Carl G. Simon, Jr., Ph.D.

Research Projects

• Active
  • Absorbance Imaging & Artificial Intelligence (AI) for Assessing Quality of a Biomanufactured Retinal Pigment Epithelium

  • Measuring Cell Viability in Scaffolds

  • Combinatorial Cassettes for Higher-Throughput Screening of Osteogenesis in Mice

  • 3D Cell-Scaffold Interactions of Human Bone Marrow Stromal Cells
  • ASTM Committee F04 on Tissue-Engineered Medical Products
  • Scaffold Fabrication: Airbrushed Scaffolds & Combinatorial Methods

• Completed
  • Scaffold Characterization (DiameterJ)
  • Workshop: Measurement Assurance Strategies for Regenerative Medicine 
  • Reference Material Scaffolds
  • Scaffold Handling Device for Fiber-Based Constructs

• NIST Research Programs
  • Tissue Engineering & Biomaterials
  • Regenerative Medicine

Honors & Activities

• Elected Fellow, American Institute of Medical & Biological Engineering (AIMBE), 2018

• Chair, ASTM/NIST/BioFabUSA Workshop on Characterization of Fiber-based Scaffolds, Manchester, NH, 2018

• Chair, ASTM, F04.43 Cells & Tissue Engineered Constructs, (2014 - present)
• Materials Measurement Lab Accolade Award, "for Teamwork", 2015
• Robert E. Fairer Award, ASTM, 2015
• Chair, NIST Workshop: "Strategies to Achieve Measurement Assurance for Cell Therapy Products", Gaithersburg, MD, 2015 (Report)
• Contributing Editor, Government News, Biomaterials Forum, 2014 - present
• Service Award, ASTM Committee F04, 2013
• Chair, ASTM Scaffolds Workshop, Indianapolis, IN, 2013 (Report)
• NIST Safety Award, 2012
• Member, Editorial Board, "Journal of Biomedical Materials Research B - Applied Biomaterials", 2011-present
• Member, Editorial Board, "Biomaterials", 2011-present
• Chair (2009-2013) & Program Chair (2007-2009), Society for Biomaterials, Proteins & Cells at Interfaces Special Interest Group
• Department of Commerce Bronze Medal, "for development of combinatorial methods", 2010

Research Opportunities

Post-doctoral Fellowship

NIST-NRC Postdoctoral Fellowship: 2-year fellowship at NIST, US citizens only, $72,000 salary plus benefits, relocation expenses included, application deadlines are Feb. 1 and Aug. 1, requires 10 page research proposal, contact me if interested in writing proposal on biomaterials research project. See these links:

• Measuring Cell Viability in Scaffolds
• Advanced Methods for Screening Human Stem Cell Function in 3D Tissue Scaffolds

Undergraduate Fellowship

• Summer Undergraduate Research Fellowship (SURF): 11-week summer research fellowship at NIST, $5500 stipend, housing is provided, travel is covered, application deadline is approximately February 1, program runs late May thru early August, contact me if interested in doing summer research on biomaterials or tissue engineering scaffolds.

Bibliography (Google Scholar Profile)

• Hunsberger J, Simon Jr CG, Zylberberg C, Ramamoorthy P, Tubon T, Ruff C, Bedi R, Gielen K, Hansen C, Fisher L, Johnson J, Baraniak P, Mahdavi B, Pereira T, Hadjisavas M, Eaker S, Miller C (2020) How Regenerative Medicine Manufacturing Society plans to move the needle forward in cell manufacturing, standards, 3D bioprinting, AI enabled automation, education and training. Stem Cells Translational Medicine, in press.
• Simon Jr CG, Kuhn LT (2020) Role of Standards for Testing and Performance Requirements of Biomaterials. In Wagner W, Sakiyama-Elbert S, Zhang G, Yaszemski M (Eds.), Biomaterials Science: An Introduction to Materials in Medicine, 4th edition. New York, NY: Elsevier. (in press)
• Garcia L, Soliman S, Francis MP, Yaszemski MJ, Doshi J, Simon CG Jr,* Robinson-Zeigler R* (2020) Workshop on the characterization of fiber-based scaffolds: challenges, progress, and future directions. Journal of Biomedical Materials Research: Part B - Applied Biomaterials, in press. (*co-corresponding authors)   DOI: 10.1002/jbm.b.34545
• Schaub NJ, Hotaling NA, Manescu P, Padi S, Wan Q, Sharma R, George A, Chalfoun J, Simon M, Ouladi M, Simon Jr CG*, Bajcsy P*, Bharti K* (2020) Deep learning predicts function of live retinal pigment epithelium from quantitative microscopy. Journal of Clinical Investigation 30, 1010-1023. (*corresponding authors)  DOI: 10.1172/JCI131187
• Padi S, Manescu P, Schaub N, Hotaling N, Simon Jr CG, Bharti K, Bajcsy P. (2020) Comparison of artificial intelligence based approaches to cell function prediction. Informatics in Medicine Unlocked 18, 100270.   DOI: 10.1016/j.imu.2019.100270
• Hunsberger J, Lundberg M, Allickson J, Simon Jr CG, Zylberberg C, Beachy S. Examining resources, initiatives, and regulatory pathways to advance regenerative medicine manufacturing (2019) Current Stem Cell Reports 5, 162-172.   DOI: org/10.1007/s40778-019-00163-0
• Bodhak S, Fernandez de Castro Diaz L, Kuznetsov SA, Maeda A, Robey PG, Simon Jr CG (2018) Combinatorial cassettes for higher-throughput screening of osteogenesis. Biomaterials 186, 31-43.  DOI: 10.1016/j.biomaterials.2018.09.035
• Pazmino Betancourt BA, Florczyk SJ, Simon M, Juba D, Douglas JF, Keyrouz W, Bajcsy P, Lee C, Simon Jr CG (2018) Effect of the scaffold microenvironment on cell polarizability and capacitance determined by probabilistic computations. Biomedical Materials 13, 025012.   DOI: 10.1088/1748-605X/aa9650
• Bajcsy P, Yoon S, Florczyk S, Hotaling N, Simon M, Szczypinski P, Schaub N, Simon Jr CG, Brady M, Sriram R (2017) Modeling, validation and verification of three-dimensional cell-scaffold contacts from terabyte-sized images. BMC Bioinformatics 19, 526.  DOI: org/10.1186/s12859-017-1928-x
• Florczyk SJ, Simon M, Juba D, Pine PS, Sarkar S, Chen D, Baker PJ, Bodhak S, Cardone A, Brady MC, Bajcsy P, Simon Jr CG (2017) A bioinformatics 3D cellular morphotyping strategy for assessing biomaterial scaffold niches. ACS Biomaterials Science & Engineering 3, 2301-2313.  DOI: org/10.1021/acsbiomaterials.7b00473
• Hotaling NA, Khristov V, Maminishkis A, Bharti K, Simon Jr CG (2017) A switchable positive and negative air pressure device for efficient and gentle handling of nanofiber scaffolds. Review of Scientific Instruments 88, 104301-1 - 104301-6.  DOI: 10.1063/1.4997894
• Tutak W, Jyotsnendu G, Bajcsy P, Simon Jr CG (2017) Nanofiber scaffolds influence organelle structure and function in bone marrow stromal cells. Journal of Biomedical Materials Research: Part B - Applied Biomaterials 105, 989-1001.  DOI: 10.1002/jbm.b.33624
• Hotaling NA, Jeon J, Wade MB, Luong D, Palmer X-L, Bharti K, Simon Jr CG (2016) Training to improve precision and accuracy in the measurement of fiber morphology. PLOS One 11, e0167664.  DOI: org/10.1371/journal.pone.0167664
• Chen D, Sarkar S, Candia J, Florczyk SJ, Bodhak S, Driscoll MK, Simon Jr CG, Dunkers JP, Losert W (2016) Machine learning based methodology to identify cell shape phenotypes associated with microenvironmental cues. Biomaterials 104, 104-118.  DOI: 10.1016/j.biomaterials.2016.06.040
• Sarkar S, Baker BA, Chen D, Pine PS, McDaniel JH, Salit ML, Losert W, Simon Jr CG, Dunkers J (2016) Roles of nanofiber scaffold structure and chemistry in directing human bone marrow stromal cell response. Advances in Tissue Engineering & Regenerative Medicine 1, 00003.  DOI: 10.15406/atroa.2016.01.00003
• Hotaling NA, Khristov V, Wan Q, Simon Jr CG, Bharti K (2016) Nanofiber scaffolds for use in development of a tissue engineered retinal pigment epithelium. Journal of Ocular Pharmacology & Therapeutics 32, 272-285.  DOI: 10.1089/jop.2015.0157
• Simon Jr CG, Lin-Gibson S, Elliott JT, Sarkar S, Plant AL (2016) Strategies for achieving measurement assurance for cell therapy products. Stem Cells Translational Medicine 5, 705-708.  DOI: 10.5966/sctm.2015-0269
• Wang P, Song Y, Weir MD, Sun J, Zhao L, Simon CG, Xu HHK (2016) A self-setting iPSMSC-alginate-calcium phosphate paste for bone tissue engineering. Dental Materials 32, 252-263.  DOI: 10.1016/j.dental.2015.11.019
• Hotaling NA, Bharti K, Kriel H, Simon Jr CG (2015) Dataset for the validation and use of DiameterJ, an open source nanofiber diameter measurement tool. Data in Brief 5, 13–22.  DOI: doi.org/10.1016/j.dib.2015.07.012
• Bajcsy P, Cardone A, Chalfoun J, Halter M, Juba D, Kociolek M, Majurski M, Peskin A, Simon Jr CG, Simon M, Vandecreme A, Brady M (2015) Survey statistics of automated segmentations applied to optical imaging of mammalian cells. BMC Bioinformatics 16, 330, 1-28.  DOI: doi.org/10.1186/s12859-015-0762-2
• Bajcsy P, Simon M, Florczyk S, Simon Jr CG, Juba D, Brady M. (2015) A method for the evaluation of thousands of automated 3D stem cell segmentations. Journal of Microscopy 260, 363-376.  DOI: 10.1111/jmi.12303
• Hotaling NA, Bharti K, Kriel H, Simon Jr CG (2015) DiameterJ: a validated open source nanofiber diameter measurement tool. Biomaterials 61, 327-338.  DOI: org/10.1016/j.biomaterials.2015.05.015
• Simon Jr CG, Yaszemski MJ, Anthony Ratcliffe A, Tomlins P, Luginbuehl R, Tesk JA (2015) ASTM International workshop on standards & measurements for tissue engineering scaffolds. Journal of Biomedical Materials Research: Part B - Applied Biomaterials, 103B, 949-959.  DOI: 10.1002/jbm.b.33286
• Jeon H, Simon Jr CG, Kim G (2014) A mini-review: Cell response to microscale, nanoscale, and hierarchical patterning of surface structure. Journal of Biomedical Materials Research: Part B - Applied Biomaterials 102B, 1580-1594.
• Baker BA, Pine PS, Chatterjee K, Kumar G, Lin NJ, McDaniel JH, Salit ML, Simon Jr CG (2014) Ontology analysis of global gene expression differences of human bone marrow stromal cells cultured on 3D scaffolds or 2D films. Biomaterials 35, 6716-6726.
• Farooque TM, Camp Jr CH, Tison CK, Kumar G, Parekh SH, Simon Jr CG (2014) Measuring stem cell dimensionality in tissue scaffolds. Biomaterials 35, 2558-2567.
• Thein-Han WW, Weir MD, Simon CG, Xu HHK (2013) Non-rigid calcium phosphate cement containing hydrogel microbeads and absorbable fibres seeded with umbilical cord stem cells for bone engineering. Journal of Tissue Engineering and Regenerative Medicine 7, 777-787.
• Juba D, Cardone A, Ip CY, Simon Jr CG, Tison CK, Kumar G, Brady M, Varshney (2013) Parallel geometric classification of stem cells by their three dimensional morphology. Computational Science & Discovery 6, 015007.
• Marszalek JE, Simon Jr CG, Thodeti C, Adapala RK, Murthy A, Karim A (2013) 2.5D constructs for characterizing phase separated polymer blend surface morphology in tissue engineering scaffolds. Journal of Biomedical Materials Research: Part A 101A, 1502-1510.
• Tutak W, Sarkar S, Lin-Gibson S, Farooque TM, Jyotsnendu G, Wang D, Kohn J, Bolikal D, Simon Jr CG (2013) The Support of Bone Marrow Stromal Cell Differentiation by Airbrushed Nanofiber Scaffolds. Biomaterials 34, 2389-2398.
• Ramalingam M, Young MF, Thomas V, Sun L, Chow LC, Tison CK, Chatterjee K, Miles WC, Simon Jr CG (2013) Nanofiber scaffold gradients for interfacial tissue engineering. Journal of Biomaterials Applications 27, 695-705.
• Yeo M-G, Simon Jr CG, Kim G-H (2012) Effect of offset values of solid freeform fabricated PCL/β-TCP scaffolds on mechanical properties and cellular activities in bone tissue regeneration. Journal of Materials Chemistry 22, 21636-21646.
• Chatterjee K, Hung S, Kumar G, Simon Jr CG (2012) Time-dependent effects of pre-aging 3D polymer scaffolds in cell culture medium on cell proliferation. Journal of Functional Biomaterials 3, 372-381.
• Chatterjee K, Kraigsley AM, Bolikal D, Kohn J, Simon Jr CG. (2012) Gas-foamed scaffold gradients for combinatorial screening in 3D. Journal of Functional Biomaterials 3, 173-182.
• Kumar G, Waters, MS, Farooque TM, Young MF, Simon Jr CG (2012) Freeform fabricated scaffolds with roughened struts that enhance both stem cell proliferation and differentiation by controlling cell shape, Biomaterials 33, 4022-4030.
• Morris DE, Mather ML, Simon Jr CG, Crowe JA (2011) Time-optimized X-ray micro CT imaging of polymer based scaffolds. Journal of Biomedical Materials Research: Applied Biomaterials, 100B, 360-367.
• Xu HHK, Weir MD, Zhao L, Moreau JL, Arola DD, Simon CG (2011) Nano-apatitic composite scaffolds for stem cell delivery and bone tissue engineering, in "Nanotechnology for Dental Applications", Eds. Karthikeyan Subramani, Waqar Ahmed, Chapter 12, 189-207. 
• Kumar G, Tison CK, Chatterjee K, Pine PS, McDaniel JH, Salit ML, Young MF, Simon Jr CG (2011) The determination of stem cell fate by 3D scaffold structures through the control of cell shape. Biomaterials 32, 9188-9196.
• Wiederhorn SM, Chae Y-H, Simon Jr CG, Cahn J*, Deng Y, Day D (2011) Cell adhesion to borate glasses: an atomic force microscopy study. Acta Biomaterialia 7, 2256-2263. (*undergraduate)
• Chatterjee K, Young MF, Simon Jr CG (2011) Fabricating gradient hydrogel scaffolds for 3D cell culture. Combinatorial Chemistry and High-Throughput Screening 14, 227-236.
• Parekh SH, Chatterjee K, Lin-Gibson S, Moore NM, Cicerone MT, Young MF, Simon Jr CG (2011) Modulus-Driven Differentiation of Marrow Stromal Cells in 3D Is Independent of Cytoskeletal Integrity, Biomaterials 32, 2256-2264.
• Simon Jr CG , Lin-Gibson S (2011) Combinatorial and high-throughput screening of biomaterials. Advanced Materials 23, 369-387.
• Chatterjee K, Sun L, Chow LC, Young MF, Simon Jr CG (2011) Combinatorial screening of osteoblast response to 3D calcium phosphate/poly(e-caprolactone) scaffolds using gradients and arrays. Biomaterials 32, 1361-1369.
• Simon Jr CG, Yang Y, Dorsey SM*, Ramalingam M, Chatterjee K (2010) 3D polymer scaffold arrays. Methods in Molecular Biology: Biological Microarrays 671, 161-174. (*undergraduate)
• Chatterjee K, Lin-Gibson S, Wallace WE, Parekh SH, Lee YJ, Cicerone MT, Young MF, Simon Jr CG (2010) The effect of 3D hydrogel scaffold modulus on osteoblast differentiation and mineralization revealed by combinatorial screening. Biomaterials 31, 5051-5062.
• Simon Jr CG, Yang Y, Thomas V, Dorsey SM*, Morgan AW (2009) Cell interactions with biomaterials gradients and arrays. Combinatorial Chemistry and High-Throughput Screening 12, 544-553. (*undergraduate) (review)
• Simon Jr CG, Yang Y, Dorsey SM*, Ramalingam M, Chatterjee K (2009) 3D polymer scaffold arrays. Methods in Molecular Biology: Biological Microarrays, in press. [invited article from editor, Ali Khademhosseini (MIT)] (*undergraduate)
• Simon Jr CG, Yang Y, Thomas V, Dorsey SM*, Morgan AW (2009) Cell interactions with biomaterials gradients and arrays. Combinatorial Chemistry and High-Throughput Screening 12, 544-553. (*undergraduate) (review)
• Dorsey SM*, Lin-Gibson S, Simon Jr CG (2009) X-ray microcomputed tomography for the measurement of cell adhesion and proliferation in polymer scaffolds. Biomaterials 30, 2967–2974. (*undergraduate) (Leading Opinion Paper)
• Xu HHK, Weir MD, Simon Jr CG (2008) Injectable and strong nano-apatite scaffolds for cell/growth factor delivery and bone regeneration. Dental Materials 24, 1212-1222.
• Yang Y, Becker ML, Bolikal D, Kohn J, Zeiger DN, Simon Jr CG (2008) Combinatorial polymer scaffold libraries for screening cell-biomaterial interactions in 3D. Advanced Materials 20, 2037-2043.
• Chen RI*, Gallant ND, Smith JR, Kipper MJ, Simon Jr CG (2008) Time-dependent effects of pre-aging polymer films in cell medium on cell adhesion and spreading. Journal of Materials Science: Materials in Medicine 19, 1759-1766. (*undergraduate)
• Morgan AW, Roskov KE, Lin-Gibson S, Kaplan DL, Becker ML, Simon Jr CG (2008) Characterization and optimization of RGD-containing silk blends to support osteoblastic differentiation. Biomaterials 29, 2556-2563.
• Yang Y, Dorsey SM*, Becker ML, Lin-Gibson S, Schumacher GE, Flaim GM, Kohn J, Simon Jr CG (2008) X-ray imaging optimization of 3D tissue engineering scaffolds via combinatorial fabrication methods. Biomaterials 29, 1901-1911. (*undergraduate)
• Xu HHK, Carey LE, Simon Jr CG (2007) Premixed macroporous calcium phosphate cement scaffold. Journal of Materials Science: Materials in Medicine 18, 1345-1353.
• Simon Jr CG, Stephens JS, Dorsey SM*, Becker ML (2007) Fabrication of combinatorial polymer scaffold libraries. Review of Scientific Instruments 78, 0722071-0722077. (*undergraduate)
• Xu HHK, Carey LE, Simon Jr CG, Takagi S, Chow LC (2007) Premixed calcium phosphate cements: synthesis, physical properties and cell toxicity. Dental Materials 23, 433-441.
• Kennedy SB, Washburn NR, Simon Jr CG, Amis EJ (2006) Combinatorial screen of the effect of surface energy on fibronectin-mediated osteoblast adhesion, spreading and proliferation. Biomaterials 27, 3817-3824.
• Weir MD, Xu HHK, Simon Jr CG (2006) Strong calcium phosphate cement-chitosan-mesh construct containing cell-encapsulating hydrogel beads for bone tissue engineering. Journal of Biomedical Materials Research 77A, 487-496. (Cover Image)
• Simon Jr CG, Eidelman N, Kennedy SB, Sehgal A, Khatri CA, Washburn NR (2005) Combinatorial screening of cell proliferation on poly(L-lactic acid)/poly(D,L-lactic acid) blends. Biomaterials 26, 6906-6915.
• Zhang K, Simon Jr CG, Washburn NR, Antonucci JM, Lin-Gibson S (2005) In situ formation of blends by photopolymerization of poly(ethylene glycol) dimethacrylate (PEGDMA) and polylactide (PLA). Biomacromolecules 6, 1615-1622.
• Simon Jr CG, Antonucci JM, Skrtic D (2005) In vitro cytotoxicity of amorphous calcium phosphate composites. Journal of Bioactive and Compatible Polymers 20, 279-295.
• Carey LE, Xu HHK, Simon Jr CG, Takagi S, Chow LC (2005) Premixed rapid-setting calcium phosphate composites for bone repair. Biomaterials 26, 5002-5014.
• Zhang K, Washburn NR, Simon Jr CG (2005) Cytotoxicity of three-dimensionally ordered macroporous sol-gel bioactive glass (3DOM-BG). Biomaterials 26, 4532-4539.
• Xu HHK, Simon Jr CG (2005) Fast setting calcium phosphate-chitosan scaffold: mechanical properties and biocompatibility. Biomaterials 26, 1337-1348.
• Simon Jr CG, Deng Y, Eidelman N, Washburn NR (2004) High-throughput method for determining modulus of polymer blends. Macromolecular Rapid Communications 25, 2003-2007.  (Cover Image)
• Simon Jr CG (2004) Imaging cells on polymer spherulites. Journal of Microscopy 216, 153-155. (Cover Image)
• Eidelman N, Simon Jr CG (2004) Characterization of combinatorial polymer blend composition gradients by FTIR microspectroscopy. Journal of Research of the National Institute of Standards and Technology 109, 219-231.
• Xu HHK, Smith DT, Simon Jr CG (2004) Strong and bioactive composites containing nano-silica-fused whiskers for bone repair. Biomaterials, 25, 4615-4626.
• Xu HHK, Simon Jr CG (2004) Self-hardening calcium phosphate cement-mesh composite: reinforcement, macropores and biocomaptibility. Journal of Biomedical Materials Research 69A, 267-278. (Cover Image)
• Xu HHK, Simon Jr CG (2004) Self-hardening calcium phosphate composite scaffold for bone tissue engineering. Journal of Orthopaedic Research 22, 535-543. 
• Bailey LO, Washburn NR, Simon Jr CG, Wang FW, Chan E. (2004) Quantification of inflammatory cellular responses using real time polymerase chain reaction.  Journal of Biomedical Materials Research 69A, 305-313.
• Simon Jr CG, Guthrie WF, Wang FW (2004) Cell seeding into calcium phosphate cement. Journal of Biomedical Materials Research 68A, 628-639.
• Washburn NR, Yamada KM, Simon Jr CG, Kennedy SB, Amis EJ. (2004) High-throughput investigation of osteoblast response to crystalline polymers: influence of nanometer-scale roughness on proliferation. Biomaterials 25, 1215-1224.
• Simon Jr CG, Khatri CA, Wight SA, Wang FW (2002) Preliminary report on the biocompatibility of a moldable, resorbable, composite bone graft consisting of calcium phosphate cement and poly(lactide-co-glycolide) microspheres. Journal of Orthopaedic Research 20, 473-482.
• Washburn NR, Simon CG, Tona A, Elgendy HM, Karim A, Amis EJ (2002) Co-extrusion of biocompatible polymers for scaffolds with controlled morphology. Journal of Biomedical Materials Research 60, 20-29.  (Cover Image)
• Dahir GA, Cui Q, Anderson P, Simon Jr CG, Joyner C, Triffitt JT, Balian G (2000) Pluripotential Mesenchymal Cells Repopulate Bone Marrow and Retain Osteogenic Properties. Clinical Orthopaedics and Related Research 379S, S134-S145.
• Simon Jr CG, Holloway PW, Gear ARL (1999) Exchange of C16-ceramide between phospholipid vesicles. Biochemistry 38, 14676-14682.
• Simon Jr CG, Gear ARL (1999) Sphingolipid metabolism during human platelet activation. Thrombosis Research 94, 13-23.
• Polanowska-Grabowska R, Simon Jr CG, Gear ARL (1999) Platelet adhesion to collagen type I, collagen type IV, von Willebrand factor, fibronectin, laminin, and fibrinogen: rapid kinetics under shear. Thrombosis and Haemostasis 81, 118-123.
• Simon Jr CG, Chatterjee S, Gear ARL (1998) Sphingomyelinase activity in human platelets. Thrombosis Research 90, 155-161.
• Simon Jr CG, Gear ARL (1998) Membrane-destabilizing properties of C2-ceramide may be responsible for its ability to inhibit platelet aggregation. Biochemistry 37, 2059-2069.
• Gear ARL, Simon CG, Polanowska-Grabowska R (1997) Platelet adhesion to collagen activates a phosphoprotein complex of heat-shock proteins and protein phosphatase 1. Journal of Neural Transmission 104, 1037-1047.
• Polanowska-Grabowska R, Simon Jr CG, Falchetto R, Shabanowitz J, Hunt DF, Gear ARL (1997) Platelet adhesion to collagen under flow causes dissociation of a phosphoprotein complex of heat-shock proteins and protein phosphatase 1. Blood 90, 1516-1526.