Electrospun PLGA nanofiber scaffolds for articular cartilage reconstruction: mechanical stability, degradation and cellular responses under mechanical stimulation in vitro

Superabsorbent 3D Scaffold Based on Electrospun Nanofibers for Cartilage Tissue Engineering

Electrospun nanofibers have been used for various biomedical applications. However, electrospinning commonly produces two-dimensional (2D) membranes, which limits the application of nanofibers for the 3D tissue engineering scaffold. In the present study, a porous 3D scaffold (3DS-1) based on electrospun gelatin/PLA nanofibers has been prepared for cartilage tissue regeneration. To further improve the repairing effect of cartilage, a modified scaffold (3DS-2) cross-linked with hyaluronic acid (HA) was also successfully fabricated. The nanofibrous structure, water absorption, and compressive mechanical properties of 3D scaffold were studied. Chondrocytes were cultured on 3D scaffold, and their viability and morphology were examined. 3D scaffolds were also subjected to an in vivo cartilage regeneration study on rabbits using an articular cartilage injury model. The results indicated that 3DS-1 and 3DS-2 exhibited superabsorbent property and excellent cytocompatibility. Both these scaffolds present elastic property in the wet state. An in vivo study showed that 3DS-2 could enhance the repair of cartilage. The present 3D nanofibrous scaffold (3DS-2) would be promising for cartilage tissue engineering application.

Dual delivery of active antibactericidal agents and bone morphogenetic protein at sustainable high concentrations using biodegradable sheath-core-structured drug-eluting nanofibers

In this study, we developed biodegradable sheath-core-structured drug-eluting nanofibers for sustainable delivery of antibiotics (vancomycin and ceftazidime) and recombinant human bone morphogenetic protein (rhBMP-2) via electrospinning. To prepare the biodegradable sheath-core nanofibers, we first prepared solutions of poly(d,l)-lactide-co-glycolide, vancomycin, and ceftazidime in 1,1,1,3,3,3-hexafluoro-2-propanol and rhBMP-2 in phosphate-buffered solution. The poly(d,l)-lactide-co-glycolide/antibiotics and rhBMP-2 solutions were then fed into two different capillary tubes controlled by two independent pumps for coaxial electrospinning. The electrospun nanofiber morphology was observed under a scanning electron microscope. We further characterized the in vitro antibiotic release from the nanofibers via high-performance liquid chromatography and that of rhBMP-2 via enzyme-linked immunosorbent assay and alkaline phosphatase activity. We showed that the biodegradable coaxially electrospun nanofibers could release high vancomycin/ceftazidime concentrations (well above the minimum inhibition concentration [MIC]₉₀) and rhBMP-2 for >4 weeks. These experimental results demonstrate that novel biodegradable nanofibers can be constructed with various pharmaceuticals and proteins for long-term drug deliveries.

Electrospinning strategies of drug-incorporated nanofibrous mats for wound recovery

Electrospun nanofibrous mats have recently been employed as drug reservoirs for their unique features, such as high surface-to-volume ratios and easy fabrication process. We describe herein various methods of fabricating drug- and gene-encapsulated nanofibrous meshes, which can be prepared by electrospinning. The electrospinning process of nanofibrous mats is affected by many parameters, including viscosity and ejection speeds of the polymeric solutions and the electrical potential applied to the system. Both single- and dual-nozzle systems are widely employed in the preparation of electrospun nanofibers encapsulating drugs and genes, which are usually incorporated into the electrospun mats either by physical mixing with polymeric solutions before electrospinning or by physical incorporation after electrospinning. Various strategies have been tailored to maintain the bioactivity of proteins for tissue regeneration before and after electrospinning. Nucleic acids, such as DNA and siRNA, are also incorporated into nanofibrous meshes to enhance tissue regeneration by expressing transgenes or silencing domestic genes in specific tissues. Drug- or gene-incorporated nanofibrous meshes can greatly increase tissue regeneration rates and reduce scar formation in normal and diabetic wounds. Hybrid nanofibers, with multiple cell layers or hydrogels, have also been used to improve wound healing efficiency by increasing cell infiltration.

Evaluation of Changes in Morphology and Function of Human Induced Pluripotent Stem Cell Derived Cardiomyocytes (HiPSC-CMs) Cultured on an Aligned-Nanofiber Cardiac Patch

Introduction

Dilated cardiomyopathy is a major cause of progressive heart failure. Utilization of stem cell therapy offers a potential means of regenerating viable cardiac tissue. However, a major obstacle to stem cell therapy is the delivery and survival of implanted stem cells in the ischemic heart. To address this issue, we have developed a biomimetic aligned nanofibrous cardiac patch and characterized the alignment and function of human inducible pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) cultured on this cardiac patch. This hiPSC-CMs seeded patch was compared with hiPSC-CMs cultured on standard flat cell culture plates.

Methods

hiPSC-CMs were cultured on; 1) a highly aligned polylactide-co-glycolide (PLGA) nanofiber scaffold (~50 microns thick) and 2) on a standard flat culture plate. Scanning electron microscopy (SEM) was used to determine alignment of PLGA nanofibers and orientation of the cells on the respective surfaces. Analysis of gap junctions (Connexin-43) was performed by confocal imaging in both the groups. Calcium cycling and patch-clamp technique were performed to measure calcium transients and electrical coupling properties of cardiomyocytes.

Results

SEM demonstrated >90% alignment of the nanofibers in the patch which is similar to the extracellular matrix of decellularized rat myocardium. Confocal imaging of the cardiomyocytes demonstrated symmetrical alignment in the same direction on the aligned nanofiber patch in sharp contrast to the random appearance of cardiomyocytes cultured on a tissue culture plate. The hiPSC-CMs cultured on aligned nanofiber cardiac patches showed more efficient calcium cycling compared with cells cultured on standard flat surface culture plates. Quantification of mRNA with qRT-PCR confirmed that these cardiomyocytes expressed α-actinin, troponin-T and connexin-43 in-vitro.

Conclusions

Overall, our results demonstrated changes in morphology and function of human induced pluripotent derived cardiomyocytes cultured in an anisotropic environment created by an aligned nanofiber patch. In this environment, these cells better approximate normal cardiac tissue compared with cells cultured on flat surface and can serve as the basis for bioengineering of an implantable cardiac patch.

DiameterJ: A validated open source nanofiber diameter measurement tool

Despite the growing use of nanofiber scaffolds for tissue engineering applications, there is not a validated, readily available, free solution for rapid, automated analysis of nanofiber diameter from scanning electron microscope (SEM) micrographs. Thus, the goal of this study was to create a user friendly ImageJ/FIJI plugin that would analyze SEM micrographs of nanofibers to determine nanofiber diameter on a desktop computer within 60 s. Additional design goals included 1) compatibility with a variety of existing segmentation algorithms, and 2) an open source code to enable further improvement of the plugin. Using existing algorithms for centerline determination, Euclidean distance transforms and a novel pixel transformation technique, a plugin called "DiameterJ" was created for ImageJ/FIJI. The plugin was validated using 1) digital synthetic images of white lines on a black background and 2) SEM images of nominally monodispersed steel wires of known diameters. DiameterJ analyzed SEM micrographs in 20 s, produced diameters not statistically different from known values, was over 10-times closer to known diameter values than other open source software, provided hundreds of times the sampling of manual measurement, and was hundreds of times faster than manual assessment of nanofiber diameter. DiameterJ enables users to rapidly and thoroughly determine the structural features of nanofiber scaffolds and could potentially allow new insights to be formed into fiber diameter distribution and cell response.

Nanofibrous scaffold with incorporated protein gradient for directing neurite outgrowth

Concentration gradient of diffusible bioactive chemicals assumes many important roles in regulating cellular behavior. Among the many factors influencing functional recovery after nerve injury, such as topographical and biochemical signals, concentration gradients of neurotrophic factors provide chemotactic cues for neurite outgrowth and targeted renervation. In this study, a concentration gradient of nerve growth factor (NGF, 0-250 μg/ml) was incorporated throughout the thickness of poly(ε-caprolactone)-poly(ethylene glycol) coaxial electrospun nanofibrous scaffolds (∼700 μm thick with ∼800 nm average fiber diameter). The existence of the protein gradient upon protein release was demonstrated using a customized under-agarose-PC12 neurite outgrowth assay. When exposed to scaffolds endowed with NGF concentration gradient (NGF-CG), a significant difference in the percentage of cells bearing neurite outgrowth was observed (7.1 ± 1.9% vs. 0.8 ± 0.3% for cells exposed to high vs. low concentration surface, respectively; p < 0.05). In contrast, no significant difference was observed when cells were exposed to scaffolds that encapsulated a fixed concentration of NGF. Direct culture of PC12 cells on the substrates demonstrated the cytocompatibility and the effect of diffusible NGF gradient on neurite outgrowth. A significant difference in the percentage of cells with neurite extensions was observed when PC12 cells were seeded on NGF-CG scaffolds (21.2 ± 3.6% vs. 10.4 ± 1.3% on high vs. low concentration surface, respectively; p < 0.05). Furthermore, Z-stack confocal microscopy tracking of neurite extensions revealed the chemotatic guidance effect of NGF concentration gradient. Directed and enhanced neurite penetration into the scaffolds towards increasing NGF concentration was observed. In vitro release study indicated that the encapsulated NGF was released in a sustained manner for at least 30 days (80.4 ± 3.6% released). Taken together, this study demonstrates the feasibility of incorporating concentration gradient of diffusible bioactive chemicals in nanofibrous scaffolds via the coaxial electrospinning technique.

Blends and Nanocomposite Biomaterials for Articular Cartilage Tissue Engineering

This review provides a comprehensive assessment on polymer blends and nanocomposite systems for articular cartilage tissue engineering applications. Classification of various types of blends including natural/natural, synthetic/synthetic systems, their combination and nanocomposite biomaterials are studied. Additionally, an inclusive study on their characteristics, cell responses ability to mimic tissue and regenerate damaged articular cartilage with respect to have functionality and composition needed for native tissue, are also provided.

Mechanical properties and dual drug delivery application of poly(lactic-co-glycolic acid) scaffolds fabricated with a poly(β-amino ester) porogen

Polymeric scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. Scaffolds can be further enhanced by enabling the release of one or more drugs to stimulate regeneration or for the treatment of a specific disease or condition. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres were mixed with poly(β-amino ester) (PBAE) particles to create novel hybrid scaffolds capable of dual release of drug and growth factor. Fast-degrading PBAE particles loaded with the drug ketoprofen acted as porogens that provided a rapid 12h release. The PLGA microspheres were loaded with a growth factor, bone morphogenetic protein 2, and fused together around the porogens to create a slow-degrading matrix that provided sustained release lasting 70days. Drug release was further tailored by varying the amount of porogen added to the scaffold. Bioactivity measurements demonstrated that the scaffold fabrication technique did not damage the drug or protein. The compressive modulus was affected by the amount of porogen added, extending from 50 to 111MPa for loadings from 60 to 40% PBAE, and after 5days of degradation, it decreased to 0.6 to 1.1kPa when the porogen was gone. PLGA containing a quick-degrading porogen can be used to release two drugs while developing a porous microarchitecture for cell ingrowth with in a matrix capable of maintaining a compressive modulus applicable for soft tissue implants.

Biodegradable polymers for electrospinning: towards biomedical applications

Electrospinning has received much attention recently due to the growing interest in nano-technologies and the unique material properties. This review focuses on recent progress in applying electrospinning technique in production of biodegradable nanofibers to the emerging field of biomedical. It first introduces the basic theory and parameters of nanofibers fabrication, with focus on factors affecting the morphology and fiber diameter of biodegradable nanofibers. Next, commonly electrospun biodegradable nanofibers are discussed, and the comparison of the degradation rate of nanoscale materials with macroscale materials are highlighted. The article also assesses the recent advancement of biodegradable nanofibers in different biomedical applications, including tissue engineering, drug delivery, biosensor and immunoassay. Future perspectives of biodegradable nanofibers are discussed in the last section, which emphasizes on the innovation and development in electrospinning of hydrogels nanofibers, pore size control and scale-up productions.

Nano/microfibrous polymeric constructs loaded with bioactive agents and designed for tissue engineering applications: a review

Nano/microfibrous polymeric constructs present various inherent advantages, such as highly porous architecture and high surface to volume ratio, making them attractive for tissue engineering purposes. Electrospinning is the most preferred technique for the fabrication of polymeric nanofibrous assemblies that can mimic the physical functions of native extracellular matrix greatly favoring cells attachment and thus influencing their morphology and activities. Different approaches have been developed to apply polymeric microfiber fabrication techniques (e.g. wet-spinning) for the obtainment of scaffolds with a three-dimensional network of micropores suitable for effective cells migration. Progress in additive manufacturing technology has led to the development of complex scaffold's shapes and microfibrous structures with a high degree of automation, good accuracy and reproducibility. Various loading methods, such as direct blending, coaxial electrospinning and microparticles incorporation, are enabling to develop customized strategies for the biofunctionalization of nano/microfibrous scaffolds with a tailored kinetics of release of different bioactive agents, ranging from small molecules, such as antibiotics, to protein drugs, such as growth factors, and even cells. Recent activities on the combination of different processing techniques and loading methods for the obtainment of biofunctionalized polymeric constructs with a complex multiscale structure open new possibilities for the development of biomimetic scaffolds endowed with a hierarchical architecture and a sophisticated release kinetics of different bioactive agents. This review is aimed at summarizing current advances in technologies and methods for manufacturing nano/microfibrous polymeric constructs suitable as tissue engineering scaffolds, and for their combination with different bioactive agents to promote tissue regeneration and therapeutic effects.

Control of scaffold degradation in tissue engineering: a review

Tissue engineering has shown a great promise as a solution to the high demand for tissue and organ transplantations. Biomaterial scaffolds serve to house and direct cells to grow, exposing them to an adequate perfusion of nutrients, oxygen, metabolic products, and appropriate growth factors to enhance their differentiation and function. The degradation of biomaterial scaffolds is a key factor to successful tissue regeneration. In this article, the existing degradation control approaches in the context of scaffold tissue engineering were reviewed and a new paradigm of thinking called active control of scaffold degradation, proposed elsewhere by us, was also revisited and discussed in light of its benefit and requirement of this new technology.

Enhancement of diabetic wound repair using biodegradable nanofibrous metformin-eluting membranes: in vitro and in vivo

This work developed biodegradable nanofibrous drug-eluting membranes that provided sustained release of metformin for repairing wounds associated with diabetes. To prepare the biodegradable membranes, poly-d-l-lactide-glycolide (PLGA) and metformin were first dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and were spun into nanofibrous membranes by electrospinning. An elution method and an HPLC assay were utilized to characterize the in vivo and in vitro release rates of the pharmaceuticals from the membranes. The biodegradable nanofibrous membranes released high concentrations of metformin for more than three weeks. Moreover, nanofibrous metformin-eluting PLGA membranes were more hydrophilic and had a greater water-containing capacity than virgin PLGA fibers. The membranes also improved wound healing and re-epithelialization in diabetic rats relative to the control. The experimental results in this work suggest that nanofibrous metformin-eluting membranes were functionally active in the treatment of diabetic wounds and very effective as accelerators in the early stage of healing of such wounds.

The chaperone protein SmgGDS interacts with small GTPases entering the prenylation pathway by recognizing the last amino acid in the CAAX motif

Ras family small GTPases localize at the plasma membrane, where they can activate oncogenic signaling pathways. Understanding the mechanisms that promote membrane localization of GTPases will aid development of new therapies to inhibit oncogenic signaling. We previously reported that SmgGDS splice variants promote prenylation and trafficking of GTPases containing a C-terminal polybasic region and demonstrated that SmgGDS-607 interacts with nonprenylated GTPases, whereas SmgGDS-558 interacts with prenylated GTPases in cells. The mechanism that SmgGDS-607 and SmgGDS-558 use to differentiate between prenylated and nonprenylated GTPases has not been characterized. Here, we provide evidence that SmgGDS-607 associates with GTPases through recognition of the last amino acid in the CAAX motif. We show that SmgGDS-607 forms more stable complexes in cells with nonprenylated GTPases that will become geranylgeranylated than with nonprenylated GTPases that will become farnesylated. These binding relationships similarly occur with nonprenylated SAAX mutants. Intriguingly, farnesyltransferase inhibitors increase the binding of WT K-Ras to SmgGDS-607, indicating that the pharmacological shunting of K-Ras into the geranylgeranylation pathway promotes K-Ras association with SmgGDS-607. Using recombinant proteins and prenylated peptides corresponding to the C-terminal sequences of K-Ras and Rap1B, we found that both SmgGDS-607 and SmgGDS-558 directly bind the GTPase C-terminal region, but the specificity of the SmgGDS splice variants for prenylated versus nonprenylated GTPases is diminished in vitro. Finally, we present structural homology models and data from functional prediction software to define both similar and unique features of SmgGDS-607 when compared with SmgGDS-558.

Therapeutic application of electrospun nanofibrous meshes

Fabricating tissue architecture-mimicking scaffolds is one of the major challenges in the field of tissue engineering. Electrospun nanofibers have been considered as potent techniques for fabricating fibrous scaffolds biomimicking extracellular frameworks. Therapeutic agent-incorporated nanofibrous meshes have widely served as excellent substrates for adhesion, proliferation and differentiation. Many drugs, proteins and nucleic acids were incorporated into the scaffolds for regeneration of skin, musculoskeletal, neural and vascular tissue engineering in aims to control the release of the therapeutic agents. In the current article, we focus on introducing various fabrication techniques for electrospun nanofiber-based scaffolds and subsequent functionalization of nanofibers for therapeutic purposes. We also detail how the therapeutic nanofibrous meshes can be employed in the field of tissue engineering.

Effects of hydrostatic pressure on biosynthetic activity during chondrogenic differentiation of MSCs in hybrid scaffolds

The objective of this study was to determine the effects of hydrostatic pressure (HP) on the biochemical properties and gene expression of mesenchymal stem cells (MSCs) on scaffolds for cartilage tissue engineering composed of poly(caprolactone) (PCL) poly(vinyl alcohol) (PVA) gelatin (GEL) semi interpenetrating polymer network (semi-IPN). The MSCs were cultured on PCL-PVA-GEL semi-IPN scaffolds in two groups (A and B) for 7 and 21 days, respectively, and then loaded with hydrostatic pressure (5 MPa, 0.5 Hz) for 2 h per day for the period of 7 days and compared with two non-loaded groups (C and D) as controls. DMMB and real-time PCR analysis for assaying cartilage-specific extracellular matrix (ECM) gene markers were carried out. According to the results, there were no significant differences in GAG amounts between the loaded and non-loaded constructs were observed after 14 days. However, significant and considerable increases in the expression amount of type II collagen mRNA levels in group A ( from 2.43 × 10-4 ± 5.32 × 10-5 to 2.09 × 10-3 ± 1.07 × 10-4 time), and in group B (from 3.04 × 10-4 ± 4.31 × 10-5 to 2.08 × 10-3 ± 1.59 × 10-4 time) in comparison with non-loaded groups (C and D) were observed, respectively. Results showed the beneficial role of hydrostatic pressure on the increase of type II collagen mRNA levels in articular cartilage tissue engineering.

Electrospun collagen-poly(L-lactic acid-co-ε-caprolactone) membranes for cartilage tissue engineering

AIM

To study the feasibility of electrospun collagen-poly(L-lactic acid-co-ε-caprolactone) (collagen-PLCL) membranes for cartilage tissue engineering.

MATERIALS & METHODS

Characteristics and mechanical properties of collagen-PLCL membranes were analyzed. The cell affinity of collagen-PLCL membranes with chondrocytes was also assessed. Then, the cell-scaffold constructs were engineered with collagen-PLCL membranes seeded chondrocytes by a sandwich model. After culture for 1 week in vitro, the constructs were implanted subcutaneously into nude mice for 4, 8 and 12 weeks, followed by evaluation of the quality of neocartilage.

RESULTS

Collagen-PLCL membranes exhibited excellent balanced properties without cytotoxicity. With the extension of implantation time in vivo, the constructs revealed more cartilage-like tissue especially at 8 and 12 weeks. The Young's modulus of the constructs also significantly increased and neared that of native cartilage at 12 weeks postimplantation.

CONCLUSION

We suggest that collagen-PLCL membranes facilitate the formation of cartilage and thus may represent a promising scaffold for cartilage tissue engineering.

Ion-exchange polymer nanofibers for enhanced osteogenic differentiation of stem cells and ectopic bone formation

Nanofibrous scaffolds with specific modifications have shown promising potential for bone tissue engineering applications. In the present study, poly(ether sulfone) (PES) and sulfonated PES (SPES) nanofibers were fabricated via electrospinning. Calcium ions were then incorporated in SPES by immersion in a Ca(OH)2 solution. The calcium-ion-exchanged SPES (Ca-SPES), PES, and SPES nanofibers were characterized and then evaluated for their osteogenic capacity: both in vitro using stem cell culture and in vivo after subcutaneous implantation in mice. After 7 days of immersion in simulated body fluid, the formation of an apatite layer was only observed on Ca-SPES nanofibers. According to the MTT results, an increasing stem cell population was detected on all scaffolds during the period of study. Using real-time reverse transcriptase-polymerase chain reaction, alkaline phosphatase activity, and calcium content assays, it was demonstrated that the osteogenic differentiation of stem cells was higher on Ca-SPES scaffolds in comparison with PES and SPES nanofibers. Interestingly, Ca-SPES scaffolds were shown to induce ectopic bone formation after 12 weeks of subcutaneous implantation in mice. This was confirmed by mineralization and the production of collagen fibers using van Kossa and Masson's trichrome staining, respectively. Taken together, it was demonstrated that the incorporation of calcium ions into the ion-exchange nanofibrous scaffolds not only gives them the ability to enhance osteogenic differentiation of stem cells in vitro but also to induce ectopic bone formation in vivo.

Biodegradable mesostructured polymer membranes

The extracellular matrix (ECM) has a quasi-ordered reticular mesostructure with feature sizes on the order of tenths of to a few hundred nanometers. Approaches to preparing biodegradable synthetic scaffolds for engineered tissues that have the critical mesostructure to mimic ECM are few. Here we present a simple and general solvent evaporation-induced self-assembly (EISA) approach to preparing concentrically reticular mesostructured polyol-polyester membranes. The mesostructures were formed by a novel self-assembly process without covalent or electrostatic interactions, which yielded feature sizes matching those of ECM. The mesostructured materials were nonionic, hydrophilic, and water-permeable and could be shaped into arbitrary geometries such as conformally molded tubular sacs and micropatterned meshes. Importantly, the mesostructured polymers were biodegradable and were used as ultrathin temporary substrates for engineering vascular tissue constructs.

Bioengineering of articular cartilage: past, present and future

The treatment of cartilage defects poses a clinical challenge owing to the lack of intrinsic regenerative capacity of cartilage. The use of tissue engineering techniques to bioengineer articular cartilage is promising and may hold the key to the successful regeneration of cartilage tissue. Natural and synthetic biomaterials have been used to recreate the microarchitecture of articular cartilage through multilayered biomimetic scaffolds. Acellular scaffolds preserve the microarchitecture of articular cartilage through a process of decellularization of biological tissue. Although promising, this technique often results in poor biomechanical strength of the graft. However, biomechanical strength could be improved if biomaterials could be incorporated back into the decellularized tissue to overcome this limitation.

Techniques for fabrication and construction of three-dimensional scaffolds for tissue engineering

Three-dimensional biomimetic scaffolds have widespread applications in biomedical tissue engineering because of their nanoscaled architecture, eg, nanofibers and nanopores, similar to the native extracellular matrix. In the conventional “top-down” approach, cells are seeded onto a biocompatible and biodegradable scaffold, in which cells are expected to populate in the scaffold and create their own extracellular matrix. The top-down approach based on these scaffolds has successfully engineered thin tissues, including skin, bladder, and cartilage in vitro. However, it is still a challenge to fabricate complex and functional tissues (eg, liver and kidney) due to the lack of vascularization systems and limited diffusion properties of these large biomimetic scaffolds. The emerging “bottom-up” method may hold great potential to address these challenges, and focuses on fabricating microscale tissue building blocks with a specific microarchitecture and assembling these units to engineer larger tissue constructs from the bottom up. In this review, state-of-the-art methods for fabrication of three-dimensional biomimetic scaffolds are presented, and their advantages and drawbacks are discussed. The bottom-up methods used to assemble microscale building blocks (eg, microscale hydrogels) for tissue engineering are also reviewed. Finally, perspectives on future development of the bottom-up approach for tissue engineering are addressed.

Chondrogenic differentiation of menstrual blood-derived stem cells on nanofibrous scaffolds

Cartilage tissue engineering is a promising technology to restore and repair cartilage lesions in the body. In recent years, significant advances have been made using stem cells as a cell source for clinical goals of cartilage tissue engineering. Menstrual blood-derived stem cells (MenSCs) is a novel population of stem cells that demonstrate the potential and differentiate into a wide range of tissues including the chondrogenic lineage. Incorporation of cell culture with extracellular matrix (ECM) like substratum plays an important role in cartilage tissue regeneration by providing attachment sites as well as bioactive signals for cells to grow and differentiate into chondrogenic lineage. The electrospun nanofibers are a class of polymer-based biomaterials that have been extensively utilized in tissue engineering as ECM-like scaffold. This chapter discusses potential of electrospun nanofibers for cell-based cartilage tissue engineering and presents detailed protocols on immunophenotyping characterization and chondrogenic differentiation of MenSCs seeded in poly-ε-caprolactone (PCL) nanofibers. The isolated MenSCs are characterized using flow cytometry, seeded on the nanofibers, imaged using scanning electron microscopy, and subsequently differentiated into chondrogenic lineage in culture medium containing specific growth factors and cytokines. Immunofluorescence and alcian blue staining are used to evaluate the development of seeded MenSCs in PCL nanofibrous scaffold into chondrogenic lineage.

Supporting Biomaterials for Articular Cartilage Repair

Orthopedic surgeons and researchers worldwide are continuously faced with the challenge of regenerating articular cartilage defects. However, until now, it has not been possible to completely mimic the biological and biochemical properties of articular cartilage using current research and development approaches. In this review, biomaterials previously used for articular cartilage repair research are addressed. Furthermore, a brief discussion of the state of the art of current cell printing procedures mimicking native cartilage is offered in light of their use as future alternatives for cartilage tissue engineering. Inkjet cell printing, controlled deposition cell printing tools, and laser cell printing are cutting-edge techniques in this context. The development of mimetic hydrogels with specific biological properties relevant to articular cartilage native tissue will support the development of improved, functional, and novel engineered tissue for clinical application.

One-step articular cartilage repair: combination of in situ bone marrow stem cells with cell-free poly(L-lactic-co-glycolic acid) scaffold in a rabbit model

Focal full-thickness articular cartilage defects are challenging to repair. The purpose of this study was to find a simple, effective 1-step articular cartilage repair method. Because stem cell niches produce a microenvironment for stem cell self-renewal, proliferation, and differentiation, we integrated in situ bone marrow stem cells with an implanted poly(L-lactic-co-glycolic acid) (PLLGA) scaffold. Marrow stem cells grew and proliferated on cell-free PLLGA scaffolds, which were evaluated by scanning electronic microscopy (SEM) and Cell Counting Kit-8 (Dojindo, Kumamoto, Japan). Twenty-seven rabbits (54 knees) with large cylinder femoral trochlear cartilage defects were created and repaired with microfracture and cell-free PLLGA scaffold implantation (group 1), microfracture (group 2), or cell-free PLLGA scaffold implantation (group 3).Outcomes were evaluated by magnetic resonance imaging, International Cartilage Repair Society scores, histology, and immunohistochemistry. The repair effects were better in group 1 than in groups 2 and 3. In group 1, hyaline-like cartilage formed at week 24. Magnetic resonance imaging showed homogeneous signals as the adjacent normal cartilage. Collagen type II and toluidine blue were stained positively as normal cartilage tissue, and the color and thickness of regenerated tissue were similar to surrounding normal tissue. The combination of microfracture and cell-free PLLGA scaffold implantation used endogenous marrow stem cells in situ and promoted hyaline-like cartilage regeneration rapidly and effectively.

Osteogenic differentiation of human placenta-derived mesenchymal stem cells (PMSCs) on electrospun nanofiber meshes

Numerous challenges remain in the successful clinical translation of cell-based therapeutic studies for skeletal tissue repair, including appropriate cell sources and viable cell delivery systems. Poly(ethylene glycol)-poly(ε-caprolactone) (PEG-PCL) amphiphilic block copolymers have been extensively explored in microspheres preparation. Due to the introduction of hydrophilic PEG segments into PCL backbones, these copolymers have shown much more potentials in carrying protein, lipophilic drugs or genes than commonly used poly (ε-caprolactone) (PCL) and poly (lactic acid). The aim of this study is to investigate the attachment and osteogenic differentiation of human placenta derived mesenchymal stem cells (PMSCs) on PEG-PCL triblock copolymers nanofiber scaffolds. Here we demonstrated that PMSCs proliferate robustly and can be effectively differentiated into osteogenic-like cells on nanofiber scaffolds. This study provides evidence for the use of nanofiber scaffolds as an ideal supporting material for in vitro PMSCs culture and an in vivo cell delivery vehicle for bone repair.

Structural and functional characterization of proteins adsorbed on hydrophilized polylactide-co-glycolide microfibers

Background:

Hydrophobic biopolymers such as polylactide-co-glycolide (PLGA, 85:15) have been extensively explored as scaffolding materials for tissue engineering applications. More recently, electrospun microfiber-based and nanofiber-based scaffolds of PLGA have received increased attention because they act as physical mimics of the fibrillar extracellular matrix. However, the hydrophobicity of the PLGA microfiber surface can limit its use in biomedical applications. Therefore, in a previous study, we fabricated Pluronic^® F-108 (PF-108)-blended PLGA microfibrous scaffolds that alleviated the hydrophobicity associated with PLGA by enriching the surface of microfibers with the ethylene oxide units present in PF-108.

Methods:

In this study, we report the influence of the extent of surface enrichment of PLGA microfibers on their interaction with two model proteins, ie, bovine serum albumin (BSA) and lysozyme. BSA and lysozyme were adsorbed onto PLGA microfiber meshes (unmodified and modified) and studied for the amount, secondary structure conformation, and bioactivity of released protein.

Results:

Irrespective of the type of protein, PF-108-blended PLGA microfibers showed significantly greater protein adsorption and release than the unblended PLGA samples. However, in comparison with BSA, lysozyme showed a 7–9-fold increase in release. The Fourier transform infrared spectroscopy studies for secondary structure determination demonstrated that irrespective of type of microfiber surface (unblended or blended), adsorbed BSA and lysozyme did not show any significant change in secondary structure (α-helical content) as compared with BSA and/or lysozyme in the free powder state. Further, the bioactivity assay of lysozyme released from blended PLGA microfiber meshes demonstrated 80%–85% bioactivity, indicating that the process of adsorption did not significantly affect biological activity. Therefore, this study demonstrated that the decreased hydrophobicity of blended PLGA microfibrous meshes not only improved the amount of protein adsorbed (lysozyme and BSA) but also maintained the secondary structure and bioactivity of the adsorbed proteins.

Conclusion:

Modulating the hydrophobicity of PLGA via blending with PF-108 could be a viable strategy to improve its interaction with proteins and subsequent cell interaction in tissue engineering applications.

Polymeric nanofibers in tissue engineering

Polymeric nanofibers can be produced using methods such as electrospinning, phase separation, and self-assembly, and the fiber composition, diameter, alignment, degradation, and mechanical properties can be tailored to the intended application. Nanofibers possess unique advantages for tissue engineering. The small diameter closely matches that of extracellular matrix fibers, and the relatively large surface area is beneficial for cell attachment and bioactive factor loading. This review will update the reader on the aspects of nanofiber fabrication and characterization important to tissue engineering, including control of porous structure, cell infiltration, and fiber degradation. Bioactive factor loading will be discussed with specific relevance to tissue engineering. Finally, applications of polymeric nanofibers in the fields of bone, cartilage, ligament and tendon, cardiovascular, and neural tissue engineering will be reviewed.

Electrospun nanofiber-based regeneration of cartilage enhanced by mesenchymal stem cells

Application of biomaterials in combination with stem cells is a novel tissue engineering approach to regenerate cartilage. The objective of this study was to investigate the potential of poly(vinyl alcohol)/polycaprolactone (PVA/PCL) nanofiber scaffolds seeded with rabbit bone marrow-mesenchymal stem cell (BM-MSC) for cartilage tissue engineering in vitro and in vivo. We tested the biocompatibility and mechanical properties of nanofibrous scaffolds using scanning electron microscope, MTT assay, and tensile measurements. The capacity of MSC for chondrogenic differentiation on scaffolds was examined using reverse transcription-polymer chain reaction and immunostaining. For in vivo assessments, PVA/PCL nanofiber scaffolds with or without MSC were implanted into rabbit full-thickness cartilage defects. To evaluate cartilage regeneration, semi-quantitative grading and histological analysis were performed. Our results showed that PVA/PCL scaffolds supported the proliferation and chondrogenic differentiation of MSC in vitro. Moreover, the animals treated with cell-seeded PVA/PCL scaffolds showed improved healing of defects compared with untreated control and those which received cell-free scaffolds. Our findings suggest that PVA/PCL scaffolds incorporated with MSC can serve as a suitable graft for articular cartilage reconstruction.

Fabrication and characterization of interconnected porous biodegradable poly(ε-caprolactone) load bearing scaffolds

In this study, poly(ε-caprolactone) (PCL)/poly(ethylene oxide) (PEO) (50:50 wt%) immiscible blend was used as a model system to investigate the feasibility of a novel solventless fabrication approach that combines cryomilling, compression molding and porogen leaching techniques to prepare interconnected porous scaffolds for tissue engineering. PCL was cryomilled with PEO to form blend powders. Compression molding was used to consolidate and anneal the cryomilled powders. Selective dissolution of the PEO with water resulted in interconnected porous scaffolds. Sodium chloride salt (NaCl) was subsequently added to cryomilled powder to increase the porosity of scaffolds. The prepared scaffolds had homogeneous pore structures, a porosity of ~50% which was increased by mixing salt with the blend (~70% for 60% wt% NaCl), and a compressive modulus and strength (ε = 10%) of 60 and 2.8 MPa, respectively. The results of the study confirm that this novel approach offers a viable alternative to fabricate scaffolds.