## 1 Introduction  
Photo-mediated ultrasound therapy (PUT) is a non-invasive technique based on photoacoustic cavitation produced by applying ultrasound bursts and laser pulses synchronously [1, 2, 3, 4]. The strong optical absorption of hemoglobin enables the selective treatment of blood vessels. PUT has been shown to cause minimal collateral damage to adjacent tissues [5] with weak optical absorptions. PUT was also shown to be highly precise in targeting the blood vessels and efficient compared to laser-only treatment [6]. The clinical potential of PUT is currently explored for treating neovascularization and vascularization in the choroid and retina, which lead to the pathogenesis of age-related macular degeneration and diabetic retinopathy [7, 8]. The main mechanism of PUT is enhanced cavitation activity in the targeted vessels [9, 10, 11, 12, 13, 14, 15, 16]. The enhanced cavitation activity can induce strong mechanical stresses in the vessels. These stresses directly influence the physiological functions of blood vessels by impacting platelets, red blood cells, and endothelial cells lining the inner walls of blood vessels [9; 10], resulting in coagulation [13], hemorrhage [12; 17], and vasoconstriction. To date, the impact of PUT on endothelial cells has not been investigated. Vascular endothelial cells play important roles in many physiological functions of blood vessels [18; 19]. Both laser treatment and ultrasound can impact endothelial functions. The effect of ultrasound on vascular endothelial cells has been examined for its applications in drug delivery [20; 21; 22; 23; 24; 25], gene therapy [24; 26; 27; 28], wound healing [29], deoxyribonucleic acid and protein synthesis [30], tumor dissection [31], and cancer therapies [32; 33; 34]. The effect of laser treatment on vascular endothelial cells has been investigated in wound repair [35; 36], tissue regeneration [37], and therapeutic angiogenesis [38]. Nitric oxide (NO) regulates vascular, biological, neurological, and immunological functions [39; 40]. It can be released when the endothelium is subjected to shear stress due to blood flow and changes related to blood flow [41; 42; 43; 44]. Prostacyclin (PGI\({}_{2}\)) is co-released with NO from the endothelial cells and forms a specific association in the regulation of vascular and platelet function [45]. Shear stress has been found to increase the release of PGI\({}_{2}\) from the endothelial cells [46]. We developed a blood vessel model based on the polydimethylsiloxane (PDMS) channel. PDMS has been widely used in developing blood vessel models in vitro for various purposes, such as studies of tumor microenvironment, endothelial biochemical production, drug transport, and blood-brain barriers [47; 48; 49; 50; 51]. PDMS is safe, biocompatible, hemocomputable, elastic, clear, and stable [52; 53; 54; 55; 56; 57; 58]. Its biologically inert surface prevents microbial growth, making it ideal for biomedical applications. It is also porous and extremely permeable to gases such as oxygen and carbon dioxide. This makes it perfect for cultivating cells for in vitro studies and hydrogels for wound healing and contact lens [59; 60]. To promote cellular adhesion to the channel, the channel is coated with type I collagen [61], fibrin [48; 62], or fibronectin [47; 49; 50; 51]. Collagen is used in this study as it constitutes the major structural protein in the body [63]. To facilitate endothelial blood vessel formation, type I collagen is used [48]. Following this, the cell is seeded and allowed to reach confluence. Though micro-circular channels fabricated using various combinations of microfabrication techniques were reported [64; 65], none of them were specifically designed for ultrasound-related testing. There is no evidence of any study that uses a similar in vitro vessel model to understand the effect of ultrasound, laser treatment and PUT on endothelial cells. We used needles as molds, as used by [PERSON] et al. [62] and [PERSON] et al. [49], to produce a circular vessel model with no irregularities.