Microflow-assisted assembling of multi-scale polymer particles by controlling surface properties and interactions
Graphical abstract
Introduction
Hydrogel particles are of great interest for a wide range of biotechnological and therapeutic applications because of their hydrophilic, biocompatible and highly tunable nature [1], [2], [3], [4]. In addition, these particles provide an essential cross-linking network for the use in sensing applications [5]. Fundamental properties and applications demand for an appropriate material selection. Major aspects, on the other side, such as size distribution, surface functionalities, degradability, and stability against different surroundings are equally influential. Swellable microparticles with incorporated metal nanoparticles are attractive for miniaturized diagnostics, labeling, sensing and catalysis [6], [7], [8]. Likewise, doping of the active materials, particularly functional polymer nanoparticles and different fluorophores in the hydrogel particles can create reliable systems for the delivery of multiple cargos at targeted sites. For example, significant concentration of insulin can be delivered (self-regulated release of actives) within a short time to the diabetic patient upon glucose responsive polymeric delivery systems [9].
Secondly, some progresses in order to mimicking the modular principles of biomolecular and cellular construction by nano-technical architectures were realized in case of thin films and surface technology. But, there is a significant inconsistency for bringing this method for continuing the bottom-up principle into the mid-nanometer and higher-nanometer range. Electrical charging, polarization, and chemical interactions are mainly responsible for the formation of complex structures in molecular nanotechnology [10]. Interactions of the nanoparticles are in a key position for bridging the technological gap between molecular dimension and high-precision mechanical manufacturing. Interestingly, electrical forces are also able to control the interactions of nanoparticles [11], [12] and the stability of colloidal solutions [13], [14]. Nucleation, growth, and assembling steps of the nanoparticles demand for a strict control of local reaction and transport conditions for well-defined in-situ interfacial interactions. Recently, the formation of colloidal clusters on the basis of assembling the small particles have emerged significantly [15], [16], [17], [18], [19]. These clusters mimic the structures and then properties of simple chemical molecules such as H2O and CO2. On the other side, single-step routes for producing complex and shape-controlled polymer nanoparticles via in-situ nanoassembling were performed [13], [20], [21]. Smaller nanoparticles are unstable in the solution due to high surface energy. Charged ligands can be applied on the surface which sustain the stability of nanoparticles in solution by inter-particles repulsive force [20], and can also be useful for tuning the surface morphology and introduce additional functionality [22], [23]. Key demand for a strong assembly is the availability of high charge density at surface. Poly-ionic electrolytes fulfill such requirement by compensating the charge of inner surface and providing a high charge density at outer surface. Layer-by-layer modification is well-known for planar surface [24], and a reversibly switching surface by external stimuli can open the opportunity for interfacial engineering [25]. Here, it is shown that desired layers of oppositely charged polyelectrolytes can be used on the polymer nanoparticles for controlled electrostatic nanoassembly formation. Assemblies of two or more different domains can combine physical, chemical and physicochemical properties of the materials for various applications. To maintain the inter-particles distance between assembling particles is another key challenge for screening the properties of particulate assembly. Appropriate concentrations, very homogeneous reaction environment and charge management, therefore, become essential components for architecting uniform nanoassemblies. Microreaction technology, where nanoliter and picoliter volumes can be manipulated in a microscale channel, is a promising strategy in order to provide such platforms [26], [27], [28]. Efficient reactant mixing, fast phase transfer, low volume and high surface areas for reactions are the advantages of this technique [29]. Moreover, nucleation and growth processes of forming nanoparticles can be realized in an extremely uniform environment and produce distinct nanoparticles as well as nanoparticle assemblies of high homogeneity. This technology can also be efficiently useful for preparing morphology controlled particles [30], [31]. Therefore, in the present work it is described how these principles can also be used for a controlled ex-situ, in-situ and flow assembling of nanoscale polymer particles. Moreover, the formation strategies and synthesis approaches of nanometer up to micrometer scale polymer particles and multi-scale tunable assembly particles are given. In case of hydrogel microparticles; nanoparticles loading capacity, controlled mixing of different fluorophores, and combined fluorescence effect are described. In nanoscale assembly; assembling strength between oppositely charged nanoparticles on the basis of their size and charge density, combined fluorescence effect during ex-situ assembling, nanoparticles size growth during in-situ assembling, and nanoparticles assembling precision by maintaining specific distance in microflow arrangement are presented.
Section snippets
Microreactor design
A complete microreactor framework was lithographically fabricated as described in our previous report [32]. Photolithographic procedures using an optical mask aligner and dry etching processes for the micro-patterning of the mask layer were applied for the fabrication of the silicon (Si) chip. The silicon microchip (Fig. S1, Supporting Information) has been placed inside a micro-channel, where it was embedded into two fluidic chamber walls. The width of the capillary slit was adjusted to about
Hydrogel microparticles assemblies
Microflow processes are promising platforms for the generation of very homogeneous functional polymer particles with tunable chemical compositions and surface properties [33], [34], [35]. By utilizing these advantages, fluorescent nanoparticles, microparticles and multi-scale assembly particles have been prepared. Fig. 1 represents the microfluidic arrangement for the synthesis of hydrogel assembly particles.
Conclusion
In this work, different types of polymer assembling architectures on the basis of controlled interfacial interactions have been prepared. Polymers are soft, amorphous (or semi-crystalline), and swellable in the solution phase. Hence, polymer hydrogel particles can be able to encapsulate and embed various types of active components in the cross-linked network for different applications. Here, microflow processes have been utilized to controllably embed size as well as color tuned polymer
Acknowledgments
The authors thank Steffen Schneider, Dr. Mike Günther and Dr. Alexander Groß for their technical support and the fruitful discussions. The financial support by Deutsche Forschungsgemeinschaft (DFG) (Project: KO1403/39-1) is gratefully acknowledged.
References (55)
- et al.
Eur. Polym. J.
(2015) - et al.
Int. J. Pharm.
(2013) - et al.
Chem. Eng. J.
(2013) Chem. Eng. Sci.
(2001)- et al.
Int. J. Pharm.
(2015) - et al.
J. Control. Release
(2013) - et al.
Mater. Lett.
(2015) - et al.
Acta Biomater.
(2014) - et al.
Chem. Rev.
(2001) - et al.
Adv. Mater.
(2006)
Acs Appl. Mater. Interfaces
Chem. – Eur. J.
J. Mater. Sci.
Chem. Eng. Technol.
Acc. Chem. Res.
Intermolecular and Surface Forces
Part. Part. Syst. Charact.
Nanotechnol. Rev.
Macromol. Chem. Phys.
Angew. Chem. Int. Ed.
Chem. Soc. Rev.
Soft Matter
Phys. Rev. X
Proc. Natl. Acad. Sci.
Acs Appl. Mater. Interfaces
Langmuir
ACS Appl. Mater. Interfaces
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