{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/109592"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/109592","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Wear mechanisms of chemically crosslinked hydrogels under mild abrasion","abstract":"The structural and mechanical resemblance of hydrogels to cartilage makes them promising candidates for cartilage replacement in load bearing joints. These biphasic materials are composed of an elastic network that retains a large volume of water allowing them to efficiently maintain smooth sliding while under high compressive loads. As with any sliding interface under high loads, the hydrogels in this application would be highly susceptible to wear. While the fluid component of these materials mediates low friction sliding, the hydrophilic polymer network of hydrogels can endure only a limited number of sliding cycles. For hydrogels to be viable candidates to replace osteoarthritic cartilage, a study of their robust long-term use and surface failure mechanism is necessary. In this dissertation, we evaluate different aspects of the wear behavior of hydrogels to develop tools for predicting their wear resistance as well as to improve future hydrogel surface design to withstand the severe environment of the body. Pristine hydrogel surfaces typically have low friction, which is controlled by composition, slip speeds, and immediate slip history. The stiffness of such samples is typically measured with bulk techniques and is assumed to be homogeneous at the surface. While the surface properties of homogeneous hydrogel samples are generally controlled by composition, the surface also interfaces with the open bath, which distinguishes it from the bulk. Because structure dictates function, the surface structural inhomogeneity inherent of hydrogels influences its wear behavior. Through the disruption of polyacrylamide hydrogel surfaces with abrasive wear, we connect the effects of the surface structure to the mechanical performance using microtribometry with a rough probe to apply wear. Through our measurements of surface stiffness and lubrication of worn and unworn hydrogels, we found that wear increases their surface stiffness and decreases their frictional speed dependence by revealing a stiffer bulk. As this newly revealed bulk interacts with the water bath, it regenerates its soft, swollen surface with its properties resembling that of the unworn surface. Because the magnitude of wear and the resulting surface features depend on the wear application parameters, we wore the surface of hydrogels under different sliding conditions. The load, hydrophilicity of the surface mold, stroke length, and experimental duration influenced the degree of microplowing and microcutting whereas the tested sliding speeds had negligible effects. Considering that wear is a microfracture process, by relating the wear rate of hydrogels with varying concentrations of polymer and crosslinker to their corresponding threshold fatigue fracture, an expression for predicting wear rate for single network chemically crosslinked hydrogels was developed. Incorporating a strengthening agent into the hydrogel network did not affect its wear behavior; however, increasing the toughness of hydrogels through a double network architecture significantly increased their wear resistance. While the double network hydrogels maintained incredibly low wear rates, their wear behavior and features were markedly different from that of porcine cartilage. Cartilage has a strong ability to swell their surface locally within the wear scar reducing the appearance of surface damage, which is a valuable property to integrate into future double network hydrogel designs. This dissertation provides a foundation to better predict the lifespan of hydrogels in different sliding applications as well as improve their design to be more resilient.","abstract_html":"The structural and mechanical resemblance of hydrogels to cartilage makes them promising candidates for cartilage replacement in load bearing joints. These biphasic materials are composed of an elastic network that retains a large volume of water allowing them to efficiently maintain smooth sliding while under high compressive loads. As with any sliding interface under high loads, the hydrogels in this application would be highly susceptible to wear. While the fluid component of these materials mediates low friction sliding, the hydrophilic polymer network of hydrogels can endure only a limited number of sliding cycles. For hydrogels to be viable candidates to replace osteoarthritic cartilage, a study of their robust long-term use and surface failure mechanism is necessary. In this dissertation, we evaluate different aspects of the wear behavior of hydrogels to develop tools for predicting their wear resistance as well as to improve future hydrogel surface design to withstand the severe environment of the body. Pristine hydrogel surfaces typically have low friction, which is controlled by composition, slip speeds, and immediate slip history. The stiffness of such samples is typically measured with bulk techniques and is assumed to be homogeneous at the surface. While the surface properties of homogeneous hydrogel samples are generally controlled by composition, the surface also interfaces with the open bath, which distinguishes it from the bulk. Because structure dictates function, the surface structural inhomogeneity inherent of hydrogels influences its wear behavior. Through the disruption of polyacrylamide hydrogel surfaces with abrasive wear, we connect the effects of the surface structure to the mechanical performance using microtribometry with a rough probe to apply wear. Through our measurements of surface stiffness and lubrication of worn and unworn hydrogels, we found that wear increases their surface stiffness and decreases their frictional speed dependence by revealing a stiffer bulk. As this newly revealed bulk interacts with the water bath, it regenerates its soft, swollen surface with its properties resembling that of the unworn surface. Because the magnitude of wear and the resulting surface features depend on the wear application parameters, we wore the surface of hydrogels under different sliding conditions. The load, hydrophilicity of the surface mold, stroke length, and experimental duration influenced the degree of microplowing and microcutting whereas the tested sliding speeds had negligible effects. Considering that wear is a microfracture process, by relating the wear rate of hydrogels with varying concentrations of polymer and crosslinker to their corresponding threshold fatigue fracture, an expression for predicting wear rate for single network chemically crosslinked hydrogels was developed. Incorporating a strengthening agent into the hydrogel network did not affect its wear behavior; however, increasing the toughness of hydrogels through a double network architecture significantly increased their wear resistance. While the double network hydrogels maintained incredibly low wear rates, their wear behavior and features were markedly different from that of porcine cartilage. Cartilage has a strong ability to swell their surface locally within the wear scar reducing the appearance of surface damage, which is a valuable property to integrate into future double network hydrogel designs. This dissertation provides a foundation to better predict the lifespan of hydrogels in different sliding applications as well as improve their design to be more resilient.","abstract_has_math":false,"creators":["Bonyadi, Shabnam Zahra"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Mechanical Engineering","degree_department":null,"school":null,"contributors":["Dunn, Alison C","Jasiuk, Iwona M","Wagoner Johnson, Amy J","Elbanna, Ahmed E"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2021,"date_issued":"2021-03-05T21:45:35Z","date_published":"2021-03-05T21:45:35Z","updated_at":"2026-07-22T22:24:50Z","subjects":["wear","hydrogels","friction","tribology","fracture","fatigue"],"languages":["en"],"rights":["Copyright 2020 Shabnam Bonyadi"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/109592","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Dunn, Alison C","Jasiuk, Iwona M","Wagoner Johnson, Amy J","Elbanna, Ahmed E"]},{"key":"dc:creator","label":"Author","values":["Bonyadi, Shabnam Zahra"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2021-03-05T21:45:35Z","2023-03-05T21:47:41Z","2020-12-02","2020-12"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Mechanical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["wear","hydrogels","friction","tribology","fracture","fatigue"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2020 Shabnam Bonyadi"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/109592"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The structural and mechanical resemblance of hydrogels to cartilage makes them promising candidates for cartilage replacement in load bearing joints. These biphasic materials are composed of an elastic network that retains a large volume of water allowing them to efficiently maintain smooth sliding while under high compressive loads. As with any sliding interface under high loads, the hydrogels in this application would be highly susceptible to wear. While the fluid component of these materials mediates low friction sliding, the hydrophilic polymer network of hydrogels can endure only a limited number of sliding cycles. For hydrogels to be viable candidates to replace osteoarthritic cartilage, a study of their robust long-term use and surface failure mechanism is necessary. In this dissertation, we evaluate different aspects of the wear behavior of hydrogels to develop tools for predicting their wear resistance as well as to improve future hydrogel surface design to withstand the severe environment of the body. Pristine hydrogel surfaces typically have low friction, which is controlled by composition, slip speeds, and immediate slip history. The stiffness of such samples is typically measured with bulk techniques and is assumed to be homogeneous at the surface. While the surface properties of homogeneous hydrogel samples are generally controlled by composition, the surface also interfaces with the open bath, which distinguishes it from the bulk. Because structure dictates function, the surface structural inhomogeneity inherent of hydrogels influences its wear behavior. Through the disruption of polyacrylamide hydrogel surfaces with abrasive wear, we connect the effects of the surface structure to the mechanical performance using microtribometry with a rough probe to apply wear. Through our measurements of surface stiffness and lubrication of worn and unworn hydrogels, we found that wear increases their surface stiffness and decreases their frictional speed dependence by revealing a stiffer bulk. As this newly revealed bulk interacts with the water bath, it regenerates its soft, swollen surface with its properties resembling that of the unworn surface. Because the magnitude of wear and the resulting surface features depend on the wear application parameters, we wore the surface of hydrogels under different sliding conditions. The load, hydrophilicity of the surface mold, stroke length, and experimental duration influenced the degree of microplowing and microcutting whereas the tested sliding speeds had negligible effects. Considering that wear is a microfracture process, by relating the wear rate of hydrogels with varying concentrations of polymer and crosslinker to their corresponding threshold fatigue fracture, an expression for predicting wear rate for single network chemically crosslinked hydrogels was developed. Incorporating a strengthening agent into the hydrogel network did not affect its wear behavior; however, increasing the toughness of hydrogels through a double network architecture significantly increased their wear resistance. While the double network hydrogels maintained incredibly low wear rates, their wear behavior and features were markedly different from that of porcine cartilage. Cartilage has a strong ability to swell their surface locally within the wear scar reducing the appearance of surface damage, which is a valuable property to integrate into future double network hydrogel designs. This dissertation provides a foundation to better predict the lifespan of hydrogels in different sliding applications as well as improve their design to be more resilient.","Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-12-01","The student, Shabnam Bonyadi, accepted the attached license on 2020-11-23 at 13:01.","The student, Shabnam Bonyadi, submitted this Dissertation for approval on 2020-11-28 at 17:47.","This Dissertation was approved for publication on 2020-12-02 at 16:32.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15941 on 2021-03-04 at 16:32:14","Made available in DSpace on 2021-03-05T21:45:35Z (GMT). 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These biphasic materials are composed of an elastic network that retains a large volume of water allowing them to efficiently maintain smooth sliding while under high compressive loads. As with any sliding interface under high loads, the hydrogels in this application would be highly susceptible to wear. While the fluid component of these materials mediates low friction sliding, the hydrophilic polymer network of hydrogels can endure only a limited number of sliding cycles. For hydrogels to be viable candidates to replace osteoarthritic cartilage, a study of their robust long-term use and surface failure mechanism is necessary. In this dissertation, we evaluate different aspects of the wear behavior of hydrogels to develop tools for predicting their wear resistance as well as to improve future hydrogel surface design to withstand the severe environment of the body. Pristine hydrogel surfaces typically have low friction, which is controlled by composition, slip speeds, and immediate slip history. The stiffness of such samples is typically measured with bulk techniques and is assumed to be homogeneous at the surface. While the surface properties of homogeneous hydrogel samples are generally controlled by composition, the surface also interfaces with the open bath, which distinguishes it from the bulk. Because structure dictates function, the surface structural inhomogeneity inherent of hydrogels influences its wear behavior. Through the disruption of polyacrylamide hydrogel surfaces with abrasive wear, we connect the effects of the surface structure to the mechanical performance using microtribometry with a rough probe to apply wear. Through our measurements of surface stiffness and lubrication of worn and unworn hydrogels, we found that wear increases their surface stiffness and decreases their frictional speed dependence by revealing a stiffer bulk. As this newly revealed bulk interacts with the water bath, it regenerates its soft, swollen surface with its properties resembling that of the unworn surface. Because the magnitude of wear and the resulting surface features depend on the wear application parameters, we wore the surface of hydrogels under different sliding conditions. The load, hydrophilicity of the surface mold, stroke length, and experimental duration influenced the degree of microplowing and microcutting whereas the tested sliding speeds had negligible effects. Considering that wear is a microfracture process, by relating the wear rate of hydrogels with varying concentrations of polymer and crosslinker to their corresponding threshold fatigue fracture, an expression for predicting wear rate for single network chemically crosslinked hydrogels was developed. Incorporating a strengthening agent into the hydrogel network did not affect its wear behavior; however, increasing the toughness of hydrogels through a double network architecture significantly increased their wear resistance. While the double network hydrogels maintained incredibly low wear rates, their wear behavior and features were markedly different from that of porcine cartilage. Cartilage has a strong ability to swell their surface locally within the wear scar reducing the appearance of surface damage, which is a valuable property to integrate into future double network hydrogel designs. This dissertation provides a foundation to better predict the lifespan of hydrogels in different sliding applications as well as improve their design to be more resilient.","Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-12-01","The student, Shabnam Bonyadi, accepted the attached license on 2020-11-23 at 13:01.","The student, Shabnam Bonyadi, submitted this Dissertation for approval on 2020-11-28 at 17:47.","This Dissertation was approved for publication on 2020-12-02 at 16:32.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15941 on 2021-03-04 at 16:32:14","Made available in DSpace on 2021-03-05T21:45:35Z (GMT). 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