The authors would like to thank Dr. Fotis Iliopoulos and Daniel Greenfield of the Evans&#39; Group for their discussion and proofreading of this manuscript. In addition, the authors would like to acknowledge support from LEO Pharma. Figure 2 was created with BioRender.com.

<ol>
	<li>Finnin, B., Walters, K. A., Franz, T. J., Benson, H. E., Watkinson, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+skin+permeation+methodology.+In+Transdermal+and+topical+drug+delivery:+principles+and+methodology.">In vitro skin permeation methodology. In Transdermal and topical drug delivery: principles and methodology.</a> Transdermal and topical drug delivery: principles and practice. , 85-108 (2012).</li><li>Shin, S. 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=On+the+road+to+development+of+an+in+vitro+permeation+test+(IVPT)+model+to+compare+heat+effects+on+transdermal+delivery+systems:+exploratory+studies+with+nicotine+and+fentanyl.">On the road to development of an in vitro permeation test (IVPT) model to compare heat effects on transdermal delivery systems: exploratory studies with nicotine and fentanyl.</a> Pharmaceutical Research. 34 (9), 1817-1830 (2017).</li><li>Hossain, 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=Preparation,+characterisation,+and+topical+delivery+of+terbinafine.">Preparation, characterisation, and topical delivery of terbinafine.</a> Pharmaceutics. 11 (10), 548 (2019).</li><li>Santos, L. L., Swofford, N. J., Santiago, B. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+permeation+test+(IVPT)+for+pharmacokinetic+assessment+of+topical+dermatological+formulations.">In vitro permeation test (IVPT) for pharmacokinetic assessment of topical dermatological formulations.</a> Current Protocols in Pharmacology. 91 (1), 79 (2020).</li><li>Iliopoulos, F., Caspers, P. J., Puppels, G. J., Lane, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Franz+cell+diffusion+testing+andquantitative+confocal+Raman+spectroscopy:+In+vitro-in+vivo+correlation.">Franz cell diffusion testing andquantitative confocal Raman spectroscopy: In vitro-in vivo correlation.</a> Pharmaceutics. 12 (9), 887 (2020).</li><li>Cordery, 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=Topical+bioavailability+of+diclofenac+from+locally-acting,+dermatological+formulations.">Topical bioavailability of diclofenac from locally-acting, dermatological formulations.</a> International Journal of Pharmaceutics. 529 (1-2), 55-64 (2017).</li><li>Pensado, 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=Stratum+corneum+sampling+to+assess+bioequivalence+between+topicalacyclovir+products.">Stratum corneum sampling to assess bioequivalence between topicalacyclovir products.</a> Pharmaceutical Research. 36 (12), 1-16 (2019).</li><li>Zhang, Y., 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=Dermal+delivery+of+niacinamide-in+vivo+studies.">Dermal delivery of niacinamide-in vivo studies.</a> Pharmaceutics. 13 (5), 726 (2021).</li><li>Bodenlenz, 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=Open+flow+microperfusion+as+a+dermal+pharmacokinetic+approach+to+evaluate+topical+bioequivalence.">Open flow microperfusion as a dermal pharmacokinetic approach to evaluate topical bioequivalence.</a> Clinical Pharmacokinetics. 56 (1), 91-98 (2017).</li><li>Eirefelt, 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=Evaluating+dermal+pharmacokinetics+and+pharmacodymanic+effect+of+soft+topical+PDE4+inhibitors:Open+flow+microperfusion+and+skin+biopsies.">Evaluating dermal pharmacokinetics and pharmacodymanic effect of soft topical PDE4 inhibitors:Open flow microperfusion and skin biopsies.</a> Pharmaceutical Research. 37 (12), 1-12 (2020).</li><li>Stagni, G., O'Donnell, D., Liu, Y. J., Kellogg, J. D. L., Shepherd, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Iontophoretic+current+and+intradermal+microdialysis+recovery+in+humans.">Iontophoretic current and intradermal microdialysis recovery in humans.</a> Journal of Pharmacological and Toxicological Methods. 41 (1), 49-54 (1999).</li><li>Garcia Ortiz, P., Hansen, S. H., Shah, V. P., Menne, T., Benfeldt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+adultatopic+dermatitis+on+topical+drug+penetration:+assessment+by+cutaneous+microdialysis+and+tape+stripping.">Impact of adultatopic dermatitis on topical drug penetration: assessment by cutaneous microdialysis and tape stripping.</a> Acta Dermato-Venereologica. 89 (1), 33-38 (2009).</li><li>Joshi, A., Patel, H., Joshi, A., Stagni, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pharmacokinetic+applications+of+cutaneous+microdialysis:+Continuous+intermittent+vs+continuous-only+sampling.">Pharmacokinetic applications of cutaneous microdialysis: Continuous+intermittent vs continuous-only sampling.</a> Journal of Pharmacological and Toxicological Methods. 83, 16-20 (2017).</li><li>Kuzma, B. 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=Evaluation+of+local+bioavailability+of+metronidazole+from+topical+formulations+using+dermal+microdialysis:+Preliminary+study+in+a+Yucatan+mini-pig+model.">Evaluation of local bioavailability of metronidazole from topical formulations using dermal microdialysis: Preliminary study in a Yucatan mini-pig model.</a> European Journal of Pharmaceutical Sciences. 159, 105741 (2021).</li><li>Begley, R., Harvey, A., Byer, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=L.Coherent+anti-Stokes+Raman+spectroscopy.">L.Coherent anti-Stokes Raman spectroscopy.</a> Applied Physics Letters. 25 (7), 387-390 (1974).</li><li>Evans, C. L., 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=Chemical+imaging+of+tissue+in+vivo+with+video-rate+coherent+anti-Stokes+Raman+scattering+microscopy.">Chemical imaging of tissue in vivo with video-rate coherent anti-Stokes Raman scattering microscopy.</a> Proceedings of the National Academy of Sciences of the United States of America. 102 (46), 16807-16812 (2005).</li><li>Hill, A. H., Manifold, B., Fu, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+imaging+depth+limit+of+stimulated+Raman+scattering+microscopy.">Tissue imaging depth limit of stimulated Raman scattering microscopy.</a> Biomedical Optics Express. 11 (2), 762-774 (2020).</li><li>Feizpour, A., Marstrand, T., Bastholm, L., Eirefelt, S., Evans, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+quantification+of+pharmacokinetics+in+skin+with+stimulated+Raman+scattering+microscopy+and+deep+learning.">Label-free quantification of pharmacokinetics in skin with stimulated Raman scattering microscopy and deep learning.</a> Journal of Investigative Dermatology. 141 (2), 395-403 (2021).</li><li>Ghosh, B., Reddy, L. H., Kulkarni, R. V., Khanam, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+skin+permeability+of+drugs+in+mice+and+human+cadaver+skin.">Comparison of skin permeability of drugs in mice and human cadaver skin.</a> Indian Journal of Experimental Biology. 38 (1), 42-45 (2000).</li><li>Nielsen, J. B., Plasencia, I., S&#248;rensen, J. A., Bagatolli, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Storage+conditions+of+skin+affect+tissue+structure+and+subsequent+in+vitro+percutaneous+penetration.">Storage conditions of skin affect tissue structure and subsequent in vitro percutaneous penetration.</a> Skin Pharmacology and Physiology. 24 (2), 93-102 (2011).</li><li>Barbero, A. M., Frasch, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+frozen+human+epidermis+storage+duration+and+cryoprotectant+on+barrier+function+using+two+model+compounds.">Effect of frozen human epidermis storage duration and cryoprotectant on barrier function using two model compounds.</a> Skin Pharmacology and Physiology. 29 (1), 31-40 (2016).</li><li>Babu, R., 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+influence+of+various+methods+of+cold+storage+of+skin+on+the+permeation+of+melatonin+and+nimesulide.">The influence of various methods of cold storage of skin on the permeation of melatonin and nimesulide.</a> Journal of Controlled Release. 86 (1), 49-57 (2003).</li><li>Skelly, J. P., 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=FDA+and+AAPS+report+of+the+workshop+on+principles+and+practices+of+in+vitro+percutaneous+penetration+studies:+relevance+to+bioavailability+and+bioequivalence.">FDA and AAPS report of the workshop on principles and practices of in vitro percutaneous penetration studies: relevance to bioavailability and bioequivalence.</a> Pharmaceutical Research. 4 (3), 265-267 (1987).</li><li>OECD. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Guidance+document+for+the+conduct+of+skin+absorption+studies.">Guidance document for the conduct of skin absorption studies.</a> OECD. , (2004).</li><li>OECD. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Test+no.+428:+Skin+absorption:+In+vitro+method.">Test no. 428: Skin absorption: In vitro method.</a> OECD. , (2004).</li><li>Saar, B. G., 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=Video-rate+molecular+imaging+in+vivo+with+stimulated+Raman+scattering.">Video-rate molecular imaging in vivo with stimulated Raman scattering.</a> Science. 330 (6009), 1368-1370 (2010).</li><li>Saar, B. G., Contreras-Rojas, L. R., Xie, X. S., Guy, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+drug+delivery+to+skin+with+stimulated+Raman+scattering+microscopy.">Imaging drug delivery to skin with stimulated Raman scattering microscopy.</a> Molecular Pharmaceutics. 8 (3), 969-975 (2011).</li><li>Pence, I. J., Kuzma, B. A., Brinkmann, M., Hellwig, T., Evans, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-windowsparse+spectral+sampling+stimulated+Raman+scattering+microscopy.">Multi-windowsparse spectral sampling stimulated Raman scattering microscopy.</a> Biomedical Optics Express. 12 (10), 6095-6114 (2021).</li><li>Herkenne, C., 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=In+vivo+methods+for+the+assessment+of+topical+drug+bioavailability.">In vivo methods for the assessment of topical drug bioavailability.</a> Pharmaceutical Research. 25 (1), 87-103 (2008).</li><li>Alfonso-Garc&#305;a, A., Mittal, R., Lee, E. S., Potma, E. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+imaging+with+coherent+Raman+scattering+microscopy:+a+tutorial.">Biological imaging with coherent Raman scattering microscopy: a tutorial.</a> Journal of Biomedical Optics. 19 (7), 071407 (2014).</li><li>Osseiran, 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=Longitudinal+monitoring+of+cancer+cell+subpopulations+in+monolayers,+3D+spheroids,+and+xenografts+using+the+photoconvertible+dye+DiR.">Longitudinal monitoring of cancer cell subpopulations in monolayers, 3D spheroids, and xenografts using the photoconvertible dye DiR.</a> Scientific Reports. 9 (1), 1-10 (2019).</li><li>Evennett, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kohler+illumination:+a+simple+interpretation.">Kohler illumination: a simple interpretation.</a> Proceedings of the Royal Microscopical Society. 28 (4), 189-192 (1983).</li><li>Sanderson, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamentals+of+microscopy.">Fundamentals of microscopy.</a> Current Protocols in Mouse Biology. 10 (2), 76 (2020).</li><li>Schindelin, J., 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=Fiji:+an+open-source+platform+for+biological-image+analysis.">Fiji: an open-source platform for biological-image analysis.</a> Nature Methods. 9 (7), 676-682 (2012).</li><li>Hunter, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matplotlib:+A+2D+graphics+environment.">Matplotlib: A 2D graphics environment.</a> Computing in Science &amp; Engineering. 9 (3), 90-95 (2007).</li><li>Wickham, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ggplot2: Elegant Graphics for Data Analysis. , (2016).</li><li>Kim, H., Han, S., Cho, Y. S., Yoon, S. K., Bae, K. <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+R+packages:'Non-Compart'+and+'ncar'+for+noncompartmental+analysis+(NCA).">Development of R packages:'Non-Compart' and 'ncar' for noncompartmental analysis (NCA).</a> Translational and Clinical Pharmacology. 26 (1), 10-15 (2018).</li></ol>

CLE is an inventor on patents for CARS microscopy that have been licensed to multiple microscope manufacturers. All other authors have no conflicts of interest to disclose.

The evaluation of topical BA/BE is an area of research the requires a multifaceted approach as no single method can fully characterize in vivo cPK. This protocol presents a methodology for the evaluation of a topical drug product&#39;s BA/BE based on coherent Raman imaging. One of the first points that might be overlooked is how thin the skin samples must be, especially for quantitative transmission SRS imaging. If the skin is too thick (i.e., light cannot readily pass through), there is little to no si...

Methodologies to assess cPK after topical drug product application have expanded from classical in vitro permeation testing (IVPT) studies1,2,3,4,5 and tape-stripping6,7,8 to additional methodologies such as open-flow microperfusion or dermal microdialysis9,10,11,12,13,14. There are potentially various local sites of therapeutic action depending on the disease of interest. Hence, there may be a corresponding number of methodologies to assess the rate and extent to which an API gets to the intended local site of action. While each of the aforementioned methodologies has its advantages, the major disadvantage is the lack of microscale cPK information (i.e., the inability to visualize where the API goes and how it permeates).
One noninvasive methodology of interest to estimate topical BA and BE is CRI, which can be broken down into two imaging modalities: CARS and SRS microscopy. These coherent Raman methods enable chemically specific imaging of molecules via nonlinear Raman effects. In CRI, two laser pulse trains are focused and scanned within a sample; the difference in energy between the laser frequencies is set to target vibrational modes specific to the chemical structures of interest. As CRI processes are nonlinear, a signal is only generated at the microscope focus, allowing for three-dimensional pharmacokinetic tomographic imaging of the tissue. In the context of cPK, CARS has been used to obtain tissue structural information, such as the location of lipid-rich skin structures15. In contrast, SRS has been utilized to quantify molecular concentration as its signal is linear with concentration. For ex vivo skin specimens, it is advantageous to carry out CARS in the epi-direction16 and SRS in transmission mode17. Therefore, tissue samples that are thin will allow for SRS signal detection and quantification.
As a model tissue, the nude mouse ear presents several advantages with minor drawbacks. One advantage is that the tissue is already ~200-300 &#181;m in thickness and does not require further sample preparation. In addition, several skin stratifications are seen by axially focusing through one field of view (e.g., stratum corneum, sebaceous glands (SGs), adipocytes, and subcutaneous fat)16,18. This allows for preliminary preclinical estimation of cutaneous permeation pathways and topical BA estimates before moving to human skin samples. However, the nude mouse model presents limitations such as difficulty in extrapolation to in vivo scenarios due to differences in skin structure19. While the nude mouse ear is an excellent model to obtain preliminary results, the human skin model is the gold standard. Although there have been various commentaries on the suitability and applicability of frozen human skin to accurately recapitulate in vivo permeation kinetics20,21,22, the use of frozen human skin is an accepted method for the evaluation of in vitro&#160;API permeation kinetics23,24,25. This protocol visualizes various skin layers in mouse and human skin while quantifying API concentrations within lipid-rich and lipid-poor structures.
While CRI has been utilized across numerous fields to specifically visualize compounds within tissues, there have been limited efforts investigating the cPK of topically applied drug products. To evaluate the topical BA/BE of topical products using CRI, it is necessary to first have a standardized protocol in place to make accurate comparisons. Previous efforts using CRI for drug delivery to the skin have demonstrated variability within the data. As this is a relatively new application of CRI, establishing a protocol is critical to obtain reliable results18,26,27. This approach only targets one specific wavenumber in the biological silent region of the Raman spectrum. However, most APIs and inactive ingredients have Raman shifts within the fingerprint region. This has previously posed challenges due to the inherent signal arising from the tissue in the fingerprint region. Recent laser and computational advances have removed this barrier, which can also be utilized in combination with the approach presented here28. This approach presented here allows for the quantification of an API, which has a Raman shift in the silent region (2,000-2,300 cm-1). This is not limited to the physiochemical properties of the drug, which might be the case for some previously mentioned cPK monitoring methodologies29.
The protocol must reduce sample-to-sample variability in skin thickness for various preparations, as thick human skin samples will produce minimal signal after drug product application due to light scattering by the thick sample. A goal of this manuscript is to present a tissue preparation methodology that assures reproducible imaging standards. In addition, the CRI system is setup as described to reduce potential sources of error as well as minimize signal-to-noise.&#160;However, this paper will not discuss the guiding principles and technical merits of the CRI microscope as this has been previously covered30. Finally, the extensive data analysis procedure is explored to allow for interpretation of the results to determine an experiment&#39;s success or failure.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Tissue Preparation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Autoclavable Biohazard Bags</td>
			<td>FisherBrand</td>
			<td>22-044562</td>
			<td>As refered to in text: biohazard bags 
			https://www.fishersci.com/shop/products/fisherbrand-polyethylene-biohazard-autoclave-bags-without-sterilization-indicator-8/22044562?searchHijack=true&#38;searchTerm= 22044562&#38;searchType=RAPID&#38; matchedCatNo=22044562</td>
		</tr>
		<tr>
			<td>Cell Culture Buffers: Dulbecco&#39;s Phosphate-Buffered Salt Solution 1x</td>
			<td>Corning</td>
			<td>MT21030CV</td>
			<td>As refered to in text: PBS 
			https://www.fishersci.com/shop/products/corning-cellgro-cell-culture-buffers-dulbecco-s-phosphate-buffered-salt-solution-1x-8/MT21030CV?searchHijack=true&#38;searchTerm= 21-030-cv&#38;searchType= RAPID&#38;matchedCatNo=21-030-cv</td>
		</tr>
		<tr>
			<td>Disposable Scalpels</td>
			<td>Exel International</td>
			<td>14-840-00</td>
			<td>As refered to in text: scalpel 
			https://www.fishersci.com/shop/products/exel-international-disposable-scalpels-3/1484000?keyword=true</td>
		</tr>
		<tr>
			<td>High Precision 45&#176; Angle Broad Point Tweezers/Forceps</td>
			<td>Fisherbrand</td>
			<td>12-000-132</td>
			<td>As refered to in text: forceps 
			https://www.fishersci.com/shop/products/high-precision-45-angle-broad-point-tweezers-forceps/12000132#?keyword=</td>
		</tr>
		<tr>
			<td>Kimwipes Delicate Task Wipers, 1-Ply</td>
			<td>Kimberly-Clark Professional Kimtech Science</td>
			<td>06-666</td>
			<td>As refered to in text: task wiper 
			https://www.fishersci.com/shop/products/kimberly-clark-kimtech-science-kimwipes-delicate-task-wipers-7/06666</td>
		</tr>
		<tr>
			<td>Parafilm M Laboratory Wrapping Film</td>
			<td>Bemis</td>
			<td>13-374-12</td>
			<td>As refered to in text: parafilm 
			https://www.fishersci.com/shop/products/curwood-parafilm-m-laboratory-wrapping-film-4/1337412</td>
		</tr>
		<tr>
			<td>Petri Dish (35 mm x 10 mm)</td>
			<td>Fisherbrand</td>
			<td>FB0875711YZ</td>
			<td>As refered to in text: small petri dish 
			https://www.fishersci.com/shop/products/fisherbrand-petri-dishes-specialty-6/FB0875711YZ?keyword=true</td>
		</tr>
		<tr>
			<td>Petri Dish (60 mm x 15 mm)</td>
			<td>Fisherbrand</td>
			<td>FB0875713A</td>
			<td>As refered to in text: large petri dish 
			https://www.fishersci.com/shop/products/fisherbrand-petri-dishes-clear-lid-12/FB0875713A?keyword=true</td>
		</tr>
		<tr>
			<td>Surgical Scissors</td>
			<td>Roboz</td>
			<td>NC9411473</td>
			<td>As refered to in text: scissors 
			https://www.fishersci.com/shop/products/scissors-327/NC9411473?searchHijack=true&#38;searchTerm= RS-5915SC&#38;searchType=RAPID&#38; matchedCatNo=RS-5915SC</td>
		</tr>
		<tr>
			<td>Laser/microscope</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>650/60 nm BrightLine single-band bandpass filter</td>
			<td>Semrock</td>
			<td></td>
			<td>As refered to in text: CARS filter - CH2 vibrations (645nm/60nm filter)</td>
		</tr>
		<tr>
			<td>Control box IX2-UCB</td>
			<td>Olympus</td>
			<td></td>
			<td>As refered to in text: Control Box</td>
		</tr>
		<tr>
			<td>D700/30m</td>
			<td>Chroma</td>
			<td></td>
			<td>As refered to in text: CARS filter - deuterated band 
			https://www.chroma.com/products/parts/d700-30m</td>
		</tr>
		<tr>
			<td>DeepSee Insight</td>
			<td>Spectra-Physics</td>
			<td></td>
			<td>As refered to in text: Laser 
			https://www.spectra-physics.com/f/insight-x3-tunable-laser</td>
		</tr>
		<tr>
			<td>Digital Handheld Optical Power and Energy Meter Console</td>
			<td>ThorLabs</td>
			<td>PM100D</td>
			<td>As refered to in text: power meter 
			https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3341</td>
		</tr>
		<tr>
			<td>Fluoview Software</td>
			<td>Olympus</td>
			<td></td>
			<td>As refered to in text: Microscope Control software</td>
		</tr>
		<tr>
			<td>Frosted Microscope Slides</td>
			<td>FisherBrand</td>
			<td></td>
			<td>As refered to in text: microscope slides 
			https://www.fishersci.com/shop/products/fisherbrand-frosted-microscope-slides-4/22265446</td>
		</tr>
		<tr>
			<td>FV1000</td>
			<td>Olympus</td>
			<td></td>
			<td>As refered to in text: Microscope</td>
		</tr>
		<tr>
			<td>Incubation Chamber</td>
			<td>Tokai Hit</td>
			<td>GM-800</td>
			<td>As refered to in text: incubation chamber</td>
		</tr>
		<tr>
			<td>Integrating Sphere Photodiode Power Sensor</td>
			<td>ThorLabs</td>
			<td>S142C</td>
			<td>As refered to in text: photodiode 
			https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3341</td>
		</tr>
		<tr>
			<td>Power supply FV31-PSU</td>
			<td>Olympus</td>
			<td></td>
			<td>As refered to in text: Power Supply</td>
		</tr>
		<tr>
			<td>Precision 4063, 80MHz Dual Channel Function Generator</td>
			<td>BK Precision</td>
			<td></td>
			<td>As refered to in text: function generator</td>
		</tr>
		<tr>
			<td>ProScan &#8211; Precision Microscope Automation</td>
			<td>Prior Scientific Instruments</td>
			<td></td>
			<td>As refered to in text: stage controller 
			https://www.prior.com/microscope-automation/inverted-microscope-systems/proscan-linear-stage-highest-precision-microscope-automation</td>
		</tr>
		<tr>
			<td>SecureSeal Imaging Spacers</td>
			<td>Grace Biolabs</td>
			<td>654004</td>
			<td>As refered to in text: spacer 
			https://gracebio.com/product/secureseal-imaging-spacers-654004/</td>
		</tr>
		<tr>
			<td>SRS Detection Kit</td>
			<td>APE</td>
			<td></td>
			<td>As refered to in text: SRS detector</td>
		</tr>
		<tr>
			<td>UPLSAPO 20X NA:0.75</td>
			<td>Olympus</td>
			<td></td>
			<td>As refered to in text: 20X Objective 
			https://www.olympus-lifescience.com/en/objectives/uplsapo/</td>
		</tr>
		<tr>
			<td>Lipid/Drug Imaging</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;35 mm Dish, No. 0 Uncoated Coverslip, 14 mm Glass Diameter</td>
			<td>MatTek Corporation</td>
			<td>NC9711297</td>
			<td>As refered to in text: Glass bottom dish 
			https://www.fishersci.com/shop/products/glass-bottom-mircrowell-dish/nc9711297</td>
		</tr>
		<tr>
			<td>Cotton-tipped applicators</td>
			<td>FisherBrand</td>
			<td></td>
			<td>As refered to in text: Cotton-tipped applicator</td>
		</tr>
		<tr>
			<td>Distriman Postive Displacement Pipette</td>
			<td>Gilson</td>
			<td></td>
			<td>As refered to in text: Postive Displacement Pipette 
			https://www.fishersci.com/shop/products/gilson-distriman-positive-displacement-repetitive-pipette/F164001G#?keyword=</td>
		</tr>
		<tr>
			<td>Distriman Postive Displacement Pipette Tips</td>
			<td>Gilson</td>
			<td></td>
			<td>As refered to in text: Tips for pipette 
			https://www.fishersci.com/shop/products/gilson-distritip-syringes-6/f164100g?keyword=true</td>
		</tr>
		<tr>
			<td>Data Analysis</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FIJI</td>
			<td>Open-source</td>
			<td></td>
			<td>As refered to in text: FIJI/ImageJ 
			https://imagej.net/software/fiji/</td>
		</tr>
		<tr>
			<td>Jupyter-Lab</td>
			<td>open-source</td>
			<td></td>
			<td>As refered to in text: JupyterLab 
			https://jupyter.org/</td>
		</tr>
		<tr>
			<td>Rstudio</td>
			<td>Open-source</td>
			<td></td>
			<td>As refered to in text: Rstudio 
			https://www.rstudio.com/</td>
		</tr>
	</tbody>
</table>

visualizing and quantifying pharmaceutical compounds within skin using coherent raman scattering imaging

Cutaneous pharmacokinetics (cPK) after topical formulation application has been a research area of particular interest for regulatory and drug development scientists to mechanistically understand topical bioavailability (BA). Semi-invasive techniques, such as tape-stripping, dermal microdialysis, or dermal open-flow microperfusion, all quantify macroscale cPK. While these techniques have provided vast cPK knowledge, the community lacks a mechanistic understanding of active pharmaceutical ingredient (API) penetration and permeation at the cellular level. 
One noninvasive approach to address microscale cPK is coherent Raman scattering imaging (CRI), which selectively targets intrinsic molecular vibrations without the need for extrinsic labels or chemical modification. CRI has two main methods-coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS)-that enable sensitive and selective quantification of APIs or inactive ingredients. CARS is typically utilized to derive structural skin information or visualize chemical contrast. In contrast, the SRS signal, which is linear with molecular concentration, is used to quantify APIs or inactive ingredients within skin stratifications. 
Although mouse tissue has commonly been utilized for cPK with CRI, topical BA and bioequivalence (BE) must ultimately be assessed in human tissue before regulatory approval. This paper presents a methodology to prepare and image ex vivo skin to be used in quantitative pharmacokinetic CRI studies in the evaluation of topical BA and BE. This methodology enables reliable and reproducible API quantification within human and mouse skin over time. The concentrations within lipid-rich and lipid-poor compartments, as well as total API concentration over time are quantified; these are utilized for estimates of micro- and macroscale BA and, potentially, BE.

Imaging is considered successful if the tissue has not significantly moved in either axial (&#60;10 &#956;m) or lateral direction upon the completion of the experiment (Figure 4). This is an immediate indication if the SRS measurement for the API of interest is not representative of the initial depth, for which quantification is layer-specific. This is mitigated by imaging z-stacks for each XY position of interest, with the trade-off being the temporal resolution. If frozen skin is used in t...

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Visualizing and Quantifying Pharmaceutical Compounds within Skin using Coherent Raman Scattering Imaging

A coherent Raman scattering imaging methodology to visualize and quantify pharmaceutical compounds within the skin is described. This paper describes skin tissue preparation (human and mouse) and topical formulation application, image acquisition to quantify spatiotemporal concentration profiles, and preliminary pharmacokinetic analysis to assess topical drug delivery.

Cutaneous pharmacokinetics (cPK) after topical formulation application has been a research area of particular interest for regulatory and drug development ...

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2.6K Views.  Massachusetts General Hospital, Harvard Medical School. A coherent Raman scattering imaging methodology to visualize and quantify pharmaceutical compounds within the skin is described. This paper describes skin tissue preparation (human and mouse) and topical formulation application, image acquisition to quantify spatiotemporal concentration profiles, and preliminary pharmacokinetic analysis to assess topical drug delivery.