Polydopamine Inter-Fiber Networks: New Strategy for Producing Rigid, Sticky, 3D Fluffy Electrospun Fibrous Polycaprolactone Sponges

A simple, green chemistry technology for fabrication of tissue-engineered scaffolds based on mussel-inspired 3D centrifugal spun

The fabrication of 3D fibrous scaffolds with highly interconnected pores has been crucial in the development of tissue regeneration techniques. The present study describes the fabrication of 3D fibrous scaffolds by freeze-drying of polydopamine (PDA) coated centrifugal spun gelatin fibers. We wanted to combine the mussel-inspired chemistry, Maillard reaction, and the 3D microstructural advantages of centrifugal spun fibers to develop the green fibrous scaffolds at low cost, high speed, and desired mold shape. The resultant PDA-gelatin fibers exhibited a smooth 3D microstructure with a uniform formation of PDA thin ad-layer that enhanced the mechanical properties and stability of the scaffolds, and thereby decreased the degradation rate. All scaffolds showed promising properties including good dimensional and mechanical stability under wet state, optimal porosity over 94%, and high water uptake of approximately 1500%. The results of cell culture studies, further confirmed that all scaffolds exhibited appropriate biocompatibility, cell proliferation, migration, and infiltration. Particularly, the PDA-coated scaffolds showed a significant enhancement in proliferation, migration, and infiltration of HDF-GFP⁺ cells. These results show that a 3D porous fibrous scaffold with simplifying tunable density and desirable shape on a large scale can be readily prepared for different fields of tissue engineering applications.

Advancing spinal fusion: Interbody stabilization by in situ foaming of a chemically modified polycaprolactone

Spinal fusion (SF) surgery relies on medical hardware such as screws, cages and rods, complemented by bone graft or substitute, to stabilize the interventioned spine and achieve adequate bone ingrowth. SF is technically demanding, lengthy and expensive. Advances in material science and processing technologies, proposed herein, allowed the development of an adhesive polymeric foam with the potential to dismiss the need for invasive hardware in SF. Herein, 3D foams of polycaprolactone doped with polydopamine and polymethacrylic acid (PCL pDA pMAA) were created. For immediate bone stabilization, in situ hardening of the foam is required; therefore, a portable high-pressure device was developed to allow CO₂ foaming within bone defects. Foams were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Adhesive properties of PCL pDA pMAA outperformed PCL when tested using glass surfaces (p < 0.001) or spinal plugs (p < 0.05). No cytotoxicity was observed, and bioactivity was confirmed by the CaP layer formed upon 7 days immersion in simulated body fluid. As proof of concept, PCL pDA pMAA was extruded in-between ex vivo porcine vertebrae, and micro-computed tomography revealed similar properties to those of trabecular bone. This novel system presents great promise for instrumentation-free interbody fusion.

Bismuth Vanadate/Bilirubin Oxidase Photo(bio)electrochemical Cells for Unbiased, Light-Triggered Electrical Power Generation

The construction of bias- and donor-free photobioelectrochemical cells for the generation of light-triggered electrical power is presented. The developed oxygen reduction biocathodes are based on bilirubin oxidase (BOD) that originates from Myrothecium verrucaria (MvBOD) and a thermophilic Bacillus pumilus (BpBOD). Methods to entrap the BOD with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) redox molecules in a polydopamine layer are presented. A pH-independent, positively charged pyrenebetaine linker was synthesized, utilized, and led to a threefold improvement to the bioelectrocatalytic current. Both the developed polydopamine/ABTS/MvBOD and the pyrenebetaine/BpBOD biocathodes were further coupled with BiVO₄ /cobalt phosphate water-oxidation photoanodes to construct biotic/abiotic photobioelectrochemical cells, which generated power outputs of 0.74 and 0.85 mW cm^-2 , respectively. The presented methods are versatile, show the strength of biotic/abiotic hybrids, and can be further used to couple different redox enzymes with electrodes.

Mussel-inspired 3D fiber scaffolds for heart-on-a-chip toxicity studies of engineered nanomaterials

Due to the unique physicochemical properties exhibited by materials with nanoscale dimensions, there is currently a continuous increase in the number of engineered nanomaterials (ENMs) used in consumer goods. However, several reports associate ENM exposure to negative health outcomes such as cardiovascular diseases. Therefore, understanding the pathological consequences of ENM exposure represents an important challenge, requiring model systems that can provide mechanistic insights across different levels of ENM-based toxicity. To achieve this, we developed a mussel-inspired 3D microphysiological system (MPS) to measure cardiac contractility in the presence of ENMs. While multiple cardiac MPS have been reported as alternatives to in vivo testing, most systems only partially recapitulate the native extracellular matrix (ECM) structure. Here, we show how adhesive and aligned polydopamine (PDA)/polycaprolactone (PCL) nanofiber can be used to emulate the 3D native ECM environment of the myocardium. Such nanofiber scaffolds can support the formation of anisotropic and contractile muscular tissues. By integrating these fibers in a cardiac MPS, we assessed the effects of TiO2 and Ag nanoparticles on the contractile function of cardiac tissues. We found that these ENMs decrease the contractile function of cardiac tissues through structural damage to tissue architecture. Furthermore, the MPS with embedded sensors herein presents a way to non-invasively monitor the effects of ENM on cardiac tissue contractility at different time points. These results demonstrate the utility of our MPS as an analytical platform for understanding the functional impacts of ENMs while providing a biomimetic microenvironment to in vitro cardiac tissue samples. Graphical Abstract Heart-on-a-chip integrated with mussel-inspired fiber scaffolds for a high-throughput toxicological assessment of engineered nanomaterials.

Tubing-Electrospinning: A One-Step Process for Fabricating Fibrous Matrices with Spatial, Chemical, and Mechanical Gradients

Guiding newly generated tissues in a gradient pattern, thereby precisely mimicking inherent tissue morphology and subsequently arranging the intimate networks between adjacent tissues, is essential to raise the technical levels of tissue engineering and facilitate its transition into the clinic. In this study, a straightforward electrospinning method (the tubing-electrospinning technique) was developed to create fibrous matrices readily with diverse gradient patterns and to induce patterned cellular responses. Gradient fibrous matrices can be produced simply by installing a series of polymer-containing lengths of tubing into an electrospinning circuit and sequentially processing polymers without a time lag. The loading of polymer samples with different characteristics, including concentration, wettability, and mechanical properties, into the tubing system enabled unique features in fibrous matrices, such as longitudinal gradients in fiber density, surface properties, and mechanical stiffness. The resulting fibrous gradients were shown to arrange cellular migration and residence in a gradient manner, thereby offering efficient cues to mediate patterned tissue formation. The one-step process using tubing-electrospinning apparatus can be used without significant modifications regardless of the type of fibrous gradient. Hence, the tubing-electrospinning system can serve as a platform that can be readily used by a wide-range of users to induce patterned tissue formation in a gradient manner, which will ultimately improve the functionality of tissue engineering scaffolds.

Three-Dimensional Polydopamine Functionalized Coiled Microfibrous Scaffolds Enhance Human Mesenchymal Stem Cells Colonization and Mild Myofibroblastic Differentiation

Electrospinning has been widely applied for tissue engineering due to its versatility of fabricating extracellular matrix (ECM) mimicking fibrillar scaffolds. Yet there are still challenges such as that these two-dimensional (2D) tightly packed, hydrophobic fibers often hinder cell infiltration and cell-scaffold integration. In this study, polycaprolactone (PCL) was electrospun into a grounded coagulation bath collector, resulting in 3D coiled microfibers with in situ surface functionalization with hydrophilic, catecholic polydopamine (pDA). The 3D scaffolds showed biocompatibility and were well-integrated with human bone marrow derived human mesenchymal stem cells (hMSCs), with significantly higher cell penetration depth compared to that of the 2D PCL microfibers from traditional electrospinning. Further differentiation of human mesenchymal stem cells (hMSCs) into fibroblast phenotype in vitro indicates that, compared to the stiff, tightly packed, 2D scaffolds which aggravated myofibroblasts related activities, such as upregulated gene and protein expression of α-smooth muscle actin (α-SMA), 3D scaffolds induced milder myofibroblastic differentiation. The flexible 3D fibers further allowed contraction with the well-integrated, mechanically active myofibroblasts, monitored under live-cell imaging, whereas the stiff 2D scaffolds restricted that.

Salt-Induced Electrospun Patterned Bundled Fibers for Spatially Regulating Cellular Responses

Implementing patterned fibrous matrices can offer a highly valuable platform for spatially orchestrating hierarchical cellular constructs, specifically for neural engineering approaches, in which striated alignment or directional growth of axons are key elements for the functional recovery of damaged nervous systems. Thus, understanding the structural parameters of patterned fibrous matrices that can effectively promote neural growth can provide crucial clues for designing state-of-the-art tissue engineering scaffolds. To this end, salt-induced electrospun patterned fiber bundles (SiEP bundles) comprising longitudinally stacked multiple fibers were fabricated, and their capabilities of spatially stimulating the responses of neural cells, including PC12 cells, human neural stem cells (hNSCs), and dorsal root ganglia (DRG), were assessed by comparing them to conventional fibrous matrices having either randomly oriented fibers or individually aligned fibers. The SiEP bundles possessed remarkably distinctive morphological and topographical characteristics: multicomplexed infrastructures with nano- and microscale fibers, rough surfaces, and soft mechanical properties. Importantly, the SiEP bundles resulted in spatial cellular elongations corresponding to the fiber directions and induced highly robust neurite extensions along the patterned fibers. Furthermore, the residence of hNSCs on the topographically rough grooves of the SiEP bundles boosted neuronal differentiation. These findings can provide crucial insights for designing fibrous platforms that can spatially regulate cellular responses and potentially offer powerful strategies for a neural growth system in which directional cellular responses are critical for the functional recovery of damaged neural tissues.