Table 1.

Variable and parameter definitions, with reference conditions

Variable	Definition	Reference condition
CHIV	Concentration of HIV	—
DHIV, semen	Diffusion coefficient of HIV in semen	3.63 × 10−8 cm2/s
dHIV	Diameter of HIV virion	125 nm
μsemen	Viscosity of semen	1 cP
T	Temperature	37°C
DHIV, gel	Diffusion coefficient of HIV in microbicide gel	0.5 Dsemen
ΦHIV	Partition coefficient between semen and gel layers	1
C0	Initial concentration of HIV in semen	5 × 104 virions/ml = 8.3 × 10−17 M
hsemen	Thickness of semen layer	340 μm
hgel	Thickness of microbicide gel layer	300 μm
htotal	Total thickness of semen and microbicide gel layers, $h_{\text{total}}=h_{\text{semen}}+h_{\text{gel}}$	640 μm
Mtissue	Amount of HIV in tissue compartment	—
Vsemen	Volume of semen	3.4 ml
Vgel	Volume of microbicide gel	3.0 ml
Avagina	Surface area of vaginal epithelium	100 cm2
ϕ	Fractional area coated by gel of given thickness	1
threshold	Threshold number of virions in tissue compartment	1.7 × 104 virions

Values were input to the model unless otherwise specified.