  The mechanics of complex soft matter often cannot be understood in the
classical physical frame of flexible polymers or rigid rods. The underlying
constituents are semiflexible polymers, whose finite bending stiffness
($\kappa$) leads to non-trivial mechanical responses. A natural model for such
polymers is the protein actin. Experimental studies of actin networks, however,
are limited since the persistence length ($l_{\text{p}} \propto \kappa$) cannot
be tuned. Here, we experimentally characterize this parameter for the first
time in entangled networks formed by synthetically produced, structurally
tunable DNA nanotubes. This material enabled the validation of characteristics
inherent to semiflexible polymers and networks thereof, i.e., persistence
length, inextensibility, reptation and mesh size scaling. While the scaling of
the elastic plateau modulus with concentration $G_0 \propto c^{7/5}$ is
consistent with previous measurements and established theories, the emerging
persistence length scaling $G_0 \propto l_{\text{p}}$ opposes predominant
theoretical predictions.
