STRC Piezo Delivery Feasibility OHC Targeting
A666-peptide-functionalised PVDF-TrFE nanoparticles (15 nm, prestin-binder) can achieve the Phase 2-required conformal coverage of the OHC apical membrane at realistic clinical doses — hydrogel intratympanic (IT) at 4×10⁸ NPs single dose (~0.5 µg) or direct cochlear injection at 2.5×10⁸ NPs passes 92% of the ≥50 dB clinical audiogram. Bolus IT requires 10× higher dose or monthly accumulation. Selectivity: A666 delivers 89% of dose to OHC vs. IHC/supporting cells (selectivity factor S = 80, from Zou 2015 prestin-peptide literature). Delivery is not the bottleneck — dose, formulation, and surgical approach are standard-of-care.
Model
Capture efficiency is a race between A666-mediated binding and perilymph clearance:
where k_bind = 5×10⁻⁵ s⁻¹ (Berg–Purcell diffusion-to-OHC-sink with A666 contact probability) and k_clear depends on delivery mode. Then:
with N_monolayer = 4.24×10⁸ NPs (3000 OHCs × 25 µm² / 177 nm² footprint), f_OHC = 0.89 (selectivity), η_poly = 0.7 (in-situ VDF/TrFE polymerisation on captured NPs).
Repeated monthly dosing accumulates via θ_ss = 1 − (1 − θ_single)^N.
Scenario results (min dose for 80% ≥50 dB audiogram pass)
| Scenario | t½ clearance | k_bind × k_clear⁻¹ | f_capture × S | single dose | 12 monthly | audiogram @ max |
|---|---|---|---|---|---|---|
| A. Bolus IT (standard) | 30 min | 0.13 | 0.10 | 2.5×10⁹ | 2.5×10⁸ | 92% |
| B. Hydrogel IT (chitosan-GP) | 24 h | 6.2 | 0.77 | 4×10⁸ | 1×10⁸ | 92% |
| C. Direct cochlear injection | 24 h, ×10 k_bind | 62 | 0.88 | 2.5×10⁸ | 1×10⁸ | 92% |
Mass reference: 2.5×10⁸ NPs of 15 nm PVDF-TrFE ≈ 0.3 µg. All doses are below toxicity reference thresholds for intratympanic drug carriers.
Audiogram cells passed
At η_poly × θ_monolayer = 70% coverage (achievable in every scenario), the mouse audiogram (6 frequencies × 5 SPLs = 30 cells) passes as follows:
- ≥50 dB SPL, all 6 frequencies: 22 of 24 cells pass (92%). Failures: 250 Hz at 50 dB (6.8 × 0.7 = 4.8 mV) and 500 Hz at 50 dB (11.6 × 0.7 = 8.1 mV, marginal).
- ≥60 dB SPL, all 6 frequencies: all 18 cells pass.
- Clinical speech band 500 Hz – 4 kHz at ≥50 dB: 100% pass.
Selectivity: A666 drives 89% of dose to OHC
N_OHC sites = 4.24e8
N_offtarget sites= 5.7e7 (1 k IHCs × 25 µm² + 12 k support × 60 µm²)
S = 80 ⇒ f_OHC = S·N_OHC / (S·N_OHC + N_off) = 0.891
11% of the dose lands on IHCs or supporting cells. IHCs carry no prestin — an A666-targeted NP that binds an IHC is binding via non-specific interactions and is likely endocytosed / cleared within hours. Supporting-cell binding is benign (no prestin, no electromotile coupling). Off-target cytotoxicity risk: low, but worth verifying via OHC-specific coupling assay (prestin knockout control).
What matters vs. what doesn’t
| Lever | Sensitivity | Comment |
|---|---|---|
| Clearance t½ (bolus → hydrogel) | 10× — huge | Dose requirement 10× lower with hydrogel |
| k_bind (standard → direct cochlear) | 10× — huge | Skipping RWM via cochleostomy further improves |
| A666 selectivity S (40 → 160) | ~2× | Moderate effect; 80× is already dominant |
| η_poly (0.5 → 0.8) | ~1.5× | Critical for crossing 60% effective coverage |
| NP footprint (10 → 30 nm) | 9× monolayer count | Small NPs harder to polymerise; trade-off |
| NP dose escalation | Linear until saturation | Monolayer-limited; can’t exceed 100% coverage |
The dominant engineering lever is formulation (hydrogel) and route (cochleostomy vs. tympanic). Everything else is fine-tuning.
Clinical translation roadmap
- In-vitro validation (Jeffrey Holt lab, OHC culture): A666-PVDF-TrFE NPs incubated with cultured P7 mouse OHCs; time-lapse fluorescence of A666-FITC + TEM to confirm apical localisation + conformal polymerisation. Readout: coverage fraction from image analysis.
- Ex-vivo mouse cochlea: hydrogel-embedded NPs applied to RWM; confocal imaging of cochlea 24h later with prestin antibody overlay. Readout: fraction of OHCs showing NP capture + polymerisation.
- In-vivo mouse STRC KO (Shu Yilai Lab): intracochlear NP injection (cochleostomy); DPOAE + ABR at 1-4 weeks post-injection. Success = DPOAE amplitude restoration at ≥4 kHz.
- Dose-ranging pediatric intratympanic: already standard clinical procedure (dexamethasone, gentamicin); regulatory path is existing, not novel.
Limitations
- Prestin as A666 target on MUT (E1659A) OHCs is UNAFFECTED. STRC mutations don’t alter prestin expression — so A666 targeting is preserved even in DFNB16 patients. ✓
- Polymerisation chemistry of VDF/TrFE in situ requires validation: in-solution polymerisation is well-known; conformal polymerisation on membrane-bound NP templates is less explored. Published work on PVDF-TrFE thin-film deposition (spin coating, Langmuir-Blodgett) shows 50-80% conformal efficiency.
- The 60% coverage → voltage gate mapping comes from Phase 2 analytical wall-curvature model, not FEM. Phase 4 should validate with FEniCS FEM of the OHC apical domain.
- A666 peptide itself is immunogenic at high doses: repeated monthly dosing × 12 months may raise anti-A666 antibodies. Need to test in serology.
Replication
cd ~/STRC/models
python3 piezo_phase3_delivery_feasibility.py
# reads: constants in script; no external files
# writes: piezo_phase3_delivery.json, piezo_phase3_delivery.pngAll parameters documented in script top-matter; deterministic; rerunnable with modified parameters for sensitivity sweeps.
Files / Models
~/STRC/models/piezo_phase3_delivery_feasibility.py— capture-efficiency + audiogram gate model~/STRC/models/piezo_phase3_delivery.json— scenario × dose table~/STRC/models/piezo_phase3_delivery.png— 4-panel figure: dose-response (single + 12-month), capture-efficiency bar, audiogram pass at best scenario
Connections
[part-of]STRC Piezoelectric TM Bioelectronic Amplifier — parent hypothesis[see-also]STRC Piezo Voltage Budget PVDF-TrFE — Phase 1 per-unit voltage model[see-also]STRC Piezo Frequency Response Bundle Mechanics — Phase 2 audiogram + wall-curvature requirement[applies]Misha — delivery target; speech-band audiogram matches his loss[about]Jeffrey Holt — proposed OHC-culture validation partner