Biomaterial scaffolds provide a potentially powerful means of creating precisely engineered bone tissue substitutes with appropriate architecture and mechanical properties. Despite many efforts, there are few satisfactory products available for clinical use, and significant challenges remain in the design of smart constructs, especially for mechanically functional scaffolds. For successful long-term repair of bone, a scaffold must be strong yet have degradation kinetics matching the healing rate of remodeling bone. Here we report a new family of elastomer-toughened composite scaffolds fabricated from poly(glycerol sebacate) and Bioglass®. These synthetic scaffolds have very similar mechanical properties to that of cancellous bone of the same porosity, and exhibit a mechanically steady state over an extended period in a physiologic environment. The second feature is of great importance to bone tissue engineering, where a lag phase of degradation following implantation is highly desirable in order to provide support to the damaged or fragmented bone tissue. This work shows that a mechanically smart construct with the three-stage profile (lag, log, and plateau phases) of ideal degradation kinetics in mechanical function is achievable with synthetic biomaterials.