It seems that model_to_save['model_state'] contains a state_dict, which is the recommended way to serialize the models.
To restore the model, create a model instance first and load the corresponding state_dict afterwards.
I would not recommend to save the model directly via torch.save(model) but to stick to saving the state_dict via torch.save(model.state_dict()) (or in your case you could also wrap it into more dicts if needed) as the former might easily break (e.g. you would need to restore the same file structure etc.).