Silver nanowire loaded poly(ε-caprolactone) nanocomposite fibers as electroactive scaffolds for skeletal muscle regeneration

Volumetric muscle loss (VML) due to trauma and tumor removal operations affects millions of people every year. Although skeletal muscle has a natural repair mechanism, it cannot provide self-healing above a critical level of VML. In this study, nanocomposite aligned fiber scaffolds as support materials were developed for volumetric skeletal muscle regeneration. For this purpose, silver nanowire (Ag NW) loaded poly(ε-caprolactone) (PCL) nanocomposite fiber scaffolds (PCL-Ag NW) were prepared to mimic the aligned electroactive structure of skeletal muscle and provide topographic and conductive environment to modulate cellular behavior and orientation. A computer-aided rotational wet spinning (RWS) system was designed to produce high-yield fiber scaffolds. Nanocomposite fiber bundles with lengths of 50 cm were fabricated via this computer-aided RWS system. The morphological, chemical, thermal properties and biodegradation profiles of PCL and PCL-Ag NW nanocomposite fibers were characterized in detail. The proliferation behavior and morphology of C2C12 mouse myoblasts were investigated on PCL and PCL-Ag NW nanocomposite fibrous scaffolds with and without electrical stimulation. Significantly enhanced cell proliferation was observed on PCL-Ag NW nanocomposite fibers compared to neat PCL fibers with electrical stimulations of 1.5 V, 3 V and without electrical stimulation.

Corrosion Resistance and Cytocompatibility of Magnesium-Calcium Alloys Modified with Zinc- or Gallium-Doped Calcium Phosphate Coatings

In orthopedic surgery, metals are preferred to support or treat damaged bones due to their high mechanical strength. However, the necessity for a second surgery for implant removal after healing creates problems. Therefore, biodegradable metals, especially magnesium (Mg), gained importance, although their extreme susceptibility to galvanic corrosion limits their applications. The focus of this study was to control the corrosion of Mg and enhance its biocompatibility. For this purpose, surfaces of magnesium-calcium (MgCa1) alloys were modified with calcium phosphate (CaP) or CaP doped with zinc (Zn) or gallium (Ga) via microarc oxidation. The effects of surface modifications on physical, chemical, and mechanical properties and corrosion resistance of the alloys were studied using surface profilometry, goniometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nanoindentation, and electrochemical impedance spectroscopy (EIS). The coating thickness was about 5-8 μm, with grain sizes of 43.1 nm for CaP coating and 28.2 and 58.1 nm for Zn- and Ga-doped coatings, respectively. According to EIS measurements, the capacitive response (Y_c) decreased from 11.29 to 8.72 and 0.15 Ω^-1 cm^-2 sⁿ upon doping with Zn and Ga, respectively. The E_corr value, which was -1933 mV for CaP-coated samples, was found significantly electropositive at -275 mV for Ga-doped ones. All samples were cytocompatible according to indirect tests. In vitro culture with Saos-2 cells led to changes in the surface compositions of the alloys. The numbers of cells attached to the Zn-doped (2.6 × 10⁴ cells/cm²) and Ga-doped (6.3 × 10⁴ cells/cm²) coatings were higher than that on the surface of the undoped coating (1.0 × 10³ cells/cm²). Decreased corrosivity and enhanced cell affinity of the modified MgCa alloys (CaP coated and Zn and Ga doped, with Ga-doped ones having the greatest positive effect) make them novel and promising candidates as biodegradable metallic implant materials for the treatment of bone damages and other orthopedic applications.

3D Printed Biodegradable Polyurethaneurea Elastomer Recapitulates Skeletal Muscle Structure and Function

Effective skeletal muscle tissue engineering relies on control over the scaffold architecture for providing muscle cells with the required directionality, together with a mechanical property match with the surrounding tissue. Although recent advances in 3D printing fulfill the first requirement, the available synthetic polymers either are too rigid or show unfavorable surface and degradation profiles for the latter. In addition, natural polymers that are generally used as hydrogels lack the required mechanical stability to withstand the forces exerted during muscle contraction. Therefore, one of the most important challenges in the 3D printing of soft and elastic tissues such as skeletal muscle is the limitation of the availability of elastic, durable, and biodegradable biomaterials. Herein, we have synthesized novel, biocompatible and biodegradable, elastomeric, segmented polyurethane and polyurethaneurea (TPU) copolymers which are amenable for 3D printing and show high elasticity, low modulus, controlled biodegradability, and improved wettability, compared to conventional polycaprolactone (PCL) and PCL-based TPUs. The degradation profile of the 3D printed TPU scaffold was in line with the potential tissue integration and scaffold replacement process. Even though TPU attracts macrophages in 2D configuration, its 3D printed form showed limited activated macrophage adhesion and induced muscle-like structure formation by C2C12 mouse myoblasts in vitro, while resulting in a significant increase in muscle regeneration in vivo in a tibialis anterior defect in a rat model. Effective muscle regeneration was confirmed with immunohistochemical assessment as well as evaluation of electrical activity produced by regenerated muscle by EMG analysis and its force generation via a custom-made force transducer. Micro-CT evaluation also revealed production of more muscle-like structures in the case of implantation of cell-laden 3D printed scaffolds. These results demonstrate that matching the tissue properties for a given application via use of tailor-made polymers can substantially contribute to the regenerative outcomes of 3D printed tissue engineering scaffolds.

Recycled algae-based carbon materials as electroconductive 3D printed skeletal muscle tissue engineering scaffolds

Skeletal muscle is an electrically and mechanically active tissue that contains highly oriented, densely packed myofibrils. The tissue has self-regeneration capacity upon injury, which is limited in the cases of volumetric muscle loss. Several regenerative therapies have been developed in order to enhance this capacity, as well as to structurally and mechanically support the defect site during regeneration. Among them, biomimetic approaches that recapitulate the native microenvironment of the tissue in terms of parallel-aligned structure and biophysical signals were shown to be effective. In this study, we have developed 3D printed aligned and electrically active scaffolds in which the electrical conductivity was provided by carbonaceous material (CM) derived from algae-based biomass. The synthesis of this conductive and functional CM consisted of eco-friendly synthesis procedure such as pre-carbonization and multi-walled carbon nanotube (MWCNT) catalysis. CM obtained from biomass via hydrothermal carbonization (CM-03) and its ash form (CM-03K) were doped within poly(ɛ-caprolactone) (PCL) matrix and 3D printed to form scaffolds with aligned fibers for structural biomimicry. Scaffolds were seeded with C2C12 mouse myoblasts and subjected to electrical stimulation during the in vitro culture. Enhanced myotube formation was observed in electroactive groups compared to their non-conductive counterparts and it was observed that myotube formation and myotube maturity were significantly increased for CM-03 group after electrical stimulation. The results have therefore showed that the CM obtained from macroalgae biomass is a promising novel source for the production of the electrically conductive scaffolds for skeletal muscle tissue engineering.

Facile modification of polycaprolactone nanofibers with egg white protein

Synthetic polymers remain to be a major choice for scaffold fabrication due to their structural stability and mechanical strength. However, the lack of functional moieties limits their application for cell-based therapies which necessitate modification and functionalization. Blending synthetic polymers with natural components is a simple and effective way to achieve the desired biological properties for a scaffold. Herein, nanofibrous mats made of polycaprolactone (PCL) and egg white protein (EWP) blend were developed and further evaluated for use as a scaffold for tissue engineering applications. Homogeneous distribution of EWP was achieved throughout the nanofibrous mats, as shown by immunohistochemistry. ATR-FTIR analysis and contact angle measurements have further confirmed the presence of EWP on the surface of the samples. The swelling test showed that PCL/EWP nanofibers have higher water uptake than PCL nanofibrous mats. Also, EWP addition on the nanofibrous mats resulted in an increase in the tensile strength and Young's modulus of the mats, indicating that the presence of protein can greatly enhance the mechanical properties of the mats. A significantly higher, more uniform, and dispersed cell spreading was observed on days 7 and 14 than that on neat PCL mats, demonstrating the importance of providing the required cues for cell homing by the availability of EWP. Hence, EWP is shown to be a simple and low-cost source for the functionalization of PCL nanofibrous mats. EWP is, therefore, a facile candidate to enhance cellular interactions of synthetic polymers for a wide range of tissue engineering applications.

Novel additive manufacturing applications for communicable disease prevention and control: focus on recent COVID-19 pandemic

COVID-19 disease caused by the SARS-CoV-2 virus has had serious adverse effects globally in 2020 which are foreseen to extend in 2021, as well. The most important of these effects was exceeding the capacity of the healthcare infrastructures, and the related inability to meet the need for various medical equipment especially within the first months of the crisis following the emergence and rapid spreading of the virus. Urgent global demand for the previously unavailable personal protective equipment, sterile disposable medical supplies as well as the active molecules including vaccines and drugs fueled the need for the coordinated efforts of the scientific community. Amid all this confusion, the rapid prototyping technology, 3D printing, has demonstrated its competitive advantage by repositioning its capabilities to respond to the urgent need. Individual and corporate, amateur and professional all makers around the world with 3D printing capacity became united in effort to fill the gap in the supply chain until mass production is available especially for personal protective equipment and other medical supplies. Due to the unexpected, ever-changing nature of the COVID-19 pandemic-like all other potential communicable diseases-the need for rapid design and 3D production of parts and pieces as well as sterile disposable medical equipment and consumables is likely to continue to keep its importance in the upcoming years. This review article summarizes how additive manufacturing technology can contribute to such cases with special focus on the recent COVID-19 pandemic.

3D cellular alignment and biomimetic mechanical stimulation enhance human adipose-derived stem cell myogenesis

Determination of a stem cell source with sufficient myogenic differentiation capacity that can be easily obtained in large quantities is of great importance in skeletal muscle regeneration therapies. Adipose-derived stem cells (ASCs) are readily available, can be isolated from fat tissue with high yield and possess myogenic differentiation capacity. Consequently, ASCs have high applicability in muscle regenerative therapies. However, a key challenge is their low differentiation efficiency. In this study, we have explored the potential of mimicking the natural microenvironment of the skeletal muscle tissue to enhance ASC myogenesis by inducing 3D cellular alignment and using dynamic biomimetic culture. ASCs were entrapped and 3D aligned in parallel within fibrin-based microfibers and subjected to uniaxial cyclic stretch. 3D cell alignment was shown to be necessary for achieving and maintaining the stiffness of the construct mimicking the natural tissue (12 ± 1 kPa), where acellular aligned fibers and cell-laden random fibers had stiffness values of 4 ± 1 and 5 ± 2 kPa, respectively, at the end of 21 d. The synergistic effect of 3D cell alignment and biomimetic dynamic culture was evaluated on cell proliferation, viability and the expression of muscle-specific markers (immunofluorescent staining for MyoD1, myogenin, desmin and myosin heavy chain). It was shown that the myogenic markers were only expressed on the aligned-dynamic culture samples on day 21 of dynamic culture. These results demonstrate that 3D skeletal muscle grafts can be developed using ASCs by mimicking the structural and physiological muscle microenvironment.

Design of a new dual mesh with an absorbable nanofiber layer as a potential implant for abdominal hernia treatment

Dual meshes are often preferred in the treatment of umbilical and incisional hernias where the abdominal wall defect is large. These meshes are generally composed of either two nonabsorbable layers or a nonabsorbable layer combined with an absorbable one that degrades within the body upon healing of the defect. The most crucial point in the design of a dual mesh is to produce the respective layers based on the structure and requirements of the recipient site. We herein developed a dual mesh that consists of two layers: a nanofibrous layer made of poly (glycerol sebacate)/poly (caprolactone) (PGS/PCL) to support the healing of the abdominal wall defect and a nondegradable, nonadhesive smooth layer made of polycarbonateurethane (PU) with suitable properties to avoid the adhesion of the viscera to the mesh. To prepare the double-sided structure, PGS/PCL was directly electrospun onto the PU film. This processing approach provided a final product with well-integrated layers as observed by a scanning electron microscope. Tensile test performed at the dry state of the samples showed that the dual mesh has the ability to elongate seven times more as compared with the commercially available counterparts, mimicking the native tissue properties. The degradation test carried out at physiological conditions revealed that PGS started to degrade within the first 15 days. in vitro studies with human umbilical vein endothelial cells demonstrated the double function of the meshes, in which PU layer did not allow cell adhesion, whereas PGS/PCL layer has the ability to support cell adhesion and proliferation. Therefore, the material developed in this study has the potential to be an alternative to the existing hernia mesh products.

Myogenic Differentiation of ASCs Using Biochemical and Biophysical Induction

Adipose-derived stem/stromal cells (ASCs) constitute a very promising source for cell therapy and tissue engineering approaches as they can be easily obtained in large quantities with comparatively minimal patient discomfort. Moreover, ASCs have multilineage differentiation capacity. Among these, differentiation capacity along the myogenic lineage is of particular interest since myogenic precursors are scarce and obtaining a large number of cells from skeletal muscle biopsies is difficult. Here, we describe a method to effectively induce ASC myogenesis through the combination of biochemical (cocktail including 5-azacytidine and horse serum) and biophysical (dynamic culture via uniaxial cyclic strain) stimulation. This method results in multinucleated cells that are positive in myogenic markers including Pax 3/7, desmin, myoD, and myosin heavy chain.

A novel polyurethane-based biodegradable elastomer as a promising material for skeletal muscle tissue engineering

A key challenge in skeletal muscle tissue engineering is the choice of a proper scaffolding material as it should demonstrate elastic behavior to withstand and support the dynamic loading of the tissue microenvironment while being biodegradable and biocompatible. In this study, we tested the applicability of a novel biodegradable polyurethane (PU) elastomer chain extended with fibrinogen (Fib) to fulfill these requirements. Biodegradable polyurethane-fibrinogen (PU-Fib) elastomers were synthesized by step-wise condensation polymerization. Firstly, PU prepolymer was synthesized and then Fib was integrated into PU prepolymer during the second step of polymerization. The chemical, thermal, viscoelastic, mechanical and biodegradation properties of PU-Fib were characterized. FTIR-ATR spectrum showed amide bands specific to PU and Fib, DSC thermograms showed the suitable integration between the components. Dynamic mechanical analysis revealed Tg and Tα* transitions at 64.5 °C and 38.4 °C, respectively. PU and Fib had shown chemically compatible interactions and when compared to PCL, PU-Fib possessed viscoelastic properties more suitable to the native tissue. PU-Fib films were produced and seeded with C2C12 mouse myoblasts. Uniaxial cyclic stretch was applied to the cell seeded films for 21 d to mimic the native dynamic tissue microenvironment. Cell proliferation, viability and the expression of muscle-specific markers (immunofluorescent staining for myogenin and myosin heavy chain) were assessed. Myoblasts proliferated well on PU-Fib films; aligned parallel along their long edge, and express myogenic markers under biomimetic dynamic culture. It was possible to culture myoblasts with high viability on PU-Fib elastomeric films mimicking native muscle microenvironment.

Infrapatellar Fat Pad-Derived Stem Cell-Based Regenerative Strategies in Orthopedic Surgery

Infrapatellar fat pad is a densely vascularized and innervated extrasynovial tissue that fills the anterior knee compartment. It plays a role in knee biomechanics as well as constitutes a source of stem cells for regeneration after knee injury. Infrapatellar fat pad-derived stem cells (IPFP-ASCs) possess enhanced and age-independent differentiation capacity as compared to other stem cells, which makes them a very promising candidate in stem cell-based regenerative therapy. The aims of this review are to outline the latest advances and potential trends in using IPFP-ASCs and to emphasize the advantages over other sources of stem cells for applications in orthopedic surgery.

Scaffold pore size modulates in vitro osteogenesis of human adipose-derived stem/stromal cells

Trabecular bone has an interconnected porous structure, which influences cellular responses, biochemical transport and mechanical strength. Appropriately mimicking this structural organization in biomaterial scaffolds can facilitate more robust bone tissue regeneration and integration by providing a native microenvironment to the cells. This study examined the effect of pore size on human adipose-derived stem/stromal cell (ASC) osteogenesis within poly(ε-caprolactone) (PCL) scaffolds. Scaffold pore size was controlled by porogen leaching of custom-made paraffin particles with three different size ranges: P200 (< 500 µm), P500 (500-1000 µm), and P1000 (1000-1500 µm). Scaffolds produced by leaching these particles exhibited highly interconnected pores and rough surface structures that were favorable for cell attachment and ingrowth. The osteogenic response of ASCs was evaluated following 3 weeks of in vitro culture using biochemical (ALP, Ca(2+)/DNA content), mechanical (compression test) and histological (H&E and von Kossa staining) analyses. It was observed that while the total number of cells was similar for all scaffolds, the cell distributions and osteogenic properties were affected by the scaffold pore size. ASCs were able to bridge smaller pores and grow uniformly within these scaffolds (P200) while they grew as a layer along the periphery of the largest pores (P1000). The cell-biomaterial interactions specific to the latter case led to enhanced osteogenic responses. The ALP activity and Ca(2+) deposition were doubled in P1000 scaffolds as compared to P200 scaffolds. A significant difference was observed between the compressive strength of unseeded and seeded P1000 scaffolds. Therefore, we demonstrated that the use of scaffolds with pores that are in the range of 1 mm enhances in vitro ASC osteogenesis, which may improve their performance in engineered bone substitutes.

Engineering anatomically shaped vascularized bone grafts with hASCs and 3D-printed PCL scaffolds

The treatment of large craniomaxillofacial bone defects is clinically challenging due to the limited availability of transplantable autologous bone grafts and the complex geometry of the bones. The ability to regenerate new bone tissues that faithfully replicate the anatomy would revolutionize treatment options. Advances in the field of bone tissue engineering over the past few decades offer promising new treatment alternatives using biocompatible scaffold materials and autologous cells. This approach combined with recent advances in three-dimensional (3D) printing technologies may soon allow the generation of large, bioartificial bone grafts with custom, patient-specific architecture. In this study, we use a custom-built 3D printer to develop anatomically shaped polycaprolactone (PCL) scaffolds with varying internal porosities. These scaffolds are assessed for their ability to support induction of human adipose-derived stem cells (hASCs) to form vasculature and bone, two essential components of functional bone tissue. The development of functional tissues is assessed in vitro and in vivo. Finally, we demonstrate the ability to print large mandibular and maxillary bone scaffolds that replicate fine details extracted from patient's computed tomography scans. The findings of this study illustrate the capabilities and potential of 3D printed scaffolds to be used for engineering autologous, anatomically shaped, vascularized bone grafts.