Human adipose-derived stromal/stem cells (hASC) are widely used for in vitro modeling of physiologically relevant human adipose tissue. These models are useful for the development of tissue constructs for soft tissue regeneration and 3-dimensional (3D) microphysiological systems (MPS) for drug discovery. In this systematic review, we report on the current state of hASC culture and assessment methods for adipose tissue engineering using 3D MPS. Our search efforts resulted in the identification of 184 independent records, of which 27 were determined to be most relevant to the goals of the present review. Our results demonstrate a lack of consensus on methods for hASC culture and assessment for the production of physiologically relevant in vitro models of human adipose tissue. Few studies have assessed the impact of different 3D culture conditions on hASC adipogenesis. Additionally, there has been a limited use of assays for characterizing the functionality of adipose tissue in vitro. Results from this study suggest the need for more standardized culture methods and further analysis on in vitro tissue functionality. These will be necessary to validate the utility of 3D MPS as an in vitro model to reduce, refine, and replace in vivo experiments in the drug discovery regulatory process.

Biological aging alters the metabolism and volume of adipose tissue depots. Recent evidence suggests that circadian mechanisms play a role in promoting adipogenesis, obesity, and lipodystrophy. The current study compared cohorts of younger (5–9 months) and older (24–28 months) C57BL/6 mice as a function of biological age and circadian time. Advanced age significantly reduced the weight of the brown, epididymal, inguinal, and retroperitoneal adipose depots but not total body weight. The older mice reduced their physical activity by >50% and delayed their activity initiation after light offset. The expressed transcriptome in brown and white adipose depots and liver of both cohorts displayed evidence of circadian rhythmicity; however, the oscillating mRNAs differed significantly between age groups and across tissues. The amplitude of Cry1, a component of the negative arm of the circadian apparatus, and downstream regulators such as Rev-erbα were elevated in the older relative to the younger cohorts as a function of circadian time. Overall, transcript levels differed significantly for 557 (inguinal adipose), 1,016 (liver), and 1,021 (brown adipose) expressed sequences between the cohorts as a function of age. These included transcripts encoding proteins within the canonical and non-canonical Wnt pathways. Since the Wnt pathway regulates adipose stem cell differentiation and shares a critical enzyme, glycogen synthase kinase 3β, with the circadian mechanism, the intersection between these two fundamental regulatory mechanisms merits further investigation with respect to biological aging of adipose tissues.

Female breast cancer accounts for 15.2% of all new cancer cases in the United States, with a continuing increase in incidence despite efforts to discover new targeted therapies. With an approximate failure rate of 85% for therapies in the early phases of clinical trials, there is a need for more translatable, new preclinical in vitro models that include cellular heterogeneity, extracellular matrix, and human-derived biomaterials. Specifically, adipose tissue and its resident cell populations have been identified as necessary attributes for current preclinical models. Adipose-derived stromal/stem cells (ASCs) and mature adipocytes are a normal part of the breast tissue composition and not only contribute to normal breast physiology but also play a significant role in breast cancer pathophysiology. Given the recognized pro-tumorigenic role of adipocytes in tumor progression, there remains a need to enhance the complexity of current models and account for the contribution of the components that exist within the adipose stromal environment to breast tumorigenesis. This review article captures the current landscape of preclinical breast cancer models with a focus on breast cancer microphysiological system (MPS) models and their counterpart patient-derived xenograft (PDX) models to capture patient diversity as they relate to adipose tissue.

International regulatory agencies such as the Food and Drug Administration have mandated that the scientific community develop humanized microphysiological systems (MPS) as an in vitro alternative to animal models in the near future. While the breast cancer research community has long appreciated the importance of three-dimensional (3D) growth dynamics in their experimental models, there are remaining obstacles preventing a full conversion to humanized MPS for drug discovery and pathophysiological studies. This perspective evaluates the current status of human tissue-derived cells and scaffolds as building blocks for an “idealized” breast cancer MPS based on bioengineering design principles. It considers the utility of adipose tissue as a potential source of endothelial, lymphohematopoietic, and stromal cells for the support of breast cancer epithelial cells. The relative merits of potential MPS scaffolds derived from adipose tissue, blood components, and synthetic biomaterials is evaluated relative to the current “gold standard” material, Matrigel, a murine chondrosarcoma-derived basement membrane-enriched hydrogel. The advantages and limitations of a humanized breast cancer MPS are discussed in the context of in-process and destructive read-out assays.

Cellulose nanofibrils (CNFs) and TEMPO-oxidized cellulose nanofibrils (TOCNFs) are hydrated, high-aspect-ratio biomaterials with tunable physicochemical properties, whereas human-derived extracellular matrix (ECM) hydrogels provide matrix-associated biochemical cues. In this study, CNF- and TOCNF-based hybrid scaffolds incorporating human ECM hydrogel components were developed and evaluated in vitro as platforms relevant to cutaneous wound repair. Hybrid formulations gelled at physiological temperature and exhibited formulation-dependent shear-thinning behavior, elastic properties, protein release/leaching profiles, and porous fibrillar microstructures. Selected formulations supported cell-associated metabolic activity of human dermal fibroblasts and adipose-derived stromal/stem cells under two-dimensional and three-dimensional culture conditions. Additional exploratory studies demonstrated qualitative compatibility with adipogenic culture and condition-dependent changes in wound-gap width. In the absence of in vivo validation and confirmatory biological assays, these findings are interpreted as proof-of-concept rather than evidence of wound-healing efficacy. Overall, the results demonstrate the feasibility of combining CNF or TOCNF structural networks with human-derived ECM hydrogels to generate hybrid scaffolds with wound-relevant material properties and preliminary cytocompatibility, supporting further mechanistic and preclinical evaluation.