The authors acknowledge Oriol Font-Bach and Albert G. Casta&#241;o for their help in dmin quantification. They also acknowledge the Advanced Digital Microscopy Unit at the Institute for Research in Biomedicine (IRB Barcelona) to let the authors record the video in their premises. This work was supported by the Networking Biomedical Research Center (CIBER), Spain. CIBER is an initiative funded by the VI National R&amp;D&amp;i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions, and the Instituto de Salud Carlos III, with the support of the European Regional Development Fund. This work has been supported by the Commission for Universities and Research of the Department of Innovation, Universities, and Enterprise of the Generalitat de Catalunya (2014 SGR 1442). It was also funded by the projects OLIGOCODES (No. MAT2012-38573-C02) and CTQ2013-41339-P, awarded by the Spanish Ministry of Economy and Competitiveness, in addition to INTERREG V-A Spain-Portugal 2014-2020 POCTEP (0245_IBEROS_1_E). C.R.P. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness grant (No. IFI15/00151).

1. Substrate Preparation
<ol>
	<li>Annealing 1.4 x 1.1 cm Au(111) on Mica Substrates.
	<ol>
		<li>Place the Au(111) substrate on a glass-ceramic hob and anneal it with a butane flame for 3 min. Allow the substrate to cool under an argon atmosphere. Repeat this step for each Au(111) substrate. 
		NOTE: Au(111) substrates should be used immediately after annealing.</li>
	</ol>
	</li>
	<li>Preparation of Poly(L-Lactic Acid) (PLLA)-Coated Glass Substrates.
	<ol>
		<li>Cut and wash the glass slides.
		<ol>
			<li>Cut microscopy slides into 18 slides of 1.25 cm x 1.25 cm with a diamond-tip cutter. Make a small indentation on the lower side of each slide, so that the upper and lower sides can be later distinguished.</li>
			<li>Wash the slides thoroughly with deionized water followed by 96% ethanol. Allow them to air-dry.</li>
		</ol>
		</li>
		<li>Prepare the 2% PLLA solution.
		<ol>
			<li>Add 200 mg of PLLA to 10 mL of 1,4-dioxane in a pressure tube. Add a stir bar and close the tube tightly.</li>
			<li>Place the pressure tube into a glycerin bath on a hot plate at 60 &#176;C under gentle stirring for 24 h, and then transfer the solution to a 15-mL glass vial.</li>
		</ol>
		</li>
		<li>Coating the glass slides with the PLLA solution.
		<ol>
			<li>Place the glass slides and the vial with the PLLA solution on a clean hot plate at 60 &#176;C. Make sure to place the slides facing upward and allow them to remain for at least 10 min to reach the necessary temperature.</li>
			<li>Prepare the spin coater and set the program specified in Table 1.</li>
			<li>Place one of the slides face up on the spin coater, using a vacuum system. With a Pasteur pipette, apply 0.25 mL of the PLLA solution to the slide, making sure that the whole surface is covered. Run the coating program. Repeat this step for each slide.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Dendrimer Nanopatterning
<ol>
	<li>Preparation of RGD-Functionalized Dendrimer (RGD-Cys-D1) 28 Solutions.
	<ol>
		<li>Dissolve 5 mg of the dendrimer in 6.494 mL of deionized water. This is solution A. 
		NOTE: Use dendrimer stock solution within 6 months of preparation.</li>
		<li>Sonicate solution A for 10 min and prepare solutions B and C following Table 2.</li>
		<li>Sonicate solution C for 10 min and prepare solutions D, E and F following Table 2.</li>
		<li>Store solutions B, C, D, E and F at 4 &#176;C until use. Solution A can be stored at -20 &#176;C for later use.</li>
	</ol>
	</li>
	<li>Nanopatterning of RGD-Cys-D1 Dendrimers on the Substrates
	<ol>
		<li>In a tissue culture hood, sterilize the substrates by irradiating them with UV light for 13 min. 
		NOTE: This step is only necessary when nanopatterned substrates are going to be used as cell culture substrates. In this case, maintain the sterile conditions (tissue culture hood, sterile materials, solutions and techniques) for the following steps.</li>
		<li>Place each substrate face up in the wells of a plate, handling them carefully with tweezers.</li>
		<li>Sonicate solutions B, C, D, E and F for 10 min.</li>
		<li>Pass the RGD-Cys-D1 dendrimer solutions through a 0.22-&#181;m diameter filter using a syringe directly in the wells containing the substrates (2 mL/well). At least three replicas per dendrimer concentration are recommended. Close and seal the plate and leave it at room temperature (RT) for 16 h.</li>
		<li>Remove and discard the solutions. Wash the substrates with sterile deionized water and dry. Store substrates at 4 &#176;C. 
		NOTE: The protocol can be paused here.</li>
	</ol>
	</li>
</ol>
3. Preparation of Control Substrates
Note: All steps were performed in a sterile tissue culture hood, and only sterile materials, solutions and techniques were used. At least, six control substrates were used (three replicas of the positive control and three replicas of the negative control).
<ol>
	<li>In a tissue culture hood, sterilize the substrates by irradiating them with UV light for 13 min.</li>
	<li>Control Substrates for Fibroblast Adhesion Experiment.
	<ol>
		<li>Use flame-annealed Au(111) substrates as the negative control. Gold has a well-known protein-denaturation effect that confers anti-cell adhesive properties28. Sonicate all solutions and filter prior to substrate incubation.</li>
		<li>For the positive controls, immerse flame-annealed Au(111) substrates in a solution of RGD-modified PEG thiol, Ac-Gly-Arg-Gly-Asp-Ser-Asp-NH-ethylene glycol mono-11-mercaptoundecanamide (RGD-PEG-SH)30 and triethylene glycol mono-11-mercaptoundecyl ether (PEG-SH) at a 1:100 molar ratio in 96% ethanol for 16 h at RT.</li>
		<li>Wash substrates thoroughly in ethanol and dry them with argon. Store substrates at 4 &#176;C.</li>
	</ol>
	</li>
	<li>Control Substrates for Chondrogenesis.
	<ol>
		<li>Use pristine PLLA substrates as the negative control. Without any surface treatment, PLLA shows poor interfacing with living cells.31</li>
		<li>For the positive controls, prepare 5 mL of 0.1 mg/mL fibronectin in phosphate-buffered saline (PBS) and incubate each PLLA substrate with 1.6 mL of the fibronectin solution for 1 h at RT.</li>
		<li>Remove and discard the fibronectin solution, and wash the substrates with PBS. Store substrates at 4 &#176;C.</li>
	</ol>
	</li>
</ol>
4. Surface Characterization
<ol>
	<li>AFM Imaging
	<ol>
		<li>Perform AFM imaging of PLLA substrates for a roughness analysis. Since dendrimers have a diameter of 4-5 nm, roughness values of 1 nm should be obtained for the proper visualization of the nanopatterns. Also, perform AFM imaging of the nanopatterns. In both cases, perform AFM in tapping mode in air.</li>
		<li>Select a silicon cantilever with a spring constant k = 40 N/m and a resonant frequency &#957; = 300 kHz and mount it onto the AFM equipment.</li>
		<li>Mount the sample on the stage of the atomic force microscope. Depending on the set-up of the apparatus, tuning and imaging specifications may vary. Consult the manufacturer&#39;s handbook.</li>
		<li>Approach the sample with the tip of the microscope until contact.</li>
		<li>To image PLLA for roughness analysis, select at least four representative areas of 20x20 &#181;m per substrate from three independent substrates. To image dendrimer nanopatterns, choose at least three representative images of 5&#215;5 &#181;m per substrate from three independent substrates per condition (initial dendrimer concentration in solution). To avoid damaging the dendrimer layer while imaging, adjust the set point to keep the force at a minimum. 
		NOTE: The choice of the imaging area also depends on the working range of the piezoelectric scanner. Please consult the instrument manual in this regard.</li>
		<li>Process the AFM height images by fitting each scan line to polynomial leveling functions using the proprietary software of the manufacturer of the AFM apparatus, and analyze those from PLLA to calculate surface roughness. Root-mean square (RMS) analysis may provide a suitable option.</li>
	</ol>
	</li>
	<li>Local RGD Surface Density Measurement.
	<ol>
		<li>Obtain the image thresholds of the processed AFM height images to select the dendrimers on the surface.</li>
		<li>Determine the particle positions using an image processing software and use them to obtain the minimum interparticle distances (dmin).</li>
		<li>Plot dmin values in z to the corresponding particle positions to obtain the probability contour maps for dmin. Adjust the color scale of the plot to visualize the regions of highest local RGD surface density (dmin &#60; 70 nm).</li>
		<li>Quantify the area of the regions with the highest local RGD surface density using an image processing software. Include the areas of dendrimer aggregates in the calculation.</li>
	</ol>
	</li>
	<li>STM Imaging. 
	Note: STM imaging can be performed only for nanopatterns on conductive Au(111) substrates. Measurements are done in air.
	<ol>
		<li>Place the nanopatterned substrate in the sample holder of the STM equipment. Check the electrical connection between sample and holder with a tester.</li>
		<li>Etch a tip of the selected probe material (i.e. Pt 0.8: Ir 0.2) with a diameter that ensures proper fitting on the head of the STM equipment. Etching can be performed either by manual cutting or by electrochemical etching.32 
		NOTE: Electrochemical etching renders more symmetric tips.</li>
		<li>Mount the tip in the head of the STM equipment and connect the sample.</li>
		<li>Set &#34;current&#34; in the feedback channel (in this type of measurement, current will be constant by feedback tuning). Adjust the bias voltage and current set point and scan size to obtain a well resolved image once the tip is engaged. 
		NOTE: The choice of the imaging area also depends on the working range of the piezoelectric scanner. Please consult the instrument manual in this regard.</li>
		<li>Process the STM topographical images by fitting each scan line to polynomial leveling functions using the proprietary software of the manufacturer of the STM apparatus.</li>
	</ol>
	</li>
	<li>CA Measurements.
	<ol>
		<li>Measure CA on the nanopatterned substrates by the sessile-drop method at three different positions on three independent substrates per condition (initial dendrimer concentration in solution) with an optical CA system.</li>
		<li>Fill the microsyringe with deionized water and set the parameters in the CA software to produce drops of 1 &#181;L.</li>
		<li>Place the sample on the stage so that the surface of the sample is clearly visible on the computer for imaging.</li>
		<li>Move the syringe with the micromanipulator until it gets close to the surface and dispense the drop onto the surface. Record the image immediately after droplet stabilization. 
		NOTE: In CA measurements, it is very important to control humidity in order to achieve reproducible results.</li>
		<li>Analyze the CAs measured with the proprietary software of the manufacturer of the CA apparatus. The fitting method can be adjusted to user requirements. The elliptic fitting method can be an option.</li>
	</ol>
	</li>
</ol>
5. Cell Culture
NOTE: All steps were performed in a tissue culture hood, and only sterile materials, solutions and techniques were used.
<ol>
	<li>Fibroblast Adhesion Experiment.
	<ol>
		<li>Culture NIH 3T3 mouse embryonic fibroblasts from early passages (&#60; 10) at 37 &#176;C and 4.6% CO2 atmosphere in basal medium with high glucose supplemented with 10% fetal bovine serum (FBS), 1% L-glutamine, 1% penicillin-streptomycin and 1% sodium pyruvate (growth medium). T75 flasks for a total seeding of 500,000 cells per flask in 10 mL of growth medium are recommended.</li>
		<li>Remove old medium with a 10 mL pipette every 2 days and replace with 10 mL of freshly prepared growth medium.</li>
		<li>Culture cells in the growth medium until they reach around 80% confluence, then remove the medium and add 5 mL of trypsin per flask. To ensure proper cell detachment from the bottom of the flask, maintain the trypsin solution in contact with the cells for 5 min at 37 &#176;C.</li>
		<li>Add 5 mL of growth medium per flask and collect the cells in a centrifuge tube. Centrifuge the cells at 470 x g for 5 min. Remove the supernatant and resuspend the cell pellet in 10 mL of growth medium. Determine the concentration of cells using a hemocytometer.</li>
		<li>Transfer the substrates to well plates not treated for tissue culture (non-adherent).</li>
		<li>Seed the cells on the substrates at a density of 4,000 cells/cm2 in growth medium and incubate them for 4.5 h at 37 &#176;C and 10% CO2 atmosphere.</li>
	</ol>
	</li>
	<li>Chondrogenic Induction of MSCs.
	<ol>
		<li>Culture human MSCs from early passages (&#60;5) at 37 &#176;C and 4.6% CO2 atmosphere in MSC growth medium. T75 flasks for a total seeding of 500,000 cells per flask in 10 mL of growth medium are recommended.</li>
		<li>Change medium every 3 days (as described in 5.1.2).</li>
		<li>Trypsinize cells before 80% confluence is reached, and centrifuge and resuspend them in MSC growth medium (as described in 5.1.3). Determine the concentration of cells using a hemocytometer.</li>
		<li>Centrifuge the cells again and resuspend them in 10 mL of chondrogenesis-inducing medium.</li>
		<li>Transfer the substrates from the plates to new well plates not treated for tissue culture (non-adherent). Seed the cells on the substrates at a density of 3,000 cells/cm2.</li>
		<li>Change the chondrogenic medium every 3 days (as described in 5.1.2).</li>
	</ol>
	</li>
</ol>
6. Cell Fixation and Immunostaining
NOTE: The following steps can be performed in non-sterile conditions.
<ol>
	<li>Remove the media and wash the cells gently with PBS. Fix them by adding a 10% formalin solution for 20 min at RT.</li>
	<li>Remove the formalin and wash the cells with PBS.</li>
	<li>Block the free aldehyde groups by adding a 50 mM solution of ammonium chloride (NH4Cl) in PBS. Leave the cells for 20 min at RT. Remove NH4Cl solution and wash the cells with PBS. 
	NOTE: The protocol can be paused here. Store samples in PBS at 4 &#176;C.</li>
	<li>Remove PBS and permeabilize the cells by adding a 0.1% solution of saponin in the blocking solution (1% albumin in PBS) for 10 min at RT. Wash the cells with PBS and transfer samples to a new well plate.</li>
	<li>Incubate the cells with a solution of primary antibodies in the blocking solution (Table 3) for 1 h at RT. Then, remove the primary antibody solution and wash the cells with PBS.</li>
	<li>Incubate the cells with secondary antibodies in the blocking solution (Table 3) for 1 h at RT. 
	NOTE: Avoid light exposure.</li>
	<li>Remove the secondary antibody solution and wash the cells with PBS and dry. 
	NOTE: The protocol can be paused here. Store the samples in PBS at 4 &#176;C in the dark.</li>
	<li>Sample mounting for microscope observation: Using a diamond-tip cutter, cut coverslips into 1.25 cm x 1.25 cm. Apply 50 &#181;L of microscopy mounting medium onto the samples and cover them gently with the cut coverslips.</li>
	<li>Transfer the samples to a convenient recipient, cover it with aluminum foil and store in the dark at 4 &#176;C until observation.</li>
</ol>
7. Cell Imaging and Data Analysis
NOTE: For opaque Au(111) and thick microslide-based substrates, an upright microscope must be used.
<ol>
	<li>Fibroblast Adhesion Experiment.
	<ol>
		<li>Use an epifluorescence microscope equipped with a digital camera and low (i.e. 10X) and high (i.e. 40X) magnification objectives. Perform measurements in air.</li>
		<li>Place the sample on the stage and image cell nuclei with the 10X objective using an ultraviolet excitation, longpass emission filter to visualize the Hoechst/DAPI stain.</li>
		<li>Image cell cytoskeleton and focal adhesions (FAs) with the 40X objective, selecting the microscope filter that matches the corresponding antibody fluorochrome specifications.</li>
		<li>For FA quantification, use an image processing software to convert images to 8-bit files. Remove the background and convert images to binary by setting a threshold. Compute at least 30 images per sample and consider FAs from 1 &#181;m2 for calculation.</li>
	</ol>
	</li>
	<li>Chondrogenic Induction of MSCs.
	<ol>
		<li>Image cell condensates at the initial stages of chondrogenic induction (&#60; 5 days) with an upright epifluorescence microscope equipped with a digital camera and a low (i.e. 10X) magnification objective. Use ultraviolet excitation and longpass emission filter to visualize the Hoechst/DAPI stain.</li>
		<li>For measuring the condensate area, use an image processing software, convert images to 8-bit files, remove the background and select a threshold that highlights the aggregate contour. Calculate the area of the particles.</li>
		<li>Image immunostained samples for FAs, cytoskeleton actin fibers, and cartilage-specific collagen type II alpha 1 (COL2A1) with an upright confocal microscope at high magnification (i.e. 40-60X). Collect sections at a representative interval (i.e. 0.5&#8211;1 &#181;m).</li>
		<li>To process the stack, use an image processing software. Convert images to 8-bit files, remove the background, and make them binary by setting a threshold. Treat a minimum of three cell condensates per condition of three independent samples.</li>
		<li>Quantify the FA protein stained areas from the basal zone of cell condensates and express them as the corresponding percentage of area divided by the number of cell nuclei in the image.</li>
		<li>To measure COL2A1 staining, use confocal z-projections and quantify the sum of the projected area (maximum COL2A1 area per sample). Normalize the area value obtained against the area of the corresponding condensate.</li>
	</ol>
	</li>
</ol>
8. Quantitative Reverse Transcription-polymerase Chain Reaction (qRT-PCR) Analysis
NOTE: To prevent RNase contamination, use disposable, sterile plastic ware and wear disposable gloves while handling reagents and RNA. Always use proper microbiological aseptic techniques and use an appropriate decontamination solution to remove RNase contamination from work surfaces and non-disposable items such as centrifuges and pipettes.
<ol>
	<li>Isolate total RNA and pulverize it in a RNA disrupter. Treat RNA samples with DNase and convert them into cDNA using a cDNA synthesis kit.</li>
	<li>Conduct qRT-PCR using primers for the transcription factor SOX9. Beta-2-microglobulin (B2M) and ribosomal protein L13a (RPL13a) can be used as housekeeping genes.</li>
	<li>Calculate the expression levels and normalize them against the negative control (PLLA).</li>
</ol>

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Chem. 20 (4), 693-701 (2009).</li><li>Albertazzi, L., Fernandez-Villamarin, M., Riguera, R., Fernandez-Megia, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peripheral+functionalization+of+dendrimers+regulates+internalization+and+intracellular+trafficking+in+living+cells.">Peripheral functionalization of dendrimers regulates internalization and intracellular trafficking in living cells.</a> Bioconjug. Chem. 23 (5), 1059-1068 (2012).</li><li>Mikhail, A. S., Jones, K. S., Sheardown, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dendrimer+grafted+cell+adhesion+peptide-modified+PDMS.">Dendrimer grafted cell adhesion peptide-modified PDMS.</a> Biotechnol. Prog. 24 (4), 938-944 (2008).</li><li>Kino-oka, M., Kim, J., Kurisaka, K., Kim, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preferential+growth+of+skeletal+myoblasts+and+fibroblasts+in+co-culture+on+a+dendrimer-immobilized+surface.">Preferential growth of skeletal myoblasts and fibroblasts in co-culture on a dendrimer-immobilized surface.</a> J. Biosci. Bioeng. 115 (1), 96 (2013).</li><li>Kim, M. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphological+regulation+and+aggregate+formation+of+rabbit+chondrocytes+on+dendrimer+immobilized+surfaces+with+D-glucose+display.">Morphological regulation and aggregate formation of rabbit chondrocytes on dendrimer immobilized surfaces with D-glucose display.</a> J. Biosci. Bioeng. 107 (2), 196-205 (2009).</li><li>Lomba, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+adhesion+on+surface+patterns+generated+by+the+photocrosslinking+of+hyperbranched+polyesters+with+a+trisdiazonium+salt.">Cell adhesion on surface patterns generated by the photocrosslinking of hyperbranched polyesters with a trisdiazonium salt.</a> React. Funct. Polym. 73 (3), 499-507 (2013).</li><li>Maheshwari, G., Brown, G., Lauffenburger, D. A., Wells, A., Griffith, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+adhesion+and+motility+depend+on+nanoscale+RGD+clustering.">Cell adhesion and motility depend on nanoscale RGD clustering.</a> J. Cell Sci. 113 (Pt 10), 1677-1686 (2000).</li><li>Kim, M. H., Kino-oka, M., Kawase, M., Yagi, K., Taya, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synergistic+effect+of+D-glucose+and+epidermal+growth+factor+display+on+dynamic+behaviors+of+human+epithelial+cells.">Synergistic effect of D-glucose and epidermal growth factor display on dynamic behaviors of human epithelial cells.</a> J. Biosci. Bioeng. 104 (5), 428-431 (2007).</li><li>Pericet-Camara, R., Cahill, B. P., Papastavrou, G., Borkovec, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nano-patterning+of+solid+substrates+by+adsorbed+dendrimers.">Nano-patterning of solid substrates by adsorbed dendrimers.</a> Chem. Commun. 3, 266-268 (2007).</li><li>Lagunas, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-scale+dendrimer-based+uneven+nanopatterns+for+the+study+of+local+arginine&#8211;glycine&#8211;aspartic+acid+(RGD)+density+effects+on+cell+adhesion.">Large-scale dendrimer-based uneven nanopatterns for the study of local arginine&#8211;glycine&#8211;aspartic acid (RGD) density effects on cell adhesion.</a> Nano Res. 7 (3), 399-409 (2014).</li><li>Lagunas, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tailoring+RGD+local+surface+density+at+the+nanoscale+toward+adult+stem+cell+chondrogenic+commitment.">Tailoring RGD local surface density at the nanoscale toward adult stem cell chondrogenic commitment.</a> Nano Res. , (2017).</li><li>Prats-Alfonso, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effective+and+Versatile+Strategy+for+the+Total+Solid-Phase+Synthesis+of+Alkanethiols+for+Biological+Applications.">Effective and Versatile Strategy for the Total Solid-Phase Synthesis of Alkanethiols for Biological Applications.</a> Eur. J. Org. Chem. 2013 (7), 1233-1239 (2013).</li><li>Zhu, Y. B., Gao, C. Y., Liu, X. Y., He, T., Shen, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immobilization+of+biomacromolecules+onto+aminolyzed+poly(L-lactic+acid)+toward+acceleration+of+endothelium+regeneration.">Immobilization of biomacromolecules onto aminolyzed poly(L-lactic acid) toward acceleration of endothelium regeneration.</a> Tissue Eng. 10 (1-2), 53-61 (2004).</li><li>G&#252;ell, A., D&#237;ez-P&#233;rez, I., Gorostiza, P., Sanz, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+reliable+probes+for+electrochemical+tunneling+spectroscopy.">Preparation of reliable probes for electrochemical tunneling spectroscopy.</a> Anal. Chem. 76 (17), 5218-5222 (2004).</li><li>Bobick, B. E., Chen, F. H., Le, A. M., Tuan, R. 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Cell Biol. 102 (4), 1151-1156 (1986).</li><li>Biebricher, A., Paul, A., Tinnefeld, P., Golzhauser, A., Sauer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+three-dimensional+immobilization+of+biomolecules+on+chemically+patterned+surfaces.">Controlled three-dimensional immobilization of biomolecules on chemically patterned surfaces.</a> J. Biotechnol. 112 (1-2), 97-107 (2004).</li><li>Tinazli, A., Piehler, J., Beuttler, M., Guckenberger, R., Tamp&#233;, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Native+protein+nanolithography+that+can+write,+read+and+erase.">Native protein nanolithography that can write, read and erase.</a> Nat. Nanotechnol. 2, 220-225 (2007).</li><li>Oberhansl, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+Modification+of+Silica+Substrates+Provides+a+Platform+for+Direct-Writing+Surface+Click+Chemistry.">Facile Modification of Silica Substrates Provides a Platform for Direct-Writing Surface Click Chemistry.</a> Small. 8 (4), 541-545 (2012).</li></ol>

The authors have nothing to disclose.

During the development of the described protocol, a number of critical steps should be considered. The first refers to nanopattern characterization with scanning probe microscopy techniques. To visualize the nanopatterns, the surface where patterning is produced must have a roughness value below the mean diameter of the dendrimers, which is around 4&#8211;5 nm as measured by STM (Figure 1B). Also, it should be taken into account that high resolution STM imaging is restricted to conductive substrates, in ...

Here we describe a simple and versatile dendrimer-based nanopatterning procedure to obtain cell culture surfaces that allow the control of local adhesiveness at the nanoscale. Nanoscale details of ECM organization have been reported,1,2,3 and the nanopatterning of cell adhesion surfaces has provided deep insights into the cellular requirements related to adhesion4,5. Experiments using micellar lithography-based nanopatterns revealed a threshold value of around 70 nm for RGD peptide nanospacing, cell adhesion being significantly delayed above this value6,7,8,9. These studies also highlighted the greater influence of local than global ligand density on cell adhesion9,10,11.
During morphogenesis, cell interactions with the surrounding environment trigger the first differentiation events, which continue until final complex tissue structures have been formed. Within this framework, nanopatterned surfaces have been used to tackle the influence of the initial cell-surface interactions on morphogenesis. Lithography-based RGD nanopatterns with a lateral spacing of 68 nm in &#946;-type Ti-40Nb alloys help to maintain the undifferentiated phenotype of non-committed stem cells12, while RGD nanospacings of between 95 and 150 nm enhance the differentiation of mesenchymal stem cells (MSCs) towards adipogenic/osteogenic13,14,15 and chondrogenic fates16. Also, self-assembling macromolecules modified with signaling components have been shown to direct cell adhesion and differentiation by providing nanoscale architectural regulation of the signaling cues17. In this regard, the deposition of dendrimers with cell-interacting moieties in their outer sphere18,19,20 onto surfaces has been used to study cell adhesion21,22, morphology23,24, and migration events25,26. Nevertheless, the lack of surface characterization in these studies makes it difficult to establish any correlation between dendrimer surface configuration and cell response.
Dendrimer nanopatterns with liquid-like order and defined spacing can be obtained when dendrimers adsorb to low-charged surfaces from solutions with low ionic strengths.27 On the basis of this property, here we present a method to obtain large-scale uneven nanopatterns of RGD-functionalized dendrimers on low-charged surfaces that permit the nanoscale control of local RGD surface density. Water contact angle (CA), X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy techniques (STM and AFM nanopatterns) show that local ligand densities can be adjusted modifying the initial dendrimer concentration in solution. The local RGD surface density is quantified from AFM images by probability contour maps of minimum interparticle distances and then correlated with cell experiments. Compared with other nanopatterning techniques4, dendrimer-based nanopatterning is straightforward and can be easily scaled up to large surface areas, thus being fully compatible with cell culture applications. Nanopatterns are used as bioactive substrates to evaluate the effect of the local RGD surface density on cell adhesion28 and on the chondrogenic induction of adult human MSCs29. Our results show that RGD dendrimer-based nanopatterns sustain cell growth and that cell adhesion is reinforced by high local RGD surface densities. In the differentiation experiments, intermediate adhesiveness of cells to the substrates favored MSC condensation and early chondrogenic differentiation. Due to the ease with which dendrimer peripheral groups can be modified, the method described here can be further extended to other ECM ligands that exert concentration-dependent effects on cells.

<table><tbody><tr><td>Gold (111) on mica. 1.4x1.1 cm&amp;nbsp;</td><td>Spi Supplies</td><td>466PS-AB</td><td></td></tr><tr><td>Glass micro slides, plain</td><td>Corning</td><td>2947-75x25</td><td></td></tr><tr><td>Deionized water</td><td>Millipore</td><td></td><td>18M&amp;Omega; cm</td></tr><tr><td>Ethanol 96%</td><td>PanReac</td><td>131085.1212</td><td></td></tr><tr><td>L-Lactide/DL-Lactide copolymer</td><td>Corbion</td><td></td><td>95/05 molar ratio</td></tr><tr><td>1,4 - dioxane</td><td>Sigma-Aldrich</td><td>296309-1L</td><td></td></tr><tr><td>Silicone oil, high temperature</td><td>Acros Organics</td><td>174665000</td><td></td></tr><tr><td>Spinner</td><td>Laurell</td><td>WS-650MZ-23NPP/Lite</td><td></td></tr><tr><td>Tissue culture laminar flow hood</td><td>Telstar</td><td>Bio II Advance</td><td>Class II biological safety cabinet</td></tr><tr><td>Filter unit</td><td>Millex-GP</td><td>SLGP033RB</td><td>0.22 &amp;micro;m</td></tr><tr><td>Syringe 10 mL</td><td>Discardit</td><td>309110</td><td></td></tr><tr><td>Atomic Force microscope</td><td>Veeco Instruments</td><td>Dimension 3000 AFM instrument</td><td></td></tr><tr><td>Silicon AFM probes</td><td>Budget Sensors</td><td>Tap300AI-G</td><td>Resonant Freq. 300 kHz, k = 40 N/m</td></tr><tr><td>Scanning tunneling microscope</td><td>Molecular Imaging</td><td>PicoSPM microscope</td><td></td></tr><tr><td>Pt0.8:Ir0.2 wire</td><td>Advent</td><td>PT671012</td><td>Diameter 0.25 mm</td></tr><tr><td>WSxM 4.0 software</td><td>Nanotec electronica</td><td></td><td></td></tr><tr><td>Optical contact angle (CA) system</td><td>Dataphysics</td><td></td><td></td></tr><tr><td>SCA20 software</td><td>Dataphysics</td><td></td><td></td></tr><tr><td>X-ray photoelectron spectrometer</td><td>Physical Electronics</td><td>Perkin-Elmer PHI 5500 Multitechnique System</td><td></td></tr><tr><td>Fibronectin from bovine plasma</td><td>Sigma-Aldrich</td><td>F1141-1MG</td><td>1.0 mL solution</td></tr><tr><td>Dulbecco&#039;s Phosphate Buffer Saline (DPBS)</td><td>Gibco</td><td>21600-10</td><td>Powder</td></tr><tr><td>Mouse embryo fibroblasts</td><td>ATCC</td><td>ATCC CRL-1658</td><td>NIH/3T3</td></tr><tr><td>Dulbecco&#039;s modified eagle medium (DMEM) liquid high glucose</td><td>Gibco</td><td>11960044</td><td>liquid high glucose, no glutamine, 500 mL</td></tr><tr><td>Fetal Bovine Serum (FBS)</td><td>Gibco</td><td>16000044</td><td>500 mL</td></tr><tr><td>L-Glutamine</td><td>Invitrogen</td><td>25030</td><td>200 mM (100X)</td></tr><tr><td>Penicillin-streptomycin</td><td>Invitrogen</td><td>15140</td><td></td></tr><tr><td>Sodium pyruvate</td><td>Invitrogen</td><td>11360039</td><td>100 mL</td></tr><tr><td>T75 culture flasks</td><td>Nunclon</td><td>156499</td><td></td></tr><tr><td>Trypsin</td><td>Life Technologies</td><td>25200072</td><td>0,25% EDTA</td></tr><tr><td>Centrifuge</td><td>Hermle Labortechnik</td><td>Z 206 A</td><td></td></tr><tr><td>Non-tissue culture treated plate, 12 well</td><td>Falcon</td><td>351143</td><td>Non-adherent</td></tr><tr><td>Adipose-derived hMSCs</td><td>ATCC</td><td>ATCC PCS-500-011</td><td>Cell vial 1 mL</td></tr><tr><td>MSC basal medium</td><td>ATCC</td><td>ATCC PCS-500-030</td><td></td></tr><tr><td>MSC growth kit</td><td>ATCC</td><td>ATCC PCS-500-040</td><td>Low serum</td></tr><tr><td>Chondrocyte differentiation tool</td><td>ATCC</td><td>ATCC PCS-500-051</td><td></td></tr><tr><td>Formalin solution</td><td>Sigma-Aldrich</td><td>HT5011-15ML</td><td>neutral buffered, 10%</td></tr><tr><td>Ammonium chloride</td><td>Sigma-Aldrich</td><td>A9434-500G</td><td>for molecular biology, suitable for cell culture, &amp;ge;99.5%</td></tr><tr><td>Saponin</td><td>Sigma-Aldrich</td><td>47036-50G-F</td><td>for molecular biology, used as non-ionic surfactant, adjuvant</td></tr><tr><td>Bovine Serum Albumin (BSA)</td><td>Sigma-Aldrich</td><td>A3059-50G</td><td></td></tr><tr><td>Rabbit monoclonal [Y113] anti-paxillin antibody</td><td>Abcam</td><td>ab32084</td><td>Diluted 1:200</td></tr><tr><td>Mouse monoclonal [1F5] anti-collagen alpha-1 XX chain&amp;nbsp;</td><td>Acris Antibodies</td><td>AM00212PU-N</td><td>Diluted: 1:400</td></tr><tr><td>Alexa Fluor 488-conjugated goat anti-mouse IgG (H+L) secondary antibody</td><td>Invitrogen</td><td>A10667</td><td>2 mg/mL. Diluted 1:1000</td></tr><tr><td>Alexa Fluor 568-conjugated goat anti-rabbit IgG (H+L) secondary antibody</td><td>Invitrogen</td><td>A11036</td><td>2 mg/mL. Diluted 1:1000</td></tr><tr><td>Hoechst 33342</td><td>Thermo Fisher</td><td>H3570 10ML</td><td>10 mg/mL. Diluted 1:1000</td></tr><tr><td>Cover glass 24x24 mm</td><td>Deltalab</td><td>D102424</td><td></td></tr><tr><td>Fluoromount</td><td>Sigma-Aldrich</td><td>F4680-25ML</td><td></td></tr><tr><td>Epifluorescence Microscope</td><td>Nikon</td><td>Eclipse E1000 upright microscope</td><td>with a CCD camera</td></tr><tr><td>Confocal Microscope</td><td>Leica Microsystems</td><td></td><td>Leica SPE Upright Confocal Microscope</td></tr><tr><td>ImageJ 1.50g freeware</td><td>http://imgej.nih.gov/ij</td><td></td><td></td></tr><tr><td>MATLAB software</td><td>The MATHWORKS, Inc.</td><td></td><td></td></tr><tr><td>OriginPro 8.5 software&amp;nbsp;</td><td>OriginLab Coorporation</td><td></td><td></td></tr></tbody></table>

dendrimer-based uneven nanopatterns to locally control surface adhesiveness: a method to direct chondrogenic differentiation

Cellular adhesion and differentiation is conditioned by the nanoscale disposition of the extracellular matrix (ECM) components, with local concentrations having a major effect. Here we present a method to obtain large-scale uneven nanopatterns of arginine-glycine-aspartic acid (RGD)-functionalized dendrimers that permit the nanoscale control of local RGD surface density. Nanopatterns are formed by surface adsorption of dendrimers from solutions at different initial concentrations and are characterized by water contact angle (CA), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The local surface density of RGD is measured using AFM images by means of probability contour maps of minimum interparticle distances and then correlated with cell adhesion response and differentiation. The nanopatterning method presented here is a simple procedure that can be scaled up in a straightforward manner to large surface areas. It is thus fully compatible with cell culture protocols and can be applied to other ligands that exert concentration-dependent effects on cells.

We present a nanopatterning method that allows surface adhesiveness to be addressed at the nanoscale (Figure 1). The chemical structure of RGD-Cys-D1 is shown in Figure 1A. Dendrimers were patterned on electrical conductive Au(111) surfaces for high resolution STM characterization. Low dendrimer concentrations in solution (up to 10-5% w/w) rendered isolated dendrimers of 4-5 nm in diameter (<strong class="xfig...

Watch this Scientific Journal Video about Dendrimer-based Uneven Nanopatterns to Locally Control Surface Adhesiveness: A Method to Direct Chondrogenic Differentiation at JoVE.com

Dendrimer-based Uneven Nanopatterns to Locally Control Surface Adhesiveness: A Method to Direct Chondrogenic Differentiation

A method to obtain dendrimer-based uneven nanopatterns that permit the nanoscale control of local arginine-glycine-aspartic acid (RGD) surface density is described and applied for the study of cell adhesion and chondrogenic differentiation.

Cellular adhesion and differentiation is conditioned by the nanoscale disposition of the extracellular matrix (ECM) components, with local concentrations ...

dendrimer-based-uneven-nanopatterns-to-locally-control-surface

Research

JoVE Journal

Bioengineering

7.8K Views.  Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST). Een werkwijze te halen Dendrimeer gebaseerde ongelijke nanopatterns waarmee de nanoschaal controle van lokale arginine-glycine-aspartic acid (RGD) oppervlakte dichtheid is beschreven en toegepast op de studie van celdifferentiatie hechting en chondrogenic.

Video: Dendrimer-based Uneven Nanopatterns to Locally Control Surface Adhesiveness: A Method to Direct Chondrogenic Differentiation

Chondrogenic Differentiation Induction of Adipose-derived Stem Cells by Centrifugal Gravity

Impaired cartilage cannot heal naturally. Currently, the most advanced therapy for defects in cartilage is the transplantation of chondrocytes differentiated from stem cells using cytokines. Unfortunately, cytokine-induced chondrogenic differentiation is costly, time-consuming, and associated with a high risk of contamination during in vitro differentiation. However, biomechanical stimuli also serve as crucial regulatory factors for chondrogenesis. For example, mechanical stress can induce chondrogenic differentiation of stem cells, suggesting a potential therapeutic approach for the repair of impaired cartilage. In this study, we demonstrated that centrifugal gravity (CG, 2,400 &#215; g), a mechanical stress easily applied by centrifugation, induced the upregulation of sex determining region Y (SRY)-box 9 (SOX9) in adipose-derived stem cells (ASCs), causing them to express chondrogenic phenotypes. The centrifuged ASCs expressed higher levels of chondrogenic differentiation markers, such as aggrecan (ACAN), collagen type 2 alpha 1 (COL2A1), and collagen type 1 (COL1), but lower levels of collagen type 10 (COL10), a marker of hypertrophic chondrocytes. In addition, chondrogenic aggregate formation, a prerequisite for chondrogenesis, was observed in centrifuged ASCs.

Mechanical stress can induce the chondrogenic differentiation of stem cells, providing a potential therapeutic approach for the repair of impaired cartilage. We present a protocol to induce the chondrogenic differentiation of adipose-derived stem cells (ASCs) using centrifugal gravity (CG). CG-induced upregulation of SOX9 results in the development of chondrogenic phenotypes.

Impaired cartilage cannot heal naturally. Currently, the most advanced therapy for defects in cartilage is the transplantation of chondrocytes ...

Developmental Biology

3D Hydrogel Scaffolds for Articular Chondrocyte Culture and Cartilage Generation

Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer cartilage tissue offer a promising solution to repair articular cartilage. To select the optimal cell source for tissue repair, it is important to develop an appropriate culture platform to systematically examine the biological and biomechanical differences in the tissue-engineered cartilage by different cell sources. Here we applied a three-dimensional (3D) biomimetic hydrogel culture platform to systematically examine cartilage regeneration potential of juvenile, adult, and osteoarthritic (OA) chondrocytes. The 3D biomimetic hydrogel consisted of synthetic component poly(ethylene glycol) and bioactive component chondroitin sulfate, which provides a physiologically relevant microenvironment for in vitro culture of chondrocytes. In addition, the scaffold may be potentially used for cell delivery for cartilage repair in vivo. Cartilage tissue engineered in the scaffold can be evaluated using quantitative gene expression, immunofluorescence staining, biochemical assays, and mechanical testing. Utilizing these outcomes, we were able to characterize the differential regenerative potential of chondrocytes of varying age, both at the gene expression level and in the biochemical and biomechanical properties of the engineered cartilage tissue. The 3D culture model could be applied to investigate the molecular and functional differences among chondrocytes and progenitor cells from different stages of normal or aberrant development.

Cartilage repair represents an unmet medical challenge and cell-based approaches to engineer human articular cartilage are a promising solution. Here, we describe three-dimensional (3D) biomimetic hydrogels as an ideal tool for the expansion and maturation of human articular chondrocytes.

Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer ...

Expanding Nanopatterned Substrates Using Stitch Technique for Nanotopographical Modulation of Cell Behavior

Substrate nanotopography has been shown to be a potent modulator of cell phenotype and function. To dissect nanotopography modulation of cell behavior, a large area of nanopatterned substrate is desirable so that enough cells can be cultured on the nanotopography for subsequent biochemical and molecular biology analyses. However, current nanofabrication techniques have limitations to generate highly defined nanopatterns over a large area. Herein, we present a method to expand nanopatterned substrates from a small, highly defined nanopattern to a large area using stitch technique. The method combines multiple techniques, involving soft lithography to replicate poly(dimethylsiloxane) (PDMS) molds from a well-defined mold, stitch technique to assemble multiple PDMS molds to a single large mold, and nanoimprinting to generate a master mold on polystyrene (PS) substrates. With the PS master mold, we produce PDMS working substrates and demonstrate nanotopographical modulation of cell spreading. This method provides a simple, affordable yet versatile avenue to generate well-defined nanopatterns over large areas, and is potentially extended to create micro-/nanoscale devices with hybrid components.

A protocol for producing a large area of nanopatterned substrate from small nanopatterned molds for study of nanotopographical modulation of cell behavior is presented.

Substrate nanotopography has been shown to be a potent modulator of cell phenotype and function. To dissect nanotopography modulation of cell behavior, a ...

3D Magnetic Stem Cell Aggregation and Bioreactor Maturation for Cartilage Regeneration

Cartilage engineering remains a challenge due to the difficulties in creating an in vitro functional implant similar to the native tissue. An approach recently explored for the development of autologous replacements involves the differentiation of stem cells into chondrocytes. To initiate this chondrogenesis, a degree of compaction of the stem cells is required; hence, we demonstrated the feasibility of magnetically condensing cells, both within thick scaffolds and scaffold-free, using miniaturized magnetic field sources as cell attractors. This magnetic approach was also used to guide aggregate fusion and to build scaffold-free, organized, three-dimensional (3D) tissues several millimeters in size. In addition to having an enhanced size, the tissue formed by magnetic-driven fusion presented a significant increase in the expression of collagen II, and a similar trend was observed for aggrecan expression. As the native cartilage was subjected to forces that influenced its 3D structure, dynamic maturation was also performed. A bioreactor that provides mechanical stimuli was used to culture the magnetically seeded scaffolds over a 21-day period. Bioreactor maturation largely improved chondrogenesis into the cellularized scaffolds; the extracellular matrix obtained under these conditions was rich in collagen II and aggrecan. This work outlines the innovative potential of magnetic condensation of labeled stem cells and dynamic maturation in a bioreactor for improved chondrogenic differentiation, both scaffold-free and within polysaccharide scaffolds.

Chondrogenesis from stem cells requires fine tuning the culture conditions. Here, we present a magnetic approach for condensing cells, an essential step to initiate chondrogenesis. In addition, we show that dynamic maturation in a bioreactor applies mechanical stimulation to the cellular constructs and enhances cartilaginous extracellular matrix production.

Cartilage engineering remains a challenge due to the difficulties in creating an in vitro functional implant similar to the native tissue. An approach ...

Patterning Bioactive Proteins or Peptides on Hydrogel Using Photochemistry for Biological Applications

There are many biological stimuli that can influence cell behavior and stem cell differentiation. General cell culture approaches rely on soluble factors within the medium to control cell behavior. However, soluble additions cannot mimic certain signaling motifs, such as matrix-bound growth factors, cell-cell signaling, and spatial biochemical cues, which are common influences on cells. Furthermore, biophysical properties of the matrix, such as substrate stiffness, play important roles in cell fate, which is not easily manipulated using conventional cell culturing practices. In this method, we describe a straightforward protocol to provide patterned bioactive proteins on synthetic polyethylene glycol (PEG) hydrogels using photochemistry. This platform allows for the independent control of substrate stiffness and spatial biochemical cues. These hydrogels can achieve a large range of physiologically relevant stiffness values. Additionally, the surfaces of these hydrogels can be photopatterned with bioactive peptides or proteins via thiol-ene click chemistry reactions. These methods have been optimized to retain protein function after surface immobilization. This is a versatile protocol that can be applied to any protein or peptide of interest to create a variety of patterns. Finally, cells seeded onto the surfaces of these bioactive hydrogels can be monitored over time as they respond to spatially specific signals.

In this method, we use photopolymerization and click chemistry techniques to create protein or peptide patterns on the surface of polyethylene glycol (PEG) hydrogels, providing immobilized bioactive signals for the study of cellular responses in vitro.

There are many biological stimuli that can influence cell behavior and stem cell differentiation. General cell culture approaches rely on soluble factors ...

Culturing Mammalian Cells in Three-dimensional Peptide Scaffolds

A useful technique for culturing cells in a self-assembling nanofiber three-dimensional (3D) scaffold is described. This culture system recreates an environment that closely mimics the structural features of non-polarized tissue. Furthermore, the particular intrinsic nanofiber structure of the scaffold makes it transparent to visual light, which allows for easy visualization of the sample under microscopy. This advantage was largely used to study cell migration, organization, proliferation, and differentiation and thus any development of their particular cellular function by staining with specific dyes or probes. Furthermore, in this work, we describe the good performance of this system to easily study the redifferentiation of expanded human articular chondrocytes into cartilaginous tissue. Cells were encapsulated into self-assembling peptide scaffolds and cultured under specific conditions to promote chondrogenesis. Three-dimensional cultures showed good viability during the 4 weeks of the experiment. As expected, samples cultured with chondrogenic inducers (compared to non-induced controls) stained strongly positive for toluidine blue (which stains glycosaminoglycans (GAGs) that are highly present in cartilage extracellular matrix) and expressed specific molecular markers, including collagen type I, II and X, according to Western Blot analysis. This protocol is easy to perform and can be used at research laboratories, industries and for educational purposes in laboratory courses.

Here, we present a protocol to obtain 3D-culture systems in self-assembling peptide scaffolds to promote the differentiation of dedifferentiated human articular chondrocytes into cartilage-like tissue.

A useful technique for culturing cells in a self-assembling nanofiber three-dimensional (3D) scaffold is described. This culture system recreates an ...

A Microfluidic Platform for Stimulating Chondrocytes with Dynamic Compression

Mechanical stimuli are known to modulate biological functions of cells and tissues. Recent studies have suggested that compressive stress alters growth plate cartilage architecture and results in growth modulation of long bones of children. To determine the role of compressive stress in bone growth, we created a microfluidic device actuated by pneumatic pressure, to dynamically (or statically) compress growth plate chondrocytes embedded in alginate hydrogel cylinders. In this article, we describe detailed methods for fabricating and characterizing this device. The advantages of our protocol are: 1) Five different magnitudes of compressive stress can be generated on five technical replicates in a single platform, 2) It is easy to visualize cell morphology via a conventional light microscope, 3) Cells can be rapidly isolated from the device after compression to facilitate downstream assays, and 4) The platform can be applied to study mechanobiology of any cell type that can grow in hydrogels.

This article provides detailed methods for fabricating and characterizing a pneumatically actuating microfluidic device for chondrocyte compression.

Mechanical stimuli are known to modulate biological functions of cells and tissues. Recent studies have suggested that compressive stress alters growth ...

Simple, Affordable, and Modular Patterning of Cells using DNA

The relative positioning of cells is a key feature of the microenvironment that organizes cell-cell interactions. To study the interactions between cells of the same or different type, micropatterning techniques have proved useful. DNA Programmed Assembly of Cells (DPAC) is a micropatterning technique that targets the adhesion of cells to a substrate or other cells using DNA hybridization. The most basic operations in DPAC begin with decorating cell membranes with lipid-modified oligonucleotides, then flowing them over a substrate that has been patterned with complementary DNA sequences. Cells adhere selectively to the substrate only where they find a complementary DNA sequence. Non-adherent cells are washed away, revealing a pattern of adherent cells. Additional operations include further rounds of cell-substrate or cell-cell adhesion, as well as transferring the patterns formed by DPAC to an embedding hydrogel for long-term culture. Previously, methods for patterning oligonucleotides on surfaces and decorating cells with DNA sequences required specialized equipment and custom DNA synthesis, respectively. We report an updated version of the protocol, utilizing an inexpensive benchtop photolithography setup and commercially available cholesterol modified oligonucleotides (CMOs) deployed using a modular format. CMO-labeled cells adhere with high efficiency to DNA-patterned substrates. This approach can be used to pattern multiple cell types at once with high precision and to create arrays of microtissues embedded within an extracellular matrix. Advantages of this method include its high resolution, ability to embed cells into a three-dimensional microenvironment without disrupting the micropattern, and flexibility in patterning any cell type.

Here we present a protocol to micropattern cells at single-cell resolution using DNA-programmed adhesion. This protocol uses a benchtop photolithography platform to create patterns of DNA oligonucleotides on a glass slide and then labels cell membranes with commercially available complementary oligonucleotides. Hybridization of the oligos results in programmed cell adhesion.

The relative positioning of cells is a key feature of the microenvironment that organizes cell-cell interactions. To study the interactions between cells ...

Control of Cell Adhesion using Hydrogel Patterning Techniques for Applications in Traction Force Microscopy

Traction force microscopy (TFM) is the main method used in mechanobiology to measure cell forces. Commonly this is being used for cells adhering to flat soft substrates that deform under cell traction (2D-TFM). TFM relies on the use of linear elastic materials, such as polydimethylsiloxane (PDMS) or polyacrylamide (PA). For 2D-TFM on PA, the difficulty in achieving high throughput results mainly from the large variability of cell shapes and tractions, calling for standardization. We present a protocol to rapidly and efficiently fabricate micropatterned PA hydrogels for 2D-TFM studies. The micropatterns are first created by maskless photolithography using near-UV light where extracellular matrix proteins bind only to the micropatterned regions, while the rest of the surface remains non-adhesive for cells. The micropatterning of extracellular matrix proteins is due to the presence of active aldehyde groups, resulting in adhesive regions of different shapes to accommodate either single cells or groups of cells. For TFM measurements, we use PA hydrogels of different elasticity by varying the amounts of acrylamide and bis-acrylamide and tracking the displacement of embedded fluorescent beads to reconstruct cell traction fields with regularized Fourier Transform Traction Cytometry (FTTC).
To further achieve precise recording of cell forces, we describe the use of a controlled dose of patterned light to release cell tractions in defined regions for single cells or groups of cells. We call this method local UV illumination traction force microscopy (LUVI-TFM). With enzymatic treatment, all cells are detached from the sample simultaneously, whereas with LUVI-TFM traction forces of cells in different regions of the sample can be recorded in sequence. We demonstrate the applicability of this protocol (i) to study cell traction forces as a function of controlled adhesion to the substrate, and (ii) to achieve a greater number of experimental observations from the same sample.

Near-UV lithography and traction force microscopy are combined to measure cellular forces on micropatterned hydrogels. The targeted light-induced release of single cells enables a high number of measurements on the same sample.

Traction force microscopy (TFM) is the main method used in mechanobiology to measure cell forces. Commonly this is being used for cells adhering to flat ...

Generation of Multicue Cellular Microenvironments by UV-Photopatterning of Three-Dimensional Cell Culture Substrates

The extracellular matrix is an important regulator of cell function. Environmental cues existing in the cellular microenvironment, such as ligand distribution and tissue geometry, have been increasingly shown to play critical roles in governing cell phenotype and behavior. However, these environmental cues and their effects on cells are often studied separately using in vitro platforms that isolate individual cues, a strategy that heavily oversimplifies the complex in vivo situation of multiple cues. Engineering approaches can be particularly useful to bridge this gap, by developing experimental setups that capture the complexity of the in vivo microenvironment, yet retain the degree of precision and manipulability of in vitro systems.
This study highlights an approach combining ultraviolet (UV)-based protein patterning and lithography-based substrate microfabrication, which together enable high-throughput investigation into cell behaviors in multicue environments. By means of maskless UV-photopatterning, it is possible to create complex, adhesive protein distributions on three-dimensional (3D) cell culture substrates on chips that contain a variety of well-defined geometrical cues. The proposed technique can be employed for culture substrates made from different polymeric materials and combined with adhesive patterned areas of a broad range of proteins. With this approach, single cells, as well as monolayers, can be subjected to combinations of geometrical cues and contact guidance cues presented by the patterned substrates. Systematic research using combinations of chip materials, protein patterns, and cell types can thus provide fundamental insights into cellular responses to multicue environments.

Traditionally, cell culture is performed on planar substrates that poorly mimic the natural environment of cells in vivo. Here we describe a method to produce cell culture substrates with physiologically relevant curved geometries and micropatterned extracellular proteins, allowing systematic investigations into cellular sensing of these extracellular cues.

Dendrimer-based Uneven Nanopatterns to Locally Control Surface Adhesiveness: A Method to Direct Chondrogenic Differentiation

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