Interactions Between Colloidal Particles and Soluble Polymers

Preparation and characterization of fast dissolving pullulan films containing BCS class II drug nanoparticles for bioavailability enhancement

The aim of this study is to assess pullulan as a novel steric stabilizer during the wet-stirred media milling (WSMM) of griseofulvin, a model poorly water-soluble drug, and as a film-former in the preparation of strip films via casting-drying the wet-milled drug suspensions for dissolution and bioavailability enhancement. To this end, pullulan films, with xanthan gum (XG) as thickening agent and glycerin as plasticizer, were loaded with griseofulvin nanoparticles prepared by WSMM using pullulan in combination with sodium dodecyl sulfate (SDS) as an ionic stabilizer. The effects of drug loading and milling time on the particle size and suspension stability were investigated, as well as XG concentration and casting thickness on film properties and dissolution rate. The nanosuspensions prepared with pullulan-SDS combination were relatively stable over 7 days; hence, this combination was used for the film preparation. All pullulan-based strip films exhibited excellent content uniformity (most <3% RSD) despite containing only 0.3-1.3 mg drug, which was ensured by the use of precursor suspensions with >5000 cP viscosity. USP IV dissolution tests revealed fast/immediate drug release (t80 < 30 min) from films <120 μm thick. Thinner films, films with lower XG loading, or smaller drug particles led to faster drug dissolution, while drug loading had no discernible effect. Overall, these results suggest that pullulan may serve as an acceptable stabilizer for media milling in combination with surfactant as well as a fast-dissolving film former for the fast release of poorly water-soluble drug nanoparticles.

Preparation and pharmacodynamic assessment of ezetimibe nanocrystals: Effect of P-gp inhibitory stabilizer on particle size and oral absorption

Drug nanocrystals have been widely accepted as potent formulations to overcome poor solubility, dissolution and bioavailability problems of hydrophobic drugs. The present study aimed to develop drug nanocrystals of ezetimibe (Eze), a model BCS class II and hypocholesterolemic drug using bottom up precipitation methods. D-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS), and L-ascorbic acid-2-glucoside (AA2G), were the two stabilizers whose potential in developing Eze nanocrystals was investigated. Particle size and zeta potential portrayed the potential of both the stabilizers in producing Eze nanocrystals. The optimized nanocrystal formulations were evaluated for in-vitro solubility, dissolution, solid state characters and in-vivo pharmacodynamic performance. The nanocrystal formulations remarkably increased the solubility of the drug (p<0.05 compared to pure drug). Pure drug could not dissolve more than 28.9% during the 60 min dissolution study whereas the drug nanocrystals prepared with AA2G and TPGS presented t90% at 41.33 ± 2.58 and 16.07 ± 2.32 min, respectively. The PXRD and DSC studies confirmed the retention of crystallinity and the SEM images indicated lack of aggregation in dried nanocrystals. The TPGS nanocrystals presented significantly superior pharmacodynamic activity upon oral administration. The current study corroborated TPGS nanocrystals to be a promising choice of formulation for the oral delivery of Eze.

D-Alpha-tocopherol acid polyethylene glycol 1000 succinate, an effective stabilizer during solidification transformation of baicalin nanosuspensions

Baicalin nanosuspensions, stabilized with 10% TPGS (relative to the weight of baicalin), were transformed into nanosuspensions powders by solidification process. Solidification methods for this transformation included freeze-drying, spray drying or vacuum drying. High pressure homogenization was applied for production of baicalin nanosuspensions used TPGS, SDS, P188, HPMC and MC as stabilizer, respectively. The influence of the different solidification transformation methods on the redispersibility of solid drug nanosuspensions was systemically investigated, such as freeze-drying, spray drying and vacuum drying. Each method was applied with three grades of process stresses called as "conservative", "moderate" and "aggressive" conditions, and the redispersibility index (RDI) of nanosuspensions stabilized by stabilizers (such as TPGS, SDS, P188, HPMC and MC) during those process was investigated. The results showed that there was significant difference in RDI of nanosuspensions after solidification process. The RDI(a) (1.09, 1.01, 1.05, 0.99), RDI(b) (1.03, 0.99, 1.06, 1.02) and RDI(c) (1.01, 1.01, 1.09, 1.08) of nanosuspensions stabilized by TPGS were more small during different solidification process, compared with those of nanosuspensions stabilized by other stabilizer. It was concluded that the baicalin nanosuspensions were subjected to agglomeration or crystal growth during solidification transformation, especially at high aggressive stress conditions. Meanwhile, compared to other stabilizer, the TPGS was more effective for stability of baicalin nanosuspensions, which could exhibit higher affinity to the drug crystal and stronger surface adsorption at different solidification stresses.

Microwave-generated bionanocomposites for solubility and dissolution enhancement of poorly water-soluble drug glipizide: in-vitro and in-vivo studies

Objectives

In oral absorption of a drug, the drug first dissolves and then is absorbed by diffusion through gastrointestinal membranes. The gastrointestinal environment is aqueous in nature and it is well-known that one-third of the drug population is water insoluble. Hence, there is a need for enhancement of the solubility and dissolution of such drugs. In this work, enhancement of the solubility and dissolution of the practically insoluble drug glipizide was achieved by formation of bionanocomposites (BNCs) using microwave-induced diffusion (MIND), which ultimately leads to bioavailability enhancement.

Methods

BNCs were formed by using natural carriers such as gelatin, acacia, cassia and ghatti gum, with the help of microwaves. Selection of carriers was based on their surfactant and wetting properties. Solubility studies were carried out to establish the solubility-enhancing property of the BNCs. To support solubility analysis results, dissolution studies (i.e. powder dissolution and in-vitro dissolution) were carried out. The BNCs were characterized by Fourier transform infra-red spectroscopy, differential scanning calorimetry, X-ray diffraction studies, scanning electron microscopy and transmission electron microscopy. In-vivo performance of the optimised formulation was assessed by glucose-induced hyperglycaemia test in male albino Wistar rats.

Key findings

It was found that as the concentration of polymer in the composite increased the solubility and dissolution of glipizide were enhanced. The optimised ratio (drug : polymer) for all the composites was found to be 1:9. In the glucose-induced hyperglycemia test in rats, the optimized formulation demonstrated a significant reduction in hyperglycemia compared with a marketed formulation, Glynase.

Conclusions

The novelty of this work is the green and cost-effective way of forming drug nanocomposites with the help of microwave, which can be scaled up to an industrial level. The method gives an immaculate means of solubilisation by generating drug dispersion at the micro and nanoscale level in natural biodegradable stabilising media. Hence, this study demonstrates the use of BNCs in solubility and dissolution enhancement.

Pharmaceutical nanocrystals by nanomilling: critical process parameters, particle fracturing and stabilization methods

OBJECTIVES

Wet milling is a common technique to produce drug nanocrystals. Stability of the nanocrystals is a critical question, and different kinds of stabilizers, e.g. polymers, celluloses, surfactants and lipids, have been tested for various drugs. Still, the question about how to select the best stabilizer to a certain drug material and also to a selected process is open.

KEY FINDINGS

Many different factors, such as surface energy, hydrophobicity, solubility, viscosity and functional groups, affect the stability of the formed nanosuspensions. Affinity of the stabilizer to the particle surfaces seems to be the most important parameter. This affinity is partly related to the surface energy and hydrophobicity of the surfaces and stabilizers.

SUMMARY

In this review the most important factors affecting nanocrystal formulation and efficacy of stabilizers are presented. In order to widen understanding of the milling process, the most important variables related to milling techniques and particle fracturing processes during the milling are briefly presented.

Effective polymeric dispersants for vacuum, convection and freeze drying of drug nanosuspensions

Drying nanosuspensions into redispersable powders is a critical issue in developing solid dosage forms of drug nanoparticles. The particle fusion and chain entanglement of polymeric steric stabilizers adsorbed onto the nanoparticle surface should be prevented to retain redispersibility after drying. Herein, we report that only a small amount of polymeric dispersants such as carrageenan, gelatin, and alginic acid between 0.5 and 3 wt.% in various drug nanosuspensions can provide sufficient redispersibility in vacuum, convection, and freeze drying. In vacuum and freeze drying of naproxen nanosuspensions, the addition of only 0.5 wt.% carrageenan resulted in the formation of redispersable nanoparticulate powders. The amounts of polymeric dispersants required for redispersibility was lowest for carrageenan and highest for gelatin. The specific interactions between the dispersants and steric stabilizers (or drugs), in addition to viscosity increase during drying, appeared to effectively prevent irreversible particle aggregation.

Hydrophilic and hydrophobic amino acid copolymers for nano-comminution of poorly soluble drugs

Nano-comminution has successfully brought nanoparticle formulations of poorly soluble drugs to our daily life. The key for the successful nano-comminution of a drug is the choice of a proper polymeric steric stabilizer. To systematically elucidate the rationale of stabilizer selection, two types of helical amino acid copolymers, relatively hydrophilic and hydrophobic copolymers, were used in nano-comminution. The hydrophilic copolymers had lysine as their major component. The addition of relatively hydrophobic leucine and phenylalanine to them could not make significant changes in particle size. However, when a small amount of hydrophilic glutamic acid or lysine was added into elastin-like hydrophobic copolymers of valine, glycine, and proline, significant composition dependence was found. Therefore, specific interactions between the functional groups of polymers and drug surfaces seem to be important for successful nano-comminution. The stimuli responsive behavior of the hydrophobic copolymer induced the temperature dependence of particle size.

Critical freezing rate in freeze drying nanocrystal dispersions

Recent advances in nanoparticle technologies have significantly enhanced the oral and parenteral delivery of poorly water-soluble active pharmaceutical ingredients (APIs). However, reports have been limited on the various drying procedures to convert a liquid nanocrystal dispersions into solid dosage forms. The solid dosage form should consist of nanocrystals that can readily reconstitute into their original size upon dissolution in water. Herein, the freeze drying process of nanocrystal dispersions was examined at varying freezing rates (speed of freezing interface). As freezing rate decreases, more particle-particle aggregation developed. A critical freezing rate, below which the dried nanocrystals cannot be re-dispersed, was identified based on the plot of the particle size of reconstituted nanocrystals versus freezing rate. Freeze drying at a freezing rate near the critical value produces dry powders of bimodal particle size distribution after re-dispersion. In addition, API concentration was found to significantly affect the critical freezing rate and therefore the re-dispersibility of dry powders. The concept of critical freezing rate is critical for the development of solid dosage forms of liquid nanocrystal dispersions.

Amphiphilic amino acid copolymers as stabilizers for the preparation of nanocrystal dispersion

The recent advance of particle size engineering in nanometer ranges has widened the formulation opportunities of relatively water-insoluble drugs. However, the 'nanoformulation' suffers from a lack of systematic understanding about the requirements of polymeric stabilizers. Furthermore, the polymers that can be used for the preparation of nanocrystals are so limited that finding a proper stabilizer for a given formulation is often difficult. In this study, amino acid copolymers whose properties can systematically be tailored are developed, and their morphological and compositional effects are investigated. Copolymers containing lysine (K) as their hydrophilic segments, and phenylalanine (F) or leucine (L) as their hydrophobic segments successfully produce stable nanocrystals (200-300 nm) in water, while copolymers of K and alanine (A) could not generate nanosized particles. Not the morphology but the hydrophobicity of copolymers seems to be a critical parameter in the preparation of drug nanocrystals by wet comminution. The effective stabilization performance of copolymers requires the hydrophobic moiety content to be higher than 15 mol%. Comminution for only 5 min is long enough for nanocrystal preparation, and the crystallinity of drug is found intact after the processing.

Microspheres for controlled release drug delivery

Controlled release drug delivery employs drug-encapsulating devices from which therapeutic agents may be released at controlled rates for long periods of time, ranging from days to months. Such systems offer numerous advantages over traditional methods of drug delivery, including tailoring of drug release rates, protection of fragile drugs and increased patient comfort and compliance. Polymeric microspheres are ideal vehicles for many controlled delivery applications due to their ability to encapsulate a variety of drugs, biocompatibility, high bioavailability and sustained drug release characteristics. Research discussed in this review is focused on improving large-scale manufacturing, maintaining drug stability and enhancing control of drug release rates. This paper describes methods of microparticle fabrication and the major factors controlling the release rates of encapsulated drugs. Furthermore, recent advances in the use of polymer microsphere-based systems for delivery of single-shot vaccines, plasmid DNA and therapeutic proteins are discussed, as well as some future directions of microsphere research.

Drug nano- and microparticles processed into solid dosage forms: physical properties

The use of nanoparticles of relatively insoluble drugs has enormously widened the window of achievable pharmacokinetic performance. For the successful development of this technology, it is essential to understand the characteristics of nanoparticles. In this study, the processability and solid dosage performance of nanoparticulates are compared with those of microparticulates. Nanoparticle suspensions are first prepared by wet comminution in the presence of stabilizers. Spray drying converts them into dried particles from which compacts are prepared. Nanoparticles easily form aggregates during spray drying. These aggregates can be slowly redispersed into nanoparticles in water. Compacts show differences in their internal structure and micromechanical deformations, according to the size of their primary particles. Stress to break and indentation hardness are found to be only slightly higher in nanoparticulate systems.

Rheological Behavior of Suspensions Flocculated by Weak Bridging of Polymer Coils

A polymer coil with weak affinity for the solid surface makes a flexible bridge between particles by reversible adsorption. When the coil size is comparable to particle diameter in solution, the suspensions flocculated by reversible bridging show shear-thickening flow in a narrow range of shear rates. The force generated by the rapid extension of bridges within the lifetime is responsible for the shear thickening. Although it is expected that the bridges become more flexible with increasing coil size, the polymers with high molecular weights do not necessarily give rise to shear thickening. The striking shear thickening is induced by polymers with molecular weights, Mw, of 2.5 x 10(5) and 4.5 x 10(5). The viscosity enhancement in the shear-thickening region is considerably suppressed for polymers with Mw = 7.5 x 10(5). From the sedimentation experiments, a large portion of the segments of a coil with Mw = 7.5 x 10(5) is adsorbed in train on the particle surface. The addition of small amounts of surfactant leads to an increase in the fraction of loops at the expense of trains and the bridges become more flexible. As a result, the flow of suspensions in the presence of surfactant becomes shear thickening. The rheology of suspensions flocculated by reversible bridging can be modified by a balance between loop and train fractions in a bridge. Copyright 1999 Academic Press.

Motion of a Colloidal Sphere Covered by a Layer of Adsorbed Polymers Normal to a Plane Surface

A combined analytical-numerical study is presented for the slow motion of a spherical particle coated with a layer of adsorbed polymers perpendicular to an infinite plane, which can be either a solid wall or a free surface. The Reynolds number is assumed to be vanishingly small, and the thickness of the surface polymer layer is assumed to be much smaller than the particle radius and the spacing between the particle and the plane boundary. A method of matched asymptotic expansions in a small parameter lambda incorporated with a boundary collocation technique is used to solve the creeping flow equations inside and outside the adsorbed polymer layer, where lambda is the ratio of the characteristic thickness of the polymer layer to the particle radius. The results for the hydrodynamic force exerted on the particle in a resistance problem and for the particle velocity in a mobility problem are expressed in terms of the effective hydrodynamic thickness (L) of the polymer layer, which is accurate to O(lambda2). The O(lambda) term for L normalized by its value in the absence of the plane boundary is found to be independent of the polymer segment distribution and the volume fraction of the segments. The O(lambda2) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant. Copyright 1999 Academic Press.