Regenerative Elastography: Monitoring Soft Tissue Reconstruction

描述（由申请人提供）：组织工程涉及时间和序列相关的程序，在修复的组织形成和功能之前，最终结果是未知的。监测组织发育、成熟、衰老和发病过程中生物力学特性的变化对于设计用于组织修复和再生的新组织工程技术至关重要。在组织生长过程中，对组织工程构建体的刚度进行非侵入性定期监测，将使组织分化和发育的瞬时非破坏性手段成为可能。磁共振弹性成像（MRE）是一种以非侵入性方式测量柔软生物组织粘弹性特性的技术。MRE生成描绘剪切波运动的图像，从中我们可以计算组织刚度的局部值。目前应用的MRE不能用于研究小型生物组织，也不能用于对体内薄组织区域成像，如厚度小于2mm的关节软骨，亚毫米层结构明显。最近，我们将MRE扩展到微观尺度，并将其称为微观MR弹性成像（<MRE）。此类5MRE研究使用低频声学剪切波激励（迄今为止高达1khz，高于传统MRE系统），强磁场（11.74 T）和高梯度强度（200 G/cm）来评估组织力学性能，具有高空间分辨率（34 <m x 34 <m x 500 <m）和提高的灵敏度。我们首先使用琼脂糖凝胶复合模型验证了该技术，然后在体外研究了不同的生物组织（青蛙卵母细胞和组织工程脂肪和骨）。在每种情况下，使用介质的各向同性和均匀模型对低振幅横波模式进行分析，可以识别粘弹性特性。本研究的目的是利用显微磁共振弹性成像技术在体外和体内监测和促进组织工程脂肪的脂肪生成。在最近与我们的组织工程合作者的工作中，使用间充质干细胞（hMSCs）和生物相容性支架相结合，形成工程脂肪组织的底物。在组织刺激下，在特定的成脂分化因子的作用下，组织工程构建体的机械性能发生了改变，因为脂质基质是通过分化hMSCs产生的。随着时间的推移，脂肪细胞生成的脂肪基质逐渐增加，脂肪组织变得柔软。该项目的最终目标是将组织工程与显微磁共振弹性成像相结合，通过提供一种实时、无创的监测技术来评估组织发育和体内宿主组织整合，从而加快组织工程技术在再生医学中的应用。具体目标是：1)优化工程脂肪生成组织的<MRE检测方案，促进体外脂肪生成；2)开发和构建用于动物体内试验的高频机械执行器；3)应用<MRE在体内监测脂肪生成组织工程构建物。

DESCRIPTION (provided by applicant): Tissue engineering involves time- and sequence-dependent procedures where the final outcome is unknown until the restored tissue is formed and functioning. Monitoring changes in the biomechanical properties during tissue development, maturation, ageing, and the onset of disease is critical to the design of new tissue engineering techniques for tissue repair and regeneration. Non-invasive periodic monitoring of the stiffness of a tissue-engineered construct during tissue growth would enable instantaneous non-destructive means for tissue differentiation and development. Magnetic resonance elastography (MRE) is such a technique that measures the viscoelastic properties of soft biological tissues in a non-invasive manner. MRE generates images that depict shear wave motion from which we can calculate local values of the tissue stiffness. MRE, as currently applied, cannot be used to study small biological tissues, or to image in vivo thin tissue regions, such as articular cartilage with thickness less than 2 mm and distinct structure in sub millimeter layers. Recently, we have extended MRE to the microscopic scale and have referred to it as microscopic MR elastography (<MRE). Such 5MRE studies have used a low frequency acoustic shear wave excitation (so far up to 1 kHz, which is higher than in conventional MRE systems), a strong magnetic field (11.74 T), and high gradient strengths (200 G/cm) to assess tissue mechanical properties with high spatial resolution (34 <m x 34 <m x 500 <m) and improved sensitivity. We validated this technique first using agarose gel composite phantoms, and second in studies of different biological tissues (frog oocyte and tissue engineered fat and bone) in vitro. In each case, analysis of the low amplitude shear wave pattern using isotropic and homogeneous models of the medium allowed the identification of the viscoelastic properties. The goal of this work is to monitor and enhance adipogenesis in tissue engineered fat using microscopic magnetic resonance elastography in vitro and in vivo. In recent work with our tissue engineering collaborators, using mesenchymal stem cells (hMSCs), and biocompatible scaffolds were combined to form substrates for engineered adipogenic tissues. Upon tissue stimulation, with specific adipogenic differentiation factors the tissue engineered constructs changed their mechanical properties as lipid matrix was produced by differentiating hMSCs. Adipogenic tissue became softer as adipogenic matrix production from the adipogenic cells gradually increases with respect to time. The ultimate goal of this project is to integrate tissue engineering with microscopic magnetic resonance elastography to speed the translation of tissue engineering technology in regenerative medicine by providing a real-time, non-invasive monitoring technique to assess tissue development and host tissue integration in vivo. The specific aims are: 1) Optimize <MRE testing protocols of engineered adipogenic tissues and enhance adipogenesis in vitro; 2) Develop and build high frequency mechanical actuators for in vivo animal testing; 3) Apply <MRE to monitor adipogenic tissue engineered constructs in vivo. PUBLIC HEALTH RELEVANCE: Current cancer treatments usually involve surgery, chemotherapy, or radiation. These treatments play a vital role in saving patient's lives but in breast cancer and head and neck cancer, for example, leave the patient with disfiguration and loss of normal function. Tissue engineering will play a vital role in rehabilitation and full organ restoration. In this project, we are proposing to monitor the tissue engineering process to speed the translation of tissue engineering in regenerative medicine.