Leveraging 3D Bioprinting and Photon-Counting Computed Tomography to Enable Noninvasive Quantitative Tracking of Multifunctional Tissue Engineered Constructs

3D bioprinting is revolutionizing the fields of personalized and precision medicine by enabling the manufacturing of bioartificial implants that recapitulate the structural and functional characteristics of native tissues. However, the lack of quantitative and noninvasive techniques to longitudinally track the function of implants has hampered clinical applications of bioprinted scaffolds. In this study, multimaterial 3D bioprinting, engineered nanoparticles (NPs), and spectral photon-counting computed tomography (PCCT) technologies are integrated for the aim of developing a new precision medicine approach to custom-engineer scaffolds with traceability. Multiple CT-visible hydrogel-based bioinks, containing distinct molecular (iodine and gadolinium) and NP (iodine-loaded liposome, gold, methacrylated gold (AuMA), and Gd2 O3 ) contrast agents, are used to bioprint scaffolds with varying geometries at adequate fidelity levels. In vitro release studies, together with printing fidelity, mechanical, and biocompatibility tests identified AuMA and Gd2 O3 NPs as optimal reagents to track bioprinted constructs. Spectral PCCT imaging of scaffolds in vitro and subcutaneous implants in mice enabled noninvasive material discrimination and contrast agent quantification. Together, these results establish a novel theranostic platform with high precision, tunability, throughput, and reproducibility and open new prospects for a broad range of applications in the field of precision and personalized regenerative medicine.

Abstract 258: Mir-155 Mitigates Acute Oscillatory Shear Stress (OSS)-Induced Vascular Inflammation and Barrier Dysfunction Through Down Regulation of the AT1R-ETS1 Pathway

Introduction: Shear stress forces play an integral role in dictating the vascular wall response to changes in blood flow, induction of pro-inflammatory response and hence development of atherosclerosis. Previously, our group and others have identified an inverse relationship between microRNA-155 (miR-155) and AT1R expression and/or activity in atheroprone areas of chronic low magnitude oscillatory shear stress (OSS) in vasculature and in-vitro.

Hypothesis: we hypothesized that acute induction of OSS mediates vascular inflammation and dysfunction, via activation of the AT1R-ETS1 pathway and dysregulation of miR-155.

Methods: 12-week old C57B/6J mice were subjected to abdominal aortic coarctation (AAC), a unique model of acute induction of acute OSS, for 3 days. Downstream segments of acute OSS were compared to upstream unidirectional shear stress (USS) segments of the thoracic aorta using RT-PCR, western blot analysis and unpaired student t-test.

Results: Acute OSS resulted in vascular inflammation evidenced by upregulation of the AT1R-ETS1 pathway and several of its downstream targets including phosphorylated ERK2, MCP-1 and VCAM-1 in OSS segments compared with USS. This was associated with loss of EC barrier function as evaluated by extravasation of Evans-blue dye assay along with increased expression of MMP3 and MMP9 in in OSS segments compared with USS. However, vascular miR-155 expression was also higher in OSS segments compared with USS (n=6-12, P<0.05). Nevertheless, tail vein injections of miR-155 overexpressing lentivirus particles after AAC resulted in further upregulation of miR-155 expression and inverse downregulation of the AT1R-ETS1 pro-inflammatory pathway and MMPs 3 and 9 expression in OSS segments compared with USS versus scramble control (n=5-6, P<0.05).

Conclusions: Despite the early upregulation of the shear-sensitive miR-155, our data suggest that it could serve as a negative feedback regulator to acute OSS-induced upregulation of the pro-inflammatory AT1R-ETS1 pathway. Further studies are in progress to evaluate the effect of exogenous miR-155 on OSS-induced oxidative stress and vascular dysfunction, which can serve as the basis for developing novel miRNA-based therapeutic modalities.

Development of a Novel Small Animal Ankle Arthrodesis Model

Category:

Basic Sciences/Biologics

Introduction/Purpose:

Ankle arthrodesis is performed for a variety of ankle joint pathology with the most common being post traumatic arthritis. It is estimated that there are nearly twenty-five thousand ankle fusions performed annually in the United States. Reported complication rates vary between studies and patient population characteristics and comorbidities. Our understanding of the biology of ankle arthrodesis is based largely upon spine fusion and long bone animal models. However, bony healing and infection is greatly influenced by local soft tissue and vascular anatomy, therefore the application of data from these models may not be entirely accurate. There is currently no small animal ankle fusion model. Accordingly, the purpose of this study is to develop a reliable small animal ankle arthrodesis model.

Methods:

A total of twenty Lewis rats were included in this study. Ankle arthrodesis was performed on one extremity of fourteen rats with the other ankle serving as an internal control. An anterior approach was used to expose the tibiotalar joint. Careful technique was utilized to protect neurovascular structures. After adequate joint exposure, a power burr and sharp curette was used to remove joint cartilage. A .042 kirschner wire was then passed through the calcaneus and through the subtalar and tibiotalar joint. Six rats served as controls and their procedures did not involve any joint cartilage removal. Radiographs were taken immediately postoperatively and at 8 weeks. Bony healing was assessed in a blinded fashion by a board certified foot and ankle orthopaedic surgeon using a grading system based upon assessment of cortical bridging and joint space.

Results:

Sixteen rats – eleven fusions and five controls - underwent the procedure without any perioperative complications and were included in analysis. Four rats were excluded due to a perioperative complication and/or death. The most common postoperative complication encountered was a wound complication (n=3). Of the eleven rats in the fusion group, six (55%) were determined to be fused radiographically. Two of the five controls were radiographically fused (40%).

Conclusion:

This study demonstrates preliminary data from a novel small animal ankle arthrodesis model. Fifty-five percent of the rats in the fusion group fused based on radiographic evaluation at eight weeks postoperatively. Further work involves improving upon the surgical technique for fusion in this small animal model to help increase fusion rates, and using CT scans and biomechanical testing to further assess fusion. The development of a small animal ankle fusion model will enhance our understanding of the biology of ankle arthrodesis and allow for development of novel therapies aimed at increasing fusion rates and decreasing complications.

Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.