Characterizing Nonuniform Hydrogel Elastic Moduli Using Autofluorescence
Characterizing Nonuniform Hydrogel Elastic Moduli Using Autofluorescence
复制标题
使用自发荧光表征不均匀水凝胶弹性模量
DOI：
10.1021/acs.macromol.2c00241
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发表时间：
2022
期刊：
影响因子：
5.5
通讯作者：
Schultz, Kelly M.
中科院分区：
文献类型：
--
作者：
McGlynn, John A.;Schultz, Kelly M.
水凝胶生物材料显示出作为可植入细胞递送载体的前景，其增强组织再生和自然愈合过程。这些材料的设计要求它们模仿自然环境以保留天然细胞功能。生物组织通常具有空间变化的刚度，允许它们在体内具有各种功能。然而，这使得它们难以用合成支架机械地模拟。为了实现这些复杂的设计，需要测量不均匀机械性能的表征技术，但这些方法是有限的。体流变测量平均样品的刚度，微观流变方法不能表征高模量材料（尽管能够解决空间变异性），原子力显微镜测量可以是所选的尖端几何形状和测量程序的函数。提出了一种测定非均匀水凝胶刚度的新方法。我们的技术测量了水凝胶的自发荧光亮度，这与其交联程度有关，并将此亮度与弹性模量联系起来。我们使用完善的3D细胞封装平台。这种光聚合的聚合物-肽水凝胶由聚（乙二醇）-藜芦烯和基质金属蛋白酶（MMP）可降解的肽组成。我们首先开发了水凝胶弹性模量和亮度之间的关系，这是系统地通过控制在光聚合过程中的紫外线曝光而变化。然后，我们将弹性模量和自发荧光亮度在每个曝光时间。这种关系使测量亮度的水凝胶图像能够转换为刚度。为了证明该技术，我们制造了具有不均匀刚度分布的水凝胶：（1）阶跃变化和（2）弹性模量的平滑梯度。这些是通过用光掩模在空间上控制UV光曝光来制造的。然后，我们用新技术表征这些凝胶。这项工作提供了一种替代的表征方法，空间非均匀刚度的水凝胶。为了有效地设计用于细胞包封的材料，必须对其进行表征，以使其性能得到微调以匹配天然组织。这将提高这些支架作为细胞递送载体和促进组织再生的有效性。
Hydrogel biomaterials show promise as implantable cell delivery vehicles that enhance tissue regeneration and the natural healing process. The design of these materials requires that they mimic the natural environment to retain native cell function. Biological tissues often have spatially varying stiffness, allowing them to have a variety of functions within the body. However, this makes them challenging to mimic mechanically with a synthetic scaffold. To enable these complex designs, characterization techniques that measure nonuniform mechanical properties are required, but these methods are limited. Bulk rheological measurements average the stiffness of the sample, microrheological methods cannot characterize high moduli materials (despite being able to resolve spatial variability), and atomic force microscopy measurements can be a function of the selected tip geometry and measurement procedure. We present a new method for determining the stiffness of nonuniform hydrogels. Our technique measures the hydrogel’s autofluorescent brightness, which is related to its degree of cross-linking, and relates this brightness to elastic modulus. We use a well-established 3D cell encapsulation platform. This photopolymerized polymer–peptide hydrogel is composed of poly(ethylene glycol)–norbornene and a matrix metalloproteinase (MMP)-degradable peptide. We first develop a relationship between hydrogel elastic modulus and brightness, which are systematically varied by controlling UV light exposure during photopolymerization. We then relate elastic modulus and autofluorescent brightness at each exposure time. This relationship enables images of hydrogels that measure brightness to be converted into stiffnesses. To demonstrate the technique, we fabricate hydrogels with nonuniform stiffness profiles: (1) step changes and (2) smooth gradients in elastic moduli. These are made by controlling UV light exposure spatially with a photomask. We then characterize these gels with the new technique. This work provides an alternative characterization method for hydrogels with spatially nonuniform stiffnesses. To effectively design materials for cell encapsulation, they must be characterized so that their properties are finely tuned to match native tissue. This will improve the effectiveness of these scaffolds as cell delivery vehicles and in promoting tissue regeneration.
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