Stem Cells in Bone Tissue Engineering: Progress, Promises and Challenges.

Bone defects from accidents, congenital conditions, and age-related diseases significantly impact quality of life. Recent advancements in bone tissue engineering (TE) involve biomaterial scaffolds, patient-derived cells, and bioactive agents, enabling functional bone regeneration. Stem cells, obtained from numerous sources including umbilical cord blood, adipose tissue, bone marrow, and dental pulp, hold immense potential in bone TE. Induced pluripotent stem cells and genetically modified stem cells can also be used. Proper manipulation of physical, chemical, and biological stimulation is crucial for their proliferation, maintenance, and differentiation. Stem cells contribute to osteogenesis, osteoinduction, angiogenesis, and mineralization, essential for bone regeneration. This review provides an overview of the latest developments in stem cell-based TE for repairing and regenerating defective bones.

3D Printed Eggshell Microparticle-Laden Thermoplastic Scaffolds for Bone Tissue Engineering.

Three-dimensional (3D) printing, an additive manufacturing technique, is increasingly used in the field of tissue engineering. The ability to create complex structures with high precision makes the 3D printing of this material a preferred method for constructing personalized and functional materials. However, the challenge lies in developing affordable and accessible materials with the desired physiochemical and biological properties. In this study, we used eggshell microparticles (ESPs), an example of bioceramic and unconventional biomaterials, to reinforce thermoplastic poly(ε-caprolactone) (PCL) scaffolds via extrusion-based 3D printing. The goal was to conceive a sustainable, affordable, and unique personalized medicine approach. The scaffolds were fabricated with varying concentrations of eggshells, ranging from 0 to 50% (w/w) in the PCL scaffolds. To assess the physicochemical properties, we employed scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and X-ray diffraction analysis. Mechanical properties were evaluated through compression testing, and degradation kinetics were studied through accelerated degradation with the remaining mass ranging between 89.4 and 28.3%. In vitro, we evaluated the characteristics of the scaffolds using the MC3T3-E1 preosteoblasts over a 14 day period. In vitro characterization involved the use of the Alamar blue assay, confocal imaging, and real-time quantitative polymerase chain reaction. The results of this study demonstrate the potential of 3D printed biocomposite scaffolds, consisting of thermoplastic PCL reinforced with ESPs, as a promising alternative for bone-graft applications.

Development of a Sprayable Hydrogel-Based Wound Dressing: An In Vitro Model.

Hydrogel-based dressings can effectively heal wounds by providing multiple functions, such as antibacterial, anti-inflammatory, and preangiogenic bioactivities. The ability to spray the dressing is important for the rapid and effective coverage of the wound surface. In this study, we developed a sprayable hydrogel-based wound dressing using naturally derived materials: hyaluronic acid and gelatin. We introduced methacrylate groups (HAMA and GelMA) to these materials to enable controllable photocrosslinking and form a stable hydrogel on the wound surface. To achieve sprayability, we evaluated the concentration of GelMA within a range of 5-15% (w/v) and then incorporated 1% (w/v) HAMA. Additionally, we incorporated calcium peroxide into the hydrogel at concentrations ranging from 0 to 12 mg/mL to provide self-oxygenation and antibacterial properties. The results showed that the composite hydrogels were sprayable and could provide oxygen for up to two weeks. The released oxygen relieved metabolic stress in fibroblasts and reduced cell death under hypoxia in in vitro culture. Furthermore, calcium peroxide added antibacterial properties to the wound dressing. In conclusion, the developed sprayable hydrogel dressing has the potential to be advantageous for wound healing due to its practical and conformable application, as well as its self-oxygenating and antibacterial functions.

Development of Human-Derived Photocrosslinkable Gelatin Hydrogels for Tissue Engineering.

Hydrogels are often used as biomimetic matrices for tissue regeneration. The source of the hydrogel is of utmost importance, as it affects the physicochemical characteristics and must be carefully selected to stimulate specific cell behaviors. Naturally derived polymeric biomaterials have inherent biological moieties, such as cell binding and protease cleavage sites, and thus can provide a suitable microenvironment for cells. Human-derived matrices can mitigate potential risks associated with the immune response and disease transmission from animal-derived biomaterials. In this article, we developed glycidyl methacrylate-modified human-derived gelatin (hGelGMA) hydrogels for use in tissue engineering applications. By adjusting the glycidyl methacrylate concentration in the reaction mixture, we synthesized hGelGMA with low, medium, and high degrees of modification referred to as hGelGMA-L, hGelGMA-M, and hGelGMA-H, respectively. The amount of polymeric networks in the hydrogels was increased proportionally with the degree of modification. This change has resulted in a decreasing trend in pore size, porosity, and consequent swelling ratio. Similarly, increasing the polymer concentration also exhibited slower enzymatic degradation. On the other hand, increasing the polymer concentration led to an improvement in mechanical properties, where the compressive moduli of hGelGMA-L, hGelGMA-M, and hGelGMA-H hydrogels have changed at 2.9 ± 1.0, 13.7 ± 0.9, and 26.4 ± 2.5 kPa, respectively. The cytocompatibility of hGelGMA was assessed by 3D encapsulation of human-derived cells, including human dermal fibroblasts (HDFs) and human mesenchymal stem cells (hMSCs), in vitro. Regardless of the degree of glycidyl methacrylate modification, the hGelGMA hydrogels preserved the viability of encapsulated cells and supported their growth and proliferation. HDF cells showed a higher metabolic activity in hGelGMA-H, while MSCs exhibited an increased metabolic activity when they were encapsulated in hGelGMA-M or hGelGMA-H. These results showed that photocrosslinkable human-derived gelatin-based hydrogels can be synthesized and their physical properties can be distinctly fine-tuned to different extents as a function of their degrees of modification depending on the needs of the target tissue. Due to its promising physical and biological properties, it is anticipated that hGelGMA can be utilized in a wide spectrum of tissue engineering applications.

Oxygen-Generating Scaffolds: One Step Closer to the Clinical Translation of Tissue Engineered Products.

The lack of oxygen supply in engineered constructs has been an ongoing challenge for tissue engineering and regenerative medicine. Upon implantation of an engineered tissue, spontaneous blood vessel formation does not happen rapidly, therefore, there is typically a limited availability of oxygen in engineered biomaterials. Providing oxygen in large tissue-engineered constructs is a major challenge that hinders the development of clinically relevant engineered tissues. Similarly, maintaining adequate oxygen levels in cell-laden tissue engineered products during transportation and storage is another hurdle. There is an unmet demand for functional scaffolds that could actively produce and deliver oxygen, attainable by incorporating oxygen-generating materials. Recent approaches include encapsulation of oxygen-generating agents such as solid peroxides, liquid peroxides, and fluorinated substances in the scaffolds. Recent approaches to mitigate the adverse effects, as well as achieving a sustained and controlled release of oxygen, are discussed. Importance of oxygen-generating materials in various tissue engineering approaches such as ex vivo tissue engineering, in situ tissue engineering, and bioprinting are highlighted in detail. In addition, the existing challenges, possible solutions, and future strategies that aim to design clinically relevant multifunctional oxygen-generating biomaterials are provided in this review paper.