Research Article pubs.acs.org/journal/ascecg
Porous Chitin Microbeads for More Sustainable Cosmetics† Catherine A. King,‡ Julia L. Shamshina,§ Oleksandra Zavgorodnya,⊥ Tatum Cutfield,‡ Leah E. Block,⊥ and Robin D. Rogers*,‡,⊥,∥ ‡
Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada Mari Signum, Ltd., 3205 Tower Oaks Boulevard, Rockville, Maryland 20852, United States ⊥ Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States ∥ 525 Solutions, Inc., 720 Second Street, P.O. Box 2206, Tuscaloosa, Alabama 35403, United States §
S Supporting Information *
ABSTRACT: The microbead form is a material architecture that is promising for use in biomedical and cosmetic applications; however, the use of petroleum-based microbeads (i.e., plastics) has raised significant environmental concerns in recent years. Microbeads prepared from renewable polymers could represent a sustainable alternative to these synthetic microbeads. This work explores the use of chitin in preparing biodegradable, biocompatible microbeads of low toxicity. Chitin microbeads were synthesized using the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]); the IL was used to both extract chitin directly from waste shrimp shell and to prepare the porous microbeads by coagulation in polypropylene glycol (PPG). The effects of biopolymer source and bead-preparation parameters on the formation of beads were investigated, as well as the effects of the drying conditions on the dry bead structure. It was found that IL-extracted chitin could be used to prepare beads of homogeneous size distribution (with 60% of beads 125−250 μm) and shape, while commercially available practical grade chitin could not, suggesting that high molecular weight chitin is required for bead-material formation. Supercritical CO2 drying and lyophilization of the wet beads led to dry chitin beads with an opaque appearance, porous interiors, and uniform shape. Loading and release studies of representative active compounds (indigo dye and sodium salicylate) into the chitin beads indicated that the dry beads could be easily loaded from an aqueous solution of active compound and could release 90% of the active compound within 7 h in deionized (DI) water at room temperature. KEYWORDS: Microspheres, Porous beads, Chitin, Ionic liquids, Cosmetic microbeads
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INTRODUCTION
Personal care companies (including Unilever, Target, Johnson & Johnson, Procter & Gamble, and L’Oréal) were some of the largest producers of microsphere-containing products.7 In 2014, the global market for microspheres had attained $2.3 billion and was expected to reach $3.5 billion by 2020, registering a compound annual growth rate (CAGR) of 7.8% from 2015 to 2020. The medical technology market segment for microspheres alone was expected to grow from $504 million in 2015 to $810 million in 2020, at a CAGR of 10.0% from 2015 to 2020.7 However, as synthetic polymers have found widespread application in the global market, they have become more ubiquitous in the environment, leading to increasing concern about their environmental impacts.8 Although quantitative studies on routes of entry of microbeads into the environment are limited, it has been suggested that the
Microbeads are spherical solid particles with diameters from 5 μm to 1 mm, which are generally produced from polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), or nylon plastics.1 The use of microbeads is becoming more popular due to improvements in microsphere quality and functionality, and accordingly, they have increasingly been used in food science2 and separations3 and as exfoliants in cosmetics and personal care products.3 Additionally, they are gaining popularity in biomedical applications, including uses in medical diagnostics as injectable biomaterials, as reagents in diagnostic devices, and as drug-delivery vehicles.4 In biotechnological applications, microspheres are less prone to aggregation, providing significant advantages over nonspherical particles which tend to aggregate, complicating injection and delivery to the targeted sites. In addition, the microsphere surface can be functionalized if necessary to induce a desired response within the surrounding tissue.5,6 © 2017 American Chemical Society
Received: August 31, 2017 Revised: October 27, 2017 Published: October 30, 2017 11660
DOI: 10.1021/acssuschemeng.7b03053 ACS Sustainable Chem. Eng. 2017, 5, 11660−11667
Research Article
ACS Sustainable Chemistry & Engineering
dimethylacetamide/lithium chloride (DMAc/LiCl),37 where chitin microspheres were obtained for enzyme immobilization. Methods using aqueous sodium hydroxide−urea (NaOH/urea) eutectic have been used as well, in one case for the direct preparation of beads. However, it should be noted that the chitin was pretreated with NaOH, which could lead to deacetylation and the formation of chitosan.38 This solvent system was also used for the preparation of chitin microspheres via the formation and processing of nanofibers (although, again, the chitin was pretreated with NaOH).39,40 Aside from neat chitin microspheres, composites of chitin with additives as well as chitosan-based (the deacetylated form of chitin) microspheres have been prepared. Composite microspheres of chitin and silica have been prepared from the IL 1-butyl-3-methylimidazolium acetate ([C4mim][OAc]); however, these were pressed into a mold and never studied as individual beads.41 Composite microspheres from chitin and poly(D,L-lactide-co-glycolide) (PLGA) have also been prepared.42 Cross-linked chitosan beads have been reported as well, using DMAc/LiCl and aqueous acetic acid (CH3COOH), respectively.43 Here, we set out to demonstrate the possibility of obtaining pure chitin microbeads, uniform in size, using a nontoxic solvent and coagulation medium. We aimed to develop an approach that would allow control of microsphere size and shape and eliminate process waste generated during current production methods in the design of more environmentally friendly processes, in order to develop a scalable process for microbeads suitable for commercial use. Scalable continuous processes have been developed for the production of cellulose beads,44 but as of yet there has been no scalable, reliable method reported for the production of neat chitin microspheres. Here, the IL [C2mim][OAc] was used for the extraction of high molecular weight chitin from shrimp shells and also for the solution processing of the biopolymer into the microsphere architecture. We also studied the effect of the source of chitin (chitin extracted from biomass with [C2mim][OAc] and commercially available chitin) on bead synthesis using IL processing. Batch-processing parameters such as the chitin solution properties, coagulation phase, and formation parameters were optimized for the preparation of uniform chitin beads. Loading and release of the chitin beads with representative active ingredients were tested with indigo dye and sodium salicylate.
effluent of wastewater treatment plants acts as one such route. One study, for example, demonstrated that although treatment plants retain a majority of the microplastic fragments, there was still substantial leakage of microplastics from the effluent water.9 The Australian Environment Protection Authority (EPA Australia) recently reported a U.K. case study that anticipated that between 4 594 and 94 500 microbeads can leak to the environment per a single use of a microbead-containing face scrub.10,11 Another study suggested the average abundance of microplastic beads in some locations to be 43 000 microplastic particles/km2.12 Although their fate once released is not fully understood, it is known that microplastics can leach toxic additives, adsorb pollutants, enter the marine food chain, and contaminate large bodies of water, from lakes to oceans.13−15 All of this has raised public support for the banning of microbeads and has prompted action from nongovernmental organizations, multinational corporations, and policymakers.16 Thus, in 2015, the United States enacted federal legislation to ban microbeads in rinse-off cosmetics,17 causing many big players in the cosmetic industry to begin eliminating microbeads from their production lines. Companies such as L’Oréal, Johnson and Johnson, and Crest have all begun phasing out microbeads in their personal care products. In fact, both Johnson & Johnson and Crest have plans in place for a complete phase out of microbeads in their products globally by the end of 2017.18 Biopolymers have recently seen increased interest as a promising alternative to petroleum-based polymers19 and could be applied here to the preparation of microbeads. Chitin, the second most abundant biopolymer, has many inherent properties such as natural biodegradability, biocompatibility, and nontoxicity, and it occurs in abundance in waste sources (such as crustacean shells),20 which can microbially and enzymatically degrade. Because of all of this, it is of particular interest for use in many of the areas in which microbeads are used, especially in cosmetics, personal care,21 pharmaceutical, and medical applications (e.g., drug delivery22 and enzyme immobilization23). In recent years, our group has reported extraction and regeneration of high molecular weight chitin directly from shrimp shell waste using the ionic liquid (IL) 1-ethyl-3methylimidazolium acetate ([C2mim][OAc]). Using solution processing, we have prepared various material architectures such as fibers,24−26 films,27 and nanomats.28−30 We hypothesized, based on our work with these architectures and work we have done in the preparation of beads from IL/cellulose solutions,31 that chitin could be used for the preparation of microbeads, which would be useful in specific applications such as the delivery of active ingredients within cosmetic applications. Also, the use of such a biodegradable biopolymer in place of synthetic ones would avoid many of the environmental problems associated with synthetic microplastic beads. General preparation methods for synthetic microspheres include spray-drying,32 emulsification,33 and ionic gelation.34,35 However, as chitin dissolution is difficult in most solvent systems, only spray-drying and emulsion methods have been used to make chitin beads, with very few studies being conducted with a commercial product in mind. Additionally, these methods require harsh solvents and lead to poor control of the sphere size and shape.36 The preparation of neat chitin beads has been done via toxic or corrosive solvents such as
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RESULTS AND DISCUSSION Bead Preparation. The preparation of neat chitin beads was attempted with both IL-extracted shrimp shell chitin and PG chitin from IL solution. The formation of homogeneous, viable beads, as well as the size and shape of the beads formed, is dependent on the chitin−IL solution properties, the properties of the coagulation phase, and the process parameters. Our previous publications have demonstrated that the ability to form a material depends on solution properties of the chitin−IL solution, such as the chitin source used, viscosity of the chitin/IL solution, and temperature of the chitin/IL solution.27,30 Other literature has suggested that the process parameters (such as rate of addition of the polymeric solution to the coagulation phase) are crucial for the size control of beads.45,46 The method used here for bead preparation was based on that of cellulose in IL.31 As our previous studies with cellulose 11661
DOI: 10.1021/acssuschemeng.7b03053 ACS Sustainable Chem. Eng. 2017, 5, 11660−11667
Research Article
ACS Sustainable Chemistry & Engineering Table 1. Optimized Parameters for Chitin Bead Preparation from IL-Extracted Chitin biopolymer/IL solution
bead formation
chitin source and loading viscosity temperature rate of biopolymer/IL solution addition coagulation bath temperature stirring method
regenerated IL-extracted chitin, 3 wt % 185 (9) cP 100 °C 5 mL/min PPG-2000 start at 100 °C, reduce to 55 °C overhead stirrer, 850 rpm
the bead size decreased to
