by Dr. Ester Carregal-Romero, Prof. Jesús Ruiz-Cabello and Dr. Susana Carregal-Romero

Towards Safe and Sustainable by Design Nanotechnology

There is an increasing demand for safer and more sustainable chemicals and materials. As chemical production is expected to steadily increase in the coming decades, ambitious policies are being implemented to minimise the negative impact of this growth [1]. In this context, the United Nations Global Framework on Chemicals (2023) and European Chemicals Strategy for Sustainability (2020) share a common vision of fostering a transition to a pollution-free environment while promoting sustainable innovation. At the core of this vision is the concept of Safe and Sustainable by Design (SSbD) [2].

In essence, the SSbD approach aims to identify and minimise the impacts on human’s health and the environment, as well as sustainability, at an early phase of the innovation process. The SSbD approach addresses the safety and sustainability of chemicals, materials, and products, alongside the associated processes, throughout the different phases of the entire life cycle. This includes research and development (R&D), production, use, recycling, and disposal. Different initiatives are actively working to implement this concept. Notably, the European Commission’s SSbD framework is still evolving [3], with chemicals and materials under scope, and the OECD’s Safe(r) and Sustainable Innovation Approach (SSIA) which builds on nanomaterials and nano-enabled applications [4].

There is a need for a mindset change starting in the innovation phase to ensure that newly developed nanomaterials combine safety and sustainability. This undoubtedly applies to the industry and R&D of nanomaterials for biomedical applications, such as drug delivery, new contrast agents, theranostic nanoprobes, and regenerative nanomedicines. A direct way to address this challenge is to use naturally abundant and biocompatible materials that can be tailored on demand using energetically inexpensive processes. In this context, calcium carbonate (CaCO3), an inorganic material highly abundant in nature as part of mollusc shells, limestone, or eggshells, is of great interest for promoting progress in new biomedical systems aligned with the SSbD concept [5].

CaCO3 holds several key properties that make it highly attractive for SSbD fabrication. Listed among them are its high abundance, biocompatibility, ease of preparation using mild methods such as co-precipitation, and its pH biodegradability in innocuous subproducts, this prevents long-term accumulation of these materials in the organism. CaCO3 is naturally found in different stable and anhydrous crystalline polymorphs (aragonite, vaterite, and calcite). And it can also be found in metastable and hydrated phases, such as monohydrocalcite and amorphous calcium carbonate (ACC), which are considered precursors to stable anhydrous phases. All these types of CaCO3 have different physicochemical properties and can lead to different applications in biomedicine [5].

Among the CaCO3 phases, calcite, and aragonite, which are the most stable, are the most extensively used in applications such as drug delivery, bone regeneration, and dental care. In addition, because of the high capacity of CaCO3 to trap bioactive molecules, it has been widely used in fundamental research as a sacrificial template to fabricate functional materials used to study the acidification of cellular vesicles or the effect of enzyme compartmentalisation in catalytic cascades [6, 7].

The biomedical potential of hydrated and metastable phases has long been overlooked owing to the challenges associated with their manipulation and stability. Nevertheless, significant advances have been made in recent years, particularly in elucidating the nucleation and crystal-growth mechanisms of CaCO3. Pioneering research led by experts like H. Cölfen not only deepened our understanding of CaCO3 biogenesis [8, 9], but also enabled the stabilisation of metastable phases such as ACC, opening new avenues for translational applications. [10, 11].

ACC has traditionally been employed to tailor the morphology of new materials and create robust inorganic/organic hybrids inspired by biological examples. Recent breakthroughs in stabilised ACC suggest its standalone potential in fields such as magnetic resonance imaging (MRI) [12]. The remarkable hydration of ACC has been found to significantly enhance the MRI contrast of cations such as Gd3+ when integrated into nanostructures. Notably, recent investigations demonstrate a ten-fold improvement in MRI contrast using ACC-based probes compared to clinically used magnetic contrast agents [13].


Advancing non-invasive assessment of Atherosclerosis

Inspired by this work, which underscores the stability of the ACC-based MRI contrast agents in biological fluids, our group has taken a new step forward in this research field. We demonstrated the stability of these nanostructures in response to chemical changes, enabling their functionalization with ligands for targeted MRI in a preclinical model of a prevalent disease. Specifically, we highlighted their potential to advance precision medicine for atherosclerosis. Precision medicine is based on the use of biomarkers to classify the risk of specific diseases or the response to treatments in order to improve and adapt medical care to patients’ needs.

Atherosclerosis, a complex and widespread disease, presents a significant global health burden, contributing to life-threatening events such as myocardial infarction and ischaemic stroke. It is a chronic inflammatory disease driven by lipid accumulation in focal areas of arteries and is the underlying cause of approximately 50% of all deaths in Western countries [14]. Despite its severity and high prevalence, diagnosing plaque vulnerability remains challenging owing to the inadequacy of the current diagnostic tools.

In response to this pressing challenge, emerging technologies promise to offer viable solutions, including precision medicine and non-invasive medical imaging of atherosclerotic plaques using tailored nanotechnology approaches such as nanofibers functionalized with apolipoprotein-mimetic peptides, NaGdF4 nanodots or sphingomyelin-based iron oxide nanomicelles [15-18]. However, many of these innovative nanostructures have not yet progressed beyond the preclinical stage because of various shortcomings, such as inadequate targeting efficiency, lack of sufficient contrast, non-scalable synthesis methods, potential biosafety issues, and high production costs.

Determining the practical feasibility of nanotechnology depends on conducting assays that comprehensively compare different parameters such as ligand type, target labels, and accumulation dynamics over time [19]. In addition, these assays must carefully consider aspects such as the sustainable and scalable production of nanoparticles and their biosafety profile. The failure to address these critical risk factors stalled the translation of these technologies to a clinical setting, leading to a dead-end.

Our research aspires to bridge this gap by highlighting the efficacy of naturally abundant ACC nanoparticles to facilitate comparative studies. Specifically, we point to their ability to target and image two pivotal biomarkers of atherosclerotic plaques, calcification, and inflammation. This not only expands the biomedical applications of ACCs, but also paves the way for novel avenues in targeted imaging and therapeutic interventions, all in line with the global vision of achieving a Safe and Sustainable by Design nanotechnology.

Figure 1. Application of Amorphous Calcium Carbonate for targeted molecular imaging of atherosclerotic biomarkers such as calcifications and macrophage infiltration. Reprinted with permission from ACS Nano 2023, 17, 14, 13811-13825. Copyright 2023 American Chemical Society.



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Biographies of the authors


Ester Carregal Romero, Ph.D., MSc., is a Junior Policy Analyst at the Environmental Health and Safety Division at the Organisation for the Economic Cooperation and Development (OECD) in Paris (France).  She coordinates different projects related to the hazard assessment of chemicals, reporting of chemical safety data, and biosafety of GMOs. A chemist by training, Ester obtained a Ph.D. in Materials Science at the Autonomous University of Barcelona (Spain). She complemented her education with a MSc. in Chemical Innovation and Regulation at the University of Bologna (Italy) and Heriot-Watt University (Scotland).


Jesús Ruiz-Cabello, Ph.D. (Complutense University Madrid, UCM) is an Ikerbasque Research Professor at CIC biomaGUNE in San Sebastián, Spain, and a Professor of Physical Chemistry at the Department of Chemistry for Pharmaceutical Sciences at the Faculty of Pharmacy of the UCM. He is also the Scientific Assistant Director of the Spanish multidisciplinary Network of Research in Respiratory Diseases (CIBERES) and member of the European Society of Molecular Imaging and the European and the Spanish Respiratory Society. His research has mainly focused on the discovery of new biomarkers for early diagnosis and therapy follow-up monitoring. He has led and coordinated different national and European projects in cardiovascular and pulmonary medicine.


Susana Carregal Romero, Ph.D. (University of Vigo), is a Research Associate RyC and Ikerbasque Fellow at CIC biomaGUNE in San Sebastián, Spain. She belongs to the CIBERES network and is a member of the European Society of Molecular Imaging. Her research focuses on the synthesis of multifunctional materials, understanding nano-biointeractions, and the applications of nanomaterials in biomedicine. In particular, she is mostly interested in chronic diseases such as pulmonary fibrosis (PF) and she is the PI of several projects aiming at delivering effective nanomedicines for PF (#BiomTher, #NanoSurf and #CAT-BIOMED).



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