{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T05:21:11Z","timestamp":1788326471210,"version":"build-2803163510"},"reference-count":48,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,8,31]],"date-time":"2026-08-31T00:00:00Z","timestamp":1788134400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Science and Technology Council","award":["NSTC 115-2314-B-075-082"],"award-info":[{"award-number":["NSTC 115-2314-B-075-082"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Bioengineering"],"abstract":"<jats:p>Adult acquired flatfoot deformity (AAFD) results from the collapse of the medial longitudinal arch (MLA), often managed conservatively with foot orthoses. While 3D printing enables rapid and cost-effective production of insoles, the biomechanical impact of different printing materials remains unclear. This study combined material testing, finite element (FE) simulation, and compression testing to evaluate four materials commonly used for 3D-printed insoles: PLA (polylactic acid), resin, EVA (ethylene vinyl acetate), and TPU (thermoplastic polyurethane). Tensile tests provided material properties for FE modeling of balanced standing using a validated healthy foot model. Outcome measures included MLA deformation (navicular drop), plantar stress distribution, and von Mises stress within the insole. A commercial semi-custom insole was tested for comparison. PLA and resin exhibited high stiffness (2228 and 880 MPa) and reduced navicular drop by 55\u201360%, compared with &lt;30% reductions by EVA and TPU. Plantar stress distribution shifted from forefoot and hindfoot toward the midfoot, with PLA increasing midfoot load share to 38%. Compression testing confirmed that PLA and resin exhibited greater arch support ability than the semi-custom insole within a 10 mm displacement threshold. Material stiffness strongly influenced the biomechanical performance of 3D-printed insoles. Within this static simulation baseline, PLA and resin provided superior arch stabilization and stress redistribution compared with EVA, TPU, and a semi-custom reference. These findings suggest that material choice is critical to optimizing 3D-printed orthotic support, providing a valuable biomechanical baseline to guide future orthotic designs for flatfoot.<\/jats:p>","DOI":"10.3390\/bioengineering13091010","type":"journal-article","created":{"date-parts":[[2026,8,31]],"date-time":"2026-08-31T09:21:19Z","timestamp":1788168079000},"page":"1010","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Impact of Material Stiffness on Medial Arch Support and Stress Redistribution in 3D-Printed Insoles for Adult Acquired Flatfoot Deformity"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-9022-1081","authenticated-orcid":false,"given":"Ping-Yen","family":"Tsai","sequence":"first","affiliation":[{"name":"Department of Physical Therapy, National Yang Ming Chiao Tung University, Taipei 112, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"investigation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"data-curation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"}]},{"given":"Chen-Sheng","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Physical Therapy, National Yang Ming Chiao Tung University, Taipei 112, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"conceptualization","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8707-1108","authenticated-orcid":false,"given":"Chien-Shun","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Orthopedics and Traumatology, Taipei Veterans General Hospital, Taipei 112, Taiwan"},{"name":"Department of Surgery, School of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"}]},{"given":"Ching-Hsuan","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Southern Taiwan University of Science and Technology, Tainan City 710, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"validation","vocabulary":"credit"},{"role":"software","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,31]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2473011418820847","DOI":"10.1177\/2473011418820847","article-title":"Adult-Acquired Flatfoot Deformity","volume":"4","author":"Henry","year":"2019","journal-title":"Foot Ankle Orthop."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2","DOI":"10.1016\/j.mporth.2022.11.001","article-title":"Adult Acquired Flatfoot Deformity: An Update in Classification","volume":"37","author":"Li","year":"2023","journal-title":"Orthop. Trauma"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"294","DOI":"10.1007\/s12178-013-9173-z","article-title":"Approach and Treatment of the Adult Acquired Flatfoot Deformity","volume":"6","author":"Vulcano","year":"2013","journal-title":"Curr. Rev. Musculoskelet. Med."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"311","DOI":"10.1053\/j.jfas.2011.02.002","article-title":"Nonoperative Care for the Treatment of Adult-Acquired Flatfoot Deformity","volume":"50","author":"Nielsen","year":"2011","journal-title":"J. Foot Ankle Surg."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"714","DOI":"10.2174\/1874325001711010714","article-title":"Posterior Tibial Tendon Dysfunction: An Overview","volume":"11","author":"Ling","year":"2017","journal-title":"Open Orthop. J."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"181","DOI":"10.1016\/j.fas.2019.01.007","article-title":"The Long-Term Structural Efect of Orthoses for Pediatric Flexible Flat Foot: A Systematic Review","volume":"26","author":"Choi","year":"2020","journal-title":"Foot Ankle Surg."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"169","DOI":"10.1080\/10400435.2022.2105438","article-title":"Effect of 3D Printed Insoles for People with Flatfeet: A Systematic Review","volume":"35","author":"Daryabor","year":"2023","journal-title":"Assist. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Lucas-Cuevas, A.G., Camacho-Garc\u00eda, A., Llinares, R., Priego Quesada, J.I., Llana-Belloch, S., and P\u00e9rez-Soriano, P. (2017). Influence of Custom-Made and Prefabricated Insoles Before and After an Intense Run. PLoS ONE, 12.","DOI":"10.1371\/journal.pone.0173179"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Brognara, L., Fantini, M., Morellato, K., Graziani, G., Baldini, N., and Cauli, O. (2022). Foot Orthosis and Sensorized House Slipper by 3D Printing. Materials, 15.","DOI":"10.3390\/ma15124064"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"22","DOI":"10.1186\/s41205-023-00187-7","article-title":"Development of an Individual Helmet Orthosis for Infants based on a 3D Scan","volume":"9","author":"Kropla","year":"2023","journal-title":"3D Print. Med."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1186\/s41205-025-00287-6","article-title":"Economic Evaluation of the Manufacturing of 3D-printed Wrist Orthoses vs Low Temperature Thermoplastic Wrist Orthoses","volume":"11","author":"Couchman","year":"2025","journal-title":"3D Print. Med."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"4989534","DOI":"10.1155\/2019\/4989534","article-title":"Biomechanical Evaluation and Strength Test of 3D-Printed Foot Orthoses","volume":"2019","author":"Lin","year":"2019","journal-title":"Appl. Bionics Biomech."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"3510","DOI":"10.12659\/MSM.916975","article-title":"Comparative Study of the Effects of Customized 3D Printed Insole and Prefabricated Iinsole on Plantar Pressure and Comfort in Patients with Symptomatic Flatfoot","volume":"25","author":"Xu","year":"2019","journal-title":"Med. Sci. Monit."},{"key":"ref_14","first-page":"237","article-title":"Effects of Customized 3D-printed Insoles on the Kinematics of Flat-footed Walking and Running","volume":"28","author":"Joo","year":"2018","journal-title":"Korean J. Appl. Biomech."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"112","DOI":"10.1177\/1938640017709906","article-title":"A Preliminary Study on the Effect of Computer-Aided Designed and Manufactured Orthoses on Chronic Plantar Heel Pain","volume":"11","author":"Gatt","year":"2018","journal-title":"Foot Ankle Spec."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1392","DOI":"10.12659\/MSM.915045","article-title":"Effect of 3D Printing Individualized Ankle-Foot Orthosis on Plantar Biomechanics and Pain in Patients with Plantar Fasciitis: A Randomized Controlled Trial","volume":"25","author":"Xu","year":"2019","journal-title":"Med. Sci. Monit."},{"key":"ref_17","first-page":"98","article-title":"A multidisciplinary review on footwear 3D printing: From biomechanics to therapeutics","volume":"11","author":"Kim","year":"2025","journal-title":"Int. J. Bioprinting"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"563","DOI":"10.1080\/10255842.2010.550165","article-title":"Biomechanical Analysis of Foot with Different Foot Arch Heights: A Finite Element Analysis","volume":"15","author":"Sun","year":"2012","journal-title":"Comput. Methods Biomech. Biomed. Eng."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"90","DOI":"10.1177\/1071100714549189","article-title":"Finite Element Analysis of Plantar Fascia during Walking: A Quasi-static Simulation","volume":"36","author":"Chen","year":"2015","journal-title":"Foot Ankle Int."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"10","DOI":"10.1016\/j.clinbiomech.2017.11.001","article-title":"Finite Element Simulation on Posterior Tibial Tendinopathy: Load Transfer Alteration and Implications to the Onset of Pes Planus","volume":"51","author":"Wong","year":"2018","journal-title":"Clin. Biomech."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"105383","DOI":"10.1016\/j.clinbiomech.2021.105383","article-title":"Peroneus Longus Overload caused by Soft Tissue Deficiencies associated with Early Adult Acquired Flatfoot: A Finite Element Analysis","volume":"86","author":"Pasapula","year":"2021","journal-title":"Clin. Biomech."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"104355","DOI":"10.1016\/j.compbiomed.2021.104355","article-title":"Influence of Arch Support Heights on the Internal foot Mechanics of Flatfoot during Walking: A Muscle-Driven Finite Element Analysis","volume":"132","author":"Peng","year":"2021","journal-title":"Comput. Biol. Med."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Raj, R., Dixit, A.R., \u0141ukaszewski, K., Wichniarek, R., Rybarczyk, J., Kuczko, W., and G\u00f3rski, F. (2022). Numerical and Experimental Mechanical Analysis of Additively Manufactured Ankle-Foot Orthoses. Materials, 15.","DOI":"10.3390\/ma15176130"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"15395","DOI":"10.1038\/s41598-022-19814-0","article-title":"Effects of Contoured Insoles with Different Materials on Plantar Pressure Offloading in Diabetic Elderly during Gait","volume":"12","author":"Shi","year":"2022","journal-title":"Sci. Rep."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1692","DOI":"10.1039\/D2BM01538B","article-title":"Photocurable and Elastic Polyurethane based on Polyether Glycol with Adjustable Hardness for 3D Printing Customized Flatfoot Orthosis","volume":"11","author":"Zhao","year":"2023","journal-title":"Biomater. Sci."},{"key":"ref_26","first-page":"105","article-title":"3D Printing of Individual Running Insoles\u2014A Case Study","volume":"15","author":"Danko","year":"2023","journal-title":"Orthop. Res. Rev."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Hsu, C.Y., Wang, C.S., Lin, K.W., Chien, M.J., Wei, S.H., and Chen, C.S. (2022). Biomechanical Analysis of the FlatFoot with Different 3D-Printed Insoles on the Lower Extremities. Bioengineering, 9.","DOI":"10.3390\/bioengineering9100563"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1799","DOI":"10.1007\/s11517-017-1623-0","article-title":"Biomechanical Evaluation of Reconstruction Plates with Locking, Nonlocking, and Hybrid Screws Configurations in Calcaneal Fracture: A Finite Element Model Study","volume":"55","author":"Chen","year":"2017","journal-title":"Med. Biol. Eng. Comput."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1016\/j.compositesb.2017.05.013","article-title":"Experimental Characterization and Micrography of 3D Printed PLA and PLA Reinforced with Short Carbon Fibers","volume":"124","author":"Ferreira","year":"2017","journal-title":"Compos. Part B Eng."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Dias Gon\u00e7alves, V.P., Vieira, C.M.F., Simonassi, N.T., Periss\u00e9 Duarte Lopes, F., Youssef, G., and Colorado, H.A. (2024). Evaluation of Mechanical Properties of ABS-like Resin for Stereolithography versus ABS for Fused Deposition Modeling in Three-Dimensional Printing Applications for Odontology. Polymers, 16.","DOI":"10.3390\/polym16202921"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"045015","DOI":"10.1088\/1361-665X\/ab6696","article-title":"A Novel 3D Re-entrant Unit Cell Structure with Negative Poisson\u2019s Ratio and Tunable Stiffness","volume":"29","author":"Li","year":"2020","journal-title":"Smart Mater. Struct."},{"key":"ref_32","unstructured":"Magee, D.J., and Manske, R.C. (2020). Orthopedic Physical Assessment-E-Book, Elsevier Health Sciences."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"3170","DOI":"10.1016\/j.jbiomech.2015.07.004","article-title":"Biomechanical Behavior of Valgus Foot in Children with Cerebral Palsy: A Comparative Study","volume":"48","author":"Guo","year":"2015","journal-title":"J. Biomech."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"396","DOI":"10.23736\/S1973-9087.23.07846-2","article-title":"The Combined Effect of Short Foot Exercises and Orthosis in Symptomatic Flexible Flatfoot: A Randomized Controlled Trial","volume":"59","author":"Elsayed","year":"2023","journal-title":"Eur. J. Phys. Rehabil. Med."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"22","DOI":"10.1016\/j.foot.2012.12.001","article-title":"Exercise Therapy and Custom-Made Insoles are Effective in Patients with Excessive Pronation and Chronic Foot Pain\u2014A Randomized Controlled Trial","volume":"23","author":"Andreasen","year":"2013","journal-title":"Foot"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"3136","DOI":"10.1589\/jpts.28.3136","article-title":"The Effects of Short Foot Exercises and Arch Support Insoles on Improvement in The Medial Longitudinal Arch and Dynamic Balance of FlexibleFlatfoot Patients","volume":"28","author":"Kim","year":"2016","journal-title":"J. Phys. Ther. Sci."},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Huang, C., Chen, L.Y., Liao, Y.H., Masodsai, K., and Lin, Y.Y. (2022). Effects of The Short-Foot Exercise on Foot Alignment and Muscle Hypertrophy in Flatfoot Individuals: A Meta-Analysis. Int. J. Environ. Res. Public Health, 19.","DOI":"10.3390\/ijerph191911994"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"8614341","DOI":"10.1155\/2017\/8614341","article-title":"The Effect of Arch Height and Material Hardness of Personalized Insole on Correction and Tissues of Flatfoot","volume":"2017","author":"Su","year":"2017","journal-title":"J. Healthc. Eng."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1007\/s40964-017-0023-1","article-title":"The Manufacture of 3D Printing of Medical Grade TPU","volume":"2","author":"Xiao","year":"2017","journal-title":"Prog. Addit. Manuf."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"070801","DOI":"10.1115\/1.4062311","article-title":"Applications of Finite Element Modeling in Biomechanical Analysis of Foot Arch Deformation: A Scoping Review","volume":"145","author":"Cen","year":"2023","journal-title":"ASME. J. Biomech. Eng."},{"key":"ref_41","first-page":"23","article-title":"Common Etiology, Pathogenesis and Potential Effective Treatments for Calcaneal Fat Pad Deterioration: A Literature","volume":"31","author":"Jaswal","year":"2022","journal-title":"Podiatr. Med. Rev."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"1345","DOI":"10.1007\/s10439-008-9516-x","article-title":"Using an Optimization Approach to Design an Insole for Lowering Plantar Fascia Stress\u2014A Finite Element Study","volume":"36","author":"Hsu","year":"2008","journal-title":"Ann. Biomed. Eng."},{"key":"ref_43","first-page":"469","article-title":"Hypermobility of The First Ray","volume":"5","author":"Myerson","year":"2000","journal-title":"Foot Ankle Clin."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"S8","DOI":"10.1016\/S0303-8467(15)30004-4","article-title":"The Effects of Total Contact Insole with Forefoot Medial Posting on Rearfoot Movement and Foot Pressure Distributions in Patients with Flexible Flatfoot","volume":"129","author":"Tang","year":"2015","journal-title":"Clin. Neurol. Neurosurg."},{"key":"ref_45","doi-asserted-by":"crossref","unstructured":"Huang, Y.P., Peng, H.T., Wang, X., Chen, Z.R., and Song, C.Y. (2020). The Arch Support Insoles Show Benefits to People with Flatfoot on Stance Time, Cadence, Plantar Pressure and Contact Area. PLoS ONE, 15.","DOI":"10.1371\/journal.pone.0237382"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1919","DOI":"10.1007\/s10237-022-01629-7","article-title":"A three-dimensional whole-body model to predict human walking on level ground","volume":"21","author":"Hu","year":"2022","journal-title":"Biomech. Model. Mechanobiol."},{"key":"ref_47","doi-asserted-by":"crossref","unstructured":"D\u2019Hondt, L., De Groote, F., and Afschrift, M. (2024). A dynamic foot model for predictive simulations of human gait reveals causal relations between foot structure and whole-body mechanics. PLoS Comput. Biol., 20.","DOI":"10.1371\/journal.pcbi.1012219"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"103802","DOI":"10.1016\/j.medengphy.2022.103802","article-title":"A novel workflow to fabricate a patient-specific 3D printed accommodative foot orthosis with personalized latticed metamaterial","volume":"104","author":"Hudak","year":"2022","journal-title":"Med. Eng. Phys."}],"container-title":["Bioengineering"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2306-5354\/13\/9\/1010\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T04:40:52Z","timestamp":1788324052000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2306-5354\/13\/9\/1010"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,31]]},"references-count":48,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["bioengineering13091010"],"URL":"https:\/\/doi.org\/10.3390\/bioengineering13091010","relation":{},"ISSN":["2306-5354"],"issn-type":[{"value":"2306-5354","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,31]]}}}