Purpose: Acetalated dextran (Ac-DEX) is a pH-sensitive, biodegradable polymer useful for drug delivery, but it degrades to methanol, which can be toxic at high concentrations or with repeated dosing. A safer analog that degrades to ethanol instead of methanol is needed for high-volume clinical applications such as multiple dosing and tissue engineering.
Hypothesis: If dextran is modified with ethoxy acetal groups instead of methoxy acetal groups, then the resulting polymer—ethoxy acetal derivatized acetalated dextran (Ace-DEX)—will degrade into ethanol, acetone, and dextran, retain pH-sensitive and tunable degradation, and show comparable biocompatibility to Ac-DEX and PLGA.
Aims: Synthesize and characterize Ace-DEX polymer with ethanol as a degradation product. - Confirm the presence of ethanol and absence of methanol by ¹H NMR. - Quantify cyclic and acyclic acetal coverage as a function of reaction time. - Fabricate Ace-DEX microparticles and electrospun fibers. - Characterize pH-sensitive degradation kinetics at pH 5.0 and pH 7.4. - Compare in vitro cytotoxicity of Ace-DEX microparticles with Ac-DEX and PLGA microparticles.
Delivery system:
Component: Polymer; Details: Ethoxy acetal derivatized acetalated dextran (Ace-DEX)
Component: Backbone; Details: Dextran (MW ≈ 10,400)
Component: Modification; Details: Reaction with 2-ethoxypropene to form cyclic and acyclic ethoxy acetals
Component: Degradation products; Details: Dextran, acetone, and ethanol (instead of methanol for Ac-DEX)
Component: Formulations; Details: Microparticles (single emulsion, solvent evaporation) and electrospun fibers
Component: Payload; Details: None tested in this study; empty microparticles were used
Component: Targeting ligand; Details: None
Component: Key feature; Details: pH-sensitive degradation; tunable degradation rate by reaction time; ethanol degradation product
Approach: In vitro only. No in vivo animal studies. - Polymer synthesis: Dextran + 2-ethoxypropene in DMSO with pyridinium p-toluenesulfonate catalyst; reaction times 5, 10, 50, 110, and 480 min. - Microparticle fabrication: Single emulsion (water/oil) with PVA stabilizer. - Fiber fabrication: Electrospinning at 30 kV, 2 mL/h, 20 cm distance. - Degradation: Incubation in pH 5.0 sodium acetate buffer or pH 7.4 PBS at 37°C; BCA assay for released dextran. - Cytotoxicity: RAW 264.7 macrophages; MTT assay after 24 h; concentrations 100 ng/mL to 1 mg/mL. - Controls: Ac-DEX microparticles and PLGA microparticles.
Key methods: ¹H NMR: Confirmation of ethanol and acetone degradation products; quantification of cyclic and acyclic acetal coverage per glucose unit. - Scanning electron microscopy (SEM): Microparticle and fiber morphology. - BCA assay: Quantification of dextran released during degradation. - MTT assay: Macrophage viability. - Half-life determination: Time to 50% degradation at pH 5.0.
Key results: Polymer synthesis: ¹H NMR confirmed ethanol and acetone as degradation products; methanol peak was absent. - Acetal coverage: Acyclic acetal coverage decreased logarithmically with reaction time; cyclic acetal coverage increased. Maximum cyclic acetal coverage reached ~0.72 per glucose unit at ~100 min. - Degradation: Ace-DEX microparticles fully degraded in pH 5.0 in about 1 h (5 min synthesis) to about 1 week (480 min synthesis). At pH 7.4, degradation was much slower; most particles were <10% degraded at the time of complete degradation at pH 5.0. - Half-life: Degradation half-life increased with reaction time and cyclic acetal coverage, and decreased with acyclic acetal coverage. - Cytotoxicity: Ace-DEX microparticles showed no significant difference in RAW macrophage viability compared with PLGA and Ac-DEX microparticles across the tested concentration range (100 ng/mL to 1 mg/mL).
Interpretation: The authors claim that Ace-DEX is a safer analog of Ac-DEX because it degrades to ethanol rather than methanol, while retaining pH-sensitive tunability and biocompatibility. Ace-DEX microparticles may be advantageous for high-volume clinical applications, multiple dosing, and tissue engineering. The polymer provides tunable degradation from hours to days and shows comparable cytotoxicity to FDA-approved PLGA in vitro.
Limitations: In vitro only: No in vivo degradation, biocompatibility, toxicity, or efficacy data. - No payload: Empty microparticles were used; no drug or vaccine encapsulation or release was tested. - Short-term cytotoxicity: Only 24 h MTT assay in RAW 264.7 macrophages; no other cell types. - No methanol comparison in vivo: The safety advantage of ethanol over methanol was not directly tested in animals. - No long-term degradation or clearance data. - No immunogenicity or repeated-dose toxicity data. - No comparison with other pH-sensitive polymers beyond Ac-DEX and PLGA. - Citation details incomplete in the supplied file (journal/year/DOI not provided).
