The authors thank the Fraunhofer ISC for the collaboration concerning the construction of the automated wounding device. The project was founded by Fraunhofer internal project &#8220;M&#228;rkte von &#220;bermorgen&#8221; (SkinHeal).

NOTE: The protocol is designed for the production of 24 full thickness skin equivalents. Human dermal fibroblasts and epidermal keratinocytes were isolated from skin biopsies according to a previously published protocol.21,22 Informed consent was obtained beforehand and the study was approved by the institutional ethics committee on human research of the Julius-Maximilians-University W&#252;rzburg (vote 182/10).
1. Production of Dermal Component
<ol>
	<li>Dissolve collagen with 0.1% acetic acid to a final concentration of 6&#160;mg/ml. For the gel neutralization solution, mix 232.5&#160;ml 2x DMEM, 7.5 ml fetal calf serum, 7.5&#160;ml 3 M&#160;HEPES, 2.5&#160;ml chondroitin sulfate (5&#160;mg/ml). Keep gel neutralization solution and collagen solution on ice. Calculate 500&#160;&#181;l of gel per insert/skin equivalent. 
	NOTE: As the gel neutralization solution will be mixed with two parts of collagen solution prepare double amount of collagen.</li>
	<li>Place 24 inserts into a 24 well plate.</li>
	<li>Resuspend human dermal fibroblasts (hDF) in 10&#160;ml DMEM, centrifuge for 5 min at 270 x g and count the cells. Extract the needed amount of hDF (5 x 104&#160;cells per 500&#160;&#956;l collagen gel) and centrifuge the cells for 5 min at 270 x g.</li>
	<li>Remove the supernatant and carefully resuspend the hDF in 4 ml cooled gel neutralization solution without producing air bubbles. From this step make sure to work as fast as possible to avoid premature solidifying of the collagen gels.</li>
	<li>Resuspend the solution with 8 ml of collagen solution.</li>
	<li>Take the collagen-cell-mixture with a multistep-pipette and fill quickly 500&#160;&#956;l of mixture in each insert. Incubate the gels for 20 min in an incubator (37 &#176;C, 5% CO2) to jell the gels.</li>
	<li>Submerge the gels in 2 ml Dulbecco&#8217;s Modified Eagle Medium (DMEM) + 10% fetal calf serum (FCS) per well and incubate it for 24 hr in an incubator (37 &#176;C, 5% CO2).</li>
</ol>
2. Addition of Human Epidermal Keratinocytes (hEK)
<ol>
	<li>Remove medium after 24 hr. Dissolve fibronectin human protein with ultrapure water to a final concentration of 50&#160;&#181;g/ml. Cover each dermal equivalent with 25&#160;&#956;l of fibronectin solution. Incubate the gels for 30 min in an incubator (37 &#176;C, 5% CO2).</li>
	<li>In the meantime, resuspend the hEK in 10&#160;ml KGM-2 and set cell concentration to 1 x 106 cells/ml with KGM-2 ready + 5% FCS. Seed 1 x 105 hEK on each gel. Incubate gels for 45 min in the incubator (37 &#176;C, 5% CO2) to allow cells to adhere.</li>
	<li>Submerse the gels with KGM-2 ready + 5% FCS and culture them in the incubator (37 &#176;C, 5%&#160;CO2).</li>
</ol>
3. Culture of Full Thickness Skin Equivalents (ftSE)
<ol>
	<li>Culture ftSE for 6-7 days in descending FCS-concentration (5%, 2%, and 0% FCS). Change the medium every 2-3 days with the next lower FCS concentration. For this, completely remove the medium and add 1.6 ml of fresh medium.</li>
	<li>On day 7, remove medium completely. 
	NOTE: Do not touch the ftSE surface with the tip of pipette while doing so.</li>
	<li>Place every insert into 1 well of a 6 well plate with sterile forceps. Add 1.5&#160;ml airlift medium per well, ensure not to wet the ftSE surface. Change medium every 2-3 days for additional 14 days. 
	NOTE: The filling level of the medium is up to the meniscus of the ftSE.</li>
</ol>
4. Histological Analysis
<ol>
	<li>Fixing and paraffin-embedding of the ftSE
	<ol>
		<li>Remove culture medium, transfer inserts in fresh 24 well plates and fix tissues by adding 1.6&#160;ml of 4%&#160;paraformaldehyde to each well and incubate the tissues for 2 hr at RT. Caution! Paraformaldehyd is toxic, manipulate under fume hood. Transfer the ftSE to a tissue-embedding cassette. Remove remaining fixative by washing with water and dehydrate the tissue using ascending ethanol concentrations.</li>
		<li>Divide the skin equivalent by a vertical cut in the middle. Place the two pieces in a paraffin-filled metal base mold with cut surfaces downwards. Add the tissue cassette on top of the mold as a backing.</li>
		<li>Cut 3-5&#160;&#181;m slices and float them on a 40 &#176;C water bath for straitening, mount slides onto suitable microscope slides. Dry slices thoroughly.</li>
	</ol>
	</li>
	<li>Hematoxylin &#38; Eosin (H&#38;E) and immunohistochemical (IHC) staining
	<ol>
		<li>Place slides into rack and incubate for 1 hr at 60 &#176;C. Make sure that paraffin is melted. Stain rehydrated slices with H&#38;E as a standardized overview staining.</li>
		<li>For H&#38;E staining prepare 4x glass staining cuvettes with xylol, 3x with ethanol 96%, 2x with ethanol 70%, 1x with ethanol 50%, 4x deionized water, 1x hematoxylin, 1x HCl-ethanol (13.7&#160;ml 1&#160;M HCl ad 200 ml 50% ethanol), 1x tab water, 1x eosin (1&#160;g eosin in 100&#160;ml deionized water) and 2x 2-propanol.</li>
		<li>Place slides 10 min in xylol I and 10 min in xylol II to deparaffinize and rehydrate slides. Dip slides 3x in ethanol 96% I, 3x in ethanol 96% II, 3x in ethanol 70% and 3x in ethanol&#160;50%. Rotate slides in deionized water. To differentiate hematoxylin dye, dip 2x in HCl-ethanol. Rinse in deionized water. For blueing, place slides 5 min in tab water. For eosin staining, place slides 1 min in eosin and wash afterwards in deionized water. For dehydration, dip slides 2x in ethanol 70%, 2x in ethanol 96% and place them for 5 min in 2-propanol I, for 5 min in 2-propanol II, 5 min in xylol I and 5 min in xylol II. After H&#38;E staining, cell nuclei are stained in blue, cytoplasm and extracellular matrix are stained in red.</li>
		<li>For antigen retrieval, remove paraffin with xylene and rehydrate slices for staining. Place slices in steam cooker and cook deparaffinized and rehydrated slices for 20 min in pre-heated 10&#160;mM citrate buffer (pH&#160;6).</li>
		<li>Place slides in washing buffer (PBS buffer + 0.5% Polysorbat&#160;20) and circle slices with a liquid repellent slide marker pen or diamond stylus.</li>
		<li>Place slides in a moisture chamber. Block endogenous peroxidase, by adding 100&#160;&#181;l 3%&#160;hydrogen peroxide solution onto each slice. Caution! Very hazardous in case of skin and eye contact. Handle with personal protective equipment. Wash slides in washing buffer.</li>
		<li>Apply primary antibody and incubate for 1 hr at RT. Wash slides three times with washing buffer. From here on, samples should be kept in the dark.</li>
		<li>Use biotin-streptavidin detection system for detection of specific antigen-antibody binding.</li>
		<li>Counterstain nuclei with Hematoxylin for 1 min. Dehydrate and mount slides.</li>
		<li>Image samples using an inverse microscope.</li>
	</ol>
	</li>
</ol>
5. Injury by Use of the Automated Wounding Device (aWD)
<ol>
	<li>Prepare the aWD by disinfecting the working area with 70% ethanol and ultraviolet light. Make sure the drilling head of the desired size (e.g., 1 mm) is attached.</li>
	<li>Place skin equivalents into designated areas of the autoclaved sample carrier plate using sterile forceps. Place the sample carrier plate into the socket below the drilling head.</li>
	<li>Use the control software to set wounding parameters as follows: spin velocity: 15,000 rpm; penetration: 1.5 mm; propulsion: 100 Hz. These parameters need to be defined for each sample type individually. Transfer wounding parameters to the aWD.</li>
	<li>Start wounding procedure. Remove sample carrier plate from the socket. Transfer wounded ftSE back into inserts used for culture using sterile forceps.</li>
	<li>Proceed with culture of wounded ftSE in the incubator (37 &#176;C, 5% CO2) for investigation of regeneration. Alternatively, use the models for histological analysis at any time.</li>
</ol>

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	<li>Proksch, E., Brandner, J. M., Jensen, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+skin:+an+indispensable+barrier.">The skin: an indispensable barrier.</a> Exp Dermatol. 17, 1063-1072 (2008).</li><li>Guo, S., Dipietro, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+affecting+wound+healing.">Factors affecting wound healing.</a> J Dent Res. 89, 219-229 (2010).</li><li>Kirsner, R. S., Eaglstein, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+wound+healing+process.">The wound healing process.</a> Dermatol Clin. 11, 629-640 (1993).</li><li>Cory, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scratch-wound+assay.">Scratch-wound assay.</a> Methods Mol Biol. 769, 25-30 (2011).</li><li>Sun, T., Jackson, S., Haycock, J. W., MacNeil, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Culture+of+skin+cells+in+3D+rather+than+2D+improves+their+ability+to+survive+exposure+to+cytotoxic+agents.">Culture of skin cells in 3D rather than 2D improves their ability to survive exposure to cytotoxic agents.</a> J Biotechnol. 122 (3), 372-381 (2006).</li><li>Harrison, C. A., Heaton, M. J., Layton, C. M., Mac Neil, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+an+in+vitro+model+of+tissue-engineered+human+skin+to+study+keratinocyte+attachment+and+migration+in+the+process+of+reepithelialization.">Use of an in vitro model of tissue-engineered human skin to study keratinocyte attachment and migration in the process of reepithelialization.</a> Wound Repair Regen. 14 (2), 203-209 (2006).</li><li>Wilkins, L. M., Watson, S. R., Prosky, S. J., Meunier, S. F., Parenteau, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+bilayered+living+skin+construct+for+clinical+applications.">Development of a bilayered living skin construct for clinical applications.</a> Biotechnol Bioeng. 43 (8), 747-756 (1994).</li><li>Gangatirkar, P., Paquet-Fifield, S., Li, A., Rossi, R., Kaur, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Establishment+of+3D+organotypic+cultures+using+human+neonatal+epidermal+cells.">Establishment of 3D organotypic cultures using human neonatal epidermal cells.</a> Nat Protoc. 2 (1), 178-186 (2007).</li><li>Boyce, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+substitutes+from+cultured+cells+and+collagen-GAG+polymers.">Skin substitutes from cultured cells and collagen-GAG polymers.</a> Med Biol Eng Comput. 36 (6), 791-800 (1998).</li><li>El-Ghalbzouri, A., Lamme, E. N., van Blitterswijk, C., Koopman, J., Ponec, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+PEGT/PBT+as+a+dermal+scaffold+for+skin+tissue+engineering.">The use of PEGT/PBT as a dermal scaffold for skin tissue engineering.</a> Biomaterials. 25 (5), 2987-2996 (2004).</li><li>Maas-Szabowski, N., Shimotoyodome, A., Fusenig, N. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocyte+growth+regulation+in+fibroblast+cocultures+via+a+double+paracrine+mechanism.">Keratinocyte growth regulation in fibroblast cocultures via a double paracrine mechanism.</a> J Cell Sci. 112 (Pt 12), 1843-1853 (1999).</li><li>Coolen, N. A., Vlig, M., vanden Bogaerdt, A. J., Middelkoop, E., Ulrich, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+an+in+vitro+burn+wound+model.">Development of an in vitro burn wound model.</a> Wound Repair Regen. 16 (4), 559-567 (2008).</li><li>Oberringer, M., Meins, C., Bubel, M., Pohlemann, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+in+vitro+wound+model+based+on+the+co-culture+of+human+dermal+microvascular+endothelial+cells+and+human+dermal+fibroblasts.">A new in vitro wound model based on the co-culture of human dermal microvascular endothelial cells and human dermal fibroblasts.</a> Biol Cell. 99 (4), 197-207 (2007).</li><li>Cribbs, R. K., Luquette, M. H., Besner, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+standardized+model+of+partial+thickness+scald+burns+in+mice.">A standardized model of partial thickness scald burns in mice.</a> J Surg Res. 80 (1), 69-74 (1998).</li><li>Reed, J. T., Ghadially, R., Elias, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+type,+but+neither+race+nor+gender,+influence+epidermal+permeability+barrier+function.">Skin type, but neither race nor gender, influence epidermal permeability barrier function.</a> Arch Dermatol. 131 (10), 1134-1138 (1995).</li><li>Pilcher, B. K., 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=Keratinocyte+collagenase-1+expression+requires+an+epidermal+growth+factor+receptor+autocrine+mechanism.">Keratinocyte collagenase-1 expression requires an epidermal growth factor receptor autocrine mechanism.</a> J Biol Chem. 274 (15), 10372-10381 (1999).</li><li>Blank, I. H., Miller, O. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+the+separation+of+the+epidermis+from+the+dermis.">A method for the separation of the epidermis from the dermis.</a> J Invest Dermatol. 15 (1), 9-10 (1950).</li><li>El Ghalbzouri, 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=Fibroblasts+facilitate+re-epithelialization+in+wounded+human+skin+equivalents.">Fibroblasts facilitate re-epithelialization in wounded human skin equivalents.</a> Lab Invest. 84 (1), 102-112 (2004).</li><li>Vaughan, M. B., 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=A+reproducible+laser-wounded+skin+equivalent+model+to+study+the+effects+of+aging+in+vitro.">A reproducible laser-wounded skin equivalent model to study the effects of aging in vitro.</a> Rejuvenation Res. 7 (2), 99-110 (2004).</li><li>Geer, D. J., Swartz, D. D., Andreadis, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+model+of+wound+healing+based+on+transplanted+tissue-engineered+skin.">In vivo model of wound healing based on transplanted tissue-engineered skin.</a> Tissue Eng. 10 (7-8), 1006-1017 (2004).</li><li>Bell, 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=The+reconstitution+of+living+skin.">The reconstitution of living skin.</a> J Invest Dermatol. 81 (1 Suppl), 2s-10s (1983).</li><li>Asselineau, D., Prunieras, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstruction+of+'simplified'+skin:+control+of+fabrication.">Reconstruction of 'simplified' skin: control of fabrication.</a> Br J Dermatol. 111, 219-222 (1984).</li><li>Pampaloni, F., Reynaud, E. 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The authors have nothing to disclose.

In vitro cells are usually expanded in two-dimensional cell cultures, in which cells adhere to plastic surfaces. However, these culture conditions do not reflect the physiological three-dimensional conditions in which cells grow in vivo. Under three-dimensional conditions, cells can form natural cell-cell and cell-matrix attachments and migrate in three-dimensions. Especially in the cutaneous wound healing the resemblance of the in vivo situation is pivotal to generate meaningful data, as cell ...

The skin is the largest organ of the body. It creates a barrier between the external environment and the internal organs. Moreover, the skin protects the body from fluid loss, environmental influences, injuries and infections and helps to regulate body temperature1. Due to its exposed location, the skin is often affected by mechanical, thermal or chemical trauma. Though the skin is generally capable of self-repair, multiple local factors such as infection, oxygenation, and venous sufficiency can lead to impaired wound healing. Wound healing can also be interfered by systemic factors as obesity, alcoholism, smoking, medication, nutrition and diseases such as diabetes.2
The process of wound healing can be divided into 3 phases: (i) the inflammatory phase, (ii) the proliferative and the (iii) remodeling phase. Upon injury to the skin, a complex signal-cascade starts, leading to the closure of the wound.3 After injury, the wound is bleeding and a blood clot is formed. Fibroblasts move into the blood clot and replace it with new tissue which is subsequently remodeled over years.
The current understanding of the biological processes underlying cutaneous repair is limited. Small animal and pig models have been used to study wound healing. However, these results cannot be directly transferred to humans due to species-specific differences. In addition to these in vivo models, some aspects of wound healing can be studied by simulating a wound situation via scratching of in vitro monolayer cultures based on immortalized cell lines or primary cells.4 These scratching models are highly standardized but do not sufficiently reflect the complex in vivo physiology.5 Besides two-dimensional models, three-dimensional human skin equivalents have been developed for dermatological research. The dermal part of these models are generated using various scaffolds including decellularized dermis,6 collagen hydrogels,7,8 glycosaminoglycans9 or synthetic materials.10 Employing these skin equivalents, the role of epithelial-mesenchymal interactions11, the re-epithelialization, the cellular crosstalk between fibroblasts and keratinocytes and the influence of different growth factors can be studied. Moreover, these models are useful to gain new knowledge about how fibroblasts migrate into the wounded area and how chemotactic factors influence tissue regeneration.12
Not only generation of the wound healing model itself is challenging, but also to establish a highly standardized wound in a model is problematic. Common techniques to create wounds are scratch tests,13 burns,14 tape abrasion,15 thermal injury,16 suction blisters,17 liquid nitrogen,18 lasers,19 scalpels,18 meshers6 and biopsy punches.20 Most of these methods have the same pitfalls. Injuries implemented manually are difficult to standardize and to reproduce between multiple tests. Size, shape and depth of the wound vary between studies and thus impair the quality of research data. The use of laser for defined skin wounding can be relatively easily standardized but leads to a situation mimicking burn wounds. Heat applied by laser can cause protein denaturation, platelets aggregation or vessels constriction, which can lead to necrotic tissue.
In an alternative approach, we developed an automated wounding device (aWD), which allows us to generate defined and precise cutaneous wounds under sterile conditions. Wounding parameters, like depth and speed of penetration as well as revolutions of the drill head can be regulated. In this study, we combined the aWD with in house developed full thickness skin equivalents (ftSE) that are comparable to a protocol published by Gangatirkar et al. 8 The dermal layer of the skin equivalent is composed of human dermal fibroblasts (hDF), which are embedded in a collagen I hydrogel. On the dermal layer, human epidermal keratinocytes (hEK) are seeded. Within two weeks at the air-liquid interface the hEK build up an epidermis composed of several vital cell layers and a stratum corneum. Besides the generation of this model, this study shows the use of the aWD to create defined and precise wounds in ftSE.

<table border="0" cellpadding="0" cellspacing="0" width="750">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Name of Material/ Equipment</td>
			<td style="width:135px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Trypsin EDTA (1:250) 0.5 % in DPBS&#160;</td>
			<td style="width:135px;">PAA</td>
			<td style="width:119px;">L11-003</td>
			<td align="right">0.05%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Dulbecco&#8217;s Phosphate Buffered Saline</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">D8537</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Collagen (6 mg/ml in 0,1 % acetic acid)</td>
			<td style="width:135px;">Produced in house</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Fibronectin Human Protein, Plasma (50 &#181;g/ml)</td>
			<td style="width:135px;">Life Technologies</td>
			<td style="width:119px;">33016-015</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Inserts</td>
			<td style="width:135px;">Nunc</td>
			<td align="right" style="width:119px;">140627</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">6 well plate&#160;</td>
			<td style="width:135px;">Nunc</td>
			<td align="right" style="width:119px;">140685</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">24 well plate</td>
			<td style="width:135px;">Nunc</td>
			<td align="right" style="width:119px;">142485</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Microscope slides</td>
			<td style="width:135px;">R. Langenbrinck</td>
			<td style="width:119px;">03-0070</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Fibroblasts culturing (500 ml):</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">DMEM, high glucose</td>
			<td style="width:135px;">Life Technologies</td>
			<td style="width:119px;">11965-092</td>
			<td>89% (445 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Fetal bovine serum</td>
			<td style="width:135px;">Bio &#38; Sell</td>
			<td style="width:119px;">FCS.ADD.0500</td>
			<td>10% (50 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td style="width:135px;">Life Technologies</td>
			<td style="width:119px;">15140-122</td>
			<td>1% (5 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Keratinozyten culture medium (500 ml):&#160;</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Keratinocyte Growth Medium 2</td>
			<td style="width:135px;">Promocell&#160;</td>
			<td style="width:119px;">C-20111</td>
			<td>89% (445 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Keratinocyte Growth Medium 2 SupplementPack</td>
			<td style="width:135px;">Promocell&#160;</td>
			<td style="width:119px;">C-39011</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td style="width:135px;">Life Technologies</td>
			<td style="width:119px;">15140-122</td>
			<td>1% (5 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Gel neutralization solution (250 ml):</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:329px;">Dulbecco&#8217;s Modified Eagle Medium, high Glucose Powder with L-Glutamine</td>
			<td style="width:135px;">PAA</td>
			<td style="width:119px;">G0001,3010</td>
			<td>93% (232,5 ml)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:329px;">Chondroitin sulfate sodium salt from shark cartilage</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">C4384-1g</td>
			<td>1% (2,5 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Fetal bovine serum</td>
			<td style="width:135px;">Bio &#38; Sell</td>
			<td style="width:119px;">FCS.ADD.0500</td>
			<td>3% (7,5 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">HEPES</td>
			<td style="width:135px;">Sigma&#160;</td>
			<td style="width:119px;">H3375-1kg</td>
			<td>3% (7,5 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Skin model submers medium (500ml):&#160;</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Keratinocyte Growth Medium 2</td>
			<td style="width:135px;">Promocell&#160;</td>
			<td style="width:119px;">C-20111</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Keratinocyte Growth Medium 2 SupplementPack</td>
			<td style="width:135px;">Promocell&#160;</td>
			<td style="width:119px;">C-39011</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Fetal calf serum</td>
			<td style="width:135px;">Bio &#38; Sell</td>
			<td style="width:119px;">FCS.ADD.0500</td>
			<td>5%-2% (25 ml-10 ml)&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td style="width:135px;">Life Technologies</td>
			<td style="width:119px;">15140-122</td>
			<td>1% (5 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Skin model air-liquid interface medium (500 ml):&#160;</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Keratinocyte Growth Medium 2</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:329px;">Keratinocyte Growth Medium 2 Supplement Pack</td>
			<td style="width:135px;">Promocell&#160;</td>
			<td style="width:119px;">C-39011</td>
			<td>adding only supplements: Insulin, Hydrocortisone, Epinephrine, Transferrin, CaCl2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td style="width:135px;">Life Technologies</td>
			<td style="width:119px;">15140-122</td>
			<td>1% (5 ml)</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:329px;">CaCl2 (300 mM)</td>
			<td style="width:135px;">Sigma&#160;</td>
			<td style="width:119px;">C7902-500g</td>
			<td>&#160;0,62% (3,1 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Histology:</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">IHC-Kit DCS SuperVision 2 HRP</td>
			<td style="width:135px;">DCS</td>
			<td style="width:119px;">PD000KIT</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Vimentin antibody</td>
			<td style="width:135px;">Abcam</td>
			<td>ab92547</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">CK14 antibody</td>
			<td style="width:135px;">Sigma&#160;</td>
			<td>HPA023040-100&#181;l</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">CK10 antibody</td>
			<td style="width:135px;">Dako</td>
			<td style="width:119px;">M7002</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Filaggrin antibody</td>
			<td style="width:135px;">Abcam</td>
			<td>ab81468</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">H&#38;E staining</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Mayer&#180;s Haemalaun</td>
			<td style="width:135px;">AppliChem</td>
			<td style="width:119px;">A0884,2500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Xylol</td>
			<td style="width:135px;">Sigma Aldrich</td>
			<td>296325-4X2L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Ethanol</td>
			<td style="width:135px;">Sigma Aldrich</td>
			<td>32205-4X2.5L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">HCl</td>
			<td style="width:135px;">Sigma Aldrich</td>
			<td>H1758-500ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Eosin</td>
			<td style="width:135px;">Sigma Aldrich</td>
			<td>E4009-5G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">2-Propanolol</td>
			<td style="width:135px;">Sigma Aldrich</td>
			<td>I9516-500ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:329px;">Mounting Medium</td>
			<td style="width:135px;">Sigma Aldrich</td>
			<td>M1289-10ML</td>
			<td></td>
		</tr>
	</tbody>
</table>

generation of a three-dimensional full thickness skin equivalent and automated wounding

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models reflect the human wound situation better than animal models. Although two-dimensional models are widely used to investigate processes such as cellular migration and proliferation, models that are more complex are required to gain a deeper knowledge about wound healing. Besides a suitable model system, the generation of precise and reproducible wounds is crucial to ensure comparable results between different test runs. In this study, the generation of a three-dimensional full thickness skin equivalent to study wound healing is shown. The dermal part of the models is comprised of human dermal fibroblast embedded in a rat-tail collagen type I hydrogel. Following the inoculation with human epidermal keratinocytes and consequent culture at the air-liquid interface, a multilayered epidermis is formed on top of the models. To study the wound healing process, we additionally developed an automated wounding device, which generates standardized wounds in a sterile atmosphere.

The isolated hDF and hEK differ both in morphology and in expression of typical markers. The hDF showed typical spindle-shape morphology, whereas morphology of hEK can be described by a cobblestone morphology. The cells were characterized by immunohistochemical staining (Figure 1) before using them for ftSE. The hDF are positive for vimentin (Figure 1A), a marker for fibroblasts. Primary hEK highly express early differentiation protein cytokeratin-14 (Figure 1B) but near...

Watch this Scientific Journal Video about Generation of a Three-dimensional Full Thickness Skin Equivalent and Automated Wounding at JoVE.com

Generation of a Three-dimensional Full Thickness Skin Equivalent and Automated Wounding

The goal of this protocol is to build up a three-dimensional full thickness skin equivalent, which resembles natural skin. With a specifically constructed automated wounding device, precise and reproducible wounds can be generated under maintenance of sterility.

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models ...

generation-three-dimensional-full-thickness-skin-equivalent-automated

Research

JoVE Journal

Bioengineering

18.5K Views.  University Hospital Würzburg. The goal of this protocol is to build up a three-dimensional full thickness skin equivalent, which resembles natural skin. With a specifically constructed automated wounding device, precise and reproducible wounds can be generated under maintenance of sterility. 

Video: Generation of a Three-dimensional Full Thickness Skin Equivalent and Automated Wounding

The Three-Dimensional Human Skin Reconstruct Model: a Tool to Study Normal  Skin and Melanoma Progression

Most in vitro studies in experimental skin biology have been done in 2-dimensional (2D) monocultures, while accumulating evidence suggests that cells behave differently when they are grown within a 3D extra-cellular matrix and also interact with other cells (1-5). Mouse models have been broadly utilized to study tissue morphogenesis in vivo. However mouse and human skin have significant differences in cellular architecture and physiology, which makes it difficult to extrapolate mouse studies to humans. Since melanocytes in mouse skin are mostly localized in hair follicles, they have distinct biological properties from those of humans, which locate primarily at the basal layer of the epidermis. The recent development of 3D human skin reconstruct models has enabled the field to investigate cell-matrix and cell-cell interactions between different cell types. The reconstructs consist of a "dermis" with fibroblasts embedded in a collagen I matrix, an "epidermis", which is comprised of stratified, differentiated keratinocytes and a functional basement membrane, which separates epidermis from dermis. Collagen provides scaffolding, nutrient delivery, and potential for cell-to-cell interaction. The 3D skin models incorporating melanocytic cells recapitulate natural features of melanocyte homeostasis and melanoma progression in human skin. As in vivo, melanocytes in reconstructed skin are localized at the basement membrane interspersed with basal layer keratinocytes. Melanoma cells exhibit the same characteristics reflecting the original tumor stage (RGP, VGP and metastatic melanoma cells) in vivo. Recently, dermal stem cells have been identified in the human dermis (6). These multi-potent stem cells can migrate to the epidermis and differentiate to melanocytes.

In this report, we describe the three-dimensional skin reconstruct model which mimics human skin in architecture and composition. Melanocyte physiology, melanoma progression and the fate of dermal stem cells have been investigated using the skin reconstruct model. The model is also useful as a preclinical tool for drug assessment.

Most in vitro studies in experimental skin biology have been done in 2-dimensional (2D) monocultures, while accumulating evidence suggests that cells ...

Planar and Three-Dimensional Printing of Conductive Inks

Printed electronics rely on low-cost, large-area fabrication routes to create flexible or multidimensional electronic, optoelectronic, and biomedical devices1-3. In this paper, we focus on one- (1D), two- (2D), and three-dimensional (3D) printing of conductive metallic inks in the form of flexible, stretchable, and spanning microelectrodes.
Direct-write assembly4,5 is a 1-to-3D printing technique that enables the fabrication of features ranging from simple lines to complex structures by the deposition of concentrated inks through fine nozzles (~0.1 - 250 &mu;m). This printing method consists of a computer-controlled 3-axis translation stage, an ink reservoir and nozzle, and 10x telescopic lens for visualization. Unlike inkjet printing, a droplet-based process, direct-write assembly involves the extrusion of ink filaments either in- or out-of-plane. The printed filaments typically conform to the nozzle size. Hence, microscale features (&lt; 1 &mu;m) can be patterned and assembled into larger arrays and multidimensional architectures.
In this paper, we first synthesize a highly concentrated silver nanoparticle ink for planar and 3D printing via direct-write assembly. Next, a standard protocol for printing microelectrodes in multidimensional motifs is demonstrated. Finally, applications of printed microelectrodes for electrically small antennas, solar cells, and light-emitting diodes are highlighted.

Planar and three-dimensional printing of conductive metallic inks is described. Our approach provides new avenues for fabricating printed electronic, optoelectronic, and biomedical devices in unusual layouts at the microscale.

Printed electronics rely on low-cost, large-area fabrication routes to create flexible or multidimensional electronic, optoelectronic, and biomedical ...

Investigating the Three-dimensional Flow Separation Induced by a Model Vocal Fold Polyp

The fluid-structure energy exchange process for normal speech has been studied extensively, but it is not well understood for pathological conditions. Polyps and nodules, which are geometric abnormalities that form on the medial surface of the vocal folds, can disrupt vocal fold dynamics and thus can have devastating consequences on a patient&#39;s ability to communicate. Our laboratory has reported particle image velocimetry (PIV) measurements, within an investigation of a model polyp located on the medial surface of an in&#160;vitro driven vocal fold model, which show that such a geometric abnormality considerably disrupts the glottal jet behavior. This flow field adjustment is a likely reason for the severe degradation of the vocal quality in patients with polyps. A more complete understanding of the formation and propagation of vortical structures from a geometric protuberance, such as a vocal fold polyp, and the resulting influence on the aerodynamic loadings that drive the vocal fold dynamics, is necessary for advancing the treatment of this pathological condition. The present investigation concerns the three-dimensional flow separation induced by a wall-mounted prolate hemispheroid with a 2:1 aspect ratio in cross flow, i.e. a model vocal fold polyp, using an oil-film visualization technique. Unsteady, three-dimensional flow separation and its impact of the wall pressure loading are examined using skin friction line visualization and wall pressure measurements.

Vocal fold polyps can disrupt vocal fold dynamics and thus can have devastating consequences on a patient&#39;s ability to communicate. Three-dimensional flow separation induced by a wall-mounted model polyp and its impact on the wall pressure loading are examined using particle image velocimetry, skin friction line visualization, and wall pressure measurements.

The fluid-structure energy exchange process for normal speech has been studied extensively, but it is not well understood for pathological conditions. ...

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to evaluate new strategies that aim at improving vascularization, reliable methods are required to make the in-growth of new blood vessels into bio-artificial scaffolds visible and quantify the results. Over the past couple of years, our group has introduced a full skin defect model that enables the direct visualization of blood vessels by transillumination and provides the possibility of quantification through digital segmentation. In this model, one surgically creates full skin defects in the back of mice and replaces them with the material tested. Molecules or cells of interest can also be incorporated in such materials to study their potential effect. After an observation time of one&#8217;s own choice, materials are explanted for evaluation. Bilateral wounds provide the possibility of making internal comparisons that minimize artifacts among individuals as well as of decreasing the number of animals needed for the study. In comparison to other approaches, our method offers a simple, reliable and cost effective analysis. We have implemented this model as a routine tool to perform high-resolution screening when testing vascularization of different biomaterials and bio-activation approaches.

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Vascularization is key to approaches in successful tissue engineering. Therefore, reliable technologies are required to evaluate the development of vascular networks in tissue-constructs. Here we present a simple and cost-effective method to visualize and quantify vascularization in vivo.

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to ...

Analysis of Cell Migration within a Three-dimensional Collagen Matrix

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic development, wound healing, and immune responses. However, cell migration is also a key mechanism in cancer enabling these cancer cells to detach from the primary tumor to start metastatic spreading. Within the past years various cell migration assays have been developed to analyze the migratory behavior of different cell types. Because the locomotory behavior of cells markedly differs between a two-dimensional (2D) and three-dimensional (3D) environment it can be assumed that the analysis of the migration of cells that are embedded within a 3D environment would yield in more significant cell migration data. The advantage of the described 3D collagen matrix migration assay is that cells are embedded within a physiological 3D network of collagen fibers representing the major component of the extracellular matrix. Due to time-lapse video microscopy real cell migration is measured allowing the determination of several migration parameters as well as their alterations in response to pro-migratory factors or inhibitors. Various cell types could be analyzed using this technique, including lymphocytes/leukocytes, stem cells, and tumor cells. Likewise, also cell clusters or spheroids could be embedded within the collagen matrix concomitant with analysis of the emigration of single cells from the cell cluster/ spheroid into the collagen lattice. We conclude that the 3D collagen matrix migration assay is a versatile method to analyze the migration of cells within a physiological-like 3D environment.

Cell migration is a biological phenomenon that is involved in a plethora of physiological, such as wound healing and immune responses, and pathophysiological processes, like cancer. The 3D-collagen matrix migration assay is a versatile tool to analyze the migratory properties of different cell types within in a 3D physiological-like environment.

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic ...

Three-dimensional Printing of Thermoplastic Materials to Create Automated Syringe Pumps with Feedback Control for Microfluidic Applications

Microfluidics has become a critical tool in research across the biological, chemical, and physical sciences. One important component of microfluidic experimentation is a stable fluid handling system capable of accurately providing an inlet flow rate or inlet pressure. Here, we have developed a syringe pump system capable of controlling and regulating the inlet fluid pressure delivered to a microfluidic device. This system was designed using low-cost materials and additive manufacturing principles, leveraging three-dimensional (3D) printing of thermoplastic materials and off-the-shelf components whenever possible. This system is composed of three main components: a syringe pump, a pressure transducer, and a programmable microcontroller. Within this paper, we detail a set of protocols for fabricating, assembling, and programming this syringe pump system. Furthermore, we have included representative results that demonstrate high-fidelity, feedback control of inlet pressure using this system. We expect this protocol will allow researchers to fabricate low-cost syringe pump systems, lowering the entry barrier for the use of microfluidics in biomedical, chemical, and materials research.

Here we present a protocol to construct a pressure-controlled syringe pump to be used in microfluidic applications. This syringe pump is made from an&#160;additively manufactured body, off-the-shelf hardware, and open-source electronics. The resulting system is low-cost, straightforward to build, and delivers well-regulated fluid flow to enable rapid microfluidic research.

Microfluidics has become a critical tool in research across the biological, chemical, and physical sciences. One important component of microfluidic ...

Cultivating a Three-dimensional Reconstructed Human Epidermis at a Large Scale

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process and the characterization of the model is described. Neonatal primary keratinocytes are grown submerged on permeable polycarbonate inserts and lifted to the air-liquid interface three days after seeding. After fourteen days of stimulation with defined growth factors and ascorbic acid in high calcium culture medium, the model is fully differentiated. Histological analysis revealed a completely stratified epidermis, mimicking the morphology of native human skin. To characterize the model and its barrier functions, protein levels and localization specific for early-stage keratinocyte differentiation (i.e., keratin 10), late-stage differentiation (i.e., involucrin, loricrin, and filaggrin) and tissue adhesion (i.e., desmoglein 1), were assessed by immunofluorescence. The tissue barrier integrity was further evaluated by measuring transepithelial electrical resistance. Reconstructed human epidermis was responsive to proinflammatory stimuli (i.e., lipopolysaccharide and tumor necrosis factor alpha), leading to increased cytokine release (i.e., interleukin 1 alpha and interleukin 8). This protocol represents a straightforward and reproducible in vitro method to cultivate reconstructed human epidermis as a tool to assess environmental effects and a broad range of skin-related studies.

This protocol describes a straightforward method to cultivate three-dimensional reconstituted human epidermis in a reproducible and robust manner. Additionally, it characterizes the structure-function relationship of the epidermal barrier model. The biological responses of the reconstituted human epidermis upon proinflammatory stimuli are also presented.

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process ...

Generation of Self-assembled Vascularized Human Skin Equivalents

Human skin equivalents (HSEs) are tissue engineered constructs that model epidermal and dermal components of human skin. These models have been used to study skin development, wound healing, and grafting techniques. Many HSEs continue to lack vasculature and are additionally analyzed through post-culture histological sectioning which limits volumetric assessment of the structure. Presented here is a straightforward protocol utilizing accessible materials to generate vascularized human skin equivalents (VHSE); further described are volumetric imaging and quantification techniques of these constructs. Briefly, VHSEs are constructed in 12 well culture inserts in which dermal and epidermal cells are seeded into rat tail collagen type I gel. The dermal compartment is made up of fibroblast and endothelial cells dispersed throughout collagen gel. The epidermal compartment is made up of keratinocytes (skin epithelial cells) that differentiate at the air-liquid interface. Importantly, these methods are customizable based on needs of the researcher, with results demonstrating VHSE generation with two different fibroblast cell types: human dermal fibroblasts (hDF) and human lung fibroblasts (IMR90s). VHSEs were developed, imaged through confocal microscopy, and volumetrically analyzed using computational software at 4- and 8-week timepoints. An optimized process to fix, stain, image, and clear VHSEs for volumetric examination is described. This comprehensive model, imaging, and analysis techniques are readily customizable to the specific research needs of individual labs with or without prior HSE experience.

The goal of this protocol is to describe the generation and volumetric analysis of vascularized human skin equivalents using accessible and simple techniques for long term culture. To the extent possible, the rationale for steps is described to allow researchers the ability to customize based on their research needs.

Human skin equivalents (HSEs) are tissue engineered constructs that model epidermal and dermal components of human skin. These models have been used to ...

Generation of a Simplified Three-Dimensional Skin-on-a-chip Model in a Micromachined Microfluidic Platform

This work presents a new, cost-effective, and reliable microfluidic platform with the potential to generate complex multilayered tissues. As a proof of concept, a simplified and undifferentiated human skin containing a dermal (stromal) and an epidermal (epithelial) compartment has been modelled. To accomplish this, a versatile and robust, vinyl-based device divided into two chambers has been developed, overcoming some of the drawbacks present in microfluidic devices based on polydimethylsiloxane (PDMS) for biomedical applications, such as the use of expensive and specialized equipment or the absorption of small, hydrophobic molecules and proteins. Moreover, a new method based on parallel flow was developed, enabling the in situ deposition of both the dermal and epidermal compartments. The skin construct consists of a fibrin matrix containing human primary fibroblasts and a monolayer of immortalized keratinocytes seeded on top, which is subsequently maintained under dynamic culture conditions. This new microfluidic platform opens the possibility to model human skin diseases and extrapolate the method to generate other complex tissues.

Here, we present a protocol to generate a three-dimensional simplified and undifferentiated skin model using a micromachined microfluidic platform. A parallel flow approach allows the in situ deposition of a dermal compartment for the seeding of epithelial cells on top, all controlled by syringe pumps.

This work presents a new, cost-effective, and reliable microfluidic platform with the potential to generate complex multilayered tissues. As a proof of ...

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.