability of theophylline tablets with a hydroxypropylcellulose matrix

The behavior of 40:60 anhydrous theophylline/hydroxypropylcellulose (HPC) direct compression tablets obtained using a variety of hydroxypropylcelluloses with low or medium-high degrees of substitution (L-HPCs and HPCs, respectively) was determined immediately following their preparation and after storage for 6 months at 20 degrees C and a relative humidity (RH) of either 70.4% or 93.9%. The lower relative humidity did not bring about hydration of the active principle in any formulation, but the higher relative humidity totally hydrated the drug in all except one L-HPC formulation, in which hydration remained incomplete. Both relative humidities caused significant tablet swelling, with L-HPC formulations being more affected than HPC formulations. Drug release was slowed by hydration of the active principle, but accelerated with tablet swelling. The lower relative humidity caused significant alteration of drug release characteristics in only two L-HPC formulations, release from which was accelerated, while the higher relative humidities only failed to cause such alterations in two HPC formulations, with release from all except one of the others slowed (in the exceptional formulation, which exhibited incompletely hydrated theophylline and the greatest swelling of all, release was accelerated).

Interfacial adsorption of polymers and surfactants: implications for the properties of disperse systems of pharmaceutical interest

This review considers basic aspects of the interfacial adsorption of polymers and surfactants, with particular reference to the relevance of these processes for the formulation of pharmaceutical disperse systems. First, we discuss different approaches to the interpretation of adsorption isotherms, paying particular attention to systems containing more than one adsorbate. Second, we consider the implications of adsorption for the properties of suspensions, emulsions, and colloidal systems, particularly as regards the use of polymers and surfactants for stabilizing disperse systems, for controlling flocculation, and for modifying the biopharmaceutical behavior of colloidal drug carriers. Finally, we present a number of representative examples of the importance of adsorption of macromolecules in pharmaceutical systems.

A comparison of gas-liquid chromatography, NMR spectroscopy and Raman spectroscopy for determination of the substituent content of general non-ionic cellulose ethers

This paper describes and compares three techniques that can be used to characterize the substituent content of hydroxypropylcellulose (HPC and L-HPC) and hydroxypropyl methylcellulose (HPMC): gas-liquid chromatography (GLC) with a BP1 column and FI detection, 13C-NMR spectroscopy of hydrolysed samples, and Raman spectroscopy. GLC and 13C-NMR spectroscopy both allow independent quantification of hydroxypropoxyl and methoxyl contents. 13C-NMR spectroscopy, though requiring lengthier sample preparation, has the advantage of also quantifying the degree of substitution at each substitutable glucopyranose hydroxyl. Raman spectroscopy may be useful for rapid approximate estimation of hydroxypropoxyl content.

Microviscosity of hydroxypropylcellulose gels as a basis for prediction of drug diffusion rates

This study investigated the influence of the rheological properties of hydroxypropylcellulose (HPC) gels on the in vitro release of theophylline included in the gel at 0.2 g/l. Experiments were performed with six HPC varieties (mean molecular weight between 5x105 and 1.2x106, nominal viscosity between 100 and 4000 mPa.s) at concentrations of 0-2% (w/w). Theophylline diffusion coefficients at 37 degrees C ranged from 3.5x10-7 to 1.1x10-3 cm2/min, and were in all cases markedly higher than those predicted on the basis of gel macroviscosity as determined by capillary viscometry. In general, the theophylline diffusion coefficient declined exponentially with HPC concentration; in the case of the lowest-molecular-weight HPC, however, the diffusion coefficient remained constant to HPC concentrations of up to 0.8%, probably because of the high entanglement concentration of the HPC. Gel microviscosities as determined by dynamic light scattering (DLS) with latex microspheres (162 nm diameter) were considerably lower than the macroviscosities determined by capillary viscometry, and similar to microviscosities estimated on the basis of theophylline diffusion. Nevertheless, macroviscosity was correlated with microviscosity, suggesting that it is of value for approximate estimates of rates of diffusion of theophylline from HPC gels.

Degradation of hydroxypropylcellulose by Rhizomucor: effects on release from theophylline-hydroxypropylcellulose tablets

The stability of several varieties of hydroxypropylcellulose was monitored during 3 years of storage (1) under the conditions recommended by manufacturers and official pharmacopoeias (simple storage in closed containers) and (2) at zero relative humidity. After 1 year, severe degradation of the varieties with lower initial pH and particle size stored at ambient relative humidity was shown by changes in their molecular weight and in the pH and apparent viscosity of 2% aqueous dispersions. Microbiological analyses showed the observed degradation to be attributable to the action of fungi of the genus Rhizomucor. The changes in apparent viscosity significantly affected the release of theophylline from direct compression tablets formulated with the degraded excipients.

Development of tablets for controlled joint release of nifedipine and atenolol

Oral combinations of nifedipine and atenolol are widely used in the treatment of hypertension, proving particularly effective when the atenolol is released immediately and the nifedipine is released in a sustained manner. This work examined the potential of combining nifedipine and atenolol in a tablet, which would be easier to manufacture than currently available combined formulations. The results indicated that a 40:60 (w/w) nifedipine-atenolol mixture forms a eutectic melting at 140 degrees C. Nevertheless, both drugs were stable when incorporated in tablets elaborated using cellulose ethers as base excipients. Tablets prepared from atenolol-lactose granules and solid dispersions of nifedipine-hydroxypropylmethylcellulose (100 cP) had more adequate dissolution profiles than a more complex reference formulation in hard capsules.