The clinical stakes are considerable. Doxil, the first FDA-approved nanomedicine, improved the therapeutic efficacy of doxorubicin against cancer while lowering its cardiotoxicity, and Onpattro, the first approved lipid nanoparticle-based siRNA therapy, produced roughly 80 percent reductions in serum transthyretin alongside neurological improvement in patients with hereditary transthyretin-mediated amyloidosis. These successes prove that rational nanoscale design can transform therapeutic outcomes. Yet relatively few polymeric nanoparticle systems have followed them into the clinic. The review attributes this gap to an incomplete understanding of how soft carriers move through complex biological environments — and to design strategies that fixate on particle size, surface charge and loading efficiency while neglecting the combined effects of polymer mechanics, hydration, deformation and interfacial interactions.

From a soft-matter perspective, a nanogel is a hydrated, crosslinked polymer network that absorbs large amounts of water while maintaining structural integrity. Its behaviour is governed by a set of interdependent parameters: elastic modulus, swelling ratio, crosslink density, mesh size, viscoelastic relaxation time and interfacial hydration. Mesh size, typically spanning 5 to 100 nanometres in representative systems, controls molecular diffusion through the network. Swelling ratios between 5 and 40 can widen network spacing and increase drug mobility, while elastic moduli ranging from 0.5 to 100 kilopascals determine how readily the particle deforms under physiological stress. Effective diffusion coefficients within hydrogel networks generally fall between 10^-12 and 10^-9 square metres per second. Crucially, these values are not fixed constants — they are condition-dependent material properties that shift with pH, ionic strength, temperature and mechanical confinement.

The transport physics underpinning the framework draws on classical continuum theory. Momentum conservation links pressure gradients and viscous forces to the velocity fields that drive convective transport in blood and interstitial fluid. A generalized advection–diffusion–reaction equation then couples that velocity field to nanoparticle and drug transport, with an effective diffusivity that evolves with mesh size, polymer volume fraction and deformation state. The relative importance of convection and diffusion is captured by the Péclet number, while the Deborah number characterizes viscoelastic memory effects — nanogels often operate near a Deborah number of order one, where solid-like and liquid-like responses coexist. A Damköhler-type comparison of reaction and transport rates defines whether delivery is transport-limited or reaction-limited. Transitions among these dimensionless regimes occur sequentially as nanoparticles move from vascular flow through tissue confinement into cells.

Each biological barrier imposes its own transport constraints and its own characteristic failure mode. In blood circulation, shear flow, opsonization and immune surveillance demand a stable, hydrated and reversibly deformable particle; aggregation, rapid clearance and premature leakage are the typical failures. At the endothelial interface, balanced stiffness and adaptive surface presentation govern adhesion, margination and translocation, with poor extravasation or endothelial trapping as the risks. Within the extracellular matrix, steric confinement, collagen density and interstitial pressure call for a deformable, swelling-controlled network — perivascular retention and shallow penetration are the common outcomes. Mucosal barriers punish adhesive or poorly hydrated particles with immobilization, while at the cell membrane, intermediate mechanics with sufficient interfacial engagement determine whether membrane wrapping and receptor clustering proceed efficiently. Inside endosomes, acidification and enzymatic degradation demand relaxation- or degradation-controlled disassembly to avoid endosomal trapping and incomplete release.

Experimental evidence increasingly supports the centrality of mechanics. Studies have shown that nanoparticle elasticity regulates phagocytosis and cancer cell uptake, and that the stiffness of targeted layer-by-layer nanoparticles impacts elimination half-life, tumour accumulation and tumour penetration. The relationship between softness and transport performance, however, is not linear. A particle that is too floppy may lack structural integrity, while one that is too rigid may struggle to penetrate confined matrices and adapt to local deformation. Optimal performance emerges from balanced viscoelastic properties — a regime the framework treats as a design target rather than an accident of formulation.

Drug release, the review stresses, is intrinsically coupled to transport because both processes occur within the same evolving polymer network. Crosslink density, swelling state, mesh size and relaxation dynamics jointly regulate molecular mobility and payload liberation. Stimulus-responsive systems add a further layer: changes in pH, enzymatic activity, redox state or temperature can alter swelling, charge distribution and network integrity, reshaping release kinetics during circulation, tissue penetration and intracellular processing. The authors argue that release should be regarded as an emergent property of coupled transport, soft-matter and reaction processes — not as a singular diffusion event measured under static laboratory conditions that differ substantially from the in vivo environment.

To illustrate the framework’s applicability, the review examines representative nanogel chemistries. Poly(ethylene glycol)-based nanogels, prized for high hydration and biocompatibility, show how increased crosslinking reduces mesh size and effective diffusivity while enhancing payload retention, whereas increased swelling widens network spacing and accelerates molecular transport. Chitosan nanogels demonstrate environmental responsiveness as a transport variable: protonation of amino groups in acidic environments alters electrostatic interactions, hydration and swelling, which in turn modify mesh size and drug release. Hyaluronic-acid nanogels couple biological recognition to transport and degradation, binding CD44 receptors for receptor-mediated uptake while enzymatic degradation modulates payload mobility — evidence that biological recognition and transport need not be modelled as separate problems.

The TSMCF is positioned not as a replacement for existing design paradigms but as an integrating layer. Conventional nanoparticle design, Quality-by-Design manufacturing frameworks, mechanobiology approaches and pharmacokinetic ADME models each capture part of the picture, but none explicitly solves for pressure-driven flow, convection, diffusion, permeability, deformation and evolving nanogel transport properties within a unified system. The framework’s computational implementation could follow a multiphysics pathway — fluid-flow equations yielding pressure and velocity fields, connected to convection–diffusion transport, with nanogel-scale effective diffusivity, permeability, swelling and degradation treated as constitutive relationships. Artificial intelligence and machine learning may further uncover multivariable structure–transport relationships, though predictive reliability depends on standardized, mechanistically meaningful datasets.

The authors are candid about limitations. Biological transport is profoundly heterogeneous — extracellular matrix composition, interstitial pressure, immune activity and disease status vary across organs, diseases and patients, so no single parameter set characterizes all physiological environments. Measuring transport-relevant properties under physiologically relevant conditions remains a standardization challenge, and fully coupled multiscale simulations are computationally demanding. Model identifiability poses another obstacle: a release curve alone may not distinguish whether observed changes arose from mesh size, swelling, degradation or drug–polymer affinity. The framework is explicitly conceptual rather than a validated predictive model, requiring experimental validation and forward computational work to identify which coupling terms dominate in specific systems.

Translational hurdles compound these scientific ones. Slight changes in polymer synthesis, crosslinking chemistry, purification or storage can shift swelling, mechanics and transport behaviour, complicating manufacturing reproducibility and regulatory assessment of adaptive, deformable systems. Preclinical nanomedicine often relies on surrogate indicators such as cellular uptake without adequate characterization of intracellular payload delivery and therapeutic efficacy. Looking forward, the review recommends that routine characterization extend beyond particle size, morphology and surface charge to include swelling behaviour, mesh size, crosslink density, mechanical stiffness, degradation kinetics, permeability and stimulus responsiveness — and that transport evaluation move from static release assays to dynamic models such as microfluidic flow systems, endothelial barriers, extracellular matrix mimics and organoids.

The most ambitious prospect is patient-specific, transport-informed nanomedicine. Next-generation systems could incorporate individual transport profiles — vascular permeability, stromal architecture, immune status, mucus barrier properties and tissue mechanics — to optimize nanogel design for individual patients, combining patient-derived biological information with computational modelling, digital twin technologies and transport-informed engineering. The same principles extend beyond drug delivery to gene delivery, immunotherapy, tissue engineering, regenerative medicine and theranostic platforms. By insisting that transport is not merely an outcome of nanogel design but a reciprocal process in which physiological conditions alter nanogel structure while evolving structure alters transport, the framework offers the nanomedicine community something it has lacked: a mechanistic, systems-level basis for designing soft nanocarriers whose journey through the body is engineered as deliberately as their chemistry.

Subject of Research: Transport phenomena in polymeric nanoparticle drug delivery systems

Article Title: Transport phenomena in polymeric nanoparticle drug delivery systems: linking soft-matter design to biological performance

Article References: Dada, S. O., Osifuwa, A. D., & Boyede, I. D. (2026). Transport phenomena in polymeric nanoparticle drug delivery systems: linking soft-matter design to biological performance. Frontiers in Soft Matter, 6, Article 1931284. https://doi.org/10.3389/frsfm.2026.1931284

Image Credits: AI Generated

DOI: 10.3389/frsfm.2026.1931284

Keywords: nanomedicine, nanogels, drug delivery, soft matter, transport phenomena, polymeric nanoparticles, TSMCF, biological barriers, Transport, phenomena, polymeric, nanoparticle