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Formulation of Nanoemulsions Stabilized by Cellulose Nanocrystals

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Formulation of Nanoemulsions Stabilized by Cellulose Nanocrystals EXAMENSARBETE INOM KEMIVETENSKAP AVANCERAD NIVÅ, 30 HP STOCKHOLM, SVERIGE 2020 Formulation of Nanoemulsions Stabilized by Cellulose Nanocrystals Marco Maccagno January 2020 Supervisors: Isabel Mira Research Institutes of Sweden, RISE (Sweden) Examiner: Prof. Mark Rutland Department of Surface and Corrosion Science, KTH (Sweden). Collaborators within RISE: Tiffany Abitbol, Elizabeth Hörlin, Niklas Nordgren Collaborators outside RISE: Prof. Emily Cranston University of British Columbia (Canada). KTH SKOLAN FÖR KEMI, BIOTEKNOLOGI OCH HÄLSA Sammanfattning Cellulosa-nanokristaller (CNC) är biobaserade nanopartiklar med förmågan att stabilisera emulsioner av olja i vatten (o/w) tack vare deras medelhöga vätbarhet och storlek i nanometerskalan. Dessa och andra typer av partikelstabiliserade emulsioner, så kallade Pickering-emulsioner, är av stort akademiskt och industriellt intresse på grund av deras överlägsna stabilitet mot droppkoalescens jämfört med klassiska tensidstabiliserade emulsioner. Det tätt packade skiktet av partiklar vid gränsytan mellan olja och vatten påverkar också inkapslingsförmågan hos emulsionsdropparna vilket kan utnyttjas för att reglera frisättning av aktiva substanser i läkemedel eller kosmetiska produkter. I dessa typer av applikationer är användningen av emulsioner med droppar i nano-storlek fördelaktig på grund av deras långsiktiga kolloidala stabilitet, förbättrad hud- och slemhinnetransport, förbättrad biotillgänglighet och hudkänsla. Denna studie hade två huvudmål. Det första var att undersöka möjligheten att producera o/w emulsioner med droppar av submikron-storlek med hjälp av mikrofluidisering och genom att använda en kombination av CNC och hydroxypropylmetylcellulosa (HPMC), ett ytaktivt cellulosa-derivat som har visat sig ha förmågan att modifiera vätbarheten hos CNC och därigenom förbättra dess förmåga att adsorbera vid olja/vatten-gränsytan. En viktig aspekt av denna första del av studien var att få bättre förståelse för hur CNC och HPMC var för sig påverkar egenskaperna hos emulsionerna. Det andra målet med arbetet var att bedöma prestandan hos o/w CNC/HPMC-emulsioner för frisättning av lutein, ett hydrofob aktivt ämne, och jämföra med tensidstabiliserade emulsioner. För den första delen av denna studie gjordes en serie o/w-emulsioner (50 och 10 viktprocent olja) innehållande olika mängder av CNC och HPMC. Droppstorleksfördelningen (vid t = 0 och över tid) och dropparnas gräddsättning följdes. Ett statistiskt försöksverktyg användes för att definiera antalet emulsionssystem som skulle beredas och karakteriseras. För frisättningsstudier med lutein användes Franz-celler med ett syntetiskt membran som in vitro-permeabilitetstest. Emulsioner av olja i vatten med droppar med genomsnittlig diameter om ca. 600 nm producerades med hjälp av mikrofluidisering av en kombination av CNC och hydroxypropylmetylcellulosa (HPMC). Inom det studerade CNC- och HPMC-koncentrationsområdet (0,03% till 1,5% CNC och 0,005% till 0,75% HPMC) gynnade höga koncentrationer av CNC i kombination med höga koncentrationer av HPMC en mindre droppstorlek. Förmågan att uppnå submikron-droppstorlekar vid ett fast mikrofluidiseringstryck visade sig dock påverkas av förändringar i systemets förhållande mellan CNC och olja. Den minsta möjliga droppstorleken vid CNC till olja-förhållandet 0,75:100 (emulsion innehållande 50% olja) var 1,68 um. Emulsioner med medelstorlekar om ca. 600 nm uppnåddes vid samma CNC-koncentration och CNC/HPMC-förhållande när förhållandet CNC till olja var 7:100 (emulsion innehållande 10% olja). Ett överskott av HPMC i vattenfasen (HPMC-koncentration 0,3%) förbättrade emulsionernas stabilitet mot krämning på grund av den kombinerade effekten av mindre droppstorlek och högre viskositet hos den kontinuerliga fasen. Emulsioner med höga koncentrationer av CNC (0,75%) och låga koncentrationer av HPMC (<0,55%) visade god stabilitet mot koalescens under en period av 2 månader utan någon förändring i droppstorleksfördelningen över tid. Av en CNC / HPMC-emulsion innehållande 1% lutein blev mängden lutein som passerat genom Franz- cellernas membran efter 24 timmar cirka dubbelt så hög (11% mot 5%) i emulsioner med en medel droppstorlek på 3 μm jämfört med emulsioner med 40 μm droppar. Samtidigt var den totalamängden frisläppt lutein från emulsioner stabiliserade med sojalecitin högre (19% mot 11%) än den från CNC/HPMC-emulsioner med jämförbara droppstorlekar. Denna skillnad kan bero på den reglerande effekten av det tätt packade CNC-HPMC-gränsskiktet men kan också vara relaterat till den mycket lägre viskositeten (5 mot ca 500 mPa.s vid 100-1 s) av lecitin-emulsionerna. Abstract Cellulose nanocrystals (CNCs) are bio-based nanoparticles with the ability to stabilize oil and water emulsions thanks to their intermediate wettability and nanometric size. These and other types of particle-stabilized emulsions, commonly referred to as Pickering emulsions, are of great academic and industrial interest due to their superior stability against drop coalescence compared to classical surfactant-stabilized emulsions. In addition, the presence of a densely packed layer of particles at the oil-water interface is expected to impact the encapsulation ability of the emulsion droplets opening up for the possibility to use these systems to modulate the release of active substances in the context of oral or topical delivery formulations used in pharmaceutical and cosmetic applications. In these types of applications, the use of emulsions with nano-sized drops is advantageous due to their long- term colloidal stability, improved dermal and mucosal transport of actives, improved bioavailability and greater aesthetic appeal and skin feel. This study had two main objectives. The first one was to explore to possibility to produce o/w emulsions with submicron-size drops by means of microfluidization using a combination of CNCs and hydroxypropyl methylcellulose (HPMC), a surface-active cellulose derivative that has been shown to have the ability to modify the wettability of CNCs (thereby enhancing their ability to adsorb at the oil/water interface). An important aspect of this first part of the study also involved gaining better understanding on the separate contributions of CNCs and HPMC to the properties of the resulting emulsions. The second objective of the work was to assess the performance of selected o/w CNC/HPMC compared to that of surfactant-stabilised emulsions in terms of their ability to deliver lutein, a hydrophobic prototype active of interest for topical delivery applications. For the first part of this study, a series of o/w emulsions (50 and 10% w oil) containing different amounts of CNCs and HPMC were prepared and characterised in terms of: drop-size distribution after (at t=0 and over time) as well as in terms of the creaming rate of the drops. A design of experiments statistical approach was used to define the number of emulsions systems to be prepared and characterised. For the lutein delivery study, an in vitro permeation test via Franz-cells using a synthetic membrane was used to study the release of lutein from different emulsion formulations. It was possible to produce o/w emulsions with submicron-size drops (average drop diameters down to ca. 600 nm) by means of microfluidization using a combination of CNCs and hydroxypropyl methylcellulose (HPMC). Within the CNCs and HPMC concentration range studied (0.03% to 1.5% CNC and 0.005% to 0.75% HPMC), high concentrations of CNCs in combination with high concentrations of HPMC favoured a reduction of the drop size. However, the ability to attain submicron drop sizes at fixed microfluidization pressures was found to be modulated by changes in the CNC to oil ratio on the system. While the minimum attainable drop size at CNC to oil ratio of 0.75:100 (emulsion containing 50% oil) was 1.68 µm, emulsions with average sizes of ca. 600 nm were attained at the same CNC concentration and CNC/HPMC ratio when the CNC to oil ratio was 7:100 (emulsion containing 10% oil).The presence of excess of HPMC in the aqueous phase (HPMC concentrations 0.3%) favoured the stability of the emulsions against creaming, due to the combined effect of having smaller drop sizes and higher continuous phase viscosities. Emulsions with high concentrations of CNCs (0.75%) and low HPMC concentrations (< 0.55%), showed good stability towards coalescence for a period of 2 months with no change in drop size distribution over time. The amount of permeated lutein after 24 hours from a CNC/HPMC emulsion containing 1% of lutein was found to be ca. twice as high (11% vs. 5%) in emulsions with a median drop size of 3 μm compared to emulsions with 40 μm drops. At the same time, the total permeated amount of lutein from emulsions stabilized with soy lecithin was found to be higher (19% vs. 11%) than that from CNC/HPMC emulsions with similar drop sizes. This difference could be due to the regulating effect of the densely packed CNC-HPMC interfacial layer but could also be related to the much lower viscosity (5 vs. ca. 500 mPa.s at 100-1 s) of the lecithin emulsions. 1 Table of contents 1 Table of contents ............................................................................................................................. 6 2 Introduction ..................................................................................................................................... 8 2.1 Objectives ..............................................................................................................................
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