Integrative Biology and Infectious Diseases Branch, DER, NIDCR
The goal of this initiative is to develop tools and technologies to allow robust, precise and predictable in vitro assembly and functional morphogenesis of three-dimensional (3D) human dental, oral and craniofacial (DOC) micro- tissues and organs, also referred to as tissue/organ chips that will mimic architecture, organization, multi-tissue interphases, physiology and disease pathology of native human DOC tissues and organs including craniofacial bone, skeletal muscle, cartilage, oral mucosa, salivary gland and facial peripheral nerve and their composite assemblies. By recapitulating key features of native tissues and organs, these 3D systems will generate the levels of functionality, which are not possible to achieve with conventional 2D monolayer cultures grown on flat surfaces. By virtue of their functionality, the tissue/organ chips will create unprecedented opportunities for addressing mechanistic questions of health and disease of DOC tissues and organs. Moreover, they will improve predictive power of identification of new therapeutic targets for these diseases, and will help to develop Precision Medicine-based drug efficacy and toxicity testing approaches focused on specific patient populations.
In vitro cultures of primary cells and transformed cell lines grown as flat monolayers on tissue culture plastic have been employed by generations of researchers. While such reductionist models have proven useful for addressing many biological questions, they frequently have been unable to recapitulate in vivo tissue responses in part due to the lack of organizational and cellular complexity and architecture of normal tissues.
To compensate for these deficiencies, 3D culture models (also sometimes referred to as organoids) composed of either natural extracellular matrices (ECMs) or synthetic polymers combined with various human and animal cell types have been developed over the years. These models better mimic physiological responses than 2D models, but they also have significant drawbacks, including limited viability due to the lack of oxygen perfusion, high variability of the organoids’ size and shape, and experimental manipulation difficulties. Further, it is difficult to expose the organoids to normal biophysical cues, such as fluid shear stress, compression and tension, and they lack multi-scale architecture and tissue-tissue interfaces that are crucial for tissue and organ function.
On the other end of the complexity spectrum, small and large animal models have been considered as gold standards in biomedical research. Unfortunately, these models are cumbersome to use, they are expensive, they raise ethical issues, and most importantly, they frequently do not recapitulate human physiology and pathology.
The present initiative will focus on bridging the capability gaps between the existing biological model systems, as they apply to human DOC tissues and organs, by developing tissue and organ chip devices that will have superior capacity to recapitulate physiological functions of human DOC tissues and organs. Tissue/organ chip are 3D in vitro systems that leverage recent advances in microfabrication technologies from the microchip industry with microfluidic approaches to create continuously perfused prefabricated micrometer-sized microenvironments for co-culturing living cells. These micro-tissue systems incorporate different mature cell types as well as stem and progenitor cells that comprise a given organ in combination with the ECM and other bioactive molecules, and microfabrication technologies endow them with exquisite capacity to mimic native tissue/organ architecture. Moreover, technical features of the chip platforms permit precise application of physiologically-relevant physical forces to these micro-tissues, including fluid shear stress, mechanical compression and strain Bhatia and Ingber, 2014 (PDF - 2,760 KB).
To meet the challenges of building functional DOC tissue/organ chips, this initiative will bring together bioengineers and other professionals with the relevant expertise in designing and building chip devices for other organ systems with DOC biologists who will define biological questions and develop design parameters for the DOC tissue/organ chip prototypes. Such collaborations between engineers and DOC biologists will also play a key role in functional validation of these new chip systems.
Lastly, because the chips are designed and manufactured as highly reproducible and mutually-compatible minimal functional units, these individual units can be integrated with each other into micro-device platforms and linked via a microfluidic circulatory system to create “human on a chip” systems with the capacity to model in vivo organ function and interactions among organs, as well as to probe dynamic metabolic processes, drug efficacy and toxicity, and drug absorption and distribution Huh et al. 2011; Esch et al. 2015 (PDF - 550 KB). Tissue/organ chips are currently being developed for a number of human organs, including liver, lung, heart, vasculature, kidney, neural tissues, and intestine, as well as for different types of tumors Luni et al. 2014; Bhatia and Ingber, 2014 (PDF - 2,760 KB), and pharmaceutical companies have already begun using them for drug development Reardon, 2015 (PDF - 204 KB). While these in vitro systems are unlikely to completely replace animals, it is envisioned that they can transform many areas of basic and translational research as paradigm-shifting alternatives to conventional tissue culture and animal models Bhatia and Ingber, 2014 (PDF - 2,760 KB).
In light of this significant promise and rapid progress in the field, it is now important to develop tissue/organ chips for DOC tissues, and to take advantage of the existing opportunities to integrate DOC chips with other micro-tissue systems by encouraging appropriate collaborations between DOC researchers and other scientific communities. These collaborations will take advantage of the available technical expertise in chip design and production (such as the ones of the NIH and DARPA consortium) and will leverage this expertise for developing unique chip systems directly relevant to NIDCR mission. Examples of potentially valuable DOC chip systems include composite tissues and organs, such as craniofacial bone-skeletal muscle, craniofacial bone-cranial suture, osteochondral composites, craniofacial bone-bone marrow, alveolar bone -bone marrow, periodontium-periodontal ligament-tooth, dentin-dental pulp, salivary gland and oral mucosa among others. Integration of these tissues with vasculature, immune system and peripheral nervous system components are also important goals.
Current Portfolio Overview and the Initiative's Feasibility and Timeliness
Until now, with an exception of a few early studies in bone Zhang et al 2011; Park et al. 2012 (PDF - 1,502), and a single study in the salivary gland Soscia et al. 2013., no significant effort has been devoted to DOC chips development, and the goal of this initiative is to close this gap. This initiative is timely because recent advances in identification of DOC tissue-specific stem and progenitor cell types, technological improvements in derivation of patient-specific induced pluripotent stem cell lines (iPSCs) and gene-editing technologies, progress in understanding the roles of ECM in tissue development and function, new developments in material science, bioengineering, microchip, microfluidics and other related technologies created a strong foundation for making this work feasible. Moreover, new knowledge and technical skills generated by the ongoing joint NIH/DARPA/FDA collaboration to develop integrative tissue/organ systems for different human tissues and organs, Fabre et al (PDF - 261 KB), (no DOC tissues are among those being currently developed by this effort) will be useful for the researchers embarking on DOC tissue chips development, and will provide ample opportunities for forging new collaborations. NIAMS and NIBIB expressed potential interest in joining this initiative. NCATS is leading the NIH component of the NIH/DARPA/FDA effort and has expressed enthusiastic support for this potential NIDCR initiative. They are willing to provide help in integrating DOC chip researchers with the existing chip consortium if this Initiative is approved.
Individuals and Groups Whose Input was Solicited for This Initiative
Since the initiation of NIH/DARPA/FDA tissue/organ chip consortium several years ago, NIDCR Program has been actively participating in the trans-NIH programmatic working group that oversees the function and progress of the NIH/DARPA/FDA Initiative. All researchers funded under the Initiative gather twice a year in Washington DC area to report on their current progress, to interact and exchange ideas with their colleagues and with the programmatic working group. These meetings provided NIDCR Program with many opportunities to obtain input from the researchers in the field (several of these researchers are current NIDCR grantees), on the feasibility of development of DOC tissue/organ chips, and on their potential interest in engaging in DOC chip development and/or collaboration with other researchers developing DOC chips. Overall, there is considerable interest in developing vascularized bone and bone-bone marrow chips, as these tissues are seen as important components that would functionally complement integrated “human on a chip” systems. Also, development of a bone-cartilage composite interfaced with the immune system is an area of high interest. Further, the NIH/DARPA/FDA consortium has several current projects focused on the development of skin and intestinal mucosa chip platforms, and this existing expertise would be of high potential value for the researchers launching their DOC tissue/organ chip development effort. Lastly, NIDCR recently issued a call for public comment for its FY2017 Initiatives, including this Initiative, and we have received an enthusiastic support for this Initiative from the extramural community.
Alignment with NIDCR Strategic Plan
This Initiative is aligned with the following Goals and Objectives of NIDCR Strategic Plan: Goal 1, Objective 3: “Conduct translational and clinical investigations to improve dental, oral, and craniofacial health”, and Goal 2, Objective 1: “Support research toward precise classification, prevention, and treatment of dental, oral, and craniofacial health and disease”.
American Academy of Pediatric Dentistry, Council of Clinical Affairs. Guidelines on Dental Management of Heritable Dental Developmental Anomalies, 2013. http://www.aapd.org/media/Policies_Guidelines/G_OHCHeritable.pdf (PDF - 206 KB)
Bhatia SN and Ingber DE. 2014. Microfluidic Organs-on-Chips. Nature Biotechnology 32(8): 760-772
Huh D, Hamilton GA, Ingber DE. 2011. From Three-Dimensional Cell Culture to Organ-on-Chips. Trends Cell Biol. 21(12): 745-754
Esch EW, Bahinski A, Huh D. 2015. Organ-on-Chips at the Frontiers of Drug Discovery. Nature Reviews Drug Discovery 14: 248-260
Luni C, Serena E, Elvassore N. 2014. Human-on-Chip for Therapy Development and Fundamental Science. Current Opinions in Biotechnology 25: 45-50
Reardon S. 2015. Organ-on-Chips Go Mainstream. Nature 523: 266
Zhang Y, Gazit Z, Pelled G, Gazit D, Vunjak-Novakovic G. 2011. Patterning Osteogenesis by Inducible gene Expression in Microfluidic Culture Systems. Integrative Biology, 3: 39-47
Park S-H, Sim WY, Min B-H, Yang SS, Khademhosseini A, Kaplan DL. 2012 Chip-Based Comparison of the Osteogenesis of Human Bone Marrow- and Adipose Tissue-Derived Mesenchymal Stem Cells under Mechanical Stimulation. PLoS One, 7(9): e46689
Soscia DA, Sequeira SJ, Schramm RA, Jayarathanam K, Cantara SI, Larsen M, Castracane J. 2013. Salivary Gland Cell Differentiation and Organization on Micropatterned PLGA Nanofiber Craters. Biomaterials, 34(28): 6773-6784
Fabre K, Livingston C, Tagle DA. 2014. Organ-on-Chips (Microphysiological Systems): Tools to Expedite Efficacy and Toxicity Testing in Human Tissue. Experimental Biology and Medicine, 239:1073-1077