ECM concentration and cell-mediated traction forces play a role in vascular network assembly in 3D bioprinted tissue

Tissue vascularization is critical to enable oxygen and nutrient supply. Therefore, establishing expedient vasculature is necessary for the survival of tissue after transplantation. The use of biomechanical forces, such as cell-induced traction forces, may be a promising method to encourage growth of the vascular network. Three-dimensional (3D) bioprinting, which offers unprecedented versatility through precise control over spatial distribution and structure of tissue constructs, can be used to generate capillary-like structures in vitro that would mimic microvessels. This study aimed to develop an in vitro, 3D bioprinted tissue model to study the effect of cellular forces on the spatial organization of vascular structures and tissue maturation. The developed in vitro model consists of a 3D bioprinted polycaprolactone (PCL) frame with a gelatin spacer hydrogel layer and a gelatin–fibrin–hyaluronic acid hydrogel layer containing normal human dermal fibroblasts and human umbilical vein endothelial cells printed as vessel lines on top. The formation of vessel-like networks and vessel lumens in the 3D bioprinted in vitro model was assessed at different fibrinogen concentrations with and without inhibitors of cell-mediated traction forces. Constructs containing 5 mg/ml fibrinogen had longer vessels compared to the other concentrations of fibrinogen used. Also, for all concentrations of fibrinogen used, most of the vessel-like structures grew parallel to the direction the PCL frame-mediated tensile forces, with very few branching structures observed. Treatment of the 3D bioprinted constructs with traction inhibitors resulted in a significant reduction in length of vessel-like networks. The 3D bioprinted constructs also had better lumen formation, increased collagen deposition, more elaborate actin networks, and well-aligned matrix fibers due to the increased cell-mediated traction forces present compared to the non-anchored, floating control constructs. This study showed that cell traction forces from the actomyosin complex are critical for vascular network assembly in 3D bioprinted tissue. Strategies involving the use of cell-mediated traction forces may be promising for the development of bioprinting approaches for fabrication of vascularized tissue constructs.     

Differentiation potential of human adipose stem cells bioprinted with hyaluronic acid/gelatin‐based bioink through microextrusion and visible light‐initiated crosslinking

Bioprinting has a great potential to fabricate three‐dimensional (3D) functional tissues and organs. In particular, the technique enables fabrication of 3D constructs containing stem cells while maintaining cell proliferation and differentiation abilities, which is believed to be promising in the fields of tissue engineering and regenerative medicine. We aimed to demonstrate the utility of the bioprinting technique to create hydrogel constructs consisting of hyaluronic acid (HA) and gelatin derivatives through irradiation by visible light to fabricate 3D constructs containing human adipose stem cells (hADSCs). The hydrogel was obtained from a solution of HA and gelatin derivatives possessing phenolic hydroxyl moieties in the presence of ruthenium(II) tris‐bipyridyl dication and sodium ammonium persulfate. hADSCs enclosed in the bioprinted hydrogel construct elongated and proliferated in the hydrogel. In addition, their differentiation potential was confirmed by examining the expression of pluripotency marker genes and cell surface marker proteins, and differentiation to adipocytes in adipogenic differentiation medium. Our results demonstrate the great potential of the bioprinting method and the resultant hADSC‐laden HA/gelatin constructs for applications in tissue engineering and regenerative medicine.     

Sustained Release of BMP-2 in Bioprinted Alginate for Osteogenicity in Mice and Rats

The design of bioactive three-dimensional (3D) scaffolds is a major focus in bone tissue engineering. Incorporation of growth factors into bioprinted scaffolds offers many new possibilities regarding both biological and architectural properties of the scaffolds. This study investigates whether the sustained release of bone morphogenetic protein 2 (BMP-2) influences osteogenicity of tissue engineered bioprinted constructs. BMP-2 loaded on gelatin microparticles (GMPs) was used as a sustained release system, which was dispersed in hydrogel-based constructs and compared to direct inclusion of BMP-2 in alginate or control GMPs. The constructs were supplemented with goat multipotent stromal cells (gMSCs) and biphasic calcium phosphate to study osteogenic differentiation and bone formation respectively. BMP-2 release kinetics and bioactivity showed continuous release for three weeks coinciding with osteogenicity. Osteogenic differentiation and bone formation of bioprinted GMP containing constructs were investigated after subcutaneous implantation in mice or rats. BMP-2 significantly increased bone formation, which was not influenced by the release timing. We showed that 3D printing of controlled release particles is feasible and that the released BMP-2 directs osteogenic differentiation in vitro and in vivo.     

Bioactive nanoparticles stimulate bone tissue formation in bioprinted three‐dimensional scaffold and human mesenchymal stem cells

Bioprinting based on thermal inkjet printing is a promising but unexplored approach in bone tissue engineering. Appropriate cell types and suitable biomaterial scaffolds are two critical factors to generate successful bioprinted tissue. This study was undertaken in order to evaluate bioactive ceramic nanoparticles in stimulating osteogenesis of printed bone marrow‐derived human mesenchymal stem cells (hMSCs) in poly(ethylene glycol)dimethacrylate (PEGDMA) scaffold. hMSCs suspended in PEGDMA were co‐printed with nanoparticles of bioactive glass (BG) and hydroxyapatite (HA) under simultaneous polymerization so the printed substrates were delivered with highly accurate placement in three‐dimensional (3D) locations. hMSCs interacted with HA showed the highest cell viability (86.62 ± 6.02%) and increased compressive modulus (358.91 ± 48.05 kPa) after 21 days in culture among all groups. Biochemical analysis showed the most collagen production and highest alkaline phosphatase activity in PEG‐HA group, which is consistent with gene expression determined by quantitative PCR. Masson's trichrome staining also showed the most collagen deposition in PEG‐HA scaffold. Therefore, HA is more effective comparing to BG for hMSCs osteogenesis in bioprinted bone constructs. Combining with our previous experience in vasculature, cartilage, and muscle bioprinting, this technology demonstrates the capacity for both soft and hard tissue engineering with biomimetic structures.     

Rotating versus perfusion bioreactor for the culture of engineered vascular constructs based on hyaluronic acid

It is generally accepted that dynamic culture conditions are required for vascular tissue engineering. We compared the effects of two dynamic culture systems, a perfusion and a rotating bioreactor, using tubular constructs based on hyaluronic acid seeded with porcine aortic smooth muscle cells (SMC), that we recently showed to be adequate for the generation of vascular tissue. In perfused constructs mechanical stimulation importantly affected cell morphology, increased the incidence of cell proliferation and reduced apoptosis. However, extracellular matrix deposition, cytoskeletal organization and mechanical properties were poor. In rotated constructs cell proliferation was also higher and apoptosis lower than in static controls. Rotated constructs showed the highest ultimate stress and the lowest elastic modulus. Our data indicate that the rotating bioreactor is more efficient than the perfusion bioreactor and we then suggest that this method can be considered a valid alternative to complex bioreactor systems described in the literature.     

Maintenance of stem cell viability and differentiation potential following cryopreservation within 3-dimensional hyaluronic acid hydrogels

While significant progress has been made in directing the behavior of cells encapsulated within three-dimensional (3D) covalently crosslinked hydrogels, the capacity of these materials to support in situ cryopreservation of cells directly within the gels has not been assessed. Here, we demonstrate the retention of human mesenchymal stem cell (hMSC) viability within hyaluronic acid (HA) and polyethylene glycol based hydrogels via a facile gradual cooling and freezing protocol. Encapsulated cell viability was retained at similar rates in both materials systems regardless of initial duration in culture or adhesive ligand incorporation, indicating the versatility of the approach. Additionally, the cryopreservation protocol maintains stem cell differentiation potential; incubation in adipogenic differentiation media induced equal rates of hMSC adipogenesis in freeze-thawed and non-frozen HA based hydrogels on a per-cell basis. Collectively, these findings highlight the cryopreservation protocol as a platform technology that, in addition to contributing to an increased understanding of three-dimensional cell-matrix interactions, could enable the long-term preservation of tissue engineering constructs for clinical applications.     

Engineering inkjet bioprinting processes toward translational therapies

Bioprinting is the assembly of three-dimensional (3D) tissue constructs by layering cell-laden biomaterials using additive manufacturing techniques, offering great potential for tissue engineering and regenerative medicine. Such a process can be performed with high resolution and control by personalized or commercially available inkjet printers. However, bioprinting's clinical translation is significantly limited due to process engineering challenges. Upstream challenges include synthesis, cellular incorporation, and functionalization of “bioinks,” and extrusion of print geometries. Downstream challenges address sterilization, culture, implantation, and degradation. In the long run, bioinks must provide a microenvironment to support cell growth, development, and maturation and must interact and integrate with the surrounding tissues after implantation. Additionally, a robust, scaleable manufacturing process must pass regulatory scrutiny from regulatory bodies such as U.S. Food and Drug Administration, European Medicines Agency, or Australian Therapeutic Goods Administration for bioprinting to have a real clinical impact. In this review, recent advances in inkjet-based 3D bioprinting will be presented, emphasizing on biomaterials available, their properties, and the process to generate bioprinted constructs with application in medicine. Current challenges and the future path of bioprinting and bioinks will be addressed, with emphasis in mass production aspects and the regulatory framework bioink-based products must comply to translate this technology from the bench to the clinic.     

Human Cartilage Tissue Fabrication Using Three-dimensional Inkjet Printing Technology

Bioprinting, which is based on thermal inkjet printing, is one of the most attractive enabling technologies in the field of tissue engineering and regenerative medicine. With digital control cells, scaffolds, and growth factors can be precisely deposited to the desired two-dimensional (2D) and three-dimensional (3D) locations rapidly. Therefore, this technology is an ideal approach to fabricate tissues mimicking their native anatomic structures. In order to engineer cartilage with native zonal organization, extracellular matrix composition (ECM), and mechanical properties, we developed a bioprinting platform using a commercial inkjet printer with simultaneous photopolymerization capable for 3D cartilage tissue engineering. Human chondrocytes suspended in poly(ethylene glycol) diacrylate (PEGDA) were printed for 3D neocartilage construction via layer-by-layer assembly. The printed cells were fixed at their original deposited positions, supported by the surrounding scaffold in simultaneous photopolymerization. The mechanical properties of the printed tissue were similar to the native cartilage. Compared to conventional tissue fabrication, which requires longer UV exposure, the viability of the printed cells with simultaneous photopolymerization was significantly higher. Printed neocartilage demonstrated excellent glycosaminoglycan (GAG) and collagen type II production, which was consistent with gene expression. Therefore, this platform is ideal for accurate cell distribution and arrangement for anatomic tissue engineering.     

Essential steps in bioprinting: From pre- to post-bioprinting

An increasing demand for directed assembly of biomaterials has inspired the development of bioprinting, which facilitates the assembling of both cellular and acellular inks into well-arranged three-dimensional (3D) structures for tissue fabrication. Although great advances have been achieved in the recent decade, there still exist issues to be addressed. Herein, a review has been systematically performed to discuss the considerations in the entire procedure of bioprinting. Though bioprinting is advancing at a rapid pace, it is seen that the whole process of obtaining tissue constructs from this technique involves multiple-stages, cutting across various technology domains. These stages can be divided into three broad categories: pre-bioprinting, bioprinting and post-bioprinting. Each stage can influence others and has a bearing on the performance of fabricated constructs. For example, in pre-bioprinting, tissue biopsy and cell expansion techniques are essential to ensure a large number of cells are available for mass organ production. Similarly, medical imaging is needed to provide high resolution designs, which can be faithfully bioprinted. In the bioprinting stage, compatibility of biomaterials is needed to be matched with solidification kinetics to ensure constructs with high cell viability and fidelity are obtained. On the other hand, there is a need to develop bioprinters, which have high degrees of freedom of movement, perform without failure concerns for several hours and are compact, and affordable. Finally, maturation of bioprinted cells are governed by conditions provided during the post-bioprinting process. This review, for the first time, puts all the bioprinting stages in perspective of the whole process of bioprinting, and analyzes their current state-of-the art. It is concluded that bioprinting community will recognize the relative importance and optimize the parameter of each stage to obtain the desired outcomes.     

Three-dimensional dynamic culture of pre-osteoblasts seeded in HA-CS/Col/nHAP composite scaffolds and treated with α-ZAL

Pre-osteoblast MC3T3-E1 cells were cultured in hyaluronic acid-modified chitosan/collagen/nano-hydroxyapatite (HA-CS/Col/nHAP) composite scaffolds and treated with phytoestrogen α-zearalanol (α-ZAL) to improve bone tissue formation for bone tissue engineering. Perfusion and dynamic strain were applied to three-dimensional (3D) cultured cells, which simulates mechanical microenvironment in bone tissue and solves mass transfer issues. The morphology of cell-scaffold constructs in vitro was then examined and markers of osteogenesis were assessed by immunohistochemistry staining and western blotting. The results showed that cells expanded their pseudopodia in an irregular manner and dispersed along the walls in 3D-dynamic culture. Osteogenic phenotype was increased or maintained by enhanced collagen I (COLI) levels, decreased osteopontin expression and having little effect on osteocalcin expression during the 12 days of in vitro culture. In response to α-ZAL, the cell-scaffold constructs showed inhibited cellular proliferation, enhanced the alkaline phosphatase (ALP) activity and increased ratio of osteoprotegerin to receptor activator of nuclear factor kappa B (NF-κB) ligand (RANKL). Application of perfusion and dynamic strain to cells-scaffold constructs treated with α-ZAL represents a promising approach in the studies of osteogenesis stimulation of bone tissue engineering.     

Nanostructured 3D Constructs Based on Chitosan and Chondroitin Sulphate Multilayers for Cartilage Tissue Engineering

Nanostructured three-dimensional constructs combining layer-by-layer technology (LbL) and template leaching were processed and evaluated as possible support structures for cartilage tissue engineering. Multilayered constructs were formed by depositing the polyelectrolytes chitosan (CHT) and chondroitin sulphate (CS) on either bidimensional glass surfaces or 3D packet of paraffin spheres. 2D CHT/CS multi-layered constructs proved to support the attachment and proliferation of bovine chondrocytes (BCH). The technology was transposed to 3D level and CHT/CS multi-layered hierarchical scaffolds were retrieved after paraffin leaching. The obtained nanostructured 3D constructs had a high porosity and water uptake capacity of about 300%. Dynamical mechanical analysis (DMA) showed the viscoelastic nature of the scaffolds. Cellular tests were performed with the culture of BCH and multipotent bone marrow derived stromal cells (hMSCs) up to 21 days in chondrogenic differentiation media. Together with scanning electronic microscopy analysis, viability tests and DNA quantification, our results clearly showed that cells attached, proliferated and were metabolically active over the entire scaffold. Cartilaginous extracellular matrix (ECM) formation was further assessed and results showed that GAG secretion occurred indicating the maintenance of the chondrogenic phenotype and the chondrogenic differentiation of hMSCs.     

Fabrication of a biomimetic spinal cord tissue construct with heterogenous mechanical properties using intrascaffold cell assembly

In tissue engineering studies, scaffolds play a very important role in offering both physical and chemical cues for cell growth and tissue regeneration. However, in some cases, tissue regeneration requires scaffolds with high mechanical properties (e.g., bone and cartilage), while cells need a soft mechanical microenvironment. In this study, to mimic the heterogenous mechanical properties of a spinal cord tissue, a biomimetic rat tissue construct is fabricated. A collagen-coated poly(lactic-co-glycolic acid) scaffold is manufactured using thermally induced phase separation casting. Primary rat neural cells (P01 Wistar rat cortex) with soft hydrogels are later printed within the scaffold using an image-guided intrascaffold cell assembly technique. The scaffolds have unidirectional microporous structure with parallel axial macrochannels (260 ± 4 µm in diameter). Scaffolds showed mechanical properties similar to rat spine (ultimate tensile strength: 0.085 MPa, Young's modulus [stretch]: 0.31 MPa). The bioink composed of gelatin/alginate/fibrinogen is precisely printed into the macrochannels and showed mechanical properties suitable for neural cells (Young's modulus [compressive]: 3.814 kPa). Scaffold interface, cell viability, and immunostaining analyses show uniform distribution of stable, healthy, and elongated neural cells and neurites over 14 culture days in vitro. The results demonstrated that this method can serve as a valuable tool to aid manufacturing of tissue constructs requiring heterogenous mechanical properties for complex cell and/or biomolecule assembly.     

Cellular Encapsulation in 3D Hydrogels for Tissue Engineering

The 3D encapsulation of cells within hydrogels represents an increasingly important and popular technique for culturing cells and towards the development of constructs for tissue engineering. This environment better mimics what cells observe in vivo, compared to standard tissue culture, due to the tissue-like properties and 3D environment. Synthetic polymeric hydrogels are water-swollen networks that can be designed to be stable or to degrade through hydrolysis or proteolysis as new tissue is deposited by encapsulated cells. A wide variety of polymers have been explored for these applications, such as poly(ethylene glycol) and hyaluronic acid. Most commonly, the polymer is functionalized with reactive groups such as methacrylates or acrylates capable of undergoing crosslinking through various mechanisms. In the past decade, much progress has been made in engineering these microenvironments - e.g., via the physical or pendant covalent incorporation of biochemical cues - to improve viability and direct cellular phenotype, including the differentiation of encapsulated stem cells (Burdick et al.).The following methods for the 3D encapsulation of cells have been optimized in our and other laboratories to maximize cytocompatibility and minimize the number of hydrogel processing steps. In the following protocols (see Figure 1 for an illustration of the procedure), it is assumed that functionalized polymers capable of undergoing crosslinking are already in hand; excellent reviews of polymer chemistry as applied to the field of tissue engineering may be found elsewhere (Burdick et al.) and these methods are compatible with a range of polymer types. Further, the Michael-type addition (see Lutolf et al.) and light-initiated free radical (see Elisseeff et al.) mechanisms focused on here constitute only a small portion of the reported crosslinking techniques. Mixed mode crosslinking, in which a portion of reactive groups is first consumed by addition crosslinking and followed by a radical mechanism, is another commonly used and powerful paradigm for directing the phenotype of encapsulated cells (Khetan et al., Salinas et al.).     

In vivo evaluation of bioprinted prevascularized bone tissue

Bioprinting can be considered as a progression of the classical tissue engineering approach, in which cells are randomly seeded into scaffolds. Bioprinting offers the advantage that cells can be placed with high spatial fidelity within three-dimensional tissue constructs. A decisive factor to be addressed for bioprinting approaches of artificial tissues is that almost all tissues of the human body depend on a functioning vascular system for the supply of oxygen and nutrients. In this study, we have generated cuboid prevascularized bone tissue constructs by bioprinting human adipose-derived mesenchymal stem cells (ASCs) and human umbilical vein endothelial cells (HUVECs) by extrusion-based bioprinting and drop-on-demand (DoD) bioprinting, respectively. The computer-generated print design could be verified in vitro after printing. After subcutaneous implantation of bioprinted constructs in immunodeficient mice, blood vessel formation with human microvessels of different calibers could be detected arising from bioprinted HUVECs and stabilization of human blood vessels by mouse pericytes was observed. In addition, bioprinted ASCs were able to synthesize a calcified bone matrix as an indicator of ectopic bone formation. These results indicate that the combined bioprinting of ASCs and HUVECs represents a promising strategy to produce prevascularized artificial bone tissue for prospective applications in the treatment of critical-sized bone defects.     

A novel perfused rotary bioreactor for cardiomyogenesis of embryonic stem cells

Developments in bioprocessing technology play an important role for overcoming challenges in cardiac tissue engineering. To this end, our laboratory has developed a novel rotary perfused bioreactor for supporting three-dimensional cardiac tissue engineering. The dynamic culture environments provided by our novel perfused rotary bioreactor and/or the high-aspect rotating vessel produced constructs with higher viability and significantly higher cell numbers (up to 4 × 10⁵ cells/bead) than static tissue culture flasks. Furthermore, cells in the perfused rotary bioreactor showed earlier gene expressions of cardiac troponin-T, α- and β-myosin heavy chains with higher percentages of cardiac troponin-I-positive cells and better uniformity of sacromeric α-actinin expression. A dynamic and perfused environment, as provided by this bioreactor, provides a superior culture performance in cardiac differentiation for embryonic stem cells particularly for larger 3D constructs.     

Preservation of critical quality attributes of mesenchymal stromal cells in 3D bioprinted structures by using natural hydrogel scaffolds

Three dimensional (3D) bioprinting is an emerging technology that enables complex spatial modeling of cell-based tissue engineering products, whose therapeutic potential in regenerative medicine is enormous. However, its success largely depends on the definition of a bioprintable zone, which is specific for each combination of cell-loaded hydrogels (or bioinks) and scaffolds, matching the mechanical and biological characteristics of the target tissue to be repaired. Therefore proper adjustment of the bioink formulation requires a compromise between: (i) the maintenance of cellular critical quality attributes (CQA) within a defined range of specifications to cell component, and (ii) the mechanical characteristics of the printed tissue to biofabricate. Herein, we investigated the advantages of using natural hydrogel-based bioinks to preserve the most relevant CQA in bone tissue regeneration applications, particularly focusing on cell viability and osteogenic potential of multipotent mesenchymal stromal cells (MSCs) displaying tripotency in vitro, and a phenotypic profile of 99.9% CD105⁺/CD45,⁻ 10.3% HLA-DR,⁺ 100.0% CD90,⁺ and 99.2% CD73⁺/CD31⁻ expression. Remarkably, hyaluronic acid, fibrin, and gelatin allowed for optimal recovery of viable cells, while preserving MSC's proliferation capacity and osteogenic potency in vitro. This was achieved by providing a 3D structure with a compression module below 8.8 ± 0.5 kPa, given that higher values resulted in cell loss by mechanical stress. Beyond the biocompatibility of naturally occurring polymers, our results highlight the enhanced protection on CQA exerted by bioinks of natural origin (preferably HA, gelatin, and fibrin) on MSC, bone marrow during the 3D bioprinting process, reducing shear stress and offering structural support for proliferation and osteogenic differentiation.     

Hyaluronic Acid Enhances the Mechanical Properties of Tissue-Engineered Cartilage Constructs

There is a need for materials that are well suited for cartilage tissue engineering. Hydrogels have emerged as promising biomaterials for cartilage repair, since, like cartilage, they have high water content, and they allow cells to be encapsulated within the material in a genuinely three-dimensional microenvironment. In this study, we investigated the mechanical properties of tissue-engineered cartilage constructs using in vitro culture models incorporating human chondrocytes from osteoarthritis patients. We evaluated hydrogels formed from mixtures of photocrosslinkable gelatin-methacrylamide (Gel-MA) and varying concentrations (0–2%) of hyaluronic acid methacrylate (HA-MA). Initially, only small differences in the stiffness of each hydrogel existed. After 4 weeks of culture, and to a greater extent 8 weeks of culture, HA-MA had striking and concentration dependent impact on the changes in mechanical properties. For example, the initial compressive moduli of cell-laden constructs with 0 and 1% HA-MA were 29 and 41 kPa, respectively. After 8 weeks of culture, the moduli of these constructs had increased to 66 and 147 kPa respectively, representing a net improvement of 69 kPa for gels with 1% HA-MA. Similarly the equilibrium modulus, dynamic modulus, failure strength and failure strain were all improved in constructs containing HA-MA. Differences in mechanical properties did not correlate with glycosaminoglycan content, which did not vary greatly between groups, yet there were clear differences in aggrecan intensity and distribution as assessed using immunostaining. Based on the functional development with time in culture using human chondrocytes, mixtures of Gel-MA and HA-MA are promising candidates for cartilage tissue-engineering applications.     

Mesenchymal stem cell cultivation in electrospun scaffolds: mechanistic modeling for tissue engineering

Tissue engineering is a multidisciplinary field of research in which the cells, biomaterials, and processes can be optimized to develop a tissue substitute. Three-dimensional (3D) architectural features from electrospun scaffolds, such as porosity, tortuosity, fiber diameter, pore size, and interconnectivity have a great impact on cell behavior. Regarding tissue development in vitro, culture conditions such as pH, osmolality, temperature, nutrient, and metabolite concentrations dictate cell viability inside the constructs. The effect of different electrospun scaffold properties, bioreactor designs, mesenchymal stem cell culture parameters, and seeding techniques on cell behavior can be studied individually or combined with phenomenological modeling techniques. This work reviews the main culture and scaffold factors that affect tissue development in vitro regarding the culture of cells inside 3D matrices. The mathematical modeling of the relationship between these factors and cell behavior inside 3D constructs has also been critically reviewed, focusing on mesenchymal stem cell culture in electrospun scaffolds.     

Fiber-based tissue engineering: Progress,challenges, and opportunities

Tissue engineering aims to improve the function of diseased or damaged organs by creating biological substitutes. To fabricate a functional tissue, the engineered construct should mimic the physiological environment including its structural, topographical, and mechanical properties. Moreover, the construct should facilitate nutrients and oxygen diffusion as well as removal of metabolic waste during tissue regeneration. In the last decade, fiber-based techniques such as weaving, knitting, braiding, as well as electrospinning, and direct writing have emerged as promising platforms for making 3D tissue constructs that can address the abovementioned challenges. Here, we critically review the techniques used to form cell-free and cell-laden fibers and to assemble them into scaffolds. We compare their mechanical properties, morphological features and biological activity. We discuss current challenges and future opportunities of fiber-based tissue engineering (FBTE) for use in research and clinical practice.     

Hydrophilic gelatin and hyaluronic acid-treated PLGA scaffolds for cartilage tissue engineering

Tissue engineering provides a new strategy for repairing damaged cartilage. Surface and mechanical properties of scaffolds play important roles in inducing cell growth.?Aim: The aim of this study was to fabricate and characterize PLGA and gelatin/hyaluronic acid-treated PLGA (PLGA-GH) sponge scaffolds for articular cartilage tissue engineering. Methods: The PLGA-GH scaffolds were cross-linked with gelatin and hyaluronic acid. Primary chondrocytes isolated from porcine articular cartilages were used to assess cell compatibility. The characteristic PLGA-GH scaffold was higher in water uptake ratio and degradation rate within 42 days than the PLGA scaffold. Results: The mean compressive moduli of PLGA and PLGA-GH scaffolds were 1.72±0.50 MPa and 1.86±0.90 MPa, respectively. The cell attachment ratio, proliferation, and extracellular matrix secretion on PLGA-GH scaffolds are superior to those of PLGA scaffolds. Conclusions: In our study, PLGA-GH scaffolds exhibited improvements in cell biocompatibility, cell proliferation, extracellular matrix synthesis, and appropriate mechanical and structural properties for potential engineering cartilage applications.