The focus of the Ortiz research program is on structural or load-bearing biological materials, in particular musculoskeletal (internal to the body) and exoskeletal (extermal to the body) tissues. Such systems have developed hierarchical and heterogeneous composite structures over millions of years of evolution in order to sustain the mechanical loads experienced in their specific environment. For this reason, they have enjoyed a long and distinguished history in the literature of more than a century with an emphasis on macroscopic, continuum-level biomechanics. The Ortiz research group studies these fascinating materials using expertise in the field of "nanomechanics," including the measurement and prediction of extremely small forces and displacements, the quantification of nanoscale spatially-varying mechanical properties, the identification of local constitutive laws, the formulation of molecular-level structure-property relationships, and the investigation of new mechanical phenomena existing at small length scales. Novel experimental and theoretical methods are employed, involving increasing levels of complexity from individual molecules to biomimetic molecular assemblies to the matrix associated with single cells and, lastly, to the nanoscale properties of the intact tissue. The result, and ultimate objective of the Ortiz research program, is a fundamental, mechanistic-based understanding of tissue function, quality, and pathology. The scientific foundation being formed has relevance to both the medical and engineering fields. Nanotechnological methods applied to the field of musculoskeletal tissues and tissue engineering hold great promise for significant and rapid advancements towards tissue repair and/or replacement, improved treatments, and possibly even a cure for people afflicted with diseases such as osteoarthritis. In addition, the discovery of new nanoscale design principles and energy-dissipating mechanisms will enable the production of improved and increasingly advanced biologically-inspired structural engineering materials and protective defense technologies that exhibit "mechanical property amplification"—that is, dramatic improvements in mechanical properties (e.g., increases in strength and toughness) for a material relative to its constituents. Their work in musculoskeletal tissues focuses on articular cartilage, bone, and intervertebral disc. Their work in exoskeletal structures involves natural flexible armor, transparent armor, armor for biochemical toxin resistance, kinetic attacks, thermal regulation, and blast dissipation. Model systems include armored fish, deep sea hydrothermal vent and antarctic molluscs, molluscs and echinoderms with articulating plate armor (e.g. chitons, C. atratus), the transparent exoskeletons of certain crustaceans and pteropods, etc.