Culture scaffolds allow microalgae cultivation with minimum water requirement using the air-liquid interface approach. However, the stability of cellulose-based scaffolds in microalgae cultivation remains questionable. In this study, the stability of regenerated cellulose culture scaffolds was enhanced by adjusting TiO2 loading and casting gap. The membrane scaffolds were synthesized using cellulose dissolved in NaOH/urea aqueous solution with various loading of TiO2 nanoparticles. The TiO2 nanoparticles were embedded into the porous membrane scaffolds as proven by Fourier transform infrared spectra, scanning electron microscopic images, and energy-dispersive X-ray spectra. Although surface hydrophilicity and porosity were enhanced by increasing TiO2 and casting gap, the scaffold pore size was reduced. Cellulose membrane scaffold with 0.05 wt% of TiO2 concentration and thickness of 100 μm attained the highest percentage of Navicula incerta growth rate, up to 37.4%. The membrane scaffolds remained stable in terms of weight, porosity and pore size even they were immersed in acidic solution, hydrogen peroxide or autoclaved at 121 °C for 15 min. The optimal cellulose membrane scaffold is with TiO2 loading of 0.5 wt% and thickness of 100 μm, resulting in supporting the highest N. incerta growth rate and and exhibits good membrane stability.
Tissue-engineered substitutes have shown great promise as a potential replacement for current tissue grafts to treat tendon/ligament injury. Herein, we have fabricated aligned polycaprolactone (PCL) and gelatin (GT) nanofibers and further evaluated their physicochemical properties and biocompatibility. PCL and GT were mixed at a ratio of 100:0, 70:30, 50:50, 30:70, 0:100, and electrospun to generate aligned nanofibers. The PCL/GT nanofibers were assessed to determine the diameter, alignment, water contact angle, degradation, and surface chemical analysis. The effects on cells were evaluated through Wharton's jelly-derived mesenchymal stem cell (WJ-MSC) viability, alignment and tenogenic differentiation. The PCL/GT nanofibers were aligned and had a mean fiber diameter within 200-800 nm. Increasing the GT concentration reduced the water contact angle of the nanofibers. GT nanofibers alone degraded fastest, observed only within 2 days. Chemical composition analysis confirmed the presence of PCL and GT in the nanofibers. The WJ-MSCs were aligned and remained viable after 7 days with the PCL/GT nanofibers. Additionally, the PCL/GT nanofibers supported tenogenic differentiation of WJ-MSCs. The fabricated PCL/GT nanofibers have a diameter that closely resembles the native tissue's collagen fibrils and have good biocompatibility. Thus, our study demonstrated the suitability of PCL/GT nanofibers for tendon/ligament tissue engineering applications.
Understanding the bioelectrical properties of bone tissue is key to developing new treatment strategies for bone diseases and injuries, as well as improving the design and fabrication of scaffold implants for bone tissue engineering. The bioelectrical properties of bone tissue can be attributed to the interaction of its various cell lineages (osteocyte, osteoblast and osteoclast) with the surrounding extracellular matrix, in the presence of various biomechanical stimuli arising from routine physical activities; and is best described as a combination and overlap of dielectric, piezoelectric, pyroelectric and ferroelectric properties, together with streaming potential and electro-osmosis. There is close interdependence and interaction of the various electroactive and electrosensitive components of bone tissue, including cell membrane potential, voltage-gated ion channels, intracellular signaling pathways, and cell surface receptors, together with various matrix components such as collagen, hydroxyapatite, proteoglycans and glycosaminoglycans. It is the remarkably complex web of interactive cross-talk between the organic and non-organic components of bone that define its electrophysiological properties, which in turn exerts a profound influence on its metabolism, homeostasis and regeneration in health and disease. This has spurred increasing interest in application of electroactive scaffolds in bone tissue engineering, to recapitulate the natural electrophysiological microenvironment of healthy bone tissue to facilitate bone defect repair.
The repair of osteochondral defects requires a tissue engineering approach that aims at mimicking the physiological properties and structure of two different tissues (cartilage and bone) using specifically designed scaffold-cell constructs. Biphasic and triphasic approaches utilize two or three different architectures, materials, or composites to produce a multilayered construct. This article gives an overview of some of the current strategies in multiphasic/gradient-based scaffold architectures and compositions for tissue engineering of osteochondral defects. In addition, the application of finite element analysis (FEA) in scaffold design and simulation of in vitro and in vivo cell growth outcomes has been briefly covered. FEA-based approaches can potentially be coupled with computer-assisted fabrication systems for controlled deposition and additive manufacturing of the simulated patterns. Finally, a summary of the existing challenges associated with the repair of osteochondral defects as well as some recommendations for future directions have been brought up in the concluding section of this article.
Hypoxia, the result of disrupted vasculature, can be categorized in the main limiting factors for fracture healing. A lack of oxygen can cause cell apoptosis, tissue necrosis, and late tissue healing. Remedying hypoxia by supplying additional oxygen will majorly accelerate bone healing. In this study, biphasic calcium phosphate (BCP) scaffolds were fabricated by robocasting, an additive manufacturing technique. Then, calcium peroxide (CPO) particles, as an oxygen-releasing agent, were coated on the BCP scaffolds. Segmental radial defects with the size of 15 mm were created in rabbits. Uncoated and CPO-coated BCP scaffolds were implanted in the defects. The empty (control) group received no implantation. Repairing of the bone was investigated via X-ray, histological analysis, and biomechanical tests at 3 and 6 months postoperatively, with immunohistochemical examinations at 6 months after operation. According to the radiological observations, formation of new bone was augmented at the interface between the implant and host bone and internal pores of CPO-coated BCP scaffolds compared to uncoated scaffolds. Histomorphometry analysis represented that the amount of newly formed bone in the CPO-coated scaffold was nearly two times higher than the uncoated one. Immunofluorescence staining revealed that osteogenic markers, osteonectin and octeocalcin, were overexpressed in the defects treated with the coated scaffolds at 6 months of postsurgery, demonstrating higher osteogenic differentiation and bone mineralization compared to the uncoated scaffold group. Furthermore, the coated scaffolds had superior biomechanical properties as in the case of 3 months after surgery, the maximal flexural force of the coated scaffolds reached to 134 N, while it was 92 N for uncoated scaffolds. The results could assure a boosted ability of bone repair for CPO-coated BCP scaffolds implanted in the segmental defect of rabbit radius because of oxygen-releasing coating, and this system of oxygen-generating coating/scaffold might be a potential for accelerated repairing of bone defects.
The potential of electrospinning process to fabricate ultrafine fibers as building blocks for tissue engineering scaffolds is well recognized. The scaffold construct produced by electrospinning process depends on the quality of the fibers. In electrospinning, material selection and parameter setting are among many factors that contribute to the quality of the ultrafine fibers, which eventually determine the performance of the tissue engineering scaffolds. The major challenge of conventional electrospun scaffolds is the nature of electrospinning process which can only produce two-dimensional electrospun mats, hence limiting their applications. Researchers have started to focus on overcoming this limitation by combining electrospinning with other techniques to fabricate three-dimensional scaffold constructs. This article reviews various polymeric materials and their composites/blends that have been successfully electrospun for tissue engineering scaffolds, their mechanical properties, and the various parameters settings that influence the fiber morphology. This review also highlights the secondary processes to electrospinning that have been used to develop three-dimensional tissue engineering scaffolds as well as the steps undertaken to overcome electrospinning limitations.
Respiratory diseases have a major impact on global health. The airway epithelium, which acts as a frontline defence, is one of the most common targets for inhaled allergens, irritants, or micro-organisms to enter the respiratory system. In the tissue engineering field, biomaterials play a crucial role. Due to the continuing high impact of respiratory diseases on society and the emergence of new respiratory viruses, in vitro airway epithelial models with high microphysiological similarities that are also easily adjustable to replicate disease models are urgently needed to better understand those diseases. Thus, the development of biomaterial scaffolds for the airway epithelium is important due to their function as a cell-support device in which cells are seeded in vitro and then are encouraged to lay down a matrix to form the foundations of a tissue for transplantation. Studies conducted in in vitro models are necessary because they accelerate the development of new treatments. Moreover, in comparatively controlled conditions, in vitro models allow for the stimulation of complex interactions between cells, scaffolds, and growth factors. Based on recent studies, the biomaterial scaffolds that have been tested in in vitro models appear to be viable options for repairing the airway epithelium and avoiding any complications. This review discusses the role of biomaterial scaffolds in in vitro airway epithelium models. The effects of scaffold, physicochemical, and mechanical properties in recent studies were also discussed.
Developing biomaterial scaffolds using tissue engineering with physical and chemical surface modification processes can improve the bioactivity and biocompatibility of the materials. The appropriate substrate and site for cell attachment are crucial in cell behavior and biological activities. Therefore, the study aims to develop a conventional electrospun nanofibrous biomaterial using reproducible surface topography, which offers beneficial effects on the cell activities of bone cells. The bioactive MgO/gC3N4 was incorporated on PAN/PEG and fabricated into a nanofibrous membrane using electrospinning. The nanocomposite uniformly distributed on the PAN/PEG nanofiber helps to increase the number of induced pores and reduce the hydrophobicity of PAN. The physiochemical characterization of prepared nanoparticles and nanofibers was carried out using FTIR, X-ray diffraction (XRD), thermogravimetry analysis (TGA), X-ray photoelectron spectroscopy (XPS), and water contact angle measurements. SEM and TEM analyses examined the nanofibrous morphology and the structure of MgO/gC3N4. In vitro studies such as on ALP activity demonstrated the membrane's ability to regenerate new bone and healing capacity. Furthermore, alizarin red staining showed the increasing ability of the cell-cell interaction and calcium content for tissue regeneration. The cytotoxicity of the prepared membrane was about 97.09% of live THP-1 cells on the surface of the MgO/gC3N4@PAN/PEG membrane evaluated using MTT dye staining. The soil burial degradation analysis exhibited that the maximum degradation occurs on the 45th day because of microbial activity. In vitro PBS degradation was observed on the 15th day after the bulk hydrolysis mechanism. Hence, on the basis of the study outcomes, we affirm that the MgO/gC3N4@PAN/PEG nanofibrous membrane can act as a potential bone regenerative substrate.
This review summarises the major developments of macroporous bioceramics used mainly for repairing bone defects. Porous bioceramics have been receiving attention ever since their larger surface area was reported to be beneficial for the formation of more rigid bonds with host tissues. The study of porous bioceramics is important to overcome the less favourable bonds formed between dense bioceramics and host tissues, especially in healing bone defects. Macroporous bioceramics, which have been studied extensively, include hydroxyapatite, tricalcium phosphate, alumina, and zirconia. The pore size and interconnections both have significant effects on the growth rate of bone tissues. The optimum pore size of hydroxyapatite scaffolds for bone growth was found to be 300 µm. The existence of interconnections between pores is critical during the initial stage of tissue ingrowth on porous hydroxyapatite scaffolds. Furthermore, pore formation on β-tricalcium phosphate scaffolds also allowed the impregnation of growth factors and cells to improve bone tissues growth significantly. The formation of vascularised tissues was observed on macroporous alumina but did not take place in the case of dense alumina due to its bioinert nature. A macroporous alumina coating on scaffolds was able to improve the overall mechanical properties, and it enabled the impregnation of bioactive materials that could increase the bone growth rate. Despite the bioinertness of zirconia, porous zirconia was useful in designing scaffolds with superior mechanical properties after being coated with bioactive materials. The pores in zirconia were believed to improve the bone growth on the coated system. In summary, although the formation of pores in bioceramics may adversely affect mechanical properties, the advantages provided by the pores are crucial in repairing bone defects.
This study aimed to evaluate the bioactivities and biocompatibilities of porous polylactic acid (PLA) reinforced with cellulose nanofiber (CNF) scaffolds. The in vitro degradation behaviors of the porous PLA/CNF scaffolds were systematically measured for up to 8 weeks in a phosphate-buffered saline medium at 37 °C. The reinforcement of CNF resisted the biodegradation of the scaffolds. The in vitro cytotoxicity and biocompatibility of the scaffolds were determined using the Beas2B American Type Culture Collection cells. The 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cytotoxicity and proliferation tests showed that the scaffolds were non-toxic, and epithelial cells grew well on the scaffold after 7 days of culture, whereas the percentage of cell proliferation on the PLA/CNF15 scaffold was the largest, 130 %. A scratch wound-healing assay was performed to evaluate the suitability of the scaffolds for cell migration. The results demonstrated that the scaffolds exhibited good cell migration towards nearly complete wound closure.
The four heart valves represented in the mammalian hearts are responsible for maintaining unidirectional, non-hinder blood flow. The heart valve leaflets synchronically open and close approximately 4 million times a year and more than 3 billion times during the life. Valvular heart dysfunction is a significant cause of morbidity and mortality around the world. When one of the valves malfunctions, the medical choice is may be to replace the original valves with an artificial one. Currently, the mechanical and biological artificial valves are clinically used with some drawbacks. Tissue engineering heart valve concept represents a new technique to enhance the current model. In tissue engineering method, a three-dimensional scaffold is fabricated as the template for neo-tissue development. Appropriate cells are seeded to the matrix in vitro. Various approaches have been investigated either in scaffold biomaterials and fabrication techniques or cell source and cultivation methods. The available results of ongoing experiments indicate a promising future in this area (particularly in combination of bone marrow stem cells with synthetic scaffold), which can eliminate the need for lifelong anti-coagulation medication, durability and reoperation problems.
A comparative study on the in vitro osteogenic potential of electrospun poly-L-lactide/hydroxyapatite/collagen (PLLA/HA/Col, PLLA/HA, and PLLA/Col) scaffolds was conducted. The morphology, chemical composition, and surface roughness of the fibrous scaffolds were examined. Furthermore, cell attachment, distribution, morphology, mineralization, extracellular matrix protein localization, and gene expression of human mesenchymal stromal cells (hMSCs) differentiated on the fibrous scaffolds PLLA/Col/HA, PLLA/Col, and PLLA/HA were also analyzed. The electrospun scaffolds with a diameter of 200-950 nm demonstrated well-formed interconnected fibrous network structure, which supported the growth of hMSCs. When compared with PLLA/H%A and PLLA/Col scaffolds, PLLA/Col/HA scaffolds presented a higher density of viable cells and significant upregulation of genes associated with osteogenic lineage, which were achieved without the use of specific medium or growth factors. These results were supported by the elevated levels of calcium, osteocalcin, and mineralization (P<0.05) observed at different time points (0, 7, 14, and 21 days). Furthermore, electron microscopic observations and fibronectin localization revealed that PLLA/Col/HA scaffolds exhibited superior osteoinductivity, when compared with PLLA/Col or PLLA/HA scaffolds. These findings indicated that the fibrous structure and synergistic action of Col and nano-HA with high-molecular-weight PLLA played a vital role in inducing osteogenic differentiation of hMSCs. The data obtained in this study demonstrated that the developed fibrous PLLA/Col/HA biocomposite scaffold may be supportive for stem cell based therapies for bone repair, when compared with the other two scaffolds.
Tissue engineering seeks strategies to design polymeric scaffolds that allow high-cell-density cultures with signaling molecules and suitable vascular supply. One major obstacle in tissue engineering is the inability to create thick engineered-tissue constructs. A pre-vascularized tissue scaffold appears to be the most favorable approach to avoid nutrient and oxygen supply limitations as well as to allow waste removal, factors that are often hurdles in developing thick engineered tissues. Vascularization can be achieved using strategies in which cells are cultured in bioactive polymer scaffolds that can mimic extracellular matrix environments. This review addresses recent advances and future challenges in developing and using bioactive polymer scaffolds to promote tissue construct vascularization.
The practice of bone implants is the standard procedure for the treatment of skeletal fissures, or to substitute and re-establish lost bone. A perfect scaffold ought to be made of biomaterials that duplicate the structure and properties of natural bone. However, the production of living tissue constructs that are architecturally, functionally and mechanically comparable to natural bone is the major challenge in the treatment and regeneration of bone tissue in orthopaedics and in dentistry. In this work, we have employed a polymeric replication method to fabricate hydroxyapatite (HAP) scaffolds using gum tragacanth (GT) as a natural binder. GT is a natural gum collected from the dried sap of several species of Middle Eastern legumes of the genus Astragalus, possessing antibacterial and wound healing properties. The synthesized porous HAP scaffolds were analyzed structurally and characterized for their phase purity and mechanical properties. The biocompatibility of the porous HAP scaffold was confirmed by seeding the scaffold with Vero cells, and its bioactivity assessed by immersing the scaffold in simulated body fluid (SBF). Our characterization data showed that the biocompatible porous HAP scaffolds were composed of highly interconnecting pores with compressive strength ranging from 0.036 MPa to 2.954 MPa, comparable to that of spongy bone. These can be prepared in a controlled manner by using an appropriate binder concentration and sintering temperature. These HAP scaffolds have properties consistent with normal bone and should be further developed for potential application in bone implants.
This study employs a computational approach to analyse the impact of morphological changes on the structural properties of biodegradable porous Mg subjected to a dynamic immersion test for its application as a bone scaffold. Porous Mg was immersed in a dynamic immersion test for 24, 48, and 72 h. Twelve specimens were prepared and scanned using micro-CT and then reconstructed into a 3D model for finite element analysis. The structural properties from the numerical simulation were then compared to the experimental values. Correlations between morphological parameters, structural properties, and fracture type were then made. The relative losses were observed to be in agreement with relative mass loss done experimentally. The degradation rates determined using exact (degraded) surface area at particular immersion times were on average 20% higher than the degradation rates obtained using original surface area. The dynamic degradation has significantly impacted the morphological changes of porous Mg in volume fraction, surface area, and trabecular separation, which in turn affects its structural properties and increases the immersion time.
Tissue engineering focuses on developing biological substitutes to restore, maintain or improve tissue functions. The three main components of its application are scaffold, cell and growthstimulating signals. Scaffolds composed of biomaterials mainly function as the structural support for ex vivo cells to attach and proliferate. They also provide physical, mechanical and biochemical cues for the differentiation of cells before transferring to the in vivo site. Collagen has been long used in various clinical applications, including drug delivery. The wide usage of collagen in the clinical field can be attributed to its abundance in nature, biocompatibility, low antigenicity and biodegradability. In addition, the high tensile strength and fibril-forming ability of collagen enable its fabrication into various forms, such as sheet/membrane, sponge, hydrogel, beads, nanofibre and nanoparticle, and as a coating material. The wide option of fabrication technology together with the excellent biological and physicochemical characteristics of collagen has stimulated the use of collagen scaffolds in various tissue engineering applications. This review describes the fabrication methods used to produce various forms of scaffolds used in tissue engineering applications.
Joint cartilage has been a significant focus on the field of tissue engineering and regenerative medicine (TERM) since its inception in the 1980s. Represented by only one cell type, cartilage has been a simple tissue that is thought to be straightforward to deal with. After three decades, engineering cartilage has proven to be anything but easy. With the demographic shift in the distribution of world population towards ageing, it is expected that there is a growing need for more effective options for joint restoration and repair. Despite the increasing understanding of the factors governing cartilage development, there is still a lot to do to bridge the gap from bench to bedside. Dedicated methods to regenerate reliable articular cartilage that would be equivalent to the original tissue are still lacking. The use of cells, scaffolds and signalling factors has always been central to the TERM. However, without denying the importance of cells and signalling factors, the question posed in this chapter is whether the answer would come from the methods to use or not to use scaffold for cartilage TERM. This paper presents some efforts in TERM area and proposes a solution that will transpire from the ongoing attempts to understand certain aspects of cartilage development, degeneration and regeneration. While an ideal formulation for cartilage regeneration has yet to be resolved, it is felt that scaffold is still needed for cartilage TERM for years to come.
The in vitro degradation and mechanical properties of a 3D porous Pennisetum purpureum (PP)/polylactic acid (PLA)-based scaffold were investigated. In this study, composite scaffolds with PP to PLA ratios of 0%, 10%, 20%, and 30% were immersed in a PBS solution at 37°C for 40 days. Compression tests were conducted to evaluate the compressive strength and modulus of the scaffolds, according to ASTM F451-95. The compression strength of the scaffolds was found to increase from 1.94 to 9.32MPa, while the compressive modulus increased from 1.73 to 5.25MPa as the fillers' content increased from 0wt% to 30wt%. Moreover, field emission scanning electron microscopy (FESEM) and X-ray diffraction were employed to observe and analyse the microstructure and fibre-matrix interface. Interestingly, the degradation rate was reduced for the PLA/PP20scaffold, though insignificantly, this could be attributed to the improved mechanical properties and stronger fibre-matrix interface. Microstructure changes after degradation were observed using FESEM. The FESEM results indicated that a strong fibre-matrix interface was formed in the PLA/PP20scaffold, which reflected the addition of P. purpureum into PLA decreasing the degradation rate compared to in pure PLA scaffolds. The results suggest that the P. purpureum/PLA scaffold degradation rate can be altered and controlled to meet requirements imposed by a given tissue engineering application.
Collagen type I is the most abundant matrix protein in the human body and is highly demanded in tissue engineering, regenerative medicine, and pharmaceutical applications. To meet the uprising demand in biomedical applications, collagen type I has been isolated from mammalians (bovine, porcine, goat and rat) and non-mammalians (fish, amphibian, and sea plant) source using various extraction techniques. Recent advancement enables fabrication of collagen scaffolds in multiple forms such as film, sponge, and hydrogel, with or without other biomaterials. The scaffolds are extensively used to develop tissue substitutes in regenerating or repairing diseased or damaged tissues. The 3D scaffolds are also used to develop in vitro model and as a vehicle for delivering drugs or active compounds.