Linear actuation is a basic need in robotized manipulation of surgical instruments, that must comply with a challenging environment in terms of safety, compactness and now often compatibility with imaging modalities like CT or MRI. In this paper, we focus on needle manipulation for interventional radiology. We propose a needle driver, i.e. a linear actuator for needle insertion, based on the inchworm principle combined with pneumatic energy. Our first contribution is to propose, model and implement the device using a so-called auxetic structure. Its use increases achievable displacement under pressure and provides sufficient off-axis stiffness to use the actuator without additional guidance. Simplified modeling is introduced for the actuator synthesis. Our second contribution is to implement the actuator with multimaterial additive manufacturing combining rigid and flexible materials to increase compactness. As a third contribution, initial assessment of component sterilization and compatibility with X-ray and MRI imaging modalities is presented.