Photochemically induced cyclic morphological dynamics via degradation of autonomously produced, self-assembled polymer vesicles

Abstract

Autonomous and out-of-equilibrium vesicles synthesised from small molecules in a homogeneous aqueous medium are an emerging class of dynamically self-assembled systems with considerable potential for engineering natural life mimics. Here we report on the physico-chemical mechanism behind a dynamic morphological evolution process through which self-assembled polymeric structures autonomously booted from a homogeneous mixture, evolve from micelles to giant vesicles accompanied by periodic growth and implosion cycles when exposed to oxygen under light irradiation. The system however formed nano-objects or gelation under poor oxygen conditions or when heated. We determined the cause to be photoinduced chemical degradation within hydrated polymer cores inducing osmotic water influx and the subsequent morphological dynamics. The process also led to an increase in the population of polymeric objects through system self-replication. This study offers a new path toward the design of chemically self-assembled systems and their potential application in autonomous material artificial simulation of living systems.

Chemoadaptive Polymeric Assemblies by Integrated Chemical Feedback in Self-Assembled Synthetic Protocells

“…Objects labeled with Rhodamine B grew into giant vesicle structures until a critical diameter was reached, after which the vesicles collapsed into small droplets which exhibited 100% brighter fluorescence signals (Figure ci–iii, Figure S21a, Supplementary Video 2), due to the local increase in concentration of the fluorescent dye confined within the object). This behavior was previously observed , in the absence of dye-labeled monomer for individual objects (Figure S8) and was observed to be prevalent in the presence of Rhodamine B-labeled monomers. The measured reduction in object diameter was 80% (Figure S21b).…”

“…The PEG- b -PAN objects increase in size and population numbers and exhibit chemotaxis-driven crowding to the spot with highest light intensity. This behavior has previously been observed over periods of 14 h. , In contrast, in this investigation we observed massive object chemotaxis within 1 h of microscopy analysis, which suggests that there is a greater anisotropy across the object membranes during irradiation. Unlike in the case where presynthesized macro-CTAs are provided to the PISA reaction, objects produced by click-PISA have additional contributions to the stability of the membrane, based on the rate of the CuAAC reaction ( Scheme ).…”

“…Individual vesicular objects were observed to reach a maximum sustainable diameter before collapsing into a small droplet (Supplementary Video 1, Figure S8), which is possibly due to the objects reaching a critical surface tension across the membrane which results in the implosion of the object. , Fluorescence microscopy and cryogenic SEM analysis of the objects postirradiation was conducted (Figure S9 and Figure S10). The objects analyzed by cryo-SEM were not observed to be spherical, which we attribute to the intense energy input causing the structures to distort and form higher energy nonequilibrium conformations.…”

“…In this context, polymerization-induced self-assembly (PISA) has emerged as an effective one-pot method to produce microscale self-assembled block copolymer vesicles in aqueous solution. , The chemical synthesis of protocells with an encapsulating semipermeable and tunable membrane from an initially isotropic and homogeneous medium through PISA offers a plausible autonomous mechanism for the formation of such essential structures. , As such, PISA offers a chemical route to obtain these structures, which is not offered by the typically used methods to synthesize protocells and vesicles, by the exogeneous delivery of amphiphiles to the media using techniques such as solvent-switch or extrusion. − Indeed, PISA provides a route to increase chemical system complexity using external energy and fuel by producing amphiphiles during the polymerization reaction through a far-from-equilibrium process as reagents are consumed and the resulting assemblies become dynamic in morphology and structure . Our group has shown that under excitation, giant vesicular objects can undergo cyclic growth-collapse “phoenix” behavior, , dynamic merging or division, or rearrange their internal structure as the result of maintaining this consumption of energy. But can we go deeper in the laboratory search for simpler origins?…”

“…The larger gap in chemical complexity between the starting reagents and products due to using these simpler components is compensated by the consumption of energy through the integrated reaction cycles. For this reason, the objects produced in this study exhibit a high sensitivity to the energetic environment compared to objects formed by nonchemically integrated approaches , and therefore morphological and population evolution occur over much shorter time scales. Changes in the chemical and (through osmotic and defect-generated processes) physical state of the system, driven by the external input of energy, provide routes to complex behavior starting with simple nonamphiphilic components.…”