In Vitro Sunscreen SPF Measurement Substrate
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Solution Overview
Problem
Current in vitro methods for measuring sunscreen protection factor (SPF) do not adequately replicate the skin surface parameters and film thickness distribution, leading to inaccurate SPF measurements, especially for photolabile sunscreen products, and fail to account for photodegradation and skin surface interactions.
Innovation Solution
A substrate with defined indentations of progressively increasing depths is used to simulate the sunscreen film thickness distribution on skin, allowing for iterative or simultaneous measurement of transmission at various thicknesses, combined with a method involving a continuous or intermittent light source and spectroscopic measurement to determine the integrated absorbance spectrum and SPF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat substrate is used for in vitro SPF measurement, then the measurement process is simple, but the substrate does not adequately match skin surface parameters and film thickness distribution
Solution Approach 1:
The substrate incorporates regions with different optical properties and surface characteristics to simulate the heterogeneous nature of human skin. Specifically, it includes scattering regions with different scattering coefficients and absorption regions with varying absorption coefficients, creating local variations that match skin parameters while maintaining a relatively simple overall substrate structure.
Solution Approach 2:
The patent transitions from measuring only surface-level properties to measuring transmission through multiple layers with varying optical properties. By creating a multi-layer substrate structure with different thicknesses and optical characteristics, it replicates the three-dimensional complexity of skin without requiring a complex three-dimensional skin model.
2Ease of operation
If a single thickness substrate is used, then the measurement is straightforward, but it cannot account for photodegradation and film thickness distribution variations
Solution Approach 1:
The substrate is divided into multiple distinct regions, each with specific optical properties and thickness characteristics. This segmentation allows different regions to simulate different aspects of sunscreen behavior - some regions maintain stable absorption while others show photodegradation, enabling comprehensive assessment of both initial protection and stability under UV exposure.
Solution Approach 2:
The substrate design enables dynamic measurement capabilities by incorporating regions that can undergo photodegradation similar to real sunscreen on skin. The varying thickness regions allow the system to assess how sunscreen protection changes over time and under different UV doses, providing adaptive measurement for both stable and photolabile formulations.
3Device complexity
If conventional substrates are used, then the device complexity is low, but the optical configuration and dynamic range are insufficient for accurate SPF determination
Solution Approach 1:
The substrate acts as an intermediary element that bridges the gap between simple measurement devices and complex skin properties. By embedding optical scattering and absorption characteristics directly into the substrate structure, it enables accurate SPF measurement using relatively simple transmission spectrophotometry equipment, without requiring complex imaging systems or multiple measurement devices.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach accurately replicates the sunscreen film thickness distribution on human skin, enabling precise SPF determination and accounting for photodegradation, thereby improving the accuracy and reliability of in vitro SPF measurements.
Implementation Method 1
measuring the absorbance or transmission properties of a sunscreen sample
Implementation Method 2
applying a continuous or intermittent (flashing) light source to the sunscreen and substrate; measuring the time course of transmission or absorbance
Data Source
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AI summary
Substrates and methods for in vitro determination of sunscreen protection factors (SPF) are disclosed.