Simple Polyacrylamide-based Multiwell Stiffness Assay for the Study of Stiffness-dependent Cell Responses
Instructor Prep
concepts
Student Protocol
1. Preparation of Hydrogel-associated Solutions and Aliquots
- Preparation of polyacrylamide gel precursor solution.
- Prepare polyacrylamide gel precursor solution by mixing acrylamide (A) (40% w/v, Mr 71.08 g/mol), the crosslinker bisacrylamide (B) (2% w/v, Mr 154.17 g/mol), and de-ionized water in the volume percentages specified in Table 1.
NOTE: These solutions can be prepared in large batches and stored at 4 °C for up to several months.- CAUTION: Acrylamide is toxic upon inhalation or ingestion, particularly, when in powder form: thus, preferably use 40% w/v solution to reduce toxicity risks. Handle only while wearing protective clothing, such as gloves, goggles, and a lab coat. Store in a light-resistant, tightly closed container in the fridge (<23 °C, well-ventilated area).
- CAUTION: Bis-acrylamide is toxic upon inhalation or ingestion, particularly, when in powder form: thus, preferably use 2% w/v solution to reduce toxicity risks. Handle only while wearing protective clothing, such as gloves, goggles, and a lab coat. Store in a light-resistant, tightly closed container in the fridge (<4 °C, well-ventilated area).
- Prepare polyacrylamide gel precursor solution by mixing acrylamide (A) (40% w/v, Mr 71.08 g/mol), the crosslinker bisacrylamide (B) (2% w/v, Mr 154.17 g/mol), and de-ionized water in the volume percentages specified in Table 1.
- Preparation and usage of N-Sulfosuccinimidyl-6-(4'-azido-2'-nitrophenylamino) hexanoate (Sulfo-SANPAH, Mr 492.40 g/mol) aliquots. CAUTION: Sulfo-SANPAH causes serious eye irritation; handle with gloves and proper eye or face protection. Store at -20 °C upon receipt and prior to aliquoting.
- To store sulfo-SANPAH: dissolve Sulfo-SANPAH in dimethylsulfoxane (DMSO) at 50 mg/ml. Aliquot the stock solution into 50 micro centrifuge tubes of 20 μl per tube. Flash freeze on dry ice or in liquid nitrogen (an optional but preferred step to preserve maximum crosslinker efficiency) and store at -80 °C.
NOTE: The aliquots can be stored for several months. - To use sulfo-SANPAH: thaw the aliquot briefly and dilute in 480 μl of de-ionized water. Use immediately. Sulfo-SANPAH hydrolyzes quickly in water: therefore take caution to perform all of the above steps quickly.
- To store sulfo-SANPAH: dissolve Sulfo-SANPAH in dimethylsulfoxane (DMSO) at 50 mg/ml. Aliquot the stock solution into 50 micro centrifuge tubes of 20 μl per tube. Flash freeze on dry ice or in liquid nitrogen (an optional but preferred step to preserve maximum crosslinker efficiency) and store at -80 °C.
- Preparation of ammonium persulfate (Mr 228.18 g/mol) aliquots.
NOTE: Ammonium persulfate causes eye, skin and respiratory irritation. Wear appropriate personal protective equipment when handling. Handle ammonium persulfate powder in a chemical fume hood. Store powder in a dry, well-ventilated place. Once aliquoted, the dilute solution could be used on the work bench.- Dissolve ammonium persulfate in deionized water to achieve a final ammonium persulfate concentration of 10% w/v. Aliquot and store at -20 °C. Thaw immediately prior to use.
- Preparation of Collagen Type I solution.
- Prepare 0.2 mg/ml collagen solution by diluting the stock solution in 1x phosphate buffered saline (PBS) of pH 7.4. Store on ice briefly or use immediately upon dilution.
2. Hydrogel Preparation (Refer to Figure 1)
- Preparation of hydrophobic glass slides.
- Place a few drops of a hydrophobic solution on a glass plate and use tissue paper to spread across the surface. Let air dry and wipe with a tissue paper again to even out the hydrophobic coating.
NOTE: Store hydrophobic solution in a flammable cabinet at RT. Wear personal protective equipment when handling. Work in a well-ventilated area.
- Place a few drops of a hydrophobic solution on a glass plate and use tissue paper to spread across the surface. Let air dry and wipe with a tissue paper again to even out the hydrophobic coating.
- Preparation of flexible plastic support.
- Cut the flexible plastic support to match the size of the hydrophobic-coated glass plate.
- Mark the hydrophobic side of the flexible plastic support by lightly scratching the surface with a sharp tool such as a scalpel.
NOTE: Once the gel — which is fully transparent — dries, the scratch marks will help distinguish which flexible plastic support side contains the gel.
NOTE: The flexible plastic support has a hydrophobic and a hydrophilic side. Once deposited, polyacrylamide permanently adheres to the hydrophilic side of the plastic support which facilitates easy subsequent hydrogel handling.
- Gel Preparation (example volumes are given for 5 ml gel precursor solutions).
NOTE: 5 ml would be sufficient to produce ~40 gels when the gel initial thickness is 0.5 mm. More gels can be produced if the gel thickness is reduced.- Place 4972.5 μl of polyacrylamide precursor solution of desired final concentration (Table 1) into a 50 ml conical tube. Place in a degassing chamber for 30 min with the cap opened.
NOTE: Oxygen acts as a free radical trap and when present, it inhibits polymerization. - Add 25 µl of 10% w/v ammonium persulfate (refer to point 1.3) to achieve a final ammonium persulfate concentration of 0.05%.
- Add 2.5 µl of N,N,N’,N’-tetramethylethylenediamine (TEMED, Mr 116.24 g/mol) to the degassed gel solution to achieve a final TEMED concentration of 0.5%.
NOTE: Store TEMED in a flammable cabinet at RT. Handle in a chemical fume hood when wearing appropriate personal protective equipment. Keep tightly closed under inert gas, as it is highly air and moisture sensitive. - Mix the solution gently by pipetting up and down 3 – 5 times. Do not vortex to avoid oxygen diffusion into the gel precursor solution.
- Pipette the gel solution onto the hydrophilic side of the flexible plastic support and sandwich with hydrophobic-coated glass slide. Separate the two slides with silicone spacers of desired thickness (e.g., 0.5 mm). Leave a small amount (~100 μl) of polymer precursor solution in the 50 ml conical tube to use as an indicator of gelation.
NOTE: Any spacer could be used. For example, a single strip of Parafilm gives a final swollen gel thickness of 100 – 120 μm. - Place another glass plate atop the flexible plastic support/gel sandwich to ascertain an even hydrogel surface upon polymerization.
- Let the gel polymerize for 45 min, although less time can be used for gels of higher % wt if desired. To ascertain that the gel has polymerized, observe the remaining solution in the 50 ml conical tube; if the remaining solution has gelled, then it is likely that gelation on the glass plate has been initiated as well. However, note that premature opening of the mold will prevent complete polymerization.
- Once the gel is formed, peel off the flexible plastic support with the covalently attached polyacrylamide gel on top, and set gel-side-up to air dry.
NOTE: Convection or heat drying can also be used to accelerate this step. Once dried onto the flexible plastic support, the gel can be stored indefinitely.- Mark any bare spots of the flexible plastic support, where polyacrylamide gels did not form due to bubbles. Mark while the gel is still hydrated as this will blend in with the flexible plastic support once the gel is dry.
- Place 4972.5 μl of polyacrylamide precursor solution of desired final concentration (Table 1) into a 50 ml conical tube. Place in a degassing chamber for 30 min with the cap opened.
3. Multiwell Plate Assembly, Collagen Coating, and Sterilization
- Multiwell plate assembly.
- Once dried, cut PA gels into desired shapes.
- For a 96-well plate, use a heavy-duty hole punch with a diameter of ~6 mm. Use a heavy-duty paper cutter to cut gels into square or rectangular shapes. Alternatively, use scissors.
- Prepare approximately 500 μl of PDMS per 96-well plate according to the manufacturer’s instructions. To glue the gels to the bottom of a multiwell plate, place a small droplet (~5 μl) of polydimethylsiloxane (PDMS) at the center of the each well. Using forceps, place one polyacrylamide gel in each well, flexible plastic support side down. To allow PDMS to cure, leave the assembled plate at 37 °C for a minimum of 4 hr.
- Once dried, cut PA gels into desired shapes.
- Collagen coating of polyacrylamide gels.
- With a transfer pipette, place a small amount (7 – 8 μl) of sulfo-SANPAH (refer to point 1.2.2) in each well and swirl from side to side to coat the gel surface evenly. Work promptly since sulfo-SANPAH is not stable in water.
- Place the well plate under a high intensity UV lamp (intensity = 37 mW, λ = 302 – 365 nm) for 5 min. Rinse the gels with PBS to remove excess sulfo-SANPAH.
- Pipette 50 µl of 0.2 mg/ml Collagen Type I solution (refer to point 1.4) into each well. Leave the plate covered at RT for at least 2 hr or O/N at 4 °C.
NOTE: To speed up the process of collagen coating, a transfer pipette can be used to add the collagen solution. Typically, 1 – 2 droplets of solution should be enough to completely cover the gel surface. - Leave the well plate at RT for at least 2 hr to allow collagen bonding.
- Rinse with PBS to remove excess collagen solution and sterilize under UV (λ = 200 nm) in a tissue culture hood for 2 hr.
- Soak the gels in complete medium (refer to section 4.1 for medium composition) O/N to hydrate and equilibrate. Use for cell seeding immediately or store in the fridge for up to 2 days.
4. Cell Seeding on PA Stiffness Assay
NOTE: Although typical for common mammalian cell lines, the protocol outlined in this section is specifically used with the breast cancer MDA-MB-231 cell line (see Figures 4 and 5).
- Collect cells from tissue culture flask by exposure to 5% trypsin/EDTA for 5 min at 37 °C. Use ~80 μl of trypsin/EDTA per each cm2 of culture flask area; for example, use 2 ml of trypsin/EDTA for a T25 cell culture flask. Re-suspend collected cells in complete medium supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin at a desired final cell concentration. Taking into account cell doubling time as well as the length of time the cells will be seeded on the assay, choose an appropriate sub-confluent cell concentration. Ensure that added medium is enough to completely submerge the hydrogels.
NOTE: Since the hydrogels have been pre-equilibrated in media (refer to step 3.2.6) 100 μl volume should be sufficient. Typical medium volumes used for multiwell plates should be sufficient since the gels have been pre-equilibrated in media in the previous step.
NOTE: The assay would be appropriate for any attachment-dependent cell type.- Count cell number under an inverted microscope by using a hemacytometer. Load 10 µl of cell suspension into each hemacytometer port and average the cell count from at least 8 quadrants. To get the final cell concentration, multiply the cell count by 104.
NOTE: Best cell count results are obtained when cell number in each hemacytometer quadrant is 20 – 50.
- Count cell number under an inverted microscope by using a hemacytometer. Load 10 µl of cell suspension into each hemacytometer port and average the cell count from at least 8 quadrants. To get the final cell concentration, multiply the cell count by 104.
- Culture the cells onto the PA stiffness assay in a humidified incubator at 37 °C and 5% CO2. Change media every 2 – 3 days. Collect cells when needed by exposure to 5% trypsin/EDTA at 37 °C for 5 min. Use ~80 μl of trypsin/EDTA per cm2 of tissue culture flask. During all cell manipulation steps, take special care not to disrupt the hydrogel surface: aspirate or pipette medium by slightly tipping the multiwell plate sideways and touching the pipette tip onto the side wall of each well, as opposed to touching the hydrogel.
NOTE: Except for taking special care not to damage the hydrogel surface during standard tissue culture handling, the cells seeded onto the stiffness assay can be manipulated the same way as if they were seeded onto a regular multiwell plate.
5. Imaging of Cells Seeded onto PA Stiffness Assay
- Image cells directly on the PA stiffness assay.
NOTE: Any microscope — inverted, fluorescent, or confocal, can be used for cell imaging.
NOTE: The flexible plastic support used to construct the stiffness assay is fully transparent and does not autofluoresce or interfere with cell imaging. However, even though the flexible plastic support itself is transparent, imaging capabilities will be limited by the working distance of the objective. The flexible plastic support has a thickness of 0.23 mm and a typical working distance of a 10X objective is ~4 mm, sharply decreasing for higher magnifications.- For live cell imaging, position PA stiffness assay in microscope plate holder and image. Keep imaging sessions under 2 hr, or use a microscope equipped with an environmental chamber for longer imaging times.
- When live cell imaging is not the goal, fix cells in 4% formaldehyde solution supplemented with 0.1% detergent. Soak cells in fixative at RT for a minimum of 2 hr. Rinse with PBS twice. Discard fixative waste in a designated waste container.
NOTE: Cells can be imaged immediately or stored submerged in PBS at 4 °C for up to 2 weeks. CAUTION: Formaldehyde is toxic upon inhalation and contact. Handle with gloves in a chemical fume hood.
NOTE: Cell fixation protocol has to be chosen based on the subsequent cell staining and handling protocols, because certain fixatives damage some cell proteins. - For fluorescent imaging, stain fixed cells with desired cell stain directly in the multiwell plate. Image immediately.
Simple Polyacrylamide-based Multiwell Stiffness Assay for the Study of Stiffness-dependent Cell Responses
Learning Objectives
Polyacrylamide (PA) hydrogels are widely used to test stiffness-dependent cell responses.17,24 By mixing various concentrations of acrylamide (A) and bis-acrylamide (B) one can make PA gels that span the stiffness range of most soft tissues in the body — 0.3 – 300 kPa Young’s modulus.1 However, preparation of polyacrylamide gels is tedious and time consuming, often limiting their usefulness in “high-throughput” applications such as for example drug screening.12 Here, a simple and rapid method for assembling PA gels in multi-well plates or any other desirable tissue culture vessel is presented (Figure 1). Figure 2A shows the Young’s modulus as a function of several A and B concentrations (also summarized in Table 1). The moduli of additional A and B combinations are reported in the literature.17,25,26 The gel stiffness of fully swollen gels was measured by rheology (AR 2000ex rheometer, TA Instruments) with a 20 mm upper parallel geometry, oscillatory frequency sweep test 1 – 10 Hz, and 2% constant strain. As anticipated, it was demonstrated that both storage modulus, G’, and loss modulus, G”, are independent of frequency (Figure 2B). It was also confirmed that drying and then re-hydrating the gels, did not affect their Young’s modulus (Figure 2C). Young’s modulus was related to the storage modulus by the following equation:
where E is Young’s modulus and v is the Poisson’s ratio which was approximated to 0.5 for PA gels.27 Note that the reported values are for hydrogels prepared with TEMED. PA hydrogels could also be prepared by UV crosslinking when exposure time and UV intensity are optimized (Table 2). Overall, it is our experience that measuring stiffness of the hydrogels regularly and especially when first establishing the protocols is very important as variations due to operator technique are not uncommon. While rheology is the best established technique for measuring bulk stiffness of hydrogels,27 other methods such as atomic force microscopy5,7 are also appropriate. Polyacrylamide hydrogels alone are inert; thus, to elicit cell attachment extracellular matrix molecules must be added separately. Collagen Type I was chosen for hydrogel coating, but the same method could be used to coat any other extracellular matrix (ECM) protein of choice. Figure 3 demonstrates that by using the crosslinker sulfo-SANPAH, a uniform collagen coating on hydrogels of any stiffness can be achieved.5
Further, it was demonstrated that cells seeded on hydrogels of different stiffness exhibited different morphology. For this experiment, breast cancer MDA-MB-231 cells were seeded on top of the PA gels for 24 – 72 hr. Cells were cultured in RPMI medium supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin in a humidified incubator at 37 °C and 5% CO2. Cells were seeded at 1 x 105 cells/ml or 1 x 104 cells/well for a 96-well plate. This is a typical cell seeding density — 4-fold lower than the confluency cell density, where confluency for a mammalian cell line is reached at ~1 x 105 cells/cm2. Images were taken on inverted fluorescent microscope and analyzed on ImageJ via the Shape Descriptor and Area software plug-ins. It was observed that when seeded on PA gels for 24 hr, breast cancer MDA-MB-231 cells remained round on the soft 0.5 and 1 kPa gels, but were able to spread and elongate on the stiff 100 kPa gel (Figure 4). Figure 4 also showcases the fact that hydrogels made on top of the flexible plastic support are transparent and allow for easy visualization and microscopy. Furthermore, the flexible plastic support does not autofluoresce and thus does not interfere with the imaging of fluorescently labeled cells. Cell morphology was further quantified in terms of overall cell spreading area and cell shape factor — circularity (Figure 5). Cell spreading area was measured by creating a mask to trace the perimeter of each cell. Cell shape (circularity) was then calculated from the following relationship:
Circularity is measured on a scale of 0 – 1, where 0.6 – 1 were taken to designate rounded cells and 0 – 0.5 were taken to designate elongated cells. Approximately three hundred cells from at least three independent experiments were analyzed for each data point. Statistical differences were calculated based on single factor analysis of variance (ANOVA) where data sets were considered significantly different when p < 0.05.
Figure 1. Schematic representation of polyacrylamide gel preparation on flexible plastic support. The figure represents the various steps involved in the preparation of PA gels on flexible plastic support. After the gel dries completely, it can be cut or punched into any desirable shape. A whole punch (~6 mm diameter) is most convenient when preparing gels for a 96-well plate, while a heavy-duty paper cutter can be used for square or rectangular shapes. The figure also highlights the edges of the wells, both with and without a gel, to demonstrate that complete well bottom coverage can be achieved with this method. Please click here to view a larger version of this figure.
Figure 2. Stiffness of PA hydrogels as measured by rheology. (A) Representative Young’s modulus for five different A&B concentrations (refer to Table 1 for acronyms); (B) storage and loss modulus as a function of frequency as measured by rheology; (C) gels exhibit the same Young’s modulus initially (Initial) and after they have been dried and re-hydrated (Re-hydrated) independent of polymer precursor concentration. All gels for the rheology measurements were prepared as slabs of 20 mm diameter and 1 – 1.5 mm height (upon complete swelling).
Figure 3. Collagen coating on PA gels. The collagen coating (green) is efficiently distributed and retained onto the PA gel (red) surface independent of hydrogel stiffness Young’s modulus). Collagen labeled with Cy5 was used for this data. Red-fluorescent beads were embedded into the PA hydrogel to aid visualization. Cross-sectional images were taken on a confocal microscope (scale bar = 100 μm). Image adapted from Zustiak et. al.5 Please click here to view a larger version of this figure.
Figure 4. Phase contract (top row) and fluorescent (bottom row) images of MDA-MB-231 cells seeded on PA gels for 24 hr. MDA-MB-231 cells remain round on soft gels (Young’s modulus of 0.5 and 1 kPa) but elongate on stiff PA gels (Young’s modulus of 100 kPa). The cells were seeded on the gels for 24 hr, fixed in ethanol and stained with acridine orange (AO — green) to visualize the cell cytoplasm and DAPI (blue) to visualize cell nucleus; scale bar = 100 μm. Please click here to view a larger version of this figure.
Figure 5. Cell spreading area and circularity are affected by the stiffness of the underlying substrate. (a) MDA-MB-231 cell spreading area is significantly increased on the 100 kPa as opposed to the 0.5 kPa gels. (b) Cell circularity decreases with increase in PA gel stiffness. Asterisks designate significant differences; p < 0.05.
Figure 6. Schematic representation of an alternative polyacrylamide gel preparation on flexible plastic support. The figure represents the various steps involved in the preparation of PA gels on flexible plastic support. Here the flexible plastic support is initially pre-cut into plastic “coverslips” of a desired shape and size. This technique works best for soft hydrogels. Please click here to view a larger version of this figure.
| Acronym | Acrylamide % | Bis-acrylamide % | Acrylamide from 40% stock solution (ml) | Bis-acrylamide from 2% stock solution (ml) | Water (ml) | G' ± SD (kPa) | E ± SD (kPa) |
| PA1 | 5 | 0.025 | 625 | 62.5 | 4312.5 | 0.62 ± 0.19 | 1.85 ± 0.57 |
| PA2 | 5 | 0.1 | 625 | 250 | 4125 | 3.55 ± 0.12 | 10.64 ± 0.36 |
| PA3 | 8 | 0.1 | 1,000 | 250 | 3750 | 9.71 ± 0.64 | 29.14 ± 1.93 |
| PA4 | 8 | 0.25 | 1,000 | 625 | 3375 | 22.00 ± 2.10 | 66.01 ± 6.31 |
| PA5 | 12 | 0.25 | 1,500 | 625 | 2875 | 37.42 ± 2.68 | 112.25 ± 8.03 |
Table 1. Concentrations of acrylamide (A) and crosslinker bis-acrylamide (B) and the resultant PA gel stiffness. Stiffness, represented here by G’ and E, was measured by rheology. G’ is the storage modulus at 1 Hz frequency. Young’s modulus, E, was calculated from Eq. 1. Standard deviation (SD) was calculated based on three independent experiments with 3-5 samples measured per experiment. The acronyms in the table correspond to the acronyms used in Figure 2A.
| UV Intensity = 15 mW/cm2 | Exposure time = 300 sec | ||
| Time (s) | E (kPa) ± SD | Intensity (mW/cm2) | E (kPa) ± SD |
| 75 | 0.14 ± 0.03 | 15 | 28.05 ± 2.62 |
| 100 | 6.98 ± 2.34 | 26 | 21.13 ± 3.01 |
| 125 | 19.11 ± 2.29 | 37 | 20.01 ± 2.38 |
| 300 | 28.05 ± 2.62 | 66 | 19.35 ± 2.86 |
Table 2. UV polymerization is an alternative and a quicker method for PA gel preparation when gelation conditions are optimized; PA3 (refer to Table 1) gel is depicted. The table summarizes the resultant Young’s modulus when either exposure time (left two columns) or UV intensity (right two columns) are varied for the same solution. Based on the results from the table, it appears that 300 sec exposure time and 15 mW/cm2 UV intensity give the highest PA gel stiffness, which is comparable to the stiffness of the traditionally polymerized gel as reported in Table 1.
List of Materials
| Reagents | |||
| 40% Acrylamide | Bio-Rad | 161-0140 | |
| 2% Bis-acrylamide | Bio-Rad | 161-0142 | |
| Ammonium Persulfate | Bio-Rad | 161-07000 | |
| TEMED | Sigma Aldrich | T9281 | |
| Sulfo-SANPAH | Thermo Scientific | 22589 | |
| Collagen Type 1, from Rat tail, 3.68 mg/mL | BD Biosciences | 354236 | |
| Dimethyl sulfoxide (DMSO) | Fisher Scientific | BP231-100 | |
| Hydrophobic solution – Repel Silane | GE Healthcare Bio-Sciences | 17-1332-01 | |
| PBS (1x), pH 7.4 | HyClone | SH30256.01 | |
| Polydimehylsiloxane (PDMS) [Slygard 182 Elastomer Kit] | Elsworth Adhesives | 3097358-1004 | |
| Tyrpsin/EDTA (10x) | Sigma Aldrich | 44174 | |
| RPMI-1640 Medium (1x) | HyClone | SH30027-02 | |
| Fetal Bovine Serum | HyClone | SH30073-03 | |
| Penicillin Streptomycin | MP Biomedicals | 1670046 | |
| Detergent – Triton-X | Sigma Aldrich | T8787 | |
| Formaldehyde 37% Solution | Sigma Aldrich | F1635 | |
| Bovine Serum Albumin (BSA) | Sigma Aldrich | A2153 | |
| BSA-based cell adhesion blocking kit – ECM Cell Adhesion Array Kit | Chemicon International | ECM540 | |
| Disposable lab equipment | |||
| flexible plastic support – GelBond PAG Film for Polyacrylamide Gels | GE Healthcare Bio-Sciences | 309819 | |
| Glass Plates | Slumpys | GBS4100SFSL | |
| 50 mL Conicals | Fisher Scinetific | 3181345107 | |
| 15 mL Conicals | FALCON | 352097 | |
| Micro centrifuge tubes | Fisher Scinetific | 2 mL: 02681258 | |
| 96-well plate (flat bottom) | Fisher Scinetific | 12565501 | |
| Disposable Pipettes (1 mL, 2mL, 5mL, 10mL, 25 mL, 50mL) | Fisher Scinetific | 1 mL: 13-678-11B, 2mL: 05214038, 5mL(FALCON): 357529, 10mL: 13-678-11E, 25mL: 13-678-11, 50mL: 13-678-11F | |
| Glass Transfer Pipettes | Fisher Scinetific | 5 3/4": 1367820A, 9":136786B | |
| Pipette Tips (1-200uL, 101-1000uL) | Fisher Scinetific | 2707509 | |
| Plastic Standard Disposable Transfer Pipettes | Fisher Scientific | 13-711-9D | |
| Parafilm | PARAFILM | PM992 | |
| Powder Free Examination Gloves | Quest | 92897 | |
| Silicone spacers – Silicone sheet, 0.5 mm thick/13 cm x 18 cm | Grace Bio-Labs | JTR-S-0.5 | |
| Large/non-disposable lab equipment | |||
| Light and Flourescent Microscope (Axiovert 200M) | Zeiss | 3820005619 | |
| Microscope Software | Zeiss | AxioVision Rel. 4.8.2 | |
| UV oven | UVITRON | UV1080 | |
| Vacuum chamber/degasser | BelArt | 999320237 | |
| Vacuum pump for degasser | KNF Lab | 5097482 | |
| Tissue Culture Hood | NUAIRE | NU-425-600 | |
| Chemical Fume Hood | KEWAUNEE | 99151 | |
| Inverted Microscope (Axiovert 25) | Zeiss | 663526 | |
| Incubator | NUAIRE | NU-8500 | |
| Pipette Aid | Drummond Scientific Co. | P-76864 | |
| Hemacytometer | Bright-Line | 383684 |
Lab Prep
Currently, most of the in vitro cell research is performed on rigid tissue culture polystyrene (~1 GPa), while most cells in the body are attached to a matrix that is elastic and much softer (0.1 – 100 kPa). Since such stiffness mismatch greatly affects cell responses, there is a strong interest in developing hydrogel materials that span a wide range of stiffness to serve as cell substrates. Polyacrylamide gels, which are inexpensive and cover the stiffness range of all soft tissues in the body, are the hydrogel of choice for many research groups. However, polyacrylamide gel preparation is lengthy, tedious, and only suitable for small batches. Here, we describe an assay which by utilizing a permanent flexible plastic film as a structural support for the gels, enables the preparation of polyacrylamide gels in a multiwell plate format. The technique is faster, more efficient, and less costly than current methods and permits the preparation of gels of custom sizes not otherwise available. As it doesn’t require any specialized equipment, the method could be easily adopted by any research laboratory and would be particularly useful in research focused on understanding stiffness-dependent cell responses.
Currently, most of the in vitro cell research is performed on rigid tissue culture polystyrene (~1 GPa), while most cells in the body are attached to a matrix that is elastic and much softer (0.1 – 100 kPa). Since such stiffness mismatch greatly affects cell responses, there is a strong interest in developing hydrogel materials that span a wide range of stiffness to serve as cell substrates. Polyacrylamide gels, which are inexpensive and cover the stiffness range of all soft tissues in the body, are the hydrogel of choice for many research groups. However, polyacrylamide gel preparation is lengthy, tedious, and only suitable for small batches. Here, we describe an assay which by utilizing a permanent flexible plastic film as a structural support for the gels, enables the preparation of polyacrylamide gels in a multiwell plate format. The technique is faster, more efficient, and less costly than current methods and permits the preparation of gels of custom sizes not otherwise available. As it doesn’t require any specialized equipment, the method could be easily adopted by any research laboratory and would be particularly useful in research focused on understanding stiffness-dependent cell responses.
Procedure
Currently, most of the in vitro cell research is performed on rigid tissue culture polystyrene (~1 GPa), while most cells in the body are attached to a matrix that is elastic and much softer (0.1 – 100 kPa). Since such stiffness mismatch greatly affects cell responses, there is a strong interest in developing hydrogel materials that span a wide range of stiffness to serve as cell substrates. Polyacrylamide gels, which are inexpensive and cover the stiffness range of all soft tissues in the body, are the hydrogel of choice for many research groups. However, polyacrylamide gel preparation is lengthy, tedious, and only suitable for small batches. Here, we describe an assay which by utilizing a permanent flexible plastic film as a structural support for the gels, enables the preparation of polyacrylamide gels in a multiwell plate format. The technique is faster, more efficient, and less costly than current methods and permits the preparation of gels of custom sizes not otherwise available. As it doesn’t require any specialized equipment, the method could be easily adopted by any research laboratory and would be particularly useful in research focused on understanding stiffness-dependent cell responses.