Novel 3D scaffold with enhanced physical and cell response properties for bone tissue regeneration, fabricated by patterned electrospinning/electrospraying

PCL-based 3D nanofibrous structure with well-designed morphology and enhanced specific surface area for tissue engineering application

Tissue engineering opens a new horizon for biological tissue replacement applications. Scaffolds, appropriate cells, and signaling induction are the main three determinant parameters in any tissue engineering applications. Designing a suitable scaffold which can mimic the cellular inherent and natural habitation is of great importance for cellular growth and proliferation. Just like a natural extracellular matrix (ECM), scaffolds provide the cells with an environment for performing biological functions. Accordingly, vast surface area and three-dimensional nanofibrous structures are among the pivotal characteristics of functional scaffolds in tissue engineering, and enhancement of their properties is the main purpose of the present research. In our previous study, a patterned structure composed of continuous nanofibers and microparticles was introduced. In this work, a new modification is applied for adjustment of the surface area of an electrospun/electrosprayed scaffold. For this purpose, at predetermined stages during electrospinning/electrospraying, the nitrogen gas is flushed through the mesh holes of the collector in the opposite direction of the jet movement. This method has led to the formation of very thin nanofibrous layers at nitrogen flush intervals by providing a cooling effect of the sweeping nitrogen. As a consequence, a straticulated structure has been fabricated which possesses extremely high surface/volume ratio. The porosity, water absorption, and morphological analysis were conducted on the obtained scaffold. In vitro cytocompatibility assessments as well as histological analysis demonstrated that the fabricated scaffold provides a proper substrate for cellular attachment, proliferation and infiltration. These findings can be advantageous in three-dimensional tissue engineering such as bone tissue engineering applications. Furthermore, according to the advanced microstructure and vast surface area of the fabricated samples, they can be applied in many other applications, such as membrane, filtration, etc.

Fabrication of multilayered electrospun poly(lactic-co-glycolic acid)/polyvinyl pyrrolidone + poly(ethylene oxide) scaffolds and biocompatibility evaluation

Poly(lactic-co-glycolic acid)/polyvinyl pyrrolidone + poly(ethylene oxide) [PLGA/(PVP + PEO)] scaffolds with different polymer concentrations were fabricated using multilayered electrospinning, and their physicochemical properties and biocompatibility were examined to screen for scaffolds with excellent performance in tissue engineering (TE). PLGA solution (15% w/v) was used as the bottom solution, and a mixed solution of 12% w/v PVP + PEO was applied as the surface layer solution. The mass ratios of PVP vs. PEO in each 10 ml surface layer mixed solution were 1.08 g: 0.12 g; 0.96 g: 0.24 g; and 0.84 g: 0.36 g. Compared to the conventional electrospinning method used to fabricate the pure PVP + PEO (0.96 g: 0.24 g, Group A) scaffold and pure PLGA (Group E) scaffold, the multilayer electrospinning technique of alternating sprays of the bottom layer solution and the surface layer solution was adopted to fabricate multilayer nanofiber scaffolds, including PLGA/(PVP + PEO) (1.08 g: 0.12 g, Group B), PLGA/(PVP + PEO) (0.96 g: 0.24 g, Group C), and PLGA/(PVP + PEO) (0.84 g: 0.36 g, Group D). The morphology and characteristics of the five scaffolds were analyzed, and the biocompatibilities of the cell-scaffold composites were assessed through methods including Cell Counting Kit-8 (CCK8) analysis, 4',6-diamidino-2-phenylindole (DAPI) staining, and scanning electron microscopy. Therefore, with a PVP-to-PEO mass ratio of 0.96 g: 0.24 g, an optimal multilayer nanofiber scaffold was fabricated by the multilayer electrospinning technique. The excellent biocompatibility and mechanical properties of the scaffold were confirmed by in vitro experiments, which demonstrated the scaffold's promising application potential in the field of TE.

PEGylated curcumin-loaded nanofibrous mats with controlled burst release through bead knot-on-spring design

APEGylatedcurcumin (PCU) loaded electrospuns based on poly(ε-caprolactone) (PCL) andpolyvinyl alcohol (PVA) were fabricated for wound dressing applications. The main reason for this wound dressing design is antibacterialactivity enhancement, and wound exudates management. PEGylation increases curcuminsantibacterial properties and PVA can help exudates management. For optimal wound dressing, first, response surface methodology (RSM) was applied to optimize the electrospinning parameters to achieve appropriate nanofibrous mats. Then a three-layer electrospun was designed by considering the water absorbability, PCU release profile as well as antibacterial and biocompatibility of the final wound dressing. The burst release in controlled release systems could be evaluated for prevention of the higher initial drug release and control the effective life time. The PCU release results illustrated that the bead knot plays a positive role in controlling the release profile andby increase in the number of beads per unit area from 3000 to 9000 mm^-2,the PCU burst release will be reduced; Also in vitro studies show that optimized three-layer dressing based on PCL/PVA/PCU can support water vapour transmission rate in optimal range and also absorb more than three times exudates in comparison with mono-layerdressing. Antibacterial tests show that the electrospun wound dressing containing 5% PCU exhibits100% antibacterial activityas well as cell viability level within an acceptable range.

Combination of electrospinning with other techniques for the fabrication of 3D polymeric and composite nanofibrous scaffolds with improved cellular interactions

The development of three-dimensional (3D) scaffolds with physical and chemical topological cues at the macro-, micro-, and nanometer scale is urgently needed for successful tissue engineering applications. 3D scaffolds can be manufactured by a wide variety of techniques. Electrospinning technology has emerged as a powerful manufacturing technique to produce non-woven nanofibrous scaffolds with very interesting features for tissue engineering products. However, electrospun scaffolds have some inherent limitations that compromise the regeneration of thick and complex tissues. By integrating electrospinning and other fabrication technologies, multifunctional 3D fibrous assemblies with micro/nanotopographical features can be created. The proper combination of techniques leads to materials with nano and macro-structure, allowing an improvement in the biological performance of tissue-engineered constructs. In this review, we focus on the most relevant strategies to produce electrospun polymer/composite scaffolds with 3D architecture. A detailed description of procedures involving physical and chemical agents to create structures with large pores and 3D fiber assemblies is introduced. Finally, characterization and biological assays including in vitro and in vivo studies of structures intended for the regeneration of functional tissues are briefly presented and discussed.

Bone Morphogenetic Protein 2-Conjugated Silica Particles Enhanced Early Osteogenic Differentiation of Adipose Stem Cells on the Polycaprolactone Scaffold

Background

Silica particles (SPs) induce cell proliferation and osteogenic differentiation. We reported that SPs in the scaffold induced early stage osteogenic differentiation.

Methods

A polycaprolactone (PCL) scaffold was fabricated with a 10 wt% SPs. The surface of PCL scaffold was coated with a 10 µg/mL collagen solution. Next, the scaffold was conjugated with 2 μM SPs, 2 μg/mL bone morphogenetic protein 2 (BMP2), or 2 μM BMP2-conjugated SPs (BCSPs). Green fluorescent protein-coupled BMP2 was applied to fabricate the scaffold. The fluorescence intensity was analyzed by confocal microscopy. The mRNA levels of the early osteogenic differentiation marker, alkaline phosphatase (ALP), were analyzed by real-time quantitative polymerase chain reaction. Levels of BMP2, RUNX2, ERK1/2, and AKT were assessed by western blotting.

Results

ALP mRNA levels were significantly higher in the BCSP-conjugated scaffold than in the other scaffolds. In the early stage of osteogenic differentiation, the protein levels of BMP2, RUNX2, ERK1/2, and AKT in cells were significantly higher in the BCSP-conjugated scaffold than in other scaffolds. Thus, the BCSP composite scaffold induced rapid osteogenic differentiation.

Conclusion

These results suggest that BCSP composite can be used to promote early stage osteogenic differentiation and show promise as a material for use in scaffolds for bone regeneration.

Encapsulated melatonin in polycaprolactone (PCL) microparticles as a promising graft material

Electrospraying assures many advantages with taking less time and costing less relatively to the other conventional particle production methods. In this research, we investigated the encapsulation of melatonin (MEL) hormone in polycaprolactone (PCL) microparticles by using electrospraying method. Morphology analysis of the produced particles completed with Scanning Electron Microscopy (SEM). SEM images demonstrated that micro-particles of 3 wt% PCL solution has the most suitable particle diameter size (2.3 ± 0.64 μm) for melatonin encapsulation. According to the characterization of the particles, electrospraying parameters like optimal collecting distance, the flow rate of the solution and voltage of the system detected as 8 cm, 0.5 ml/h, and 10 kV respectively. For determining the chemical bonds of scaffold Fourier-Transform Infrared Spectroscopy (FTIR) were used and FTIR results showed that melatonin successfully loaded into PCL micro-particles. Drug release kinetics of the melatonin loaded particles indicated that melatonin released with a burst at the beginning and release behavior became sustainable over a period of 8 h with the encapsulation efficiency of about 73%. In addition, both in-vitro and in-vivo studies of the graft materials also completed. Primary human osteoblasts (HOB) cells and female Sprague Dawley rats were used in in-vitro and in-vivo studies. Test results demonstrate cell population, and bone volume of the rats grafted with composites has remarkably increased, this caused remodelling in bone structure. Overall, these findings indicate that encapsulation of melatonin in the PCL particles with electrospray method is optimum for new synthetic graft material.

Platelet-functionalized three-dimensional poly-ε-caprolactone fibrous scaffold prepared using centrifugal spinning for delivery of growth factors

Bone and cartilage are tissues of a three-dimensional (3D) nature. Therefore, scaffolds for their regeneration should support cell infiltration and growth in all 3 dimensions. To fulfill such a requirement, the materials should possess large, open pores. Centrifugal spinning is a simple method for producing 3D fibrous scaffolds with large and interconnected pores. However, the process of bone regeneration is rather complex and requires additional stimulation by active molecules. In the current study, we introduced a simple composite scaffold based on platelet adhesion to poly-ε-caprolactone 3D fibers. Platelets were used as a natural source of growth factors and cytokines active in the tissue repair process. By immobilization in the fibrous scaffolds, their bioavailability was prolonged. The biological evaluation of the proposed system in the MG-63 model showed improved metabolic activity, proliferation and alkaline phosphatase activity in comparison to nonfunctionalized fibrous scaffold. In addition, the response of cells was dose dependent with improved biocompatibility with increasing platelet concentration. The results demonstrated the suitability of the system for bone tissue.

Roll-designed 3D nanofibrous scaffold suitable for the regeneration of load bearing bone defects

In this work, an innovative and easy method for the fabrication of 3D scaffold from 2D electrospun structures is introduced. For this aim, coral microparticles were fixed inside the nanofibrous PCL/Gelatin mat and the obtained structure was post assembled into a cylindrical design. Scaffold fabrication procedure is described in detail and morphological properties, physical and mechanical characteristics and in vitro assessments of the prepared scaffold are reported. Presences of coral microparticles in the structure led to the formation of empty spaces (3D pores) between nanofibrous layers which in turn prevent the compact accumulation of nanofibers. Post-assembly of the obtained nanofibrous coral-loaded structures makes it possible to prepare a scaffold with any desired dimension (diameter and height). Existence of coral particles within the nanofibrous mats resulted in distant placement of layers toward each other in the assembling step, which in turn create vacancy in the structure for cellular migration and fluid and nutrients exchange of the scaffold with the surrounding environment. Cell morphology within the scaffolds is investigated and cytotoxicity and cytocompatibility of the structure is evaluated using Alamar blue assay. Enhancement in mineralization of the seeded cells within the prepared coral-loaded scaffolds is demonstrated by the use of SEM-EDX. Performed compression mechanical test revealed excellent modulus and stiffness values for the cylindrical samples which are comparable to those of natural bone tissue.