Papers by Ibrahim Tarik Ozbolat
Small diameter blood vessels Vascularized thick tissues Extrusion-based bioprinting Droplet-based... more Small diameter blood vessels Vascularized thick tissues Extrusion-based bioprinting Droplet-based bioprinting Laser-based bioprinting a b s t r a c t Bioprinting is a promising technology to fabricate design-specific tissue constructs due to its ability to create complex, heterocellular structures with anatomical precision. Bioprinting enables the deposition of various biologics including growth factors, cells, genes, neo-tissues and extra-cellular matrix-like hydrogels. Benefits of bioprinting have started to make a mark in the fields of tissue engineering, regen-erative medicine and pharmaceutics. Specifically, in the field of tissue engineering, the creation of vascu-larized tissue constructs has remained a principal challenge till date. However, given the myriad advantages over other biofabrication methods, it becomes organic to expect that bioprinting can provide a viable solution for the vascularization problem, and facilitate the clinical translation of tissue engineered constructs. This article provides a comprehensive account of bioprinting of vascular and vascular-ized tissue constructs. The review is structured as introducing the scope of bioprinting in tissue engineering applications, key vascular anatomical features and then a thorough coverage of 3D bioprint-ing using extrusion-, droplet-and laser-based bioprinting for fabrication of vascular tissue constructs. The review then provides the reader with the use of bioprinting for obtaining thick vascularized tissues using sacrificial bioink materials. Current challenges are discussed, a comparative evaluation of different bioprinting modalities is presented and future prospects are provided to the reader. Statement of Significance Biofabrication of living tissues and organs at the clinically-relevant volumes vitally depends on the integration of vascular network. Despite the great progress in traditional biofabrication approaches, building perfusable hierarchical vascular network is a major challenge. Bioprinting is an emerging technology to fabricate design-specific tissue constructs due to its ability to create complex, heterocellular structures with anatomical precision, which holds a great promise in fabrication of vascular or vascularized tissues for transplantation use. Although a great progress has recently been made on building perfusable tissues and branched vascular network, a comprehensive review on the state-of-the-art in vascular and vascu-larized tissue bioprinting has not reported so far. This contribution is thus significant because it discusses the use of three major bioprinting modalities in vascular tissue biofabrication for the first time in the literature and compares their strengths and limitations in details. Moreover, the use of scaffold-based and scaffold-free bioprinting is expounded within the domain of vascular tissue fabrication.
Since the first printing of biologics with cytoscribing as demonstrated by Klebe in 1986, three d... more Since the first printing of biologics with cytoscribing as demonstrated by Klebe in 1986, three dimensional (3D) bioprinting has made a substantial leap forward, particularly in the last decade. It has been widely used in fabrication of living tissues for various application areas such as tissue engineering and regen-erative medicine research, transplantation and clinics, pharmaceutics and high-throughput screening, and cancer research. As bioprinting has gained interest in the medical and pharmaceutical communities , the demand for bioprinters has risen substantially. A myriad of bioprinters have been developed at research institutions worldwide and several companies have emerged to commercialize advanced bio-printer technologies. This paper prefaces the evolution of the field of bioprinting and presents the first comprehensive review of existing bioprinter technologies. Here, a comparative evaluation is performed for bioprinters; limitations with the current bioprinter technologies are discussed thoroughly and future prospects of bioprinters are provided to the reader.
Biomater. Sci., 2014
The ability to create three dimensional (3D) thick tissues is still a major tissue engineering ch... more The ability to create three dimensional (3D) thick tissues is still a major tissue engineering challenge. It requires the development of a suitable vascular supply for an efficient media exchange. An integrated vasculature network is particularly needed when building thick functional tissues and/or organs with high metabolic activities, such as the heart, liver and pancreas. In this work, human umbilical vein smooth muscle cells (HUVSMCs) were encapsulated in sodium alginate and printed in the form of vasculature conduits using a coaxial deposition system. Detailed investigations were performed to understand the dehydration, swelling and degradation characteristics of printed conduits. In addition, because perfusional, permeable and mechanical properties are unique characteristics of natural blood vessels, for printed conduits these properties were also explored in this work. The results show that cells encapsulated in conduits had good proliferation activities and that their viability increased during prolonged in vitro culture. Deposition of smooth muscle matrix and collagen was observed around the peripheral and luminal surface in long-term cultured cellular vascular conduit through histology studies.
Recent advances in bioprinting have granted tissue engineers the ability to assemble biomaterials... more Recent advances in bioprinting have granted tissue engineers the ability to assemble biomaterials, cells, and signaling molecules into anatomically relevant functional tissues or organ parts. Scaffold-free fabrication has recently attracted a great deal of interest due to the ability to recapitulate tissue biology by using self-assembly, which mimics the embryonic development process. Despite several attempts, bioprinting of scale-up tissues at clinically-relevant dimensions with closely recapitulated tissue biology and functionality is still a major roadblock. Here, we fabricate and engineer scaffold-free scalable tissue strands as a novel bioink material for robotic-assisted bioprinting technologies. Compare to 400 μm-thick tissue spheroids bioprinted in a liquid delivery medium into confining molds, near 8 cm-long tissue strands with rapid fusion and self-assemble capabilities are bioprinted in solid form for the first time without any need for a scaffold or a mold support or a liquid delivery medium, and facilitated native-like scale-up tissues. The prominent approach has been verified using cartilage strands as building units to bioprint articular cartilage tissue. Given its unmatched capability and rapid advancement, three-dimensional (3D) bioprinting has drawn enormous attention and become increasingly popular for engineering functional tissues and organs 1. As the development of 3D bioprinting techniques has progressed, great attention has been paid to adopting this cutting-edge technology for a broad spectrum of applications in medicine 2–4. Three-dimensional bioprinting uses an additive manufacturing strategy, which can offer precise temporal and special control of biomaterials, cells, growth factors, and other functional components 5–7. There are three major elements of bioprinting: biomimicry, which strives to reproduce the identical components of a tissue or organ 8 ; biological self-assembly, which mimics embryonic organ development by using cellular organization and tissue fusion 9 ; and use of mini-tissues as building blocks for the fabrication of larger constructs in anatomically-correct shapes 10. Among these approaches, self-assembly of cellular components implements principles of embryonic development while taking advantage of 3D bioprint-ing techniques. It is fully biological, scaffold-free, and considered to be a promising direction for bioprinting. In contrast to scaffold-based bioprinting, where tissue development depends on cell proliferation within or on top of hydrogel or other scaffolding materials, scaffold-free bioprinting can offer relatively high cell density initially without the inclusion of biomaterials. This can facilitate the deposition of extracellular matrix (ECM) in a defined manner with better cell-to-cell interactions 11 , generation of tissues with close biomimicry 12 , preservation of cell phenotype and functionality for longer term 13 , acceleration of tissue maturation 14 , and elimination of complications with biodegradation of scaffolds 15. Using tissue spheroids, scaffold-free bioprinting has been successfully demonstrated for the fabrication of thin tubular tissues such as blood vessels 11 and nerve grafts 16 ; however, bio-printing tissues with a scalable bioink material enabling scaffold-and mold-free bioprinting of scale-up tissues is still elusive 17 .
There is an urgent for a novel approach to cancer research with 1.7 million new cases of cancer o... more There is an urgent for a novel approach to cancer research with 1.7 million new cases of cancer occurring every year in the United States of America. Tumor models offer promise as a useful platform for cancer research without the need for animal models, but there remains a challenge to fabricate a relevant model which mimics the structure, function and drug response of human tumors. Bioprinting can address this need by fabricating three-dimensional constructs that mimic tumor heterogeneity, vasculature and spheroid structures. Furthermore, bioprinting can be used to fabricate tissue constructs within microfluidic platforms, forming " tumor-on-a-chip " devices which are ideal for high-throughput testing in a biomimetic microenvironment. Applications of tumors-on-a-chip include facilitating basic research to better understand tumor development, structure and function as well as drug screening to improve the efficiency of cancer drug discovery.
Droplet-based bioprinting (DBB) offers greater advantages due to its simplicity and agility with ... more Droplet-based bioprinting (DBB) offers greater advantages due to its simplicity and agility with precise control on deposition of biologics including cells, growth factors, genes, drugs and biomaterials, and has been a prominent technology in the bioprinting community. Due to its immense versatility, DBB technology has been adopted by various application areas, including but not limited to, tissue engineering and regenerative medicine, transplantation and clinics, pharmaceutics and high-throughput screening, and cancer research. Despite the great benefits, the technology currently faces several challenges such as a narrow range of available bioink materials, bioprinting-induced cell damage at substantial levels, limited mechanical and structural integrity of bioprinted constructs, and restrictions on the size of constructs due to lack of vascularization and porosity. This paper presents a first-time review of DBB and comprehensively covers the existing DBB modalities including inkjet, electrohydrodynamic, acoustic, and micro-valve bioprinting. The recent notable studies are highlighted, the relevant bioink biomaterials and bioprinters are expounded, the application areas are presented, and the future prospects are provided to the reader.
Bioprinting is a powerful technology in the fabrication of living tissues and organs for tissue e... more Bioprinting is a powerful technology in the fabrication of living tissues and organs for tissue engineering and regenerative medicine, transplantation and clinics, pharmaceutics and high-throughput screening, as well as cancer research.
Extrusion-based bioprinting (EBB) is a rapidly growing technology that has made substantial progr... more Extrusion-based bioprinting (EBB) is a rapidly growing technology that has made substantial progress during the last decade. It has great versatility in printing various biologics, including cells, tissues, tissue constructs, organ modules and microfluidic devices, in applications from basic research and pharmaceutics to clinics. Despite the great benefits and flexibility in printing a wide range of bioinks, including tissue spheroids, tissue strands, cell pellets, decellularized matrix components, micro-carriers and cellladen hydrogels, the technology currently faces several limitations and challenges. These include impediments to organ fabrication, the limited resolution of printed features, the need for advanced bioprinting solutions to transition the technology bench to bedside, the necessity of new bioink development for rapid, safe and sustainable delivery of cells in a biomimetically organized microenvironment, and regulatory concerns to transform the technology into a product. This paper, presenting a first-time comprehensive review of EBB, discusses the current advancements in EBB technology and highlights future directions to transform the technology to generate viable end products for tissue engineering and regenerative medicine.
Bioprinting is an emerging technology to fabricate artificial tissues and organs through additive... more Bioprinting is an emerging technology to fabricate artificial tissues and organs through additive manufacturing of living cells in a tissues-specific pattern by stacking them layer by layer. Two major approaches have been proposed in the literature: bioprinting cells in a scaffold matrix to support cell proliferation and growth, and bioprinting cells without using a scaffold structure. Despite great progress, particularly in scaffold-based approaches along with recent significant attempts, printing large-scale tissues and organs is still elusive. This paper demonstrates recent significant attempts in scaffoldbased and scaffold-free tissue printing approaches, discusses the advantages and limitations of both approaches, and presents a conceptual framework for bioprinting of scale-up tissue by complementing the benefits of these approaches.
In this note, we report a practical and efficient method based on a coaxial extrusion and microin... more In this note, we report a practical and efficient method based on a coaxial extrusion and microinjection technique for biofabrication of scaffold-free tissue strands. Tissue strands were obtained using tubular alginate conduits as mini-capsules with well-defined permeability and mechanical properties, where their removal by ionic decrosslinking allowed the formation of scaffold-free cell aggregates in the form of cylindrical strands with well-defined morphology and geometry. Rat dermal fibroblasts and mouse insulinoma beta TC3 cells were used to fabricate both single-cellular and heterocellular tissue strands with high cell viability, self-assembling capability and the ability to express cell-specific functional markers. By taking advantage of tissue self-assembly, we succeeded in guiding the fusion of tissue strands to fabricate larger tissue patches. The presented approach enables fabrication of cell aggregates with controlled dimensions allowing highly long strands, which can be used for various applications, including fabrication of scale-up complex tissues and of tissue models for drug screening and cancer studies.
Bioprinting is an emerging technology for constructing and fabricating artificial tissue and orga... more Bioprinting is an emerging technology for constructing and fabricating artificial tissue and organ constructs. This technology surpasses the traditional scaffold fabrication approach in tissue engineering (TE). Currently, there is a plethora of research being done on bioprinting technology and its potential as a future source for implants and full organ transplantation. This review paper overviews the current state of the art in bioprinting technology, describing the broad range of bioprinters and bioink used in preclinical studies. Distinctions between laser-, extrusion-, and inkjet-based bioprinting technologies along with appropriate and recommended bioinks are discussed. In addition, the current state of the art in bioprinter technology is reviewed with a focus on the commercial point of view. Current challenges and limitations are highlighted, and future directions for next-generation bioprinting technology are also presented.
This paper highlights the development of 'Multi-arm Bioprinter (MABP)' capable of concurrent mult... more This paper highlights the development of 'Multi-arm Bioprinter (MABP)' capable of concurrent multimaterial deposition with independent motion path and dispensing parameters including deposition speed, material dispensing rate, and nozzle travel velocity for use in tissue engineering. In this research, the system is designed to concurrently print a filament structure and deposit cell spheroids between the filaments to create a hybrid structure to support the cell spheroids in three dimensions (3Ds). This process can be used with multiple cell types and is capable of reducing the fabrication time while using optimized dispensing parameters for each material. A novel method of dispensing the crosslinking solution using a co-axial nozzle was also developed and demonstrated in this paper. Cell-laden structures were fabricated through concurrent deposition of cell-encapsulated filaments and with cell spheroids to validate this concept. Rheology studies were then conducted to determine the effects of crosslink flow on filament width, hydrogel dispensing pressure on filament width, and dispensing time interval on spheroid diameter.
Biofabrication, 2013
Tissue engineering has been a promising field of research, offering hope of bridging the gap betw... more Tissue engineering has been a promising field of research, offering hope of bridging the gap between organ shortage and transplantation needs. However, building three-dimensional (3D) vascularized organs remains the main technological barrier to be overcome. One of the major challenges is the inclusion of a vascular network to support cell viability in terms of nutrients and oxygen perfusion. This paper introduces a new approach to the fabrication of vessel-like microfluidic channels that has the potential to be used in thick tissue or organ fabrication in the future. In this research, we investigate the manufacturability of printable micro-fluidic channels, where micro-fluidic channels support mechanical integrity as well as enable fluid transport in 3D. A pressure-assisted solid freeform fabrication platform is developed with a coaxial needle dispenser unit to print hollow hydrogel filaments. The dispensing rheology is studied, and effects of material properties on structural formation of hollow filaments are analyzed. Sample structures are printed through the developed computer-controlled system. In addition, cell viability and gene expression studies are presented in this paper. Cell viability shows that cartilage progenitor cells (CPCs) maintained their viability right after bioprinting and during prolonged in vitro culture. Real-time PCR analysis yielded a relatively higher expression of cartilage-specific genes in alginate hollow filament encapsulating CPCs, compared with monolayer cultured CPCs, which revealed that printable semi-permeable micro-fluidic channels provided an ideal environment for cell growth and function.
Tissue engineering has been a promising field of research, offering hope for bridging the gap bet... more Tissue engineering has been a promising field of research, offering hope for bridging the gap between organ shortage and transplantation needs. However, building threedimensional (3D) vascularized organs remains the main technological barrier to be overcome. Organ printing, which is defined as computer-aided additive biofabrication of 3D cellular tissue constructs, has shed light on advancing this field into a new era. Organ printing takes advantage of rapid prototyping (RP) technology to print cells, biomaterials, and cell-laden biomaterials individually or in tandem, layer by layer, directly creating 3D tissue-like structures. Here, we overview RP-based bioprinting approaches and discuss the current challenges and trends towards fabricating living organs for transplant in the near future.
Abstract: Tissue Engineering aims to restore tissue functions by developing engineered scaffolds ... more Abstract: Tissue Engineering aims to restore tissue functions by developing engineered scaffolds providing optimum environment for tissue regeneration. In this dissertation, hybrid tissue scaffolds are modeled, designed and fabricated to control release kinetics spatially ...
Uploads
Papers by Ibrahim Tarik Ozbolat