Polymer-based nanotherapeutics (PNs), such as polymeric nanoparticles, nanocarriers and polymer conjugates, have emerged as one of the most versatile platforms in nanomedicine, offering controlled drug release, targeted delivery, and improved pharmacokinetics for a wide range of therapeutic agents (Kamaly et al., 2012; Beach et al., 2024). Their tunable composition, surface functionality, and biodegradability make them particularly attractive for oncology, infectious diseases, and gene therapy applications (Karlsson et al., 2018; Cano et al., 2020; Li et al., 2024). However, their structural complexity and nanoscale behavior challenge traditional pharmaceutical evaluation paradigms. Unlike conventional small molecules, PNs exhibit properties, such as size-dependent biodistribution, dynamic surface interactions, and potential immunogenicity, that are highly sensitive to manufacturing conditions and formulation design (Elsabahy and Wooley, 2012; Beach et al., 2024).

Regulatory authorities, including the European Medicines Agency (EMA) and U.S. Food and Drug Administration (FDA), currently assess nanotechnology-based medicines under existing pharmaceutical and biological product frameworks (EMA/HMA, 2025). However, this regulatory practice does not fully account for nanoscale-dependent behaviors, such as size-driven biodistribution, dynamic surface interactions, and high sensitivity to manufacturing variations, that fundamentally distinguish PNs from traditional medicines. As a result, the evaluation of PNs often relies on case-by-case judgments, reflecting the absence of dedicated nanomedicine-specific standards and contributing to uncertainty and inconsistency in regulatory expectations. Clarifying these limitations is essential to understanding why existing frameworks remain insufficient for ensuring adequate and scientifically robust assessment of PNs.

This review examines the current regulatory landscape governing PNs in clinical translation, highlighting existing frameworks, methodological gaps, and global harmonization efforts. By analyzing critical quality attributes, analytical requirements, and methodological gaps, and by discussing emerging approaches such as Safe-by-Design and artificial intelligence (AI) tools, the review underscores the need for a more tailored, science-driven regulatory paradigm to support predictable and consistent clinical development of PNs.

PNs have been explored as versatile carriers in nanomedicine and drug delivery, offering precise control over size, shape, surface properties, and chemical functionality (Kamaly et al., 2016; Gagliardi et al., 2021; Mitchell et al., 2021). Their modular design allows encapsulation of small molecules, proteins, and nucleic acids while enabling controlled release at targeted sites (Mitchell et al., 2021; Machtakova et al., 2022; Rodriguez-Cruz et al., 2025). Clinical successes of PNs such as protein-polymer conjugates (Moncalvo et al., 2020), drug-loaded polymeric micelles (Park et al., 2017), synthetic polypetides (Aharoni et al., 2024) highlight their therapeutic promise. However, widespread clinical adoption is limited due to biological barriers, patient variability, and challenges in translating preclinical findings. Ongoing research focuses on rational design of polymers and nanostructures to overcome clearance mechanisms, enhance targeting, and achieve stimulus-responsive delivery (Luo et al., 2023; Beach et al., 2024).

Currently, new medicines based on nanotechnology are evaluated by the US Food and Drug Administration (FDA), the European Medicines Agency (EMA), and other agencies including Health Canada (HC, Canada), Pharmaceuticals and Medical Devices Agency (PMDA, Japan) under the Japanese Ministry of Health, Labour and Welfare (MHLW), and National Medical Products Administration (NMPA, China) (Halwani, 2022; Clogston et al., 2024), Medicines and Healthcare products Regulatory Agency (MHRA, United Kingdom) (MHRA, 2025). These regulatory authorities generally use a case-by-case approach under the traditional framework of benefit/risk analysis (Desai, 2012; Soares et al., 2018; Halwani, 2022). Nanotechnology-based health products are regulated under existing frameworks for medicinal products or medical devices, depending on their primary mode of action. However, due to their unique nanoscale properties, regulatory authorities require additional characterization, as outlined in recent guidance documents (Halamoda-Kenzaoui et al., 2021), as summarized in Table 2.

The EMA regulates nanomedicines under the same frameworks as conventional medicinal products, including biologicals, small molecules, and advanced therapy medicinal products (ATMPs), without a dedicated regulatory pathway. They are evaluated under Directive 2001/83/EC on Medicinal Products for Human Use (EC, 2001), which governs the EU marketing authorization process and is supported by additional Directives, Commission regulations, and various legal reference documents. Evaluation covers preclinical studies, GMP compliance, quality documentation, and clinical performance to ensure safety, efficacy, and consistency. While no specific EU framework exists for nanomedicines, the EMA has issued reflection papers offering preliminary guidance on their development and evaluation (EMA, 2008b; EMA, 2011b; EMA, 2013a; EMA, 2013b; EMA, 2016), offering recommendations for preparing marketing authorization applications (Soares et al., 2018). Although these documents are not legally binding, they indicate EMA expectations and provide a basis for dialogue between developers and regulators. Key documents include: -

Reflection Paper on Block Copolymer Micelle Products (2013): Relevant for amphiphilic polymeric nanocarriers, this guidance discusses the need for rigorous analysis of micelle formation, stability, and potential release of unbound polymeric species (EMA, 2013a).

Other reflection papers on iron colloids (EMA, 2015; EMA, 2011b), liposomes and other lipid-based nanocarriers (EMA, 2013c), while not specific to PNs, highlight critical aspects of physicochemical characterization, stability, and biological fate applicable across nanomedicine classes.

The Nanotechnology-based medicinal products for human use EU-IN Horizon Scanning Report (EMA/HMA, 2025), reviews nanotechnology-based medicinal products, highlighting trends, applications in drug delivery, and potential in cancer and infectious disease treatment. It stresses the need for strong regulatory frameworks and early identification of innovations to guide EMA in ensuring product quality, safety, efficacy, and future readiness.

In terms of definitions and classifications, the EU first established a definition for nanomaterials in 2011, identifying them as materials with dimensions between 1 and 100 nm (EC, 2011). This definition was revised in 2022 to encompass more complex nanoscale systems (EC, 2022). For polymeric nanocarriers typically ranging from 20 to 200 nm, this classification entails additional regulatory requirements, including advanced physicochemical characterization and comprehensive toxicological assessments (ECHA, 2022; JRC/EU, 2022; Bleeker et al., 2023).

The EMA assesses PNs as either biological or nonbiological medicinal products, with classification determined by the active substance and primary mechanism of action (Hussaarts et al., 2017). Both categories require evaluation beyond plasma pharmacokinetics, including stepwise comparison with a reference product to establish bioequivalence, safety, quality, and therapeutic efficacy (Astier et al., 2017; Soares et al., 2018). Regulatory approaches for nonbiological complex drugs (NBCDs) often draw from biological frameworks, as both involve incomplete structural characterization and manufacturing-dependent in vivo activity, thereby necessitating ongoing comparability assessments (Schellekens et al., 2014; Soares et al., 2018).

The FDA regulates pharmaceutical products under two main laws: the Federal Food, Drug, and Cosmetic (FDA, 2018a) and the Public Health Service Act, which covers biologically derived therapies (Mühlebach, 2018; Halwani, 2022). These laws classify products by primary mode of action: chemical (drug), mechanical (device), or biological (Mühlebach, 2018).

Nanomedicines are treated as complex products and not categorically deemed safe or harmful; each is evaluated individually. Since December 2016, FDA procedures for classifying and assessing combination products (those combining drugs, devices, and/or biologics) have included nanomedicines (Mühlebach, 2018). Examples include FDA-approved nanoformulations of paclitaxel and doxorubicin for cancer treatment.

Concerns remain over nanoparticle toxicity, ability to cross the blood–brain barrier, and long-term effects (Bawa and Johnson, 2007; Resnik and Tinkle, 2007; Mühlebach, 2018). In the last years, the FDA has issued specific guidance documents on nanotechnology and nanomedicines, urging manufacturers to consult the agency before marketing (FDA, 2014a; FDA, 2018a; FDA, 2018d; FDA, 2018c; FDA, 2020c).

In 2017, the FDA released draft guidance on requirements for drug products, including biologics, containing nanomaterials (FDA, 2017). The final version of this guidance was issued in April 2022 (FDA, 2022).

Regarding PNs, guidance documents and reflection papers have been provided by EMA, FDA and other international regulatory authorities, specifically EMA/MHLW for block-copolymer-micelle medicinal products (EMA, 2013a), and MHLW for nucleic acid (siRNA)-loaded nanotechnology-based drug products (MHLW, 2016).

For medical devices containing nanomaterials, guidance has been issued by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) (EC, 2015) and the International Organization for Standardization (ISO) (ISO, 2012).

More references are reported in Table 2. These documents outline specific nanotechnology-related properties that may influence product quality, safety, and efficacy.

In summary, despite differences in terminology and procedural steps, regulatory authorities share a common principle whereby nanomedicines, including PNs, are evaluated under the same legal frameworks that govern conventional pharmaceuticals. Neither EMA nor FDA agency applies nanomedicine-specific approval pathways; instead, nanoscale considerations are integrated into existing drug and biologic evaluations. EMA Reflection papers (EMEA/CHMP, 2006; EMA, 2013a; EMA, 2013b; EMA, 2013c; EMA/HMA, 2025) and the FDA Nanomaterials Guidance (FDA, 2022) consistently note that current tools are adaptations of traditional pharmaceutical assessment approaches. This results in heterogeneous, product-specific data requests and regulatory uncertainty, especially for emerging polymeric architectures whose physicochemical characterization, surface interactions, and biological fate are more complex than conventional dosage forms. Developers therefore face unpredictability in meeting expectations for comparability, stability, and clinical performance.

The FDA Nanotechnology Task Force, created to assess emerging scientific and regulatory challenges, reported in the Nanotechnology Task Force Report (FDA, 2007) that limited understanding of nanomaterial behavior, inadequate testing methods, and unclear regulatory pathways required stronger scientific capacity and clearer guidance to ensure product safety. More recently, the report “The Nanotechnology-Over a Decade of Progress and Innovation” (FDA, 2020b) details FDA’s progress, including expanded research infrastructure, improved staff training, strengthened collaborations, and development of standards, thereby highlighting the benefits of a science-based, product-focused regulatory approach supporting innovation while maintaining safety oversight.

Regulatory agencies demand rigorous, multi-method validation of nanoscale properties, tied directly to manufacturing control and therapeutic function. Collectively, the guidance documents emphasize characterization needs that extend beyond conventional requirements, including detailed physicochemical and biological assessments. Key considerations include stability, sterility, pharmacokinetic and pharmacodynamic behavior, and bioburden. While not stand-alone requirements, these parameters complement existing regulatory guidelines, addressing the unique challenges posed by nanotechnology-based products, particularly in the context of drug delivery systems (JRC/EC, 2019; Halamoda-Kenzaoui et al., 2021; Floyd et al., 2025). The regulatory information required to nanotechnology-based health products, specifically PNs, is summarized in Table 3.

The development and regulatory acceptance of PNs require validated analytical methods that capture their distinct physicochemical and biological characteristics. Despite progress in standardisation, major methodological gaps persist in areas such as polymer characterization, physicochemical properties of the nanocarrier, drug loading and release, behavior in biological media, pharmacokinetics, and immune interactions. Current ISO and ASTM standards remain biased toward classical physicochemical metrics, while neglecting nanospecific attributes such as stability in complex fluids and immune compatibility. Addressing these gaps is essential for regulatory confidence and scientific reproducibility.

Surface properties largely determine nanoparticle behavior in biological environments, influencing protein binding, membrane interaction, and immune recognition (Díez-Pascual, 2022; Ly et al., 2024; Zheng et al., 2025). While standards exist for charge measurement, there are no validated methods for assessing hydrophobicity, ligand density, or coating uniformity. Many nanocarriers rely on polymer coatings such as PEG for stability or targeting, yet current bulk analyses fail to capture particle heterogeneity. Advanced techniques such as atomic force microscopy (AFM), hydrophobic interaction chromatography, and affinity-based binding assays, show research potential but lack regulatory maturity. Even surface area measurement remains problematic; traditional BET gas adsorption applies only to dry powders, not to polymeric nanoparticles in aqueous suspension (Joudeh and Linke, 2022). Thus, reliable characterization of surface attributes remains one of the greatest unmet needs.

Drug loading and release represent the core functional aspects of nanomedicines. Although total drug content can often be quantified by dissolving the carrier followed by chromatographic analysis, determining the fraction of encapsulated versus free drug is technically challenging. Separation techniques such as ultrafiltration risk disrupting the drug–carrier equilibrium, and validated methods are limited to specific formulations. For complex APIs such as mRNA or oligonucleotides, quantification and impurity detection remain under development (Camperi et al., 2024). Standardized assays capable of evaluating release kinetics and carrier integrity across nanocarrier classes are urgently needed to enable meaningful comparisons of therapeutic performance.

Kinetic behavior in biological media presents further complexity. Nanocarriers must be evaluated for both chemical and physical stability, as well as for protein interactions leading to “corona” formation. Measuring release and aggregation in plasma is difficult due to interference from abundant proteins. Methods such as AF4 improve resolution but cannot reliably analyze small organic nanoparticles under 30 nm (Babick et al., 2016). Protein corona analysis, typically using gel electrophoresis and mass spectrometry, applies only to separable particles and lacks consensus on plasma composition, limiting reproducibility and regulatory applicability (Hajipour et al., 2023).

Absorption, distribution, metabolism, and excretion (ADME) studies determine nanoparticle fate in vivo (Mitchell et al., 2021). Detecting intact nanocarriers remains challenging, as conventional bioanalytical methods generally measure only released APIs. Metal-based or fluorescently labeled particles allow limited tracking, while most organic systems lack suitable markers. In vitro absorption models like Caco-2 cells poorly represent non-oral nanocarriers, and intracellular trafficking assays remain underused (Donahue et al., 2019). Animal models provide essential biodistribution data but often fail to predict human outcomes. Physiologically based pharmacokinetic (PBPK) models could integrate in vitro and in vivo results to reduce animal testing, yet current models require further validation and standardisation before regulatory implementation (Loisios-Konstantinidis and Dressman, 2021).

Interactions with the immune and circulatory systems represent perhaps the most complex domain. Endotoxin contamination can distort toxicity results, yet standard LAL assays are prone to nanoparticle interference and cannot detect encapsulated endotoxins. Alternative monocyte activation tests provide partial solutions but lack specificity. Hemocompatibility assays, including hemolysis and coagulation studies, are used to predict thrombogenic potential, though none are universally validated (Loisios-Konstantinidis and Dressman, 2021). Immune hypersensitivity reactions such as CARPA are well documented but remain difficult to model accurately in vitro (La-Beck et al., 2021; Saxena et al., 2025). Broader innate immune effects (macrophage activation, inflammasome signaling, oxidative stress) are measurable only with assays still at the research stage (Dobrovolskaia, 2022). Adaptive immune assessments, including anti-polymer antibody formation, remain reliant on in vivo testing, as no in vitro model can yet reproduce human immune complexity.

In summary, analytical methods for PNs evaluation remain fragmented, often adapted from conventional pharmaceutical testing rather than designed for nanoscale systems. Surface characterization, drug release kinetics, in-plasma stability, biodistribution, and immunological assessments all lack standardized, validated procedures. Progress will depend on coordinated collaboration among researchers, regulators, and standardisation bodies to unified protocols, validate emerging analytical techniques, and bridge the gap between experimental capability and regulatory need.

International harmonization efforts, notably the OECD Working Party on Manufactured Nanomaterials and its associated guidance documents, have advanced standardized approaches for nanoscale characterization and safety testing, providing an important foundation for regulatory convergence relevant to nanomedicine (OECD, 2025).

The recent success COVID-19 nanovaccines is expected to catalyze rapid growth in nanomedicine across oncology, infectious diseases, rare disorders, and beyond (Friedrichs and Bowman, 2021). This progress will bring more frequent and complex regulatory submissions, requiring closer collaboration between industry and regulators to establish best practices for development, presentation, and characterization (Clogston et al., 2024). Ultimately, the future of nanomedicine rests on sustained innovation, cohesive regulatory frameworks, and a shared commitment to delivering safe and transformative therapies to patients worldwide (Halamoda-Kenzaoui et al., 2022).

Advancing analytical methods for precise characterization of PNs is essential to address increasing product complexity, alongside transparent and collaborative engagement with regulatory authorities to ensure successful submissions (Clogston et al., 2024; Floyd et al., 2025). PNs are complex, multicomponent systems in which small variations in synthesis parameters, such as polymer concentration, solvent ratio, mixing speed, or temperature, can markedly influence CQAs such as particle size, surface charge, and drug loading or release profiles.

Since these properties dictate efficacy, safety, and biodistribution, regulatory authorities (FDA, EMA, ICH) increasingly emphasize the use of Process Analytical Technologies (PATs) for real-time process monitoring and control (Gerzon et al., 2022; Floyd et al., 2025). PAT tools such as online light scattering and spectroscopic methods, enable detection of changes in particle formation, solvent removal, and drug encapsulation kinetics. This can facilitate immediate process adjustments, ensuring reproducibility, batch consistency, and compliance with GMP standards, while supporting regulatory expectations for robust QbD manufacturing.

A key future challenge in regulating PNs is the systematic definition of nanomedicine-specific quality attributes (nano-CQAs) that capture nanoscale behavior. Unlike conventional drugs, nano-CQAs such as size-dependent biodistribution, dynamic surface transformations, protein corona formation, and sensitivity to manufacturing variability, are not fully addressed by traditional CQAs (Taha et al., 2020; Dri et al., 2023). Future regulatory approaches should therefore integrate attributes linking nanoscale structure, biological interactions, and in vivo performance. Standardized and context-relevant testing methods are essential to ensure reproducible and clinically meaningful characterization of key nanoscale properties. Measurements should combine complementary techniques and be performed under physiologically relevant conditions, enabling comparability across laboratories and development stages.

In nanomedicine design and development, a Safe-by-Design (SbD) approach should be tailored for PNs (Schmutz et al., 2020). Building on general SbD principles from EU initiatives such as NANoREG, NanoReg2, and ProSafe, this framework adapts them to the specific requirements of nanomedicine (Soeteman-Hernandez et al., 2019). SbD aims to identify and mitigate risks early in product development, contrasting with conventional risk assessment applied post-design. While widely used in engineering and conceptually linked to QbD in pharmaceuticals, SbD remains absent from formal regulatory guidelines (ICH, EMA, FDA) (Schmutz et al., 2020).

Currently, PNs lack a systematic approach to incorporate safety throughout the innovation pipeline. The GoNanoBioMat framework (EMPA, 2020) positions SbD as an iterative, feedback-driven process that replaces the linear stage-gate model, integrating safety from concept to commercialization. Built on the three pillars Safe Nanobiomaterials, Safe Production, and Safe Storage and Transport (Figure 3), it promotes innovation efficiency and alignment among industry, regulators, and academia. The process spans Material Design, Characterization, Human and Environmental Risk Assessment, Manufacturing and Control, and Storage and Transport, ensuring regulatory alignment at each stage. Material Design defines intended use and predicts toxicity using literature data and modeling tools (e.g., QSAR, OECD, 2007), though experimental validation remains necessary due to assay limitations. Characterization links polymer and nanoscale traits to biological outcomes, while Risk Assessment evaluates human and environmental hazards. Manufacturing ensures GMP compliance and control of critical attributes. Iterative decision points balance safety, efficacy, and cost, optimizing regulatory-ready PNs. Since absolute safety is unattainable, SbD should be viewed as a strategy to minimize risks while maintaining efficacy. Although not legally binding, it provides guidance for coordinating interdisciplinary collaboration across PN stakeholders. Future expansions should integrate preclinical and clinical testing according to GLP and GCP standards (Schmutz et al., 2020).

Emerging technologies such as artificial intelligence (AI), machine learning (ML), and advanced computational modeling are transforming the development of PNs (Chou et al., 2025). These tools enable the integration and interpretation of complex, multidimensional datasets generated during formulation, characterization, and clinical testing. AI-driven analytics can identify patterns linking polymer chemistry, process parameters, and CQAs such as particle size, stability, and release kinetics, thereby accelerating formulation optimization and reducing experimental workload.

The integration of AI-driven predictive tools within adapted QbD and SbD frameworks enables more anticipatory, risk-informed nanomedicine development. These approaches can predict the evolution of nanoscale attributes during manufacturing and biological interaction, strengthening links between quality, safety, and performance and supporting more transparent and consistent regulatory evaluation.

Coupled with digital twins and physiologically based pharmacokinetic (PBPK) models (Khakpour et al., 2025), predictive simulations can forecast in vivo performance, biodistribution, and toxicity profiles with increasing accuracy, helping to refine designs before clinical testing. At the same time, global regulatory harmonization (Caputo et al., 2024), through coordinated efforts among different regulatory authorities worldwide, is essential to ensure these advances lead into equitable patient access. Divergent requirements for nanomedicine classification, characterization, and quality assessment currently create significant barriers to international development and approval (Rodríguez-Gómez et al., 2025). Establishing aligned guidelines for data standards, AI validation, and model-informed regulatory submissions would streamline approval pathways, foster transparency, and enable cross-border manufacturing and distribution of safe, high-quality PN therapeutics.

Together, AI-driven innovation and regulatory convergence will be central to realizing the full clinical and societal potential of PNs.

PNs represent one of the most dynamic frontiers in pharmaceutical innovation, yet their clinical progression remains constrained by analytical, manufacturing, and regulatory challenges. Despite major advances in polymer chemistry and nanocarrier design, regulatory evaluation still relies largely on conventional approaches that do not adequately capture nanoscale complexity, resulting in case-by-case decision-making and limited predictability. Addressing this gap requires international standards that integrate physicochemical characterization, biological evaluation, and QbD principles into coherent, reproducible methodologies. Future progress will depend on the convergence of SbD approaches, real-time process analytics, and emerging digital technologies such as AI and modeling, which can enhance predictability, optimize production, and strengthen regulatory confidence. At the same time, regulatory agencies must continue fostering open dialogue with academia and industry to accelerate the safe, transparent, and evidence-based approval of PNs. Ultimately, achieving global harmonization and methodological rigor will transform PNs from promising laboratory constructs into clinically reliable, patient-centered therapeutics capable of addressing complex and unmet medical needs.