Implementing a Bio-Physical Loss Function (Fisher-KPP/Diffusion) for 3D Swin UNETR or for 3D-unet

[Rut328]

Hi MONAI Team,
I am using Swin UNETR for 3D brain tumor segmentation (BraTS 2021). I want to add a Physics-Informed Loss term based on the Reaction-Diffusion equation to improve biological plausibility.
Does MONAI have existing utilities or examples for integrating PDE-based constraints into a loss function?
What is the recommended way to compute spatial gradients (like the Laplacian) on the model's output tensors within the MONAI framework?
Any pointers to examples or relevant documentation would be very helpful.

Thanks!