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Imagine the day when organs are produced in the lab and are available for transplant, a scenario often repeated by doctors, patients, and medical reporters alike. What seems like a scene from a science-fiction movie may one day become reality—and sooner than we may imagine. Our understanding of biological systems and cellular mechanisms is rapidly expanding, accompanied and supported by advances in bioengineering. 3D printing, now a household word, has been hailed among the most exciting inventions of this decade with hardly a week passing by without new “firsts” using 3D printing technology. This novel technology has vast potential for multiscale innovations in almost every discipline: health-care, industry, academia, and the arts. In health-care, 3D printing is often called a game changer. It has already customized prosthetic and implant design and impacted the pharmaceutical industry and drug delivery systems, medical education, and most of all—tissue engineering and regenerative medicine. Here we briefly describe the basic concepts of this technology for the busy clinician and how it can be applied to tissue engineering with a special focus on airway regeneration.
3D printing process
3D printing, also known as rapid prototyping or additive manufacturing, was introduced in the 80s for industrial purposes. Not until a miniaturized “desktop” version of the printer was developed did its role in medicine begin to expand. All 3D printers, regardless of their types, follow similar principles. Products of 3D printers are objects made by sequential addition (z-stacking) of 2D layers creating three-dimensional structures. The objects of interest can be designed using computer-aided design (CAD) software or taken directly from 3D-reconstructed images of CT scans and MRIs. The image files are saved as a (.STL) file and processed by “slicer” software to generate G-code files that relay the control instructions to the printer. Depending on the size of the printer, the “ink” used, and the size and geometrical complexity of the desired object, it can take from a few minutes to several hours or days to print. Unlike the monochromatic older generations of 3D printers, newer devices are emerging on the market with either multiple printing heads or “ink” chambers. The latter provides greater freedom in materials choice and is of particular interest in tissue regeneration for its ability to print and compartmentalize different cellular components.
Types of 3D printers
There are multiple types of 3D printers available commercially, benefiting from an open-source platform that allows customization and improvement of the current devices. Similarly, different types of “inks” are utilized depending on the printer’s design but also on the desired end-product. We mention some of the common types of printers and direct our focus to the last two, given their particular application in regenerative medicine:
• Selective laser sintering
• Electron beam melting
• Direct laser metal sintering
• Selective heat sintering
• Electron beam freeform fabrication
• Fused deposition modeling
• Photopolymerized extrusion stereolithography
Fused deposition modeling printers
Fused deposition modeling (FDM) printers utilize a heated extrusion head and are closely similar to a desktop inkjet printer. FDM printers benefit from their wide commercial availability and relatively low cost, making them among the most popular 3D printers currently in use. The “ink” utilized is a thermoplastic material typically prepared as a thread spool fed to the heated head and sequentially deposited as droplets with an approximate 100-micron resolution. The thermoplastics harden within few seconds, allowing fast and precise 3D object production. Several thermoplastics are used, some of which are also biocompatible and have been traditionally used in implant manufacturing and have shown promise for tissue engineering, such as polylactic acid (PLA), polylactic-glycolic acid (PLGA), and polycaprolactone (PCL). PCL has attracted substantial interests within the medical community given its low inflammatory profile, slow rate of hydrolysis, and ability to promote cellular attachment and growth (Shimao. Curr Opin Biotechnol. 2001;12[3]:242). In fact, PCL has been successfully printed as a splint for bronchial malacia in a baby suffering from repeated bouts of pneumonia and difficulty breathing (Zopf et al. N Engl J Med. 2013;368[21]:2043). FDM printers are thus most suitable for manufacturing prosthetic devices and possibly tissue scaffolds for cellular growth.
Photopolymerized extrusion stereolithography printers
In this form of 3D printing, the extrusion head consists of a motorized syringe-plunger containing the liquid ink. This is polymerized into a solid shape after extrusion and upon exposure to UV light (or another light source depending on the chemical content of the mixture). Polymerizable liquid inks are grouped under the term hydrogels, formerly defined by the International Union of Pure and Applied Chemistry (IUPAC) as “nonfluid colloidal network or polymer network that is expanded throughout its whole volume by a fluid.” Several formulations of hydrogels exist and we have used varying combinations of polyethylene glycol diacrylate and alginate to create hydrogels with different mechanical properties. Photopolymerization is slower than FDM; however, it has the added benefit of incorporating the cells into the prepolymerized liquid mix, which allows cellular inclusion into the final product. In essence, this type of printing will likely represent the future of “bioprinting” with its ability to compartmentalize cellular components within the scaffold. 3D printed ears (Manoor et al. Nano Lett. 2013;13[6]:2634) and aortic valves (Hockaday et al. Biofabrication. 2012;4[3]:035005) were generated using this approach. 3D printing was successful in replicating the shape of the desired organs with high fidelity while permitting maintained cellular growth, ushering a new era for regenerative medicine. However, the current mechanical properties of these structures do not permit organ transplantation and lack the necessary vascularized network for maintained in vivo growth.
3D printing and tracheal regeneration
In the setting of large segment tracheal pathologies, both benign and malignant, surgical resection and reconstruction may be challenging. Our lab has been working on creating a bioengineered tissue alternative for repair and/or replacement of large tracheal defects. The ideal material should have longitudinal flexibility, while maintaining lateral rigidity and concurrently supporting chondrogenesis, neovascularization, and re-epithelialization. Using a combination of mesenchymal stem cells, biologic collagen membranes, and 3D printing, we have achieved preliminary and encouraging results in large animal models. 3D-reconstructed CT scan of the neck and chest is obtained, and we isolate the tracheobronchial tree below the cricoid cartilage extending toward the carina and the major bronchi. Large tracheal defects, long segment airway stenosis, or tracheobronchomalacia can then be corrected virtually using CAD software applications. The improved anatomical 3D image is next converted to a (.STL) file readable by the printer, which generates the tracheal scaffold. The latter is subsequently incubated with mesenchymal stem cells, which are allowed to grow and differentiate to chondrogenic progenitor cells in a bioreactor in vitro. Chondrogenesis is a complex and well-orchestrated process. We incubate the stem cells in growth media containing a specific mixture of TGF-ß; BMP-2,-4, and -7; and FGF-2 to induce the formation of the chondrogenic lineage. Additionally, the scaffold with the adherent cells are mounted on a mandrel in a bioreactor and subjected to slow and continuous rotation to improve chondrogenesis via mechanical stimulation. In the early phases of differentiation, collagen I and fibronectin are deposited around the cells creating the earliest form of extracellular matrix for chondrocytes growth. With this approach, we have seen maintained cellular growth and differentiation of the stem cells into chondrogenic progenitors in vitro and chondrocytes in vivo in the animal model (Al-Ayoubi et al. Presented at the STS 51st Annual Meeting. Orlando, FL 2013). Current efforts are underway to understand the airway dynamics, mucosal epithelial function, and long-term effects of the bioengineered trachea.
Final word
3D printing is an exciting technology with significant impact on regenerative medicine. It particularly allows precise and customized reproduction of the engineered tissue while maintaining form and function. Further identification of suitable biomaterials is warranted, as well as the biological interactions of the stem cells with their potential environments. While substantial information remains to be discovered and technical challenges overcome, the field of tissue engineering is undoubtedly heading toward amazing findings, hoping to find cures for many debilitating illnesses.
Drs. Al-Ayoubi and Bhora are with the Department of Thoracic Surgery; Mount Sinai St. Luke’s Hospital and Mount Sinai Roosevelt Hospital; Icahn School of Medicine at Mount Sinai; New York, NY.
Imagine the day when organs are produced in the lab and are available for transplant, a scenario often repeated by doctors, patients, and medical reporters alike. What seems like a scene from a science-fiction movie may one day become reality—and sooner than we may imagine. Our understanding of biological systems and cellular mechanisms is rapidly expanding, accompanied and supported by advances in bioengineering. 3D printing, now a household word, has been hailed among the most exciting inventions of this decade with hardly a week passing by without new “firsts” using 3D printing technology. This novel technology has vast potential for multiscale innovations in almost every discipline: health-care, industry, academia, and the arts. In health-care, 3D printing is often called a game changer. It has already customized prosthetic and implant design and impacted the pharmaceutical industry and drug delivery systems, medical education, and most of all—tissue engineering and regenerative medicine. Here we briefly describe the basic concepts of this technology for the busy clinician and how it can be applied to tissue engineering with a special focus on airway regeneration.
3D printing process
3D printing, also known as rapid prototyping or additive manufacturing, was introduced in the 80s for industrial purposes. Not until a miniaturized “desktop” version of the printer was developed did its role in medicine begin to expand. All 3D printers, regardless of their types, follow similar principles. Products of 3D printers are objects made by sequential addition (z-stacking) of 2D layers creating three-dimensional structures. The objects of interest can be designed using computer-aided design (CAD) software or taken directly from 3D-reconstructed images of CT scans and MRIs. The image files are saved as a (.STL) file and processed by “slicer” software to generate G-code files that relay the control instructions to the printer. Depending on the size of the printer, the “ink” used, and the size and geometrical complexity of the desired object, it can take from a few minutes to several hours or days to print. Unlike the monochromatic older generations of 3D printers, newer devices are emerging on the market with either multiple printing heads or “ink” chambers. The latter provides greater freedom in materials choice and is of particular interest in tissue regeneration for its ability to print and compartmentalize different cellular components.
Types of 3D printers
There are multiple types of 3D printers available commercially, benefiting from an open-source platform that allows customization and improvement of the current devices. Similarly, different types of “inks” are utilized depending on the printer’s design but also on the desired end-product. We mention some of the common types of printers and direct our focus to the last two, given their particular application in regenerative medicine:
• Selective laser sintering
• Electron beam melting
• Direct laser metal sintering
• Selective heat sintering
• Electron beam freeform fabrication
• Fused deposition modeling
• Photopolymerized extrusion stereolithography
Fused deposition modeling printers
Fused deposition modeling (FDM) printers utilize a heated extrusion head and are closely similar to a desktop inkjet printer. FDM printers benefit from their wide commercial availability and relatively low cost, making them among the most popular 3D printers currently in use. The “ink” utilized is a thermoplastic material typically prepared as a thread spool fed to the heated head and sequentially deposited as droplets with an approximate 100-micron resolution. The thermoplastics harden within few seconds, allowing fast and precise 3D object production. Several thermoplastics are used, some of which are also biocompatible and have been traditionally used in implant manufacturing and have shown promise for tissue engineering, such as polylactic acid (PLA), polylactic-glycolic acid (PLGA), and polycaprolactone (PCL). PCL has attracted substantial interests within the medical community given its low inflammatory profile, slow rate of hydrolysis, and ability to promote cellular attachment and growth (Shimao. Curr Opin Biotechnol. 2001;12[3]:242). In fact, PCL has been successfully printed as a splint for bronchial malacia in a baby suffering from repeated bouts of pneumonia and difficulty breathing (Zopf et al. N Engl J Med. 2013;368[21]:2043). FDM printers are thus most suitable for manufacturing prosthetic devices and possibly tissue scaffolds for cellular growth.
Photopolymerized extrusion stereolithography printers
In this form of 3D printing, the extrusion head consists of a motorized syringe-plunger containing the liquid ink. This is polymerized into a solid shape after extrusion and upon exposure to UV light (or another light source depending on the chemical content of the mixture). Polymerizable liquid inks are grouped under the term hydrogels, formerly defined by the International Union of Pure and Applied Chemistry (IUPAC) as “nonfluid colloidal network or polymer network that is expanded throughout its whole volume by a fluid.” Several formulations of hydrogels exist and we have used varying combinations of polyethylene glycol diacrylate and alginate to create hydrogels with different mechanical properties. Photopolymerization is slower than FDM; however, it has the added benefit of incorporating the cells into the prepolymerized liquid mix, which allows cellular inclusion into the final product. In essence, this type of printing will likely represent the future of “bioprinting” with its ability to compartmentalize cellular components within the scaffold. 3D printed ears (Manoor et al. Nano Lett. 2013;13[6]:2634) and aortic valves (Hockaday et al. Biofabrication. 2012;4[3]:035005) were generated using this approach. 3D printing was successful in replicating the shape of the desired organs with high fidelity while permitting maintained cellular growth, ushering a new era for regenerative medicine. However, the current mechanical properties of these structures do not permit organ transplantation and lack the necessary vascularized network for maintained in vivo growth.
3D printing and tracheal regeneration
In the setting of large segment tracheal pathologies, both benign and malignant, surgical resection and reconstruction may be challenging. Our lab has been working on creating a bioengineered tissue alternative for repair and/or replacement of large tracheal defects. The ideal material should have longitudinal flexibility, while maintaining lateral rigidity and concurrently supporting chondrogenesis, neovascularization, and re-epithelialization. Using a combination of mesenchymal stem cells, biologic collagen membranes, and 3D printing, we have achieved preliminary and encouraging results in large animal models. 3D-reconstructed CT scan of the neck and chest is obtained, and we isolate the tracheobronchial tree below the cricoid cartilage extending toward the carina and the major bronchi. Large tracheal defects, long segment airway stenosis, or tracheobronchomalacia can then be corrected virtually using CAD software applications. The improved anatomical 3D image is next converted to a (.STL) file readable by the printer, which generates the tracheal scaffold. The latter is subsequently incubated with mesenchymal stem cells, which are allowed to grow and differentiate to chondrogenic progenitor cells in a bioreactor in vitro. Chondrogenesis is a complex and well-orchestrated process. We incubate the stem cells in growth media containing a specific mixture of TGF-ß; BMP-2,-4, and -7; and FGF-2 to induce the formation of the chondrogenic lineage. Additionally, the scaffold with the adherent cells are mounted on a mandrel in a bioreactor and subjected to slow and continuous rotation to improve chondrogenesis via mechanical stimulation. In the early phases of differentiation, collagen I and fibronectin are deposited around the cells creating the earliest form of extracellular matrix for chondrocytes growth. With this approach, we have seen maintained cellular growth and differentiation of the stem cells into chondrogenic progenitors in vitro and chondrocytes in vivo in the animal model (Al-Ayoubi et al. Presented at the STS 51st Annual Meeting. Orlando, FL 2013). Current efforts are underway to understand the airway dynamics, mucosal epithelial function, and long-term effects of the bioengineered trachea.
Final word
3D printing is an exciting technology with significant impact on regenerative medicine. It particularly allows precise and customized reproduction of the engineered tissue while maintaining form and function. Further identification of suitable biomaterials is warranted, as well as the biological interactions of the stem cells with their potential environments. While substantial information remains to be discovered and technical challenges overcome, the field of tissue engineering is undoubtedly heading toward amazing findings, hoping to find cures for many debilitating illnesses.
Drs. Al-Ayoubi and Bhora are with the Department of Thoracic Surgery; Mount Sinai St. Luke’s Hospital and Mount Sinai Roosevelt Hospital; Icahn School of Medicine at Mount Sinai; New York, NY.
Imagine the day when organs are produced in the lab and are available for transplant, a scenario often repeated by doctors, patients, and medical reporters alike. What seems like a scene from a science-fiction movie may one day become reality—and sooner than we may imagine. Our understanding of biological systems and cellular mechanisms is rapidly expanding, accompanied and supported by advances in bioengineering. 3D printing, now a household word, has been hailed among the most exciting inventions of this decade with hardly a week passing by without new “firsts” using 3D printing technology. This novel technology has vast potential for multiscale innovations in almost every discipline: health-care, industry, academia, and the arts. In health-care, 3D printing is often called a game changer. It has already customized prosthetic and implant design and impacted the pharmaceutical industry and drug delivery systems, medical education, and most of all—tissue engineering and regenerative medicine. Here we briefly describe the basic concepts of this technology for the busy clinician and how it can be applied to tissue engineering with a special focus on airway regeneration.
3D printing process
3D printing, also known as rapid prototyping or additive manufacturing, was introduced in the 80s for industrial purposes. Not until a miniaturized “desktop” version of the printer was developed did its role in medicine begin to expand. All 3D printers, regardless of their types, follow similar principles. Products of 3D printers are objects made by sequential addition (z-stacking) of 2D layers creating three-dimensional structures. The objects of interest can be designed using computer-aided design (CAD) software or taken directly from 3D-reconstructed images of CT scans and MRIs. The image files are saved as a (.STL) file and processed by “slicer” software to generate G-code files that relay the control instructions to the printer. Depending on the size of the printer, the “ink” used, and the size and geometrical complexity of the desired object, it can take from a few minutes to several hours or days to print. Unlike the monochromatic older generations of 3D printers, newer devices are emerging on the market with either multiple printing heads or “ink” chambers. The latter provides greater freedom in materials choice and is of particular interest in tissue regeneration for its ability to print and compartmentalize different cellular components.
Types of 3D printers
There are multiple types of 3D printers available commercially, benefiting from an open-source platform that allows customization and improvement of the current devices. Similarly, different types of “inks” are utilized depending on the printer’s design but also on the desired end-product. We mention some of the common types of printers and direct our focus to the last two, given their particular application in regenerative medicine:
• Selective laser sintering
• Electron beam melting
• Direct laser metal sintering
• Selective heat sintering
• Electron beam freeform fabrication
• Fused deposition modeling
• Photopolymerized extrusion stereolithography
Fused deposition modeling printers
Fused deposition modeling (FDM) printers utilize a heated extrusion head and are closely similar to a desktop inkjet printer. FDM printers benefit from their wide commercial availability and relatively low cost, making them among the most popular 3D printers currently in use. The “ink” utilized is a thermoplastic material typically prepared as a thread spool fed to the heated head and sequentially deposited as droplets with an approximate 100-micron resolution. The thermoplastics harden within few seconds, allowing fast and precise 3D object production. Several thermoplastics are used, some of which are also biocompatible and have been traditionally used in implant manufacturing and have shown promise for tissue engineering, such as polylactic acid (PLA), polylactic-glycolic acid (PLGA), and polycaprolactone (PCL). PCL has attracted substantial interests within the medical community given its low inflammatory profile, slow rate of hydrolysis, and ability to promote cellular attachment and growth (Shimao. Curr Opin Biotechnol. 2001;12[3]:242). In fact, PCL has been successfully printed as a splint for bronchial malacia in a baby suffering from repeated bouts of pneumonia and difficulty breathing (Zopf et al. N Engl J Med. 2013;368[21]:2043). FDM printers are thus most suitable for manufacturing prosthetic devices and possibly tissue scaffolds for cellular growth.
Photopolymerized extrusion stereolithography printers
In this form of 3D printing, the extrusion head consists of a motorized syringe-plunger containing the liquid ink. This is polymerized into a solid shape after extrusion and upon exposure to UV light (or another light source depending on the chemical content of the mixture). Polymerizable liquid inks are grouped under the term hydrogels, formerly defined by the International Union of Pure and Applied Chemistry (IUPAC) as “nonfluid colloidal network or polymer network that is expanded throughout its whole volume by a fluid.” Several formulations of hydrogels exist and we have used varying combinations of polyethylene glycol diacrylate and alginate to create hydrogels with different mechanical properties. Photopolymerization is slower than FDM; however, it has the added benefit of incorporating the cells into the prepolymerized liquid mix, which allows cellular inclusion into the final product. In essence, this type of printing will likely represent the future of “bioprinting” with its ability to compartmentalize cellular components within the scaffold. 3D printed ears (Manoor et al. Nano Lett. 2013;13[6]:2634) and aortic valves (Hockaday et al. Biofabrication. 2012;4[3]:035005) were generated using this approach. 3D printing was successful in replicating the shape of the desired organs with high fidelity while permitting maintained cellular growth, ushering a new era for regenerative medicine. However, the current mechanical properties of these structures do not permit organ transplantation and lack the necessary vascularized network for maintained in vivo growth.
3D printing and tracheal regeneration
In the setting of large segment tracheal pathologies, both benign and malignant, surgical resection and reconstruction may be challenging. Our lab has been working on creating a bioengineered tissue alternative for repair and/or replacement of large tracheal defects. The ideal material should have longitudinal flexibility, while maintaining lateral rigidity and concurrently supporting chondrogenesis, neovascularization, and re-epithelialization. Using a combination of mesenchymal stem cells, biologic collagen membranes, and 3D printing, we have achieved preliminary and encouraging results in large animal models. 3D-reconstructed CT scan of the neck and chest is obtained, and we isolate the tracheobronchial tree below the cricoid cartilage extending toward the carina and the major bronchi. Large tracheal defects, long segment airway stenosis, or tracheobronchomalacia can then be corrected virtually using CAD software applications. The improved anatomical 3D image is next converted to a (.STL) file readable by the printer, which generates the tracheal scaffold. The latter is subsequently incubated with mesenchymal stem cells, which are allowed to grow and differentiate to chondrogenic progenitor cells in a bioreactor in vitro. Chondrogenesis is a complex and well-orchestrated process. We incubate the stem cells in growth media containing a specific mixture of TGF-ß; BMP-2,-4, and -7; and FGF-2 to induce the formation of the chondrogenic lineage. Additionally, the scaffold with the adherent cells are mounted on a mandrel in a bioreactor and subjected to slow and continuous rotation to improve chondrogenesis via mechanical stimulation. In the early phases of differentiation, collagen I and fibronectin are deposited around the cells creating the earliest form of extracellular matrix for chondrocytes growth. With this approach, we have seen maintained cellular growth and differentiation of the stem cells into chondrogenic progenitors in vitro and chondrocytes in vivo in the animal model (Al-Ayoubi et al. Presented at the STS 51st Annual Meeting. Orlando, FL 2013). Current efforts are underway to understand the airway dynamics, mucosal epithelial function, and long-term effects of the bioengineered trachea.
Final word
3D printing is an exciting technology with significant impact on regenerative medicine. It particularly allows precise and customized reproduction of the engineered tissue while maintaining form and function. Further identification of suitable biomaterials is warranted, as well as the biological interactions of the stem cells with their potential environments. While substantial information remains to be discovered and technical challenges overcome, the field of tissue engineering is undoubtedly heading toward amazing findings, hoping to find cures for many debilitating illnesses.
Drs. Al-Ayoubi and Bhora are with the Department of Thoracic Surgery; Mount Sinai St. Luke’s Hospital and Mount Sinai Roosevelt Hospital; Icahn School of Medicine at Mount Sinai; New York, NY.