Porous morphology and mechanical properties of poly(lactide-co-glycolide) hollow fiber membranes governed by ternary-phase inversion

A Comprehensive Review of Hollow-Fiber Membrane Fabrication Methods across Biomedical, Biotechnological, and Environmental Domains

This work presents methods of obtaining polymeric hollow-fiber membranes produced via the dry-wet phase inversion method that were published in renowned specialized membrane publications in the years 2010-2020. Obtaining hollow-fiber membranes, unlike flat membranes, requires the use of a special installation for their production, the most important component of which is the hollow fiber forming spinneret. This method is most often used in obtaining membranes made of polysulfone, polyethersulfone, polyurethane, cellulose acetate, and its derivatives. Many factors affect the properties of the membranes obtained. By changing the parameters of the spinning process, we change the thickness of the membranes' walls and the diameter of the hollow fibers, which causes changes in the membranes' structure and, as a consequence, changes in their transport/separation parameters. The type of bore fluid affects the porosity of the inner epidermal layer or causes its atrophy. Porogenic compounds such as polyvinylpyrrolidones and polyethylene glycols and other substances that additionally increase the membrane porosity are often added to the polymer solution. Another example is a blend of two- or multi-component membranes and dual-layer membranes that are obtained using a three-nozzle spinneret. In dual-layer membranes, one layer is the membrane scaffolding, and the other is the separation layer. Also, the temperature during the process, the humidity, and the composition of the solution in the coagulating bath have impact on the parameters of the membranes obtained.

An anisotropic immerse precipitation process for the preparation of polymer membranes

We study the immerse precipitation process in a ternary polymer/solvent/non-solvent system by numerically solving the two-dimensional Cahn-Hilliard phase field equation. In particular, we introduce anisotropic mobility, namely the mobility of a polymer varies over different spatial directions, and focus on the porosity morphology of the obtained polymer membrane. Simulations reveal that as the anisotropy increases in the polymer mobility, the polymer pattern changes from nearly isotropic and random voids to strips parallel to the direction with smaller mobility. The influence of anisotropy quickly saturates. The anisotropic mobility model is also applied to a ternary system mimicking the preparation of a hollow fiber membrane, and shows strong effects on the membrane porosity pattern.

Bioactive Poly(lactic acid)-Cocoa Bean Shell Composites for Biomaterial Formulation: Preparation and Preliminary In Vitro Characterization

The unique lignocellulosic and solvent-extractive chemical constituents of most natural fibers are rich in natural polymers and bioactive molecules that can be exploited for biomaterial formulation. However, although natural fibers’ main constituents have been already incorporated as material reinforcement and improve surface bioactivity of polymeric materials, the use of the whole natural fibers as bioactive fillers remains largely unexplored. Thus, we put forward the formulation of natural fiber filling and functionalization of biomaterials by studying the chemical composition of cocoa bean shells (CBS) and proposing the fabrication and characterization of polylactic acid (PLA) and CBS-based composite by solvent-casting. As was expected from previous studies of agro-industrial wastes, the main components of CBS were to cellulose (42.23 wt.%), lignin (22.68 wt.%), hemicellulose (14.73 wt.%), and solvent extractives (14.42 wt.%). Structural analysis (FTIR) confirms the absence of covalent bonding between materials. Thermal degradation profiles (DSC and TGA) showed similar mass losses and thermal-reaction profiles for lignocellulosic-fibers-based composites. The mechanical behavior of the PLA/CBS composite shows a stiffer material behavior than the pristine material. The cell viability of Vero cells in the presence of the composites was above 94%, and the hemolytic tendency was below 5%, while platelet aggregation increased up to 40%. Antioxidant activity was confirmed with comparable 2,2-diphe-277 nyl-1-picryl-hydrazyl-hydrate (DPPH) free-radical scavenging than Vitamin C even for PLA/CBS composite. Therefore, the present study elucidates the significant promise of CBS for bioactive functionalization in biomaterial-engineering, as the tested composite exhibited high biocompatibility and strong antioxidant activity and might induce angiogenic factors’ release. Moreover, we present an eco-friendly alternative to taking advantage of chocolate-industry by-products.

Fabrication of a dual-layer cell-laden tubular scaffold for nerve regeneration and bile duct reconstruction

Tubular scaffolds serve as a controllable extracellular environment to guide the repair and regeneration of tissues. But it is still a challenge to achieve both excellent mechanical properties and cell compatibility of artificial scaffolds for long-term structural and biological stability. In this study, a four-step solution casting method was developed to fabricate dual-layer cell-laden tubular scaffolds for nerve and bile duct regeneration. The dual-layer tubular scaffold consisted of a bone marrow mesenchymal stem cells (BMSCs)-laden hydrogel inner layer and an outer layer of gelatin methacrylate (GelMA)/polyethylene glycol diacrylate. While the inner layer had a good biocompatibility, the outer layer had desired mechanical properties. The interfacial toughness, Young's modulus, maximum tensile strain, and compressive modulus of dual-layer tubular scaffolds were 65 J m^-2, 122.37 ± 23.21 kPa, 100.87 ± 40.10%, and 39.14 ± 18.56 N m^-1, respectively. More importantly, the fabrication procedure was very cell-friendly, since the BMSC viability encapsulated in the inner layer of 10% (w/v) GelMA reached 94.68 ± 0.43% after 5 d of culture. Then, a preliminary evaluation of the potential application of dual-layer tubular scaffolds as nerve conduits and biliary scaffolds was performed, and demonstrated that the cell-laden dual-layer tubular scaffolds proposed in this work are expected to extend the application of tubular scaffolds in tissue engineering.

Additive-lathe 3D bioprinting of bilayered nerve conduits incorporated with supportive cells

Nerve conduits have been identified as one of the most promising treatments for peripheral nerve injuries, yet it remains unsolved how to develop ideal nerve conduits with both appropriate biological and mechanical properties. Existing nerve conduits must make trade-offs between mechanical strength and biocompatibility. Here, we propose a multi-nozzle additive-lathe 3D bioprinting technology to fabricate a bilayered nerve conduit. The materials for printing consisted of gelatin methacrylate (GelMA)-based inner layer, which was cellularized with bone marrow mesenchymal stem cells (BMSCs) and GelMA/poly(ethylene glycol) diacrylate (PEGDA)-based outer layer. The high viability and extensive morphological spreading of BMSCs encapsulated in the inner layer was achieved by adjusting the degree of methacryloyl substitution and the concentration of GelMA. Strong mechanical performance of the outer layer was obtained by the addition of PEGDA. The performance of the bilayered nerve conduits was assessed using in vitro culture of PC12 cells. The cell density of PC12 cells attached to cellularized bilayered nerve conduits was more than 4 times of that on acellular bilayered nerve conduits. The proliferation rate of PC12 cells attached to cellularized bilayered nerve conduits was over 9 times higher than that on acellular bilayered nerve conduits. These results demonstrate the additive-lathe 3D bioprinting of BMSCs embedded bilayered nerve conduits holds great potential in facilitating peripheral nerve repair.

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A multi-nozzle additive-lathe 3D bioprinting technology is developed to fabricate a bilayered nerve conduit.

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The outer layer of nerve conduit provide a strong mechanical property and the inner layer has a good biocompatibility.

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Bone marrow mesenchymal stem cells (BMSCs) are incorporated in the inner layer of nerve conduit using bioprinting.

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In vitro culture of PC12 cells demonstrates the neuron outgrowth is significantly improved in BMSCs embedded nerve conduits.

Three-Dimensional Bioprinting of Perfusable Hierarchical Microchannels with Alginate and Silk Fibroin Double Cross-linked Network

Vascularization is essential for the regeneration of three-dimensional (3D) bioprinting organs. As a general method to produce microfluidic channels in 3D printing constructs, coaxial extrusion has attracted great attention. However, the biocompatible bioinks are very limited for coaxial extrusion to fabricate microchannels with regular structure and enough mechanical properties. Herein, a hybrid bioink composed of alginate (Alg) and silk fibroin (SF) was proposed for 3D bioprinting of microchannel networks based on coaxial extrusion. The rheological properties of the bioink demonstrated that the hybrid Alg/SF bioink exhibited improved viscosity and shear thinning behavior compared with either pure Alg or SF bioink and had similar storage and loss modulus in a wide range of shear frequency, indicating a sound printability. Using a coaxial extrusion system with calcium ions and Pluronic F127 flowing through the core nozzle as cross-linkers, the Alg/SF bioink could be extruded and deposited to form a 3D scaffold with interconnected microchannels. The regular structure and smooth pore wall of microchannels inside the scaffold were demonstrated by optical coherence tomography. Micropores left by the rinse of F127 were observed by scanning electron microscope, constituting a hierarchical structure together with the microchannels and printed macropores. Fourier transform infrared spectroscopy analysis proved the complete rinse of F127 and the formation of β-sheet SF structure. Thus, Alg/SF could form a double cross-linked network, which was much stronger than the pure Alg network. Moreover, cells in the Alg/SF scaffold showed higher viability and proliferation rate than in the Alg scaffold. Therefore, Alg/SF is a promising bioink for coaxial extrusion-based 3D bioprinting, with the printed microchannel network beneficial for complex tissue and organ regeneration.