Disc-Shaped, Deformable Nanoparticles Break the 1% Delivery Barrier in Cancer and Stroke

For two decades, the promise of nanomedicine has been haunted by an uncomfortable statistic: a landmark meta-analysis estimated that, on average, less than 1% of an intravenously administered nanoparticle dose actually reaches solid tumor tissue. Spherical polymeric particles and liposomes in the 100–200 nanometer range, even after successive generations of PEGylation, active targeting ligands, and stimuli-responsive release mechanisms, have struggled to navigate the gauntlet of biological barriers between the injection site and the tumor microenvironment. Now, a comprehensive review published in Biomedical Microdevices by Raffaele Spanò, Roberto Palomba, Alessia Felici, Paolo Decuzzi, and Anna Lisa Palange makes the case that the problem may lie not in the chemistry of nanocarriers, but in their shape and mechanical character. The authors synthesize more than a decade of work on Deformable Discoidal Polymeric Nanoconstructs, or DPN, a biomimetic platform whose flat, soft architecture deliberately abandons the spherical norm and instead borrows its design logic from circulating blood cells.

The biological inspiration for DPN comes from erythrocytes. Native red blood cells evade immune clearance through two complementary traits: surface protein expression and geometric deformability. While several research groups have pursued the first strategy by cloaking synthetic particles with membranes harvested directly from red blood cells, the Decuzzi group focused on the second, purely mechanical property. Their reasoning draws on well-established hemodynamic principles. In flowing blood, particles with a high aspect ratio and flat profile experience asymmetric hydrodynamic forces that push them laterally toward the vessel wall, a phenomenon known as margination. Unlike spheres, which tend to remain suspended in the central stream, discoidal particles drift into the red-cell-depleted plasma layer adjacent to the endothelium, positioning themselves for adhesion or drug release at pathological sites. Computational fluid dynamics studies have confirmed that margination efficiency improves with increasing particle size and with departure from spherical symmetry, because the reduced rotational freedom of flat particles near a surface prolongs their residence time at the vessel wall.

What distinguishes DPN from the vast body of PLGA-based nanoparticle research is not the choice of materials but the precision of their fabrication. Rather than relying on thermodynamic self-assembly, which produces predominantly spherical particles with limited independent control over geometry, DPN are manufactured through a top-down, template-assisted strategy. Particle diameter, height, aspect ratio, and mechanical stiffness can each be tuned independently by modifying the template geometry or the polymer paste composition, without altering any other property. The structural matrix is formed by the physical entanglement and crosslinking of PLGA and PEG chains, yielding a hydrogel-like composite that degrades through the well-characterized hydrolytic breakdown of PLGA into lactic and glycolic acid, metabolites with an extensively documented safety profile in humans and a place in several FDA-approved drug delivery products.

Perhaps the most conceptually novel aspect of the platform is the treatment of mechanical stiffness as an independently tunable design variable. By systematically varying the ratio of PLGA to PEG while holding all other parameters constant, the researchers produced DPN variants spanning from soft constructs with a Young’s modulus of approximately 1.3 kilopascals to rigid ones at around 15 kilopascals, all sharing the same 1,000 by 400 nanometer disc geometry and a surface zeta potential of roughly minus 14 millivolts. The biological consequences are substantial. Mechanistic studies with liquid-filled silica nanocapsules of calibrated stiffness have shown that softer particles resist macrophage internalization far more effectively than rigid counterparts, because the energetic cost of membrane wrapping around a deformable object exceeds that of engulfing a geometrically stable one. Quantitatively, macrophage uptake of soft nanocapsules has been found to be reduced by approximately threefold relative to stiff equivalents of comparable size and surface chemistry. Within the DPN framework, a systematic experimental study spanning circular, quadrangular, and elliptical geometries across stiffness values from roughly 100 kilopascals to 10 megapascals confirmed that reduced Young’s modulus consistently and substantially lowered phagocytic uptake regardless of particle shape. Crucially, this immune evasion is achieved through purely synthetic means, by tuning crosslink density, offering reproducibility and scalability advantages that become critical as the platform moves toward clinical development.

The pharmacokinetic payoff of combining discoidal geometry with mechanical softness has been striking in preclinical models. In tumor-bearing mice, including brain and skin cancer xenografts, intravenously administered soft DPN maintained detectable blood concentrations for approximately 24 hours post-injection and achieved tumor tissue accumulation of up to 20% of the injected dose per gram of tumor. That figure stands in dramatic contrast to the field-wide average of below 1%, and it is accomplished passively, without active targeting ligands, relying entirely on the physical properties of the construct. The mechanistic basis lies in the tumor microvasculature itself: irregular caliber, high tortuosity, and sluggish perfusion create flow conditions under which flat, deformable particles are more readily arrested and retained at the vascular wall than spherical ones.

Translating these advantages into effective chemotherapy required solving a genuine formulation problem. The soft, spongy polymer matrix that minimizes macrophage uptake retains small molecules of 500 to 1,000 daltons poorly, a limitation the authors addressed through three distinct engineering strategies. The first, a multi-passage approach, applies multiple polymer deposition layers without altering the PLGA-to-PEG ratio, achieving a twofold improvement in docetaxel loading efficiency. The resulting docetaxel-loaded DPN showed significantly higher in vivo efficacy than free intravenous docetaxel in an orthotopic murine model of triple-negative breast cancer, demonstrating therapeutic benefit at a low dose of 3 milligrams per kilogram. The second strategy involved synthesizing a series of docetaxel prodrugs conjugated to PEG chains of varying length, informed by coarse-grained molecular dynamics simulations of drug release from PLGA matrices. While an oleic acid conjugate showed excessively slow release, intermediate hydrophilic PEG derivatives performed well, and the lead candidate, PEG550-docetaxel-DPN, significantly slowed disease progression in an orthotopic glioblastoma model compared with temozolomide and untreated controls, with only 40% of treated mice succumbing before day 40 versus 80% of temozolomide-treated animals.

The third strategy pushed the platform further with micro-Combinatorial Hydrogel Particles, or µCGP, two-micrometer discoidal hydrogels built from a hydrolytically labile PEG network that encapsulates smaller nanoparticles of roughly 200 nanometers along with molecules, exosomes, or antibodies. Fabricated without organic solvents, these hierarchical particles combine the vascular margination and long circulation of DPN with the deep tissue penetration of small nanoparticles. Loaded with docetaxel-carrying polymeric nanoparticles and tested in a late-stage lung metastasis model of triple-negative breast cancer, µCGP showed preferential accumulation within the lung capillary network, preserved alveolar architecture in treated animals, and enabled approximately 50% of mice to survive four months post-treatment, whereas all control groups died within three months. Imaging confirmed substantial lung accumulation and markedly enhanced penetration of the released nanoparticles into metastatic nodules, supporting the authors’ argument that the enhanced permeability and retention effect is not a dominant mechanism in metastatic disease and that engineered delivery platforms must compensate.

Beyond oncology, the vascular confinement of DPN has enabled a compelling application in thrombolytic therapy. Tissue plasminogen activator, marketed as Alteplase, is the standard treatment for acute ischemic stroke, but systemically administered tPA can cross the disrupted blood-brain barrier and exacerbate neurological injury. By covalently conjugating tPA onto the DPN surface through EDC/NHS bioconjugation, the researchers confined the drug within the vascular compartment. In a mesenteric thrombosis model, tPA-DPN recanalized 90% of occluded vessels and reduced clot size by 50% within 35 minutes, compared with 40% recanalization and 20% clot reduction for free tPA. In a severe middle cerebral artery occlusion model of ischemic stroke, mice treated with tPA-DPN showed survival rates and behavioral scores comparable to saline controls, while free tPA-treated animals displayed severely impaired survival and neurological deficits, with histology and MRI confirming smaller infarcts and reduced blood-brain barrier leakage. Notably, enhanced thrombolytic efficacy was achieved with only 1 milligram per kilogram of tPA in mice, roughly one-tenth of the conventional murine equivalent of the clinical human dose. The team has further decorated tPA-DPN with fucoidan, a sulfated polysaccharide with strong affinity for P-selectin expressed on activated platelets and endothelial cells, and preliminary experiments showed stable binding of these functionalized particles to artificial clots where conventional tPA-DPN failed to remain attached.

Significant hurdles remain before clinical translation. The template-assisted fabrication process, though precise, involves sequential operations that must be scaled while preserving uniform cavity filling and consistent particle recovery, and the authors note that variations in polymer-paste rheology, solvent evaporation, and drying conditions could introduce batch-to-batch variability. Robust quality control, suitable sterilization methods, long-term storage conditions, and comprehensive characterization of biodistribution, immunogenicity, and toxicity will all be required, and multi-compartment platforms such as µCGP may be classified as combination products under FDA and EMA frameworks, complicating their regulatory pathway. The authors also point to computational and machine-learning approaches as a means to reduce the experimental design space and accelerate optimization of particle size, shape, and deformability. Still, the evidence assembled in this review presents a persuasive argument that geometry, mechanics, and surface functionality, engineered together rather than separately, can deliver what surface chemistry alone has not: a nanocarrier whose performance advantages are structurally built in rather than bolted on.

Subject of Research: Biomimetic deformable discoidal polymeric nanoconstructs for targeted drug delivery in cancer and thrombotic disease

Article Title: Deformable discoidal polymeric nanoconstructs: Design principles, therapeutic applications, and translational perspectives

Article References: Spanò, R., Palomba, R., Felici, A., Decuzzi, P., & Palange, A. L. (2026). Deformable discoidal polymeric nanoconstructs: Design principles, therapeutic applications, and translational perspectives. Biomedical Microdevices, 28(4), Article 69. https://doi.org/10.1007/s10544-026-00854-6

Image Credits: AI Generated

DOI: 10.1007/s10544-026-00854-6

Keywords: nanomedicine, drug delivery, PLGA nanoparticles, discoidal nanoconstructs, cancer nanotechnology, triple-negative breast cancer, glioblastoma, ischemic stroke, thrombolytic therapy, tissue plasminogen activator, particle mechanics, margination