Subchondral defect repair is a multitask challenge requiring the simultaneous regeneration of cartilage and bone.
In turn, quantitatively modeling more complex decisions poses a challenge, requiring adequate sampling of behavior over a larger state space.
This presents a software engineering challenge requiring coherence of solutions at all levels: structures, consistency, security, models, and protocols.
Restoring endodontically treated teeth with large coronal defects remains a challenge, requiring posts with coronal retention and high bending resistance.
Skin regeneration remains a challenge, requiring a well-orchestrated interplay of cell cell and cell matrix signalling.
Radiation risk estimate in space is a moral obligation and a scientific challenge requiring the combined efforts of physicists and biologists.
Arresting the recent observed warming of the earth's climate is a challenge requiring the reduction of anthropogenic emissions of carbon dioxide.
However, as regional states and their international partners gather in Abuja on Saturday to discuss their strategy, Boko Haram remains a major security challenge requiring a coordinated response.
Steve Lee, of the Chartered Institute of Waste Management, said meeting the targets for the UK would be a challenge requiring "leadership and ambition" from the government.
For some of us, accustomed to English tack, the Western gear was bulky and unfamiliar, the cinch a challenge requiring close supervision from Skip and his crew.
But producing CIGS cells on a mass scale has turned out to be a formidable technological challenge, requiring the invention of specialized manufacturing equipment.
