Interdisciplinary engineering education: A review of vision, teaching, and support

Societal challenges that call for a new type of engineer suggest the need for the implementation of interdisciplinary engineering education (IEE). The aim of IEE is to train engineering students to bring together expertise from different disciplines in a single context. This review synthesizes IEE research with a focus on characterizing vision, teaching practices, and support.


| INTRODUCTION
Today's social, economic, environmental, and medical challenges are complex and often open ended and ill-defined (Gómez Puente, Van Eijck, & Jochems, 2013a). These challenges go beyond the traditional image of engineers' tasks and responsibilities (Vojak, Price, & Griffin, 2010). They call for a type of engineer who is socially connected and who can work both within and outside the boundaries of his or her own discipline (Barut, Yildirim, & Kilic, 2006). As a result, future engineers need the ability to access, understand, evaluate, synthesize, and apply perspectives and knowledge from fields other than their own (Czerniak, 2007). This ability would help engineers consider a large range of environmental and social factors for approaching contemporary challenges (Lattuca, Knight, & Bergom, 2013).
In response to these demands, the implementation of interdisciplinary engineering education (IEE) is recommended (Lattuca, 2001) to train engineering students to bring together combinations of theories, concepts, and methods from different disciplines in a single context (Lattuca, Voight, & Fath, 2004). Previous review studies have shown that engineering education treats interdisciplinarity as a concrete capability in this respect (Gero, 2014;Lam, Walker, & Hills, 2014), which can and should be taught and acquired in educational settings (Barth & Michelsen, 2013;Czerniak, 2007). But these educational settings are often diverse in form and approach (Becerik-Gerber, Ku, & Jazizadeh, 2012). Given this diversity, it is important to align instructional design, learning goals, learning activities, and learning spaces specifically to support IEE (Gütl & Chang, 2008).
Based on a review of the research on the nature and structure of interdisciplinarity (Frodeman, Klein, & Mitcham, 2010) and on the practice of IEE, this study aims to analyze the empirical studies on current curriculum and course interventions in IEE. Earlier literature reviews have usually focused on subareas of IEE such as student barriers (Richter & Paretti, 2009) or educational programs (Becerik-Gerber et al., 2012;Lam et al., 2014). Other reviews have focused on general interdisciplinary programs broadly (Knight, Lattuca, Kimball, & Reason, 2013). As a result, these reviews have not given a comprehensive view of approaches; reported success factors and challenges in IEE; nor how educators and researchers can use this knowledge to develop, improve, and evaluate programs, courses, and assessments. We argue that, in addition and in response to the earlier review studies, the current state of the field is such that a comprehensive overview of local experiments and cases is needed (Borrego, Foster, & Froyd, 2014). Such an overview would contribute a level of awareness that will allow teachers and educational leadership to take the next step toward a more systematic and less diffuse approach to IEE.

| This review study
This review provides an analysis of studies exploring interdisciplinary courses and curricula in higher engineering education. We propose and apply a conceptual framework (see Section 1.3) to help organize and categorize the results of the studies included. We position and interpret the results through this conceptual framework to understand existing empirical descriptions of interdisciplinary engagement along with providing recommendations to synthesize what it means to engage in interdisciplinary teaching and learning. Thus, we aim to contribute to an understanding of the challenges of vision, teaching, and support, and their interrelations specifically for IEE. By doing so, this review helps give a structured overview of the current state of research, useful for drawing links between otherwise potentially disparate results and, in turn, identifying opportunities and potential requirements for future research to advance our knowledge of this topic effectively.
Our examination and analysis and the resulting implications for practice allow us to identify approaches and list reported success factors and challenges for the three levels of vision, teaching, and support of IEE. Such an analysis appears timely. Studies of IEE have both increased and diversified in numerous directions (Graham, 2012). Funding for interdisciplinary education and interest from administrators in interdisciplinarity have increased over the last 15 years (Jacobs & Frickel, 2009;National Academy of Sciences, 2006;National Science Foundation, 2008). Yet at the same time, the need for an integrated perspective on curriculum development and the professional development of teachers has been identified as a pressing issue (Meijers & Den Brok, 2013). Although many search for this integrated perspective as the holy grail of IEE, in practice interdisciplinarity in higher education is often implemented by mono-disciplinary people (Blizzard, Klotz, Pradhan, & Dukes, 2012). As such, the added value of this review consists of bringing together approaches and reported success factors and challenges from individual case studies that can serve as points of attention for teachers, curriculum designers, and researchers of IEE.

| Defining interdisciplinarity
One principal challenge of IEE research is defining or agreeing upon what skills, knowledge, and values are at play in effective interdisciplinary problem-solving and interactions. Any review of studies of IEE should be able to identify what counts as a contribution to interdisciplinary education. This ability depends upon having some concept of what interdisciplinary interactions are in the first place and how to distinguish them particularly from multidisciplinary and transdisciplinary interactions. However, it is not our intention to give a final definition of interdisciplinarity (cf. Frodeman et al., 2010), nor to give an historical account of the concept (cf. Czerniak, 2007), nor to dig deep into epistemological aspects of interdisciplinarity (cf. MacLeod, 2016). Because we want to do justice to the reality of the ambivalent and interchangeable use of interdisciplinarity and multidisciplinarity in educational practice, it suffices in our opinion to offer a working definition.
The working definition that studies of IEE seem to agree on is that interaction between fields of expertise requires some level of integration among those fields to count as interdisciplinary (Huutoniemi, Klein, Bruun, & Hukkinen, 2010;Klein, 2010). By contrast, multidisciplinary interactions are less likely to employ integrative processes, and the individuals involved do not necessarily learn from other disciplinary perspectives (Borrego & Newswander, 2010). Multidisciplinarity can be characterized as a combination of disciplinary components, whereas interdisciplinarity requires methodological or conceptual synthesis with the aim of deepening knowledge and skills (English, 2016). Transdisciplinarity takes this synthesis a step further by starting from two or more disciplines and applying their knowledge and skills to real-world problems or projects in collaboration with stakeholders outside the university, thus aiming to enhance the learning experience (English, 2016). Individuals in interdisciplinary teams learn from others' perspectives and produce work in an integrative process that would not have been possible in a mono-disciplinary setting (McNair, Newswander, Boden, & Borrego, 2011). The result, at least in theory, is that participants emerge from such interactions speaking "one language." The progression from multidisciplinarity to interdisciplinarity and transdisciplinarity could be considered as an increase in the complexity of the integrative task facing participants (Klein, 2013). This increasing complexity, as a result, requires learning goals that are broader-reaching than those required for a domain-specific course, which, in turn, calls for specific competence and a specific attitude among teachers (Gresnigt, Taconis, Van Keulen, Gravemeijer, & Baartman, 2014). In this context, our working definition considers interdisciplinary interactions as attempts to address real-world cases and problems by integrating heterogeneous knowledge bases and knowledge-making practices, whether these are gathered under the institutional cover of a discipline or not (Krohn, 2010). This working definition offers space for those reports and case studies that strive for interdisciplinary goals with multidisciplinary teams of teachers or students as well as those that attempt to integrate knowledge and skill from external disciplines within an otherwise disciplinary program. Yet, this definition helps distinguish interdisciplinarity from transdisciplinarity by focusing less on entirely novel problem-driven methodological development or on collaboration with participants outside the university.

| Conceptual framework
Due to its relatively nascent state (Borrego et al., 2014), research on IEE attempts to tackle educational aspects across a wide range, from basic conceptual questions about interdisciplinary education to full-scale curricula implementations. We believe it is essential to provide a conceptual framework to guide the analysis of interdisciplinary learning and practices in higher education so that teachers and curriculum designers can make sense of the literature. Our conceptual framework builds on a basic why-how-what approach (Sinek, 2009), which supports thinking about educational strategies from the ground-up. These strategies result in interdisciplinary courses and curricula based on an institution's educational vision, which is operationalized into a specific pedagogical approach, resting on specific institutional support structures. Exploring interdisciplinary courses and curricula, therefore, needs to identify educational processes at three levels: vision, teaching, and support (Van den Akker, 2003; Figure 1). The boundaries of our review are defined by a focus on teaching and learning, with connections to the other two process layers.
Vision serves as a foundation for an interdisciplinary approach by describing the basic motivations and goals that are to govern an educational program. It, thus, refers to the why of an educational program (Hansen & Dohn, 2017). It ensures coherence across a program and frames, among other things, curriculum development (Marder, 2013), educational policy, and collaboration and knowledge sharing across scientific and educational faculties (Karal & Bahcekapili, 2010). For example, the vision that "graduating engineers should be able to Conceive-Design-Implement-Operate (CDIO) complex value-added engineering systems in a modern team-based environment" (Crawley, 2001, p. 4) is stipulated in the CDIO-initiative.
Our reasons for singling out vision for assessing current studies of IEE are several. First, the use of interdisciplinarity as a concept in educational contexts is often ambiguous (see Section 1.2). Furthermore, since in engineering education motivations for interdisciplinarity might be questioned by both students and staff, they require clear articulation and justification. Finally, anyone engaging with IEE needs to be aware of the values underlying particular visions and the relations between different visions and chosen teaching approaches.
Teaching processes depend on conditions and resources being in place that facilitate their development and operation, thus addressing the why, how, and what of IEE. Support consists of aspects such as infrastructure and institutional support, including available instruction rooms and laboratories, learning management systems, and other information and communication technologies (Larsen et al., 2009), tools and techniques, practice-based management, resources for developing teacher skills, incentives, and allocated time for curriculum development. Important reasons for singling out support as an issue in interdisciplinary contexts are the institutional constraints that make it difficult to work across disciplinary boundaries. For instance, while in many disciplinary educational contexts support and facilities are already in place and can be taken for granted, these resources might be insufficient or inappropriate for interdisciplinary undertakings. As such, our review focuses also on the degree to which current studies of curriculum and courses in IEE address aspects of support.

| Research questions
To do justice to the complex situation of factors and considerations related to interdisciplinarity in curricula and courses in higher engineering education, this literature review intends to synthesize existing research using the perspectives of vision, teaching, and support. Our aim to contribute to a more comprehensive understanding of the interrelated challenges of vision, teaching, and support specifically for IEE leads to the following research questions: • What aspects of vision, teaching, and support have emerged as topics of interest in empirical studies of IEE?
• What points of attention regarding vision, teaching, and support can be identified in empirical studies of IEE as supporting or challenging IEE?

| METHOD
To find examples of interdisciplinarity in engineering education and empirical evidence on whether the suggested IEE approach worked, we followed a predefined procedure (Petticrew & Roberts, 2006; see also Borrego et al., 2014) that emphasizes the following steps: formulation of research questions, searching for and screening of studies according to inclusion/exclusion criteria, description of study characteristics, appraisal, and synthesis of results. In this study, the approach chosen was an aggregative synthesis of results (Dixon-Woods et al., 2006). Searching, selecting, and data F I G U R E 1 Interdisciplinary engineering education (IEE) educational processes and main themes at three key levels van den BEEMT ET AL. extraction were done systematically (see also Petticrew & Roberts, 2006). As we started from the conceptual model, vision-teaching-support, we did not use a straight bottom-up approach (see also Thomas & Harden, 2008). Our aggregative synthesis combined both bottom-up and top-down approaches in an iterative manner. In contrast to a systematic review, which analyses a set of studies from a statistical perspective (Grant & Booth, 2009), our review is a qualitative analysis across studies (Dixon-Woods et al., 2006), which allows for identifying aspects and themes. This approach aligns with our aim of organizing and situating current results in IEE.

| Step 1: Searching for studies
Target articles were identified through the Web of Science and Scopus databases. These databases include scientific publications from all fields and from societies such as the Institute of Electrical and Electronics Engineers (IEEE) and the American Society for Engineering Education (ASEE). The ERIC database was used as well to include educational sources. Queries were performed with the search terms "interdisciplinary" OR "multidisciplinary" OR "transdisciplinary" AND "engineering education." Additional queries with hyphenation were performed (i.e., "inter-disciplinary," "multidisciplinary," and "trans-disciplinary") to account for differences in English language writing. The search terms were applied on the fields title, abstract, and keywords. Based on the aims and research questions, empirical studies with the document type article were selected. Articles published in international peer-reviewed journals were preferred over conference papers because they undergo rigorous review and to avoid additional criteria for evaluating the quality of potentially numerous papers. Because of our group's language proficiencies, only articles written in English were considered.
Initially, the search was conducted at the end of 2015. To better reflect the nascent state of the literature, a 10-year period was chosen. As the final search was conducted in November 2016, it was decided to include 2016 as well. This review, thus, covers articles published from 2005 up to and including 2016. The searches resulted in 996 unique abstracts ( Figure 2). All search results were merged in a Microsoft Excel spreadsheet, including abstracts of all papers.

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Step 2: Surface level screening based on criteria for inclusion Step 2 consisted of surface level screening by reading titles and abstracts and aimed to identify only relevant articles that met the following criteria for inclusion: 1. The article investigated curriculum or course-related aspects of IEE (e.g., curriculum analysis; curricular aspects such as goals, content, structure, and design of instruction; interdisciplinary student-projects; or courses within the context of interdisciplinary fields). 2. Interdisciplinarity in engineering education needed to be central to the case and/or argumentation; both interactions between engineering fields and between engineering and other scientific fields were considered.
The remaining 99 papers were evaluated in terms of study quality. However, since we intended to situate and interpret current research, this evaluation was not used to exclude any of the papers. We reserve our comments on the quality of current research for the Discussion section.

| RESULTS
In this section, we first give methodological characteristics of the studies in our review. The descriptive results indicate that a majority of the included studies used a case study approach to investigate professional skills, problem-based learning (PBL), or interdisciplinary learning. The descriptive results are followed by a discussion of topics of interest surrounding vision, teaching, and support as they emerged from the included studies (see Section 3.2.1). For vision, we identified a variety of motivations for IEE. Topics of interest for teaching addressed characteristics of learning, instruction, and assessment. The main topics for support addressed institutional barriers and support for students and teachers. Finally, we focus on points of attention regarding vision, teaching, and support that were reported as success factors and challenges in individual cases. The reported success factors include taking a system approach, employing real-world problems as exemplars and tasks, involving reflective dialogue, and aspects of infrastructure and collaboration. Reported challenges address institutional barriers, complexity, and acquiring adequate levels of support.

| Methods and participants
Descriptive results of our review (Table 1) show a majority of empirical case studies, followed by perception research and curriculum analyses. Quantitative survey methods for measuring student or teacher perceptions of interdisciplinary projects or courses were applied more frequently than other methodological options (n = 32). Also, many used a combination of quantitative and qualitative approaches to help develop both a general and a deeper understanding of what happened in courses or programs. The nine studies reporting literature reviews, all applied qualitative methods. One of the eight studies reporting curriculum analysis applied quantitative methods and one mixed methods. A total of 64 studies reported the number of students involved, ranging from 4 to 5,249, with a median of 38 and two-third of these studies having 100 or fewer participants (see also the overview of the studies included in the Appendix). Methods sections usually did not report the participants' gender, age, or other demographics. Exceptions are, for instance, Barnard, Hassan, Dainty, and Bagilhole (2013), who reported gender division, and Barut et al. (2006), who reported country of origin of respondents. Approximately 20% (n = 16) of all case studies involved interdisciplinary learning within a single discipline with the aim of incorporating outside materials and nondisciplinary project goals. One example is a chemical engineering case study in which the main goal was to expose engineers to nonengineering knowledge for the development of their professional skills in a societal context (Abbas & Romagnoli, 2007). This example implies that authors do not always conceptualize cross-disciplinary collaboration as an essential aspect of interdisciplinarity or interdisciplinary learning. Sustainability issues often offered an educational context for cases (n = 15), while PBL or project-based learning (PjBL) appeared to be the dominant educational paradigms used in IEE. One substantive conceptual framing for structuring and motivating IEE often drawn upon in our collection was a systems approach. In this context, engineering education and research perceive a system as a collection of components undergoing dynamic interaction with one another, often across disciplinary domains, and a system approach as the required set of skills needed to handle such systems (Gero, 2014). Such skills include metacognitive abilities such as systems-thinking and T-shape competencies, in which a core strength of disciplinary expertise (the vertical axis of the "T") is coupled with the ability to value and work with a broad range of people and situations (the horizontal axis of the "T") (Brown, 2005).
Systems thinking and T-shape learning were explicitly mentioned in 15 of the articles reviewed. However, many articles investigated a combination of skills and knowledge that we defined as systems thinking without referring directly to the concept. Most of these articles explicitly advocated that instruction should start by focusing on a single discipline. The horizontal axis of the T-shape was subsequently described as a capstone or a combination of knowledge from different disciplines or systems, or as a combination of professional skills, such as communication, project management, presentations, or the understanding of cultural differences. Twenty-five articles explicitly used the term "soft skills" to refer to these professional skills as part of the course or project.
We now focus on the levels vision, teaching, and support, of our framework, in an effort to identify main themes as topics of interest and reported factors that support or challenge IEE. Following our objective, we aimed for a synthesized review of results rather than an annotated bibliography. The references included serve as examples of studies that reported a particular result.

| Vision
Vision covers the motivations for interdisciplinary education-why it is advocated and what benefits are sought in the studies included here. Our results identified variation in the underlying motivations across the literature, ranging from (a) learning to solve complex real-world problems, (b) developing entrepreneurial competencies, and (c) developing socially aware engineers to the perceived need to improve existing disciplinary programs. Apart from some predominance of the first motivation, the studies reviewed were spread in terms of the motivations reported. Some studies focused on just one motivation, others on multiple motivations. Additionally, we identified support factors and challenges with respect to framing the goals of IEE.

| Emerging themes for IEE vision
Complex real-world problem-solving The central reported motivation behind interdisciplinarity in engineering education in the included articles is that engineers are not yet being trained well to address complex real-world problems, which require interactions across disciplinary boundaries (Lansu, Boon, Sloep, & Van Dam-Mieras, 2013). This category includes motivations from new interdisciplinary research areas such as robotics (Do, 2013) and biomedical engineering , which require solving complex interdisciplinary problems.

Entrepreneurial competencies
Today's economic pressure on engineers to be entrepreneurial motivated authors to stress the value of interdisciplinary team projects for better preparing engineering students to work in industry (Borrego, Karlin, McNair, & Beddoes, 2013) or even learning to start their own business (Klapper & Tegtmeier, 2010). This motivation appears to be guided by ideas about what future workplaces will look like and what industry demands from its employees (see also Cantillon-Murphy, McSweeney, Burgoyne, O'Tuathaigh, & O'Flynn, 2015;Cobb, Hey, Agogino, Beckman, & Kim, 2016).

Socially aware engineers
Articles that focus less specifically on industry engagement and collaboration often cite an imperative to produce engineers capable of shaping their professional work. For instance, many articles in which sustainability is seen as a common motivating factor (Apul & Philpott, 2011;Brundiers, Wiek, & Redman, 2010) concluded that interdisciplinary engineers need to be capable of handling and integrating environmental, social, and economical objectives into their work not only through engagement with social scientists or societal groups outside academia but also in terms of their own values (El-Adaway, Pierrakos, & Truax, 2015). Authors motivated by ecological sustainability stressed the need for awareness among engineers of social, political, economic, and environmental constraints (Apul & Philpott, 2011;Dewoolkar, George, Hayden, & Rizzo, 2009). They emphasized that IEE should promote this awareness through realworld, problem-solving scenarios and experiences instead of through disciplinary learning alone (Krohn, 2010). When the purpose of IEE is perceived as cultural, it can serve to reshape engineering attitudes and facilitate open-mindedness and improved cultural knowledge (Kabo & Baillie, 2009).

Improving disciplinary programs
Internal disciplinary benefits of interdisciplinarity were sometimes prioritized in articles that detail such benefits in terms of disciplinary knowledge and understanding, creativity or adaptability (Collier, Duran, & Ordys, 2013;Lattuca et al., 2004). From this point of view, included studies rationalize interdisciplinarity as a good source for training relevant professional skills (Hayden et al., 2011;Iyer & Wales, 2012) such as project management, working in teams, or making presentations (Aquere, Mesquita, Lima, Monteiro, & Zindel, 2012). Gardner et al. (2014) emphasize students learning the values and norms of outside disciplines with which a student is interacting, requiring a degree of socialization to interdisciplinarity among students and faculty alike.
Furthermore, when students are forced to think about their knowledge structures in a critical and relational way, interdisciplinarity both generates and relies on the development of meta-cognitive skills (Goddiksen & Andersen, 2014). These specific skills enable students not only to spot the limitations and capabilities of different disciplinary perspectives and to learn how to integrate them (Ivanitskaya, Clark, Montgomery, & Primeau, 2002) but also to develop knowledge of their own disciplinary structure. Several articles conceptualized the goal and motivation for IEE in these terms and studied empirically what engineers and others gain through interdisciplinary collaboration in terms of higher order cognitive skills (Ertas, Frias, Tate, & Back, 2015;Gardner et al., 2014;Gorbet, Schoner, & Taylor, 2008).

Supporting factors
Concepts and theory related to a systems approach as we described above provide a set of resources to help conceptualize interdisciplinarity in more concrete terms. They promote a contextual understanding of concepts and awareness of the contextual problems of related disciplines. A system approach to curriculum and courses integrates contentbased teaching methods with PBL (Hayden et al., 2011;Rashid, 2015) and, thus, provides specific guidance knowledge and skill requirements, and learning goals for IEE.
Furthermore, one study reported that identifying vision and related demands can be supported by involving engineering professionals (Lansu et al., 2013). These professionals, it is suggested, can play a strong role in identifying the skills relevant for today's engineers to help define vision and design curricula that can meet professional demands.

Challenges
Institutional barriers, such as the disciplinary departmental structure of colleges and universities, are reported to appear particularly resistant to interdisciplinary programs (McNair et al., 2011). These barriers could impede clear conceptualizations of notions of interdisciplinarity and attendant goals governing course or curricula designs. As a result, there may be little attempt to integrate course subject-matter or assessment regimes. Two of our studies reported that without shared notions of interdisciplinarity, engineers will usually find it easier to avoid crossing institutional boundaries and confronting institutional conflicts such as scheduling and time-frame conflicts by maintaining a largely mono-disciplinary program (Bacon et al., 2011;Cantillon-Murphy et al., 2015). Borrego and Newswander (2010) reported that the complexity and diversity of interdisciplinary engineering complicates the ability of teachers to conceptualize the goals of interdisciplinary learning in any concrete way. Many specifications of skills, such as communication and teamwork, reported in the articles included appear vague: "ability to list, give and receive feedback" or "acquire language skills to move comfortably across disciplinary boundaries" (Borrego & Newswander, 2010, p. 76). Vague conceptualizations from vision to teaching can, thus, lead to unclear learning goals, making it also difficult to translate these into concrete assessments that measure what they are supposed to.

| Teaching
The primary process of teaching includes, among other elements, learning goals, pedagogies, assignments, and assessment. The main themes emerging from our results address (a) student participation and group composition, (b) pedagogies and scaffolding applied, (c) assessment characteristics, and (d) procedures. Again, we also identified various supporting and challenging factors with respect to structuring teaching.

Student participation and group composition
One of the course design aspects reported is whether and how to combine students from different disciplines collaboratively or whether to simply import knowledge and skills. It appeared that in 16 articles, IEE was organized within a single discipline by bringing in materials from other fields, for instance by bringing sustainability to a chemical engineering program (Abbas & Romagnoli, 2007) or system thinking skills to an engineering program (Gero, 2014;Rashid, 2015). This disciplinary approach is reported to encourage students to consider multiple perspectives, while a multidisciplinary teacher team supervises the course. Other programs (n = 37) organized interdisciplinary education by having students from different engineering disciplines in one course (Dewoolkar et al., 2009) or by combining engineering students with medical students (Cantillon-Murphy et al., 2015;Tafa, Rakocevic, Mihailovic, & Milutinovic, 2011) or with students from social sciences (Kabo & Baillie, 2009). Learning to work with specialists from other fields and learning to know and appreciate methods and vocabulary from these fields are, thus, included in the learning goals of these courses.
Pedagogies and scaffolding PBL and PjBL are the most often applied educational formats in IEE settings in the studies included here. PBL aims to cover relevant content and procedures through careful selection of authentic problems that student teams have to study through an enquiry process (Barrows & Tamblyn, 1980). In PjBL student, teams are offered open and ill-defined real-world challenges and problems (Brundiers et al., 2010). Student teams collaborate over a long period of time, sometimes scaffolded by milestones to present their working plan, draft ideas, or prototype artefacts. Real problem owners were reported to be involved not only as stakeholders but also as reviewers of solutions (Dewoolkar et al., 2009;Redshaw & Frampton, 2014).
To avoid overly difficult problem tasks, research suggests that courses and projects should provide structures that scaffold students toward success (Borrego et al., 2013). Scaffolding structures useful for open-ended assignments and illdefined problems (Gómez Puente et al., 2013a) include problems structured around goals that are achievable in one term and assignments defined according to levels of difficulty, with learning goals related to those levels (Do, 2013). Additionally, integration of introductory laboratory practicals was reported to help students tie concepts together (Rashid, 2015).

Assessment characteristics
Included studies suggest that assignments for interdisciplinary education need careful construction, balancing all involved disciplines and offering tasks that allow active engagement of all team members (Apul & Philpott, 2011). Assignments can include directions with respect to roles that student teams should divide among their members (Hamade & Ghaddar, 2011). Some included studies discussed how complex problem-solving skills are linked to realworld problems that often bring interdisciplinary settings and multiple stakeholders (Gomez- Puente et al., 2013a). Also, studies suggested how in courses focused on entrepreneurial skills, market research or business case tasks can be part of the assignments (Cobb et al., 2016;Klapper & Tegtmeier, 2010). Strategies such as CDIO (Crawley, 2001) and challenge-based learning (Kohn Rådberg, Lundqvist, Malmqvist & Hagvall Svensson, 2018) can be used to decide if and how each of these typical engineering phases will be addressed.

Assessment procedures
Assessment in general is considered underdeveloped and underdiscussed in interdisciplinary educational contexts (Boix Mansilla et al., 2009;Richter & Paretti, 2009). Only 11 of the articles in our review discussed aspects of assessment. Half of those presented a solid assessment strategy directly targeting interdisciplinary skills (Hasna, 2010). The others relied on a preexisting strategy for their otherwise interdisciplinary courses. Despite some attention to measuring levels of integration in student knowledge (Borrego, Newswander, McNair, McGinnis, & Paretti, 2009) or for assessment regimes (Cantillon-Murphy et al., 2015;Soares, Sepulveda, Monteiro, Lima, & Dinis-Carvalho, 2013), our set of articles and the extent to which they tackled assessment raised specific supporting aspects and challenges with respect to handling assessment in IEE (see next sections).
When interdisciplinarity is conceptualized in terms of professional skills, it appears that traditional means, such as reflective journals, meeting notes, or peer assessment, can be effective for measuring student learning in both interdisciplinary and disciplinary contexts (Kavanagh & Cokley, 2011). However, when assessing the quality of interdisciplinary student work, the different epistemic values, learning goals, and evaluation standards brought in by the disciplines involved appear to complicate the construction of assessment procedures for interdisciplinary courses (Borrego et al., 2009).

Support factors
The use of interdisciplinary, real-world problems as a hook for projects was reported to increase student motivation (Brundiers et al., 2010;Guardiola, Dagli, & Corns, 2013). Students reported higher motivation if they feel the topic is directly related to practical needs. Students, thus, also learn to understand decision-making processes and the ambiguity and lack of information that can attend real projects. Related IEE supporting factors which were also reported included role-based learning within student teams or other supporting formats and exercises for teamwork (Hamade & Ghaddar, 2011). Additionally, Do (2013) reported the importance for students to have a good understanding of the content required to handle their project topic. One often identified point of attention was the importance of having students learn about the other disciplines involved in the course and learn to respect these disciplines (McNair et al., 2011), despite their different epistemologies.
Assessing students through a dialogue that stimulates reflection is reported as an alternative approach for measuring, monitoring, and promoting interdisciplinarity effectively, at least in the case of graduate students (Manathunga, Lant, & Mellick, 2006. Instead of perceiving interdisciplinarity as a matter of hitting interdisciplinary skill targets or assessment goals, this type of dialogue mediates the development of interdisciplinary attributes. In this approach, students assemble evidence of interdisciplinary and other learning (in what is called a Research Student Virtual Portfolio) and receive direct feedback from their supervisors on how to improve their learning. Such an approach is likely to be a fine-grained and contextually sensitive way to assess interdisciplinarity in a given case.

Challenges
Challenges reported with respect to teaching include a possible underestimation by curriculum designers of the level of support students need in interdisciplinary contexts (Soares et al., 2013). The project management and teamwork required for modern professional contexts need targeted instructional intervention and support based on effective group coordination models that help students to structure and manage their teams (Aquere et al., 2012). Students have been reported to view interdisciplinarity with ambivalence in general (Barnard et al., 2013). Some articles reviewed here argue that engineers can be highly resistant to interdisciplinary learning goals, such as improving their cultural, social, and political sensitivity (Kabo & Baillie, 2009).
Some authors argue that systems thinking is needed rather than integrated courses or projects, yet they notice a lack of dedicated courses dealing with systems thinking for beginner students (Frank & Elata, 2005). This lack might be caused by the absence of enough educational materials (Blizzard et al., 2012) as well as a lack of ideas on how systems thinking could be taught within the time constraints of current curricula (Blizzard et al., 2012). Another reported cause is the complexity of designing an interdisciplinary curriculum, such as deciding on an order of topics or describing content from different domains (Bächtold, 2013). Two frequently found lines of thinking can be distinguished regarding what students should learn first: single discipline knowledge (Bächtold, 2013) or broader skills (Borrego et al., 2013). By referring to constructivist theories, the single discipline approach argues that students need to develop in-depth knowledge of their chosen discipline first before they can construct knowledge together with others. The other approach prefers a broad overview of the field before students can understand the depth of their specific field. A third, less often encountered approach starts with a whole-systems design and subsequently works in iterative cycles going between disciplinary and broad learning (Blizzard et al., 2012;Iyer & Wales, 2012).
Various types of problems reported in other educational contexts for any group project setting, such as social loafing and lack of trust or shared mental models (Borrego et al., 2013), appear in interdisciplinary contexts as well. They raise the issue of the degree to which instructors need to actively scaffold and reinforce professional identities over institutional ones during an interdisciplinary program or project rather than leaving students to develop such identities themselves (McNair et al., 2011).
Open-ended problems might be thought to encourage interdisciplinary interaction and flexible thinking. However, Gómez Puente et al. (2013b) report that students, when asked, preferred a scenario with more detail and clearer signposts on what was required for a result that would be advanced enough for their educational level. Learning how to cope with the challenge of interdisciplinary work can be accomplished by starting with less open-ended, more structured problems, while working toward open-ended and ill-defined projects (Gómez Puente et al., 2013b).
Some of these results point to the importance of the constructive alignment between learning goals and assessment tools (Biggs, 1999), particularly in interdisciplinary learning contexts in which the expectations of students may seem less structured or clear. However, the paucity of articles addressing assessment suggests there are still challenges to be faced, particularly with respect to aligning learning goals of interdisciplinary courses and programs. Problems related to assessment and alignment can be avoided through the reflective dialectic process between students and their supervisors reported above (Manathunga et al., 2007). Students are supported through this communication and can adapt their research toward developing their own interdisciplinary skills. This approach may not yield any type of standardized results, but it does bring the assessment process into strong constructive alignment with skill development in a flexible way. The involvement of assessment specialists might help in constructing better tools for disciplinary experts to use such as rubrics, surveys, and interviews (Borrego & Cutler, 2010) or a press conference (Redshaw & Frampton, 2014). Similarly, including community partners (Dewoolkar et al., 2009) or industrial partners (Larsen et al., 2009) can help ensure that students acquire skill-development goals related to professional communication and communication with stakeholders.

| Support
Support of education covers the availability of, among other things, laboratories, instruction rooms, a learning management system, information and communication technologies, and infrastructure (Larsen et al., 2009). Coordination (Aquere et al., 2012) and institutional support for the development of teacher skills (Karlsson, Anderberg, Booth, Odenrick, & Christmansson, 2008) are also considered part of support. The general educational research literature has found that support of teacher professional learning (Jansen in de Wal, Den Brok, Hooijer, Martens, & Van den Beemt, 2014), social learning (Darling Hammond, Wei, Andree, Richardson, & Orphanos, 2009), and infrastructure (Becerik-Gerber et al., 2012) are essential for reaching desired quality standards in teaching and learning. We focus here on the main emerging themes (a) teacher support, (b) institutional barriers, and (c) student support. Subsequently, we identify support-related challenges although we note exploration of this topic is limited and insufficient for distinct support and challenges sections.

| Emerging themes for IEE support
Teacher support Providing instructors with the right type of training and advice for preparing and educating students in interdisciplinary work appeared a large concern in the studies reviewed (Gardner et al., 2014). This concern included training teachers in the use of nontraditional or research-level problems (Ding, 2014), or in concepts of interdisciplinarity (Gardner et al., 2014), or showing teachers how to structure their role as supervisors who provide timely interaction with students during open-ended problem-solving (Gómez Puente et al., 2013b).
Strategies for enhancing interfaculty relationships to support interdisciplinary education were often discussed in the studies reviewed here (Ferrer-Balas et al., 2008). These strategies were reported to include creating the right external links to business partners and internal links among different university programs to generate viable interdisciplinary entrepreneurship programs (Lehman, 2013). In this context, a shortage of the all-important institutional support and resources for teachers to develop external relationships for collaborative PBL purposes was reported (Lantada, Bayo, & Sevillano, 2014). Some authors discussed support in terms of availability of laboratories (Rashid, 2015) or a dynamic infrastructure or classroom design (Bocconi, Kampylis, & Punie, 2012;Larsen et al., 2009) as a prerequisite for IEE.

Institutional barriers
Teachers who lack interdisciplinary experience themselves may also lack enthusiasm or willingness to invest in the development of interdisciplinary programs (Gardner et al., 2014). Dewoolkar et al. (2009), for instance, reported a shortage of institutional incentives on the instructor's behalf to put time into interdisciplinary course design. Nonetheless, some included studies suggested that teachers need more institutional training and support to play a role in their student's professional skills development (Lantada, et al. 2014) and interdisciplinary training (Gardner et al., 2014).

Student support
Redshaw and Frampton (2014) report that from a student's point of view, a student needs support to communicate, integrate disciplines, and utilize peer-related skills. This support can include the use of evidence-based group structures that best facilitate interdisciplinary teamwork (Borrego et al., 2013). A few authors argued for the use of information technology and computer software to encourage and facilitate the group interactions necessary for collaborative work and interactive learning (Klein, 2013;Makrakis & Kostoulas-Makrakis, 2012). Students in interdisciplinary contexts are reported to have explicitly asked for access to experts (Redshaw & Frampton, 2014) and to connect with ideas, interests and people (Bocconi et al., 2012). Nonetheless, a face-to-face learning environment was not explicitly designed nor analyzed in most of the reviewed articles.

| Supporting and challenging factors for IEE support
Institutional practices and standards tend to hinder IEE because funding, tenure, and review processes are oriented along disciplinary lines (McNair et al., 2011;Hasna, 2010). In this context, the "siloed nature" of academia was referred to using various phrases (Borrego & Newswander, 2010;McNair et al., 2011). Apart from the availability of laboratories and related infrastructure (Rashid, 2015), these results suggest teachers need institutional support to collaborate on course building. Hence, there is a reported overall need for educational management to cultivate interdisciplinarity as a legitimate institutional identity and goal (McNair et al., 2011).

| DISCUSSION
This review applied a conceptual framework of vision, teaching, and support to synthesize and categorize current results and emerging themes in IEE. These aspects are interrelated because vision (the why) needs to be translated into teaching (how and what), which, in turn, requires support. Conversely, teaching should aim to meet a guiding vision, and support should be applied to remove barriers for students and teachers. Our work in this review intended to support or facilitate practice related to IEE, in which the interrelated challenges of vision, teaching, and support are all at play, by collecting and organizing current results based on these elements. In what follows, we discuss the limitations of our review, the implications of both the results and this study in general for IEE implementation, and suggestions for future research.

| Limitations
Our Results section outlined the results from the set of studies reviewed here. Many of these results were often derived from only a few studies based on specific cases. Furthermore, as we suggest below, there is a lack of conceptual consistency across studies. As a consequence, there is uncertainty about the generalizability of these case results. We have avoided for the most part drawing generalizations about what may or may not work extensively across all IEE contexts in favor of those reporting findings as individual results, and we would caution against applying these results without due attention to the details of the case reported. We would also note that some of our suggestions stemming from the limited attention we report on aspects of both vision and support may be somewhat influenced by our study selection. For instance, confining ourselves to engineering education papers alone means that papers in more general educational literature covering support and vision aspects extensively or at a theoretical level were not included, giving the impression that there is little relevant literature on these themes. Of course, such general material may be relevant to engineering education as well as to other areas. A further limitation likely arises from the search terms used to identify studies. Our focus on inter-, multi-, and transdisciplinary work left out possibly relevant work using "cross-disciplinarity" or "cross-disciplinary" as its central terms for interdisciplinary interaction. Finally, the inclusion criteria of full-text available studies might have caused a bias in our results.

| Implications
While the recommendations derived from our results represent a core of findings educators and researchers can draw on, we believe the scope and limits of these results suggest opportunities and directions for future research in IEE and for improving IEE design. In the rest of this Discussion section, we concentrate on providing some directions, with the overall goal of improving our understanding of the challenges facing IEE and best practices for handling them.

| Development of vision
Despite our identification of several overlapping and distinct visions underlying contemporary research, there remains some lack of concreteness with respect to how IEE is conceptualized and motivated in the studies included here. The primary motivation for IEE is found in the perceived complex nature of modern engineering practice (Gómez Puente et al., 2013a;Vojak et al., 2010), and the main advice is to organize education by means of real-world, problem-solving scenarios and experiences (Bacon et al., 2011;Barut et al., 2006;Brundiers et al., 2010;Hasna, 2010;Larsen et al., 2009). However, as some of our results show, visions of interdisciplinarity constructed around metaphorical or abstract concepts such as integration and communication render it difficult for interdisciplinarity to be translated into procedural skills and abilities (see Sections 3.1 and 3.2, particularly on assessment). As a result, it appears challenging to define clear learning goals and, in turn, concrete assessment formats. Many of the challenges of IEE may ultimately, we think, have their root in the difficulties of conceptualizing interdisciplinarity in terms of skills and learning goals, and the predominance of professional skill-based learning goals in our set of articles may owe something to this difficulty. More research seems to be required on translating IEE into sets of deeper cognitive and concrete procedural skills for this reason.

| Creating shared visions to help compare results
Current diverse or loose conceptualizations may contribute to difficulties drawing comparisons between results. This can prevent researchers and educators from setting standards on what counts as a good educational result in IEE. On our advice, defining clearer skills would help give a clearer set of learning or cognitive goals against which different IEE teaching strategies could be effectively identified and evaluated. T-shape learning is perhaps one of the clearest concepts to serve in this role in current IEE research (Hayden et al., 2011;Rashid, 2015). However, this approach calls for making clear to students that what they learn at university is actually of some use (Lantada et al., 2014) and to ensure that students learn how to link both axes of the T-shape model (Rashid, 2015). What we have tried to do here is at least identify the types of motivations guiding interdisciplinary education (see Section 3.2.1), each of which can be developed further into fully rationalized and articulated positions and then linked to specific learning goals. In this regard, system thinking and the CDIO framework (Crawley, 2001) as well as T-shape learning offer valuable starting points. The field should welcome research which takes up this task.

| Factoring in teacher experience
Third, interdisciplinarity seems highly desirable in course design, especially problem or project design. However, in our view there remains a lack of investigation into how to facilitate this process or what kinds of features problems or van den BEEMT ET AL. projects need for interdisciplinary learning goals to be reached, despite the preponderance of papers advocating PBL as the central educational framework for IEE. Hence, while it is accepted that problems need to be collaboratively constructed by teams of teachers from distinct disciplines (Abbas & Romagnoli, 2007;Gardner et al., 2014), interdisciplinarity still appears a relatively unfamiliar activity for many teachers.
Managing student team dynamics in interdisciplinary contexts needs its own investigation and management. It has been recommended, for instance, that teachers avoid social loafing and conflict while building trust among team members to ensure equal effort (Borrego et al., 2013). Indeed, a recent study suggests the need to define explicit discussion items for teams, including interaction rules, mutual expectations of one another's contributions and providing rules and methods for how to deal with conflict (Sortland, 2019).

| Putting more attention on assessment
As mentioned previously, in general the results show relatively infrequent attention to assessment (only 15% of papers in our review) such that it is not always clear in what sense interdisciplinary education should be measured as effective. In addition, more attention could be paid to effective pedagogies and the actual process of teaching. The current focus of results appears to be primarily on students and their learning processes, with less literature critically discussing pedagogies and assessment in IEE (Richter & Paretti, 2009). A we have noted, however, generating constructive alignment between interdisciplinary learning goals and assessment procedures raises significant challenges (Borrego & Cutler, 2010;Borrego et al., 2009), and common practices for assessing professional skills may need to be updated for interdisciplinary purposes (Borrego et al., 2009;Cantillon-Murphy et al., 2015;Soares et al., 2013). That said, measuring the interdisciplinarity of a project or course result is likely to be a major challenge. We note that integration remains a vague notion which is rarely defined, making it difficult to measure in a concrete way (MacLeod & Nagatsu, 2018).
Lastly, assessment procedures should, in theory, rely on techniques that can evaluate a body of interdisciplinary work and learning as a whole. However, educational practice shows that evaluators defer to others' expertise rather than seeking genuinely common standards (Borrego et al., 2009). Even when integration is specified as an explicit learning goal, assessing and evaluating (individual) performance within teams may still be difficult (Becerik-Gerber et al., 2012).
As such, while we think employing assessors from the different fields represented in an interdisciplinary project might not be ideal, it could be the start of increased sensitivity toward interdisciplinarity among the staff involved. Not all teachers involved can be expected to be interdisciplinary experts, especially in young domains. We think there is, thus, room for investigation of a teacher team approach, guided by a course coordinator who has experience with interdisciplinary projects (Gast, Schildkamp, & Van der Veen, 2017). Such an approach might help limit teachers from deferring to their colleagues on how to grade the aspects not part of their expertise and support them in learning to recognize what good integration looks like.

| Incorporating studies of scaffolding strategies
Two-thirds of papers in this review constructed their study around a PBL or PjBL scenario. While we accept there are good reasons for treating PjBL as a canonical platform for interdisciplinary learning, we would caution against investigating only pure PjBL scenarios, and not alternatives such as course-work designs or combinations which apply both PBL and structured coursework. Indeed, given the added difficulty of handling open-ended problems when collaborators come from different fields, one would hypothesize a beneficial role to forms of scaffolding which, for instance, might give students relevant methodological tools or theoretical concepts useful for integration or indeed background preparation on the challenges of interdisciplinarity. We would, thus, suggest research in IEE not restrict itself too narrowly to PBL in this context and put time and energy into the investigation of more structured educational alternatives and scaffolding methods.

| More study of support aspects
This review found a need for further research. In approximately 20% of papers, support aspects are raised but primarily with respect to a specific teaching strategy. As mentioned, part of the reason why little research on support emerged in our review may have something to do with our focus on engineering education. Research on support may in general transcend specific disciplinary contexts and may have been studied as such. That said, leaving aside support issues in IEE may have consequences for the applicability of IEE results, and the study of support can help better gauge the generalizability of results. For instance, if we can better understand the constraints (institutional or cognitive) which inhibit the development of interdisciplinary programs and the background circumstances, including elements of facilitation, important for a program's success, we may be better able to transfer educational strategies that are successful in one context to another or at least describe the conditions under which a program design might be most effective.

| Improving the quality of current studies
This review is limited to the data that could be extracted from the articles reviewed. In general, these studies, even if they presented an IEE intervention, did not necessarily present clear implications for practice or research. If implications were formulated, we found they were often not drawn from the empirical results of the study. Furthermore, case descriptions of courses or programs often do not describe the study limitations. In this review, we give an overall impression of the important research over the decade 2005 to 2016 and how authors approach IEE. What this review cannot do is make a reliable judgement as to the precise effectiveness of certain approaches in IEE, for instance in terms of increased average scores, student satisfaction, or student numbers. No such statistical analysis has yet been attempted. Additionally, this review does not criticize the idea that interdisciplinarity is usually approached in a strongly normative rather noncritical manner.
As suggested previously, future reviews could show more awareness of support aspects and their critical role, which did not appear frequently in the studies reviewed. Studies of IEE often operate on the implicit assumption that everything is well organized in terms of teacher support, classroom organization, or scheduling, or at least that interdisciplinary courses do not differ from disciplinary ones in the extent to which these are problems. However, Lattuca et al. (2017) have investigated and identified the influence of support factors, including the potential of engineering students to gain interdisciplinary skills through cocurricular activities, the role of faculty beliefs about interdisciplinary learning, and the value of promoting interdisciplinary learning in the curriculum. Their research makes a case for specific interdisciplinary engineering programs guided by interdisciplinary teaching teams (Lattuca, Knight, Kyoung Ro & Novoselich, 2017).

| Future work
Based on our study, we raise a couple of hypotheses for future investigation. First, teachers with experience in interdisciplinary research or practice with their own interdisciplinary examples are likely to be better at designing courses and conveying interdisciplinary skills than teachers without these experiences (see also Gardner et al., 2014). We expect that educators do try to structure a course design process as a collaborative process, but this requires more interaction (Gast et al., 2017) and is accordingly more time-consuming and subject to the kinds of conflict researchers often face trying to work across disciplinary boundaries.
Second, although the literature suggests that all teachers need to be interdisciplinary, we would further hypothesize that challenges regarding teachers' mindsets and beliefs might be tackled by building a course-team around one teacher with interdisciplinary skills and knowledge, supplemented with discipline-oriented teachers.

| CONCLUSION
In this review, we analyzed 99 articles to capture the current state in research of IEE, and summarize and organize the information available for the benefit of educators and researchers. To do so, we developed and applied an analytical framework of vision, teaching, and support, which we believe captures the main issues governing the implementation of IEE. The result of this work is an expansive picture of what has been investigated since 2005, and the specific results that have been drawn from these investigations under the categories of vision, teaching, and support. Based on these results, we have identified areas where we think future research is warranted and how such research might be structured. Furthermore, we explored the role of having such a framework in IEE for providing structure, orientation, and ultimately generalizability. As such we have tried to both map current results and sketch the beginnings of a roadmap for enhancing our knowledge of IEE. Current results that reported success factors and challenges with respect to teaching promote the value of T-shape learning and the importance of both constructive alignment and more tailored assessment strategies to meet this alignment in interdisciplinary learning contexts. Our framework in this respect helps single out the importance of shared visions to the ability of IEE researchers and instructors to generate relevant and effective teaching resources and design relevant forms of institutional support. Within the topic of support, some studies have raised the need for institutional incentives, better teacher training and the application of technology to support cross-boundary interaction among students. Support remains, however, the least investigated of our themes.
Based on this review, it can be concluded that interdisciplinarity has typically been interpreted as connecting different engineering domains, with only a few examples of broader collaborations with medical sciences or social sciences thus far. Explorations of new fruitful ways to integrate interdisciplinarity into engineering education are often impeded by the historically discipline-oriented nature of academia. Overcoming this impediment can open up new opportunities if we want our students to acquire interdisciplinary skills for their future professions and professional development. Such a step when guided by educational design based on a coherent vision and supported by university management will bring us closer to the holy grail of truly IEE.

ACKNOWLEDGMENT
This study was funded by 4TU/Centre for Engineering Education, The Netherlands.  Success factor: involving students in real-life projects; "vertically integrated projects"starting from simplified tools in the first year, followed by a progression onto more complex methods and strategies; distributed design teams; increased product complexity; design for extended product lifecycle. Challenge: how to encourage students to think critically.
Author ( Future changes in engineering education should be guided by research on expertise and the learning processes that support its development. Engineering education should encompass a set of learning experiences that allow students to construct deep conceptual knowledge, to develop the ability to apply key technical and professional skills fluently, and to engage in a number of authentic engineering projects. Engineering curricula and teaching methods are often not well aligned with these goals. Curriculum-level instructional design processes should be used to design and implement changes that will improve alignment. The academic culture in engineering may discourage development and implementation of experiences that promote the use of deep approaches to learning. (Continues) van den BEEMT ET AL.
Author ( Learning activities were designed to offer the chance for students to interact asynchronously and synchronously, negotiate meaning and reflect on their learning and viewpoints through collaborative problem solving. Using a participatory curriculum development approach ensures that all the groups and individuals who have a real interest in the program are actively involved in some way in the project during various stages. Through this approach contextualized teaching and learning become more feasible as those involved bring their own experiences to the learning process. A rich learning environment encourages shared meaning and shared inquiry as well as multiple learning styles and multiple representations of knowledge.
Author ( Two or more courses joining in a designette results in a multidisciplinary learning activity; multiple subjects are integrated and applied to open-ended problems and grand challenges. This practice helps foster a culture of design and enables the introduction of multidisciplinary design challenges.
Designettes are found to increase students' understanding of engineering concepts.