Session Item

The microvasculature is essential to the microenvironment, delivering metabolites and clearing tissue from wastes. Ionizing radiations have a detrimental effect on such small vessels, possibly contributing to healthy tissue damage, i.e. toxicity, following radiotherapy.
We present an advanced radiobiological model of microvasculature that allows (i) sample irradiation in a controlled 3D environment and (ii) the evaluation of vessel wall permeability.

Microfluidic chips (Figure 1) are produced via soft-lithography with PDMS, then plasma-bonded on a coverslip glass. The microvascular network is generated via pseudo-vasculogenesis in the central region of the chip using GFP-HUVEC (4.5 M/ml), dermal fibroblast (4.5 M/ml), and fibrinogen-thrombin gel (3 mg/ml-4UI/ml). The network is cultured for seven days and then irradiated at 2, 5, 8, and 10 Gy (Figure 1) with 6 MV photons produced by a Varian linear accelerator (dose rate 2.8 Gy/min). An ad-hoc slab phantom was built to simulate surrounding tissues, and the irradiation was planned with the treatment planning systems to deliver the specified doses to the entire chip (Figure 1). Radiation damage was assessed at two different time points (3h and 24 h post-irradiation) by quantifying γH2AX foci, to evaluate double-strand breaks (DSBs), and wall permeability, monitoring TRITC dextran (MW= 40 kDa) diffusion.

We consistently generated perfusable microvascular networks on a chip (Figure 1 and 2). Their morphological evaluation showed an average vessel length of 128.5 ± 21.9 µm, a length density equal to 7.0 ± 1.7 mm/mm2, an average diameter of 80.8 ± 10.1 μm, and junctions’ density equal to 34.9 ± 12.7 mm(-2). We demonstrated network perfusion by injecting 4 µm diameter microspheres, with a volume comparable to red blood cells. Irradiation altered the permeability of the network to 40 kDa dextran (Figure 2). Such an alteration is dose-dependent and is recovered 24h after irradiation. DSB analysis shows a similar dose-dependent response and a DNA damage repair in time, reducing the number of γH2AX foci at 24h as compared to 3h (figure 2).

As far as we know, this is the first application of a perfusable microvascular network to study alterations of vessel wall permeability due to ionizing radiation. Such an advanced model enables a better reproduction of the microenvironment, leveraging 3D culture techniques to include the microvascular component. Our first analyses showed a permeability increase after photon-based irradiation.