Regenerative Elastography: Monitoring Soft Tissue Reconstruction

描述（由申请人提供）：组织工程涉及时间和顺序依赖性程序，其中最终结果是未知的，直到恢复的组织形成和发挥功能。监测组织发育、成熟、衰老和疾病发生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。在组织生长期间对组织工程化构造的刚度的非侵入性周期性监测将使得能够实现用于组织分化和发育的瞬时非破坏性手段。磁共振弹性成像（MRE）是一种以非侵入性方式测量软生物组织粘弹性的技术。MRE生成描绘剪切波运动的图像，我们可以从中计算组织刚度的局部值。目前应用的MRE不能用于研究小的生物组织，或对体内薄组织区域成像，例如厚度小于2 mm且亚毫米层中具有明显结构的关节软骨。最近，我们已经将MRE扩展到微观尺度，并将其称为微观MR弹性成像（<MRE）。这样的5 MRE研究已经使用低频声剪切波激励（迄今为止高达1 kHz，这高于常规MRE系统）、强磁场（11.74T）和高梯度强度（200 G/cm）来评估具有高空间分辨率（34 <mX34 <mX500 <m）和改进的灵敏度的组织机械特性。我们首先使用琼脂糖凝胶复合体验证了该技术，然后在不同生物组织（青蛙卵母细胞和组织工程脂肪和骨）的体外研究中验证了该技术。在每种情况下，使用各向同性和均匀模型的介质的低振幅剪切波图案的分析允许的粘弹性特性的识别。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。在最近的工作与我们的组织工程合作者，使用间充质干细胞（hMSCs），和生物相容性支架相结合，形成工程化脂肪组织的基板。在组织刺激后，用特定的成脂分化因子，组织工程构建物改变了它们的机械性质，因为通过分化hMSCs产生脂质基质。随着成脂细胞的成脂基质产量随时间逐渐增加，成脂组织变得更柔软。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，通过提供实时，非侵入性的监测技术来评估组织发育和体内宿主组织整合，从而加速组织工程技术在再生医学中的转化。具体目标是：1）优化成脂组织工程化的<MRE测试方案，促进体外成脂; 2）开发和构建用于体内动物测试的高频机械致动器; 3）应用<MRE监测体内成脂组织工程化构建物。 公共卫生相关性：目前的癌症治疗通常涉及手术，化疗或放疗。这些治疗在挽救患者生命方面发挥着至关重要的作用，但在乳腺癌和头颈癌中，例如，使患者毁容和丧失正常功能。组织工程将在康复和全器官重建中发挥重要作用。在这个项目中，我们建议监测组织工程过程，以加快组织工程在再生医学中的转化。

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.