The production of protein-loaded microparticles by supercritical fluid enhanced mixing and spraying

Intra-articular delivery of an indoleamine 2,3-dioxygenase galectin-3 fusion protein for osteoarthritis treatment in male Lewis rats

OBJECTIVE

Osteoarthritis (OA) is driven by low-grade inflammation, and controlling local inflammation may offer symptomatic relief. Here, we developed an indoleamine 2,3-dioxygenase and galectin-3 fusion protein (IDO-Gal3), where IDO increases the production of local anti-inflammatory metabolites and Gal3 binds carbohydrates to extend IDO's joint residence time. In this study, we evaluated IDO-Gal3's ability to alter OA-associated inflammation and pain-related behaviors in a rat model of established knee OA.

METHODS

Joint residence was first evaluated with an analog Gal3 fusion protein (NanoLuc™ and Gal3, NL-Gal3) that produces luminescence from furimazine. OA was induced in male Lewis rats via a medial collateral ligament and medial meniscus transection (MCLT + MMT). At 8 weeks, NL or NL-Gal3 were injected intra-articularly (n = 8 per group), and bioluminescence was tracked for 4 weeks. Next, IDO-Gal3s's ability to modulate OA pain and inflammation was assessed. Again, OA was induced via MCLT + MMT in male Lewis rats, with IDO-Gal3 or saline injected into OA-affected knees at 8 weeks post-surgery (n = 7 per group). Gait and tactile sensitivity were then assessed weekly. At 12 weeks, intra-articular levels of IL6, CCL2, and CTXII were assessed.

RESULTS

The Gal3 fusion increased joint residence in OA and contralateral knees (p < 0.0001). In OA-affected animals, both saline and IDO-Gal3 improved tactile sensitivity (p = 0.008), but IDO-Gal3 also increased walking velocities (p ≤ 0.033) and improved vertical ground reaction forces (p ≤ 0.04). Finally, IDO-Gal3 decreased intra-articular IL6 levels within the OA-affected joint (p = 0.0025).

CONCLUSION

Intra-articular IDO-Gal3 delivery provided long-term modulation of joint inflammation and pain-related behaviors in rats with established OA.

Solid Dosage Forms of Biopharmaceuticals in Drug Delivery Systems Using Sustainable Strategies

Drug delivery systems (DDS) often comprise biopharmaceuticals in aqueous form, making them susceptible to physical and chemical degradation, and therefore requiring low temperature storage in cold supply and distribution chains. Freeze-drying, spray-drying, and spray-freeze-drying are some of the techniques used to convert biopharmaceuticals-loaded DDS from aqueous to solid dosage forms. However, the risk exists that shear and heat stress during processing may provoke DDS damage and efficacy loss. Supercritical fluids (SCF), specifically, supercritical carbon dioxide (scCO₂), is a sustainable alternative to common techniques. Due to its moderately critical and tunable properties and thermodynamic behavior, scCO₂ has aroused scientific and industrial interest. Therefore, this article reviews scCO₂-based techniques used over the year in the production of solid biopharmaceutical dosage forms. Looking particularly at the use of scCO₂ in each of its potential roles—as a solvent, co-solvent, anti-solvent, or co-solute. It ends with a comparison between the compound’s stability using supercritical CO₂-assisted atomization/spray-drying and conventional drying.

PLA/PLGA-Based Drug Delivery Systems Produced with Supercritical CO2-A Green Future for Particle Formulation?

Supercritical carbon dioxide (SC-CO₂) can serve as solvent, anti-solvent and solute, among others, in the field of drug delivery applications, e.g., for the formulation of polymeric nanocarriers in combination with different drug molecules. With its tunable properties above critical pressure and temperature, SC-CO₂ offers control of the particle size, the particle morphology, and their drug loading. Moreover, the SC-CO₂-based techniques overcome the limitations of conventional formulation techniques e.g., post purification steps. One of the widely used polymers for drug delivery systems with excellent mechanical (T_g, crystallinity) and chemical properties (controlled drug release, biodegradability) is poly (lactic acid) (PLA), which is used either as a homopolymer or as a copolymer, such as poly(lactic-co-glycolic) acid (PLGA). Over the last 30 years, extensive research has been conducted to exploit SC-CO₂-based processes for the formulation of PLA carriers. This review provides an overview of these research studies, including a brief description of the SC-CO₂ processes that are widely exploited for the production of PLA and PLGA-based drug-loaded particles. Finally, recent work shows progress in the development of SC-CO₂ techniques for particulate drug delivery systems is discussed in detail. Additionally, future perspectives and limitations of SC-CO₂-based techniques in industrial applications are examined.

Nano, micro particulate and cosmetic delivery systems of polylactic acid: A mini review

BACKGROUND

Poly lactic acid and its copolymers are considered to be the preferred substrates for drug delivery devices. Poly lactic acid is a biocompatible, biodegradable and nontoxic polymer. It was approved by Food and Drug Administration and thought to be among the most attractive polymeric candidates intended for controlling drug delivery. It was utilized for the development of devices for the delivery of small molecules, proteins, genes, vaccines, anticancer drugs, and macromolecules.

OBJECTIVES AND METHODS

This manuscript lists the different techniques for synthesizing poly lactic acid-based nano and microparticles such as emulsion-based methods, precipitation-based methods, direct compositing methods, in situ forming micro-particles, and microfluidic technique.

CONCLUSIONS

In addition, it describes the application and use of poly lactic acid in biomedical and cosmetic delivery systems.

Formulation of Bioerodible Ketamine Microparticles as an Analgesic Adjuvant Treatment Produced by Supercritical Fluid Polymer Encapsulation

Pain is inadequately relieved by escalating doses of a strong opioid analgesic such as morphine in up to 25% of patients with cancer-related severe pain complicated by a neuropathic (nerve damage) component. Hence, there is an unmet medical need for research on novel painkiller strategies. In the present work, we used supercritical fluid polymer encapsulation to develop sustained-release poly(lactic-co-glycolic acid) (PLGA) biodegradable microparticles containing the analgesic adjuvant drug ketamine, for injection by the intrathecal route. Using this approach with a range of PLGA co-polymers, drug loading was in the range 10⁻60%, with encapsulation efficiency (EE) of 60⁻100%. Particles were mainly in the size range 20⁻45 µm and were produced in the absence of organic solvents and surfactants/emulsifiers. Investigation of the ketamine release profiles from these PLGA-based microparticles in vitro showed that release took place over varying periods in the range 0.5⁻4.0 weeks. Of the polymers assessed, the ester end-capped PLGA5050DLG-1.5E gave the best-controlled release profile with drug loading at 10%.

Antimicrobial peptide encapsulation and sustained release from polymer network particles prepared in supercritical carbon dioxide

Antimicrobial peptide loaded poly(2-hydroxyethyl methacrylate) particles were synthesized in supercritical carbon dioxide via one-pot free-radical dispersion polymerisation of 2-hydroxyethyl methacrylate and a cross-linker. Discrete particles with a well-defined spherical morphology and a diameter as low as 450 nm have been obtained in mild conditions. The encapsulation and release of the peptide were confirmed by antimicrobial tests that demonstrated for the first time a sustained release of the peptide from poly(2-hydroxyethyl methacrylate) microgels prepared by one-pot dispersion polymerization in supercritical carbon dioxide and then dispersed in water.

Production of pure drug nanocrystals and nano co-crystals by confinement methods

The use of drug nanocrystals in the drug formulation is increasing due to the large number of poorly water-soluble drug compounds synthetized and due to the advantages brought by the nanonization process. The downsizing processes are done using a top-down approach (milling and homogenization currently employed at the industrial level), while the crystallization process is performed by bottom-up techniques (e.g., antisolvent precipitation, use of supercritical fluids or spray and freeze drying). In addition, the production of nanocrystals in confined environment can be achieved within microfluidics channels. This review analyzes the processes for the preparation of nanocrystals and co-crystals, divided by top-down and bottom-up approaches, together with their combinations. The combination of both strategies merges the favorable features of each process and avoids the disadvantages of single processes. Overall, the applicability of drug nanocrystals is highlighted by the widespread research on the production processes at the engineering, pharmaceutical, and nanotechnology level.

Mild synthesis of poly(HEMA)-networks as well-defined nanoparticles in supercritical carbon dioxide

Free-radical dispersion polymerisation of 2-hydroxyethyl methacrylate was carried out in supercritical carbon dioxide (scCO₂) in the presence of stabilisers based on polyethylene oxide (PEO) and poly(heptadecafluorodecyl acrylate) (PFDA). Different architectures of copolymers (random, palm-tree and diblock) were tested for their surface tension, cloud point and as a stabilising agent. The diblock architecture was found to be the best candidate resulting in poly(HEMA) spherical particles with a size of 316 nm. Furthermore, the effect of the CO₂-phobic block (PEO) in the diblock architecture was investigated by using three different chain lengths (1000, 2000, 5000 g mol^-1). By optimizing the stabiliser composition and structure, mild reaction conditions have been identified allowing us to obtain well-defined spherical cross-linked poly(HEMA) particles with a mean diameter of unprecedented low size (216 nm) at a temperature as low as 35 °C.

Supramolecular nanoparticles of calcitonin and dipeptide for long-term controlled release

Salmon calcitonin (sCT) is a therapeutic polypeptide drug widely used to treat bone diseases such as osteoporosis (more than 200 million patients all over the world). The half-life of sCT is very short (~1h), thus various delivery systems have been developed for sCT in order to avoid frequent injections. However, most delivery systems use polymeric materials, which may limit their applications in clinic formulations due to the biocompatibility issue. We observed that a very simple dipeptide (Asp-Phe, DF) was co-assembled with sCT into supramolecular nanoparticles. These nanoparticles can significantly prolong the acting time of sCT to beyond one month after just a single subcutaneous injection. The assembling and releasing mechanisms were thoroughly investigated by both in vitro and in vivo methods, as well as by molecular dynamics simulations. This work provides an alternative strategy of designing protein/peptide drug delivery systems with long-lasting therapeutic effects.

PLA micro- and nano-particles

Poly(d,l-lactic acid) (PLA) has been widely used for various biomedical applications for its biodegradable, biocompatible, and nontoxic properties. Various methods, such as emulsion, salting out, and precipitation, have been used to make better PLA micro- and nano-particle formulations. They are widely used as controlled drug delivery systems of therapeutic molecules, including proteins, genes, vaccines, and anticancer drugs. Even though PLA-based particles have challenges to overcome, such as low drug loading capacity, low encapsulation efficiency, and terminal sterilization, continuous innovations in particulate formulations will lead to development of clinically useful formulations.

Aerosol-Assisted Fast Formulating Uniform Pharmaceutical Polymer Microparticles with Variable Properties toward pH-Sensitive Controlled Drug Release

Microencapsulation is highly attractive for oral drug delivery. Microparticles are a common form of drug carrier for this purpose. There is still a high demand on efficient methods to fabricate microparticles with uniform sizes and well-controlled particle properties. In this paper, uniform hydroxypropyl methylcellulose phthalate (HPMCP)-based pharmaceutical microparticles loaded with either hydrophobic or hydrophilic model drugs have been directly formulated by using a unique aerosol technique, i.e., the microfluidic spray drying technology. A series of microparticles of controllable particle sizes, shapes, and structures are fabricated by tuning the solvent composition and drying temperature. It is found that a more volatile solvent and a higher drying temperature can result in fast evaporation rates to form microparticles of larger lateral size, more irregular shape, and denser matrix. The nature of the model drugs also plays an important role in determining particle properties. The drug release behaviors of the pharmaceutical microparticles are dependent on their structural properties and the nature of a specific drug, as well as sensitive to the pH value of the release medium. Most importantly, drugs in the microparticles obtained by using a more volatile solvent or a higher drying temperature can be well protected from degradation in harsh simulated gastric fluids due to the dense structures of the microparticles, while they can be fast-released in simulated intestinal fluids through particle dissolution. These pharmaceutical microparticles are potentially useful for site-specific (enteric) delivery of orally-administered drugs.

Survey of supercritical fluid techniques for producing drug delivery systems for a potential use in cancer therapy

Standard drug delivery systems for cancer treatment usually comprise a device with a specific size and shape (depending on the type of cancer that has to be treated), which is composed by a biodegradable compound with a chemotherapeutic entrapped within it. This device should have a molecule (mainly a protein) bound to its surface to target only cancer cells. On the contrary, supercritical fluids (SCF) have been widely used in the pharmaceutical industry for creating drug delivery systems or for extracting drugs from natural sources. This review explains the potential of SCFs for cancer therapies by studying the current uses of the different high-pressure processes that can be useful for this medical treatment, such as the development of new drug delivery systems (with their drug release) or the extraction of chemotherapeutics from a vegetal matrix.

Preformulation Studies of Bee Venom for the Preparation of Bee Venom-Loaded PLGA Particles

It is known that allergic people was potentially vulnerable to bee venom (BV), which can induce an anaphylactic shock, eventually leading to death. Up until recently, this kind of allergy was treated only by venom immunotherapy (VIT) and its efficacy has been recognized worldwide. This treatment is practiced by subcutaneous injections that gradually increase the doses of the allergen. This is inconvenient for patients due to frequent injections. Poly (D,L-lactide-co-glycolide) (PLGA) has been broadly studied as a carrier for drug delivery systems (DDS) of proteins and peptides. PLGA particles usually induce a sustained release. In this study, the physicochemical properties of BV were examined prior to the preparation of BV-loaded PLGA nanoparticles NPs). The content of melittin, the main component of BV, was 53.3%. When protected from the light BV was stable at 4 °C in distilled water, during 8 weeks. BV-loaded PLGA particles were prepared using dichloromethane as the most suitable organic solvent and two min of ultrasonic emulsification time. This study has characterized the physicochemical properties of BV for the preparation BV-loaded PLGA NPs in order to design and optimize a suitable sustained release system in the future.

The application of non-linear curve fitting routines to the analysis of mid-infrared images obtained from single polymeric microparticles

For the first time, we report a series of time resolved images of a single PLGA microparticle undergoing hydrolysis at 70 °C that have been obtained using attenuated total reflectance-Fourier transform infrared spectroscopic (ATR-FTIR) imaging. A novel partially supervised non-linear curve fitting (NLCF) tool was developed to identify and fit peaks to the infrared spectrum obtained from each pixel within the 64 × 64 array. The output from the NLCF was evaluated by comparison with a traditional peak height (PH) data analysis approach and multivariate curve resolution alternating least squares (MCR-ALS) analysis for the same images, in order to understand the limitations and advantages of the NLCF methodology. The NLCF method was shown to facilitate consistent spatial resolution enhancement as defined using the step-edge approach on dry microparticle images when compared to images derived from both PH measurements and MCR-ALS. The NLCF method was shown to improve both the S/N and sharpness of images obtained during an evolving experiment, providing a better insight into the magnitude of hydration layers and particle dimension changes during hydrolysis. The NLCF approach facilitated the calculation of hydrolysis rate constants for both the glycolic (kG) and lactic (kL) acid segments of the PLGA copolymer. This represents a real advantage over MCR-ALS which could not distinguish between the two segments due to colinearity within the data. The NLCF approach made it possible to calculate the hydrolysis rate constants from a single pixel, unlike the peak height data analysis approach which suffered from poor S/N at each pixel. These findings show the potential value of applying NLCF to the study of real-time chemical processes at the micron scale, assisting in the understanding of the mechanisms of chemical processes that occur within microparticles and enhancing the value of the mid-IR ATR analysis.

Challenges in the delivery of peptide drugs: an industry perspective

Due mainly to their poor stability and short plasma half-life, peptides are usually administered by injection, often several times daily. Injectable sustained-release formulations of peptides based on biodegradable polymer microparticles or implants early demonstrated the power of drug delivery technologies to enhance patient adherence and convenience, and increase safety and efficacy. Injectable sustained-release formulations are likely to remain a significant part of new peptide products. However, a new generation of technologies that enable solvent-free formulations and manufacturing processes, injection through narrow gauge needles and ready-to-use presentations will be increasingly used. In addition, the tremendous developments in noninvasive routes of delivery are likely to result in more and more peptides being delivered by the oral, transdermal, nasal or inhalation routes.

Preparation of polymeric particles in CO2 medium using non-toxic solvents: discussions on the mechanism of particle formation

Development of a novel and effective process for protein encapsulation into PLGA microparticles by the emulsification–extraction method in CO₂ medium using non-toxic solvents.

Evaluation of P(L)LA-PEG-P(L)LA as processing aid for biodegradable particles from gas saturated solutions (PGSS) process

A series of biodegradable P(L)LA-PEG1.5 kDa-P(L)LA copolymers have been synthesized and compared as processing aid versus Poloxamer 407 (PEO-PPO-PEO), in the formulation of protein encapsulated microparticles, using supercritical carbon dioxide (scCO2). Bovine serum albumin (BSA) loaded microcarriers were prepared applying the particles from the gas saturated solutions (PGSS) technique using scCO2 and thus, avoiding the standard practice of organic solvent encapsulation. Four triblock copolymers were synthesized and characterized, particularly in terms of thermal properties and behaviour when exposed to scCO2. The effects of the inclusion of these copolymers in the formulation of poly(α-hydroxy acids) based microparticles - e.g. poly(D,L-lactic-co-glycolic acid) (PLGA) and poly(D,L-lactide) (PLA) - were analysed in terms of yield, particle size, morphology and drug release. The use of P(L)LA-PEG1.5 kDa-P(L)LA triblock copolymers were found to increase the yield of the PGSS-based process and to decrease the size of the microparticles produced, in comparison with the formulation containing the Poloxamer 407. Moreover the microparticles formulated with the triblock copolymers possessing the higher hydrophobic character were able to maintain a controlled drug release profile.

Effect of polymer porosity on aqueous self-healing encapsulation of proteins in PLGA microspheres

Self-healing (SH) poly(lactic-co-glycolic acid) (PLGA) microspheres are a unique class of functional biomaterials capable of microencapsulating process-sensitive proteins by simple mixing and heating the drug-free polymer in aqueous protein solution. Drug-free SH microspheres of PLGA 50/50 with percolating pore networks of varying porosity (ϵ = 0.49-73) encapsulate increasing lysozyme (≈1 to 10% w/w) with increasing ϵ, with typically ≈20 to 25% pores estimated accessible to entry by the enzyme from the external solution. Release kinetics of lysozyme under physiological conditions is continuous over more than two weeks and most strongly influenced by ϵ and protein loading before reaching a lag phase until 28 d at the study completion. Recovered enzyme after release is typically predominantly monomeric and active. Formulations containing acid-neutralizing MgCO3 at ≥ 4.3% exhibit >97% monomeric and active protein after the release with full mass balance recovery. Hence, control of SH polymer ϵ is a key parameter to development of this new class of biomaterials.

Suitability of polymer materials for production of pulmonary microparticles using a PGSS supercritical fluid technique: preparation of microparticles using PEG, fatty acids and physical or chemicals blends of PEG and fatty acids

The production of microparticles using a supercritical carbon dioxide based PGSS technique (CriticalMix™) has been exploited to develop blended systems targeted at pulmonary delivery. Hence, PEG based polymers of different molecular weights (1000-6000 Da) were blended in situ with fatty acids (stearic, palmitic or myristic acid) or with commercially available PEG-stearates. The effect of the different thermodynamic properties of the polymers was evaluated by characterising the microparticles produced in terms of their melting temperature by conventional DSC and in the presence of high pressure CO(2) using a high pressure variable volume view cell. The microparticles produced were also assessed by SEM and particle size distribution. It is well known that as the molecular weight of the PEG chains increases, so does the viscosity of the melt and this leads to an increase in the particle size. In the paper we show that blending with myristic acid provides optimal control of particle size when the blend is sprayed from scCO(2) leading to high yields in the optimal aerodynamic size range of 2-5 μm for the deep lung delivery. The highest yield and smallest particles (~5 μm) were produced with a blend of PEG 3000 and myristic acid (1:1) whereas the batches containing palmitic acid and stearic acid showed lower yields and larger particle sizes.

Self-healing microencapsulation of biomacromolecules without organic solvents

Microencapsulation of biomacromolecules in PLGA is routinely performed with organic solvent through multiple complex steps deleterious to the biomacromolecule. The new self-healing based PLGA microencapsulation obviates micronization- and organic solvent-induced protein damage, provides very high encapsulation efficiency, exhibit stabilization and slow release of labile tetanus protein antigen, and provides long-term testosterone suppression in rats following a single injection of encapsulated leuprolide.

Preparation of polymeric particles in CO(2) medium using non-toxic solvents: formulation and comparisons with a phase separation method

The aim of this work was to elaborate formulation strategies to encapsulate a protein into biodegradable polymeric particles for sustained release purpose. In this paper, two encapsulation methods will be presented, one dealing with a phase separation phenomenon while the other involving an emulsification/extraction process in CO(2) medium. In those methods, only non-volatile injectable solvents such as glycofurol or isosorbide dimethyl ether were used to dissolve the polymer. Moreover, experimental designs were built up to help us to go further in the understanding of the processes and to better predict output responses in design space. Spherical particles were successfully generated with a satisfactory encapsulation yield. Further characterization steps such as in vitro, in vivo releases will be carried out to validate the interest of our encapsulation methods in the development of drug delivery systems.

Recent advances in polymeric microspheres for parenteral drug delivery--part 2

INTRODUCTION

Currently marketed microsphere products are manufactured with the use of organic solvents which have a negative impact on the environment and stability of biological molecules. With recent advances in fabrication technologies, solvent free methods have demonstrated potential for the preparation of microspheres.

AREAS COVERED

New technical advances recently achieved in solvent based microsphere manufacturing processes have allowed for major improvement in product quality and properties. Novel solvent free fabrication methods combined with newly functionalized biodegradable polymers have been explored for their application in the preparation of microspheres containing biological molecules.

EXPERT OPINION

Novel fabrication methods for microspheres have been recently reported but technical challenges and development risks remain high for scale up from bench to industrial commercialization. While the applications of microspheres for delivery of proteins, genes and vaccines have shown promise for clinical use, the approval of newly functionalized polymers as carriers may still face scrutiny on safety and biocompatibility, which can be key factors in securing the regulatory approval of the product.

Formulation strategies for sustained release of proteins

Proteins constitute an increasing proportion of the drugs in development. The barriers to their entry into the blood stream and rapid clearance means that they often have to be injected several times a day, affecting patient compliance. This paper reviews the major technologies enabling the development of injectable sustained-release products and formulation strategies to maintain protein integrity and modify release rates. Whilst many injectable sustained-release products are on the market, these are all delivering small molecular weight drugs and peptides. This is due to the manufacturing processes that denature and degrade the proteins upon encapsulation and release into the body. Formulation strategies are discussed and a number of new technologies reviewed that are able to overcome the issues with conventional manufacturing processes. The reliance of many processes on organic solvents has prevented their application to the development of injectable sustained release protein products. The development of entirely solvent free and aqueous methods of manufacture of these products has meant that numerous sustained-release protein products are close to reaching the market.

Self-assembling nanoparticles for intra-articular delivery of anti-inflammatory proteins

Intra-articular delivery of therapeutics to modulate osteoarthritis (OA) is challenging. Delivery of interleukin-1 receptor antagonist (IL-1Ra), the natural protein inhibitor of IL-1, to modulate IL-1-based inflammation through gene therapy or bolus protein injections has emerged as a promising therapy for OA. However, these approaches suffer from rapid clearance and reduced potency over time. Nano/microparticles represent a promising strategy for overcoming the shortcomings of intra-articular drug delivery. However, these delivery vehicles are limited for delivery of protein therapeutics due to their hydrophobic character, low drug loading efficiency, and harsh chemical conditions during particle processing. We designed a new block copolymer that assembles into submicron-scale particles and provides for covalently tethering proteins to the particle surface for controlled intra-articular protein delivery. This block copolymer self-assembles into 300 nm-diameter particles with a protein tethering moiety for surface covalent conjugation of IL-1Ra protein. This copolymer particle system efficiently bound IL-1Ra and maintained protein bioactivity in vitro. Furthermore, particle-tethered IL-1Ra bound specifically to target synoviocyte cells via surface IL-1 receptors. Importantly, IL-1Ra nanoparticles inhibited IL-1-mediated signaling to equivalent levels as soluble IL-1Ra. Finally, the ability of nanoparticles to retain IL-1Ra in the rat stifle joint was evaluated by in vivo imaging over 14 days. IL-1Ra-tethered nanoparticles significantly increased the retention time of IL-1Ra in the rat stifle joint over 14 days with enhanced IL-1Ra half-life (3.01 days) compared to that of soluble IL-1Ra (0.96 days) and without inducing degenerative changes in cartilage structure or composition.

Supercritical fluid-mediated methods to encapsulate drugs: recent advances and new opportunities

With the advent of the development of novel pharmaceutical products and therapies, there is a need for effective delivery of these products to patients. Dependent on whether they are small-molecular weight drugs or biologics, many new compounds may suffer from poor solubility, poor stability or require frequent administration and therefore require optimized delivery. For example, the utilization of polymorphism and the enhanced solubility in the amorphous state is being exploited to improve the dissolution of small-molecular weight poorly soluble drugs. This can be achieved by the formation of solid dispersions in water-soluble matrices. In addition, encapsulation in biodegradable polymeric materials is one potential route to reduce the frequency of administration through the formation of sustained-release formulations. This is desirable for biologics, for example, which generally require administration once or twice daily. Supercritical fluid processing can achieve both of these outcomes, and this review focuses on the use of supercritical CO2 to encapsulate active pharmaceutical ingredients to enhance solubility or achieve sustained release. Using supercritical CO2-mediated processes provides a clean and potentially solvent-free route to prepare novel drug products and is therefore an attractive alternative to conventional manufacturing technologies.

Dense CO₂ as a Solute, Co-Solute or Co-Solvent in Particle Formation Processes: A Review

The application of dense gases in particle formation processes has attracted great attention due to documented advantages over conventional technologies. In particular, the use of dense CO₂ in the process has been subject of many works and explored in a variety of different techniques. This article presents a review of the current available techniques in use in particle formation processes, focusing exclusively on those employing dense CO₂ as a solute, co-solute or co-solvent during the process, such as PGSS (Particles from gas-saturated solutions^®), CPF (Concentrated Powder Form^®), CPCSP (Continuous Powder Coating Spraying Process), CAN-BD (Carbon dioxide Assisted Nebulization with a Bubble Dryer^®), SEA (Supercritical Enhanced Atomization), SAA (Supercritical Fluid-Assisted Atomization), PGSS-Drying and DELOS (Depressurization of an Expanded Liquid Organic Solution). Special emphasis is given to modifications introduced in the different techniques, as well as the limitations that have been overcome.

Single shot tetanus vaccine manufactured by a supercritical fluid encapsulation technology

Single shot vaccines of tetanus toxoid (TT) were manufactured using the NanoMix process - a low temperature solvent free encapsulation technology using supercritical fluids. The formulations were injected into mice, and compared to multiple injections of a commercially available alum adsorbed TT vaccine. After 5 months the antibody titres were found to be similar for both the alum adsorbed and microparticle formulations, demonstrating for the first time the potential of formulating antigens in PLA microparticles using the supercritical fluid (NanoMix) technique to produce single shot vaccines. The results are likely to be due to the maintenance of toxoid bioactivity and some degree of sustained release of the encapsulated antigens, resulting in repeated stimulation of antigen presenting cells eliminating the need for multiple immunisations. This demonstrates the potential of this supercritical fluid processing technique to reduce the need for booster doses in a vaccine regimen.

Surface characterisation of bioadhesive PLGA/chitosan microparticles produced by supercritical fluid technology

PURPOSE

Novel biodegradable and mucoadhesive PLGA/chitosan microparticles with the potential for use as a controlled release gastroretentive system were manufactured using supercritical CO(2) (scCO(2)) by the Particle Gas Saturated System (PGSS) technique (also called CriticalMix(TM)).

METHODS

Microparticles were produced from PLGA with the addition of mPEG and chitosan in the absence of organic solvents, surfactants and crosslinkers using the PGSS technique. Microparticle formulations were morphologically characterized by scanning electron microscope; particle size distribution was measured using laser diffraction. Microparticle surface was analyzed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to evaluate the presence of chitosan on the surface. Mucoadhesiveness of the microparticles was evaluated in vitro using a mucin assay employing two different kinds of mucin (Mucin type III and I-S) with different degrees of sialic acid contents, 0.5-1.5% and 9-17%, respectively.

RESULTS

The two analytical surface techniques (XPS and ToF-SIMS) demonstrated the presence of the chitosan on the surface of the particles (<100 μm), dependent on the polymer composition of the microparticles. The interaction between the mucin solutions and the PLGA/chitosan microparticles increased significantly with an increasing concentration of mucin and chitosan.

CONCLUSIONS

The strong interaction of mucin with the chitosan present on the surface of the particles suggests a potential use of the mucoadhesive carriers for gastroretentive and oral controlled drug release.

Sustained release hGH microsphere formulation produced by a novel supercritical fluid technology: in vivo studies

Novel sustained release formulations of hGH prepared by supercritical fluid processing of PLGA/PLA (the CriticalMix process) were produced in the form of microparticles for subcutaneous injection. The basis of the process is that PLGA/PLA polymers liquefy when exposed to supercritical CO(2), thereby allowing the hGH to be mixed efficiently into the polymers at an ambient temperature and in the absence of solvents. The CO(2) was removed from the mixture by depressurisation through a nozzle, resulting in the production of microparticles containing the hGH, which were collected in a cyclone. The best microparticle formulations showed an initial in vitro burst of around 35% and a sustained release over 14 days. When tested in the rat model, which displays a faster clearance rate of hGH than other animal models, two formulations showed prolonged release over 2-3 days with sustained plasma levels at 1-5 ng/ml whereas the soluble hGH formulation was cleared within 24h. Two selected sustained release formulations were tested in cynomolgus monkeys and compared to a single injection of soluble hGH. The burst release from the sustained release formulations was similar in magnitude to a daily dose of hGH and serum hGH levels were maintained for a seven day period. It is probable from the data that the sustained release would have continued for up to 14 days if sampling had been continued. The IGF-1 results showed there was no significant difference between the levels obtained for once daily injection of soluble hGH and the two sustained release formulations.