In vitro remodeling and structural characterization of degradable polymer scaffold-based tissue-engineered vascular grafts using optical coherence tomography

Application of medical imaging methods and artificial intelligence in tissue engineering and organ-on-a-chip

Organ-on-a-chip (OOC) is a new type of biochip technology. Various types of OOC systems have been developed rapidly in the past decade and found important applications in drug screening and precision medicine. However, due to the complexity in the structure of both the chip-body itself and the engineered-tissue inside, the imaging and analysis of OOC have still been a big challenge for biomedical researchers. Considering that medical imaging is moving towards higher spatial and temporal resolution and has more applications in tissue engineering, this paper aims to review medical imaging methods, including CT, micro-CT, MRI, small animal MRI, and OCT, and introduces the application of 3D printing in tissue engineering and OOC in which medical imaging plays an important role. The achievements of medical imaging assisted tissue engineering are reviewed, and the potential applications of medical imaging in organoids and OOC are discussed. Moreover, artificial intelligence - especially deep learning - has demonstrated its excellence in the analysis of medical imaging; we will also present the application of artificial intelligence in the image analysis of 3D tissues, especially for organoids developed in novel OOC systems.

Vascular Smooth Muscle Cells Mechanosensitive Regulators and Vascular Remodeling

Blood vessels are subjected to mechanical loads of pressure and flow, inducing smooth muscle circumferential and endothelial shear stresses. The perception and response of vascular tissue and living cells to these stresses and the microenvironment they are exposed to are critical to their function and survival. These mechanical stimuli not only cause morphological changes in cells and vessel walls but also can interfere with biochemical homeostasis, leading to vascular remodeling and dysfunction. However, the mechanisms underlying how these stimuli affect tissue and cellular function, including mechanical stimulation-induced biochemical signaling and mechanical transduction that relies on cytoskeletal integrity, are unclear. This review focuses on signaling pathways that regulate multiple biochemical processes in vascular mesangial smooth muscle cells in response to circumferential stress and are involved in mechanosensitive regulatory molecules in response to mechanotransduction, including ion channels, membrane receptors, integrins, cytoskeletal proteins, nuclear structures, and cascades. Mechanoactivation of these signaling pathways is closely associated with vascular remodeling in physiological or pathophysiological states.

Critical Considerations for Regeneration of Vascularized Composite Tissues

Effective vascularization is vital for survival and functionality of complex tissue-engineered organs. The formation of the microvasculature, composed of endothelial cells (ECs) alone, has been mostly used to restore the vascular networks in organs. However, recent heterocellular studies demonstrate that co-culturing is a more effective approach in revascularization of engineered organs. This review presents key considerations for manufacturing of artificial vascularized composite tissues. We summarize the importance of co-cultures and the multicellular interactions with ECs, as well as design and use of bioreactors, as critical considerations for tissue vascularization. In addition, as an emerging scaffolding technique, this review also highlights the current caveats and hurdles associated with three-dimensional bioprinting and discusses recent developments in bioprinting strategies such as four-dimensional bioprinting and its future outlook for manufacturing of vascularized tissue constructs. Finally, the review concludes with addressing the critical challenges in the regulatory pathway and clinical translation of artificial composite tissue grafts. Impact statement Regeneration of composite tissues is critical as biophysical and biochemical characteristics differ between various types of tissues. Engineering a vascularized composite tissue has remained unresolved and requires additional evaluations along with optimization of methodologies and standard operating procedures. To this end, the main hurdle is creating a viable vascular endothelium that remains functional for a longer duration postimplantation, and can be manufactured using clinically appropriate source of cell lines that are scalable in vitro for the fabrication of human-scale organs. This review presents key considerations for regeneration and manufacturing of vascularized composite tissues as the field advances.

Simultaneous intraluminal imaging of tissue autofluorescence and eGFP-labeled cells in engineered vascular grafts inside a bioreactor

The growing demand for tissue engineered vascular grafts (TEVG) motivates the development of optimized fabrication and monitoring procedures. Bioreactors which provide physiologically-relevant conditions are important for improving holistic TEVG properties and performance. Herein we describe a fiber-based intraluminal imaging system that allows for in situ assessment of vascular materials and re-cellularization processes inside a bioreactor by simultaneous and co-registered measurements of endogenous fluorescence lifetime and exogenous marker fluorescence intensity. The lumen of 6 vascular grafts (∼4 mm diameter) were scanned by reciprocally rotating a 41° angle polished multimode optical fiber inside a protective glass tube with outer diameter of 3 mm. Tubular bovine pericardium constructs were recellularized using enhanced Green Fluorescent Protein (eGFP) transfected cells in a custom bioreactor. The imaging system has resolved consistently the cellular autofluorescence from that of tissue matrix in situ based on the lifetime fluorescence properties of endogenous molecular species. The location of the re-cellularized area was validated by the eGFP emission. Current results demonstrate the potential of this system as a valuable tool in tissue engineering for in situ studies of cell-tissue interactions in cylindrical or other 3-dimensional structures.

In Vivo Tracking of Tissue Engineered Constructs

To date, the fields of biomaterials science and tissue engineering have shown great promise in creating bioartificial tissues and organs for use in a variety of regenerative medicine applications. With the emergence of new technologies such as additive biomanufacturing and 3D bioprinting, increasingly complex tissue constructs are being fabricated to fulfill the desired patient-specific requirements. Fundamental to the further advancement of this field is the design and development of imaging modalities that can enable visualization of the bioengineered constructs following implantation, at adequate spatial and temporal resolution and high penetration depths. These in vivo tracking techniques should introduce minimum toxicity, disruption, and destruction to treated tissues, while generating clinically relevant signal-to-noise ratios. This article reviews the imaging techniques that are currently being adopted in both research and clinical studies to track tissue engineering scaffolds in vivo, with special attention to 3D bioprinted tissue constructs.

Nondestructive Monitoring of Degradable Scaffold-Based Tissue-Engineered Blood Vessel Development Using Optical Coherence Tomography

Engineered vascular grafts with structural and mechanical properties similar to natural blood vessels are expected to meet the growing demand for arterial bypass. Characterization of the growth dynamics and remodeling process of degradable polymer scaffold-based tissue-engineered blood vessels (TEBVs) with pulsatile stimulation is crucial for vascular tissue engineering. Optical imaging techniques stand out as powerful tools for monitoring vascularization of engineered tissue enabling high-resolution imaging in real-time culture. This paper demonstrates a nondestructive and fast real-time imaging strategy to monitor the growth and remodeling of TEBVs in long-term culture by using optical coherence tomography (OCT). Geometric morphology is evaluated, including vascular remodeling process, wall thickness, and comparison of TEBV thickness in different culture time points and presence of pulsatile stimulation. Finally, OCT provides practical possibilities for real-time observation of the degradation of polymer in the reconstructing tissues under pulsatile stimulation or not and in each vessel segment, by compared with the assessment of polymer degradation using scanning electron microscopic(SEM) and polarized microscope.