Multi-modal characterization of polymeric gels to determine the influence of testing method on observed elastic modulus David M. Kingsley, Caitlin H.McCleery, Christopher D.L.Johnson, Michael T.K.Bramson, Deniz Rende, Ryan J.Gilbert, David T.Corr Journal of the Mechanical Behavior of Biomedical Materials, available online 10 January 2019, https://doi.org/10.1016/j.jmbbm.2019.01.003 Demand for materials that mechanically replicate native tissue has driven development and characterization of various new biomaterials. However, a consequence of materials and characterization technique diversity is a lack of consensus within the... Read More https://www.sciencedirect.com/science/article/pii/S1751616118308518#f0015 Cross-linked Cellulose Nanocrystal Aerogels as Viable Bone Tissue Scaffolds Daniel A. Osorioa, Bryan E.J. Lee, Jacek M. Kwiecien, Xiaoyue Wang, Iflah Shahid, Ariana L. Hurley, Emily D. Cranston, Kathryn Grandfield Acta Biomaterialia, 2019, https://doi.org/10.1016/j.actbio.2019.01.049 Chemically cross-linked cellulose nanocrystal (CNC) aerogels possess many properties beneficial for bone tissue scaffolding applications. CNCs were extracted using sulfuric acid or phosphoric acid, to produce CNCs with sulfate and phosphate... Read More https://www.sciencedirect.com/science/article/pii/S1742706119300716 Viscoelasticity and histology of the human cartilage in healthy and degenerated conditions of the knee Michael Seidenstuecker, Julius Watrinet , Anke Bernstein, Norbert P. Suedkamp , Sergio H. Latorre Anastasija Maks and Hermann O. Mayr Journal of Orthopaedic Surgery and Research, November 2019, 14:256. DOI: 10.1186/s13018-019-1308-5 Background: There are many studies on osteoarthritis, but only a few studies deal with human arthrosis, comparing the mechanical properties of healthy and diseased samples. In most of these studies, only isolated areas of the tibia are... Read More https://www.researchgate.net/publication/335156117_Viscoelasticity_and_histology_of_the_human_cartilage_in_healthy_and_degenerated_conditions_of_the_knee High Impact Exercise Improves Bone Microstructure and Strength in Growing Rats M. Tanvir, I. Londono, F. Moldovan and I. Villemure Nature Scientific Reports, volume 9, Article number: 13128 (2019) https://doi.org/10.1038/s41598-019-49432-2 Physical activity is beneficial for skeletal development. However, impact sports during adolescence, leading to bone growth retardation and/or bone quality improvement, remains unexplained. This study investigated the effects of in vivo low... Read More https://www.nature.com/articles/s41598-019-49432-2 A study of saliva lubrication using a compliant oral mimic G. Carpenter, S. Bozorgi, S. Vladescu, A.E. Forte, C. Myant, R.V. Potineni, T. Reddyhoff, and S.K. Baier Food Hydrocolloids, Elsevier, Available online 23 January 2019, https://doi.org/10.1016/j.foodhyd.2019.01.049 Due to ethical issues and the difficulty in obtaining biological tissues, it is important to find synthetic elastomers that can be used as replacement test media for research purposes. An important example of this is friction testing to... Read More https://www.sciencedirect.com/science/article/pii/S0268005X1831885X Experimental and finite element analyses of bone strains in the growing rat tibia induced by in vivo axial compression Tanvir Mustafy, Irène Londono, Isabelle Villemure Journal of the Mechanical Behavior of Biomedical Materials The objective of this study was to develop and validate a voxel based FE modeling approach to investigate bone strains from in vivo rat tibial compression during the adolescent period. To do so, in vivo strain gauge measurements and voxel based... Read More https://doi.org/10.1016/j.jmbbm.2019.03.009 Properties of Biopolymer Films in Ionic Solutions and Their Applications as 3D Printed Personalized Wound Dressings D.P. Ramos University of Toronto (Canada), ProQuest Dissertations Publishing, 2019. 13805509. This thesis describes the effects of ionic solutions on biopolymer films and the development of a 3D printed personalized wound dressing. Chitosan, gelatin, and composite chitosan/gelatin films were exposed to NaCl, Na2SO4, and CaCl2... Read More https://search.proquest.com/openview/1e26de46c42e25c0898d7b9ab138b6c7/1?pq-origsite=gscholar&cbl=18750&diss=y Quantifying vocal fold wound?healing biomechanical property changes G. R. Dion, T. Guda, S. Mukudai, R.Bing, J-F. Lavoie and R.C. Branski Laryngoscope. 2019 May 6. doi: 10.1002/lary.27999 Objectives Development of novel vocal fold (VF) therapeutics is limited by a lack of standardized, meaningful outcomes. We hypothesize that automated microindentation?based VF biomechanical property mapping matched to histology... Read More https://www.ncbi.nlm.nih.gov/pubmed/31059589 Compressive Mechanical Properties of Porcine Brain: Experimentation and Modeling of the Tissue Hydration Effects R.K. Prabhu, M.T. Begonia, W.R. Whittington, M.A. Murphy, Y. Mao, J. Liao, L.N. Williams, M.F. Horstemeyer and J. Sheng Bioengineering 2019, 6, 40; doi:10.3390/bioengineering6020040 Abstract: Designing protective systems for the human head—and, hence, the brain—requires understanding the brain’s microstructural response to mechanical insults. We present the behavior of wet and dry porcine brain undergoing... Read More https://www.ncbi.nlm.nih.gov/pubmed/31067801 Injectable Poly(oligoethylene glycol methacrylate)-Based Hydrogels Fabricated from Highly Branched Precursor Polymers: Controlling Gel Properties by Precursor Polymer Morphology Ivan Urosev, Helen Dorrington, Nicola Muzzin, Richard Alsop, Emilia Bakaic, Trevor Gilbert, Maikel Rheinst?dter and Todd Hoare ACS Applied Polymer Materials, 2019, 1, 3, 369-380 January 24, 2019 https://doi.org/10.1021/acsapm.8b00085 The physicochemical properties of injectable hydrogels are typically modified by altering the chemistry of the precursor polymer and/or the amount or type of cross-linker, both of which can lead to hydrogels with altered mechanics, swelling,... Read More https://pubs.acs.org/doi/10.1021/acsapm.8b00085 Intervertebral disc implant R Kandel, JP Santerre, SQ Li US Patent App. 10195044, 2019 The present inventors have generated the tissues that comprise the intervertebral disc and have established viable protocols and tissue conditions that facilitate integration of all the tissue components into one functional tissue so it can... Read More https://patentimages.storage.googleapis.com/42/7a/ef/ff71221c3da781/US10195044.pdf Comparative study on complexes formed by chitosan and different polyanions: Potential of chitosan-pectin biomaterials as scaffolds in tissue engineering Fernanda Carla Bombaldi de Souza, Renata Francielle Bombaldi de Souza, Bernard Drouin, Diego Mantovani and Angela Maria Moraes International Journal of Biological Macromolecules, Volume 132, 1 July 2019, Pages 178-189 Polyelectrolyte complexes of chitosan (Ch) and pectin (Pc) or alginate (Alg) were produced in the presence or absence of the silicone gel Silpuran? 2130 A/B (Sil) and the surfactant Kolliphor? P188 (Kol). Ch-Pc-Kol-based formulations presented... Read More https://www.sciencedirect.com/science/article/pii/S0141813019308141 On-Demand Radial Electrodeposition of Alginate Tubular Structures D. M. Kingsley, J. A. Capuano and D. T. Corr ACS Biomater. Sci. Eng. Publication Date:June 12, 2019, https://doi.org/10.1021/acsbiomaterials.9b00415 We present an electrodeposition technique for fabricating tubular alginate structures. In this technique, two electrodes (anode and cathode) are suspended in a solution of alginate and insoluble calcium carbonate particles, and the application of... Read More https://pubs.acs.org/doi/abs/10.1021/acsbiomaterials.9b00415 Osteochondral Repair and Electromechanical Evaluation of Custom 3D Scaffold Microstructured by Direct Laser Writing Lithography J. Maciulaitis, M. Miskiniene, S. Rekstyte, M.Bratchikov, A. Darinskas, A.Simbelyte, G. Daunoras, A. Laurinaviciene, A. Laurinavicius, R. Gudas, M. Malinauskas and R. Maciulaitis Cartilage · May 2019, https://doi.org/10.1177/1947603519847745 Objective The objective of this study was to assess a novel 3D microstructured scaffold seeded with allogeneic chondrocytes (cells) in a rabbit osteochondral defect model. Design Direct laser writing lithography in... Read More https://journals.sagepub.com/doi/abs/10.1177/1947603519847745?journalCode=cara Magnesium phosphate hydrogels F Tamimi Marino, A Ali Al-Hashedi, M Laurenti, A Ebraheem Al Subaie, M-N Abdallah, I Tamimi Marino https://patents.google.com/patent/US20190002282A1/en The present invention relates to magnesium phosphate hydrogels. More specifically, the present invention is concerned with such gels and their uses as scaffolds for bone tissue engineering, as drug delivery systems and in pastes for cleaning dental... Read More https://patents.google.com/patent/US20190002282A1/en Injectable Poly(Oligoethylene Glycol Methacrylate)-Based Hydrogels Fabricated from Highly Branched Precursor Polymers: Controlling Gel Properties by Precursor Polymer Morphology I. Urosev, H. Dorrington, N. Muzzin, R.J. Alsop, E. Bakaic, T. Gilbert, M.C. Rheinstadter, and T. Hoare ACS Applied Polymer Materials Just Accepted Manuscript, DOI: 10.1021/acsapm.8b00085 The physicochemical properties of injectable hydrogels are typically modified by altering the chemistry of the precursor polymer and/or the... Read More https://pubs.acs.org/doi/pdf/10.1021/acsapm.8b00085 Bone-Specific Overexpression of PITX1 Induces Senile Osteoporosis in Mice Through Deficient Self-Renewal of Mesenchymal Progenitors and Wnt Pathway Inhibition N. Karam, J-F. Lavoie, B. St-Jacques, S. Bouhanik, A. Franco, N. Ladoul and A. Moreau Scientific Reports volume 9, Article number: 3544 (2019) The cellular and molecular mechanisms underlying senile osteoporosisremain poorly understood. In this study, transgenic mCol1?1-Pitx1 miceoverexpressing paired-like homeodomain 1 (PITX1), a homeobox transcriptionfactor, rapidly develop a severe... Read More https://www.nature.com/articles/s41598-019-40274-6 GO-Modified flexible polymer nanocomposites fabricated via 3D stereolithography C.H.A. Tsang, A. Zhakeyev, D. Y.C. Leung and J. Xuan Front. Chem. Sci. Eng. (2019). https://doi.org/10.1007/s11705-019-1836-x Graphene oxide (GO) induced enhancement of elastomer properties showed a great deal of potential in recent years, but it is still limited by the barrier of the complicated synthesis processes. Stereolithography(SLA),used in fabrication of... Read More https://link.springer.com/article/10.1007/s11705-019-1836-x High-throughput synthesis, analysis, and optimization of injectable hydrogels for protein delivery Fei Xu, Brandon Corbett, Sydney Bell, Chiyan Zhang, Monika Budi Hartono, Zohreh Jomeh Farsangi, John F MacGregor and Todd Hoare Biomacromelecules 2019, Publication Date: November 5, 2019, https://doi.org/10.1021/acs.biomac.9b01132 The development of in situ-gelling hydrogels that can enable prolonged protein release is increasingly important due to the emergence of a growing number of protein-based therapeutics. Herein, we describe a high-throughput strategy to fabricate,... Read More https://pubs.acs.org/doi/abs/10.1021/acs.biomac.9b01132 Simulation of Acoustic Propagation in 3D Viscoelastic Inhomogeneous Media with Application to Medical Shear Wave Elastography P. S. Bidari, H. Assi, R. S. C. Cobbold, J. Alirezaie and J. Tavakkoli Journal of Theoretical and Computational Acoustics Vol. 27, No. 03, 1950003 (2019) Research Papers, https://doi.org/10.1142/S2591728519500038 This paper proposes a new numerical framework to simulate ultrasound wave propagation in 3D viscoelastic heterogeneous media based on the elastodynamic wave equation including a 3D second-order time-domain perfectly matched layer formulation. A... Read More https://www.worldscientific.com/doi/abs/10.1142/S2591728519500038 High-Throughput Synthesis and Characterization of Aryl Silicones Using the Piers-Rubinsztajn Reaction A.F. Schneider and M.A. Brook Chemistry–A European Journal 09 October 2019 https://doi.org/10.1002/chem.201903658 Arylsilicones are widely exploited for their thermal and optical properties. The creation of phenylsilicone elastomers with specific physical properties is typically done by a ‘one off’ formulation and test process. We demonstrate that... Read More https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.201903658 Synthetic presentation of noncanonical Wnt5a motif promotes mechanosensing-dependent differentiation of stem cells and regeneration R. Li, S. Lin, M.Zhu, Y. Deng, X. Chen, K. Wei, J. Xu, G. Li and L. Bian Sci Adv 5, 10, eaaw 3896, DOI: 10.1126/sciadv.aaw3896 Noncanonical Wnt signaling in stem cells is essential to numerous developmental events. However, no prior studies have capitalized on the osteoinductive potential of noncanonical Wnt ligands to functionalize biomaterials in enhancing the... Read More https://advances.sciencemag.org/content/advances/5/10/eaaw3896.full.pdf Morphology and composition play distinct and complementary roles in the tolerance of plantar skin to mechanical load Colin J. Boyle, Magdalena Plotczyk, Sergi Fayos Villalta, Sharad Patel, Shehan Hettiaratchy, Spyros D. Masouros, Marc A. Masen and Claire A. Higgins Science Advances, 09 Oct 2019: Vol. 5, no. 10, eaay0244, DOI: 10.1126/sciadv.aay0244 Plantar skin on the soles of the feet has a distinct morphology and composition that is thought to enhance its tolerance to mechanical loads, although the individual contributions of morphology and composition have never been quantified. Here,... Read More https://advances.sciencemag.org/content/5/10/eaay0244.full Characterization of a novel decellularized bone marrow scaffold as an inductive environment for hematopoietic stem cells J.E. Romero Bianco, R. Giardini Rosa, A. Congrains-Castillo, P.P. Joazeiro, S.D. Waldman, J.F. Weber, and S.T. Olalla Saad Biomater. Sci., 2019, Advance Article, first published on 19 Jan 2019, DOI 10.1039/C8BM01503A Due to the increasing demand for a bone marrow study model, we developed a natural... Read More https://pubs.rsc.org/en/content/articlelanding/2019/bm/c8bm01503a#!divAbstract Ultrashort Time to Echo Magnetic Resonance Evaluation of Calcium Pyrophosphate Crystal Deposition in Human Menisci Finkenstaedt T, Biswas R, Abeydeera NA, Siriwanarangsun P, Healey R, Statum S, Bae WC and Chung CB Invest Radiol. 2019 Jun. 54(6):349-355. OBJECTIVES: In human menisci, we aimed to investigate whether calcium pyrophosphate crystal deposition (CPPD) affects biomechanical and quantitative MR properties, and their zonal distribution. Read More https://www.ncbi.nlm.nih.gov/pubmed/30688685 Moderate exercise prevents cartilage softening and muscle structural changes in a rat model of obesity J.L. Rios, J.W. Mather, J. Michaiel, S.M. Mattiello and W. Herzog OARSI Journal, April 2019 Volume 27, Supplement 1, Page S155 Purpose: Osteoarthritis (OA) is a debilitating chronicdisease. Currently, there is no cure or disease modifying treatment for OA.Using a Sprague-Dawley rat model, it has been shown that ahigh-fat/high-sucrose (HFS) diet induced... Read More https://www.oarsijournal.com/article/S1063-4584(19)30267-5/ppt Development of a dispensing based additive manufacturing technique for the creation of alginate bone scatfolds J.J. Varun UBC Theses and Dissertations, 2019. https://open.library.ubc.ca/cIRcle/collections/ubctheses/24/items/1.0378434 Bone scaffolds are used to treat large bone defects. There are noted advantages for moving away from the standard of using human bone to create these... Read More https://open.library.ubc.ca/cIRcle/collections/ubctheses/24/items/1.0378434 Automated Indentation of Femoral and Temporomandibular Joints for Characterization of Cartilage Tissue Quality in Fgf2 KO Mice. Tannin Schmidt Poster SAT-996. American Society for Bone and Mineral Research, 21 Sep 2019, Orlando, Florida, USA PURPOSE: Degenerative disorders affecting the mandibular condylar cartilage (MCC) of the temporomandibular joint (TMJ), and the articular cartilage (AC) of the knee joint, are common chronic conditions. Fibroblast Growth Factor 2 (FGF2) is a... Read More https://www.asbmr.org/ItineraryBuilder/PresentationDetail.aspx?pid=b268f23b-6e58-4d3d-bea7-863d43c7f010&ptag=WebItinerarySearch Biomechanical characterization of tibial articular cartilage in Hyp mice, a murine model of osteoarthritis in X-linked hypophosphatemia Michael J. Desimone, Steven M. Tommasini, Christopher Cape and Carolyn M. Macica Poster SUN-929. American Society for Bone and Mineral Research, 22 Sep 2019, Orlando, Florida, USA The clinical picture of adult XLH is dominated by a pervasive, early-onset osteoarthritis (OA). Using a murine XLH model, we have shown that the femoral/tibial joint of Hyp mice lacks the mineralized zone of articular cartilage, a transitional tissue... Read More https://www.asbmr.org/ItineraryBuilder/PresentationDetail.aspx?pid=6cc2af0d-9083-4d85-aeea-e0b063ca07af&ptag=WebItinerarySearch A Col1a2 Mutation Reveals Bone Fragility, Hyperelasticity of Skin and Degeneration of Articular Cartilage in Mice S. Sim, A. Blease, M. Garon, E. Quenneville and P. Potter Poster SUN-053. American Society for Bone and Mineral Research, 22 Sep 2019, Orlando, Florida, USA Read More https://www.asbmr.org/ItineraryBuilder/PresentationDetail.aspx?pid=d998ad4c-3407-44f6-ac34-713e2a65b750&ptag=WebItinerarySearch Hierarchically Structured, Self-Healing, Fluorescent, Bioactive Hydrogels with Self-Organizing Bundles of Phage Nanofilaments A. Peivandi, L. Tian, R. Mahabir and Z. Hosseinidoust Chem. Mater. 201931155442-5449 Publication Date:July 24, 2019 https://doi.org/10.1021/acs.chemmater.9b00720 Bacteriophages are essentially bionanoparticles with a protein coat, the composition of which can be controlled with atomic precision via genetic engineering, a property that makes them superior to synthetic nanoparticles as building blocks for... Read More https://pubs.acs.org/doi/abs/10.1021/acs.chemmater.9b00720 Development of an In Vitro Outer Annulus Fibrosus Cartilage Endplate Model and its Response to Dynamic Mechanical Loading J. E. Chong University of Toronto Tissue-engineering research to date has neglected to address the annulus fibrosus (AF) cartilage endplate (CEP) interface of the intervertebral disc. It was hypothesized that in vitro formed outer AF and cartilage tissues will integrate... Read More https://tspace.library.utoronto.ca/bitstream/1807/96075/3/Chong_Jasmine_E_201906_MAS_thesis.pdf Bottlebrush polymer compositions, lubricating fluid, porous materials comprising said compositions, and surface bearing said compositions X. Banquy, J. Faivre, B.R.Shrestha, K. Matyjaszewski, J.Burdynska and F. Moldovan US Patent App. 16/095,051, 2019 A mixture of polymers with lubricating properties is provided. The polymer can be used to produce a lubricating fluid. They can also be born on a surface or embedded in a porous material. This mixture of polymers comprises (a) a pharmaceutically... Read More https://patents.google.com/patent/US20190099521A1/en Setting up a pre-clinical human model for mechanical induced osteoarthritis to investigate potential pharmacological agents E. Houtman, M. van Hoolwerff, R. Coutinho De Almeida, A. Rodriguez Ruiz, N. Lakenberg, H.E. Suchiman, M. Tuerlings, R.G. Timmermans, R.G. Nelissen, Y.F. Ramos and I. Meulenbelt Osteoarthritis and Cartilage, April 2019, Volume 27, Supplement 1, Pages S80–S81. https://doi.org/10.1016/j.joca.2019.02.114 Purpose: Osteoarthritis (OA) is a joint disease characterized by cartilage degeneration and bone spur formation. Due to the fact that there are no disease modifying drugs, OA is placing a high burden on society occurring during... Read More https://www.oarsijournal.com/article/S1063-4584(19)30156-6/abstract Cross-Linked Elastin-like Polypeptide Membranes as a Model for Medial Arterial Calcification O. Gourgas, L. D. Muiznieks, D. G.Bello, A. Nanci, S.Sharpe and M. Cerruti Publication Date:June 21, 2019 https://doi.org/10.1021/acs.biomac.9b00417 Calcium phosphate minerals deposit on the elastin-rich medial layers of arteries in the majority of seniors, diabetic, and chronic kidney disease patients, causing severe cardiovascular complications. There is no cure for medial calcification, and... Read More https://pubs.acs.org/doi/full/10.1021/acs.biomac.9b00417 The effect of in vivo chondrocyte depletion on the structural and functional properties of murine articular cartilage A.O. Masson, J.M. Corpuz, W.B. Edwards and R.J. Krawetz Osteoarthritis and Cartilage, April 2019, Volume 27, Supplement 1, Page S80 Articular cartilage is an intricate and remarkable tissue found within synovial joints. It is essential for providing low-friction and load bearing during movement, resulting in pain-free mobility. Chondrocytes are the sole cell population present... Read More https://www.oarsijournal.com/article/S1063-4584(19)30155-4/abstract A 3D Bioprinted Meniscus Implant Reinforced by Chitosan/Poly(Vinyl Alcohol) Fibres E. Kapyla, M. K. Khan, S. Pan, R. Nickmanesh, S. Beyer, J. Ault, J. Hwang, T. Mohamed, and S. Wadsworth 30th Annual Conference of the European Society for Biomaterials, IX-OS31-01, #270, 12 September 2019, Dresden, Germany.
Multi-modal characterization of polymeric gels to determine the influence of testing method on observed elastic modulus
David M. Kingsley, Caitlin H.McCleery, Christopher D.L.Johnson, Michael T.K.Bramson, Deniz Rende, Ryan J.Gilbert, David T.Corr
Journal of the Mechanical Behavior of Biomedical Materials, available online 10 January 2019, https://doi.org/10.1016/j.jmbbm.2019.01.003
Demand for materials that mechanically replicate native tissue has driven development and characterization of various new biomaterials. However, a consequence of materials and characterization technique diversity is a lack of consensus within the field, with no clear way to compare values measured via different modalities. This likely contributes to the difficulty in replicating findings across the research community; recent evidence suggests that different modalities do not yield the same mechanical measurements within a material, and direct comparisons cannot be made across different testing platforms. Herein, we examine whether “material properties” are characterization modality-specific by analyzing the elastic moduli determined by five typical biomaterial mechanical characterization techniques: unconfined-compression, tensiometry, rheometry, and micro-indentation at the macroscopic level, and microscopically using nanoindentation. These analyses were performed in two different polymeric gels frequently used for biological applications, polydimethylsiloxane (PDMS) and agarose. Each was fabricated to span a range of moduli, from physiologic to supraphysiologic values. All five techniques identified the same overall trend within each material group, supporting their ability to appreciate relative moduli differences. However, significant differences were found across modalities, illustrating a difference in absolute moduli values, and thereby precluding direct comparison of measurements from different characterization modalities. These observed differences may depend on material compliance, viscoelasticity, and microstructure. While determining the underlying mechanism(s) of these differences was beyond the scope of this work, these results demonstrate how each modality affects the measured moduli of the same material, and the sensitivity of each modality to changes in sample material composition.

Compression testing
Cylindrical test specimens were punched from the prepared gels, using a 4-mm biopsy punch, to approximate the ratio of sample geometries (4-mm diameter, 2-mm thickness) specified by ASTM standard D575-91. Samples were characterized on a Mach-1 mechanical tester (BMM Inc., Laval, QC, Canada) equipped with either a 70-N or 1.5-N load cell, depending on sample rigidity. Each test specimen was compressed to approximately 0.50 strain (absolute compression distance of 1.125 mm) at a constant rate of 0.03 mm/s. A stress-strain curve was constructed based on the measured force and displacement data (normalized to initial sample cross-sectional area and length, respectively). The elastic modulus was estimated from the linear region of this curve, which occurred between 0.05–0.25 strain for PDMS, and 0–0.10 strain for agarose. Six material test specimens were punched from three independently made gels, for all PDMS and agarose groups (n = 18 per group).

Indentation testing
Indentation characterization was performed on samples within 90-mm Petri dishes, using a Mach-1 mechanical tester (BMM Inc., Laval, QC, Canada) with a spherical tip probe (6.35 mm diameter). A 1.5-N or 70-N load cell was used for all samples, depending on sample rigidity. To characterize, the probe height was first calibrated to a Petri dish containing no gel, to standardize the height of the probe. Gel tests began using the system's “Find Contact” mode, wherein the probe is lowered at a rate of 0.03 mm/s until a load was detected. Based on the determined initial sample height, the test was set to a total probe displacement of 30% strain, at a constant rate of 0.03 mm/s for all samples. The elastic moduli of indentation data were estimated using a Hertzian model, which accounts for the contact mechanics between a sphere and an elastic solid [12, 13]. To utilize the Hertz model, measured indenter force was plotted against the indentation depth raised to the 3/2 power, and the slope of the initial linear region, (between 0–0.1 strain for PDMS, and 0.03–0.09 strain for agarose), was used to solve for elastic modulus, E, in Eq. (2),
(2)F=43ER12d3/21(1+?),
where F is detected force, R is the radius of the indenter, d is the displacement, and ? is the Poisson's ratio of the sample. Three independent gels were fabricated for testing per sample condition with six indentations per gel (n = 18).

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