About

Robert Sah has been a member of the bioengineering faculty at the UCSD Jacobs School of Engineering since 1992. He earned his M.D. at Harvard Medical School in 1991 and his Sc.D. from MIT in 1990. His research focuses on cartilage repair and tissue engineering, specifically the relationship between biomechanical function, metabolism, composition, and structure of cartilage during growth, aging, degeneration (osteoarthritis), repair, and regeneration. Professor Sah's goal is to pave the way for successful tissue-engineered total joint replacement for people suffering from cartilage damage due to injury or aging. His work combines quantitative experiments across multiple biological scales with systematic model-based analyses of biomechanics and biotransport. He has made seminal contributions to the multi-scale understanding of the biomechanical function and dysfunction of articular cartilage during growth, aging, and osteoarthritic degeneration, as well as to cartilage restoration through engineered tissues. Recently, his team fabricated a bioreactor that maintained a knee joint, demonstrating how mechanical stimuli regulate the synthesis of the lubricant molecular proteoglycan-4 and developing a joint-scale model of lubricant metabolism. These studies help elucidate the physiology of the normal joint, which is crucial for the development of tissue-engineered implants that can function mechanically and adapt over time. Professor Sah has received numerous honors, including being named a Professor by the Howard Hughes Medical Institute in 2006, the Van C. Mow Medal from the American Society of Mechanical Engineers, the NSF Young Investigator Award, the American Academy of Orthopaedic Surgeons Kappa Delta Award (twice), and the Arthritis Foundation Hulda Irene Duggan Investigator Award. His work, particularly his 'Mechanical Blueprint for Cartilage,' has been recognized as one of the Great Advances in Scientific Discovery in Disease and Injury Treatment by The Science Coalition.

Research topics

• Biology
• Chemistry
• Cell biology
• Anatomy
• Medicine
• Biotechnology
• Biomedical engineering
• Surgery
• Internal medicine
• Genetics
• Pathology
• Cancer research

Selected publications

• Ultrashort echo time magnetization transfer (UTE-MT) MRI detects non-enzymatic crosslinking of collagen in ex vivo rat bones

  Proceedings on CD-ROM - International Society for Magnetic Resonance in Medicine. Scientific Meeting and Exhibition/Proceedings of the International Society for Magnetic Resonance in Medicine, Scientific Meeting and Exhibition · 2025-09-16

  article

  Motivation: Type 2 diabetes (T2D) patients suffer from increased bone fracture risk despite preserved or even elevated bone mineral density (BMD). A better diagnostic tool that accurately reports the bone health of T2D patients is urgently needed. Goal(s): To develop an MRI method that can probe non-enzymatic crosslinking of bone collagen and compromise of bone mechanical properties. Approach: We used ultrashort echo time magnetization transfer (UTE-MT) MRI for measuring the degree of collagen crosslinking in ex vivo rat bones with ribosylation. Results: The UTE-MT showed sensitivity to bone collagen crosslinking via ribosylation and subsequent compromise of bone mechanical properties. Impact: The UTE-MT technique showed significant sensitivity to non-enzymatic crosslinking of bone collagen, a key mechanism that explains the increased fracture risk of T2D patients. The UTE-MT can be an accurate noninvasive diagnostic tool for probing bone health of T2D patients.

  PublisherDOI

• Quantitative UTE Imaging of the Meniscus Across Different Zones: A Study on Knee Osteoarthritis

  Proceedings on CD-ROM - International Society for Magnetic Resonance in Medicine. Scientific Meeting and Exhibition/Proceedings of the International Society for Magnetic Resonance in Medicine, Scientific Meeting and Exhibition · 2025-09-16

  article

  Motivation: Investigating compositional changes in each meniscal vascular zone at various stages of degeneration provides valuable insights into the progression of knee osteoarthritis. However, conventional sequences with relatively long TEs are suboptimal for this purpose due to the menisci's short T2. Goal(s): To investigate the correlation between UTE biomarkers and osteoarthritic degeneration in each meniscal zone using quantitative UTE imaging techniques. Approach: UTE imaging techniques, including UTE-T1, UTE-MT modeling, UTE-AdiabT1ρ, and UTE-T2*, were used to quantitatively assess meniscal degeneration in vivo. Results: T1, T1ρ, and T2* demonstrate a significant positive correlation with meniscal degeneration grades, whereas MMF shows a significant negative correlation. Impact: This study, to our knowledge is the first to employ UTE-T1, UTE-MT modeling, UTE-AdiabT1ρ, and UTE-T2*to investigate compositional changes of each of the 3 vascular zones of the meniscus due to osteoarthritis.

  PublisherDOI

• UTE MRI technical developments and applications in osteoporosis: a review

  Frontiers in Endocrinology · 2025-02-06 · 7 citations

  reviewOpen access

  Osteoporosis (OP) is a metabolic bone disease that affects more than 10 million people in the USA and leads to over two million fractures every year. The disease results in serious long-term disability and death in a large number of patients. Bone mineral density (BMD) measurement is the current standard in assessing fracture risk; however, the majority of fractures cannot be explained by BMD alone. Bone is a composite material of mineral, organic matrix, and water. While bone mineral provides stiffness and strength, collagen provides ductility and the ability to absorb energy before fracturing, and water provides viscoelasticity and poroelasticity. These bone components are arranged in a complex hierarchical structure. Both material composition and physical structure contribute to the unique strength of bone. The contribution of mineral to bone's mechanical properties has dominated scientific thinking for decades, partly because collagen and water are inaccessible using X-ray based techniques. Accurate evaluation of bone requires information about its components (mineral, collagen, water) and structure (cortical porosity, trabecular microstructure), which are all important in maintaining the mechanical integrity of bone. Magnetic resonance imaging (MRI) is routinely used to diagnose soft tissue diseases, but bone is "invisible" with clinical MRI due to its short transverse relaxation time. This review article discusses using ultrashort echo time (UTE) sequences to evaluate bone composition and structure. Both morphological and quantitative UTE MRI techniques are introduced. Their applications in osteoporosis are also briefly discussed. These UTE-MRI advancements hold great potential for improving the diagnosis and management of osteoporosis and other metabolic bone diseases by providing a more comprehensive assessment of bone quantity and quality.

  PublisherDOI

• Ultrashort echo time quantitative magnetization transfer MRI detects non-enzymatic crosslinking of collagen in ex vivo rat bones

  JBMR Plus · 2025-11-23

  articleOpen access

  Abstract Increased bone fragility despite preserved or elevated BMD in type 2 diabetes mellitus (T2DM) is linked to nonenzymatic collagen crosslinking via advanced glycation end-products (AGEs). However, there is no noninvasive method clinically available to probe these collagen alterations in the bone. We examined the potential of ultrashort echo time quantitative magnetization transfer (UTE-qMT) MRI for detecting AGE-induced collagen crosslinking in bones. Rat tibial bones were subject to ribosylation ex vivo to induce AGE accumulation. UTE-qMT MRI was performed to quantify the magnetization exchange rate (kba) and macromolecular fraction (MMF), which were compared to mechanical properties from 3-point bending tests and AGE concentrations from fluorometric assays. Ribosylation significantly increased AGE crosslinking, confirmed by a 3-fold rise in AGE fluorescence intensity. UTE-qMT MRI revealed a significantly higher kba and MMF in ribosylated bones, whereas BMD did not show significant differences. A 3-point bending test showed that ribosylation reduced post-yield displacement, fracture displacement, and work-to-fracture from load–displacement curves, indicating reduced bone ductility and toughness. Importantly, kba and MMF correlated significantly with these mechanical properties, whereas BMD showed no significant correlations. These findings demonstrate that UTE-qMT MRI is a novel noninvasive tool sensitive to AGE-mediated collagen crosslinking and its critical role in predicting bone fragility.

  PublisherDOI

• Comprehensive zonal assessment of meniscal degeneration using quantitative UTE MRI

  Osteoarthritis and Cartilage · 2025-12-01

  articleOpen access

  OBJECTIVE: *, to assess compositional differences across meniscal zones and their changes with early degeneration. METHODS: * in the meniscus within RR, RW, and WW zones. Clinical MRI classified meniscal degeneration into three grades. Regions-of-interest (ROIs) were placed within three zones in four different meniscal regions: the anterior and posterior horns of the lateral meniscus and those of the medial meniscus in each participant. Statistical comparisons were performed between meniscal zones and across degeneration grades. RESULTS: * significantly increased with increasing degeneration, whereas MMF decreased significantly. CONCLUSION: The study highlights the potential of UTE measurements to differentiate normal meniscal zonal composition and detect early changes due to degeneration, offering a promising tool for comprehensive knee-OA assessment and treatment monitoring.

  PublisherDOI

• Cellular and genetic mechanisms that shape the development and evolution of tail vertebral proportion in mice and jerboas

  Nature Communications · 2025-10-10

  articleOpen access

  Limbs and vertebrae elongate by endochondral ossification, but local growth control is highly modular such that not all bones are the same length. Compared to limbs, which have a different evolutionary and developmental origin, far less is known about how individual vertebrae establish proportion. Using the jerboa and mouse tail skeletons, we find that cell number is a common driver of limb and vertebral proportion in both species. However, chondrocyte hypertrophy, which is a major driver of proportion in all mammal limbs, is limited to the extreme disproportionate growth of jerboa mid-tail vertebrae. The genes associated with differential growth in the vertebral skeleton overlap significantly, but not substantially, with genes associated with limb proportion. Among shared candidates, loss of Natriuretic Peptide Receptor 3 in mice causes disproportionate elongation of the proximal and mid-tail vertebrae, in addition to the proximal limb. Our findings therefore, reveal cellular processes that tune the growth of individual vertebrae while also identifying natriuretic peptide signaling among genetic control mechanisms that shape the entire skeleton.

  PublisherDOI

• Finite Element Analysis of CFFT and CFDTS Columns as a Replacement for CFST Columns in Composite Construction by Using ABAQUS

  NPI Journal of Science and Technology. · 2024-08-20

  articleOpen access1st authorCorresponding

  In the field of composite construction of steel and concrete, concrete filled steel tube CFST columns have been proven to be greater performance structural members. The properties of steel and concrete are used efficiently. But CSFT columns are prone to corrosion in outdoor structures as the outer encasing tube is made up of steel. The outdoor use of CFST column due to its high risk of corrosion requires frequent maintenance and may prove costly. Hence, the possible replacement of steel tubes with fiber-reinforced polymer (FRP) Tubes has to be investigated. FRPs are the most suitable material for encasing concrete columns due to its orthotropic behaviour. In solution to this, the paper is aimed at numerical study of CFST, CFFT and CFDTS short columns to study the axial compression behavior of these short columns analytically and examine the best suitable alternatives of CFST column. The concrete in-fill double tube section CFDTS with better axial compression, stiffness and ductility are also investigated as a suitable replacement of CFST columns. For these three different specimens of CFST columns of steel tube thickness 3mm, 4.5mm and 6mm, CFFT columns of GFRP tube thickness 3mm, 4.5mm and 6mm and CFDTS column with GFRP outer tube of thickness 3mm, 4.5mm and 6mm as well as inner steel tube of thickness 1.5mm, 2mm and 2.5mm are analyzed and compared. Consequently, CFDTS columns, with 1872 kN are proven to be superior to CFST columns with axial capacity 1653 kN and CFFT with axial capacity 689 kN columns. The confinement effect in CFDTS is more than CFST and CFFT column.

  PublisherOA PDFDOI

• Cellular and molecular mechanisms that shape the development and evolution of tail vertebral proportion in mice and jerboas

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-10-26 · 1 citations

  preprintOpen access

  Despite the functional importance of the vertebral skeleton, little is known about how individual vertebrae elongate or achieve disproportionate lengths as in the giraffe neck. Rodent tails are an abundantly diverse and more tractable system to understand mechanisms of vertebral growth and proportion. In many rodents, disproportionately long mid-tail vertebrae form a 'crescendo-decrescendo' of lengths in the tail series. In bipedal jerboas, these vertebrae grow exceptionally long such that the adult tail is 1.5x the length of a mouse tail, relative to body length, with four fewer vertebrae. How do vertebrae with the same regional identity elongate differently from their neighbors to establish and diversify adult proportion? Here, we find that vertebral lengths are largely determined by differences in growth cartilage height and the number of cells progressing through endochondral ossification. Hypertrophic chondrocyte size, a major contributor to differential elongation in mammal limb bones, differs only in the longest jerboa mid-tail vertebrae where they are exceptionally large. To uncover candidate molecular mechanisms of disproportionate vertebral growth, we performed intersectional RNA-Seq of mouse and jerboa tail vertebrae with similar and disproportionate elongation rates. Many regulators of posterior axial identity and endochondral elongation are disproportionately differentially expressed in jerboa vertebrae. Among these, the inhibitory natriuretic peptide receptor C (NPR3) appears in multiple studies of rodent and human skeletal proportion suggesting it refines local growth rates broadly in the skeleton and broadly in mammals. Consistent with this hypothesis, NPR3 loss of function mice have abnormal tail and limb proportions. Therefore, in addition to genetic components of the complex process of vertebral evolution, these studies reveal fundamental mechanisms of skeletal growth and proportion.

  PublisherDOI

• Nanoscale Morphologies on the Surface of Substrates/Scaffolds Enhance Chondrogenic Differentiation of Stem Cells: A Systematic Review of the Literature

  International Journal of Nanomedicine · 2024-11-01 · 8 citations

  reviewOpen access

  Nanoscale morphologies on the surface of substrates/scaffolds have gained considerable attention in cartilage tissue engineering for their potential to improve chondrogenic differentiation and cartilage regeneration outcomes by mimicking the topographical and biophysical properties of the extracellular matrix (ECM). To evaluate the influence of nanoscale surface morphologies on chondrogenic differentiation of stem cells and discuss available strategies, we systematically searched evidence according to the PRISMA guidelines on PubMed, Embase, Web of Science, and Cochrane (until April 2024) and registered on the OSF (osf.io/3kvdb). The inclusion criteria were (in vitro) studies reporting the chondrogenic differentiation outcomes of nanoscale morphologies on the surface of substrates/scaffolds. The risk of bias (RoB) was assessed using the JBI-adapted quasi-experimental study assessment tool. Out of 1530 retrieved articles, 14 studies met the inclusion criteria. The evidence suggests that nanoholes, nanogrills, nanoparticles with a diameter of 10-40nm, nanotubes with a diameter of 70-100nm, nanopillars with a height of 127-330nm, and hexagonal nanostructures with a periodicity of 302-733nm on the surface of substrates/scaffolds result in better cell adhesion, growth, and chondrogenic differentiation of stem cells compared to the smooth/unpatterned ones through increasing integrin expression. Large nanoparticles with 300-1200nm diameter promote pre-chondrogenic cellular aggregation. The synergistic effects of the surface nanoscale topography and other environmental physical characteristics, such as matrix stiffness, also play important in the chondrogenic differentiation of stem cells. The RoB was low in 86% (12/14) of studies and high in 14% (2/14). Our study demonstrates that nanomorphologies with specific controlled properties engineered on the surface of substrates/scaffolds enhance stem cells' chondrogenic differentiation, which may benefit cartilage regeneration. However, given the variability in experimental designs and lack of reporting across studies, the results should be interpreted with caution.

  PublisherOA PDFDOI

• Human Septal Cartilage Tissue Engineering: Current Methodologies and Future Directions

  Bioengineering · 2024-11-07 · 6 citations

  reviewOpen access

  Nasal septal cartilage tissue engineering is a promising and dynamic field with the potential to provide surgical options for patients with complex reconstruction needs and mitigate the risks incurred by other tissue sources. Developments in cell source selection, cell expansion, scaffold creation, and three-dimensional (3D) bioprinting have advanced the field in recent years. The usage of medicinal signaling cells and nasal chondroprogenitor cells can enhance chondrocyte proliferation, stimulate chondrocyte growth, and limit chondrocyte dedifferentiate. New scaffolds combined with recent innovations in 3D bioprinting have allowed for the creation of more durable and customizable constructs. Future developments may increase technical accessibility and manufacturability, and lower costs, to help incorporate these methods into pre-clinical studies and clinical applications of septal cartilage tissue engineering.

  PublisherOA PDFDOI

Recent grants

• NIH Grant U13EB009284

  NIH · $33k · 2009

• NIH Grant P01AG007996

  NIH · $34.8M · 2018

• NIH Grant R21EB004905

  NIH · $398k · 2007

• NIH Grant R01AR051565

  NIH · $2.0M · 2011

• NIH Grant R01AR044058

  NIH · $3.3M · 2011

Frequent coauthors

• Albert C. Chen

  California Institute of Technology

  120 shared

• Won C. Bae

  University of California, San Diego

  114 shared

• Koichi Masuda

  Nihon University

  89 shared

• Van W. Wong

  University of California, San Diego

  69 shared

• Deborah Watson

  University of California, San Diego

  63 shared

• Barbara L. Schumacher

  61 shared

• Michele M. Temple

  University of California, San Diego

  49 shared

• Amanda K. Williamson

  48 shared

Education

• SB, Electrical Engineering

  Massachusetts Institute of Technology

• MD

  Harvard Medical School

• ScD, Medical Engineering Medical Physics

  Massachusetts Institute of Technology

• SM, Electrical Engineering

  Massachusetts Institute of Technology

Awards & honors

• Howard Hughes Medical Institute Professor (2006)
• Van C. Mow Medal from the American Society of Mechanical Eng…
• National Science Foundation Young Investigator Award
• American Academy of Orthopaedic Surgeons Kappa Delta Award (…
• Arthritis Foundation Hulda Irene Duggan Investigator Award