Impact of Controlled Ice Nucleation and Lyoprotectants on Nanoparticle Stability during Freeze-drying and upon Storage

The freezing step of the lyophilization process can impact nanoparticle stability due to increased particle concentration in the freeze-concentrate. Controlled ice nucleation is a technique to achieve uniform ice crystal formation between vials in the same batch and has attracted increasing attention in pharmaceutical industry. We investigated the impact of controlled ice nucleation on three types of nanoparticles: solid lipid nanoparticles (SLNs), polymeric nanoparticles (PNs), and liposomes. Freezing conditions with different ice nucleation temperatures or freezing rates were employed for freeze-drying all formulations. Both in-process stability and storage stability up to 6 months of all formulations were assessed. Compared with spontaneous ice nucleation, controlled ice nucleation did not cause significant differences in residual moisture and particle size of freeze-dried nanoparticles. The residence time in the freeze-concentrate was a more critical factor influencing the stability of nanoparticles than the ice nucleation temperature. Liposomes freeze-dried with sucrose showed particle size increase during storage regardless of freezing conditions. By replacing sucrose with trehalose, or adding trehalose as a second lyoprotectant, both the physical and chemical stability of freeze-dried liposomes improved. Trehalose was a preferable lyoprotectant than sucrose to better maintain the long-term stability of freeze-dried nanoparticles at room temperature or 40°C.

Large-Scale Freeze-Thaw of Protein Solutions: Study of the Relative Contributions of Freeze-Concentration and Ice Surface Area on Stability of Lactate Dehydrogenase

Although bulk biotherapeutics are often frozen during fill finish and shipping to improve their stability, they can undergo degradation leading to losses in biological activity during sub-optimal freeze-thaw (F/T) process. Except for a few small-scale studies, the relative contribution of various F/T stresses to the instability of proteins has not been addressed. Thus, the objective of this study was to determine the individual contributions of freeze-concentration, ice surface area, and processing time to protein destabilization at a practical manufacturing-scale. Lactate dehydrogenase (LDH) in histidine buffer solutions were frozen in 1L containers. The frozen solutions were sliced into representative samples and assessed for the ice specific surface area (SSA) and extent of solutes freeze-concentration. For the first time to our knowledge, ice SSA was measured in dried samples from large-volume protein solutions using volumetric nitrogen adsorption isotherms. SSA measurements of the freeze-dried cakes showed that the ice surface area increased with an increase in the freezing rate. The ice SSA was also impacted by the position of the sample within the container: samples closer to the active cooled surface of the container exhibited smaller ice surface area compared to ice-cored samples from the center of the bottle. The freeze-concentrate composition was determined by measuring LDH concentration in the ice-cored samples. The protein distributed more evenly throughout the frozen solution after fast freezing which also correlated with enhanced protein stability compared to slow freezing conditions. Overall, better protein stability parameters correlated with higher ice SSA and lower freeze-concentration extent which was achieved at a faster freezing rate. Thus, extended residence time of the protein at the freeze-concentrated microenvironment is the critical destabilizing factor during freezing of LDH in bulk histidine buffer system. This study expands the understanding of the relative contributions of freezing stresses which, coupled with the knowledge of cryoprotection mechanisms, is imperative to the development of optimized processes and formulations aiming stable frozen protein solutions.

Impact of process stress on protein stability in highly-loaded solid protein/PEG formulations from small-scale melt extrusion

As protein-based therapeutics often exhibit a limited stability in liquid formulations, there is a growing interest in the development of solid protein formulations due to improved protein stability in the solid state. We used small-scale (<3 g) ram and twin-screw extrusion for the solid stabilization of proteins (Lysozyme, BSA, and human insulin) in PEG-matrices. Protein stability after extrusion was systematically investigated using ss-DSC, ss-FTIR, CD spectroscopy, SEM-EDX, SEC, RP-HPLC, and in case of Lysozyme an activity assay. The applied analytical methods offered an accurate assessment of protein stability in extrudates, enabling the comparison of different melt extrusion formulations and process parameters (e.g., shear stress levels, screw configurations, residence times). Lysozyme was implemented as a model protein and was completely recovered in its active form after extrusion. Differences seen between Lysozyme- and BSA- or human insulin-loaded extrudates indicated that melt extrusion could have an impact on the conformational stability. In particular, BSA and human insulin were more susceptible to heat exposure and shear stress compared to Lysozyme, where shear stress was the dominant parameter. Consequently, ram extrusion led to less conformational changes compared to TSE. Ram extrusion showed good protein particle distribution resulting in the preferred method to prepare highly-loaded solid protein formulations.

Enhancing the Stabilization Potential of Lyophilization for Extracellular Vesicles

Extracellular vesicles (EV) are an emerging technology as immune therapeutics and drug delivery vehicles. However, EVs are usually stored at -80 °C which limits potential clinical applicability. Freeze-drying of EVs striving for long-term stable formulations is therefore studied. The most appropriate formulation parameters are identified in freeze-thawing studies with two different EV types. After a freeze-drying feasibility study, four lyophilized EV formulations are tested for storage stability for up to 6 months. Freeze-thawing studies revealed improved colloidal EV stability in presence of sucrose or potassium phosphate buffer instead of sodium phosphate buffer or phosphate-buffered saline. Less aggregation and/or vesicle fusion occurred at neutral pH compared to slightly acidic or alkaline pH. EVs colloidal stability can be most effectively preserved by addition of low amounts of poloxamer 188. Polyvinyl pyrrolidone failed to preserve EVs upon freeze-drying. Particle size and concentration of EVs are retained over 6 months at 40 °C in lyophilizates containing 10 mm K- or Na-phosphate buffer, 0.02% poloxamer 188, and 5% sucrose. The biological activity of associated beta-glucuronidase is maintained for 1 month, but decreased after 6 months. Here optimized parameters for lyophilization of EVs that contribute to generate long-term stable EV formulations are presented.

Freeze-thaw stability of aluminum oxide nanoparticles

The use of inorganic nanoparticles (NPs) gains interest for pharmaceutical applications, e.g. as adjuvants or drug delivery vehicles. Colloidal stability of NPs in aqueous suspensions is a major development challenge. Both frozen and lyophilized liquids are alternative presentations to liquid dispersion. To improve the basic understanding, we investigated the freeze-thawing stability of model α-Al₂O₃ NPs. Freeze-thawing was conducted in three different buffer types at pH5 and 8 without and with additives to determine fundamental formulation principles. Before freeze-thawing, α-Al₂O₃ NPs could be stabilized in sodium citrate buffer at pH5 and 8, and in sodium or potassium phosphate at pH8. Particles revealed low zeta potential values in phosphate buffers at pH5 indicating insufficient electrostatic stabilization. After freeze-thawing, an increase in NP size was strongly reduced in potassium phosphate and sodium citrate buffers. Subsequent pH measurements upon freezing revealed a drastic acidic pH shift in sodium phosphate which was further demonstrated to destabilize NPs. The ionic stabilizers gelatin A/B, Na-CMC, and SDS, were suitable to improve colloidal stability in phosphate buffers at pH5 highlighting the importance of charge stabilization. Freeze-thawing stability was best in presence of gelatin A/B, followed by PVA, mannitol, or sucrose. Depletion and steric stabilization were insufficient using PEG and surfactants respectively. Thus, we could identify the fundamental formulation principles to preserve inorganic NPs upon freezing: i) sufficient charge stabilization, ii) a maintained pH during freezing, and iii) the addition of a suitable stabilizer, preferably gelatin, not necessarily surfactants. This forms the basis for future studies, e.g. on lyophilization.

Formulation, process, and storage strategies for lyophilizates of lipophilic nanoparticulate systems established based on the two models paliperidone palmitate and solid lipid nanoparticles

Lyophilization formulation and process development for lipophilic nanoparticle (NPs) products is highly challenging as the NPs have a low colloidal stability. We compared two different NP types, pure paliperidone palmitate nanocrystals and trimyristin solid lipid nanoparticles regarding formulation, process, and storage stability aspects. Freeze-thaw studies were conducted to investigate the basic formulation aspects such as buffer type, pH, and ionic strength as well as different cryoprotectants. In freeze-drying conventional ramp freezing was performed and compared to freezing with an annealing step added or with controlled ice nucleation. Different formulations were lyophilized and tested for short-term storage stability up to 6 weeks. Samples were analyzed for particle size, subvisible particle number, specific surface area, residual moisture, crystallinity, and glass transition temperature. Sucrose significantly better stabilized both NP types against freeze-thaw stress compared to mannitol demonstrating the importance of a fully amorphous matrix. While the impact of buffer type and pH was negligible, the aggregation propensity of NPs was reduced in presence of NaCl. The freezing step also impacted NP aggregation but the effect was less important than the formulation design. Surfactants did not necessarily improve the colloidal stability but resulted in a lower glass transition temperature of the lyophilizates and may cause phase separation which limits storage stability. This hurdle can be overcome by using a hydroxypropyl-β-cyclodextrin/ sucrose mixture as cryoprotectant. In general, we could show a similar freeze-drying behavior of the two NP types. Thus, we established a formulation and process approach to achieve stable lyophilizates of lipophilic NPs based on two different types of NPs. The general rules should be transferable to other NPs facilitating lyophilization development.

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.

A Kinetic Model for Spray-Freezing of Pharmaceuticals

Spray freeze-drying (SFD), which includes spray-freezing into droplets and dynamic vacuum drying, presents a promising alternative approach to manufacture dried pharmaceuticals more efficiently than conventional vial freeze-drying. Without reliable predictive models for the SFD conditions of interest, any respective process development still relies on empirical approaches. In this work, we propose an improved modeling framework to describe the fast freezing (<1 s) that sub-millimeter droplets undergo in the present SFD process. The modeled freezing rate accounts for both the kinetics of ice growth and droplet heat transfer mechanisms. Computational fluid dynamics (CFD) simulations and experiments on bulk spray-freezing are combined to refine and validate the proposed reduced-order model. While this study is limited to water-sucrose solutions, the present modeling approach can be extended to other pharmaceutical excipients. For the cooling rates of interest, model results indicate that droplets with initial sucrose concentration higher than 20% w/w will transit to a glassy state before completion of crystallization and, consequently, devitrification is expected during post spray-freezing manipulation of the bulk material. In practice, such compact model does not only allow quantification of process parameters that cannot be measured in real time but also enable the choice of optimal spraying conditions for production of free-flowing, high-quality frozen droplets that meet the target product profile.

Phase-Field Modeling of Freeze Concentration of Protein Solutions

Bulk solutions of therapeutic proteins are often frozen for long-term storage. During the freezing process, proteins in liquid solution redistribute and segregate in the interstitial space between ice crystals. This is due to solute exclusion from ice crystals, higher viscosity of the concentrated solution, and space confinement between crystals. Such segregation may have a negative impact on the native conformation of protein molecules. To better understand the mechanisms, we developed a phase-field model to describe the growth of ice crystals and the dynamics of freeze concentration at the mesoscale based on mean field approximation of solute concentration and the underlying heat, mass and momentum transport phenomena. The model focuses on evolution of the interfaces between liquid solution and ice crystals, and the degree of solute concentration due to partition, diffusive, and convective effects. The growth of crystals is driven by cooling of the bulk solution, but suppressed by a higher solute concentration due to increase of solution viscosity, decrease of freezing point, and the release of latent heat. The results demonstrate the interplay of solute exclusion, space confinement, heat transfer, coalescence of crystals, and the dynamic formation of narrow gaps between crystals and Plateau border areas along with correlations of thermophysical properties in the supercooled regime.

Progress in formulation development and sterilisation of freeze-dried oligodeoxynucleotide-loaded gelatine nanoparticles

Oligodeoxynucleotide (ODN)-loaded gelatine nanoparticles (GNPs) have proven their outstanding potential in the treatment of allergic diseases such as equine asthma and canine atopic dermatitis, which are appropriate models for the corresponding human diseases. To encourage the development of a marketable product, long term stability and sterility needs to be ensured. In this work, we aimed to advance freeze-drying options to stabilise ODN-loaded GNPs. Matrix-assisted laser desorption/ionisation mass spectrometry time-of-flight was implemented as a versatile tool to assess ODN stability. With this method long-term storage stability of lyophilised ODN-loaded GNPs formulated in sucrose or trehalose was achieved. Controlled nucleation was further introduced to optimise the lyophilisation approach. This allowed shortening of the process in comparison to standard freeze-drying procedures. Particle sizes, polydispersity indices, ODN stability, residual moisture and glass transition temperature were maintained upon storage. Excipient portfolio was enlarged by novel amino acid containing formulations for lyophilisates. His emerged as an excellent excipient in stabilising lyophilised ODN-loaded GNPs, whereas addition of Arg and Gly revealed to be inadequate at accelerated conditions. Lastly, gamma irradiation was evaluated as a suitable sterilisation method of ODN-loaded GNPs.

Development of a Parenteral Formulation of NTS-Polyplex Nanoparticles for Clinical Purpose

Neurotensin (NTS)-polyplex is a nanoparticle system for targeted gene delivery that holds great promise for treatment of Parkinson’s disease and various types of cancer. However, the high instability in aqueous suspension of NTS-polyplex nanoparticles is a major limitation for their widespread clinical use. To overcome this obstacle, we developed a clinical formulation and a lyophilization process for NTS-polyplex nanoparticles. The reconstituted samples were compared with fresh preparations by using transmission electron microscopy, dynamic light scattering, electrophoretic mobility, circular dichroism and transfection assays in vitro and in vivo. Our formulation was able to confer lyoprotection and stability to these nanoparticles. In addition, transmission electron microscopy (TEM) and size exclusion-high performance liquid chromatography (SEC-HPLC) using a radioactive tag revealed that the interaction of reconstituted nanoparticles with fetal bovine or human serum did not alter their biophysical features. Furthermore, the formulation and the lyophilization procedure guaranteed functional NTS-polyplex nanoparticles for at least six months of storage at 25 °C and 60% relative humidity. Our results offer a pharmaceutical guide for formulation and long-term storage of NTS-polyplex nanoparticles that could be applied to other polyplexes.

Electrospun nanofibers as versatile interfaces for efficient gene delivery

The integration of gene delivery technologies with electrospun nanofibers is a versatile strategy to increase the potential of gene therapy as a key platform technology that can be readily utilized for numerous biomedical applications, including cancer therapy, stem cell therapy, and tissue engineering. As a spatial template for gene delivery, electrospun nanofibers possess highly advantageous characteristics, such as their ease of production, their ECM-analogue nature, the broad range of choices for materials, the feasibility of producing structures with varied physical and chemical properties, and their large surface-to-volume ratios. Thus, electrospun fiber-mediated gene delivery exhibits a great capacity to modulate the spatial and temporal release kinetics of gene vectors and enhance gene delivery efficiency. This review discusses the powerful characteristics of electrospun nanofibers, which can function as spatial interfaces capable of promoting controlled and efficient gene delivery.

Studying the morphology of lyophilized protein solids using X-ray micro-CT: effect of post-freeze annealing and controlled nucleation

The objective of this study was to determine how different techniques used during the freezing step of lyophilization affect morphology of the dried protein solids. Aqueous solutions containing recombinant human albumin, trehalose, and sodium phosphate buffer were dried after their freezing by shelf-ramp cooling, immersion in liquid nitrogen, or controlled ice nucleation. Some shelf-frozen solutions were heat treated (annealed) before the vacuum drying. We used three-dimensional (3D) X-ray micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) to study the morphology of solids. The X-ray micro-CT images of the lyophilized microporous solids showed traces of varied size and structure ice crystals that were comparable to corresponding SEM images. A post-freeze heat treatment and a controlled nucleation both induced larger ice crystal ghosts in the solids. The variations in the structure of walls surrounding ice crystals, formed by the different freezing procedures, should affect the water vapor transition during the primary and secondary drying. Some solids also showed higher-density layer in the upper surface. Overall, the simple sample preparation procedures and the ample morphological information make the X-ray micro-CT appropriate for analyzing lyophilized pharmaceuticals.

Effects of formulation and process factors on the crystal structure of freeze-dried Myo-inositol

The objective of this study was to elucidate effects of formulation and process variables on the physical forms of freeze-dried myo-inositol. Physical properties of myo-inositol in frozen solutions, freeze-dried solids, and cooled heat-melt solids were characterized by powder X-ray diffraction (PXRD), thermal analysis (differential scanning calorimetry [DSC] and thermogravimetric), and simultaneous PXRD-DSC analysis. Cooling of heat-melt myo-inositol produced two forms of metastable anhydrate crystals that change to stable form (melting point 225 °C-228 °C) with transition exotherms at around 123 °C and 181 °C, respectively. Freeze-drying of single-solute aqueous myo-inositol solutions after rapid cooling induced crystallization of myo-inositol as metastable anhydrate (transition at 80 °C-125 °C) during secondary drying segment. Contrarily, postfreeze heat treatment (i.e., annealing) induced crystallization of myo-inositol dihydrate. Removal of the crystallization water during the secondary drying produced the stable-form myo-inositol anhydrate crystal. Shelf-ramp slow cooling of myo-inositol solutions resulted in the stable and metastable anhydrous crystal solids depending on the solute concentrations and the solution volumes. Colyophilization with phosphate buffer retained myo-inositol in the amorphous state. Crystallization in different process segments varies crystal form of freeze-dried myo-inositol solids.

Miscibility as a factor for component crystallization in multisolute frozen solutions

The relationship between the miscibility of formulation ingredients and their crystallization during the freezing segment of the lyophilization process was studied. The thermal properties of frozen solutions containing myo-inositol and cosolutes were obtained by performing heating scans from -70 °C before and after heat treatment at -20 °C to -5 °C. Addition of dextran 40,000 reduced and prevented crystallization of myo-inositol. In the first scan, some frozen solutions containing an inositol-rich mixture with dextran showed single broad transitions (Tg's: transition temperatures of maximally freeze-concentrated solutes) that indicated incomplete mixing of the concentrated amorphous solutes. Heat treatment of these frozen solutions induced separation of the solutes into inositol-dominant and solute mixture phases (Tg' splitting) following crystallization of myo-inositol (Tg' shifting). The crystal growth involved myo-inositol molecules in the solute mixture phase. The amorphous-amorphous phase separation and resulting loss of the heteromolecular interaction in the freeze-concentrated inositol-dominant phase should allow ordered assembly of the solute molecules required for nucleation. Some dextran-rich and intermediate concentration ratio frozen solutions retained single Tg's of the amorphous solute mixture, both before and after heat treatments. The relevance of solute miscibility on the crystallization of myo-inositol was also indicated in the systems containing glucose or recombinant human albumin.

Lyophilization of a triply unsaturated phospholipid: effects of trace metal contaminants

As liquid liposomal formulations are prone to chemical degradation and aggregation, these formulations often require freeze drying (e.g., lyophilization) to achieve sufficient shelf-life. However, liposomal formulations may undergo oxidation during lyophilization and/or during prolonged storage. The goal of the current study was to characterize the degradation of 1,2-dilinolenoyl-sn-glycero-3-phosphocholine (DLPC) during lyophilization and to also probe the influence of metal contaminants in promoting the observed degradation. Aqueous sugar formulations containing DLPC (0.01 mg/ml) were lyophilized, and DLPC degradation was monitored using HPLC/UV and GC/MS methods. The effect of ferrous ion and sucrose concentration, as well as lyophilization stage promoting lipid degradation, was investigated. DLPC degradation increased with higher levels of ferrous ion. After lyophilization, 103.1 ± 1.1%, 66.9 ± 0.8%, and 28.7 ± 0.7% DLPC remained in the sucrose samples spiked with 0.0 ppm, 0.2 ppm, and 1.0 ppm ferrous ion, respectively. Lipid degradation predominantly occurs during the freezing stage of lyophilization. Sugar concentration and buffer ionic strength also influence the extent of lipid degradation, and DLPC loss correlated with degradation product formation. We conclude that DLPC oxidation during the freezing stage of lyophilization dramatically compromises the stability of lipid-based formulations. In addition, we demonstrate that metal contaminants in sugars can become highly active when lyophilized in the presence of a reducing agent.