Incorporation of Elastin to Improve Polycaprolactone-Based Scaffolds for Skeletal Muscle via Electrospinning

Emerging perspectives on 3D printed bioreactors for clinical translation of engineered and bioprinted tissue constructs

3D printed/bioprinted tissue constructs are utilized for the regeneration of damaged tissues and as in vitro models. Most of the fabricated 3D constructs fail to undergo functional maturation in conventional in vitro settings. There is a challenge to provide a suitable niche for the fabricated tissue constructs to undergo functional maturation. Bioreactors have emerged as a promising tool to enhance tissue maturation of the engineered constructs by providing physical/biological cues along with a controlled nutrient supply under dynamic in vitro conditions. Bioreactors provide an ambient microenvironment most appropriate for the development of functionally matured tissue constructs by promoting cell proliferation, differentiation, and maturation for transplantation and drug screening applications. Due to the huge cost and limited availability of commercial bioreactors, there is a need to develop strategies to make customized bioreactors. Additive manufacturing (AM) may be a viable tool to fabricate custom designed bioreactors with better efficiency and at low cost. In this review, we have extensively discussed the importance of bioreactors in functionalizing tissue engineered/3D bioprinted scaffolds for bone, cartilage, skeletal muscle, nerve, and vascular tissue. In addition, the importance and fabrication of customized 3D printed bioreactors for the maturation of tissue engineered constructs are discussed in detail. Finally, the current challenges and future perspectives in translating commercial and custom 3D printed bioreactors for clinical applications are outlined.

Investigation of osteogenesis and angiogenesis in perfusion bioreactors using improved multi-layer PCL-nHA-nZnO electrospun scaffolds

PURPOSE

Bone tissue engineering aims to create a three-dimensional, matured, angiogenic scaffold with a suitable thickness that resembles a natural bone matrix. On the other hand, electrospun fibers, which researchers have considered due to their good biomimetic properties, are considered 2D structures. Due to the highly interwoven network and small pore size, achieving the desired thickness for bone lesions has always been challenging. In bone tissue engineering, bioreactors are crucial for achieving initial tissue maturity and introducing certain signals as flow parameters for differentiation.

METHODS

In the present study, Human bone marrow mesenchymal stem cells (hBMSCs) and human umbilical vein endothelial cells (HUVECs) were co-cultured in a perfusion bioreactor on treated (improved pore size by gelatin sacrification and subsequent ultrasonication) 5-layer polycaprolactone-nano hydroxyapatite-nano zinc oxide (T-PHZ) scaffolds to investigate osteogenesis and angiogenesis simultaneously. The flow parameters and stresses on the cells were studied using two patterns of parallel and vertical scaffolds relative to the flow of the culture medium. In dynamic vertical flow (DVF), the culture medium flows perpendicular to the scaffolds, and in dynamic parallel flow (DPF), the culture medium flows parallel to the scaffolds. In all evaluations, static samples (S) served as the control group.

RESULTS

Live/dead, and MTT assays demonstrated the biocompatibility of the 5-layer scaffolds and the suitability of the bioreactor's functional conditions. ALP activity, EDAX analysis, and calcium content measurements exhibited greater osteogenesis for T-PHZ scaffolds in DVF conditions. Calcium content increased by a factor of 2.2, 1.8, and 1.6 during days 7 to 14 of culture under DVF, DPF and S conditions, respectively. After 21 days of co-culturing, an immunohistochemistry (IHC) test was performed to investigate angiogenesis and osteogenesis. Five antibodies were investigated in DVF, CD31, VEGFA, and VEGFR2 for angiogenesis, osteocalcin, and RUNX2 for osteogenesis. Compressive stress applied in DVF mode has increased osteogenic activity compared to DPF.

CONCLUSION

The results indicated the development of ideal systems for osteogenesis and angiogenesis on the treated multilayer electrospun scaffolds in the perfusion bioreactor.

Functionalised Hybrid Collagen-Elastin for Acellular Cutaneous Substitute Applications

Wound contracture, which commonly happens after wound healing, may lead to physical distortion, including skin constriction. Therefore, the combination of collagen and elastin as the most abundant extracellular matrix (ECM) skin matrices may provide the best candidate biomaterials for cutaneous wound injury. This study aimed to develop a hybrid scaffold containing green natural resources (ovine tendon collagen type-I and poultry-based elastin) for skin tissue engineering. Briefly, freeze-drying was used to create the hybrid scaffolds, which were then crosslinked with 0.1% (w/v) genipin (GNP). Next, the physical characteristics (pore size, porosity, swelling ratio, biodegradability and mechanical strength) of the microstructure were assessed. Energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FTIR) spectrophotometry were used for the chemical analysis. The findings showed a uniform and interconnected porous structure with acceptable porosity (>60%) and high-water uptake capacity (>1200%), with pore sizes ranging between 127 ± 22 and 245 ± 35 µm. The biodegradation rate of the fabricated scaffold containing 5% elastin was lower (<0.043 mg/h) compared to the control scaffold (collagen only; 0.085 mg/h). Further analysis with EDX identified the main elements of the scaffold: it contained carbon (C) 59.06 ± 1.36-70.66 ± 2.89%, nitrogen (N) 6.02 ± 0.20-7.09 ± 0.69% and oxygen (O) 23.79 ± 0.65-32.93 ± 0.98%. FTIR analysis revealed that collagen and elastin remained in the scaffold and exhibited similar functional amides (amide A: 3316 cm^-1, amide B: 2932 cm^-1, amide I: 1649 cm^-1, amide II: 1549 cm^-1 and amide III: 1233 cm^-1). The combination of elastin and collagen also produced a positive effect via increased Young's modulus values. No toxic effect was identified, and the hybrid scaffolds significantly supported human skin cell attachment and viability. In conclusion, the fabricated hybrid scaffolds demonstrated optimum physicochemical and mechanical properties and may potentially be used as an acellular skin substitute in wound management.

Bioactive cellulose acetate nanofiber loaded with annatto support skeletal muscle cell attachment and proliferation

Electrospinning emerged as a promising technique to produce scaffolds for cultivated meat in function of its simplicity, versatility, cost-effectiveness, and scalability. Cellulose acetate (CA) is a biocompatible and low-cost material that support cell adhesion and proliferation. Here we investigated CA nanofibers, associated or not with a bioactive annatto extract (CA@A), a food-dye, as potential scaffolds for cultivated meat and muscle tissue engineering. The obtained CA nanofibers were evaluated concerning its physicochemical, morphological, mechanical and biological traits. UV-vis spectroscopy and contact angle measurements confirmed the annatto extract incorporation into the CA nanofibers and the surface wettability of both scaffolds, respectively. SEM images revealed that the scaffolds are porous, containing fibers with no specific alignment. Compared with the pure CA nanofibers, CA@A nanofibers showed increased fiber diameter (420 ± 212 nm vs. 284 ± 130 nm). Mechanical properties revealed that the annatto extract induces a reduction of the stiffness of the scaffold. Molecular analyses revealed that while CA scaffold favored C2C12 myoblast differentiation, the annatto-loaded CA scaffold favored a proliferative state of these cells. These results suggest that the combination of cellulose acetate fibers loaded with annatto extract may be an interesting economical alternative for support long-term muscle cells culture with potential application as scaffold for cultivated meat and muscle tissue engineering.

Advances in electrospinning and 3D bioprinting strategies to enhance functional regeneration of skeletal muscle tissue

Skeletal muscles are essential for body movement, and the loss of motor function due to volumetric muscle loss (VML) limits the mobility of patients. Current therapeutic approaches are insufficient to offer complete functional recovery of muscle damages. Tissue engineering provides viable ways to fabricate scaffolds to regenerate damaged tissues. Hence, tissue engineering options are explored to address existing challenges in the treatment options for muscle regeneration. Electrospinning is a widely employed fabrication technique to make muscle mimetic nanofibrous scaffolds for tissue regeneration. 3D bioprinting has also been utilized to fabricate muscle-like tissues in recent times. This review discusses the anatomy of skeletal muscle, defects, the healing process, and various treatment options for VML. Further, the advanced strategies in electrospinning of natural and synthetic polymers are discussed, along with the recent developments in the fabrication of hybrid scaffolds. Current approaches in 3D bioprinting of skeletal muscle tissues are outlined with special emphasis on the combination of electrospinning and 3D bioprinting towards the development of fully functional muscle constructs. Finally, the current challenges and future perspectives of these convergence techniques are discussed.

Evaluation of Magnesium-Phosphate Particle Incorporation into Co-Electrospun Chitosan-Elastin Membranes for Skin Wound Healing

Major challenges facing clinicians treating burn wounds are the lack of integration of treatment to wound, inadequate mechanical properties of treatments, and high infection rates which ultimately lead to poor wound resolution. Electrospun chitosan membranes (ESCM) are gaining popularity for use in tissue engineering applications due to their drug loading ability, biocompatibility, biomimetic fibrous structure, and antimicrobial characteristics. This work aims to modify ESCMs for improved performance in burn wound applications by incorporating elastin and magnesium-phosphate particles (MgP) to improve mechanical and bioactive properties. The following ESCMs were made to evaluate the individual components’ effects; (C: chitosan, CE: chitosan-elastin, CMg: chitosan-MgP, and CEMg: chitosan-elastin-MgP). Membrane properties analyzed were fiber size and structure, hydrophilic properties, elastin incorporation, MgP incorporation and in vitro release, mechanical properties, degradation profiles, and in vitro cytocompatibility with NIH3T3 fibroblasts. The addition of both elastin and MgP increased the average fiber diameter of CE (~400 nm), CMg (~360 nm), and CEMg (565 nm) compared to C (255 nm). Water contact angle analysis showed elastin incorporated membranes (CE and CEMg) had increased hydrophilicity (~50°) compared to the other groups (C and CMg, ~110°). The results from the degradation study showed mass retention of ~50% for C and CMg groups, compared to ~ 30% seen in CE and CEMg after 4 weeks in a lysozyme/PBS solution. CMg and CEMg exhibited burst-release behavior of ~6 µg/ml or 0.25 mM magnesium within 72 h. In vitro analysis with NIH3T3 fibroblasts showed CE and CEMg groups had superior cytocompatibility compared to C and CMg. This work has demonstrated the successful incorporation of elastin and MgP into ESCMs and allows for future studies on burn wound applications.

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.

Tissue Engineering Strategies for Peripheral Nerve Regeneration

A peripheral nerve injury (PNI) has severe and profound effects on the life of a patient. The therapeutic approach remains one of the most challenging clinical problems. In recent years, many constructive nerve regeneration schemes are proposed at home and abroad. Nerve tissue engineering plays an important role. It develops an ideal nerve substitute called artificial nerve. Given the complexity of nerve regeneration, this review summarizes the pathophysiology and tissue-engineered repairing strategies of the PNI. Moreover, we discussed the scaffolds and seed cells for neural tissue engineering. Furthermore, we have emphasized the role of 3D printing in tissue engineering.