Abstract
Lipids and amphiphilic block copolymers spontaneously self-assemble in water to form a plethora of micelles and vesicles. They are typically fluidic in nature and often mechanically weak for applications such as drug delivery and gene therapeutics. Mechanical properties of polymeric materials could be improved by forming crystalline structures. However, most of the self-assembled micelles and vesicles have curved surfaces and precisely tuning crystallization within a nanoscale curved space is challenging, as the curved geometry is incommensurate with crystals having three-dimensional translational symmetry. Herein, we report using a miniemulsion crystallization method to grow nanosized, polymer single-crystal-like capsules. We coin the name crystalsome to describe this unique structure, because they are formed by polymer lamellar crystals and their structure mimics liposomes and polymersomes. Using poly(L-lactic acid) (PLLA) as the model polymer, we show that curved water/p-xylene interface formed by the miniemulsion process can guide the growth of PLLA single crystals. Crystalsomes with the size ranging from ∼148 nm to over 1 μm have been formed. Atomic force microscopy measurement demonstrate a two to three orders of magnitude increase in bending modulus compared with conventional polymersomes. We envisage that this novel structure could shed light on investigating spherical crystallography and drug delivery.
Highlights
Lipids and amphiphilic block copolymers spontaneously self-assemble in water to form a plethora of micelles and vesicles
Two solutions are mixed and ultrasonicated to generate a miniemulsion system with poly(L-lactic acid) (PLLA)/p-xylene droplets stabilized by cetyltrimethylammonium bromide (CTAB) in water
90 °C is chosen as the crystallization temperature; the crystallization rate is relatively slow and the crystals formed at this temperature is relatively isotropic[25]
Summary
Lipids and amphiphilic block copolymers spontaneously self-assemble in water to form a plethora of micelles and vesicles They are typically fluidic in nature and often mechanically weak for applications such as drug delivery and gene therapeutics. Dinsmore et al.[17] used this technique to fabricate solid capsules, named as colloidosome, with precise control of size, permeability and mechanical strength The fundamentals of these two-dimensional spherical crystals are intriguing and some key concepts of crystallography such as grain boundaries, defect formation and elastic instability are interestingly different from those occurring in a flat space[18,19,20]. We disclose a new strategy to grow nanosized polymer single-crystal-like capsules using directed crystallization at curved liquid/liquid interface In this approach, crystalline polymers are dissolved in an oil phase and emulsified with an aqueous solution using a miniemulsion approach[23]. Nanosized polymer single-crystal-like capsules (named as crystalsomes) have been formed and they show significantly enhanced mechanical properties compared with liposomes and polymersomes
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