Emerging delivery systems based on aqueous two-phase systems: A review

Abstract

The aqueous two-phase system (ATPS) is an all-aqueous system fabricated from two immiscible aqueous phases. It is spontaneously assembled through physical liquid-liquid phase separation (LLPS) and can create suitable templates like the multicompartment of the intracellular environment. Delicate structures containing multiple compartments make it possible to endow materials with advanced functions. Due to the properties of ATPSs, ATPS-based drug delivery systems exhibit excellent biocompatibility, extraordinary loading efficiency, and intelligently controlled content release, which are particularly advantageous for delivering drugs in vivo. Therefore, we will systematically review and evaluate ATPSs as an ideal drug delivery system. Based on the basic mechanisms and influencing factors in forming ATPSs, the transformation of ATPSs into valuable biomaterials is described. Afterward, we concentrate on the most recent cutting-edge research on ATPS-based delivery systems. Finally, the potential for further collaborations between ATPS-based drug-carrying biomaterials and disease diagnosis and treatment is also explored.

Graphical abstract

Figure 1

This overview describes the formation of all-aqueous droplets from ATPS and the stabilization and transformation to obtain ATPS-based biomaterials, which can then participate in drug and cell delivery in vivo. The combination of ATPSs with other delivery systems to improve their delivery capacity is also an important part of ATPS-based delivery systems.

Figure 2

The properties and principles of ATPSs: The horizontal and vertical coordinates indicate the different phases. The blue area indicates the mixed phase (single phase), and the red area indicates two aqueous phases (phase separation). Points 1 and 3 of the tie lines indicate the final compositions of the two immiscible aqueous phases after complete phase separation, and the critical point and point 2 represent conditions in which the two phases are of equal concentration. The trend of phase separation is influenced by the variation in the influencing factors on the left and right sides.

Figure 3

Schematic diagram of the stabilization and transformation of all-aqueous droplets.

Figure 4

Stabilization of all-aqueous droplets. (A) Liposome-stabilized all-aqueous droplets. Diagram of the enzymatic reaction and production of artificial mineralizing vesicles to generate CaCO₃(s). Additionally, the confocal images in the bottom right corner display the different calcium ion concentrations in the liposomes. Reprinted with the permission from Ref. . Copyright © 2015 American Chemical Society. (B) Sheet-like particle-stabilized all-aqueous droplets. Schematic representation of the formation of w/w Pickering emulsions via g-CN stabilization. Confocal images below show g-CN stabilized Pickering emulsions containing PEG (stained with FITC) and DEX (stained with RhB). Reprinted with the permission from Ref. . Copyright © 2020 Wiley-VCH. (C) Charged particle-stabilized all-aqueous droplets. Preparation and interface interactions of pectin-chitosan-collagen composite microcapsules. Reprinted with the permission from Ref. . Copyright © 2021 Elsevier. (D) Cross-linking monomer-stabilized all-aqueous droplets. Graphics of lysozyme protein assembly during various fibrillization stages. Reprinted with the permission from Ref. . Copyright © 2016 The Authors.

Figure 5

Transformation of all-aqueous droplets. (A) Crescent-shaped, peptide-modified hydrogel microparticles fabricated via microfluidics, self-orient underwater and function as cell carriers. Reprinted with the permission from Ref. . Copyright © 2018 Wiley-VCH. (B) A schematic of the osmo-solidification process is presented alongside optical images of the procedure and the final particles dyed with Nile red, as well as SEM images of osmo-solidified starch particles (scale bar: 400 μm) and DEX nanoparticles (scale bar: 4 μm). Reprinted with the permission from Ref. . Copyright © 2016 Royal Society of Chemistry. (C) The figure illustrates the process and outcomes of spike formation on DEX-alginate droplets in a PEG-CaCl₂ polymerization bath, emphasizing the roles of diffusion, chemical equilibrium, and concentration gradients in shaping the unique morphology of the polymerized particles. Reprinted with the permission from Ref. . Copyright © 2019 Royal Society of Chemistry. (D) Depiction of the production of size-tunable water-in-water emulsions via all-aqueous electrospray and their size dependence on an applied voltage. Reprinted with the permission from Ref. . Copyright © 2015 American Chemical Society.

Figure 6

Application of ATPS-based biomaterials with complex structures. (A) Characteristics of ATPS-based biomaterials with complex structures: multiple independent compartments structure and mechanisms triggering drug release. (B) A series of diagrams illustrating the fabrication, drug loading, ultrasound-triggered actuation, and subsequent payload release of biphasic microcapsules created with mixed molecular weight PEGDA and high molecular weight DEX. Reprinted with the permission from Ref. . Copyright © 2022 Wiley-VCH. (C) Diagram of preparing alginate microcapsules and confocal images reflecting their structure. Reprinted with the permission from Ref. . Copyright © 2019 American Chemical Society. (D) Depiction of the creation of a triple-compartment system with real-time pH-monitoring capabilities and glucose-responsive, spatiotemporally regulated insulin-PEG-PBA transportation. Reprinted with the permission from Ref. . Copyright © 2022 Wiley-VCH. (E) The figures illustrate the use of a microfluidic aqueous two-phase system for fabricating multi-aqueous core hydrogel capsules, showcasing the system layout, microfluidic chip structure, capsule generation, and an alginate reaction under acidic conditions. Reprinted with the permission from Ref. . Copyright © 2020 Wiley-VCH.

Figure 7

Cancer treatment and organ regeneration based on cell delivery in vivo. (A) Cancer treatment: (i) Multiple chemokines released from tumor tissue activate the relevant receptors on MSCs, attracting MSCs to migrate toward the tumor tissue. (ii) After the chemotactic effect, MSCs with genetic modification express the corresponding cytotoxic proteins, thus inhibiting cancer cell proliferation or inducing apoptosis. (B) Organ regeneration: (i) MSCs regulate cells in injured kidney tissue through the paracrine effect. (ii) Regulated renal cells can complete kidney repair and regeneration.

Figure 8

Prospective discussion of ATPS-based biomaterials in drug delivery and disease therapy. (A) Rapid sample identification and disease diagnosis can be achieved by adding ATPS-based carriers containing immunoglobulin to exploit the enrichment of the ATPS system. (B) Real-time fluorescence imaging can be achieved in vitro by adding fluorescent markers to ATPS-based carriers. (C) Targeted-modified ATPS-based carriers carrying drugs can achieve vaccine-like functions and clear pathogens.

Figure 9

An overview illustrating the emerging delivery systems based on ATPSs and application prospects.