Ethical aspects of tissue engineering: a review

Perspectives on Recent Developments and Directions in Tissue Engineering and Regenerative Medicine

This perspective article draws on lessons learned at the 7th TERMIS World Congress held in Seattle, Washington in June 2024. This gathering of prominent researchers and translational scientists in tissue engineering and regenerative medicine (TERM) from around the world provided a forum to consider the impact of tissue engineering and its future directions. New frontiers are considered in the context of global challenges, including clinical translation and recent advances in pediatric tissue engineering, supercritical fluid technology for scaffold fabrication and sterilization, and learning from successful failures in tissue engineering and regenerative medicine. Bench-to-bedside translational strategies, inclusive research strategies, regulatory hurdles, and ethics linked to navigating responsibilities and innovations, are identified as important drivers in the field.

Personalized 3D printed scaffolds: The ethical aspects

Personalized 3D printed scaffolds are a new generation of implants for tissue engineering and regenerative medicine purposes. Scaffolds support cell growth, providing an artificial extracellular matrix for tissue repair and regeneration and can biodegrade once cells have assumed their physiological and structural roles. The ethical challenges and opportunities of these implants should be mapped in parallel with the life cycle of the scaffold to assist their development and implementation in a responsible, safe, and ethically sound manner. This article provides an overview of these relevant ethical aspects. We identified nine themes which were linked to three stages of the life cycle of the scaffold: the development process, clinical testing, and the implementation process. The described ethical issues are related to good research and clinical practices, such as privacy issues concerning digitalization, first-in-human trials, responsibility and commercialization. At the same time, this article also creates awareness for underexplored ethical issues, such as irreversibility, embodiment and the ontological status of these scaffolds. Moreover, it exemplifies how to include gender in the ethical assessment of new technologies. These issues are important for responsible development and implementation of personalized 3D printed scaffolds and in need of more attention within the additive manufacturing and tissue engineering field. Moreover, the insights of this review reveal unresolved qualitative empirical and normative questions that could further deepen the understanding and co-creation of the ethical implications of this new generation of implants.

Three-Dimensional Bioprinting of Human Organs and Tissues: Bioethical and Medico-Legal Implications Examined through a Scoping Review

Three-dimensional bioprinting is a rapidly evolving technology that holds the promise of addressing the increasing demand for organs, tissues, and personalized medicine. By employing computer-aided design and manufacturing processes, 3D bioprinting allows for the precise deposition of living cells, biomaterials, and biochemicals to create functional human tissues and organs. The potential applications of this technology are vast, including drug testing and development, disease modeling, regenerative medicine, and ultimately, organ transplantation. However, as with any groundbreaking technology, 3D bioprinting presents several ethical, legal, and regulatory concerns that warrant careful consideration. As the technology progresses towards clinical applications, it is essential to address these challenges and establish appropriate frameworks to guide the responsible development of 3D bioprinting. This article, utilizing the Arksey and O'Malley scoping review model, is designed to scrutinize the bioethical implications, legal and regulatory challenges, and medico-legal issues that are intertwined with this rapidly evolving technology.

In Vitro and In Vivo Biological Assessments of 3D-Bioprinted Scaffolds for Dental Applications

Three-dimensional (3D) bioprinting is a unique combination of technological advances in 3D printing and tissue engineering. It has emerged as a promising approach to address the dilemma in current dental treatments faced by clinicians in order to repair or replace injured and diseased tissues. The exploration of 3D bioprinting technology provides high reproducibility and precise control of the bioink containing the desired cells and biomaterial over the architectural and dimensional features of the scaffolds in fabricating functional tissue constructs that are specific to the patient treatment need. In recent years, the dental applications of different 3D bioprinting techniques, types of novel bioinks, and the types of cells used have been extensively explored. Most of the findings noted significant challenges compared to the non-biological 3D printing approach in constructing the bioscaffolds that mimic native tissues. Hence, this review focuses solely on the implementation of 3D bioprinting techniques and strategies based on cell-laden bioinks. It discusses the in vitro applications of 3D-bioprinted scaffolds on cell viabilities, cell functionalities, differentiation ability, and expression of the markers as well as the in vivo evaluations of the implanted bioscaffolds on the animal models for bone, periodontal, dentin, and pulp tissue regeneration. Finally, it outlines some perspectives for future developments in dental applications.

Recent advances on 3D-printed PCL-based composite scaffolds for bone tissue engineering

Population ageing and various diseases have increased the demand for bone grafts in recent decades. Bone tissue engineering (BTE) using a three-dimensional (3D) scaffold helps to create a suitable microenvironment for cell proliferation and regeneration of damaged tissues or organs. The 3D printing technique is a beneficial tool in BTE scaffold fabrication with appropriate features such as spatial control of microarchitecture and scaffold composition, high efficiency, and high precision. Various biomaterials could be used in BTE applications. PCL, as a thermoplastic and linear aliphatic polyester, is one of the most widely used polymers in bone scaffold fabrication. High biocompatibility, low cost, easy processing, non-carcinogenicity, low immunogenicity, and a slow degradation rate make this semi-crystalline polymer suitable for use in load-bearing bones. Combining PCL with other biomaterials, drugs, growth factors, and cells has improved its properties and helped heal bone lesions. The integration of PCL composites with the new 3D printing method has made it a promising approach for the effective treatment of bone injuries. The purpose of this review is give a comprehensive overview of the role of printed PCL composite scaffolds in bone repair and the path ahead to enter the clinic. This study will investigate the types of 3D printing methods for making PCL composites and the optimal compounds for making PCL composites to accelerate bone healing.

Tissue Engineering for Gastrointestinal and Genitourinary Tracts

The gastrointestinal and genitourinary tracts share several similarities. Primarily, these tissues are composed of hollow structures lined by an epithelium through which materials need to flow with the help of peristalsis brought by muscle contraction. In the case of the gastrointestinal tract, solid or liquid food must circulate to be digested and absorbed and the waste products eliminated. In the case of the urinary tract, the urine produced by the kidneys must flow to the bladder, where it is stored until its elimination from the body. Finally, in the case of the vagina, it must allow the evacuation of blood during menstruation, accommodate the male sexual organ during coitus, and is the natural way to birth a child. The present review describes the anatomy, pathologies, and treatments of such organs, emphasizing tissue engineering strategies.

Early-Phase Clinical Trials of Bio-Artificial Organ Technology: A Systematic Review of Ethical Issues

Regenerative medicine has emerged as a novel alternative solution to organ failure which circumvents the issue of organ shortage. In preclinical research settings bio-artificial organs are being developed. It is anticipated that eventually it will be possible to launch first-in-human transplantation trials to test safety and efficacy in human recipients. In early-phase transplantation trials, however, research participants could be exposed to serious risks, such as toxicity, infections and tumorigenesis. So far, there is no ethical guidance for the safe and responsible design and conduct of early-phase clinical trials of bio-artificial organs. Therefore, research ethics review committees will need to look to related adjacent fields of research, including for example cell-based therapy, for guidance. In this systematic review, we examined the literature on early-phase clinical trials in these adjacent fields and undertook a thematic analysis of relevant ethical points to consider for early-phase clinical trials of transplantable bio-artificial organs. Six themes were identified: cell source, risk-benefit assessment, patient selection, trial design, informed consent, and oversight and accountability. Further empirical research is needed to provide insight in patient perspectives, as this may serve as valuable input in determining the conditions for ethically responsible and acceptable early clinical development of bio-artificial organs.

Carbon-Based Materials for Articular Tissue Engineering: From Innovative Scaffolding Materials toward Engineered Living Carbon

Carbon materials constitute a growing family of high-performance materials immersed in ongoing scientific technological revolutions. Their biochemical properties are interesting for a wide set of healthcare applications and their biomechanical performance, which can be modulated to mimic most human tissues, make them remarkable candidates for tissue repair and regeneration, especially for articular problems and osteochondral defects involving diverse tissues with very different morphologies and properties. However, more systematic approaches to the engineering design of carbon-based cell niches and scaffolds are needed and relevant challenges should still be overcome through extensive and collaborative research. In consequence, this study presents a comprehensive description of carbon materials and an explanation of their benefits for regenerative medicine, focusing on their rising impact in the area of osteochondral and articular repair and regeneration. Once the state-of-the-art is illustrated, innovative design and fabrication strategies for artificially recreating the cellular microenvironment within complex articular structures are discussed. Together with these modern design and fabrication approaches, current challenges, and research trends for reaching patients and creating social and economic impacts are examined. In a closing perspective, the engineering of living carbon materials is also presented for the first time and the related fundamental breakthroughs ahead are clarified.

Immuno-regenerative biomaterials for in situ cardiovascular tissue engineering - Do patient characteristics warrant precision engineering?

In situ tissue engineering using bioresorbable material implants - or scaffolds - that harness the patient's immune response while guiding neotissue formation at the site of implantation is emerging as a novel therapy to regenerate human tissues. For the cardiovascular system, the use of such implants, like blood vessels and heart valves, is gradually entering the stage of clinical translation. This opens up the question if and to what extent patient characteristics influence tissue outcomes, necessitating the precision engineering of scaffolds to guide patient-specific neo-tissue formation. Because of the current scarcity of human in vivo data, herein we review and evaluate in vitro and preclinical investigations to predict the potential role of patient-specific parameters like sex, age, ethnicity, hemodynamics, and a multifactorial disease profile, with special emphasis on their contribution to the inflammation-driven processes of in situ tissue engineering. We conclude that patient-specific conditions have a strong impact on key aspects of in situ cardiovascular tissue engineering, including inflammation, hemodynamic conditions, scaffold resorption, and tissue remodeling capacity, suggesting that a tailored approach may be required to engineer immuno-regenerative biomaterials for safe and predictive clinical applicability.

Biofabrication Strategies for Musculoskeletal Disorders: Evolution towards Clinical Applications

Biofabrication has emerged as an attractive strategy to personalise medical care and provide new treatments for common organ damage or diseases. While it has made impactful headway in e.g., skin grafting, drug testing and cancer research purposes, its application to treat musculoskeletal tissue disorders in a clinical setting remains scarce. Albeit with several in vitro breakthroughs over the past decade, standard musculoskeletal treatments are still limited to palliative care or surgical interventions with limited long-term effects and biological functionality. To better understand this lack of translation, it is important to study connections between basic science challenges and developments with translational hurdles and evolving frameworks for this fully disruptive technology that is biofabrication. This review paper thus looks closely at the processing stage of biofabrication, specifically at the bioinks suitable for musculoskeletal tissue fabrication and their trends of usage. This includes underlying composite bioink strategies to address the shortfalls of sole biomaterials. We also review recent advances made to overcome long-standing challenges in the field of biofabrication, namely bioprinting of low-viscosity bioinks, controlled delivery of growth factors, and the fabrication of spatially graded biological and structural scaffolds to help biofabricate more clinically relevant constructs. We further explore the clinical application of biofabricated musculoskeletal structures, regulatory pathways, and challenges for clinical translation, while identifying the opportunities that currently lie closest to clinical translation. In this article, we consider the next era of biofabrication and the overarching challenges that need to be addressed to reach clinical relevance.

The path toward ectogenesis: looking beyond the technical challenges

BACKGROUND

Breakthroughs in animal studies make the topic of human application of ectogenesis for medical and non-medical purposes more relevant than ever before. While current data do not yet demonstrate a reasonable expectation of clinical benefit soon, several groups are investigating the feasibility of artificial uteri for extracorporeal human gestation.

MAIN TEXT

This paper offers the first comprehensive and up to date discussion of the most important pros and cons of human ectogenesis in light of clinical application, along with an examination of crucial ethical (and legal) issues that continued research into, and the clinical translation of, ectogenesis gives rise to. The expected benefits include advancing prenatal medicine, improving neonatal intensive care, and providing a novel pathway towards biological parenthood. This comes with important future challenges. Prior to human application, important questions have to be considered concerning translational research, experimental use of human fetuses and appropriate safety testing. Key questions are identified regarding risks to ectogenesis' subjects, and the physical impact on the pregnant person when transfer from the uterus to the artificial womb is required. Critical issues concerning proportionality have to be considered, also in terms of equity of access, relative to the envisaged application of ectogenesis. The advent of ectogenesis also comes with crucial issues surrounding abortion, extended fetal viability and moral status of the fetus.

CONCLUSIONS

The development of human ectogenesis will have numerous implications for clinical practice. Prior to human testing, close consideration should be given to whether (and how) ectogenesis can be introduced as a continuation of existing neonatal care, with due attention to both safety risks to the fetus and pressures on pregnant persons to undergo experimental and/or invasive procedures. Equally important is the societal debate about the acceptable applications of ectogenesis and how access to these usages should be prioritized. It should be anticipated that clinical availability of ectogenesis, possibly first as a way to save extremely premature fetuses, may spark demand for non-medical purposes, like avoiding physical and social burdens of pregnancy.

Regenerative medicine for skeletal muscle loss: a review of current tissue engineering approaches

Skeletal muscle is capable of regeneration following minor damage, more significant volumetric muscle loss (VML) however results in permanent functional impairment. Current multimodal treatment methodologies yield variable functional recovery, with reconstructive surgical approaches restricted by limited donor tissue and significant donor morbidity. Tissue-engineered skeletal muscle constructs promise the potential to revolutionise the treatment of VML through the regeneration of functional skeletal muscle. Herein, we review the current status of tissue engineering approaches to VML; firstly the design of biocompatible tissue scaffolds, including recent developments with electroconductive materials. Secondly, we review the progenitor cell populations used to seed scaffolds and their relative merits. Thirdly we review in vitro methods of scaffold functional maturation including the use of three-dimensional bioprinting and bioreactors. Finally, we discuss the technical, regulatory and ethical barriers to clinical translation of this technology. Despite significant advances in areas, such as electroactive scaffolds and three-dimensional bioprinting, along with several promising in vivo studies, there remain multiple technical hurdles before translation into clinically impactful therapies can be achieved. Novel strategies for graft vascularisation, and in vitro functional maturation will be of particular importance in order to develop tissue-engineered constructs capable of significant clinical impact.

Long-term in vivo integrity and safety of 3D-bioprinted cartilaginous constructs

Long-term stability and biological safety are crucial for translation of 3D-bioprinting technology into clinical applications. Here, we addressed the long-term safety and stability issues associated with 3D-bioprinted constructs comprising a cellulose scaffold and human cells (chondrocytes and stem cells) over a period of 10 months in nude mice. Our findings showed that increasing unconfined compression strength over time significantly improved the mechanical stability of the cell-containing constructs relative to cell-free scaffolds. Additionally, the cell-free constructs exhibited a mean compressive stress and stiffness (compressive modulus) of 0.04 ± 0.05 MPa and 0.14 ± 0.18 MPa, respectively, whereas these values for the cell-containing constructs were 0.11 ± 0.08 MPa (p = .019) and 0.53 ± 0.59 MPa (p = .012), respectively. Moreover, histomorphologic analysis revealed that cartilage formed from the cell-containing constructs harbored an abundance of proliferating chondrocytes in clusters, and after 10 months, resembled native cartilage. Furthermore, extension of the experiment over the complete lifecycle of the animal model revealed no signs of ossification, fibrosis, necrosis, or implant-related tumor development in the 3D-bioprinted constructs. These findings confirm the in vivo biological safety and mechanical stability of 3D-bioprinted cartilaginous tissues and support their potential translation into clinical applications.

Three-Dimensional Bioprinting: Role in Craniomaxillary Surgery Ethics and Future

Three-dimensional (3D) printing and bioprinting is gaining lot of momentum, especially in surgical specialties. These two technologies have wide array of applications in presurgical, surgical, and in vitro scenarios. Bioprinting can generate customized patient specific tissue engineered from specialized cells. This technology can be a gold standard in reconstructive and regenerative surgeries, if used in regulated and ethical environment. This communication focuses on basics of these technologies, their role in surgical specialties, ethical issues specific to these technologies, and its future.

Ethics and Policy for Bioprinting

3D bioprinting involves engineering live cells into a 3D structure, using a 3D printer to print cells, often together with a compatible 3D scaffold. 3D-printed cells and tissues may be used for a range of purposes including medical research, in vitro drug testing, and in vivo transplantation. The inclusion of living cells and biomaterials in the 3D printing process raises ethical, policy, and regulatory issues at each stage of the bioprinting process that include the source of cells and materials, stability and biocompatibility of cells and materials, disposal of 3D-printed materials, intended use, and long-term effects. This chapter focuses on the ethical issues that arise from 3D bioprinting in the lab-from consideration of the source of cells and materials, ensuring their quality and safety, through to testing of bioprinted materials in animal and human trials. It also provides guidance on where to seek information concerning appropriate regulatory frameworks and guidelines, including on classification and patenting of 3D-bioprinted materials, and identifies regulatory gaps that deserve attention.

How Can Systematic Reviews Teach Us More about the Implementation of the 3Rs and Animal Welfare?

Simple Summary

The three Rs stand for Replacement, Reduction, and Refinement of animal studies and were published for the first time in 1959 by Russell and Burch. Replacement refers to avoiding the use of (non-human) animals in research. Reduction implies using fewer animals, for example, by better statistical methods and better literature studies, and Refinement means reducing the discomfort and improving the welfare of animals used in experiments. The three Rs have gained more interest and popularity since the 1970s, and have now become the crucial central element in the revised legislation in Europe, the EU Directive 2010/63EU, controlling the proper use of animals in experiments in the European member states. Animals are used in order to improve the health and welfare of other non-human animals, in veterinary medicine, and of humans, for toxicological purposes and in clinical medicine. Using animals in experiments has always been subject to ethical and societal debate. At Syrcle, we have introduced the methodology of systematic reviews for preclinical animal studies since 2012. This methodology comes from the clinical field and is a key element in evidence-based medicine, as systematic reviews summarise the scientific evidence as objectively as possible. A systematic review (SR) is defined as a literature review focused on a single question that tries to identify, appraise, select, and synthesise all high-quality research evidence relevant to that question. Introducing this methodology for the preclinical animal studies seems very logical, as animal studies in clinical medicine are performed for protecting humans from ineffective or unsafe treatments. Systematic reviews thus lead to summarising evidence from preclinical studies before entering clinical trials. In addition to protecting humans, systematic reviews can also be used to implement the three Rs. Examples of how systematic reviews contribute to implementing the three Rs are provided in the following article, thus demonstrating the value for protecting animals as well.

Abstract

This paper describes the introduction of the systematic review methodology in animal-based research and the added value of this methodology in relation to the 3Rs and beyond. The 3Rs refer to Replacement, Reduction, and Refinement of animal studies. A systematic review (SR) is defined as a literature review focused on a single question that tries to identify, appraise, select, and synthesise all high-quality research evidence relevant to that question. Examples are given on how SRs lead to the implementation of the 3Rs and better science. Additionally, a broader context is given regarding societal, political, and scientific developments. Various examples of systematic reviews are given to illustrate the current situation regarding reporting, quality, and translatability of animal-based research. Furthermore, initiatives that have emerged to move further towards more responsible and sustainable research is of benefit for both animals and humans.

Bone Grafts, Bone Substitutes and Regenerative Medicine Acceptance for the Management of Bone Defects Among French Population: Issues about Ethics, Religion or Fear?

Several techniques exist to manage bone defects in patients: bone grafts (autograft, allograft, xenograft), use of synthetic bone substitutes, or use of the products of bone regenerative medicine. Studies generally focus on their efficacy, but few focus on their acceptance. Our objectives were to assess their theoretical acceptance among the French general population, and to identify issues justifying refusals, by mean of an open e-questionnaire. The questionnaire was submitted to a general French population, and explained these techniques in an understandable way. Participants were asked to say whether they would accept or refuse these techniques, specifying why in case of refusal (fear of the technique, ethical reasons, religious reasons). In total, 562 persons participated. Autograft and use of the products of bone regenerative medicine were the most accepted techniques (93.4% and 94.1%, respectively). Xenograft was the least accepted technique (58.2%). Most refusals were due to fear such as failure, pain, infection (autograft 8%, allograft 14.9%, xenograft 25.3%, synthetic bone substitutes 14.6%, and products of bone regenerative medicine 6.8%). Ethical reasons were mostly mentioned for allograft (6.4%) and xenograft (18.3%). Religious reasons were scarcely mentioned, only for xenograft (1.2%). Thus, acceptance of techniques does not seem to be greatly linked to sociodemographic characteristics in France. However, other countries with their own cultural, religious, and population patterns may show different levels of acceptance. This study shows that bone regenerative medicine is a promising research direction, reaching biological and also humanist quality standards, expected to improve the health of patients. Information is still the cornerstone to defuse issues about fear.

Beyond the Present Constraints That Prevent a Wide Spread of Tissue Engineering and Regenerative Medicine Approaches

Despite the success of tissue engineered medical products (TEMPs) in preclinical translational research, very few have had success in the clinical market place. This gap, referred to as the “valley of death” is due to the large number of ventures that failed to attract or retain investor funding, promotion, and clinical acceptance of their products. This loss can be attributed to a focus on a bench to bedside flow of ideas and technology, which does not account for the multitude of adoption, commercial, and regulatory constraints. The implementation of an alternative bedside to bench and back again approach permits investigators to focus on a specific unmet clinical need, defining crucial translation related questions early in the research process. Investigators often fail to accurately identify critical clinical adoption criteria due to their focus on improved patient outcomes. Other adoption criteria (such as price, time, ethical concerns, and place in the workflow) can cause a product to fail despite improved patient outcomes. By applying simplified business principles such as the build-measure-learn loop and the business model canvas to early-stage research projects, investigators can narrow in on appropriate research topics and define design constraints. Additionally, 86% of all clinical trials fail to result in Federal Drug Administration approval, resulting in significant economic burdens. On the reverse side, approval through the European Medical Agency is widely considered to be more direct but has its challenges. The Committee for Advanced Therapies within the European Medical Agency has received 22 market authorization applications for advanced therapy medicinal products, of which only 10 received authorization. A thorough understanding of the various regulatory pathways permits investigators to plan for future regulatory obstacles and potentially increase their chances of success. By utilizing a bedside to bench and back again approach, investigators can improve the odds that their research will have a meaningful clinical impact.

Print Me an Organ? Ethical and Regulatory Issues Emerging from 3D Bioprinting in Medicine

Recent developments of three-dimensional printing of biomaterials (3D bioprinting) in medicine have been portrayed as demonstrating the potential to transform some medical treatments, including providing new responses to organ damage or organ failure. However, beyond the hype and before 3D bioprinted organs are ready to be transplanted into humans, several important ethical concerns and regulatory questions need to be addressed. This article starts by raising general ethical concerns associated with the use of bioprinting in medicine, then it focuses on more particular ethical issues related to experimental testing on humans, and the lack of current international regulatory directives to guide these experiments. Accordingly, this article (1) considers whether there is a limit as to what should be bioprinted in medicine; (2) examines key risks of significant harm associated with testing 3D bioprinting for humans; (3) investigates the clinical trial paradigm used to test 3D bioprinting; (4) analyses ethical questions of irreversibility, loss of treatment opportunity and replicability; (5) explores the current lack of a specific framework for the regulation and testing of 3D bioprinting treatments.

Bone substitutes: a review of their characteristics, clinical use, and perspectives for large bone defects management

Bone replacement might have been practiced for centuries with various materials of natural origin, but had rarely met success until the late 19th century. Nowadays, many different bone substitutes can be used. They can be either derived from biological products such as demineralized bone matrix, platelet-rich plasma, hydroxyapatite, adjunction of growth factors (like bone morphogenetic protein) or synthetic such as calcium sulfate, tri-calcium phosphate ceramics, bioactive glasses, or polymer-based substitutes. All these substitutes are not suitable for every clinical use, and they have to be chosen selectively depending on their purpose. Thus, this review aims to highlight the principal characteristics of the most commonly used bone substitutes and to give some directions concerning their clinical use, as spine fusion, open-wedge tibial osteotomy, long bone fracture, oral and maxillofacial surgery, or periodontal treatments. However, the main limitations to bone substitutes use remain the management of large defects and the lack of vascularization in their central part, which is likely to appear following their utilization. In the field of bone tissue engineering, developing porous synthetic substitutes able to support a faster and a wider vascularization within their structure seems to be a promising way of research.

Ethical considerations in the translation of regenerative biofabrication technologies into clinic and society

Biofabrication technologies have the potential to improve healthcare by providing highly advanced and personalized biomedical products for research, treatment and prevention. As the combining of emerging techniques and integrating various biological and synthetic components becomes increasingly complex, it is important that relevant stakeholders anticipate the translation of biofabricated 3D tissue products into patients and society. Ethics is sometimes regarded as a brake on scientific progress, yet from our perspective, ethics in parallel with research anticipates societal impacts of emerging technologies and stimulates responsible innovation. For the ethical assessment, the biofabrication field benefits from similarities to regenerative medicine and an increasing ethical awareness in the development of tissue-engineered products. However, the novelty of the technology itself, the increase in attainable structural complexity, and the potential for automation and personalization are distinguishing facets of biofabrication that call for a specific exploration of the ethics of biofabrication. This review aims to highlight important points of existing ethical discussions, as well as to call attention to emerging issues specific to 3D biofabrication in bench and bedside research and the translation to society.

Scientific collaboration: a social network analysis based on literature of animal-derived regenerative implantable medical devices

The collaboration network of English publications on animal-derived regenerative implantable medical devices based on tissue engineering technology and its evolving processes and current states were mapped in this paper. A total of 10 159 English papers published before 1 January 2015 were obtained in eight databases. Social network analysis was conducted on these papers by utilizing UCINET software and Statistical Analysis Software for Informatics researched and developed by Peking University. The collaboration network has evolved from scattered formation to single-core dominated, and then to a core-edge one; collaboration has become more frequent and wider; network density and centrality have decreased; USA, UK and China are the top three countries with Wake Forest University, Harvard University and Tufts University being the top three contributing institutions cooperated mostly during the period between 2010 and 2014; plenty of edge institutes exist. In conclusion, more collaboration among different institutions and countries is needed; Edge institutions and developing countries should expand their scope of collaboration.

Ethical considerations in tissue engineering research: Case studies in translation

Tissue engineering research is a complex process that requires investigators to focus on the relationship between their research and anticipated gains in both knowledge and treatment improvements. The ethical considerations arising from tissue engineering research are similarly complex when addressing the translational progression from bench to bedside, and investigators in the field of tissue engineering act as moral agents at each step of their research along the translational pathway, from early benchwork and preclinical studies to clinical research. This review highlights the ethical considerations and challenges at each stage of research, by comparing issues surrounding two translational tissue engineering technologies: the bioartificial pancreas and a tissue engineered skeletal muscle construct. We present relevant ethical issues and questions to consider at each step along the translational pathway, from the basic science bench to preclinical research to first-in-human clinical trials. Topics at the bench level include maintaining data integrity, appropriate reporting and dissemination of results, and ensuring that studies are designed to yield results suitable for advancing research. Topics in preclinical research include the principle of "modest translational distance" and appropriate animal models. Topics in clinical research include key issues that arise in early-stage clinical trials, including selection of patient-subjects, disclosure of uncertainty, and defining success. The comparison of these two technologies and their ethical issues brings to light many challenges for translational tissue engineering research and provides guidance for investigators engaged in development of any tissue engineering technology.

Tooth-derived stem cells: Update and perspectives

Tissue engineering is an emerging field of science that focuses on creating suitable conditions for the regeneration of tissues. The basic components for tissue engineering involve an interactive triad of scaffolds, signaling molecules, and cells. In this context, stem cells (SCs) present the characteristics of self-renewal and differentiation capacity, which make them promising candidates for tissue engineering. Although they present some common markers, such as cluster of differentiation (CD)105, CD146 and STRO-1, SCs derived from various tissues have different patterns in relation to proliferation, clonogenicity, and differentiation abilities in vitro and in vivo. Tooth-derived tissues have been proposed as an accessible source to obtain SCs with limited morbidity, and various tooth-derived SCs (TDSCs) have been isolated and characterized, such as dental pulp SCs, SCs from human exfoliated deciduous teeth, periodontal ligament SCs, dental follicle progenitor cells, SCs from apical papilla, and periodontal ligament of deciduous teeth SCs. However, heterogeneity among these populations has been observed, and the best method to select the most appropriate TDSCs for regeneration approaches has not yet been established. The objective of this review is to outline the current knowledge concerning the various types of TDSCs, and discuss the perspectives for their use in regenerative approaches.

Tissue engineered constructs: perspectives on clinical translation

In this article, a "bedside to bench and back" approach for developing tissue engineered medical products (TEMPs) for clinical applications is reviewed. The driving force behind this approach is unmet clinical needs. Preclinical research, both in vitro and in vivo using small and large animal models, will help find solutions to key research questions. In clinical research, ethical issues regarding the use of cells and tissues, their sources, donor consent, as well as clinical trials are important considerations. Regulatory issues, at both institutional and government levels, must be addressed prior to the translation of TEMPs to clinical practice. TEMPs are regulated as drugs, biologics, devices, or combination products by the U.S. Food and Drug Administration (FDA). Depending on the mode of regulation, applications for TEMP introduction must be filed with the FDA to demonstrate safety and effectiveness in premarket clinical studies, followed by 510(k) premarket clearance or premarket approval (for medical devices), biologics license application approval (for biologics), or new drug application approval (for drugs). A case study on nerve cuffs is presented to illustrate the regulatory process. Finally, perspectives on commercialization such as finding a company partner and funding issues, as well as physician culture change, are presented.

Towards a richer debate on tissue engineering: a consideration on the basis of NEST-ethics

In their 2007 paper, Swierstra and Rip identify characteristic tropes and patterns of moral argumentation in the debate about the ethics of new and emerging science and technologies (or "NEST-ethics"). Taking their NEST-ethics structure as a starting point, we considered the debate about tissue engineering (TE), and argue what aspects we think ought to be a part of a rich and high-quality debate of TE. The debate surrounding TE seems to be predominantly a debate among experts. When considering the NEST-ethics arguments that deal directly with technology, we can generally conclude that consequentialist arguments are by far the most prominently featured in discussions of TE. In addition, many papers discuss principles, rights and duties relevant to aspects of TE, both in a positive and in a critical sense. Justice arguments are only sporadically made, some "good life" arguments are used, others less so (such as the explicit articulation of perceived limits, or the technology as a technological fix for a social problem). Missing topics in the discussion, at least from the perspective of NEST-ethics, are second "level" arguments-those referring to techno-moral change connected to tissue engineering. Currently, the discussion about tissue engineering mostly focuses on its so-called "hard impacts"-quantifiable risks and benefits of the technology. Its "soft impacts"-effects that cannot easily be quantified, such as changes to experience, habits and perceptions, should receive more attention.

The potential of tissue engineering for developing alternatives to animal experiments: a systematic review

An underexposed ethical issue raised by tissue engineering is the use of laboratory animals in tissue engineering research. Even though this research results in suffering and loss of life in animals, tissue engineering also has great potential for the development of alternatives to animal experiments. With the objective of promoting a joint effort of tissue engineers and alternative experts to fully realise this potential, this study provides the first comprehensive overview of the possibilities of using tissue-engineered constructs as a replacement of laboratory animals. Through searches in two large biomedical databases (PubMed, Embase) and several specialised 3R databases, 244 relevant primary scientific articles, published between 1991 and 2011, were identified. By far most articles reviewed related to the use of tissue-engineered skin/epidermis for toxicological applications such as testing for skin irritation. This review article demonstrates, however, that the potential for the development of alternatives also extends to other tissues such as other epithelia and the liver, as well as to other fields of application such as drug screening and basic physiology. This review discusses which impediments need to be overcome to maximise the contributions that the field of tissue engineering can make, through the development of alternative methods, to the reduction of the use and suffering of laboratory animals.

Reducing the number of laboratory animals used in tissue engineering research by restricting the variety of animal models. Articular cartilage tissue engineering as a case study

The use of laboratory animals in tissue engineering research is an important underexposed ethical issue. Several ethical questions may be raised about this use of animals. This article focuses on the possibilities of reducing the number of animals used. Given that there is considerable debate about the adequacy of the current animal models in tissue engineering research, we investigate whether it is possible to reduce the number of laboratory animals by selecting and using only those models that have greatest predictive value for future clinical application of the tissue engineered product. The field of articular cartilage tissue engineering is used as a case study. Based on a study of the scientific literature and interviews with leading experts in the field, an overview is provided of the animal models used and the advantages and disadvantages of each model, particularly in terms of extrapolation to the human situation. Starting from this overview, it is shown that, by skipping the small models and using only one large preclinical model, it is indeed possible to restrict the number of animal models, thereby reducing the number of laboratory animals used. Moreover, it is argued that the selection of animal models should become more evidence based and that researchers should seize more opportunities to choose or create characteristics in the animal models that increase their predictive value.

Cell therapeutic options in liver diseases: cell types, medical devices and regulatory issues

Although significant progress has been made in the field of orthotopic liver transplantation, cell-based therapies seem to be a promising alternative to whole-organ transplantation. The reasons are manifold but organ shortage is the main cause for this approach. However, many problems such as the question which cell type should be used or which application site is best for transplantation have been raised. In addition, some clinicians have had success by cultivating liver cells in bioreactors for temporary life support. Besides answering the question which cell type, which injection site or even which culture form should be used for liver support recent international harmonization of legal requirements is needed to be addressed by clinicians, scientists and companies dealing with cellular therapies. We here briefly summarize the possible cell types used to partially or temporarily correct liver diseases, the most recent development of bioreactor technology and important regulatory issues.

Is tissue engineering a new paradigm in medicine? Consequences for the ethical evaluation of tissue engineering research

Ex-vivo tissue engineering is a quickly developing medical technology aiming to regenerate tissue through the introduction of an ex-vivo created tissue construct instead of restoring the damaged tissue to some level of functionality. Tissue engineering is considered by some as a new medical paradigm. We analyse this claim and identify tissue engineering's fundamental characteristics, focusing on the aim of the intervention and on the complexity and continuity of the process. We inquire how these features have an impact not only on the scientific research itself but also on the ethical evaluation of this research. We suggest that viewing tissue engineering as a new medical paradigm allows us to develop a wider perspective for successful investigation instead of focusing on isolated steps of the tissue engineering process in an anecdotal way, which may lead to an inadequate ethical evaluation. We argue that the concept of tissue engineering as a paradigm may benefit the way we address the ethical challenges presented by tissue engineering.