126 TESTING
arm enable the user to sample the receptor solution - usually manually with a pipette - at predetermined times: every time a sample volume is collected, it must be topped up with a same volume of fresh receptor solution. By measuring the mass content in each
sampled volume via HPLC, MS or similar analytical techniques, cumulative amount profiles of the molecule of interest penetrated over time can be plotted, and transport parameters can be derived. Manually operated diffusion cells usually
require an apparatus that includes, as a minimum: a holder with 6 to 12 slots for positioning the diffusion cells; a water heating circulation system for providing a constant and fast flow of warm water in each heating jackets to maintain the diffusion cells at the desired temperature; and magnetic stirring plates (one per each diffusion cell). Though widely used, Franz cells have limitations that affect the efficiency and the operability of penetration studies.
Tedious manual setup and operating procedures Setting-up and testing procedures for an FDC apparatus are known to be inefficient and reliant on tedious manual operations. Sampling of the receptor solution is most often performed manually by the user, in long, overnight experiments. While some automated systems are available in the market, they come at high prices and still require laborious setting-up and mass balance operations, are rather bulky on a lab bench, and include complex systems of auto samplers, water heaters and magnetic stirrers (Table 1).
Large skin explants required Diffusion cells come with orifices’ diameters ranging from 5 to 25 mm (i.e. diffusion areas of 0.2 to 4.9 cm2
A ■ Fresh Human Skin (n=4)
45 40 35 30 25 20 15 10 5 0
0 5 10 Time (h) 15 20
900 800 700 600 500 400 300 200 100 0
0 5 10 Time (h)
Figure 3: Example of an infinite dose study using the automated ReleGO platform and the REVex chips. Cumulative amount profiles for an infinite dose of caffeine penetrating through native human skin explants (a) and a commercial synthetic membrane (b) placed in REVex chips
in many countries, there is high competition amongst the CROs in sourcing large native skin tissues.
Large receptor volumes affect analytical sensitivity The receptor volumes of vertical diffusion cells are typically 3-5 mL (with larger volumes also available). This design is meant to reduce the gradient and guarantee sink conditions, especially in infinite dose studies. However, large receptor volumes may excessively dilute the penetrated molecules and affect their quantification. This is a critical issue for molecules that have a low skin permeation rate and may risk going undetected.
). However, regardless of the
orifice size, even the smallest FDC requires a rather large skin specimen of at least 2-4 cm2 As availability of donated excised human
.
skin (explants) from cosmetic surgery waste or cadavers often low and increasingly regulated
Occurrence of unstirred water layer (UWL) When highly permeable membranes and lipophilic chemicals are used, the penetrated compound may accumulate close to the receptor-side of the membranes. The formation of this UWL in static Franz cells causes an additional resistance to the flux, and therefore a misrepresentation. Supplementary experiments and calculations are then required to assess the effect of the UWL on the chemical’s permeability.
The revolution of the microfluidic approach In the last years, there has been a great interest in the development of novel technologies for a high-throughput screening of chemicals, ingredients, drugs, and cosmetic formulations that strive to move away from reliance on animal testing and generate human-relevant data. Revivo BioSystems has overcome the limitations of diffusion cells apparatuses by developing an automated testing platform (ReleGO™) that uses miniaturized, bubble- free, dynamic flow-through microfluidic devices (REVex™ chips) for penetration studies and IVRT. This platform is fully compatible with a wide variety of tissue models such as human skin explants, commercially available reconstructed tissue equivalents and synthetic membranes. Some of the unique benefits include higher precision and efficient testing,1
explants required, 10-fold saving in specialized manpower, and long-term culture of skin explants.
The REVex chip is a three-chamber
microfluidic device where three tissue (e.g. skin) explants or simulants can be loaded, cultured,
TABLE 1: COMPARISON OF TRADITIONAL TECHNOLOGY AND REVIVO BIO’S PLATFORM ReleGO system 1
Automated sampler apparatus for vertical diffusion cells
Cost factor
Lab bench space required (in multiples of a ReleGO system: 80cm x 50cm x 25cm [WxDxH]
Weight (in multiples of 15kg) Diffusion device
Throughput (total skins per run) Size of skin specimen per replicate Automated sampling
Automated mass balance collection Mimic natural conditions Enable explants culture
Figure 2: Application of an infinite dose of active ingredients in the REVex chips mounted on the ReleGO system for a penetration study through human skin explants
PERSONAL CARE April 2023 Automated cleaning & disinfection
Manhours for a 24-hour study with mass balance
Sampled columns are collected in 1 1
REVex chip 12
0.5 cm2 ✓ ✓ ✓ ✓ ✓
1h 96-well plates 5 6 5-6
Vertical Diffusion Cell 12
2-4cm2 ✓
Automated sampler apparatus for
flow-through cells 2
3 3-4
Flow-through cell 7
2-4cm2 ✓
15 20 B ■ Strat-M (n=6)
five times smaller
9h Cuvettes
9h Customized cuvettes
www.personalcaremagazine.com
Cumulative amount (µg/cm2
)
Cumulative amount (µg/cm2
)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143
