The chorioallantoic membrane (CAM) is a highly vascularized avian extraembryonic membrane widely used as an in vivo model to study angiogenesis and its inhibition in response to tissues, cells, or soluble factors. In recent years, the use of CAM has become an integral part of the biocompatibility testing process for developing biomaterials intended for regenerative strategies and tissue engineering applications. In this study, we used the chicken ex ovo CAM assay to investigate the angiogenic potential of innovative acellular biopolymer polyhydroxybutyrate/chitosan (PHB/CHIT) scaffold, which is intended for the treatment of hard tissue defects, depending on treatment with pro- and anti-angiogenic substances. On embryonic day (ED) 7, the experimental biomaterials were placed on the CAM alone or soaked in vascular endothelial growth factor (VEGF-A), saline solution (PHY), or tyrosine kinase inhibitor (SU5402). After 72 h, the formation of vessels was analyzed in the surrounding area of the scaffold and inside the pores of the implants, using markers of embryonic endothelium (WGA, SNA), myofibroblasts (α-SMA), and macrophages (KUL-01). The morphological and histochemical analysis showed strong angiogenic potential of untreated scaffolds without additional effect of the angiogenic factor, VEGF-A. The lowest angiogenic potential was observed in scaffolds soaked with SU5402. Gene expression of pro-angiogenic growth factors, i.e., VEGF-A, ANG-2, and VE-CAD, was upregulated in untreated scaffolds after 72 h, indicating a pro-angiogenic environment. We concluded that the PHB/CHIT has a strong endogenous angiogenic potential and could be promising biomaterial for the treatment of hard tissue defects.

Replicating the in vitro properties of tissue barriers-such as the blood-brain barrier, gut, skin, lung, kidney, retina, nasal epithelium, and placenta-is crucial for many applications, including drug screening, studying molecular transport, drug delivery, and disease modeling in preclinical studies. Organ-on-a-chip (OoC) platforms are advanced three-dimensional (3D) in vitro models that aim to replicate various aspects of organ functionality within microfluidic systems by providing microenvironments akin to native tissue. When used to model the interface between two different tissue compartments, OoC technology offers a promising platform for more accurately replicating the physiology and pathophysiology of various tissue barriers in the body. This review focuses on the state-of-the-art biomimetic tissue barrier models, ranging from two-channel tissue barrier-on-a-chip systems with a thin porous membrane to hydrogel-based membrane models. Specifically, it explores the engineering of tissue barrier-on-a-chip platforms, highlighting various fabrication techniques for microfluidic chips and membranes, as well as methods for functional characterization of the engineered tissue barriers. Additionally, we discuss the development of organ-specific barrier models and multi-organ-on-a-chip systems for studying inter-organ communication. Finally, we highlight the current challenges in the field and future directions in advancing tissue barrier modeling using OoC technology.

In recent years, the chorioallantoic membrane (CAM) has emerged as a crucial component of biocompatibility testing for biomaterials designed for regenerative strategies and tissue engineering applications. This study explores angiogenic potential of an innovative acellular and porous biopolymer scaffold, based on polyhydroxybutyrate and chitosan (PHB/CHIT), using the ex ovo quail CAM assay as an alternative to the conventional chick CAM test. On embryonic day 6 (ED6), we placed the tested biomaterials on the CAM alone or soaked them with various substances, including vascular endothelial growth factor (VEGF-A), saline, or the endogenous angiogenesis inhibitor Angiostatin. After 72 h (ED9), we analyzed blood vessels formation, a sign of ongoing angiogenesis, in the vicinity of the scaffold and within its pores. We employed marker for cell proliferation (PHH3), embryonic endothelium (WGA, SNA), myofibroblasts (α-SMA), and endothelial cells (QH1) for morphological and histochemical analysis. Our findings demonstrated the robust angiogenic potential of the untreated scaffold without additional influence from the angiogenic factor VEGF-A. Furthermore, gene expression analysis revealed an upregulation of pro-angiogenic growth factors, including VEGF-A, ANG-2, and VE-Cadherin after 5 days of implantation, indicative of a pro-angiogenic microenvironment. These results underscore the inherent angiogenic potential of the PHB/CHIT composite. Additionally, monitoring of CAM microvilli growing to the scaffold provides a methodology for investigating the biocompatibility of materials using the ex ovo quail CAM assay as a suitable alternative model compared to the chicken CAM platform. This approach offers a rapid screening method for biomaterials in the field of tissue repair/regeneration and engineering.

Blood vessel embolization is a well-established treatment modality for liver cancer. Novel shear-thinning hydrogels (STH) have been developed to address the need for safer and more effective local delivery of embolic agents and therapeutics. However, embolization therapies are currently optimized in animal models, which often differ from humans at the cellular, tissue, and organ levels. We aim to evaluate the efficacy of novel embolic agents such as STH using a human-relevant in vitro model that recapitulates human hepatocellular carcinoma capillary networks. A vascularized human liver-tumor-on-a-chip model was developed to assess embolic agent performance. The effects of drug-eluting STH (DESTH) on tumor cell viability, surface marker expression, vasculature morphology, and cytokine responses were evaluated. To study the effects of embolization on microvasculature morphology independent of the chemotherapy compound, we evaluated the effect of different drug-free embolic agents on the vascular tumor microenvironment under flow conditions. DESTH treatment induced tumor cell death, downregulated the expression of epithelial cell adhesion molecules in HepG2, increased levels of cytokines such as interleukin-4 (IL-4), granulocyte-macrophage colony-stimulating factor, and vascular endothelial growth factor, and decreased albumin secretion. Furthermore, different embolic agents exert distinct effects on microvascular morphology, with STH causing complete regression of the microvascular networks. This vascularized liver tumor-on-a-chip model enables human-relevant, real-time assessment of embolic agent efficacy and vascular response and can be applied for the development of innovative and effective embolization therapies for liver cancer.