Hierarchically ordered polymer nanofiber shish kebabs as a bone scaffold material

Electrospun PVA Fibers for Drug Delivery: A Review

Innovation in biomedical science is always a field of interest for researchers. Drug delivery, being one of the key areas of biomedical science, has gained considerable significance. The utilization of simple yet effective techniques such as electrospinning has undergone significant development in the field of drug delivery. Various polymers such as PEG (polyethylene glycol), PLGA (Poly(lactic-co-glycolic acid)), PLA(Polylactic acid), and PCA (poly(methacrylate citric acid)) have been utilized to prepare electrospinning-based drug delivery systems (DDSs). Polyvinyl alcohol (PVA) has recently gained attention because of its biocompatibility, biodegradability, non-toxicity, and ideal mechanical properties as these are the key factors in developing DDSs. Moreover, it has shown promising results in developing DDSs individually and when combined with natural and synthetic polymers such as chitosan and polycaprolactone (PCL). Considering the outstanding properties of PVA, the aim of this review paper was therefore to summarize these recent advances by highlighting the potential of electrospun PVA for drug delivery systems.

Physicochemical Characterization of Thermally Processed Goose Bone Ash for Bone Regeneration

Goose bone is traditionally applied for many ailments including bone fractures. Goose bone that consists of calcium phosphate plays a major role in bone regeneration. In this study, the production of goose bone ash (GBA) was translated from a traditional process into one of a laboratory scale via thermal and mechanical methods. The GBA was thermally processed via calcination at 300 °C and 900 °C. The differences in physicochemical properties between studied GBA (SGBA) and commercial GBA (CGBA) were elucidated via Fourier transform infrared (FT-IR), X-ray fluorescence (XRF), X-ray diffraction (XRD) and electron diffraction X-Ray (EDX). The morphological properties of SGBA and CGBA were characterized using field emission scanning electron microscopy (FESEM) in which nano-sized particles were detected. The results showed that the SGBA of 300 °C had comparable physicochemical properties to those of CGBA. A high processing temperature was associated with decreasing organic compounds and increasing crystallinity. The finding from EDX suggests that sintering at 900 °C (SGBA 900) demonstrated the presence of hydroxyapatite in the mineralogical phase and had a Ca/P atomic ratio of 1.64 which is comparable to the ideal stoichiometric ratio of 1.67. Findings from this study could be used for the further exploration of GBA as a potential material for bone regeneration via the elucidation of their biological properties in the next experimental setting.

Three-Dimensional Scaffolds for Bone Tissue Engineering

Immobilization using external or internal splints is a standard and effective procedure to treat minor skeletal fractures. In the case of major skeletal defects caused by extreme trauma, infectious diseases or tumors, the surgical implantation of a bone graft from external sources is required for a complete cure. Practical disadvantages, such as the risk of immune rejection and infection at the implant site, are high in xenografts and allografts. Currently, an autograft from the iliac crest of a patient is considered the "gold standard" method for treating large-scale skeletal defects. However, this method is not an ideal solution due to its limited availability and significant reports of morbidity in the harvest site (30%) as well as the implanted site (5-35%). Tissue-engineered bone grafts aim to create a mechanically strong, biologically viable and degradable bone graft by combining a three-dimensional porous scaffold with osteoblast or progenitor cells. The materials used for such tissue-engineered bone grafts can be broadly divided into ceramic materials (calcium phosphates) and biocompatible/bioactive synthetic polymers. This review summarizes the types of materials used to make scaffolds for cryo-preservable tissue-engineered bone grafts as well as the distinct methods adopted to create the scaffolds, including traditional scaffold fabrication methods (solvent-casting, gas-foaming, electrospinning, thermally induced phase separation) and more recent fabrication methods (fused deposition molding, stereolithography, selective laser sintering, Inkjet 3D printing, laser-assisted bioprinting and 3D bioprinting). This is followed by a short summation of the current osteochondrogenic models along with the required scaffold mechanical properties for in vivo applications. We then present a few results of the effects of freezing and thawing on the structural and mechanical integrity of PLLA scaffolds prepared by the thermally induced phase separation method and conclude this review article by summarizing the current regulatory requirements for tissue-engineered products.

Multilayer functional bionic fabricated polycaprolactone based fibrous membranes for osteochondral integrated repair

Osteochondral defect repair is one of the challenging problems in orthopedics. In this study, a multilayer polycaprolactone (PCL) based fibrous membrane for osteochondral defect repair was biomimetically fabricated by combining self-induced crystallization, biomimetic mineralization and layer-by-layer electrospinning techniques. The multilayer functional bionic fibrous membrane consisted of cartilage repair layer, intermediate transition repair layer and subchondral bone repair layer. Glucosamine hydrochloride (GAH) encapsulated in core-shell structured PCL fibrous membrane (MGPCL) was suitable for cartilage repair. Shish-kebab (SK) structured PCL fibrous membrane with calcium phosphate coating (MSKPCL) was designed for subchondral bone repair. SK structured MGPCL fibrous membrane (SKMGPCL) was used as intermediate transition repair. The tensile modulus of MG/SKMG/MSKPCL fibrous membrane was 34.24 ± 2.39 MPa which met the requirements of cartilage and subchondral bone repair scaffolds, and in vitro culture results showed that MG/SKMG/MSKPCL fibrous membrane had good biological activity and osteogenic ability. These results showed that MG/SKMG/MSKPCL fibrous membrane provides a promising material basis for osteochondral integrated repair scaffold.

Insight on the Role of Poly(acrylic acid) for Directing Calcium Phosphate Mineralization of Synthetic Polymer Bone Scaffolds

Bone is a complex tissue with robust mechanical and biological properties originating from its nanoscale composite structure. Although much research has been conducted on designing bioinspired artificial bone, the role of biological macromolecules such as noncollagenous proteins (NCPs) in influencing the formation of biominerals is not fully understood. In this work, we have designed nanofiber shish-kebab (NFSK) structures that can template mineral location by recruiting calcium cations from an ion-rich mineralization solution. Poly(acrylic acid) (PAA) is used as the NCP analogue to understand the role of polyelectrolytes in scaffold mineralization. We demonstrate that the addition of PAA in the mineralization solution suppresses the development of extrafibrillar minerals as well as slows down the accumulation and development of mineral phases within NFSKs. We probe the mechanism behind this effect by monitoring the free calcium ion concentration, investigating the PAA molecular weight effect, and conducting mineralization in membrane-partitioned solutions. Our results suggest the 2-fold effect of PAA as a solution stabilizer and physical barrier on the NFSK surface. This work could shed light on the understanding of the NCP effect in biomineralization.

Bone Tissue Engineering through 3D Bioprinting of Bioceramic Scaffolds: A Review and Update

Trauma and bone loss from infections, tumors, and congenital diseases make bone repair and regeneration the greatest challenges in orthopedic, craniofacial, and plastic surgeries. The shortage of donors, intrinsic limitations, and complications in transplantation have led to more focus and interest in regenerative medicine. Structures that closely mimic bone tissue can be produced by this unique technology. The steady development of three-dimensional (3D)-printed bone tissue engineering scaffold therapy has played an important role in achieving the desired goal. Bioceramic scaffolds are widely studied and appear to be the most promising solution. In addition, 3D printing technology can simulate mechanical and biological surface properties and print with high precision complex internal and external structures to match their functional properties. Inkjet, extrusion, and light-based 3D printing are among the rapidly advancing bone bioprinting technologies. Furthermore, stem cell therapy has recently shown an important role in this field, although large tissue defects are difficult to fill by injection alone. The combination of 3D-printed bone tissue engineering scaffolds with stem cells has shown very promising results. Therefore, biocompatible artificial tissue engineering with living cells is the key element required for clinical applications where there is a high demand for bone defect repair. Furthermore, the emergence of various advanced manufacturing technologies has made the form of biomaterials and their functions, composition, and structure more diversified, and manifold. The importance of this article lies in that it aims to briefly review the main principles and characteristics of the currently available methods in orthopedic bioprinting technology to prepare bioceramic scaffolds, and finally discuss the challenges and prospects for applications in this promising and vital field.

Poly(lactic acid)/Poly(butylene succinate) (PLA/PBS) Layered Composite Gas Barrier Membranes by Anisotropic Janus Nanosheets Compartibilizers

Poly(lactic acid) (PLA), one of the most promising biodegradable polymer products, has achieved wide applications for its relatively good mechanical properties and moderate degradability. Here we report an environment-friendly filler, the organic-inorganic composite Janus nanosheets (PLA/PBS JNs), which can jam at the interface of the PLA/PBS blend with a low threshold as the compatibilizer and can simultaneously toughen the composites and improve the gas barrier performance due to better interfacial interaction and tortuous path effect. With 0.3 wt % of PLA/PBS JNs added, the tensile strength and elongation at break of the PLA/PBS blend can be improved by 37% and 224%, respectively. After a further hot-pressing process, the barrier performance of the PLA/PBS composite membranes can be significantly enhanced since PLA, PLA/PBS JNs, and PBS are arranged in a nearly lamellar structure with oxygen permeability of 0.63 × 10^-15 cm³ cm·cm^-2 s^-1 Pa^-1 with only 0.5 wt % of PLA/PBS JNs.

Hierarchical Shish-Kebab Structures Functionalizing Nanofibers for Controlled Drug Release and Improved Antithrombogenicity

The functionalization of the fibrous scaffolds including drug loading and release is of significance in tissue engineering and regenerative medicine. Our previous results have shown that the shish-kebab structure-modified fibrous scaffold shows a completely different microenvironment that mimics the topography of the collagen fibers, which interestingly facilitates the cell adhesion and migration. However, the functionalization of the unique structure needs to be further investigated. In this study, we modified the heparin-loaded fiber with a shish-kebab structure and tuned the kebab structure as the barrier for the sustained release of heparin. The introduction of the kebab structure increases the diffusion energy barrier by extending the diffusion distance. Moreover, the discontinued surface topography of the shish-kebab structure altered the surface chemistry from hydrophobic for the original poly(ε-caprolactone) (PCL) nanofibers to hydrophilic for the PCL nanofibers with the shish-kebab structure, which might have inhibited the activation of fibrinogen and thus improved the anticoagulant ability. This synergistic effect of heparin and the kebab structure significantly promotes the endothelial cell affinity and antithrombogenicity. This method might be a viable and versatile drug delivery strategy in vascular tissue engineering.

Core-Shell Nanofibers with a Shish-Kebab Structure Simulating Collagen Fibrils for Bone Tissue Engineering

The repair of bone defects is one of the great challenges facing modern orthopedics clinics. Bone tissue engineering scaffold with a nanofibrous structure similar to the original microstructure of a bone is beneficial for bone tissue regeneration. Here, a core-shell nanofibrous membrane (MS), MS containing glucosamine (MS-GLU), MS with a shish-kebab (SK) structure (SKMS), and MS-GLU with a SK structure (SKMS-GLU) were prepared by micro-sol electrospinning technology and a self-induced crystallization method. The diameter of MS nanofibers was 50-900 nm. Contact angle experiments showed that the hydrophilicity of SKMS was moderate, and its contact angle was as low as 72°. SK and GLU have a synergistic effect on cell growth. GLU in the core of MS was demonstrated to obviously promote MC3T3-E1 cell proliferation. At the same time, the SK structure grown on MS-GLU nanofibers mimicked natural collagen fibers, which facilitated MC3T3-E1 cell adhesion and differentiation. This study showed that a biomimetic SKMS-GLU nanofibrous membrane was a promising tissue engineering scaffold for bone defect repair.

MC3T3 E1 cell response to mineralized nanofiber shish kebab structures

Block copolymers (BCPs) are of growing interest because of their extensive utility in tissue engineering, particularly in biomimetic approaches where multifunctionality is critical. We synthesized polycaprolactone-polyacrylic acid (PCL-b-PAA) BCP and crystallized it onto PCL nanofibers, making BCP nanofiber shish kebab (BCP NFSK) structures. When mineralized in 2× simulated body fluid, BCP NFSK mimic the structure of mineralized collagen fibrils. We hypothesized that the addition of a calcium phosphate layer of graded roughness on the nano-structure of the nanofiber shish kebabs would enhance preosteoblast alkaline phosphatase (ALP) activity, which has been shown to be a critical component in bone matrix formation. The objectives in the study were to investigate the effect of mineralization on cell proliferation and ALP activity, and to also investigate the effect of BCP NFSK periodicity, a structural feature describing the distance between PCL-b-PAA crystals on the nanofiber core, on cell proliferation, and ALP activity. ALP activity of cells cultured on the mineralized BCP NFSK template was significantly higher than the nonmineralized BCP NFSK templates. Interestingly, no statistical difference was observed in ALP activity when the periodic varied, indicating that surface chemistry seemed to play a larger role than the surface roughness.

Controlled Delivery of Growth Factor by Hierarchical Nanostructured Core-Shell Nanofibers for the Efficient Repair of Critical-Sized Rat Calvarial Defect

Electrospun nanofibers have received much attention as bone tissue-engineered scaffolds for their capacity to mimic the structure of natural extracellular matrix (ECM). Most studies have reproduced nanofibers with smooth surface for tissue engineering. This is quite different from the triple-helical nanotopography of natural collagen nanofibrils. In this study, hierarchical nanostructures were coated on the surface of drug-loaded core-shell nanofibers to mimic natural collagen nanofibrils. The nanoshish-kebab (SK) structure was decorated regularly on the surface of the nanofibers, and the inner-loaded bone morphogenetic protein 2 (BMP2) exhibited a gentle release pattern, similar to a zero-order release pattern in kinetics. The in vitro study also showed that the SK structure could accelerate cell proliferation, attachment, and osteogenic differentiation. Four groups of scaffolds were implanted in vivo to repair critical-sized rat calvarial defects: (1) PCL/PVA (control); (2) SK-PCL/PVA; (3) PCL/PVA-BMP2; and (4) SK-PCL/PVA-BMP2. Much more bone was formed in the SK-PCL/PVA group (24.57 ± 3.81%) than in the control group (1.21 ± 0.23%). The BMP2-loaded core-shell nanofibers with nanopatterned structure (SK-PCL/PVA-BMP2) displayed the best repair efficacy (76.38 ± 4.13%), followed by the PCL/PVA-BMP2 group (39.86 ± 5.74%). It was believed that the hierarchical nanostructured core-shell nanofibers could promote osteogeneration and that the SK structure showed synergistic ability with nanofiber-loaded BMP2 in vivo for bone regeneration. Thus, this BMP2-loaded core-shell nanofiber scaffold with hierarchical nanostructure holds great potential for bone tissue engineering applications.

The Use of Electrospun Organic and Carbon Nanofibers in Bone Regeneration

There has been an increasing amount of research on regenerative medicine for the treatment of bone defects. Scaffolds are needed for the formation of new bone, and various scaffolding materials have been evaluated for bone regeneration. Materials with pores that allow cells to differentiate into osteocytes are preferred in scaffolds for bone regeneration, and porous materials and fibers are well suited for this application. Electrospinning is an effective method for producing a nanosized fiber by applying a high voltage to the needle tip containing a polymer solution. The use of electrospun nanofibers is being studied in the medical field, and its use as a scaffold for bone regeneration therapy has become a topic of growing interest. In this review, we will introduce the potential use of electrospun nanofiber as a scaffold for bone regenerative medicine with a focus on carbon nanofibers produced by the electrospinning method.

Structure and Morphology of Poly(lactic acid) Stereocomplex Nanofiber Shish Kebabs

We report the formation and structure of poly(lactic acid) (PLA) nanofiber shish kebabs (NFSKs) containing stereocomplex crystal (SC) shish and SC/homocrystal (HC) kebabs. PLA-based NFSKs were obtained by combining electrospinning and controlled polymer crystallization in order to investigate the interplay between PLA SC and HC formation. Nanofibers were produced by electrospinning poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) blends and were used as the shish. A secondary polymer (either PDLA or PLLA/PDLA blends) was decorated on the nanofiber by an incubation method to form kebab lamellae. We show that both SC and HC kebab crystals can be formed using a SC shish following a soft epitaxy mechanism, while the subtle morphological differences in the resultant NFSKs reveal the propensity of SC nuclei in SC/HC crystallization.

Recent Developments in Nanofiber Fabrication and Modification for Bone Tissue Engineering

Bone tissue engineering is an alternative therapeutic intervention to repair or regenerate lost bone. This technique requires three essential components: stem cells that can differentiate into bone cells, growth factors that stimulate cell behavior for bone formation, and scaffolds that mimic the extracellular matrix. Among the various kinds of scaffolds, highly porous nanofibrous scaffolds are a potential candidate for supporting cell functions, such as adhesion, delivering growth factors, and forming new tissue. Various fabricating techniques for nanofibrous scaffolds have been investigated, including electrospinning, multi-axial electrospinning, and melt writing electrospinning. Although electrospun fiber fabrication has been possible for a decade, these fibers have gained attention in tissue regeneration owing to the possibility of further modifications of their chemical, biological, and mechanical properties. Recent reports suggest that post-modification after spinning make it possible to modify a nanofiber's chemical and physical characteristics for regenerating specific target tissues. The objectives of this review are to describe the details of recently developed fabrication and post-modification techniques and discuss the advanced applications and impact of the integrated system of nanofiber-based scaffolds in the field of bone tissue engineering. This review highlights the importance of nanofibrous scaffolds for bone tissue engineering.

Directed Nanoparticle Assembly through Polymer Crystallization

Nanoparticles can be assembled into complex structures and architectures by using a variety of methods. In this review, we discuss recent progress of using polymer crystallization (particularly polymer single crystals, PSCs) to direct nanoparticle assembly. PSCs have been extensively studied since 1957. Mainly appearing as quasi-two-dimensional (2D) lamellae, PSCs are typically used as model systems to determine polymer crystalline structures, or as markers to investigate the crystallization process. Recent research has demonstrated that they can also be used as nanoscale functional materials. Herein, we show that nanoparticles can be directed to assemble into complex shapes by using in situ or ex situ polymer crystal growth. End-functionalized polymers can crystallize into 2D nanosheet PSCs, which are used to conjugate with complementary nanoparticles, leading to a nanosandwich structure. These nanosandwiches can find interesting applications for catalysis, surface-enhanced Raman spectroscopy, and nanomotors. Dissolution of the nanosandwich leads to the formation of Janus nanoparticles, providing a unique method for asymmetric nanoparticle synthesis.

[Structural control and characterization of hierarchically structured fibrous scaffolds]

OBJECTIVE

To prepare hierarchically structured fibrous scaffolds with different morphologies, and to explore the additional dimensionality for tuning the physicochemical properties of the scaffolds and the effect of their hemocompatibility and cytocompatibility.

METHODS

Electrospinning poly (e-caprolactone) (PCL)/polyvinylpyrrolidone (PVP) bicomponent fibers (PCL∶PVP mass ratios were 8∶2 and 5∶5 respectively), and the surface porous fibrous scaffolds were prepared by extracting PVP components. The scaffolds were labeled PCL-P8 and PCL-P5 respectively according to the mass ratio of polymer. In addition, shish-kebab (SK) structured scaffolds with different kebab sizes were created by solution incubation method, which use electrospun PCL fibers as shish while PCL chains in solution crystallizes on the fiber surface. The PCL fibrous scaffolds with smooth surface was established as control group. The hierarchically structured fibrous scaffolds were characterized by field emission scanning electron microspore, water contact angle tests, and differential scanning calorimeter (DSC) experiments. The venous blood of New Zealand white rabbits was taken and hemolysis and coagulation tests were used to characterize the blood compatibility of the scaffolds. The proliferation of the pig iliac artery endothelial cell (PIEC) on the scaffolds was detected by cell counting kit 8 (CCK-8) method, and the biocompatibility of the scaffolds was evaluated.

RESULTS

Field emission scanning electron microscopy showed that porous morphology appeared on the surface of PCL/PVP bicomponent fibers after extracting PVP. In addition, SK structure with periodic arrangement was successfully prepared by solution induction, and the longer the crystallization time, the larger the lamellar size and periodic distance. The contact angle and DSC measurements showed that when compared with smooth PCL fiber scaffolds, the crystallinity of PCL surface porous fibrous scaffolds and PCL-SK fibrous scaffolds increased, while the hydrophobicity of PCL-SK fibrous scaffolds increased, but the hydrophobicity of PCL porous scaffolds did not change significantly. The hemolysis test showed that the hemolysis rate of PCL surface porous fibrous scaffolds and PCL-SK fibrous scaffolds was higher than that of PCL fibrous scaffolds. According to American Society of Materials and Tests (ASTM) F756-08 standard, all scaffolds were non-hemolytic materials and were suitable for blood contact materials. Coagulation test showed that the coagulation index of PCL surface porous fibrous scaffolds and PCL-SK fibrous scaffolds was higher than that of PCL fibrous scaffolds at 5 and 10 minutes of culture. CCK-8 assay showed that both hierarchically structured fibrous scaffolds were more conducive to PIEC proliferation than PCL fibrous scaffold.

CONCLUSION

Based on electrospinning technology, solution-induced and blend phase separation methods can be used to construct multi-scale fiber scaffolds with different morphologies, which can not only regulate the surface physicochemical properties of the scaffolds, but also have good blood compatibility and biocompatibility. The hierarchically structured fibrous scaffolds have high application potential in the field of tissue engineering.

Polymer-Based Electrospun Nanofibers for Biomedical Applications

Electrospinning has been considered a promising and novel procedure to fabricate polymer nanofibers due to its simplicity, cost effectiveness, and high production rate, making this technique highly relevant for both industry and academia. It is used to fabricate non-woven fibers with unique characteristics such as high permeability, stability, porosity, surface area to volume ratio, ease of functionalization, and excellent mechanical performance. Nanofibers can be synthesized and tailored to suit a wide range of applications including energy, biotechnology, healthcare, and environmental engineering. A comprehensive outlook on the recent developments, and the influence of electrospinning on biomedical uses such as wound dressing, drug release, and tissue engineering, has been presented. Concerns regarding the procedural restrictions and research contests are addressed, in addition to providing insights about the future of this fabrication technique in the biomedical field.