Influence of the Dispersion Medium and Cryoprotectants on the Physico-Chemical Features of Gliadin- and Zein-Based Nanoparticles

The evaluation of the physico-chemical features of nanocarriers is fundamental because the modulation of these parameters can influence their biological and in vivo fate. This work investigated the feasibility of saline, 5% w/v glucose and phosphate-buffered saline solution, as polar media for the development of nanoparticles made up of two vegetal proteins, zein from corn and gliadin from wheat, respectively. The physico-chemical features of the various systems were evaluated using dynamic and multiple light scattering techniques, and the results demonstrate that the 5% w/v glucose solution is a feasible medium to be used for their development. Moreover, the best formulations were characterized by the aforementioned techniques following the freeze-drying procedure. The aggregation of the zein nanoparticles prepared in water or glucose solution was prevented by using various cryoprotectants. Mannose confirmed its crucial role in the cryopreservation of the gliadin nanosystems prepared in both water and glucose solution. Sucrose and glucose emerged as additional useful excipients when they were added to gliadin nanoparticles prepared in a 5% glucose solution. Specifically, their protective effect was in the following order: mannose > sucrose > glucose. The results obtained when using specific aqueous media and cryoprotectants permitted us to develop stable zein or gliadin nanoparticles as suspension or freeze-dried formulations.

Lyophilization of Nanocapsules: Instability Sources, Formulation and Process Parameters

Polymeric nanocapsules have gained more and more interest in the medical sciences. Their core-shell structure offers numerous advantages, especially regarding their use as drug delivery systems. This review begins by presenting the different intrinsic sources of the instability of nanocapsules. The physical and chemical potential instabilities of nanocapsules reduce their shelf-life and constitute a barrier to their clinical use and to their commercialization. To overcome these issues, lyophilization is often used as a process of choice in the pharmaceutical industry especially when labile compounds are used. The state of the art of lyophilization nanocapsules is reviewed. The formulation properties and the process parameters are discussed for a complete understanding of their impact on the stability and storage of the final dried product. To assess the quality of the dried product, various characterization methods are also discussed.

Freeze-drying of nanoparticles: How to overcome colloidal instability by formulation and process optimization

Lyophilization of nanoparticle (NP) suspensions is a promising technology to improve stability, especially during long-term storage, and offers new routes of administration in solid state. Although considered as a gentle drying process, freeze-drying is also known to cause several stresses leading to physical instability, e.g. aggregation, fusion, or content leakage. NPs are heterogeneous regarding their physico-chemical properties which renders them different in their sensitivity to lyophilization stress and upon storage. But still basic concepts can be deducted. We summarize basic colloidal stabilization mechanisms of NPs in the liquid and the dried state. Furthermore, we give information about stresses occurring during the freezing and the drying step of lyophilization. Subsequently, we review the most commonly investigated NP types including lipophilic, polymeric, or vesicular NPs regarding their particle properties, stabilization mechanisms in the liquid state, and important freeze-drying process, formulation and storage strategies. Finally, practical advice is provided to facilitate purposeful formulation and process development to achieve NP lyophilizates with high colloidal stability.

Development and Characterization of Venetoclax Nanocrystals for Oral Bioavailability Enhancement

Venetoclax (VX) used in the treatment of chronic lymphocytic leukemia possesses low oral bioavailability (5.4%) and undergoes first-pass metabolism. Development of a formulation to overcome its bioavailability problem can be done by using nanocrystals which has many scientific applications. Nanocrystals of VX were formulated using amalgamation of precipitation and high-pressure homogenization method, in which polyvinyl alcohol (PVA) was selected as stabilizer. Process parameters like concentration of stabilizer, homogenization pressure, number of homogenization cycle, and concentration of lyoprotectant were optimized to obtain the desired particle size for the preparation of nanocrystal formulation. HPLC methods were developed and validated in-house for determination of in vitro dissolution data and in vivo bioavailability data. Physicochemical characterization was done to determine the particle size (zeta sizer), crystalline nature (DSC and XRPD), solubility (shaker bath), and dissolution (USP type 2 apparatus). Lyophilized VX nanocrystals of size less than 350 nm showed substantial increase in saturation solubility (~20 folds) and dissolution in comparison with free VX. In vitro release study revealed that 100% dissolution was achieved in 120 min as compared to VX free base which is having less than 43.5% dissolution in 120 min. Formulations of VX remain stable for 6 months under accelerated stability conditions. In vivo pharmacokinetic data in male Sprague-Dawley rats showed (~2.02 folds) significant increase in oral bioavailability of VX formulation as compared to free drug because of rapid dissolution and absorption which makes the nanocrystal formulation a better approach for oral administration of poorly soluble drugs.

Lyophilization stabilizes clinical-stage core-crosslinked polymeric micelles to overcome cold chain supply challenges

BACKGROUND

CriPec technology enables the generation of drug-entrapped biodegradable core-crosslinked polymeric micelles (CCPM) with high drug loading capacity, tailorable size, and drug release kinetics. Docetaxel (DTX)-entrapped CCPM, also referred to as CPC634, have demonstrated favorable pharmacokinetics, tolerability, and enhanced tumor uptake in patients. Clinical efficacy evaluation is ongoing. CPC634 is currently stored (shelf life > 5 years) and shipped as a frozen aqueous dispersion at temperatures below -60°C, in order to prevent premature release of DTX and hydrolysis of the core-crosslinks. Consequently, like other aqueous nanomedicine formulations, CPC634 relies on cold chain supply, which is unfavorable for commercialization. Lyophilization can help to bypass this issue.

METHODS AND RESULTS

Freeze-drying methodology for CCPM was developed by employing CPC634 as a model formulation, and sucrose and trehalose as cryoprotectants. We studied the residual moisture content and reconstitution behavior of the CPC634 freeze-dried cake, as well as the size, polydispersity index, morphology, drug retention, and release kinetics of reconstituted CPC634. Subsequently, the freeze-drying methodology was validated in an industrial setting, yielding a CPC634 freeze-dried cake with a moisture content of less than 0.1 wt%. It was found that trehalose-cryoprotected CPC634 could be rapidly reconstituted in less than 5 min at room temperature. Critical quality attributes such as size, morphology, drug retention, and release kinetics of trehalose-cryoprotected freeze-dried CPC634 upon reconstitution were identical to those of non-freeze-dried CPC634.

CONCLUSION

Our findings provide proof-of-concept for the lyophilization of drug-containing CCPM and our methodology is readily translatable to large-scale manufacturing for future commercialization.

Freeze-Drying of Pharmaceutical and Nutraceutical Nanoparticles: The Effects of Formulation and Technique Parameters on Nanoparticles Characteristics

Nanoparticles (NPs) are of the most interesting novel vehicles for effective drug delivery to humans. Freeze drying is known as an engaging process to improve the long lasting stability of NPs formulations. This study aims to elucidate the importance of various parameters involving in freeze-drying of the most common pharmaceutical/nutraceutical NPs including nanosuspensions, nanocrystals (NCs), cocrystals/nanococrystals, nanoemulsions (NEs), nanocapsules (NCPs) and nanospheres (NSPs). Regarding this, the therapeutic goals of NPs and specifications of drug must be considered. According to our survey, the most influential factors for achieving optimum results include type and concentration of cryoprotectant/lyoprotectant, stabilizer structure and concentration, the NPs concentration in solution, freezing, annealing, and drying rate, the interaction between protectants and stabilizer, solvent type and antisolvent to solvent ratio. The study shows that for each class of NPs, specific variables are of highest significance and should be optimized. For instance, about NCs, freezing rate and antisolvent/solvent ratio should be particularly considered and for emulsified NPs, the best results have been obtained by 5-20% of saccharides as cryoprotectants. These findings suggest that to obtain a product with the lowest aggregation and particle size (PS), optimization of the effective factors in formulation and lyophilization process are essential.

Formation of nanosuspensions in bottom-up approach: theories and optimization

BACKGROUND

Nanosuspensions, liquid dispersions with nanometer size distribution, are becoming trendy in pharmaceutical practice to formulate poorly water-soluble drugs and to enhance their bioavailability. Generally, nanosuspensions are produced in two main approaches; top-down or bottom-up. The former is based on size-reduction of large particles via milling or high pressure homogenization. The latter is focused on the mechanisms of nucleation and particle growth.

METHODS

In this review, the critical factors influencing the kinetics or dynamics of nucleation and growth are discussed. Subsequently, the mechanisms of nanosuspension instability as well as strategies for stabilization are elaborated. Furthermore, the effects of stabilizers on key parameters of instability as well as the process of choosing an appropriate stabilizer is discussed.

RESULTS

Steric and electrostatic stabilizations or combination of them is essential for nanosuspensions formulation to prevent coagulation. Accordingly, some characteristics of stabilizers play critical role on stability and optimization of nanosuspensions; i.e., HLB and concentration. Nevertheless, after reviewing various articles, it is ascertained that each formulation requires individual selection of surfactants according to the parameters of the particle surface and the medium.

CONCLUSIONS

Based on the results, application of excipients such as stabilizers requires proper optimization of type and concentration. This implies that each formulation requires its own optimization process. Graphical Abstract ᅟ.

Redispersible spray-dried lipid-core nanocapsules intended for oral delivery: the influence of the particle number on redispersibility

This study proposes a new approach to produce easily redispersible spray-dried lipid-core nanocapsules (LNC) intended for oral administration, evaluating the influence of the particle number density of the fed sample. The proposed approach to develop redispersible spray-dried LNC formulations intended for oral route is innovative, evidencing the needing of an optimization of the initial particle number density in the liquid suspension of nanocapsules. A mixture of maltodextrin and L-leucine (90:10 w/w) was used as drying adjuvant. Dynamic light scattering, turbidimetry, determination of surface area and pore size distribution, electron microscopy and confocal Raman microscopy (CRM) were used to characterize the proposed system and to better understand the differences in the redispersion behavior. An easily aqueous redispersion of the spray-dried powder composed of maltodextrin and L-leucine (90:10 w/w) was obtained, depending on the particle number density. Their surface area decreased in the presence of LNC. CRM enabled the visualization of the spatial distribution of the different compounds in the powders affording to better understand the influence of the particle number density of the fed sample on their redispersion behavior. This study shows the need for optimizing initial particle number density in the liquid formulation to develop redispersible spray-dried LNC powders.

Facts and evidences on the lyophilization of polymeric nanoparticles for drug delivery

Lyophilization has been used to improve the long-term stability of polymeric nanoparticles for drug delivery applications, avoiding their instability in suspension. However, this dehydration process may induce stresses to nanoparticles, mitigated by the use of some excipients such as cryo- and lyoprotectants. Still, the lyophilization of polymeric nanoparticles is frequently based in empirical principles, without considering the physical-chemical properties of formulations and the engineering principles of lyophilization. Therefore, the optimization of formulations and the lyophilization cycle is crucial to obtain a good lyophilizate, and guarantee the preservation of nanoparticle stability. The proper characterization of the lyophilizate and nanoparticles has a great importance in achieving these purposes. This review updates the fundaments involved in the optimization procedures for lyophilization of polymeric nanoparticles, with the aim of obtaining the maximum stability of formulations. Different characterization methods to obtain and guarantee a good lyophilized product are also discussed. A special focus is given to encapsulated therapeutic proteins. Overall, this review is a contribution for the understanding of the parameters involved in the lyophilization of polymeric nanoparticles. This may definitely help future works to obtain lyophilized nanoparticles with good quality and with improved therapeutic benefits.

Surface-stabilized lopinavir nanoparticles enhance oral bioavailability without coadministration of ritonavir

Aim: The aim of the present study was to prepare surface-stabilized nanoparticles (NPs) for oral bioavailability enhancement of lopinavir (LPN), a Biopharmaceutics Classification System class II antiretroviral drug that possesses low oral bioavailability due to its poor aqueous solubility and extensive metabolism by liver microsomal enzymes. Materials & methods: Surfactant-stabilized LPN-NPs were prepared by combination of antisolvent precipitation and high-pressure homogenization techniques using polyvinyl alcohol as a suitable stabilizer. LPN-NPs were freeze dried by a universal stepwise freeze-drying cycle using mannitol as the cryoprotectant. Pharmacokinetics after oral administration of LPN-NPs were evaluated in male Sprague–Dawley rats and were compared with free LPN coadministered with ritonavir (conventional formulation). Results & conclusion: Freeze-dried stabilized LPN-NPs possessed particle sizes of approximately 320 nm and a narrow particle size distribution (polydispersity index <0.2). The surface-stabilized LPN-NPs (without ritonavir) demonstrated a 3.11-fold enhancement in bioavailability in comparison to free LPN with ritonavir (conventional formulation).

Original submitted 26 March 2012; Revised submitted 14 September 2012; Published online 25 January 2013

Nanoparticle-based topical ophthalmic formulations for sustained celecoxib release

Celecoxib-loaded NPs were prepared from biodegradable polymers such as poly-ε-caprolactone (PCL), poly(L-lactide) (PLA), and poly(D,L-lactide-co-glycolide) (PLGA) by spontaneous emulsification solvent diffusion method. Different concentrations of polymers, emulsifier, and cosurfactants were used for formulation optimization. Nanoparticles (NPs) were characterized regarding their particle size, PDI, zeta potential, shape, morphology, and drug content. Celecoxib-loaded NPs were incorporated into eye drops, in situ gelling system, and gel and characterized regarding their pH, viscosity, uniformity of drug content, in vitro release, and cytotoxicity. The results of optimized celecoxib-loaded PCL-, PLGA-, and PLA-NPs, respectively, are particle size 119 ± 4, 126.67 ± 7.08, and 135.33 ± 4.15 nm; zeta potential -22.43 ± 2.91, -25.46 ± 2.35, and -31.81 ± 2.54 mV; and encapsulation efficiency 93.44 ± 3.6%, 86.00 ± 1.67%, and 79.04 ± 2.6%. TEM analyses revealed that NPs have spherical shapes with dense core and distinct coat. Formulations possessed uniform drug content with pH and viscosity compatible with the eye. Formulations showed sustained release without any burst effect with the Higuchi non-fickian diffusion mechanism. Cytotoxicity studies revealed that all formulations are nontoxic. Our formulations provide a great deal of flexibility to formulation scientist whereby sizes and zeta potentials of our NPs can be tuned to suit the need using scalable and robust methodologies. These formulations can thus serve as a potential drug delivery system for both anterior and posterior eye diseases.

Controlling drug nanoparticle formation by rapid precipitation

Nanoparticles are a drug delivery platform that can enhance the efficacy of active pharmaceutical ingredients, including poorly-water soluble compounds, ionic drugs, proteins, peptides, siRNA and DNA therapeutics. To realize the potential of these nano-sized carriers, manufacturing processes must be capable of providing reproducible, scalable and stable formulations. Antisolvent precipitation to form drug nanoparticles has been demonstrated as one such robust and scalable process. This review discusses the nucleation and growth of organic nanoparticles at high supersaturation. We present process considerations for controlling supersaturations as well as physical and chemical routes for modifying API solubility to optimize supersaturation and control particle size. We conclude with a discussion of post-precipitation factors which influence nanoparticle stability and efficacy in vivo and techniques for stabilization.

Modified nanoprecipitation method for preparation of cytarabine-loaded PLGA nanoparticles

The present investigation was aimed at developing cytarabine-loaded poly(lactide-coglycolide) (PLGA)-based biodegradable nanoparticles by a modified nanoprecipitation which would have sustained release of the drug. Nine batches were prepared as per 3(2) factorial design to optimize volume of the co-solvent (0.22-0.37 ml) and volume of non-solvent (1.7-3.0 ml). A second 3(2) factorial design was used for optimization of drug: polymer ratio (1:5) and stirring time (30 min) based on the two responses, mean particle size (125 ± 2.5 nm), and percentage entrapment efficiency (21.8 ± 2.0%) of the Cyt-PLGA nanoparticles. Optimized formulation showed a zeta potential of -29.7 mV indicating good stability; 50% w/w of sucrose in Cyt-PLGA NP was added successfully as cryoprotectant during lyophilization for freeze-dried NPs and showed good dispersibility with minimum increase in their mean particle sizes. The DSC thermograms concluded that in the prepared PLGA NP, the drug was present in the amorphous phase and may have been homogeneously dispersed in the PLGA matrix. In vitro drug release from the pure drug was complete within 2 h, but was sustained up to 24 h from PLGA nanoparticles with Fickian diffusion. Stability studies showed that the developed PLGA NPs should be stored in the freeze-dried state at 2-8°C where they would remain stable in terms of both mean particle size and drug content for 2 months.

Freeze thaw: a simple approach for prediction of optimal cryoprotectant for freeze drying

The present study evaluates freeze thaw as a simple approach for screening the most appropriate cryoprotectant. Freeze-thaw study is based on the principle that an excipient, which protects nanoparticles during the first step of freezing, is likely to be an effective cryoprotectant. Nanoparticles of rifampicin with high entrapment efficiency were prepared by the emulsion-solvent diffusion method using dioctyl sodium sulfosuccinate (AOT) as complexing agent and Gantrez AN-119 as polymer. Freeze-thaw study was carried out using trehalose and fructose as cryoprotectants. The concentration of cryoprotectant, concentration of nanoparticles in the dispersion, and the freezing temperature were varied during the freeze-thaw study. Cryoprotection increased with increase in cryoprotectant concentration. Further, trehalose was superior to fructose at equivalent concentrations and moreover permitted use of more concentrated nanosuspensions for freeze drying. Freezing temperature did not influence the freeze-thaw study. Freeze-dried nanoparticles revealed good redispersibility with a size increase that correlated well with the freeze-thaw study at 20% w/v trehalose and fructose. Transmission electron microscopy revealed round particles with a size approximately 400 nm, which correlated with photon correlation spectroscopic measurements. Differential scanning calorimetry and X-ray diffraction suggested amorphization of rifampicin. Fourier transfer infrared spectroscopy could not confirm interaction of drug with AOT. Nanoparticles exhibited sustained release of rifampicin, which followed diffusion kinetics. Nanoparticles of rifampicin were found to be stable for 12 months. The good correlation between freeze thaw and freeze drying suggests freeze-thaw study as a simple and quick approach for screening optimal cryoprotectant for freeze drying.

Investigations on the lyophilisation of MPEG-hexPLA micelle based pharmaceutical formulations

Lyophilisation is a common procedure to increase the long-term stability of pharmaceutical formulations. Its applicability to polymeric micelles is usually an issue because of the aggregation of materials during freeze-drying steps. The feasibility of this process was studied on polymeric micelles based on methoxy poly(ethylene glycol)-poly(hexyl-lactide) (MPEG-hexPLA) with and without Cyclosporin A, in order to increase the stability of these pharmaceutical formulations. Freeze-thawing tests were carried out to determine the protective effect of various excipients on the freezing step. Mannitol, trehalose, glucose and sucrose showed the best effectiveness in micelle protection. The lyophilisation process was optimised by thermal analysis (DSC) on excipients to determine the glass transition temperature of the cryoconcentrate solutions (T(g)') and their glass transition temperature (T(g)). The freeze-dried powders were characterized in terms of morphology (SEM) and of moisture content (Karl Fisher titration). The reconstituted micelle formulations were analysed for size by DLS with and without goniometer, for morphology by TEM, for drug loading by HPLC. The formulation presenting the best characteristics before and after reconstitution contained 10% (w/v) sucrose in phosphate buffer. This lyophilised formulation was constituted of a brittle and white cake, with a residual water content of around 2% and it was easily reconstituted in a transparent and clear solution giving back a colloidal system with spherical micelles in the submicron range (<250 nm). The drug loading was not affected by the freeze-drying procedure. This study showed that the MPEG-hexPLA micelles can be efficiently lyophilised and this process can be usefully applied to increase the pharmaceutical stability of these pharmaceutical micelle formulations.

Amorphous compositions using concentration enhancing polymers for improved bioavailability of itraconazole

Amorphous engineered particle compositions of itraconazole (ITZ) and potential concentration enhancing polymers, cellulose acetate phthalate (CAP) and polyvinyl acetate phthalate (PVAP), were produced by ultra-rapid freezing to investigate the effect of these polymers on the bioavailability of ITZ solid dispersions. X-ray diffraction analyses of engineered particle compositions were shown to be amorphous. Modulated differential scanning calorimetry demonstrated that ITZ:CAP engineered particle compositions exhibited a strong correlation with the Gordon-Taylor relationship while ITZ:PVAP formulations exhibited positive deviations from predicted values attributed to hydrogen bonding interactions between the drug and polymer. Energy dispersive spectroscopy mapping demonstrated that the drug was homogenously distributed within all compositions, supporting the miscibility of the drug with the polymers. Scanning electron microscopy imaging of the particles demonstrated that the material existed in two general forms, discrete particles of approximately 5 microm and larger aggregates in excess of 30 microm, with engineered particle compositions having approximately 15 times higher measured specific surfaces areas compared to micronized ITZ. In vitro supersaturated dissolution results showed that all compositions provided significantly lower levels of supersaturation in acidic media and greater extents of supersaturation in neutral media compared to Sporanox pellets. ITZ: CAP formulations provided the greatest degree and extent of supersaturation in neutral media. Dissolution data were fitted to an exponential relationship based on a simplified model of particle growth, allowing for the determination of drug half-life in solution for evaluation of stabilization behavior. 1:2 ITZ:CAP showed superior in vitro performance compared to all other engineered particle compositions and was selected for in vivo testing. Although not fully elucidated, data indicated that the stabilization mechanism was due to interactions between the drug and polymer, primarily attributed to steric hindrance resulting from the molecular weight of the polymer chain and chemical composition of the polymer backbone relative to position of hydrogen bonding sites. In vivo testing conducted in Sprague-Dawley rats (n = 6) demonstrated a significant improvement in oral bioavailability from the 1:2 ITZ:CAP (AUC = 4,516 +/- 1,949 ng x h/mL) compared to the Sporanox pellets (AUC = 2,132 +/- 1,273 ng x h/mL) (p < or = 0.05). Additionally, the more rapid onset of action indicated superior targeting of the upper small intestines, and the prolonged half-life suggested the utility of CAP to maintain supersaturated concentrations, in vivo. These results demonstrated that amorphous compositions of ITZ and enteric concentration enhancing polymers provided improved bioavailability due to enhanced intestinal targeting and increased durations of supersaturation.

Methods for the preparation and manufacture of polymeric nanoparticles

This review summarizes the different methods of preparation of polymer nanoparticles including nanospheres and nanocapsules. The first part summarizes the basic principle of each method of nanoparticle preparation. It presents the most recent innovations and progresses obtained over the last decade and which were not included in previous reviews on the subject. Strategies for the obtaining of nanoparticles with controlled in vivo fate are described in the second part of the review. A paragraph summarizing scaling up of nanoparticle production and presenting corresponding pilot set-up is considered in the third part of the review. Treatments of nanoparticles, applied after the synthesis, are described in the next part including purification, sterilization, lyophilization and concentration. Finally, methods to obtain labelled nanoparticles for in vitro and in vivo investigations are described in the last part of this review.

Formulation development of freeze-dried oligonucleotide-loaded gelatin nanoparticles

The freeze-drying properties of gelatin nanoparticles were investigated with the goal of providing practicable nanoparticle formulations for in vitro applications or clinical studies. Various excipients and rehydration protocols were assessed, and gelatin nanoparticles loaded with oligonucleotides were successfully freeze-dried and rehydrated. An NF-kappaB decoy oligonucleotide-loaded gelatin nanoparticle formulation was developed and applied in a drug targeting approach in an animal model. The high concentrations of nanoparticles achieved after rehydration with reduced volumes proved to be critical for the in vivo effect. Finally, short term storage stability under accelerated conditions was assessed for dried gelatin nanoparticles formulated in sucrose, trehalose, mannitol, or a mannitol/sucrose mixture. Size, size distribution, and residual moisture content were investigated. Sucrose- and trehalose-containing formulations exhibited the greatest stability, but mannitol-containing formulations also showed notable stabilization despite their crystalline nature.

Suspensions for intravenous (IV) injection: a review of development, preclinical and clinical aspects

There has been growing interest in nanoparticles as an approach to formulate poorly soluble drugs. Besides enhanced dissolution rates, and thereby, improved bioavailability, nanoparticles can also provide targeting capabilities when injected intravenously. The latter property has led to increased research and development activities for intravenous suspensions. The first intravenously administered nanoparticulate product, Abraxane (a reformulation of paclitaxel), was approved by the FDA in 2006. Additional clinical trials have been conducted or are ongoing for multiple other indications such as oncology, infective diseases, and restenosis. This article reviews various challenges associated with developing intravenous nanosuspension dosage forms. In addition, various formulation considerations specific to intravenous nanosuspensions as well as reported findings from various clinical studies have been discussed.

Effect of various formulation parameters on the properties of polymeric nanoparticles prepared by multiple emulsion method

This work evaluates and interprets underlying mechanisms behind various aspects related to preparation and physical characteristics of polymeric nanoparticles (NP). These were prepared from different biodegradable polymers according to a water-in-oil-in-water emulsion solvent evaporation method. Polymers used were poly(lactic-co-glycolic) acid (PLGA), poly (lactic acid) (PLA), (PLA-PEG-PLA) triblock and (PLA-PEG-PLA)n multi-block co-polymers. A model DNA, as an example of a hydrophilic drug, was encapsulated in the internal aqueous phase. The primary emulsion was prepared using a high shear turbine mixer. The secondary emulsion was prepared by high-pressure homogenization. Surface morphology and internal structure were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Influence of process variables on the physical properties of NP has been studied. Release of DNA was evaluated. In addition, changes occurring to NP porosity and surface area during degradation were followed. Nanoparticle size was ranging between 200-700 nm, according to the preparation conditions. Homogenizing pressure, concentration of the emulsifying agent used, polymer concentration and type and the concentration of a cryoprotectant had variable effects on NP size, surface area and porosity. Batches of NP where no emulsifying agent was added were obtained successfully. The release rate of the DNA from NP was mainly dependent on porosity, which varied significantly among used polymers. The preparation technique was efficient in encapsulating the model DNA and will be used for plasmid encapsulation in a future work.

A Practical Approach to the use of Nanoparticles for Vaccine Delivery

The objective of this work was to obtain a nanoparticle formulation that could be sterile filtered, lyophilized, and resuspended to the initial size with excipients appropriate for use as a vaccine formulation. Poly(lactide-co-glycolide) (PLG) polymers were used to create nanoparticles ranging in size from 110 to 230 nm. Protein antigens were adsorbed to the particles; the protein-nanoparticles were then lyophilized with the excipients. Vaccine compatible excipient combinations of sugars alone, surfactants alone, and sugars and surfactants were tested to find conditions where initial particle size was recovered. Sterile filtration of smaller nanoparticles led to minimal PLG losses and allowed the particle preparation to be a nonaseptic process. We found that the smaller nanoparticles of size approximately 120 nm required higher surfactant concentration to resuspend postlyophilization than slightly larger ( approximately 220 nm) particles. To resuspend 120 nm nanoparticles formulations of poly(vinyl alcohol) (PVA) with sucrose/mannitol or dioctyl sodium sulfosuccinate (DSS) with trehalose/mannitol were sufficient. The protein-nanoparticles resuspension with the same excipients was dependent on the protein and protein loading level. The nanoparticle formulations in vivo were either similar or had enhanced immunogenicity compared to aluminum hydroxide formulations. A lyophilized nanoparticle formulation with adsorbed protein antigen and minimal excipients is an effective vaccine delivery system.

Effect of cryoprotectants on the reconstitution of surfactant-free nanoparticles of poly(DL-lactide-co-glycolide)

Various cryoprotectants were tested to reconstitute the surfactant-free nanoparticles of poly(DL-lactide-co-glycolide) (PLGA). When 2.0% (w/v) of sucrose, trehalose and lactose were used, nanoparticles were completely reconstituted into aqueous solution and particle size was not significantly changed. Above 1.0% (w/v) of sucrose, trehalose and lactose, nanoparticles are well reconstituted whereas it was precipitated with 1.0% (w/v) of mannitol. Drug-encapsulated surfactant-free nanoparticles were quite reconstituted when 2.0% (w/v) of sucrose, trehalose and lactose. Drug release kinetics of nanoparticles was not significantly changed by cryoprotectants.

Freeze-drying of nanocapsules: impact of annealing on the drying process

Freeze-drying process was recently applied to improve the long-term storage stability of nanocapsules. Thermal treatment by annealing is an interesting process to optimize a freeze-drying cycle of these colloidal vectors. The objective of this paper is to investigate the impact of annealing on primary and secondary drying characteristics and on nanocapsules (NC) properties. Nanocapsules were prepared from poly-epsilon-caprolactone (PCL) biodegradable polymer and stabilized by polyvinyl alcohol (PVA), and then freeze-dried with two cryoprotectants: sucrose and poly vinyl pyrrolidone (PVP). Freeze-dried nanocapsules were characterized by size measurement and transmission electron microscopy after reconstitution. The effect of annealing on the kinetics of sublimation, on the mass transfer resistance and on the porosity of the freeze-dried product has been studied in the case of PVP. Finally, the effect of annealing on the kinetic of secondary drying was studied and the results were coupled with the isotherm of sorption. Results showed that PCL nanocapsules could be freeze-dried without any modification of their properties in presence of the two cryoprotectants used. Annealing of nanocapsules suspensions could accelerate the sublimation rate without any modification of nanocapsules size in the case of the two studied cryoprotectants. Such improvement could be explained by the increase of ice crystals size after annealing and by the diminution of mass transfer resistance by the dried layer. The acceleration of sublimation rate seems to depend on the temperature of annealing. The annealing of sucrose solution slows down the secondary drying kinetic whereas no effect is observed in the case of PVP.

Physical stability, centrifugation tests, and entrapment efficiency studies of carnauba wax–decyl oleate nanoparticles used for the dispersion of inorganic sunscreens in aqueous media

Aqueous nanoscale lipid dispersions consisting of carnauba wax-decyl oleate mixtures acting as carriers or accompanying vehicles for inorganic sunscreens such as barium sulfate, strontium carbonate, and titanium dioxide were prepared by high pressure homogenization. For the manufacture of these nanosuspensions, three pigment concentrations (%wt), namely 2, 4, and 6, and two carnauba wax-decyl oleate ratios, 1:1 and 2:1, were used, being some of these combinations chosen for stability studies. Six-month physical stability tests at 4, 20, and 40 degrees C selecting the mean particle size and the polydispersity index of the nanosuspensions as reference parameters were performed. Centrifugation tests of the nanosuspensions assessed by transmission electron microscopy and by the determination of the content of pigments and carnauba wax in the separated fractions were done. The mean particle sizes and the polydispersity indices of the nanosuspensions were not altered after six-month storages at 20 and at 40 degrees C. However, the storage of those at 4 degrees C considerably increased the particle size and polydispersity of the systems, particularly when wax-oil ratios (2:1) were used for the entrapment of the pigments. Transmission electron micrographs of centrifuged samples denoted the presence of three major fractions showing the different types of particles integrated into the nanosuspensions. Furthermore, it was observed that not all the carnauba wax participated in the entrapment of the pigment. Regarding the amount of pigment being encapsulated or bonded by the wax-oil matrices, entrapment efficiencies higher than 85.52% were reported.

Investigation of nanocapsules stabilization by amorphous excipients during freeze-drying and storage

Freeze-drying was recently applied to improve the long-term storage stability of nanoparticles. Nanocapsules have a thin polymeric envelope that may not withstand the stresses of such process. So, cryoprotectants and lyoprotectants are usually added to the formulation to protect these vectors during freezing and desiccation steps. The aim of this paper was to investigate the importance of the vitrification of cryoprotectants on the stabilization of nanocapsules during freezing, desiccation, and storage steps. Furthermore, the effect of stabilizer crystallization on the conservation of nanocapsules properties was studied. Finally, the effect of temperature storage and relative humidity on the stability of nanocapsules was tested through an accelerated stability study. Results indicate that nanocapsules stabilization during the different steps of freeze-drying requires their dispersion within a vitrified matrix of amorphous excipient to protect them against the stress of freezing and dehydration. The crystallization of this stabilizer during the freezing, the desiccation or the storage steps can destabilize these fragile particles. Electron spectroscopy for chemical analysis revealed the adsorption of nanocapsules at the interface ice/liquid during the freezing step. Such adsorption must be avoided in the case of freeze-drying of immuno-nanoparticles to preserve the native structure of proteins attached to their surface.

A pilot study of freeze drying of poly(epsilon-caprolactone) nanocapsules stabilized by poly(vinyl alcohol): Formulation and process optimization

A common limitation of using polymeric nanoparticles in aqueous suspension is due to their poor chemical and physical stability when conserved for a long time. Therefore, freeze drying of these colloidal systems is an alternative method to achieve long-term stability. Nanocapsules have thin and fragile shell structure, which may not resist to the stress of such process. The aim of this study is to investigate the formulation and process parameters in order to ensure the stability of polycaprolactone nanocapsules (PCL NC) by freeze drying. In this paper, we studied the freeze drying of PCL NC prepared by the emulsion-diffusion method and stabilized by poly(vinyl alcohol) (PVA). Different parameters have been tested throughout the freeze-thawing study including PVA and PCL concentration, cooling rate, cryoprotectant concentrations, nature of encapsulated oil and NC purification. On the other hand, nanocapsules have been freeze dried both before and after purification. Freeze dried purified PCL NC were characterized by particle size measurement, collapse temperature, T'g determination, scanning electron microscope observation, environmental scanning electron microscope imaging and residual humidity quantification. Finally, the effect of annealing on the NC stability and the sublimation rate has been well explored. The results suggest that PCL NC could be freeze dried without a cryoprotectant if the concentration of PVA stabilizer is sufficient (5%), while for the purified NC the addition of 5% of cryoprotectant seems to be necessary to ensure the stability of NC. The type of cryoprotectants had practically negligible effects on the size and the rehydration of freeze dried nanocapsules. The annealing process could accelerate the sublimation with the conservation of nanocapsules size.

Poly-epsilon-caprolactone microspheres and nanospheres: an overview

Poly-epsilon-caprolactone (PCL) is a biodegradable, biocompatible and semicrystalline polymer having a very low glass transition temperature. Due to its slow degradation, PCL is ideally suitable for long-term delivery extending over a period of more than one year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanospheres and implants. Various categories of drugs have been encapsulated in PCL for targeted drug delivery and for controlled drug release. Microspheres of PCL either alone or of PCL copolymers have been prepared to obtain the drug release characteristics. This article reviews the advancements made in PCL-based microspheres and nanospheres with special reference to the method of preparation of these and their suitability in developing effective delivery systems.

Preparation and characterization of sterile and freeze-dried sub-200 nm nanoparticles

The feasibility of producing sterile and freeze-dried polyester nanoparticles was investigated. Various poly(D,L-lactide-co-glycolide) and poly(D,L-lactide) were selected as biodegradable polymers. Using the salting-out procedure, process parameters were optimized to obtain sub-200 nm particles. After purification, the nanoparticle suspensions containing different lyoprotectants were sterilized by filtration. Freeze-drying was performed using vials covered with 0.22 microm membrane filters in order to preserve the suspensions from bacterial contamination. Sterility was assessed on the final product according to pharmacopoeial requirements using the membrane filtration method. With all polymers tested, sub-200 nm particles could be obtained. Nanoparticles with a size as low as 102 nm were prepared with good reproducibility and narrow size distribution. Upon freeze-drying, it appeared that complete redispersion of all types of polyester nanoparticles could be obtained in presence of the lyoprotectants tested such as saccharides while aggregation was observed without lyoprotectant. Sterility testing showed no microbial contamination indicating that sterile nanoparticulate formulations have been achieved.

Freeze-drying and lyopreservation of diblock and triblock poly(lactic acid)-poly(ethylene oxide) (PLA-PEO) copolymer nanoparticles

In this study, the formulation and process parameters that determine successful production and long-term stability of freeze-dried poly(lactic acid) (PLA) nanoparticles with "hairy-like" poly(ethylene oxide) (PEO) surfaces were investigated. Nanoparticles with grafted (covalently bound) PEO coatings were produced by the salting-out method from blends of PLA and PLA-PEO diblock or triblock copolymers. PLA nanoparticles with physically adsorbed PEO were also produced. The redispersibility of the nanoparticles after freeze-drying under various conditions was assessed. The surface of the nanoparticles was characterized and classified in terms of "brush" and "loop" conformations. Upon freeze-drying, it appeared that the presence of PEO at the nanoparticle surface could severely impair the redispersibility of the particles, especially in the PEO-grafted systems. This effect was shown to be related to the amount and molecular weight of PEO in the various formulations. In most cases, particle aggregation was prevented by use of trehalose as lyoprotective agent. Increasing the concentration of particles in the suspension to be freeze-dried was shown to induce much less damage to the nanoparticles, and freezing the suspension at a very low temperature (-196 degrees C) was found to further improve the lyoprotective effect. Most of the lyoprotected nanoparticles remained stable for at least 12 weeks at 4 and -25 degrees C. The production and preservation of freeze-dried PLA-PEO diblock and triblock copolymer nanoparticles is feasible under optimized lyoprotective conditions.

Trends in antifungal research

With the increasing use of aggressive immunosuppressive therapies in the management of a variety of patient populations, the continuing presence of the AIDS pandemic and the therapeutic advances employed in critical care settings, an increasing number of serious fungal infections are being encountered by today's practicing clinicians. Traditionally, antifungal drug therapy has been delivered by means of intravenous infusion, oral administration, or topical application. Recently, a number of alternative routes of antifungal drug delivery have been developed and investigated, and the traditional means of antifungal administration have been improved to facilitate the therapeutic use of new and reformulated antifungal agents. Organized based on the route of administration, this chapter reviews these advances in antifungal drug delivery.

Freeze-drying of polycaprolactone and poly(D,L-lactic-glycolic) nanoparticles induce minor particle size changes affecting the oral pharmacokinetics of loaded drugs

The present study was geared at identifying the conditions to stabilize poly (D,L-lactic-glycolic) (PLGA) and polycaprolactone (PCL) nanoparticles (NP) by freeze-drying with several cryoprotective agents. Differential scanning calorimetry and freeze-thawing studies were used to optimize the lyophilization process. These studies showed that all samples were totally frozen at -45 degrees C and evidenced the necessity of adding sucrose, glucose, trehalose or gelatine to preserve the properties of NP regardless of the freezing procedure. However, only 20% sucrose and 20% glucose exerted an acceptable lyoprotective effect on PLGA and PCL NP, respectively. Nonetheless, the final to initial size ratios ( approximately 1.5) indicated that particle size was slightly affected in both cases. In vivo studies with CyA-loaded PCL NP whose sizes matched those obtained after NP preparation (100 nm) and after being lyophilized (160 nm) showed that the changes of particle size might have some relevance on drug pharmacokinetics. The MRT was significantly (P<0.05) modified after an oral CyA dose of 5 mg/kg and the treatment with 160-nm sized CyA-loaded NP produced a higher drug partition into the liver of Wistar rats potentially affecting the toxic and immunosuppressive profile of the drug. Therefore, although the particle size changes induced by NP lyophilization were slight, they need to be carefully evaluated and cannot be neglected.

Stability and freeze-drying of cyclosporine loaded poly(D,L lactide-glycolide) carriers

The present paper describes the stability of poly (D, L-lactide-glycolide) nanoparticles (PLGA NP) and microspheres (MS), either alone or loaded with cyclosporine (CyA), stored at 8 degrees C and room temperature (RT). Freeze-drying of these formulations was evaluated as an alternative method to achieve long term stability. A significant polymer rupture was detected during PLGA MS preparation by solvent evaporation, which correlated with the stirring rates used for the formation of the primary emulsion. On the other hand, the polymer remained unchanged during NP formation. After 6 months of storage, PLGA NP of a size below 80 nm aggregated when stored at RT whereas no changes of particle size were observed for the remaining formulations and experimental conditions. Drug entrapment significantly increased by about 9.5% only during PLGA NP storage at RT. The PLGA molecular weight of NP dropped at RT being these changes related to the initial particle size and amount of CyA incorporated. The same effect was observed at 8 degrees C but only the particle size showed a significant influence. The drop of PLGA molecular weight observed during storage of MS was not dependent on the storage temperature but it was directly related to the molecular weights obtained after MS preparation. Freeze-drying studies revealed that it was not feasible to maintain the initial PLGA NP characteristics after reconstitution. On the other hand, MS lyophilized in the absence of cryoprotectants retained the drug initially entrapped; however, the presence of at least 5% cryoprotectant was essential to keep the initial particle size. Therefore, PLGA NP and MS show a significant instability when stored as suspensions. Freeze-drying offers a good alternative to stabilize polymeric MS but the preservation of the PLGA NP characteristics by freeze-drying needs for further investigations.