Polyimides (PIs) represent a benchmark for high-performance polymers on the basis of a remarkable collection of valuable traits and accessible production pathways and therefore have incited serious attention from the ever-demanding medical field. Their characteristics make them suitable for service in hostile environments and purification or sterilization by robust methods, as requested by most biomedical applications. Even if PIs are generally regarded as “biocompatible”, proper analysis and understanding of their biocompatibility and safe use in biological systems deeply needed. This mini-review is designed to encompass some of the most robust available research on the biocompatibility of various commercial or noncommercial PIs and to comprehend their potential in the biomedical area. Therefore, it considers (i) the newest concepts in the field, (ii) the chemical, (iii) physical, or (iv) manufacturing elements of PIs that could affect the subsequent biocompatibility, and, last but not least, (v) in vitro and in vivo biocompatibility assessment and (vi) reachable clinical trials involving defined polyimide structures. The main conclusion is that various PIs have the capacity to accommodate in vivo conditions in which they are able to function for a long time and can be judiciously certified as biocompatible.

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Stimuli-responsive, “smart” polymeric materials used in the biomedical field function in a bio-mimicking manner by providing a non-linear response to triggers coming from a physiological microenvironment or other external source. They are built based on various chemical, physical, and biological tools that enable pH and/or temperature-stimulated changes in structural or physicochemical attributes, like shape, volume, solubility, supramolecular arrangement, and others. This review touches on some particular developments on the topic of stimuli-sensitive molecular tools for biomedical applications. Design and mechanistic details are provided concerning the smart synthetic instruments that are employed to prepare supra- and macro-molecular architectures with specific responses to external stimuli. Five major themes are approached: (i) temperature- and pH-responsive systems for controlled drug delivery; (ii) glycodynameric hydrogels for drug delivery; (iii) polymeric non-viral vectors for gene delivery; (iv) metallic nanoconjugates for biomedical applications; and, (v) smart organic tools for biomedical imaging.

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The development of high-performance bio-based polyimides (PIs) seems a difficult task due to the incompatibility between petrochemical-derived, aromatic monomers and renewable, natural resources. Moreover, their production usually implies less eco-friendly experimental conditions, especially in terms of solvents and thermal conditions. In this chapter, we touch some of the most significant research endeavors that were devoted in the last decade to engineering naturally derived PI building blocks based on nontoxic, bio-renewable feedstocks. In most cases, the structural motifs of natural products are modified toward amine functionalities that are then used in classical or nonconventional methods for PI synthesis. We follow their evolution as viable alternatives to traditional starting compounds and prove they are able to generate eco-friendly PI materials that retain a combination of high-performance characteristics, or even bring some novel, enhanced features to the field. At the same time, serious progress has been made in the field of nonconventional synthetic and processing options for the development of PI-based materials. Greener experimental conditions such as ionic liquids, supercritical fluids, microwaves, and geothermal techniques represent feasible routes and reduce the negative environmental footprint of PIs' development. We also approach some insights regarding the sustainability, degradation, and recycling of PI-based materials.