Rheologica Acta strives to both archive the field of rheology while also capturing and identifying the new directions in our rapidly changing field. Since 2012, the editors and editorial advisory board have been selecting a group of researchers at the early stages of their careers and asking them to contribute an invited paper to a special issue. The selection is intended to sample a range of areas, fields, and researchers from different parts of the world and is in no way exhaustive. At each version of the issue, we are pleased at the enthusiastic response to the invitations and quality of the manuscripts resulting. These papers are original contributions and undergo the same rigorous peer review of all manuscripts published in the journal. Following the success of earlier issues (Vermant and Winter 2013, 2014; Vermant and Walker 2019), we selected a group of authors, and the results of that effort are found in this issue. The work covers a wide range of topics, techniques, and materials which suggest some of the directions of our field and identify some of the topics that will likely always be of core importance to the field. In many ways, these issues provide a snapshot of the topics that are actively being pursued by researchers in the field.

This issue includes nine manuscripts which demonstrate the breadth of the field of rheology in both fundamental and applied areas; and we see work bridging some extremely applied problems and detailed molecular-level understanding. Contributors to this issue focus on the relevance and impact of rheology in the growing field of additive manufacturing and 3D printing, both of traditional soft materials (Tammaro 2022) and complex glassy materials (Dudukovic et al. 2022). The importance of interfaces in multiphase complex materials is seen through studies of coalescence at multiple length scales (Chatzigiannakis et al. 2022) and new methods to measure interfacial rheology using microscale interfaces. (Moghaddam et al. 2022) As the growth of data driven and machine-learning-based approaches to science grow, these tools are being applied to rheometric data, and this is an area of focus of many members of the rheological community, including authors in this issue (Saadat et al. 2022). Finally, a group of manuscripts in this issue show that even the mature field of polymer melt rheology has exciting new directions, as we see work on materials as well studied as LDPE (Poh et al. 2022), which is of course vitally important as we face needing to re-process and upcycle these materials. A contribution on the high frequency behavior of polystyrene near the glass transition shows the rich behavior of this regime of material properties (Zhong et al. 2022). The last two decades have seen remarkable growth in the ability of the rheology community to connect the details of polymer structure to flow behavior, and here we see work on constitutive modelling and characterization of blends containing H-polymers, (Ianniello and Costanzo 2022) dumbbell, and ring polymers (Doi et al. 2022).

At this point, we reflect on the impact of these special issues. At the time of publication, the first three special issues (2013, 2014, and 2019) have resulted in 29 manuscripts that have been cited (as a group) more than 600 times. The most cited manuscripts from each of the three special issues include a manuscript on developing intrinsic material functions (Ewoldt and Bharadwaj 2013), characterizing swimming dynamics of micro-organisms (Li et al. 2014) and the rheology of bacteria under confinement (Liu et al. 2019). Also, worth noting is that the principal investigators of those three manuscripts all received the Metzner early career award from the Society of Rheology, as have other authors in the collection (Khair and Star 2012; Jolley and Graham 2013; Bozorgi and Underhill 2014; Golkaram et al. 2018; Callura et al. 2018; Han et al. 2019; Rogers et al. 2019). While we claim no causality, it is heartening to see that these special issues are identifying early career researchers that have a significant impact on the rheology community.

We thank the authors for their fine contributions to the journal and the field of rheology. This collection reflects current trends in the field. We hope that you enjoy these contributions by researchers in the early stages of their career as much as we have done.