Novel biomimetic fiber incorporated scaffolds for tissue engineering

Poly(ε-Caprolactone)-Based Composites Modified With Polymer-Grafted Magnetic Nanoparticles and L-Ascorbic Acid for Bone Tissue Engineering

The aim of this study was to develop multifunctional magnetic poly(ε-caprolactone) (PCL) mats with antibacterial properties for bone tissue engineering and osteosarcoma prevention. To provide good dispersion of magnetic iron oxide nanoparticles (IONs), they were first grafted with PCL using a novel three-step approach. Then, a series of PCL-based mats containing a fixed amount of ION@PCL particles and an increasing content of ascorbic acid (AA) was prepared by electrospinning. AA is known for increasing osteoblast activity and suppressing osteosarcoma cells. Composites were characterized in terms of morphology, mechanical properties, hydrolytic stability, antibacterial performance, and biocompatibility. AA affected both the fiber diameter and the mechanical properties of the nanocomposites. All produced mats were nontoxic to rat bone marrow-derived mesenchymal cells; however, a composite with 5 wt.% of AA suppressed the initial proliferation of SAOS-2 osteoblast-like cells. Moreover, AA improved antibacterial properties against Staphylococcus aureus and Escherichia coli compared to PCL. Overall, these magnetic composites, reported for the very first time, can be used as scaffolds for both tissue regeneration and osteosarcoma prevention.

Nanofiber-induced hierarchically-porous magnesium phosphate bone cements accelerate bone regeneration by inhibiting Notch signaling

Magnesium phosphate bone cements (MPC) have been recognized as a viable alternative for bone defect repair due to their high mechanical strength and biodegradability. However, their poor porosity and permeability limit osteogenic cell ingrowth and vascularization, which is critical for bone regeneration. In the current study, we constructed a novel hierarchically-porous magnesium phosphate bone cement by incorporating extracellular matrix (ECM)-mimicking electrospun silk fibroin (SF) nanofibers. The SF-embedded MPC (SM) exhibited a heterogeneous and hierarchical structure, which effectively facilitated the rapid infiltration of oxygen and nutrients as well as cell ingrowth. Besides, the SF fibers improved the mechanical properties of MPC and neutralized the highly alkaline environment caused by excess magnesium oxide. Bone marrow stem cells (BMSCs) adhered excellently on SM, as illustrated by formation of more pseudopodia. CCK8 assay showed that SM promoted early proliferation of BMSCs. Our study also verified that SM increased the expression of OPN, RUNX2 and BMP2, suggesting enhanced osteogenic differentiation of BMSCs. We screened for osteogenesis-related pathways, including FAK signaing, Wnt signaling and Notch signaling, and found that SM aided in the process of bone regeneration by suppressing the Notch signaling pathway, proved by the downregulation of NICD1, Hes1 and Hey2. In addition, using a bone defect model of rat calvaria, the study revealed that SM exhibited enhanced osteogenesis, bone ingrowth and vascularization compared with MPC alone. No adverse effect was found after implantation of SM in vivo. Overall, our novel SM exhibited promising prospects for the treatment of critical-sized bone defects.

IVM Advances for Early Antral Follicle-Enclosed Oocytes Coupling Reproductive Tissue Engineering to Inductive Influences of Human Chorionic Gonadotropin and Ovarian Surface Epithelium Coculture

In vitro maturation (IVM) is not a routine assisted reproductive technology (ART) for oocytes collected from early antral (EA) follicles, a large source of potentially available gametes. Despite substantial improvements in IVM in the past decade, the outcomes remain low for EA-derived oocytes due to their reduced developmental competences. To optimize IVM for ovine EA-derived oocytes, a three-dimensional (3D) scaffold-mediated follicle-enclosed oocytes (FEO) system was compared with a validated cumulus-oocyte complex (COC) protocol. Gonadotropin stimulation (eCG and/or hCG) and/or somatic cell coculture (ovarian vs. extraovarian-cell source) were supplied to both systems. The maturation rate and parthenogenetic activation were significantly improved by combining hCG stimulation with ovarian surface epithelium (OSE) cells coculture exclusively on the FEO system. Based on the data, the paracrine factors released specifically from OSE enhanced the hCG-triggering of oocyte maturation mechanisms by acting through the mural compartment (positive effect on FEO and not on COC) by stimulating the EGFR signaling. Overall, the FEO system performed on a developed reproductive scaffold proved feasible and reliable in promoting a synergic cytoplasmatic and nuclear maturation, offering a novel cultural strategy to widen the availability of mature gametes for ART.

3D Printed Conductive Multiscale Nerve Guidance Conduit with Hierarchical Fibers for Peripheral Nerve Regeneration

Nerve guidance conduits (NGCs) have become a promising alternative for peripheral nerve regeneration; however, the outcome of nerve regeneration and functional recovery is greatly affected by the physical, chemical, and electrical properties of NGCs. In this study, a conductive multiscale filled NGC (MF-NGC) consisting of electrospun poly(lactide-co-caprolactone) (PCL)/collagen nanofibers as the sheath, reduced graphene oxide /PCL microfibers as the backbone, and PCL microfibers as the internal structure for peripheral nerve regeneration is developed. The printed MF-NGCs presented good permeability, mechanical stability, and electrical conductivity, which further promoted the elongation and growth of Schwann cells and neurite outgrowth of PC12 neuronal cells. Animal studies using a rat sciatic nerve injury model reveal that the MF-NGCs promote neovascularization and M2 transition through the rapid recruitment of vascular cells and macrophages. Histological and functional assessments of the regenerated nerves confirm that the conductive MF-NGCs significantly enhance peripheral nerve regeneration, as indicated by improved axon myelination, muscle weight increase, and sciatic nerve function index. This study demonstrates the feasibility of using 3D-printed conductive MF-NGCs with hierarchically oriented fibers as functional conduits that can significantly enhance peripheral nerve regeneration.

Transparent and Cell-Guiding Cellulose Nanofiber 3D Printing Bioinks

For three-dimensional (3D) bioprinting to fulfill its promise and enable the automated fabrication of complex tissue-mimicking constructs, there is a need for developing bioinks that are not only printable and biocompatible but also have integrated cell-instructive properties. Toward this goal, we here present a scalable technique for generating nanofiber 3D printing inks with unique tissue-guiding capabilities. Our core methodology relies on tailoring the size and dispersibility of cellulose fibrils through a solvent-controlled partial carboxymethylation. This way, we generate partially negatively charged cellulose nanofibers with diameters of ∼250 nm and lengths spanning tens to hundreds of microns. In this range, the fibers structurally match the size and dimensions of natural collagen fibers making them sufficiently large to orient cells. Yet, they are simultaneously sufficiently thin to be optically transparent. By adjusting fiber concentration, 3D printing inks with excellent shear-thinning properties can be established. In addition, as the fibers are readily dispersible, composite inks with both carbohydrates and extracellular matrix (ECM)-derived proteins can easily be generated. We apply such composite inks for 3D printing cell-laden and cross-linkable structures, as well as tissue-guiding gel substrates. Interestingly, we find that the spatial organization of engineered tissues can be defined by the shear-induced alignment of fibers during the printing procedure. Specifically, we show how myotubes derived from human and murine skeletal myoblasts can be programmed into linear and complex nonlinear architectures on soft printed substrates with intermediate fiber contents. Our nanofibrillated cellulose inks can thus serve as a simple and scalable tool for engineering anisotropic human muscle tissues that mimic native structure and function.

Advanced Nanofiber-Based Scaffolds for Achilles Tendon Regenerative Engineering

The Achilles tendon (AT) is responsible for running, jumping, and standing. The AT injuries are very common in the population. In the adult population (21–60 years), the incidence of AT injuries is approximately 2.35 per 1,000 people. It negatively impacts people’s quality of life and increases the medical burden. Due to its low cellularity and vascular deficiency, AT has a poor healing ability. Therefore, AT injury healing has attracted a lot of attention from researchers. Current AT injury treatment options cannot effectively restore the mechanical structure and function of AT, which promotes the development of AT regenerative tissue engineering. Various nanofiber-based scaffolds are currently being explored due to their structural similarity to natural tendon and their ability to promote tissue regeneration. This review discusses current methods of AT regeneration, recent advances in the fabrication and enhancement of nanofiber-based scaffolds, and the development and use of multiscale nanofiber-based scaffolds for AT regeneration.

Vascular Endothelial Growth Factor-Capturing Aligned Electrospun Polycaprolactone/Gelatin Nanofibers Promote Patellar Ligament Regeneration

Ligament injuries are common in sports and other rigorous activities. It is a great challenge to achieve ligament regeneration after an injury due the avascular structure and low self-renewal capability. Herein, we developed vascular endothelial growth factor (VEGF)-binding aligned electrospun poly(caprolactone)/gelatin (PCL/Gel) scaffolds by incorporating prominin-1-binding peptide (BP) sequence and exploited them for patellar ligament regeneration. The adsorption of BP onto scaffolds was discerned by various techniques, such as Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and confocal laser scanning microscope. The accumulation of VEGF onto scaffolds correlated with the concentration of the peptide in vitro. BP-anchored PCL/Gel scaffolds (BP@PCL/Gel) promoted the tubular formation of human umbilical vein endothelial cells (HUVECs) and wound healing in vitro. Besides, BP containing scaffolds exhibited higher content of CD31+ cells than that of the control scaffolds at 1 week after implantation in vivo. Moreover, BP containing scaffolds improved biomechanical properties and facilitated the regeneration of matured collagen in patellar ligament 4 weeks after implantation in mice. Overall, this strategy of peptide-mediated orchestration of VEGF provides an enticing platform for the ligament regeneration, which may also have broad implications for tissue repair applications. STATEMENT OF SIGNIFICANCE: Ligament injuries are central to sports and other rigorous activities. Given to the avascular nature and poor self-healing capability of injured ligament tissues, it is a burgeoning challenge to fabricate tissue-engineered scaffolds for ligament reconstruction. Vascular endothelial growth factor (VEGF) is pivotal to the neo-vessel formation. However, the high molecular weight of VEGF as well as its short half-life in vitro and in vivo limits its therapeutic potential. To circumvent these limitations, herein, we functionalized aligned electrospun polycaprolactone/gelatin (PCL/Gel)-based scaffolds with VEGF-binding peptide (BP) and assessed their biocompatibility and performance in vitro and in vivo. BP-modified scaffolds accumulated VEGF, improved tube formation of HUVECs, and induced wound healing in vitro, which may have broad implications for regenerative medicine and tissue engineering.

Converging 3D Printing and Electrospinning: Effect of Poly(l-lactide)/Gelatin Based Short Nanofibers Aerogels on Tracheal Regeneration

Recently, various tissue engineering based strategies have been pursued for the regeneration of tracheal tissues. However, previously developed tracheal scaffolds do not accurately mimic the microstructure and mechanical behavior of the native trachea, which restrict their clinical translation. Here, tracheal scaffolds are fabricated by using 3D printing and short nanofibers (SF) dispersion of poly(l-lactide)/gelatin (0.5-1.5 wt%) to afford tracheal constructs. The results display that the scaffolds containing 1.0 wt % of SF exhibit low density, good water absorption capacity, reasonable degradation rate, and stable mechanical properties, which were comparable to the native trachea. Moreover, the designed scaffolds possess good biocompatibility and promote the growth and infiltration of chondrocytes in vitro. The biocompatibility of tracheal scaffolds is further assessed after subcutaneous implantation in mice for up to 4 and 8 weeks. Histological assessment of tracheal constructs explanted at week 4 shows that scaffolds can maintain their structural integrity and support the formation of neo-vessels. Furthermore, cell-scaffold constructs gradually form cartilage-like tissues, which mature with time. Collectively, these engineered tracheal scaffolds not only possess appropriate mechanical properties to afford a stabilized structure but also a biomimetic extracellular matrix-like structure to accomplish tissue regeneration, which may have broad implications for tracheal regeneration.

Rationally design of electrospun polysaccharides polymeric nanofiber webs by various tools for biomedical applications: A review

Nanofibers have a particular benefit when delivering a spectrum of therapeutic drugs for diverse biomedical applications. Nanofibers are easily fabricated from cellulose acetate, chitosan, polycaprolactone, and other polymers with regulated morphology and release profiles due to nanotechnology's recent advancement. This review will provide the latest approaches to the fabrication of electrospun nanofibers containing herbal extracts, antimicrobial peptides, and antibiotics for wound-healing potential. Besides, synthesis and evaluation of nanofibrous mats, including conducting polymer and evaluate their possibility for wound healing. In addition, nanofibers are loaded with some drugs for skin cancer treatment and contain growth factors for tissue regeneration. Also, the current two-dimensional nanofibers limitations and the various techniques for convert two-dimensional to three-dimension nanofibers to avoid these drawbacks. Moreover, the future direction in improving the three-dimensional structure and functionality has been including.

Controlling Structure with Injectable Biomaterials to Better Mimic Tissue Heterogeneity and Anisotropy

Tissue regeneration of sensitive tissues calls for injectable scaffolds, which are minimally invasive and offer minimal damage to the native tissues. However, most of these systems are inherently isotropic and do not mimic the complex hierarchically ordered nature of the native extracellular matrices. This review focuses on the different approaches developed in the past decade to bring in some form of anisotropy to the conventional injectable tissue regenerative matrices. These approaches include introduction of macroporosity, in vivo pattering to present biomolecules in a spatially and temporally controlled manner, availability of aligned domains by means of self-assembly or oriented injectable components, and in vivo bioprinting to obtain structures with features of high resolution that resembles native tissues. Toward the end of the review, different techniques to produce building blocks for the fabrication of heterogeneous injectable scaffolds are discussed. The advantages and shortcomings of each approach are discussed in detail with ideas to improve the functionality and versatility of the building blocks.

Engineering a Highly Biomimetic Chitosan-Based Cartilage Scaffold by Using Short Fibers and a Cartilage-Decellularized Matrix

Engineering scaffolds with structurally and biochemically biomimicking cues is essential for the success of tissue-engineered cartilage. Chitosan (CS)-based scaffolds have been widely used for cartilage regeneration due to its chemostructural similarity to the glycosaminoglycans (GAGs) found in the extracellular matrix of cartilage. However, the weak mechanical properties and inadequate chondroinduction capacity of CS give rise to compromised efficacy of cartilage regeneration. In this study, we incorporated short fiber segments, processed from electrospun aligned poly(lactic-co-glycolic acid) (PLGA) fiber arrays, into a citric acid-modified chitosan (CC) hydrogel scaffold for mechanical strengthening and structural biomimicking and meanwhile introduced cartilage-decellularized matrix (CDM) for biochemical signaling to promote the chondroinduction activity. We found that the incorporation of PLGA short fibers and CDM remarkably strengthened the mechanical properties of the CC hydrogel (+349% in compressive strength and +153% in Young's modulus), which also exhibited a large pore size, appropriate porosity, and fast water absorption ability. Biologically, the engineered CDM-Fib/CC scaffold significantly promoted the adhesion and proliferation of chondrocytes and supported the formation of matured cartilage tissue with a cartilagelike structure and deposition of abundant cartilage ECM-specific GAGs and type II collagen (+42% in GAGs content and +295% in type II collagen content). The enhanced mechanical competency and chondroinduction capacity with the engineered CDM-Fib/CC scaffold eventually fulfilled successful in situ osteochondral regeneration in a rabbit model. This study thereby demonstrated a great potential of the engineered highly biomimetic chitosan-based scaffold in cartilage tissue repair and regeneration.

Development of biodegradable webs of PLA/PCL blends prepared via electrospinning: Morphological, chemical, and thermal characterization

Biodegradable polymers have a mean role to mimic native tissues and allow cells to penetrate, grow, and proliferate with their advanced features in tissue engineering applications. The physiological, chemical, mechanical, and biological qualities of the surfaces, which are presented from biodegradable polymers, affect the final properties of the scaffolds. In this study, it is aimed to produce fibrous webs by electrospinning method for tissue engineering applications using two different biopolymers, polylactic acid (PLA) and polycaprolactone (PCL). These polymers are used either alone or in a blended form (PLA/PCL, 1/1 wt.). Within the scope of the study, polymer concentrations (6, 8 and 10%) and solvent types (used for chloroform/ethanol/acetic acid mixture, PCL and PLA/PCL mixtures, and chloroform/acetone, PLA) vary as solution parameters. Fibrous webs are investigated in terms of morphological, chemical, and thermal characteristics. Results show continuous fibers are examined for 8 or 10% polymer concentrations with an average fiber diameter of 1.3-2.7 μm and pore area of 4-9 μm² . No fiber formation is observed in sample groups with a polymer concentration of 6% and beaded structures are formed. Water contact angle analysis proves the hydrophobic properties of PLA and PCL, whereas Fourier-transform infrared results show there is no solution residue on the surfaces, so there is no toxic effect. Also, in differential scanning calorimetry analysis, the characteristic crystallization peaks of the polymers are recognized, and when the polymers are in a blend, it beholds that they have effects on each other's crystallization.

From cells-on-a-chip to organs-on-a-chip: scaffolding materials for 3D cell culture in microfluidics

It is an emerging research area to integrate scaffolding materials in microfluidic devices for 3D cell culture (organs-on-a-chip). The technology of organs-on-a-chip holds the potential to obviate the gaps between pre-clinical and clinical studies. As accumulating evidence shows the importance of extracellular matrix in in vitro cell culture, significant efforts have been made to integrate 3D ECM/scaffolding materials in microfluidics. There are two families of materials that are commonly used for this purpose: hydrogels and electrospun fibers. In this review, we briefly discuss the properties of the materials, and focus on the various technologies to obtain the materials (e.g. extraction of collagen from animal tissues) and to include the materials in microfluidic devices. Challenges and potential solutions of the current materials and technologies were also thoroughly discussed. At the end, we provide a perspective on future efforts to make these technologies more translational to broadly benefit pharmaceutical and pathophysiological research.