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  1. ABSTRACT Materials processing and additive manufacturing afford exciting opportunities in biomedical research, including the study of cell-material interactions. However, some of the most efficient materials for microfabrication are not wholly suitable for biological applications, require extensive post-processing or exhibit high mechanical stiffness that limits the range of applications. Conversely, materials exhibiting high cytocompatibility and low stiffness require long processing times with typically decreased spatial resolution of features. Here, we investigated the use of hexanediol diacrylate (HDDA), a classic and efficient polymer for stereolithography, for oligodendrocyte progenitor cell (OPC) culture. We developed composite HDDA-polyethylene glycol acrylate hydrogels that exhibited high biocompatibility, mechanical stiffness in the range of muscle tissue, and high printing efficiency at ∼5 μm resolution. 
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  2. ABSTRACT In today’s technology, organ transplantation is found very challenging as it is not easy to find the right donor organ in a short period of time. In the last several decades, tissue engineering was rapidly developed to be used as an alternative approach to the organ transplantation. Tissue engineering aims to regenerate the tissues and also organs to help patients who waits for the organ transplantation. Recent research showed that in order to regenerate the tissues, cells must be seeded onto the 3D artificial laboratory fabricated matrices called scaffolds. If cells show healthy growth within the scaffolds, they can be implanted to the injured tissue to do the regeneration. One of the biggest limitation that reduces the success rate of tissue regeneration is the fabrication of accurate thick 3D scaffolds. In this research “maskless photolithography” was used to fabricate the scaffolds. Experiment setup consist of digital micro-mirror devices (DMD) (Texas Instruments, DLi4120), optical lens sets, UV light source (DYMAX, BlueWave 200) and PEGDA which is a liquid form photo-curable solution. In this method, scaffolds are fabricated in layer-by-layer fashion to control the interior architecture of the scaffolds. Working principles of the maskless photolithography is, first layer shape is designed with AutoCAD and the designed image is uploaded to the DMD as a bitmap file. DMD consists of hundreds of tiny micro-mirrors. When the UV light is turned on and irradiated the DMD, depending on the micro-mirrors’ angles, UV light is selectively reflected to the low percentage Polyethylene (glycol) Diacrylate (PEGDA) photo-curable solution. When UV light penetrates into the PEGDA, only the illuminated part is solidified and non-illuminated area still remains in the liquid phase. In this research, scaffolds were fabricated in three layers. First layer and the last layer are solid layers and y-shape open structure was sandwiched between these layers. After the first layer is fabricated with DMD, a “y-shape” structure was fabricated with the 3D printer by using the dissolvable filament. Then, it was placed onto the first solid layer and covered with fresh high percentage PEGDA solution. UV light was reflected to the PEGDA solution and solidified to make the second and third layers. After the scaffold was fabricated, it is dipped into the limonene solution to dissolve the y-shape away. Our results show that thick scaffolds can be fabricated in layer-by-layer fashion with “maskless photolithography”. Since the UV light is stable and does not move onto the PEGDA, entire scaffold can be fabricated in one single UV shot which makes the process faster than the current fabrication techniques. 
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  3. ABSTRACT Hydrogels have been widely used in many applications from tissue engineering to drug delivery systems. For both tissue engineering and drug delivery, the mechanical properties are important because they would affect cell-materials interactions and injectability of drugs encapsulated in hydrogel carriers. Therefore, it is important to study the mechanical properties of these hydrogels, particularly at physiological temperature (37°C). This study adopted strain sweep and frequency sweep rotational rheological tests to investigate the rheological characteristics of various tissue engineering relevant hydrogels with different concentrations at 37°C. These hydrogels include alginate, RGD-alginate, and copolymerized collagen/alginate/fibrin. It has revealed that the addition of RGD has negligible effect on the elastic modulus and viscosity of alginate. Alginate gels have demonstrated shear thinning behavior which indicates that they are suitable candidates as carriers for cells or drug delivery. The addition of collagen and fibrin would reinforce the mechanical properties of alginate which makes it a strong scaffold material. 
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