Table 2.
Examples of capsules prepared by solid templating approach.
| Polymer 1/Polyelectrolyte 1 | Polymer 2/Polyelectrolyte 2 | Solid Template/Core | Template Dissolving Agent | Template/Core Synthesis Method | Shell-Type and Deposition | APC and Location | EE (%) | Capsule Surface Charge (mV) |
Template/Core Size and Capsule Size | Core-Polymer and Polymer–Polymer Interactions | Crosslinking between Core and Layers | Ref. |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| BSA polycation (+5.05 mV) |
Alginate polyanion (−24.6 mV) |
Template: amine modified-SiO2 (+11.8 mV) |
NH4F/HF | Stöber process | Multiwalled (seven alternate layers of BSA and Alginate) |
Betamethasone disodium phosphate (BSP); shell; post-synthesis introduction | 56% | +5.05 mV | ~128 nm; ~170 to188 nm |
Non-covalent (hydrogen bonding, electrostatic, van der Waals, and hydrophobic interaction) |
- | [17] |
| BSA | Tannic Acid | Template: CaCO3. Core: BSA |
Ethyl-enediaminetetraacetic acid trisodium salt (EDTA) | Co-precipitation | Multiwalled (six bilayers of BSA/Tannic Acid) |
Tetramethylrhodamine-isothiocyanate labeled BSA; core; co-precipitated with the solid template during synthesis | - | (−30 ± 1.9) mV | - | Hydrogen bonding | - | [33] |
| Silk fibroin (anionic) |
Aminopropyl triethoxysilane (APTES) (cationic) |
Template: polystyrene |
N,N-dimethyl formamide (DMF) | - | Multiwalled (nine layers of Silk fibroin) | chlorin e6 (Ce6) and doxorubicin (DOX); shell; post-synthesis introduction | DOX = 80% Ce6 = 90% |
− | ~150 to 250 nm; ~230 nm |
Electrostatic interactions | - | [8] |
| Silk fibroin | - | Solid core: poly(lactic-co-glycolic acid) |
- | Single emulsion-solvent evaporation method |
Single layer of silk fibroin | Simvastatin; Core; in-synthesis encapsulation |
59.4% to 70.3% | - | ~15.3 μm | Covalent bonding | Chemical crosslinking by Glutaraldehyde | [24] |
| calcium cross-linked k-carrageenan | k-carrageenan and chitosan polyelectrolyte complex | Template: CaCO3. Core: BSA |
EDTA | Co-precipitation | Multiwalled | Curcumin; after core synthesis, before layer assembly |
6.25 to 8% | - | - | Electrostatic interactions | - | [100] |
| Gelatin A | (−)-epigallocatechin gallate (EGCG) | Template: MnCO3 | EDTA | - | Multiwalled (four layers) |
- | - | −25 mV | ~4.0 μm; ~4–5 μm |
Non-covalent (hydrophobic and electrostatic interactions) |
- | [36] |
| Chitosan polycation |
Alginate Polyanion |
Template: E. coli cells (−32.70 ± 3.2 mV) |
Lysis buffer (0.1% Triton X-100, 2 mM EDTA in 10 mM Tris-pH8) | Cultured | Multiwalled (four bilayers of chitosan–alginate) |
- | - | (−36.08 ± 8.8) mV | - | Electrostatic interactions | - | [56] |
| Thiolated-chitosan polycation |
Thiolated-hyaluronic acid polyanion |
Template: CaCO3 −15.8 mV |
EDTA | Co-precipitation | Multiwalled (four bilayers of chitosan/hyaluronic acid) |
BSA and Dextran; Core; Co-precipitated with the solid template during synthesis |
20.2% | −11 to −25 mV | 3.0 µm; 4 to 6 µm |
Covalent interactions by disulfide bonding | Enzymatic crosslinking using horseradish peroxidase and tyramine hydrochloride | [55] |
| Chitosan | - | Solid; Ca-alginate |
- | Extrusion | A single layer of chitosan | Insulin and probiotic cells; post-synthesis | - | - | -- | - | Electrostatic interactions | [101] |