Abstract
In this paper we study the release of cargo from polymeric nano-carriers under shear. Vesicles formed by two star block polymers— () and ()—and one linear block copolymer— (), are investigated using dissipative particle dynamics (DPD) simulations. - and -blocks are solvophobic and -block is solvophilic. The three polymers form vesicles of different structures. The vesicles are subjected to shear both in bulk and between solvophobic walls. In bulk shear, the mechanisms of cargo release are similar for all vesicles, with cargo travelling through vesicle membrane with no preferential release location. When sheared between walls, high cargo release rate is only observed with vesicle after it touches the wall. For vesicle, the critical condition for high cargo release rate is the formation of wall-polymersome interface after which the effect of shear rate in promoting cargo release is secondary. High release rate is achieved by the formation of solvophilic pathway allowing cargo to travel from the vesicle cavity to the vesicle exterior. The results in this paper show that well controlled target cargo release using polymersomes can be achieved with polymers of suitable design and can potentially be very useful for engineering applications. As an example, polymersomes can be used as carriers for surface active friction reducing additives which are only released at rubbing surfaces where the additives are needed most.
Highlights
Nano-carriers are nanoscale containers which can enclose small molecules and protect inclusions from reactions with the outer environment or help separate incompatible components in different compartments [1]
The radius of the vesicle r0 is defined as the minimum distance between the centre of mass of the aggregate and the nearest solvophilic B-beads in the outer skin of the aggregate. r00 defines the cavity of the vesicle and is the maximum distance between the centre of mass of the vesicle and the B-beads forming the inner skin
Vesicles made of three different polymer architectures, ABC, A12B6 A2 (ABA) and AB, experience bulk shear and shear between walls
Summary
Nano-carriers are nanoscale containers which can enclose small molecules and protect inclusions from reactions with the outer environment or help separate incompatible components in different compartments [1]. Vesicles are a popular type of nano-carriers with membranes made of lipids or polymers [2] which can encapsulate cargo such as drugs [3,4,5,6] or agrochemicals [7] during formation. These cargo could be released steadily or quickly (controlled release) when desired conditions are reached. Mable et al [8,9] encapsulated silica nanoparticles with vesicles made of poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymers. They found that the polymersomes partially collapsed and Polymers 2018, 10, 336; doi:10.3390/polym10030336 www.mdpi.com/journal/polymers
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