Chapter Four · failure evidence
What Microencapsulation Technologies got wrong, from 32 dissertations
The records evaluate various microencapsulation formulations and processing techniques across drug delivery, self-healing materials, and thermal storage applications. Many investigated systems encountered failures including mechanical shell fracture during drying, poor retention leading to cargo leakage, and insufficient loading capacity. These records come from PhD theses at 14 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Shell rupture and morphological defects occur during microcapsule synthesis and drying
Microcapsule shells frequently ruptured, collapsed, or fractured when subjected to spray drying, antisolvent precipitation, or core volume expansion. Insufficient incubation or formulation imbalances such as absent surfactant also led to thin leaking walls, nonspherical tailed particles, and polymer aggregation.
Tried and failed
thermogelling polymer nanoemulsion formulation without surfactant applied to hydrophobic drug encapsulation hydrogels. Outcome: unstable. Reason: insufficient surfactant led to large droplet size and low viscosity, forming tailed particles instead of spheres
Nanoemulsion-Loaded Hydrogels For Advanced Pharmaceutical Formulations · MIT
Tried and failed
thin single-layer ALD oxide encapsulation applied to phase-change materials undergoing volume changes. Outcome: unstable. Reason: mechanical stress from volume expansion caused encapsulation failure, surface roughening, and material volatilization
Improving the reliability of optical phase change materials-based devices · MIT
Tried and failed
fatty alcohol phase change material coating applied to microcapsule pore sealing. Outcome: unstable. Reason: formed uneven, cracked layers that adhered poorly and detached easily
Bioinspired microrobotic systems for targeted and on-demand cargo delivery · Imperial
Tried and failed
sacrificial core dissolution in layer-by-layer assembly applied to hollow biopolymer microcapsule fabrication. Outcome: unstable. Reason: Core dissolution solvent caused irreversible bridging flocculation and aggregation of outer polymer layers
Platelet-inspired microparticles for targeted drug delivery to the atherosclerotic plaque · Imperial
Tried and failed
lower speed homogenization for Pickering emulsion templating applied to hollow microcapsule fabrication. Outcome: unstable. Reason: larger emulsion droplets formed fragile shells that ruptured during antisolvent precipitation
NOVEL STARCH MODIFICATIONS: FABRICATION AND APPLICATIONS · Cornell
Tried and failed
short-duration culture for bio-capsule shell synthesis applied to bacterial cellulose capsule formation. Outcome: unstable. Reason: insufficient incubation time resulted in thin, fragile shells that ruptured and leaked
Functional Materials Grown from Engineered Bacteria · Harvard
Considered and rejected
Considered and rejected: Rejected air drying and spray drying for fumed silica microcapsule powder preparation due to capsule collapse and high fracture rates
Synthesizing Semiconductor Nanowires in Hollow Microcapsules via the Geode Process · Georgia Tech
Tried and failed
spray drying applied to hollow inorganic microcapsules. Outcome: unstable. Reason: thermal and shear stresses caused extensive shell fracturing and particle breakage
Synthesizing Semiconductor Nanowires in Hollow Microcapsules via the Geode Process · Georgia Tech
Inadequate wall materials and processing methods lead to low encapsulation efficiency
Formulations relying on single wall materials, nanoprecipitation, or specific polymers such as PEG-PLGA and maltodextrin failed to achieve acceptable payload levels. Conventional double emulsion processes and unmodified liposomes also exhibited deficient loading capacity, excessive protein loss, or sub-therapeutic morpholino delivery.
Lost to a baseline
Untreated SFPC liposomes had slightly higher initial encapsulation efficiency for vitamin E (89 ± 3%) and vitamin C (72 ± 5%) compared to untreated MFGM liposomes (77 ± 5% and 65 ± 4%).
Considered and rejected
Considered and rejected: Rejected conventional solvent extraction/evaporation double emulsion encapsulation due to resulting polydisperse microcapsules, low encapsulation efficiency, and excessive protein loss.
Considered and rejected
Considered and rejected: Rejected PEG-PLGA and maltodextrin (MDX) polymers for HB encapsulation due to low encapsulation efficiency (<5%) compared to CMC.
Considered and rejected
Considered and rejected: Rejected using single wall material (such as maltodextrin alone) due to quick gastrointestinal release, deficient emulsification, and lower encapsulation efficiency.
Considered and rejected
Considered and rejected: Rejected single-step traditional nanoprecipitation due to low drug encapsulation caps (<10 wt%).
Post Exposure Prophylaxis for HIV in the sexual exposure scenario (PEPSE): Development of a novel nanoformulation · University of Nottingham Repository
Considered and rejected
Considered and rejected: Abandoned polymersome encapsulation of antisense morpholinos for in vivo gene knockdown because released concentration was too low (~350 pmol/mL) to reach functional in vivo doses without aggregation.
Regulating Gene Expression With Light-Activated Oligonucleotides · Penn
Membrane permeability and phase separation cause premature cargo leakage and burst release
Encapsulated payloads frequently leaked into external phases or across carrier membranes because of low lipid phase transition temperatures or acidic deposition conditions. Polymer matrices exceeding entrapment capacity suffered liquid phase separation, while nanoparticle carriers exhibited rapid burst release that prevented functional delivery.
Tried and failed
double emulsion solvent evaporation encapsulation applied to hydrophilic small molecule drug loading. Reason: hydrophilic drug partitioned into external aqueous phase, resulting in zero encapsulation
Tried and failed
direct liposome encapsulation of proteins applied to protein delivery vehicle preparation. Reason: low phase transition temperature caused cargo leakage, while higher transition temperature lipids caused thermal artifacts
Tried and failed
freeze-thaw polymer hydrogel encapsulation of ionic liquids applied to drug delivery ionogel patches. Outcome: unstable. Reason: ionic liquid concentrations exceeding capacity could not be entrapped, leading to liquid phase separation onto surfaces
Overcoming Barriers in the Gastrointestinal Tract with Ionic Liquids · Harvard
Considered and rejected
Considered and rejected: Rejected calcium carbonate-PSS/PSS-PAH multilayer microcapsules due to ~58% cargo leakage during layer-by-layer polymer deposition at acidic pH
Lost to a baseline
PAA NPs loaded with Dox via encapsulation failed to deliver Dox in vitro due to rapid burst release compared to PEI-functionalized NPs
Hierarchical Assemblies of Soft Matters From Polymers and Liquid Crystals on Structured Surfaces · Penn
Embedded self-healing microcapsules suffer mechanical destruction and degrade composite durability
Embedded healing capsules suffered premature destruction under high-shear mixing and degraded composite fatigue life or structural strength. Capsule systems also failed because self-healing chemicals were irreversibly consumed after initial repair or because strain energy dissipated before activating crack bridging.
Tried and failed
embedded deployable metamaterial capsules for mechanical actuation applied to crack bridging in polymer composites. Reason: strain energy dissipated completely before reaching actuation loads, preventing structural resilience under stress
Self-healing mechanism in polymer composite materials · Cranfield
Lost to a baseline
Capsule addition reduced unhealed fatigue cycles compared to neat asphalt at certain low loads (e.g., at 621 N, neat SMA resisted 5800 cycles vs 3900 cycles for capsule F)
Optimisation of encapsulated oil properties to maximise asphalt self-healing · University of Nottingham Repository
Considered and rejected
Considered and rejected: Extrinsic self-healing (microcapsules) was rejected due to vulnerability to destruction under high-shear mixing and short service lifespan for 20-25 year turbine applications.
Improved Material Formulations for Thick Adhesive Joints in Wind Turbine Blades · EPFL
Considered and rejected
Considered and rejected: Chemical self-healing mechanisms requiring microcapsules were rejected because self-healing agents are consumed during repair, preventing repeated autonomous healing.
Multifunctional flexible conductive materials for supercapacitors and biosensors · MSpace - University of Manitoba
Considered and rejected
Considered and rejected: Rejected vascular networks / embedded extrinsic capsule healing systems due to vascular network blockage over time and severe degradation of structural strength.
Self-Healing Polymer Nanocomposites for Composite Structure applications · Cranfield
Left open by the authors
Problems the authors named and did not get to.
Left open
Test non-pH responsive, PBS-soluble anticancer drugs for encapsulation and release in pH-responsive methacrylic polymersomes. Blocker: Requires a wet chemistry and biology lab to synthesize polymersomes and perform drug encapsulation/release assays
Self-assembled block copolymers: micelles, polymersomes and gels · Imperial
Left open
Optimize polymer composition and crosslinking density of poly(amine) microcapsules and evaluate their responsiveness in biologically relevant conditions. Blocker: Requires a wet lab, microfluidic devices, chemical synthesis, and biological testing assays.
Engineering Functional Microcapsules for Controlled Cargo Delivery · Harvard
Left open
Develop a single-capsule combined formulation of curcumin and ursolic acid lipid microspheres to reduce daily pill burden. Blocker: Requires a wet lab and pharmaceutical manufacturing equipment (hot-melt rotating disk and encapsulation tools).
Left open
Develop encapsulation and on-demand release mechanisms for diverse antibacterial molecules using polyCu-MOF@AgNPs. Blocker: Requires a wet chemistry and biological testing laboratory to synthesize MOFs and test drug release.
New Metal Complexes and Metal-Organic Frameworks (MOFs) with Potential Biological Applications · IRIS - UNICAM - prod
Left open
Develop advanced encapsulation techniques such as nanocarriers, coacervation systems, and dual-phase emulsions to co-stabilize vitamin D and zinc. Blocker: Requires a wet chemistry/food science laboratory and sensory/bioavailability testing apparatus.
Fortified Foods with Vitamin D and Zinc · Cornell
Left open
Test nanoparticle treatment of chronic biofilm airway infections in βENaC-overexpressing transgenic mice without using artificial bead encapsulation. Blocker: Requires wet lab, animal facility access, and transgenic βENaC-overexpressing mouse models for in vivo infection experiments.
Left open
Optimize encapsulation efficiency of hydrophilic and hydrophobic payloads in DSPC liposomes across varying concentration gradients. Blocker: Requires wet lab equipment for liposome synthesis, extrusion, dialysis, and chemical encapsulation measurement
Biomimetic water-based lubrication: an exploration into vesicle lubrication · Imperial
Left open
Synthesize a microencapsulated phase change material with latent heat >=390 J/g and improved encapsulation for pavement thermal delay. Blocker: Requires chemical synthesis wet lab and encapsulation apparatus to produce and test the physical material.
Left open
Model layer-by-layer assembly and thermal heat transfer performance for phase change material microcapsules with more than two polyelectrolyte layers. Blocker: None
Development of Energy Systems Towards a Low Carbon Future: From Atoms to Policies · Cornell
Left open
Investigate phase separation kinetics and cargo diffusion pathways in PFH-hexane liquid-shell microcapsules under thermal stimuli. Blocker: Requires wet lab equipment, microfluidic devices, chemical synthesis, and specialized thermal imaging/characterization apparatus.
Engineering Functional Microcapsules for Controlled Cargo Delivery · Harvard
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