Microfluidic elaboration of polymer microfibers from miscible phases: Effect of operating and material parameters on fiber diameter
Graphical abstract
Introduction
Microfibers have attracted a lot of attention due to (i) their large surface area to volume ratio, (ii) their diverse properties arising from the great variety of materials they are made of, and (iii) their ability to assemble into 3D complex structures and foldability [1]. These benefits enable polymer microfibers to have an excellent potential in many applications such as biomedicine [2], [3], [4], [5], [6], fiber optics [7], sensors [8,9], and water treatment [10,11]. Different approaches have been employed to produce micro- and nanofibers such as melt spinning [12], wet spinning [13], draw spinning [14], macromolecular assembly [15], and electrospinning [16], techniques relying on the physical mechanism of solidification to produce fibers, i.e. the starting raw material is a polymer solution. As such they suffer from limitations regarding (i) the nature of the material employed and (ii) the morphologies of fibers that can be achieved [17]. Hence, it is difficult to produce fibers with diverse morphologies and with a broad range of materials. Recently, microfluidic spinning has shown a great potential for the production of microfibers with diverse compositions, morphologies, and surface functionalities. This technique consists in stretching a stream of monomer or polymer solution (core phase) by an immiscible or miscible solution (continuous or sheath phase) inside a microfluidic device. Due to the small size of the device microchannel (ca. 100 µm), laminar flow is commonly achieved affording reproducibility and stability to the flow; two highly desirable features required for the production of fibers with given diameters and morphologies. By manipulating the flow inertia (i.e. individual solution flow rates), solution viscosity, interfacial tension between the core and sheath phases and taking possibly advantage of gravity forces, fibers with diverse morphologies such as grooved, flat, core-shell, hollow, and Janus can be easily produced. The choice of material becomes broader due to the panel of solidification methods, i.e. photopolymerization, ionic and chemical crosslinking, solvent exchange, and solvent evaporation. Fiber surface functionalization is also possible by encapsulation method or in situ chemistry [1].
Surface to volume ratio is one of the foremost fiber parameters that drive their applications. Since the latter is inversely proportional to the fiber diameter [18], many properties such as mechanical [19,20], cell adhesion and proliferation [20], biomimicking extracellular matrix [21], optical extinction capacity [22], and filtration performance [23] depend on the fiber diameter. Although, fiber diameter is a crucial parameter, the literature scarcely and partially reports on all the possible parameters responsible for controlling the fiber diameter in microfluidic spinning. Most reports address only the effect of sheath/continuous fluid and core/disperse fluids flow rates independently [24,25] or in the form of sheath to core flow rate ratio (Qs/Qc) [26], [27], [28], [29]. Liu et al. observed the effect of the capillary diameter on the fiber diameter using the thermoinitiated polymerization induced phase separation technique [30]. But there is no literature in which researchers interpreted these results into some mathematical form to predict the fiber diameter.
Herein, we developed an empirical relationship which can predict the fiber diameter in relation with others operating and materials parameters for the case where the monomer and its polymer are miscible with the continuous phase. The investigation of operating parameters was not only limited to flow rates and capillary diameter, but the effect of viscosity of sheath fluid and monomer volume fraction in the core phase were also investigated. Two monomers, tri(propylene glycol) diacrylate (TPGDA), poly(ethylene glycol) diacrylate (PEGDA), and one prepolymer, UV-curable adhesive NOA 89, were used as reference materials for the synthesis of fibers using in situ photoirradiation in a capillary-based microfluidic device. All results were used to extract an empirical correlation which predicted the final microfiber diameter upon variation of the capillary number ratio, monomer volume fraction, and internal capillary diameter.
Section snippets
Results and discussion
The fibers were produced using a capillary-based microfluidic device (Fig. 1) involving two phases: (1) the core fluid (Φc) becoming the fiber upon photopolymerization and (2) the sheath fluid (Φs) consisting in poly(ethylene glycol) (PEG), whose flow rates are Qc and Qs respectively. PEG was used due to its miscibility with core fluid, commercial availability, high tunable viscosity with its molecular weight which prevents fast diffusion of Φc into Φs, and reasonable shearing force to produce
Conclusion
Polymer microfibers of two different monomers and one photocurable adhesive with diameters as low as 23 µm were produced by in situ photopolymerization using a capillary-based coaxial microfluidic device and a miscible PEG sheath fluid. The impact of different operating and material parameters such as volume fraction of monomer in core phase, flow rate ratio of sheath to core fluid, viscosity of the sheath fluid and dimensions of the capillary on the resulting fiber diameter were studied. The
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Authors thank W. Drenckhan for discussions and A. Collard for all technical aspects. Authors are grateful to P. Allgayer for mechanical engineering support. WR would like to acknowledge the Higher Education Commission of Pakistan (HEC) for his Ph.D. fellowship.
References (39)
- et al.
Composite ECM–alginate microfibers produced by microfluidics as scaffolds with biomineralization potential
Mater Sci Eng C
(2015) - et al.
Novel technique to control inner and outer diameter of calcium-alginate hydrogel hollow microfibers, and immobilization of mammalian cells
Biochem Eng J
(2010) - et al.
Polymer fibers with magnetic core decorated with titanium dioxide prospective for photocatalytic water treatment
J Environ Chem Eng
(2018) - et al.
Intensification of wastewater treatment with polymer fiber-based biofilm carriers
Microchem J
(2013) - et al.
A novel nano/micro-fibrous scaffold by melt-spinning method for bone tissue engineering
J Bionic Eng
(2015) - et al.
From short peptides to nanofibers to macromolecular assemblies in biomedicine
Biotechnol Adv
(2012) - et al.
The effect of fibre diameter on filtration and flux distribution-relevance to submerged hollow fibre modules
J Membr Sci
(2001) - et al.
Hydrodynamic spinning of hydrogel fibers
Biomaterials
(2010) - et al.
Effects of capillary number and flow rates on the hydrodynamics of droplet generation in two-phase cross-flow microfluidic systems
J Taiwan Inst Chem Eng
(2021) - et al.
Polymerization-induced phase separation fabrication: a versatile microfluidic technique to prepare microfibers with various cross sectional shapes and structures
Chem Eng J
(2017)
Microfluidics based synthesis of coiled hydrogel microfibers with flexible shape and dimension control
Sens Actuators B
Multifunctional micro/nanoscale fibers based on microfluidic spinning technology
Adv Mater
Microfluidic synthesis of microfibers for magnetic-responsive controlled drug release and cell culture
PLoS One
Microfluidics-produced collagen fibers show extraordinary mechanical properties
Nano Lett
Assembly of alginate microfibers to form a helical structure using micromanipulation with a magnetic field
J Micromech Microeng
Recent advances in optical fiber devices for microfluidics integration
J Biophotonics
Polyaniline nanofiber wrapped fabric for high performance flexible pressure sensors
Polymers
Conductive cotton fabrics for motion sensing and heating applications
Polymers
Wet spinning of chitosan fibers: effect of sodium dodecyl sulfate adsorption and enhanced dope temperature
ACS Appl Polym Mater
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2022, European Polymer JournalCitation Excerpt :min−1. The side-by-side capillary-based microfluidic system previously reported[31] was used to prepare the thermoresponsive Janus fibers. Thermoresponsive Janus fibers, in which one part consisted of thermoresponsive polymer and the other one of non-thermoresponsive polymer, were produced using two core phases and one sheath phase (Φsheath).