Controlled Vascularization Using Acoustic Droplet-Hydrogel Composites

描述：工程化组织植入物的生存能力和临床实用性依赖于与受者血液供应的快速整合。血管生成生长因子，包括碱性 成纤维细胞生长因子(BFGF)和血小板衍生生长因子BB(PDGF-BB)是血管侵袭的重要调节因子。在伤口愈合过程中，这些生长因子表现出空间和时间受限的表达模式。通过传统方法给予血管生成生长因子在促进临床相关的血管对植入物的反应方面取得了有限的成功-部分原因是这些方法对生长因子活性的时间和定位提供了最小的控制。其长期目标是使用超声波来主动控制参与组织再生的细胞行为，如迁移、存活、增殖和分化，从而提高构建的活性和功能。超声波是 非常适合于调节植入支架内的细胞活动，因为它可以非侵入性地应用，以亚毫米精度聚焦，以时空受控的方式传递到身体深处的部位，并在临床上翻译。这项应用的目的是使用超声波--具体地说，是一种称为声学液滴汽化(ADV)的机制--通过控制血管生成生长因子的释放，在植入的组织支架内产生严格受控的血管形成。ADV是一种现象，当暴露在高于一定声幅的超声波下时，乳化的液滴转化为气泡。治疗药物被封装在乳剂中，在ADV时释放。中心假设是ADV可以用来在植入的组织支架内时空控制包裹的bFGF和PDGF-BB的释放。这项研究的基本原理是，ADV可以顺序释放碱性成纤维细胞生长因子和PDGF-BB，当同时呈现时显示出相互拮抗，而当呈现顺序呈现时则协同促进血管生长。在强劲的初步数据指导下，这一假设将通过三个具体目标进行验证：1)开发具有不同释放阈值的声学敏感乳剂配方；2)证明在超声触发释放bFGF后，皮下植入的复合支架中有血管生长；以及3)在血管损伤部位连续释放bFGF和PDGF-BB后，在缺血后肢模型中证实血管生长抑制。总体而言，在第一个目标中优化的两个生长因子传递系统将分别在第二个和第三个目标中使用异位和原位模型进行体内评估。这些研究的成功完成具有重要意义，因为血管生成生长因子的控制释放和支架内随后的血管形成有望促进工程组织的临床转化。归根结底，这种超声响应支架系统是一种平台技术，可以在空间和时间上控制对组织再生和整合至关重要的其他再生生长因子的释放。

DESCRIPTION: The viability, and hence clinical utility of an engineered tissue implant relies on rapid integration with the blood supply of the recipient. Angiogenic growth factors including basic fibroblast growth factor (bFGF) and platelet- derived growth factor-BB (PDGF-BB) are critical regulators of vascular invasion. During wound healing, these growth factors exhibit spatially- and temporally-restricted patterns of expression. The administration of angiogenic growth factors by conventional methods has yielded limited success in promoting clinically-relevant vascular responses to implants - in part because these methods provide minimal control over the timing and localization of growth factor activity. The long-term goal is to use ultrasound to actively control cellular behavior - such as migration, survival, proliferation, and differentiatio - involved in tissue regeneration thus enhancing construct viability and functionality. Ultrasound is ideally suited to modulate cellular activities within implanted scaffolds since it can be applied non-invasively, focused with sub-millimeter precision, delivered in a spatio-temporally controlled manner to sites deep within the body, and translated clinically. The objective of this application is to use ultrasound - specifically a mechanism termed acoustic droplet vaporization (ADV) - to generate tightly controlled vascularization within an implanted tissue scaffold via the controlled release of angiogenic growth factors. ADV is a phenomenon whereby emulsified liquid droplets are converted into gas bubbles upon exposure to ultrasound above a certain acoustic amplitude. Therapeutic agents, encapsulated within the emulsion, are released upon ADV. The central hypothesis is that ADV can be used to spatio- temporally control the release of encapsulated bFGF and PDGF-BB within an implanted tissue scaffold. The rationale for the proposed research is that ADV enables the sequential release of bFGF and PDGF-BB, which exhibit mutual antagonism when presented simultaneously but synergistically enhance vascular growth when presented sequentially. Guided by strong preliminary data, the hypothesis will be tested via three specific aims: 1) Develop acoustically-sensitive emulsion formulations with distinct release thresholds; 2) Demonstrate vascular in-growth in a subcutaneously implanted composite scaffold following the ultrasound-triggered release of bFGF; and 3) Demonstrate vascular in-growth in an ischemic hind limb model following the sequential release of bFGF and PDGF-BB at the site of vascular injury. Overall, the two growth factor delivery system optimized in the first aim will be evaluated in vivo using ectopic and orthotopic models in the second and third aims, respectively. Successful completion of these studies is significant since controlled release of angiogenic growth factors and subsequent vascularization within scaffolds is expected to facilitate the clinical translation of engineered tissue. Ultimately, this ultrasound-responsive scaffold system is a platform technology that could enable spatial and temporal control over the release of other regenerative growth factors critical for tissue regeneration and integration.