Abstract
The encapsulation of small molecule drugs in nanomaterials has become an increasingly popular approach to the delivery of therapeutics. The use of emulsions as templates for the synthesis of drug impregnated nanomaterials is an exciting area of research, and a great deal of progress has been made in understanding the interfacial chemistry that is critical to controlling the physicochemical properties of both the encapsulated material and the templated material. For example, control of the interfacial tension between an oil and aqueous phase is a fundamental concern when designing drug delivery vehicles that are stabilized by particulate surfactants at the fluid interface. Particles in general are capable of self-assembly at a fluid interface, with a preference for one or the other of the phases, and much work has focussed on modification of the particle properties to optimize formation and stability of the emulsion. An issue arises however when a model, single oil system is translated into more complex, real-world scenarios, which are often multi-component, with the incorporation of charged active ingredients and other excipients. The result is potentially a huge change in the properties of the dispersed phase which can lead to a failure in the capability of particles to continue to stabilize the interface. In this mini-review, we will focus on two encapsulation strategies based on the selective deposition of particles or proteins on a fluid-fluid interface: virus-like particles and polymer microcapsules formed from particle-stabilized emulsion templates. The similarity between these colloidal systems lies in the fact that particulate entities are used to stabilize fluid cores. We will focus on those studies that have described the effect of subtle changes in core composition on the self-assembly of particles at the fluid-fluid interface and how this influences the resulting capsule structure.
Highlights
Encapsulation in nanomaterials is a powerful approach to the delivery of active components that require protection from harsh external environments
The use of a fluid-fluid interface as a template for the synthesis of polymer microcapsules encapsulating an active component is an exciting area and a great deal of progress has been made in understanding the interfacial chemistry that is critical to controlling the physicochemical properties of both the encapsulated material and the templated material
The increasing use of particle-stabilized fluid-fluid interfaces to template the formation of micro/nanostructured capsules that encapsulate an active component has led to increasing complexity of the components that make up the template emulsion
Summary
Encapsulation in nanomaterials is a powerful approach to the delivery of active components that require protection from harsh external environments. Based on observations in our laboratory and others (Manuela et al, 2017), the physicochemical properties of the active component itself can have a profound effect on the stability of this interface and this has prompted us to review existing literature in this area. Whilst it is well-known that the contact angle is a key parameter for stabilization of emulsions using particles (Binks et al, 2007), the literature surrounding the effect of core composition on the organization of stabilizers at the interface is scarce. We will focus on capsule-like structures and not solid microparticles where the active ingredient is absorbed into a solid matrix, or covalently bonded to a micro/nanostructure or protein, and the interested reader is instead directed to several recent reviews in these areas (Duncan, 2011; Kopecek, 2013; Chudasama et al, 2016; Han et al, 2016; Ramazani et al, 2016)
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