DOI: 10.25349/d9261m
title: Data from: pH-Dependent friction of Polyacrylamide hydrogels

description: Polyacrylamide hydrogels are widely used in biomedical applications due to
 their tunable mechanical properties and charge neutrality. Our recent
 tribological investigations of polyacrylamide gels have revealed tunable
 and pH-dependent friction behavior. To determine the origins of this
 pH-responsiveness, we prepared polyacrylamide hydrogels with two different
 initiating chemistries: a reduction-oxidation (redox)-initiated system
 using ammonium persulfate (APS) and N,N,N’N’-tetramethylethylenediamine
 (TEMED) and a UV-initiated system with
 2-hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959).
 Hydrogel swelling, mechanical properties, and tribological behavior were
 investigated in response to solution pH (ranging from ~ 0.34 to 13.5). For
 polyacrylamide hydrogels in sliding contact with glass hemispherical
 probes, friction coefficients decreased from µ = 0.07 ± 0.02 to µ = 0.002
 ± 0.002 (redox-initiated) and from µ = 0.05 ± 0.03 to µ = 0.003 ± 0.003
 (UV-initiated) with increasing solution pH. With hemispherical
 polytetrafluoroethylene (PTFE) probes, friction coefficients of
 redox-initiated hydrogels similarly decreased from µ = 0.06 ± 0.01 to µ =
 0.002 ± 0.001 with increasing pH. Raman spectroscopy measurements
 demonstrated hydrolysis and the conversion of amide groups to carboxylic
 acid in basic conditions. We therefore propose that the mechanism for
 pH-responsive friction in polyacrylamide hydrogels may be credited to
 hydrolysis-driven swelling through the conversion of side chain amide
 groups into carboxylic groups and/or crosslinker degradation. Our results
 could assist in the rational design of hydrogel-based tribological pairs
 for biomedical applications from acidic to alkaline conditions.
description: Microindentations and sliding experiments were conducted with a
 custom-built linear reciprocating tribometer. Data was analyzed and
 processed with the following Matlab codes (Tribometer_Indent_Analysis_v5
 and Compiling_Friction_Data_v7).  Raman spectroscopy
 was conducted with a confocal Raman microscope (Horiba Jobin Yvon T640000)
 with an excitation wavelength of 488 nm and laser power of 400 mW. A 50x
 objective lens was used to focus the laser light 10 µm below the sample
 surface. Spectra data was obtained with a resolution of 0.66
 cm<sup>-1</sup>.   X-ray photoelectron
 spectroscopy was conducted with a Thermo Scientific
 ESCALAB<sup>TM</sup> Xi+. A monochromatic Al/Kα x-ray
 radiation with a pass energy of 100 eV, dwell time of 50 ms, and spot size
 of 650 µm was used. Spectra were obtained after 105 s of etching using a 6
 kV Ar1000+ cluster ion source. 
description: All data is in .csv or .txt format and can be opened with any
 open-source software. 
description: Data from peer-reviewed article: Title: pH-Dependent Friction of
 Polyacrylamide Hydrogels Journal: Tribology Letters Authors: Allison L.
 Chau, Conor D. Pugsley, Madeleine E. Miyamoto, Yongkui Tang, Claus D.
 Eisenbach, Thomas E. Mates, Craig J. Hawker, Megan T. Valentine, and
 Angela A. Pitenis Corresponding author: Angela Pitenis, apitenis@ucsb.edu
 *** File List A) Fig\_2a.csv B) Fig\_2b.csv C) Fig\_3a.csv D) Fig\_3b.csv
 E) Fig\_5\_FigS4.csv F) Fig\_S1.txt G) Fig\_S2.csv H) Fig\_S3.csv I)
 Fig\_S5a.csv J) Fig\_S5b.csv K) Fig\_S5c.csv L) Fig\_S5d.csv M)
 Fig\_S5e.csv N) Fig\_S5f.csv O) Fig\_S5gcsv P) Fig\_S5h.csv Q) Fig\_S6.csv
 R) Fig\_S7a.csv S) Fig\_S7b.csv T) Friction\_Irgacure.csv U)
 Friction\_TEMED\_APS.csv V) Modulus\_Irgacure.csv W)
 Modulus\_TEMED\_APS.csv X) Swelling\_Irgacure.csv Y)
 Swelling\_TEMED\_APS.csv Z) Volume\_change\_TEMED\_APS.csv FIGURE 2:
 friction and reduced elastic modulus data --- A) Fig\_2a.csv: friction
 coefficient vs. solution pH * row 1: x and y axis, corresponding to
 solution pH (x) and friction coefficient average (y) and friction
 coefficient standard deviation (+/- y) * row 2: initiating system (redox
 [TEMED + APS] or UV initiated [Irgacure]) and probe material (glass or
 PTFE) * row 3 and beyond: data * dataset 1: redox (TEMED + APS) hydrogels
 with glass probe - columns A + B + C * dataset 2: redox (TEMED + APS)
 hydrogels with PTFE probe - columns A + D + E * dataset 3: UV initiated
 (Irgacure) hydrogels with glass probe - columns A + F + G * cells with
 n/a: data was not gathered for those conditions (pH = 2, pH = 10) * Notes:
 data from Friction\_Irgacure.csv and Friction\_TEMED\_APS.csv B)
 Fig\_2b.csv: reduced elastic modulus vs. solution pH * row 1: x and y
 axis, corresponding to solution pH (x) and reduced elastic modulus average
 (y) and reduced elastic modulus standard deviation (+/- y) * row 2: units
 for corresponding axes * row 3: initiating system (redox [TEMED + APS] or
 UV initiated [Irgacure]) * row 4 and beyond: data * dataset 1: redox
 (TEMED + APS) hydrogels with glass probe - columns A + B + C * dataset 2:
 UV initiated (Irgacure) hydrogels with glass probe - columns A + D + E *
 cells with n/a: data was not gathered for those conditions (UV initiated
 gels, pH = 13.5) * Notes: data from Modulus\_Irgacure.csv and
 Modulus\_TEMED\_APS.csv *** FIGURE 3: swelling data --- C) Fig\_3a.csv:
 water content vs. solution pH * row 1: x and y axis, corresponding to
 solution pH (x) and water content average (y) and water content standard
 deviation (+/- y) * row 2: initiating system (redox [TEMED + APS] or UV
 initiated [Irgacure]) * row 3 and beyond: data * dataset 1: redox (TEMED +
 APS) hydrogels - columns A + B + C * dataset 2: UV initiated (Irgacure)
 hydrogels - columns A + D + E * cells with n/a: data was not gathered for
 those conditions (UV initiated gels, pH = 13.5) * Notes: data from
 Swelling\_Irgacure.csv and Swelling\_TEMED\_APS.csv D) Fig\_3b.csv: volume
 change vs. solution pH * row 1: x and y axis, corresponding to solution pH
 (x) and volume change average (y) and volume change standard deviation
 (+/- y) * row 2: initiating system (redox [TEMED + APS]) * row 3 and
 beyond: data * dataset 1: redox (TEMED + APS) hydrogels - columns A + B +
 C * Notes: data from Volume\_change\_TEMED\_APS.csv *** FIGURE 5: Raman
 spectroscopy data (same data as shown in Figure S4) --- E)
 Fig\_5\_FigS4.csv: Raman spectroscopy normalized intensity vs. wavenumber
 * row 1: x and y axis, corresponding to wavenumber (x) and normalized
 intensity (y) * row 2: units for corresponding axes * row 3: solution (0.5
 M HCl, DI water, or 0.5 M NaOH) or hydrogel type
 (polyacrylamide-co-acrylic acid [P(AAm-co-AA)]) with AA concentration (1,
 5, 6, 9, or 12 wt) * row 4 and beyond: data * dataset 1: redox (TEMED +
 APS) hydrogels in 0.5 M HCl - columns A + B * dataset 2: redox (TEMED +
 APS) hydrogels in DI water - columns C + D * dataset 3: redox (TEMED +
 APS) hydrogels in 0.5 M NaOH - columns E + F * dataset 4: P(AAm-co-AA)
 hydrogel with 1 wt AA in DI water - columns G + H * dataset 5:
 P(AAm-co-AA) hydrogel with 5 wt AA in DI water - columns I + J * dataset
 6: P(AAm-co-AA) hydrogel with 6 wt AA in DI water - columns K + L *
 dataset 7: P(AAm-co-AA) hydrogel with 9 wt AA in DI water - columns M + N
 * dataset 8: P(AAm-co-AA) hydrogel with 12 wt AA in DI water - columns O +
 P *** FIGURE S1: surface topography map information --- F) Fig\_S1.txt
 --&gt; surface topography map information * information about how the
 surface topography map was processed as well as the sample identifier
 (internal use) *** FIGURE S2: x-ray photoelectron spectroscopy data --- G)
 Fig\_S2.csv --&gt; x-ray photoelectron spectroscopy counts vs. binding
 energy * row 1: x and y axis, corresponding to binding energy (x) and
 counts per second (y) * row 2: units for corresponding axes * row 3:
 sample (acrylamide [AAm] powder, ammonium persulfate [APS] powder,
 bisacrylamide [MBAm] powder, or polyacrylamide [PAAm] hydrogel) * row 4
 and beyond: data * dataset 1: AAm powder - columns A + B * dataset 2: APS
 powder - columns C + D * dataset 3: MBAm powder - columns E + F * dataset
 4: PAAm hydrogel (argon etched for 105 s) - columns G + H *** FIGURE S3:
 Raman spectroscopy data --- H) Fig\_S3.csv --&gt; Raman spectroscopy
 normalized intensity vs. wavenumber * row 1: x and y axis, corresponding
 to wavenumber (x) and normalized intensity (y) * row 2: units for
 corresponding axes * row 3: solution (0.5 M HCl, DI water, or 0.5 M NaOH)
 or hydrogel type (polyacrylamide-co-acrylic acid [P(AAm-co-AA)]) with AA
 concentration (1, 5, 6, 9, or 12 wt) * row 4 and beyond: data * dataset 1:
 redox (TEMED + APS) hydrogels in 0.5 M HCl for three gels - columns A (x)
 + B (y for gel 1) + C (y for gel 2) + D (y for gel 3) * dataset 2: redox
 (TEMED + APS) hydrogels in DI water for three gels - columns E (x) + F (y
 for gel 1) + G (y for gel 2) + H (y for gel 3) * dataset 3: redox (TEMED +
 APS) hydrogels in 0.5 M NaOH for three gels - columns I (x) + J (y for gel
 1) + K (y for gel 2) + L (y for gel 3) * dataset 4: P(AAm-co-AA) hydrogel
 with 1 wt AA in DI water for three gels - columns M (x) + N (y for gel 1)
 + O (y for gel 2) + P (y for gel 3) * dataset 5: P(AAm-co-AA) hydrogel
 with 5 wt AA in DI water for three gels - columns Q (x) + R (y for gel 1)
 + S (y for gel 2) + T (y for gel 3) * dataset 6: P(AAm-co-AA) hydrogel
 with 6 wt AA in DI water for three gels - columns U (x) + V (y for gel 1)
 + W (y for gel 2) + X (y for gel 3) * dataset 7: P(AAm-co-AA) hydrogel
 with 9 wt AA in DI water for three gels - columns Y (x) + Z (y for gel 1)
 + AA (y for gel 2) + AB (y for gel 3) * dataset 8: P(AAm-co-AA) hydrogel
 with 12 wt AA in DI water for three gels - columns AC (x) + AD (y for gel
 1) + AE (y for gel 2) + AF (y for gel 3) *** FIGURE S5: Raman band
 deconvolution data --- I) Fig\_S5a.csv --&gt; Raman band deconvolution
 curve fitting - PAAm gels at pH = 0.34 * row 1: x and y axis,
 corresponding to wavenumber (x) and normalized intensity (y) * row 2:
 units for corresponding axes * row 3: data indentifier (peak number,
 cumulative fit, or measurement) * row 4 and beyond: data * dataset 1: peak
 fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D * dataset 3:
 peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G + H *
 dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 - columns K
 + L * dataset 7: peak fit 7 - columns M + N * dataset 8: peak fit 8 -
 columns O + P * dataset 9: cumulative peak fit - columns Q + R * dataset
 10: measurement - columns S + T J) Fig\_S5b.csv --&gt; Raman band
 deconvolution curve fitting - PAAm gels at pH = 7 * row 1: x and y axis,
 corresponding to wavenumber (x) and normalized intensity (y) * row 2:
 units for corresponding axes * row 3: data indentifier (peak number,
 cumulative fit, or measurement) * row 4 and beyond: data * dataset 1: peak
 fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D * dataset 3:
 peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G + H *
 dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 - columns K
 + L * dataset 9: cumulative peak fit - columns M + N * dataset 10:
 measurement - columns O + P K) Fig\_S5c.csv --&gt; Raman band
 deconvolution curve fitting - P(AAm-co-AA) gel with 1 wt AA * dataset 1:
 peak fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D *
 dataset 3: peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G
 + H * dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 -
 columns K + L * dataset 7: peak fit 7 - columns M + N * dataset 8: peak
 fit 8 - columns O + P * dataset 9: cumulative peak fit - columns Q + R *
 dataset 10: measurement - columns S + T L) Fig\_S5d.csv --&gt; Raman
 band deconvolution curve fitting - P(AAm-co-AA) gel with 5 wt AA * dataset
 1: peak fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D *
 dataset 3: peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G
 + H * dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 -
 columns K + L * dataset 7: peak fit 7 - columns M + N * dataset 8: peak
 fit 8 - columns O + P * dataset 9: cumulative peak fit - columns Q + R *
 dataset 10: measurement - columns S + T M) Fig\_S5e.csv --&gt; Raman
 band deconvolution curve fitting - P(AAm-co-AA) gel with 6 wt AA * dataset
 1: peak fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D *
 dataset 3: peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G
 + H * dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 -
 columns K + L * dataset 7: peak fit 7 - columns M + N * dataset 8: peak
 fit 8 - columns O + P * dataset 9: cumulative peak fit - columns Q + R *
 dataset 10: measurement - columns S + T N) Fig\_S5f.csv --&gt; Raman
 band deconvolution curve fitting - P(AAm-co-AA) gel with 9 wt AA * dataset
 1: peak fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D *
 dataset 3: peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G
 + H * dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 -
 columns K + L * dataset 7: peak fit 7 - columns M + N * dataset 8: peak
 fit 8 - columns O + P * dataset 9: cumulative peak fit - columns Q + R *
 dataset 10: measurement - columns S + T O) Fig\_S5g.csv --&gt; Raman
 band deconvolution curve fitting - P(AAm-co-AA) gel with 12 wt AA *
 dataset 1: peak fit 1 - columns A + B * dataset 2: peak fit 2 - columns C
 + D * dataset 3: peak fit 3 - columns E + F * dataset 4: peak fit 4 -
 columns G + H * dataset 5: peak fit 5 - columns I + J * dataset 6: peak
 fit 6 - columns K + L * dataset 7: peak fit 7 - columns M + N * dataset 8:
 peak fit 8 - columns O + P * dataset 9: cumulative peak fit - columns Q +
 R * dataset 10: measurement - columns S + T P) Fig\_S5h.csv --&gt;
 Raman band deconvolution curve fitting - PAAm gels at pH = 13.5 * dataset
 1: peak fit 1 - columns A + B * dataset 2: peak fit 2 - columns C + D *
 dataset 3: peak fit 3 - columns E + F * dataset 4: peak fit 4 - columns G
 + H * dataset 5: peak fit 5 - columns I + J * dataset 6: peak fit 6 -
 columns K + L * dataset 7: peak fit 7 - columns M + N * dataset 8: peak
 fit 8 - columns O + P * dataset 9: peak fit 9 - columns Q + R * dataset
 10: cumulative peak fit - columns S + T * dataset 11: measurement -
 columns U + V FIGURE S6: Raman linear calibration curve data --- Q)
 Fig\_S6.csv --&gt; Raman linear calibration curve data * Table 1:
 ratio of peaks vs. acrylic acid mol percent (A1-A9, E1-E9) * Column A:
 hydrogel sample (polyacrylamide [PAAm] or poly(acrylamide-co-acrylic acid)
 [P(AAm-co-AA)] and solution (DI water, HCl, or NaOH) * Column B: acrylic
 acid (AA) mol% average * Column C: acrylic acid (AA) mol% standard
 deviation * Column D: ratio of peak areas (peak at 1555 cm^-1/peaks at
 1670 cm^-1 and 1716 cm^-1) average * Column E: ratio of peak areas (peak
 at 1555 cm^-1/peaks at 1670 cm^-1 and 1716 cm^-1) standard deviation *
 cells with n/a: no standard deviation for those conditions (P(AAm-co-AA)
 gels) * Table 2: ratio of peaks vs. ratio of acrylic acid/amide (G1-G9,
 J1-J9) * Column A: ratio of acrylic acid mol/amide mol average * Column B:
 ratio of acrylic acid mol/amide mol standard deviation * Column C: ratio
 of peak areas (peak at 1555 cm^-1/peaks at 1617 cm^-1) average * Column D:
 ratio of peak areas (peak at 1555 cm^-1/peaks at 1617 cm^-1) standard
 deviation * cells with n/a: no standard deviation for those conditions
 (P(AAm-co-AA) gels) *** FIGURE S7: switchable friction data --- R)
 Fig\_S7a.csv --&gt; friction coefficient vs. solution pH - switchable
 friction data * Table 1: raw data for hydrogel with TEMED + APS initiating
 system (A2-A7, K2-K7) * Column A: sample identifer (internal use) * Column
 B: solution pH (pH = 0.35, 7, or 10) * Column C + D: normal force average
 and standard deviation * Column E + F: friction force average and standard
 deviation * Column G + H: kinetic friction coefficient average and
 standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 2: raw data for
 hydrogel with Irgacure initiating system (A9-A14, K9-K14) * Column A:
 sample identifer (internal use) * Column B: solution pH (pH = 0.35, 7, or
 10) * Column C + D: normal force average and standard deviation * Column E
 + F: friction force average and standard deviation * Column G + H: kinetic
 friction coefficient average and standard deviation * Column I: cycle #
 where analysis begins (internal use) * Column J: number of cycles analyzed
 * Column K: range of x position analyzed on the friction force loop
 (internal use) * Table 3: data for Figure S7a (A19-A23, E19-E23) * Column
 A: solution pH * Column B + C: friction coefficient average and standard
 deviation for the hydrogel with TEMED + APS initiating system * Column D +
 E: friction coefficient average and standard deviation for the hydrogel
 with Irgacure initiating system *** S) Fig\_S7b.csv --&gt; reduced
 elastic modulus vs. solution pH - TEMED + APS initiated gels --- * Table
 1: elastic modulus for PAAm sample in pH = 0.35 (0.5 M HCl) (B2-B24,
 J2-J24) * Column B: sample identifier (internal use) * Column C: position
 * Column D: cycle number * Column E: maximum force reached during analysis
 * Column F: maximum contact pressure reached during analysis * Column G:
 maximum contact radius reached during analysis * Column H: estimated
 reduced elastic modulus using the Hertz model * Column I + J: averages and
 standard deviation of reduced elastic modulus per position * cells with
 n/a: no cycle data at the specified position * Table 2: elastic modulus
 for PAAm sample in pH = 7 (DI water) (L2-L24, T2-T24) * Column L: sample
 identifier (internal use) * Column M: position * Column N: cycle number *
 Column O: maximum force reached during analysis * Column P: maximum
 contact pressure reached during analysis * Column Q: maximum contact
 radius reached during analysis * Column R: estimated reduced elastic
 modulus using the Hertz model * Column S + T: averages and standard
 deviation of reduced elastic modulus per position * Table 3: elastic
 modulus for PAAm sample in pH = 10.01 (0.001 M NaOH) (V2-V24, AD2-AD24) *
 Column V: sample identifier (internal use) * Column W: position * Column
 X: cycle number * Column Y: maximum force reached during analysis * Column
 Z: maximum contact pressure reached during analysis * Column AA: maximum
 contact radius reached during analysis * Column AB: estimated reduced
 elastic modulus using the Hertz model * Column AC + AD: averages and
 standard deviation of reduced elastic modulus per position * cells with
 n/a: no cycle data at the specified position * Table 4: data for Figure
 S7a (A28-A33, C28-C33) * Column A: solution pH * Column B + C: elastic
 modulus average and standard deviation for the hydrogel with TEMED + APS
 initiating system *** Compilation of raw friction coefficient data --- T)
 Friction\_Irgacure.csv * Table 1: raw data for hydrogel with UV (Irgacure)
 initiating system at pH = 0.34 (0.5 M HCl) with glass probe (A1-A9, K1-K9)
 * Column A: hydrogel type (polyacrylamide) * Column B: sample identifier
 (internal use) * Column C + D: normal force average and standard deviation
 * Column E + F: friction force average and standard deviation * Column G +
 H: kinetic friction coefficient average and standard deviation * Column I:
 cycle # where analysis begins (internal use) * Column J: number of cycles
 analyzed * Column K: range of x position analyzed on the friction force
 loop (internal use) * Table 2: raw data for hydrogel with UV (Irgacure)
 initiating system at pH = 2 (0.01 M HCl) with glass probe (A12-A19,
 K12-K19) * Column A: hydrogel type (polyacrylamide) * Column B: sample
 identifier (internal use) * Column C + D: normal force average and
 standard deviation * Column E + F: friction force average and standard
 deviation * Column G + H: kinetic friction coefficient average and
 standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 3: raw data for
 hydrogel with UV (Irgacure) initiating system at pH = 7 (DI water) with
 glass probe (A22-A29, K22-K29) * Column A: hydrogel type (polyacrylamide)
 * Column B: sample identifier (internal use) * Column C + D: normal force
 average and standard deviation * Column E + F: friction force average and
 standard deviation * Column G + H: kinetic friction coefficient average
 and standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 4: raw data for
 hydrogel with UV (Irgacure) initiating system at pH = 10 (0.001 M NaOH)
 with glass probe (A32-A39, K32-K39) * Column A: hydrogel type
 (polyacrylamide) * Column B: sample identifier (internal use) * Column C +
 D: normal force average and standard deviation * Column E + F: friction
 force average and standard deviation * Column G + H: kinetic friction
 coefficient average and standard deviation * Column I: cycle # where
 analysis begins (internal use) * Column J: number of cycles analyzed *
 Column K: range of x position analyzed on the friction force loop
 (internal use) U) Friction\_TEMED\_APS.csv * Table 1: raw data for
 hydrogel with TEMED + APS initiating system at pH = 0.34 (0.5 M HCl) with
 glass probe (A2-A10, K2-K10) * Column A: hydrogel type (polyacrylamide) *
 Column B: sample identifier (internal use) * Column C + D: normal force
 average and standard deviation * Column E + F: friction force average and
 standard deviation * Column G + H: kinetic friction coefficient average
 and standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 2: raw data for
 hydrogel with TEMED + APS initiating system at pH = 2 (0.01 M HCl) with
 glass probe (A12-A19, K12-K19) * Column A: hydrogel type (polyacrylamide)
 * Column B: sample identifier (internal use) * Column C + D: normal force
 average and standard deviation * Column E + F: friction force average and
 standard deviation * Column G + H: kinetic friction coefficient average
 and standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 3: raw data for
 hydrogel with TEMED + APS initiating system at pH = 7 (DI water) with
 glass probe (A21-A28, K21-K28) * Column A: hydrogel type (polyacrylamide)
 * Column B: sample identifier (internal use) * Column C + D: normal force
 average and standard deviation * Column E + F: friction force average and
 standard deviation * Column G + H: kinetic friction coefficient average
 and standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 4: raw data for
 hydrogel with TEMED + APS initiating system at pH = 10 (0.001 M NaOH) with
 glass probe (A30-A37, K30-K37) * Column A: hydrogel type (polyacrylamide)
 * Column B: sample identifier (internal use) * Column C + D: normal force
 average and standard deviation * Column E + F: friction force average and
 standard deviation * Column G + H: kinetic friction coefficient average
 and standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 5: raw data for
 hydrogel with TEMED + APS initiating system at pH = 13.5 (0.5 M NaOH) with
 glass probe (A39-A46, K39-K46) * Column A: hydrogel type (polyacrylamide)
 * Column B: sample identifier (internal use) * Column C + D: normal force
 average and standard deviation * Column E + F: friction force average and
 standard deviation * Column G + H: kinetic friction coefficient average
 and standard deviation * Column I: cycle # where analysis begins (internal
 use) * Column J: number of cycles analyzed * Column K: range of x position
 analyzed on the friction force loop (internal use) * Table 6: raw data for
 hydrogel with TEMED + APS initiating system at pH = 0.34 (0.5 M HCl) with
 PTFE probe (N2-N10, Y2-Y10) * Column N: hydrogel type (polyacrylamide) *
 Column O: sample identifier (internal use) * Column P: date/attempt
 (internal use) * Column Q + R: normal force average and standard deviation
 * Column S + T: friction force average and standard deviation * Column U +
 V: kinetic friction coefficient average and standard deviation * Column W:
 cycle # where analysis begins (internal use) * Column X: number of cycles
 analyzed * Column Y: range of x position analyzed on the friction force
 loop (internal use) * Table 7: raw data for hydrogel with TEMED + APS
 initiating system at pH = 7 (DI water) with PTFE probe (N12-N19, Y12-Y19)
 * Column N: hydrogel type (polyacrylamide) * Column O: sample identifier
 (internal use) * Column P: date/attempt (internal use) * Column Q + R:
 normal force average and standard deviation * Column S + T: friction force
 average and standard deviation * Column U + V: kinetic friction
 coefficient average and standard deviation * Column W: cycle # where
 analysis begins (internal use) * Column X: number of cycles analyzed *
 Column Y: range of x position analyzed on the friction force loop
 (internal use) * Table 8: raw data for hydrogel with TEMED + APS
 initiating system at pH = 13.5 (0.5 M NaOH) with PTFE probe (N21-N28,
 Y21-Y28) * Column N: hydrogel type (polyacrylamide) * Column O: sample
 identifier (internal use) * Column P: date/attempt (internal use) * Column
 Q + R: normal force average and standard deviation * Column S + T:
 friction force average and standard deviation * Column U + V: kinetic
 friction coefficient average and standard deviation * Column W: cycle #
 where analysis begins (internal use) * Column X: number of cycles analyzed
 * Column Y: range of x position analyzed on the friction force loop
 (internal use) *** Compilation of raw elastic modulus data --- V)
 Modulus\_Irgacure.csv * Table 1: raw data for hydrogel sample 1 with
 Irgacure initiating system at pH = 0.34 (0.5 M HCl) (A2-A24, I2-I24) *
 Column A: hydrogel type (polyacrylamide) * Column B: position * Column C:
 cycle number * Column D: maximum force reached during analysis * Column E:
 maximum contact pressure reached during analysis * Column F: maximum
 contact radius reached during analysis * Column G: estimated reduced
 elastic modulus using the Hertz model * Column I + J: averages and
 standard deviation of reduced elastic modulus per position * Table 2: raw
 data for hydrogel sample 2 with Irgacure initiating system at pH = 0.34
 (0.5 M HCl) (K2-K24, S2-S24) * Column K: hydrogel type (polyacrylamide) *
 Column L: position * Column M: cycle number * Column N: maximum force
 reached during analysis * Column O: maximum contact pressure reached
 during analysis * Column P: maximum contact radius reached during analysis
 * Column Q: estimated reduced elastic modulus using the Hertz model *
 Column R + S: averages and standard deviation of reduced elastic modulus
 per position * Table 3: raw data for hydrogel sample 3 with Irgacure
 initiating system at pH = 0.34 (0.5 M HCl) (U2-U24, AC2-AC24) * Column U:
 hydrogel type (polyacrylamide) * Column V: position * Column W: cycle
 number * Column X: maximum force reached during analysis * Column Y:
 maximum contact pressure reached during analysis * Column Z: maximum
 contact radius reached during analysis * Column AA: estimated reduced
 elastic modulus using the Hertz model * Column AB + AC: averages and
 standard deviation of reduced elastic modulus per position * Table 4: raw
 data for hydrogel sample 1 with Irgacure initiating system at pH = 2 (0.01
 M HCl) (A27-A49, I27-I49) * Column A: hydrogel type (polyacrylamide) *
 Column B: position * Column C: cycle number * Column D: maximum force
 reached during analysis * Column E: maximum contact pressure reached
 during analysis * Column F: maximum contact radius reached during analysis
 * Column G: estimated reduced elastic modulus using the Hertz model *
 Column I + J: averages and standard deviation of reduced elastic modulus
 per position * Table 5: raw data for hydrogel sample 2 with Irgacure
 initiating system at pH = 2 (0.01 M HCl) (K27-K49, S27-S49) * Column K:
 hydrogel type (polyacrylamide) * Column L: position * Column M: cycle
 number * Column N: maximum force reached during analysis * Column O:
 maximum contact pressure reached during analysis * Column P: maximum
 contact radius reached during analysis * Column Q: estimated reduced
 elastic modulus using the Hertz model * Column R + S: averages and
 standard deviation of reduced elastic modulus per position * Table 6: raw
 data for hydrogel sample 3 with Irgacure initiating system at pH = 2 (0.01
 M HCl) (U27-U49, AC27-AC49) * Column U: hydrogel type (polyacrylamide) *
 Column V: position * Column W: cycle number * Column X: maximum force
 reached during analysis * Column Y: maximum contact pressure reached
 during analysis * Column Z: maximum contact radius reached during analysis
 * Column AA: estimated reduced elastic modulus using the Hertz model *
 Column AB + AC: averages and standard deviation of reduced elastic modulus
 per position * Table 7: raw data for hydrogel sample 1 with Irgacure
 initiating system at pH = 7 (DI water) (A52-A74, I52-I74) * Column A:
 hydrogel type (polyacrylamide) * Column B: position * Column C: cycle
 number * Column D: maximum force reached during analysis * Column E:
 maximum contact pressure reached during analysis * Column F: maximum
 contact radius reached during analysis * Column G: estimated reduced
 elastic modulus using the Hertz model * Column I + J: averages and
 standard deviation of reduced elastic modulus per position * Table 8: raw
 data for hydrogel sample 2 with Irgacure initiating system at pH = 7 (DI
 water) (K52-K74, S52-S74) * Column K: hydrogel type (polyacrylamide) *
 Column L: position * Column M: cycle number * Column N: maximum force
 reached during analysis * Column O: maximum contact pressure reached
 during analysis * Column P: maximum contact radius reached during analysis
 * Column Q: estimated reduced elastic modulus using the Hertz model *
 Column R + S: averages and standard deviation of reduced elastic modulus
 per position * Table 9: raw data for hydrogel sample 3 with Irgacure
 initiating system at pH = 7 (DI water) (U52-U74, AC52-AC74) * Column U:
 hydrogel type (polyacrylamide) * Column V: position * Column W: cycle
 number * Column X: maximum force reached during analysis * Column Y:
 maximum contact pressure reached during analysis * Column Z: maximum
 contact radius reached during analysis * Column AA: estimated reduced
 elastic modulus using the Hertz model * Column AB + AC: averages and
 standard deviation of reduced elastic modulus per position * Table 10: raw
 data for hydrogel sample 1 with Irgacure initiating system at pH = 10
 (0.001 M NaOH) (A77-A99, I77-I99) * Column A: hydrogel type
 (polyacrylamide) * Column B: position * Column C: cycle number * Column D:
 maximum force reached during analysis * Column E: maximum contact pressure
 reached during analysis * Column F: maximum contact radius reached during
 analysis * Column G: estimated reduced elastic modulus using the Hertz
 model * Column I + J: averages and standard deviation of reduced elastic
 modulus per position * Table 11: raw data for hydrogel sample 2 with
 Irgacure initiating system at pH = 10 (0.001 M NaOH) (K77-K99, S77-S99) *
 Column K: hydrogel type (polyacrylamide) * Column L: position * Column M:
 cycle number * Column N: maximum force reached during analysis * Column O:
 maximum contact pressure reached during analysis * Column P: maximum
 contact radius reached during analysis * Column Q: estimated reduced
 elastic modulus using the Hertz model * Column R + S: averages and
 standard deviation of reduced elastic modulus per position * Table 12: raw
 data for hydrogel sample 3 with Irgacure initiating system at pH = 10
 (0.001 M NaOH) (U77-U99, AC77-AC99) * Column U: hydrogel type
 (polyacrylamide) * Column V: position * Column W: cycle number * Column X:
 maximum force reached during analysis * Column Y: maximum contact pressure
 reached during analysis * Column Z: maximum contact radius reached during
 analysis * Column AA: estimated reduced elastic modulus using the Hertz
 model * Column AB + AC: averages and standard deviation of reduced elastic
 modulus per position * Column AD + AE: averages and standard deviations of
 the three hydrogel samples at their specified solution pH W)
 Modulus\_TEMED\_APS.csv * Table 1: raw data for hydrogel sample 1 with
 TEMED + APS initiating system at pH = 0.34 (0.5 M HCl) (A2-A24, I2-I24) *
 Column A: hydrogel type (polyacrylamide) * Column B: position * Column C:
 cycle number * Column D: maximum force reached during analysis * Column E:
 maximum contact pressure reached during analysis * Column F: maximum
 contact radius reached during analysis * Column G: estimated reduced
 elastic modulus using the Hertz model * Column I + J: averages and
 standard deviation of reduced elastic modulus per position * Table 2: raw
 data for hydrogel sample 2 with TEMED + APS initiating system at pH = 0.34
 (0.5 M HCl) (K2-K24, S2-S24) * Column K: hydrogel type (polyacrylamide) *
 Column L: position * Column M: cycle number * Column N: maximum force
 reached during analysis * Column O: maximum contact pressure reached
 during analysis * Column P: maximum contact radius reached during analysis
 * Column Q: estimated reduced elastic modulus using the Hertz model *
 Column R + S: averages and standard deviation of reduced elastic modulus
 per position * Table 3: raw data for hydrogel sample 3 with TEMED + APS
 initiating system at pH = 0.34 (0.5 M HCl) (U2-U24, AC2-AC24) * Column U:
 hydrogel type (polyacrylamide) * Column V: position * Column W: cycle
 number * Column X: maximum force reached during analysis * Column Y:
 maximum contact pressure reached during analysis * Column Z: maximum
 contact radius reached during analysis * Column AA: estimated reduced
 elastic modulus using the Hertz model * Column AB + AC: averages and
 standard deviation of reduced elastic modulus per position * Table 4: raw
 data for hydrogel sample 1 with TEMED + APS initiating system at pH = 2
 (0.01 M HCl) (A27-A46, I27-I46) * Column A: hydrogel type (polyacrylamide)
 * Column B: position * Column C: cycle number * Column D: maximum force
 reached during analysis * Column E: maximum contact pressure reached
 during analysis * Column F: maximum contact radius reached during analysis
 * Column G: estimated reduced elastic modulus using the Hertz model *
 Column I + J: averages and standard deviation of reduced elastic modulus
 per position * Table 5: raw data for hydrogel sample 2 with TEMED + APS
 initiating system at pH = 2 (0.01 M HCl) (K27-K46, S27-S46) * Column K:
 hydrogel type (polyacrylamide) * Column L: position * Column M: cycle
 number * Column N: maximum force reached during analysis * Column O:
 maximum contact pressure reached during analysis * Column P: maximum
 contact radius reached during analysis * Column Q: estimated reduced
 elastic modulus using the Hertz model * Column R + S: averages and
 standard deviation of reduced elastic modulus per position * Table 6: raw
 data for hydrogel sample 3 with TEMED + APS initiating system at pH = 2
 (0.01 M HCl) (U27-U46, AC27-AC46) * Column U: hydrogel type
 (polyacrylamide) * Column V: position * Column W: cycle number * Column X:
 maximum force reached during analysis * Column Y: maximum contact pressure
 reached during analysis * Column Z: maximum contact radius reached during
 analysis * Column AA: estimated reduced elastic modulus using the Hertz
 model * Column AB + AC: averages and standard deviation of reduced elastic
 modulus per position * cells with n/a: no cycle data at the specified
 position * Table 7: raw data for hydrogel sample 1 with TEMED + APS
 initiating system at pH = 7 (DI water) (A49-A71, I49-I71) * Column A:
 hydrogel type (polyacrylamide) * Column B: position * Column C: cycle
 number * Column D: maximum force reached during analysis * Column E:
 maximum contact pressure reached during analysis * Column F: maximum
 contact radius reached during analysis * Column G: estimated reduced
 elastic modulus using the Hertz model * Column I + J: averages and
 standard deviation of reduced elastic modulus per position * cells with
 n/a: no cycle data at the specified position * Table 8: raw data for
 hydrogel sample 2 with TEMED + APS initiating system at pH = 7 (DI water)
 (K49-K71, S49-S71) * Column K: hydrogel type (polyacrylamide) * Column L:
 position * Column M: cycle number * Column N: maximum force reached during
 analysis * Column O: maximum contact pressure reached during analysis *
 Column P: maximum contact radius reached during analysis * Column Q:
 estimated reduced elastic modulus using the Hertz model * Column R + S:
 averages and standard deviation of reduced elastic modulus per position *
 Table 9: raw data for hydrogel sample 3 with TEMED + APS initiating system
 at pH = 7 (DI water) (U49-U71, AC49-AC71) * Column U: hydrogel type
 (polyacrylamide) * Column V: position * Column W: cycle number * Column X:
 maximum force reached during analysis * Column Y: maximum contact pressure
 reached during analysis * Column Z: maximum contact radius reached during
 analysis * Column AA: estimated reduced elastic modulus using the Hertz
 model * Column AB + AC: averages and standard deviation of reduced elastic
 modulus per position * Table 10: raw data for hydrogel sample 1 with TEMED
 + APS initiating system at pH = 10 (0.001 M NaOH) (A75-A94, I75-I94) *
 Column A: hydrogel type (polyacrylamide) * Column B: position * Column C:
 cycle number * Column D: maximum force reached during analysis * Column E:
 maximum contact pressure reached during analysis * Column F: maximum
 contact radius reached during analysis * Column G: estimated reduced
 elastic modulus using the Hertz model * Column I + J: averages and
 standard deviation of reduced elastic modulus per position * Table 11: raw
 data for hydrogel sample 2 with TEMED + APS initiating system at pH = 10
 (0.001 M NaOH) (K75-K94, S75-S94) * Column K: hydrogel type
 (polyacrylamide) * Column L: position * Column M: cycle number * Column N:
 maximum force reached during analysis * Column O: maximum contact pressure
 reached during analysis * Column P: maximum contact radius reached during
 analysis * Column Q: estimated reduced elastic modulus using the Hertz
 model * Column R + S: averages and standard deviation of reduced elastic
 modulus per position * cells with n/a: no cycle data at the specified
 position * Table 12: raw data for hydrogel sample 3 with TEMED + APS
 initiating system at pH = 10 (0.001 M NaOH) (U75-U94, AC75-AC94) * Column
 U: hydrogel type (polyacrylamide) * Column V: position * Column W: cycle
 number * Column X: maximum force reached during analysis * Column Y:
 maximum contact pressure reached during analysis * Column Z: maximum
 contact radius reached during analysis * Column AA: estimated reduced
 elastic modulus using the Hertz model * Column AB + AC: averages and
 standard deviation of reduced elastic modulus per position * Table 13: raw
 data for hydrogel sample 1 with TEMED + APS initiating system at pH = 13.5
 (0.5 M NaOH) (A97-A119, I97-I119) * Column A: hydrogel type
 (polyacrylamide) * Column B: position * Column C: cycle number * Column D:
 maximum force reached during analysis * Column E: maximum contact pressure
 reached during analysis * Column F: maximum contact radius reached during
 analysis * Column G: estimated reduced elastic modulus using the Hertz
 model * Column I + J: averages and standard deviation of reduced elastic
 modulus per position * Table 14: raw data for hydrogel sample 2 with TEMED
 + APS initiating system at pH = 13.5 (0.5 M NaOH) (K97-K119, S97-S119) *
 Column K: hydrogel type (polyacrylamide) * Column L: position * Column M:
 cycle number * Column N: maximum force reached during analysis * Column O:
 maximum contact pressure reached during analysis * Column P: maximum
 contact radius reached during analysis * Column Q: estimated reduced
 elastic modulus using the Hertz model * Column R + S: averages and
 standard deviation of reduced elastic modulus per position * Table 12: raw
 data for hydrogel sample 3 with TEMED + APS initiating system at pH = 13.5
 (0.5 M NaOH) (U97-U119, AC97-AC119) * Column U: hydrogel type
 (polyacrylamide) * Column V: position * Column W: cycle number * Column X:
 maximum force reached during analysis * Column Y: maximum contact pressure
 reached during analysis * Column Z: maximum contact radius reached during
 analysis * Column AA: estimated reduced elastic modulus using the Hertz
 model * Column AB + AC: averages and standard deviation of reduced elastic
 modulus per position * Column AD + AE: averages and standard deviations of
 the three hydrogel samples at their specified solution pH *** Compilation
 of raw swelling data --- X) Swelling\_Irgacure.csv * Table 1: raw data for
 hydrogels with Irgacure initiating system at pH = 0.34 (0.5 M HCl) (A2-A7,
 L2-L7) * Column A: hydrogel type (polyacrylamide) * Column B: acrylic acid
 mol% (0%) * Column C: acrylamide mol% (100%) * Column D: sample identifier
 (internal use) * Column E: swollen mass (g) * Column F: dried mass (g) *
 Column G: q = swollen mass/dried mass ratio * Column H: Q = ((swollen mass
 - dried mass)/swollen mass)\*100 * Column I + J: q average and standard
 deviation of the three samples after 2 weeks of drying * Column K + L: Q
 average and standard deviation of the three samples after 2 weeks of
 drying * Table 2: raw data for hydrogels with Irgacure initiating system
 at pH = 2 (0.01 M HCl) (A9-A14, L9-L14) * Column A: hydrogel type
 (polyacrylamide) * Column B: acrylic acid mol% (0%) * Column C: acrylamide
 mol% (100%) * Column D: sample identifier (internal use) * Column E:
 swollen mass (g) * Column F: dried mass (g) * Column G: q = swollen
 mass/dried mass ratio * Column H: Q = ((swollen mass - dried mass)/swollen
 mass)\*100 * Column I + J: q average and standard deviation of the three
 samples after 2 weeks of drying * Column K + L: Q average and standard
 deviation of the three samples after 2 weeks of drying * Table 3: raw data
 for hydrogels with Irgacure initiating system at pH = 7 (DI water)
 (A17-A22, L17-L22) * Column A: hydrogel type (polyacrylamide) * Column B:
 acrylic acid mol% (0%) * Column C: acrylamide mol% (100%) * Column D:
 sample identifier (internal use) * Column E: swollen mass (g) * Column F:
 dried mass (g) * Column G: q = swollen mass/dried mass ratio * Column H: Q
 = ((swollen mass - dried mass)/swollen mass)\*100 * Column I + J: q
 average and standard deviation of the three samples after 2 weeks of
 drying * Column K + L: Q average and standard deviation of the three
 samples after 2 weeks of drying * Table 4: raw data for hydrogels with
 Irgacure initiating system at pH = 10 (0.001 M NaOH) (A25-A30, L25-L30) *
 Column A: hydrogel type (polyacrylamide) * Column B: acrylic acid mol%
 (0%) * Column C: acrylamide mol% (100%) * Column D: sample identifier
 (internal use) * Column E: swollen mass (g) * Column F: dried mass (g) *
 Column G: q = swollen mass/dried mass ratio * Column H: Q = ((swollen mass
 - dried mass)/swollen mass)\*100 * Column I + J: q average and standard
 deviation of the three samples after 2 weeks of drying * Column K + L: Q
 average and standard deviation of the three samples after 2 weeks of
 drying Y) Swelling\_TEMED\_APS.csv * Table 1: raw data for hydrogels with
 TEMED + APS initiating system at pH = 2 (0.01 M HCl) (A1-A6, L1-L6) *
 Column A: hydrogel type (polyacrylamide) * Column B: acrylic acid mol%
 (0%) * Column C: acrylamide mol% (100%) * Column D: sample identifier
 (internal use) * Column E: swollen mass (g) * Column F: dried mass (g) *
 Column G: q = swollen mass/dried mass ratio * Column H: Q = ((swollen mass
 - dried mass)/swollen mass)\*100 * Column I + J: q average and standard
 deviation of the three samples after 2 weeks of drying * Column K + L: Q
 average and standard deviation of the three samples after 2 weeks of
 drying * Table 2: raw data for hydrogels with TEMED + APS initiating
 system at pH = 10 (0.001 M NaOH) (A10-A15, L10-L15) * Column A: hydrogel
 type (polyacrylamide) * Column B: acrylic acid mol% (0%) * Column C:
 acrylamide mol% (100%) * Column D: sample identifier (internal use) *
 Column E: swollen mass (g) * Column F: dried mass (g) * Column G: q =
 swollen mass/dried mass ratio * Column H: Q = ((swollen mass - dried
 mass)/swollen mass)\*100 * Column I + J: q average and standard deviation
 of the three samples after 2 weeks of drying * Column K + L: Q average and
 standard deviation of the three samples after 2 weeks of drying * Table 3:
 raw data for hydrogels with TEMED + APS initiating system at pH = 0.34
 (0.5 M HCl), pH = 7 (DI water), and pH = 13.5 (0.5 M NaOH) * Column A:
 solution pH (pH = 0.34 [0.5 M HCl], pH = 7 [DI water], or pH = 13.5 [0.5 M
 NaOH]) * Column B: sample identifier (internal use) * Column C: swollen
 mass (mg) * Column D: dried mass (mg) * Column E: Q = ((swollen mass -
 dried mass)/swollen mass)\*100 * Column F + G: Q average and standard
 deviation of the three samples at the specified pH Z)
 Volume\_change\_TEMED\_APS.csv * Column A: solution pH (pH = 0.3 [0.5 M
 HCl], pH = 7 [DI water], pH = 13.5 [0.5 M NaOH]) * Column B: sample
 identifier (internal use) * Column C: hydrogel diameter (mm) after
 polymerization before swelling (triplicate measurements per sample) *
 Column D: hp = hydrogel height (mm) after polymerization before swelling
 (triplicate measurements per sample) * Column E: mp = hydrogel mass (g)
 after polymerization before swelling * Column F: hydrogel diameter (mm)
 after swelling for 14 days in specified solution (triplicate measurements
 per sample) * Column G: hs = hydrogel height (mm) after swelling for 14
 days in specified solution (triplicate measurements per sample) * Column
 H: ms = hydrogel mass (g) after swelling for 14 days in specified solution
 * Column I: Vp = hydrogel volume (mm^3) after polymerization before
 swelling (assuming V = pi*r^2*h) * Column J: Vs = hydrogel volume (mm^3)
 after swelling for 14 days in specified solution (assuming V = pi*r^2*h) *
 Column K: volume change = ((Vs-Vp)/Vp)\*100 * Column L: Q = (hs/hp)^3 *
 Column M: mass change = ((ms-mp)/mp)\*100 * Column N + O: volume change
 average and standard deviation of the three samples at the specified pH *
 cells with n/a: mass data was only collected once per sample ***
 ############################################################################################# ## MATLAB CODES MATLAB Codes: all codes are under MIT license- please cite the code if a significant portion has been used A) Tribometer\_Indent\_Analysis\_v5 --&gt; uses natsortfiles function B) Compiling\_Friction\_Data\_v7 --&gt; uses natsortfiles function ANALYZING TRIBOMETER DATA --- A) Tribometer\_Indent\_Analysis\_v5: opens microtribometer indentation data from Excel files and fits the data with the Hertz contact mechanics model using the lsqcurvefit function B) Compiling\_Friction\_Data\_v7: opens microtribometer friction data from Excel files and calculates the friction coefficient from the specified x-range in the friction force loop over a specified number of cycles FUNCTIONS TO DOWNLOAD --- * Author: Stephen Cobeldick * Download from: https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort * Citation: Stephen23 (2023). Natural-Order Filename Sort (https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort), MATLAB Central File Exchange. Retrieved 2021. * Function of codes: reads and sorts through the files to analyze * Functions: A) natsortfiles B) natsort * Notes: natsortfiles calls natsort