Histological Processing of Scaffolds: Challenges and Solutions.

Scaffolds are widely used in bioengineering, both as 3D native tissue-mimicking models for investigating mechanisms under physiological and pathological conditions and also as implantable agents in regenerative medicine. Histological approaches, mainly formalin-fixed paraffin-embedded (FFPE) and frozen sample sectioning, are commonly applied to evaluate cell distribution and tissue-like properties of scaffolds. However, standard histological processing is not always compatible with the materials that scaffolds are made of. Thus, some adaptations to protocols are required to obtain intact sections. In this review we discuss challenges related to the histological processing of scaffolds and solutions to overcome them. We sequentially cover processing steps of the three main histological techniques for sample preparation-cryomicrotomy, FFPE samples microtomy and vibrating microtomy. Furthermore, we highlight the critical considerations in choosing the most appropriate method based on scaffold composition, mechanical properties and the specific research question. The goal of this review is to provide practical guidance on choosing reliable histological evaluation of complex scaffold-based systems in tissue engineering research.