The liver is an important organ and plays major roles in the human body. Because of the lack of l... more The liver is an important organ and plays major roles in the human body. Because of the lack of liver donors after liver failure and drug-induced liver injury, much research has focused on developing liver alternatives and liver in vitro models for transplantation and drug screening. Although numerous studies have been conducted, these systems cannot faithfully mimic the complexity of the liver. Recently, three-dimensional (3D) cell printing technology has emerged as one of a number of innovative technologies that may help to overcome this limitation. However, a great deal of work in developing biomaterials optimized for 3D cell printing-based liver tissue engineering remains. Therefore, in this work, we developed a liver decellularized extracellular matrix (dECM) bioink for 3D cell printing applications and evaluated its characteristics. The liver dECM bioink retained the major ECM components of the liver while cellular components were effectively removed and further exhibited suit...
International Journal of Machine Tools and Manufacture, 2002
In Parts 1 and 2 of this three-part paper, a mechanistic cutting force model was developed and ma... more In Parts 1 and 2 of this three-part paper, a mechanistic cutting force model was developed and machined surface errors for steady cuts under fixed cutting conditions were predicted. The virtual machining system aims to simulate and analyze the machining and the machined states in a general flat end-milling process. This frequently involves transient as well as steady cuts. Therefore, a method for simulating the cutting process of transient cuts needs to be developed to realize the virtual machining system concept. For this purpose, this paper presents a moving edge-node (ME) Z-map model for the cutting configuration calculation. The simulation results of four representative transient cuts in two-dimensional pocket milling and an application of off-line feed-rate scheduling are also given. In transient cuts, the cutting configurations that are used to predict the cutting force vary during the machining operation. The cutting force model (Part 1) and surface error prediction method (Part 2) were developed for steady cuts; these are extended to transient situations using the ME Z-map model to calculate the varying cutting configurations efficiently. The cutting force and surface errors are then predicted. To validate the feasibility of the proposed scheme, the measured and predicted cutting forces for transient test cuts were compared. The predicted surface error maps for transient cuts were constructed using a computer simulation. Also, off-line feed-rate scheduling is shown to be more accurately performed by applying the instantaneous cutting coefficients that were defined in Part I.
Silicon dioxide composites have been found to enhance the mechanical properties of scaffolds and ... more Silicon dioxide composites have been found to enhance the mechanical properties of scaffolds and to support growth of human adipose tissue-derived stem cells (hADSCs) both in vitro and in vivo. Silica (silicon dioxide alone) exists as differently sized particles when suspended in culture medium, but it is not clear whether particle size influences the beneficial effect of silicon dioxide on hADSCs. In this study, we examined the effect of different sized particles on growth and mitogen-activated protein kinase signaling in hADSCs. Silica gel was prepared by a chemical reaction using hydrochloric acid and sodium silicate, washed, sterilized, and suspended in serum-free culture medium for 48 hours, and then sequentially filtered through a 0.22 μm filter (filtrate containing nanoparticles smaller than 220 nm; silica NPs). hADSCs were incubated with silica NPs or 3 μm silica microparticles (MPs), examined by transmission electron microscopy, and assayed for cell proliferation, apoptosis...
In septal surgery, the surgeon preserves the L-strut, the portion anterior to a vertical line dra... more In septal surgery, the surgeon preserves the L-strut, the portion anterior to a vertical line drawn from the rhinion to the anterior nasal spine (ANS) and at least a 1-cm width of the dorsal and caudal septal segment, to decrease the potential for loss of the tip and dorsal nasal support. However, nasal tip collapse and saddle deformities occur occasionally. We utilized a mechanical approach to determine the safe width size for the L-strut in contact with the maxillary crest. Five L-strut models were designed based on computed tomography data (80 patients) and previous studies (55 patients). All L-strut models connected the perpendicular plate of the ethmoid bone (PPE) and the maxillary crest and were assumed to be fixed to the PPE and maxillary crest. An approximated daily load was applied to the dorsal portion of the L-strut. Finite element analyses were performed to compare the stress, strain, and displacement distribution of all L-strut models. According to the differences in th...
The ability to print and pattern all the components that make up a tissue (cells and matrix mater... more The ability to print and pattern all the components that make up a tissue (cells and matrix materials) in three dimensions to generate structures similar to tissues is an exciting prospect of bioprinting. However, the majority of the matrix materials used so far for bioprinting cannot represent the complexity of natural extracellular matrix (ECM) and thus are unable to reconstitute the intrinsic cellular morphologies and functions. Here, we develop a method for the bioprinting of cell-laden constructs with novel decellularized extracellular matrix (dECM) bioink capable of providing an optimized microenvironment conducive to the growth of three-dimensional structured tissue. We show the versatility and flexibility of the developed bioprinting process using tissue-specific dECM bioinks, including adipose, cartilage and heart tissues, capable of providing crucial cues for cells engraftment, survival and long-term function. We achieve high cell viability and functionality of the printed...
The development of scaffolds for use in cell-based therapies to repair damaged bone tissue has be... more The development of scaffolds for use in cell-based therapies to repair damaged bone tissue has become a critical component in the field of bone tissue engineering. However, design of scaffolds using conventional fabrication techniques has limited further advancement, due to a lack of the required precision and reproducibility. To overcome these constraints, bone tissue engineers have focused on solid free-form fabrication (SFF) techniques to generate porous, fully interconnected scaffolds for bone tissue engineering applications. This paper reviews the potential application of SFF fabrication technologies for bone tissue engineering with respect to scaffold fabrication. In the near future, bone scaffolds made using SFF apparatus should become effective therapies for bone defects.
International Journal of Advanced Manufacturing Technology, 2005
This paper presents a systematic and practical method for determining cutting-condition-independe... more This paper presents a systematic and practical method for determining cutting-condition-independent coefficients in ball-end milling. An approach for estimating the runout offset and its location angle is also described based on a single cutting force measurement. An in-depth analysis of the characteristics of these cutting coefficients, which can be determined from only a few test cuts, is provided. The size
International Journal of Machine Tools & Manufacture, 1999
Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gai... more Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gaining increased attention in a wide spectrum of precision production industries. Alternative methods such as EDM, laser drilling, etc. can sometimes replace mechanical micro-hole drilling, but are not acceptable in PCB manufacture because they yield inferior hole quality and accuracy. The major difficulties in
Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems, 2007
We investigate the reliability of the focused ion beam (FIB) system with the designed evaluation ... more We investigate the reliability of the focused ion beam (FIB) system with the designed evaluation patterns. The reliability test patterns are composed of three parts, which are the ion beam quality patterns, the ion beam scanning ability patterns and the stage system patterns. The designed patterns are fabricated with the commercial FIB system, and the common nanometer scale measurement systems,
Demands for miniature components are rapidly increased in the field of optics, electronics, and m... more Demands for miniature components are rapidly increased in the field of optics, electronics, and medicine. Various machining methods have been introduced for the fabrication of complex three-dimensional microfeatures. However, burrs, which are an undesired but unavoidable by-product of most machining processes, cause many problems in assembly, inspection, process automation, and precision component operation. Moreover, as feature sizes decrease, burr problems
Focused ion beam (FIB) systems are one of the most important pieces of equipment in nanoscale mac... more Focused ion beam (FIB) systems are one of the most important pieces of equipment in nanoscale machining, and can etch material and deposit 3-D nanoscale structures with high aspect ratios. However, despite considerable research effort, a definitive method for evaluating the reliability of FIB systems had not been developed. In this paper, we propose a reliability assessment method that utilizes fabricated nanopatterns. Since the characteristics of a FIB system are included in the nanopatterns, these can be used to assess its reliability. We suggest items and nanopatterns that can be applied to the reliability assessment tests. To determine the suitability of the proposed method, we fabricated several nanopatterns using different FIB systems and measured them under a scanning electron microscope to compare the actual and designed dimensions. The results showed that the proposed method is suitable for assessing the reliability of FIB systems.
Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems - MICROSYST TECHNOL, 2005
In this paper, new replication techniques for a metal microcomponent having a real 3D shape were ... more In this paper, new replication techniques for a metal microcomponent having a real 3D shape were introduced. A helical gear was selected as one of a real 3D microcomponents for this study. The helical gear, which was made of photo-curable resin, was fabricated as a master pattern by microstereolithography (MSL) technology. Then, a silicone rubber mold was fabricated from the master pattern. Lastly, a final bismuth alloy pattern was transferred from the silicone rubber mold by the microcasting process. In this paper, the replication technique is described in detail from the master pattern to the final pattern with some investigation on factors related to the technique.
International Journal of Advanced Manufacturing Technology - INT J ADV MANUF TECHNOL, 2003
Off-line feedrate scheduling is an advanced methodology to automatically determine optimum feedra... more Off-line feedrate scheduling is an advanced methodology to automatically determine optimum feedrates for NC code modification. However, most existing feedrate scheduling systems have limitations in generating the optimised feedrates because they use the material removal rate or the cutting force model which is dependent on cutting conditions. This paper proposes a feedrate scheduling system based on an improved cutting force model that can predict cutting forces accurately in general end milling situations. Original blocks of NC code were divided into smaller ones with the optimised feedrates to adjust the peak value of cutting forces to a constant value. The acceleration and deceleration characteristics for a given machine tool were considered for realistic feedrate scheduling. Moreover, a modified type of Z-map model was developed to reduce the entry/exit angle calculation error in the cutting force prediction and named the moving edge node Z-map (ME Z-map). Pocket machining exper...
International Journal of Machine Tools & Manufacture - INT J MACH TOOL MANUF, 2006
Leveling is an important part of a machine tool installation process because it significantly inf... more Leveling is an important part of a machine tool installation process because it significantly influences the product quality, machine tool accuracy, and machine lifetime. Conventional leveling procedures are performed by skilled engineers using leveling instruments such as spirit or electronic levels. It is difficult to monitor the level of a machine tool because an accurate leveling instrument is expensive and difficult to install. Therefore, a novel methodology for estimating the inclination angle of a machine tool feed drive is proposed in this paper to overcome the difficulties of leveling. The proposed methodology utilizes motor current measurements and a new mathematical model of the machine tool feed drive that considers the inclination. Experimental results showed that the proposed method successfully estimates the inclination angle and enhances the accuracy of the machine tool feed drive model by considering the inclination effects.
Worldwide, many micro-actuators have been developed for various applications in biotechnology, bi... more Worldwide, many micro-actuators have been developed for various applications in biotechnology, biochemistry, micro-sensors, etc. However, most of these actuators have been made using 2D-based micro-electro-mechanical systems (MEMS) technology, so they cannot perform long-travel 3D motion. This substantially limits the applications of these actuators. In this study, we developed a new bellows-shaped micro-actuator using micro-stereolithography (MSTL) technology, which makes it possible to fabricate complex 3D microstructures. The total travel and 3D motion of the new actuator could be easily adjusted during the design process. Using a finite element method (FEM) simulation, the actuation characteristics were analyzed and compared with experimental results. The analysis verified the adjustability of the total travel. In addition, to demonstrate the feasibility of the actuation principle in 3D space, two different kinds of micro-gripper were successfully demonstrated.
Precise control over the biomaterial, porosity, and inner architecture of a scaffold is essential... more Precise control over the biomaterial, porosity, and inner architecture of a scaffold is essential for tissue regeneration. This paper proposes a new bi-pore scaffold that has both global and local pores in its structure. The global pores can serve as channels for supplying cells with nutrients and oxygen, while the local pores provide space for cell growth. A lost mold shape-forming process based on high-resolution microstereolithography technology was used to form the global pores, and conventional scaffold fabrication methods, such as salt leaching and phase inversion, were added to the molding process to generate local pores. This resulted in the fabrication of 300 to 400 μm global pores with the lost molding process; local pores of 30 to 100 μm and 1 to 5 μm were achieved with salt leaching and phase inversion, respectively. Compared to other processes, this fabrication process provides a powerful method for bi-pore scaffold fabrication.
Recently, many groups have researched the reconstruction of bone tissue and the development of bo... more Recently, many groups have researched the reconstruction of bone tissue and the development of bone scaffolds using solid freeform fabrication technology. However, the capacity to produce three-dimensional hydroxyapatite (HA) scaffolds with a very accurate architecture is limited by difficulties in the manufacturing process. In this study, a HA scaffold with an accurate pore size of 300 ± 10 lm was fabricated using a microstereolithography (MSTL) system and molding technology. In addition, an agar-overlay test was performed to investigate the cytotoxicity of the fabricated scaffold.
Dispersion polymerization of N-vinyl caprolactam (NVCL) was carried out in supercritical carbon d... more Dispersion polymerization of N-vinyl caprolactam (NVCL) was carried out in supercritical carbon dioxide (scCO2) using three surfactants. The polymerization was performed in the presence of fluorine-based poly(heptadecafluorodecyl acrylate) (PHDFDA), poly(heptadecafluorodecyl methacrylate) (PHDFDMA) or siloxane-based PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA) as a surfactant. FE-SEM and image analyzer were used to characterize particle morphology, size, and size distribution. When fluorine-based surfactants were used,
Journal of Tissue Engineering and Regenerative Medicine, 2013
Regenerative medicine is targeted to improve, restore or replace damaged tissues or organs using ... more Regenerative medicine is targeted to improve, restore or replace damaged tissues or organs using a combination of cells, materials and growth factors. Both tissue engineering and developmental biology currently deal with the process of tissue self-assembly and extracellular matrix (ECM) deposition. In this investigation, additive manufacturing (AM) with a multihead deposition system (MHDS) was used to fabricate three-dimensional (3D) cell-printed scaffolds using layer-by-layer (LBL) deposition of polycaprolactone (PCL) and chondrocyte cell-encapsulated alginate hydrogel. Appropriate cell dispensing conditions and optimum alginate concentrations for maintaining cell viability were determined. In vitro cell-based biochemical assays were performed to determine glycosaminoglycans (GAGs), DNA and total collagen contents from different PCL-alginate gel constructs. PCL-alginate gels containing transforming growth factor-b (TGFb) showed higher ECM formation. The 3D cell-printed scaffolds of PCL-alginate gel were implanted in the dorsal subcutaneous spaces of female nude mice. Histochemical [Alcian blue and haematoxylin and eosin (H&E) staining] and immunohistochemical (type II collagen) analyses of the retrieved implants after 4 weeks revealed enhanced cartilage tissue and type II collagen fibril formation in the PCL-alginate gel (+TGFb) hybrid scaffold. In conclusion, we present an innovative cell-printed scaffold for cartilage regeneration fabricated by an advanced bioprinting technology.
The liver is an important organ and plays major roles in the human body. Because of the lack of l... more The liver is an important organ and plays major roles in the human body. Because of the lack of liver donors after liver failure and drug-induced liver injury, much research has focused on developing liver alternatives and liver in vitro models for transplantation and drug screening. Although numerous studies have been conducted, these systems cannot faithfully mimic the complexity of the liver. Recently, three-dimensional (3D) cell printing technology has emerged as one of a number of innovative technologies that may help to overcome this limitation. However, a great deal of work in developing biomaterials optimized for 3D cell printing-based liver tissue engineering remains. Therefore, in this work, we developed a liver decellularized extracellular matrix (dECM) bioink for 3D cell printing applications and evaluated its characteristics. The liver dECM bioink retained the major ECM components of the liver while cellular components were effectively removed and further exhibited suit...
International Journal of Machine Tools and Manufacture, 2002
In Parts 1 and 2 of this three-part paper, a mechanistic cutting force model was developed and ma... more In Parts 1 and 2 of this three-part paper, a mechanistic cutting force model was developed and machined surface errors for steady cuts under fixed cutting conditions were predicted. The virtual machining system aims to simulate and analyze the machining and the machined states in a general flat end-milling process. This frequently involves transient as well as steady cuts. Therefore, a method for simulating the cutting process of transient cuts needs to be developed to realize the virtual machining system concept. For this purpose, this paper presents a moving edge-node (ME) Z-map model for the cutting configuration calculation. The simulation results of four representative transient cuts in two-dimensional pocket milling and an application of off-line feed-rate scheduling are also given. In transient cuts, the cutting configurations that are used to predict the cutting force vary during the machining operation. The cutting force model (Part 1) and surface error prediction method (Part 2) were developed for steady cuts; these are extended to transient situations using the ME Z-map model to calculate the varying cutting configurations efficiently. The cutting force and surface errors are then predicted. To validate the feasibility of the proposed scheme, the measured and predicted cutting forces for transient test cuts were compared. The predicted surface error maps for transient cuts were constructed using a computer simulation. Also, off-line feed-rate scheduling is shown to be more accurately performed by applying the instantaneous cutting coefficients that were defined in Part I.
Silicon dioxide composites have been found to enhance the mechanical properties of scaffolds and ... more Silicon dioxide composites have been found to enhance the mechanical properties of scaffolds and to support growth of human adipose tissue-derived stem cells (hADSCs) both in vitro and in vivo. Silica (silicon dioxide alone) exists as differently sized particles when suspended in culture medium, but it is not clear whether particle size influences the beneficial effect of silicon dioxide on hADSCs. In this study, we examined the effect of different sized particles on growth and mitogen-activated protein kinase signaling in hADSCs. Silica gel was prepared by a chemical reaction using hydrochloric acid and sodium silicate, washed, sterilized, and suspended in serum-free culture medium for 48 hours, and then sequentially filtered through a 0.22 μm filter (filtrate containing nanoparticles smaller than 220 nm; silica NPs). hADSCs were incubated with silica NPs or 3 μm silica microparticles (MPs), examined by transmission electron microscopy, and assayed for cell proliferation, apoptosis...
In septal surgery, the surgeon preserves the L-strut, the portion anterior to a vertical line dra... more In septal surgery, the surgeon preserves the L-strut, the portion anterior to a vertical line drawn from the rhinion to the anterior nasal spine (ANS) and at least a 1-cm width of the dorsal and caudal septal segment, to decrease the potential for loss of the tip and dorsal nasal support. However, nasal tip collapse and saddle deformities occur occasionally. We utilized a mechanical approach to determine the safe width size for the L-strut in contact with the maxillary crest. Five L-strut models were designed based on computed tomography data (80 patients) and previous studies (55 patients). All L-strut models connected the perpendicular plate of the ethmoid bone (PPE) and the maxillary crest and were assumed to be fixed to the PPE and maxillary crest. An approximated daily load was applied to the dorsal portion of the L-strut. Finite element analyses were performed to compare the stress, strain, and displacement distribution of all L-strut models. According to the differences in th...
The ability to print and pattern all the components that make up a tissue (cells and matrix mater... more The ability to print and pattern all the components that make up a tissue (cells and matrix materials) in three dimensions to generate structures similar to tissues is an exciting prospect of bioprinting. However, the majority of the matrix materials used so far for bioprinting cannot represent the complexity of natural extracellular matrix (ECM) and thus are unable to reconstitute the intrinsic cellular morphologies and functions. Here, we develop a method for the bioprinting of cell-laden constructs with novel decellularized extracellular matrix (dECM) bioink capable of providing an optimized microenvironment conducive to the growth of three-dimensional structured tissue. We show the versatility and flexibility of the developed bioprinting process using tissue-specific dECM bioinks, including adipose, cartilage and heart tissues, capable of providing crucial cues for cells engraftment, survival and long-term function. We achieve high cell viability and functionality of the printed...
The development of scaffolds for use in cell-based therapies to repair damaged bone tissue has be... more The development of scaffolds for use in cell-based therapies to repair damaged bone tissue has become a critical component in the field of bone tissue engineering. However, design of scaffolds using conventional fabrication techniques has limited further advancement, due to a lack of the required precision and reproducibility. To overcome these constraints, bone tissue engineers have focused on solid free-form fabrication (SFF) techniques to generate porous, fully interconnected scaffolds for bone tissue engineering applications. This paper reviews the potential application of SFF fabrication technologies for bone tissue engineering with respect to scaffold fabrication. In the near future, bone scaffolds made using SFF apparatus should become effective therapies for bone defects.
International Journal of Advanced Manufacturing Technology, 2005
This paper presents a systematic and practical method for determining cutting-condition-independe... more This paper presents a systematic and practical method for determining cutting-condition-independent coefficients in ball-end milling. An approach for estimating the runout offset and its location angle is also described based on a single cutting force measurement. An in-depth analysis of the characteristics of these cutting coefficients, which can be determined from only a few test cuts, is provided. The size
International Journal of Machine Tools & Manufacture, 1999
Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gai... more Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gaining increased attention in a wide spectrum of precision production industries. Alternative methods such as EDM, laser drilling, etc. can sometimes replace mechanical micro-hole drilling, but are not acceptable in PCB manufacture because they yield inferior hole quality and accuracy. The major difficulties in
Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems, 2007
We investigate the reliability of the focused ion beam (FIB) system with the designed evaluation ... more We investigate the reliability of the focused ion beam (FIB) system with the designed evaluation patterns. The reliability test patterns are composed of three parts, which are the ion beam quality patterns, the ion beam scanning ability patterns and the stage system patterns. The designed patterns are fabricated with the commercial FIB system, and the common nanometer scale measurement systems,
Demands for miniature components are rapidly increased in the field of optics, electronics, and m... more Demands for miniature components are rapidly increased in the field of optics, electronics, and medicine. Various machining methods have been introduced for the fabrication of complex three-dimensional microfeatures. However, burrs, which are an undesired but unavoidable by-product of most machining processes, cause many problems in assembly, inspection, process automation, and precision component operation. Moreover, as feature sizes decrease, burr problems
Focused ion beam (FIB) systems are one of the most important pieces of equipment in nanoscale mac... more Focused ion beam (FIB) systems are one of the most important pieces of equipment in nanoscale machining, and can etch material and deposit 3-D nanoscale structures with high aspect ratios. However, despite considerable research effort, a definitive method for evaluating the reliability of FIB systems had not been developed. In this paper, we propose a reliability assessment method that utilizes fabricated nanopatterns. Since the characteristics of a FIB system are included in the nanopatterns, these can be used to assess its reliability. We suggest items and nanopatterns that can be applied to the reliability assessment tests. To determine the suitability of the proposed method, we fabricated several nanopatterns using different FIB systems and measured them under a scanning electron microscope to compare the actual and designed dimensions. The results showed that the proposed method is suitable for assessing the reliability of FIB systems.
Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems - MICROSYST TECHNOL, 2005
In this paper, new replication techniques for a metal microcomponent having a real 3D shape were ... more In this paper, new replication techniques for a metal microcomponent having a real 3D shape were introduced. A helical gear was selected as one of a real 3D microcomponents for this study. The helical gear, which was made of photo-curable resin, was fabricated as a master pattern by microstereolithography (MSL) technology. Then, a silicone rubber mold was fabricated from the master pattern. Lastly, a final bismuth alloy pattern was transferred from the silicone rubber mold by the microcasting process. In this paper, the replication technique is described in detail from the master pattern to the final pattern with some investigation on factors related to the technique.
International Journal of Advanced Manufacturing Technology - INT J ADV MANUF TECHNOL, 2003
Off-line feedrate scheduling is an advanced methodology to automatically determine optimum feedra... more Off-line feedrate scheduling is an advanced methodology to automatically determine optimum feedrates for NC code modification. However, most existing feedrate scheduling systems have limitations in generating the optimised feedrates because they use the material removal rate or the cutting force model which is dependent on cutting conditions. This paper proposes a feedrate scheduling system based on an improved cutting force model that can predict cutting forces accurately in general end milling situations. Original blocks of NC code were divided into smaller ones with the optimised feedrates to adjust the peak value of cutting forces to a constant value. The acceleration and deceleration characteristics for a given machine tool were considered for realistic feedrate scheduling. Moreover, a modified type of Z-map model was developed to reduce the entry/exit angle calculation error in the cutting force prediction and named the moving edge node Z-map (ME Z-map). Pocket machining exper...
International Journal of Machine Tools & Manufacture - INT J MACH TOOL MANUF, 2006
Leveling is an important part of a machine tool installation process because it significantly inf... more Leveling is an important part of a machine tool installation process because it significantly influences the product quality, machine tool accuracy, and machine lifetime. Conventional leveling procedures are performed by skilled engineers using leveling instruments such as spirit or electronic levels. It is difficult to monitor the level of a machine tool because an accurate leveling instrument is expensive and difficult to install. Therefore, a novel methodology for estimating the inclination angle of a machine tool feed drive is proposed in this paper to overcome the difficulties of leveling. The proposed methodology utilizes motor current measurements and a new mathematical model of the machine tool feed drive that considers the inclination. Experimental results showed that the proposed method successfully estimates the inclination angle and enhances the accuracy of the machine tool feed drive model by considering the inclination effects.
Worldwide, many micro-actuators have been developed for various applications in biotechnology, bi... more Worldwide, many micro-actuators have been developed for various applications in biotechnology, biochemistry, micro-sensors, etc. However, most of these actuators have been made using 2D-based micro-electro-mechanical systems (MEMS) technology, so they cannot perform long-travel 3D motion. This substantially limits the applications of these actuators. In this study, we developed a new bellows-shaped micro-actuator using micro-stereolithography (MSTL) technology, which makes it possible to fabricate complex 3D microstructures. The total travel and 3D motion of the new actuator could be easily adjusted during the design process. Using a finite element method (FEM) simulation, the actuation characteristics were analyzed and compared with experimental results. The analysis verified the adjustability of the total travel. In addition, to demonstrate the feasibility of the actuation principle in 3D space, two different kinds of micro-gripper were successfully demonstrated.
Precise control over the biomaterial, porosity, and inner architecture of a scaffold is essential... more Precise control over the biomaterial, porosity, and inner architecture of a scaffold is essential for tissue regeneration. This paper proposes a new bi-pore scaffold that has both global and local pores in its structure. The global pores can serve as channels for supplying cells with nutrients and oxygen, while the local pores provide space for cell growth. A lost mold shape-forming process based on high-resolution microstereolithography technology was used to form the global pores, and conventional scaffold fabrication methods, such as salt leaching and phase inversion, were added to the molding process to generate local pores. This resulted in the fabrication of 300 to 400 μm global pores with the lost molding process; local pores of 30 to 100 μm and 1 to 5 μm were achieved with salt leaching and phase inversion, respectively. Compared to other processes, this fabrication process provides a powerful method for bi-pore scaffold fabrication.
Recently, many groups have researched the reconstruction of bone tissue and the development of bo... more Recently, many groups have researched the reconstruction of bone tissue and the development of bone scaffolds using solid freeform fabrication technology. However, the capacity to produce three-dimensional hydroxyapatite (HA) scaffolds with a very accurate architecture is limited by difficulties in the manufacturing process. In this study, a HA scaffold with an accurate pore size of 300 ± 10 lm was fabricated using a microstereolithography (MSTL) system and molding technology. In addition, an agar-overlay test was performed to investigate the cytotoxicity of the fabricated scaffold.
Dispersion polymerization of N-vinyl caprolactam (NVCL) was carried out in supercritical carbon d... more Dispersion polymerization of N-vinyl caprolactam (NVCL) was carried out in supercritical carbon dioxide (scCO2) using three surfactants. The polymerization was performed in the presence of fluorine-based poly(heptadecafluorodecyl acrylate) (PHDFDA), poly(heptadecafluorodecyl methacrylate) (PHDFDMA) or siloxane-based PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA) as a surfactant. FE-SEM and image analyzer were used to characterize particle morphology, size, and size distribution. When fluorine-based surfactants were used,
Journal of Tissue Engineering and Regenerative Medicine, 2013
Regenerative medicine is targeted to improve, restore or replace damaged tissues or organs using ... more Regenerative medicine is targeted to improve, restore or replace damaged tissues or organs using a combination of cells, materials and growth factors. Both tissue engineering and developmental biology currently deal with the process of tissue self-assembly and extracellular matrix (ECM) deposition. In this investigation, additive manufacturing (AM) with a multihead deposition system (MHDS) was used to fabricate three-dimensional (3D) cell-printed scaffolds using layer-by-layer (LBL) deposition of polycaprolactone (PCL) and chondrocyte cell-encapsulated alginate hydrogel. Appropriate cell dispensing conditions and optimum alginate concentrations for maintaining cell viability were determined. In vitro cell-based biochemical assays were performed to determine glycosaminoglycans (GAGs), DNA and total collagen contents from different PCL-alginate gel constructs. PCL-alginate gels containing transforming growth factor-b (TGFb) showed higher ECM formation. The 3D cell-printed scaffolds of PCL-alginate gel were implanted in the dorsal subcutaneous spaces of female nude mice. Histochemical [Alcian blue and haematoxylin and eosin (H&E) staining] and immunohistochemical (type II collagen) analyses of the retrieved implants after 4 weeks revealed enhanced cartilage tissue and type II collagen fibril formation in the PCL-alginate gel (+TGFb) hybrid scaffold. In conclusion, we present an innovative cell-printed scaffold for cartilage regeneration fabricated by an advanced bioprinting technology.
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Papers by Dong-Woo Cho