Preparation of electrospun nanofibers with desired microstructures using a programmed three-dimensional (3D) nanofiber collector

In Vivo Cell Migration and Growth Within Electrospun Porous Nanofibrous Scaffolds with Different Pore Sizes in a Mouse Pouch Model

Cellular infiltration into traditional electrospun nanofibers (NFs) is limited due to their dense structures. We were able to obtain polycaprolactone (PCL) NFs with variable and defined pore sizes and thicknesses by using a customized programmed NF collector that controls the moving speed during electrospinning. NFs obtained by this method were tested in vitro and have shown better cell proliferation within the NFs with larger pore sizes. This study investigated in vivo host cell migration and neovascularization within implanted porous PCL NF discs using a mouse pouch model. Four types of PCL NFs were prepared and classified based on the electrospinning speed: NF-zero (static control), NF-low (0.085 mm/min), NF-mid (0.158 mm/min) and NF-high (0.232 mm/min) groups. With the increase in the speed, we observed an increase in the pore area; NF-zero (11.6 ± 6.2 μm2), NF-low (37.4 ± 28.6 μm2), NF-mid (67.6 ± 54.8 μm2), and NF-high (292.3 ± 286.5 μm2) groups. The NFs were implanted into air pouches of BALB/cJ mice. Mice without NFs served as control. Animals were sacrificed at 7 and 28 days after the implantation. Pouch tissues with implanted NFs were collected for histology (n = three per group and time point). The efficiency of the tissue penetration into PCL NF sheets was closely linked to the pore size and area. NFs with the highest pore area had more efficient tissue migration and new blood vessel formation compared to those with a smaller pore area. No newly formed blood vessels were observed in NF-zero sheets up to 28 days. We believe that a porous NF scaffold with a controllable pore size and thickness has great potential for tissue repair/regeneration and for other healthcare applications.

Electrospun nanofibers and their application as sensors for healthcare

Electrospinning is a type of electrohydrodynamics that utilizes high-voltage electrostatic force to stretch a polymer solution into nanofibers under the influence of an electric field, with most of the fibers falling onto a collector. This technology is favored by researchers across various fields due to its simple and inexpensive device for producing nanofibers in a straightforward manner. Nanofibers prepared through electrospinning have a high specific surface area and high porosity. Electrospinning technology shows extensive potential, especially within biomedical sensors. This article provides a systematic overview of the factors influencing electrospinning, the parameters of the electrospinning process, the types of electrospun nanofibers, and the applications of electrospinning technology in the field of sensors, including wearable sensors, pressure sensors, and glucose sensors. The paper summarizes the research progress in this field and points out the direction of development for electrospinning technology, as well as the future challenges.

Potential of Liposomal FTY720 for Bone Regeneration: Proliferative, Osteoinductive, Chemoattractive, and Angiogenic Properties Compared to Free Bioactive Lipid

Introduction

FTY720 bioactive lipid has proliferative, osteoinductive, chemo attractive, and angiogenic properties, being thus a potential exogenous administered agent for promotion of bone regeneration. Herein we developed FTY720-loaded liposomes as a potential delivery system that could retain and prolong the bioactivity of the bioactive lipid and at the same time reduce its cytotoxicity (at high doses).

Methods

FTY720 liposomes were prepared by thin-lipid hydration and microfluidic flow focusing, and evaluated for their ability to induce proliferation, osteoinduction, and chemoattraction in three cell types: MC3T3-E1 pre-osteoblast cells, L929 fibroblast cells, and ATDC5 chondrogenic cells. The angiogenic activity of free and liposomal FTY720 was investigated using a chick chorioallantoic membrane assay. NBD-FTY720 cellular uptake was quantitated using flow cytometry and morphologically assessed by confocal microscopy. Implicated cellular signaling mechanisms were investigated by quantifying phosphorylated MAPK and CREB proteins.

Results

FTY720 liposomes (~80-110 nm) with low polydispersity and ~100% loading were prepared using both methods. FTY720 demonstrated the ability to increase cell proliferation at 10-300nM doses but was cytotoxic at doses>400nM while the corresponding liposomal-FTY720 doses were non-cytotoxic, proving its reduced toxicity. In several cases (cells and doses), FTY720 liposomes demonstrated increased osteogenic differentiation of cells, proliferation, and migration compared to free FTY720, whereas both FTY720 forms demonstrated substantial angiogenic activity. Liposomal FTY720 cellular uptake was substantially higher than that of free FTY720 in some cases, a fact that may be connected to its higher bioactivity. Increased phosphorylated MAPK and CREB protein concentrations provided information about the potential cellular signaling mechanisms involved in FTY720-induced osteogenesis.

Discussion

The current results confirm the high potential of FTY720 bioactive lipid, especially in its liposomal form, that demonstrated substantial reduction of cytotoxicity and prolonged preservation of the lipids bioactivity (compared to the free lipid), for accelerated treatment of bone defects. Interestingly, the current studies prove the potential of FTY720, especially in its liposomal form, to promote reprogramming of L929 fibroblasts into osteoblasts, a novel finding deserving future exploitation.

Cell migration within porous electrospun nanofibrous scaffolds in a mouse subcuticular implantation model

Cellular infiltration into electrospun nanofibers (NFs) is limited due to the dense structure and small pore sizes. We developed a programmed NF collector that can fabricate porous NFs with desired pore sizes and thickness. Previously we demonstrated improved cellular proliferation and differentiation of osteoblasts, osteoclasts, and fibroblasts with increased pore sizes of polycaprolactone (PCL) NF in-vitro. This study investigated in-vivo host cell migration and vascular ingrowth within porous NF sheets implanted subcutaneously in a mouse model. Two types of PCL NFs with well-defined pore sizes were created using varying speeds of the NF collector: NF-zero (no movement, pore size 14.4 ± 8.9 µm2) and NF-high (0.232 mm/min, pore size 286.7 ± 381.9 µm2). The NF obtained by using classical flat NF collector (2D NF, pore size 1.09 ± 1.7 µm2) was a control. The three formulae of NFs were implanted subcutaneously in 18 BALB/cJ mice. Animals were killed 7 and 28-days after implantation (n = 3 per group per time point). The tissue with implanted NFs were collected for histologic analysis. Overall, 7-day samples showed little inflammatory response. At 28-days, the degree of tissue penetration of PCL NF sheet matrices was linked to pore size and area. NFs with the largest pore area had more efficient tissue migration and new blood vessel formation compared to those with smaller pore sizes. No newly formed blood vessels were observed in the 2D NF group. A porous NF scaffold with controllable pore size has potential for tissue repair/regeneration in situ with potential for many applications in orthopaedics.

Electrospun and 3D printed polymeric materials for one-stage critical-size long bone defect regeneration inspired by the Masquelet technique: Recent Advances

Critical-size long bone defects represent one of the major causes of fracture non-union and remain a significant challenge in orthopaedic surgery. Two-stage procedures such as a Masquelet technique demonstrate high level of success however their main disadvantage is the need for a second surgery, which is required to remove the non-resorbable cement spacer and to place the bone graft into the biological chamber formed by the 'induced membrane'. Recent research efforts have therefore been dedicated towards the design, fabrication and testing of resorbable implants that could mimic the biological functions of the cement spacer and the induced membrane. Amongst the various manufacturing techniques used to fabricate these implants, three-dimensional (3D) printing and electrospinning methods have gained a significant momentum due their high-level controllability, scalable processing and relatively low cost. This review aims to present recent advances in the evaluation of electrospun and 3D printed polymeric materials for critical-size, long bone defect reconstruction, emphasizing both their beneficial properties and current limitations. Furthermore, we present and discuss current state-of-the art techniques required for characterisation of the materials' physical, mechanical and biological characteristics. These represent the essential first steps towards the development of personalised implants for single-surgery, large defect reconstruction in weight-bearing bones.

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.

Osteoblastic differentiation and bactericidal activity are enhanced by erythromycin released from PCL/PLGA-PVA coaxial nanofibers

Prosthesis with antibiotic-eluting nanofibrous (NF) coating represents coating alternative to prevent periprosthetic joint infection (PJI). In this study, four formulas of erythromycin (EM)-embedded both in core and sheath components of coaxial PCL/PLGA-PVA NF coatings were developed: EM 0 (no EM), EM 100 (100 μg/mL), EM500 (500 μg/mL) and EM1000 (1000 μg/mL). EM doping altered the physicochemical and structural properties of NFs to some extent, including the increase of NF porosity and surface wettability. A sustained EM release from EM-NFs for >4 weeks was observed. Eluents collected from EM-NFs showed strong zone of inhibition (ZOI) to Staphylococcus aureus growth and the sizes of ZOI positively related to the amount of EM released. EM-NFs were nontoxic to rat bone marrow stem cells (rBMSCs). Cell growth was significantly enhanced when comparing rBMSCs cultured on EM-NFs (EM0 and EM 100) to those cultured on NF-free control. Cell differentiation (ALP activity) was notably enhanced by EM100, compared to control and EM0. Eluents from EM-NFs on rBMSCs were also investigated. The presence of 10% EM-NF eluents inhibited the growth of rBMSCs, which was proportional to the amount of EM doped. The ALP activity was notably enhanced by eluents from EM-NFs with the highest activity in EM100 compared to control and EM0. Our data indicate that EM-doped PCL/PLGA-PVA coaxial NF coatings have a great potential to be applied as a new implant coating matrices. Further in vivo testing in animal models is currently planned that should represent the first step in predicting the clinical outcomes of EM-eluting NF coating approach.

Tailored PCL Scaffolds as Skin Substitutes Using Sacrificial PVP Fibers and Collagen/Chitosan Blends

Electrospinning is a versatile technique for fabrication of made-on-purpose biomimetic scaffolds. In this study, optimized electrospun fibrous membranes were produced by simultaneous electrospinning of polycaprolactone (PCL) and polyvinylpyrrolidone (PVP), followed by the selective removal of PVP from the PCL/PVP mesh. After aminolysis, a blend of collagen/chitosan was grafted on the surface. Physicochemical characterizations as well as in vitro evaluations were conducted using different methods. Successful cell infiltration into samples was observed. It seems that the positive trend of cell ingress originates from the proper pore size obtained after removal of pvp (from 4.46 μm before immersion in water to 33.55 μm after immersion in water for 24 h). Furthermore, grafting the surface with the collagen/chitosan blend rendered the scaffolds more biocompatible with improved attachment and spreading of keratinocyte cell lines (HaCaT). Viability evaluation through MTT assay for HDF cells did not reveal any cytotoxic effects. Antibacterial assay with Staphylococcus aureus as Gram-positive and Escherichia coli as Gram-negative species corroborated the bactericidal effects of chitosan utilized in the composition of the coated blend. The results of in vitro studies along with physicochemical characterizations reflect the great potentials of the produced samples as scaffolds for application in skin tissue engineering.