The aim of this contribution is to design, produce and characterize size-tuneable core-shell micelles from amphiphilic Tat-b-poly(trimethylene carbonate) (Tat-b-PTMC) molecular chimeras, and to explore their biological properties. Because the extensive characterization of nanomaterials is a pre-requisite to understand and rationalize their ensuing properties, we present a detailed description of Tat-b-PTMC micelles thanks to light scattering, AFM imaging and small angle neutron scattering analyses. In vitro, Tat-b-PTMC micelles were found to be rapidly and efficiently internalized by HeLa cells, with cellular uptake kinetics being mostly related to Tat peptide content and, to a lesser extent, to nanoparticle size. We also demonstrated that, after a first membrane-binding step, Tat-b-PTMC micelles were taken up by cells via an energy-dependent endocytotic process.