A method of characterising the complex anatomy of vascular occlusions and 3D printing biomimetic analogues.

Chronic total occlusions (CTOs) occur in approximately 40% of individuals with symptomatic peripheral arterial disease and are indicative of critical limb ischaemia. Currently, few medical devices can effectively treat CTOs long-term, with amputation often required. This is due to a lack of knowledge of CTO anatomy, making device design and testing difficult. This study is a proof-of-concept study, which aimed to develop a workflow for further characterising the complex multi-material anatomy of CTOs and creating 3D models of CTO components, which may be useful in producing a vascular CTO biomimetic for device testing. Here, we establish such a workflow using samples of atheromatous plaques. We focus on a high-resolution, non-destructive microcomputed tomography (µCT) technique which enables visualisation of occlusion anatomy at a greater resolution than computed tomography angiography (CTA), which is the typical modality used for CTO clinical visualisation. Four arteries (n = 2 superficial femoral; n = 2 popliteal) with evidence of atheromatous plaques were cut into 8 cm segments, which were then stained with iodine and scanned at low resolution, with calcified regions rescanned at high resolution. Resulting files were manually segmented to generate 3D models, which were then 3D printed in resin using a stereolithography printer to produce parts suitable for creating a biomimetic. In total, µCT files from three arterial segments (n = 2 high resolution, n = 1 low resolution) were deemed suitably calcified for segmentation, and thus were segmented to produce 3D models. 3D models of the arterial wall, intima and atheromatous calcium deposits from a high-resolution popliteal artery scan were successfully 3D printed at several scales. While this research is at an early stage, it holds great promise. The workflow for segmentation and 3D printing various components of an atheromatous plaque established here is replicable and uses software and equipment which are accessible to research laboratories in both academia and industry. The ability to print detailed models on a desktop 3D printer is unprecedented and can be improved further, which is promising for future development of biomimetics with multi-material detail of both soft tissue and calcified components of a vascular occlusion. Indeed, this workflow provides a solid foundation for future studies of CTO anatomy and the creation of true, multi-material CTO biomimetics. Such biomimetics may enable the development of improved interventional devices, as they would mimic the general in vivo CTO environment. As this method cannot be applied in vivo, we cannot yet produce patient-specific biomimetics, however, these analogues would still be important in device development, which would improve patient outcomes in critical limb ischaemia.

Exploring therapy transport from implantable medical devices using experimentally informed computational methods.

Implantable medical devices that can facilitate therapy transport to localized sites are being developed for a number of diverse applications, including the treatment of diseases such as diabetes and cancer, and tissue regeneration after myocardial infraction. These implants can take the form of an encapsulation device which encases therapy in the form of drugs, proteins, cells, and bioactive agents, in semi-permeable membranes. Such implants have shown some success but the nature of these devices pose a barrier to the diffusion of vital factors, which is further exacerbated upon implantation due to the foreign body response (FBR). The FBR results in the formation of a dense hypo-permeable fibrous capsule around devices and is a leading cause of failure in many implantable technologies. One potential method for overcoming this diffusion barrier and enhancing therapy transport from the device is to incorporate local fluid flow. In this work, we used experimentally informed inputs to characterize the change in the fibrous capsule over time and quantified how this impacts therapy release from a device using computational methods. Insulin was used as a representative therapy as encapsulation devices for Type 1 diabetes are among the most-well characterised. We then explored how local fluid flow may be used to counteract these diffusion barriers, as well as how a more practical pulsatile flow regimen could be implemented to achieve similar results to continuous fluid flow. The generated model is a versatile tool toward informing future device design through its ability to capture the expected decrease in insulin release over time resulting from the FBR and investigate potential methods to overcome these effects.

Soft robotic platform for progressive and reversible aortic constriction in a small-animal model.

Our understanding of cardiac remodeling processes due to left ventricular pressure overload derives largely from animal models of aortic banding. However, these studies fail to enable control over both disease progression and reversal, hindering their clinical relevance. Here, we describe a method for progressive and reversible aortic banding based on an implantable expandable actuator that can be finely tuned to modulate aortic banding and debanding in a rat model. Through catheterization, imaging, and histologic studies, we demonstrate that our platform can recapitulate the hemodynamic and structural changes associated with pressure overload in a controllable manner. We leveraged soft robotics to enable noninvasive aortic debanding, demonstrating that these changes can be partly reversed because of cessation of the biomechanical stimulus. By recapitulating longitudinal disease progression and reversibility, this animal model could elucidate fundamental mechanisms of cardiac remodeling and optimize timing of intervention for pressure overload.

Soft robotic platform for controlled, progressive and reversible aortic constriction in a small animal model.

Our understanding of cardiac remodeling processes due to left ventricular pressure overload derives largely from animal models of aortic banding. However, these studies fail to simultaneously enable control over disease progression and reversal, hindering their clinical relevance. Here, we describe a method for controlled, progressive, and reversible aortic banding based on an implantable expandable actuator that can be finely controlled to modulate aortic banding and debanding in a rat model. Through catheterization, imaging, and histologic studies, we demonstrate that our model can recapitulate the hemodynamic and structural changes associated with pressure overload in a controllable manner. We leverage the ability of our model to enable non-invasive aortic debanding to show that these changes can be partly reversed due to cessation of the biomechanical stimulus. By recapitulating longitudinal disease progression and reversibility, this model could elucidate fundamental mechanisms of cardiac remodeling and optimize timing of intervention for pressure overload.

Soft robot-mediated autonomous adaptation to fibrotic capsule formation for improved drug delivery.

The foreign body response impedes the function and longevity of implantable drug delivery devices. As a dense fibrotic capsule forms, integration of the device with the host tissue becomes compromised, ultimately resulting in device seclusion and treatment failure. We present FibroSensing Dynamic Soft Reservoir (FSDSR), an implantable drug delivery device capable of monitoring fibrotic capsule formation and overcoming its effects via soft robotic actuations. Occlusion of the FSDSR porous membrane was monitored over 7 days in a rodent model using electrochemical impedance spectroscopy. The electrical resistance of the fibrotic capsule correlated to its increase in thickness and volume. Our FibroSensing membrane showed great sensitivity in detecting changes at the abiotic/biotic interface, such as collagen deposition and myofibroblast proliferation. The potential of the FSDSR to overcome fibrotic capsule formation and maintain constant drug dosing over time was demonstrated in silico and in vitro. Controlled closed loop release of methylene blue into agarose gels (with a comparable fold change in permeability relating to 7 and 28 days in vivo) was achieved by adjusting the magnitude and frequency of pneumatic actuations after impedance measurements by the FibroSensing membrane. By sensing fibrotic capsule formation in vivo, the FSDSR will be capable of probing and adapting to the foreign body response through dynamic actuation changes. Informed by real-time sensor signals, this device offers the potential for long-term efficacy and sustained drug dosing, even in the setting of fibrotic capsule formation.

Dynamic actuation enhances transport and extends therapeutic lifespan in an implantable drug delivery platform.

Fibrous capsule (FC) formation, secondary to the foreign body response (FBR), impedes molecular transport and is detrimental to the long-term efficacy of implantable drug delivery devices, especially when tunable, temporal control is necessary. We report the development of an implantable mechanotherapeutic drug delivery platform to mitigate and overcome this host immune response using two distinct, yet synergistic soft robotic strategies. Firstly, daily intermittent actuation (cycling at 1 Hz for 5 minutes every 12 hours) preserves long-term, rapid delivery of a model drug (insulin) over 8 weeks of implantation, by mediating local immunomodulation of the cellular FBR and inducing multiphasic temporal FC changes. Secondly, actuation-mediated rapid release of therapy can enhance mass transport and therapeutic effect with tunable, temporal control. In a step towards clinical translation, we utilise a minimally invasive percutaneous approach to implant a scaled-up device in a human cadaveric model. Our soft actuatable platform has potential clinical utility for a variety of indications where transport is affected by fibrosis, such as the management of type 1 diabetes.

A versatile technique for high-resolution three-dimensional imaging of human arterial segments using microcomputed tomography.

BACKGROUND: Quantitative methods for evaluating microstructure of arterial specimens typically rely on histologic techniques that involve random sampling, which cannot account for the unique spatial distribution of features in three dimensions. METHODS: To overcome this limitation, we demonstrate a nondestructive method for three-dimensional imaging of intact human blood vessels using microcomputed tomography (microCT). Human artery segments were dehydrated and stained in an iodine solution then imaged with a standard laboratory microCT scanner. Image visualization and segmentation was performed using commercially available and open source software. RESULTS: Staining of cadaveric vessels with iodine enabled clear visualization of the arterial wall with microCT, preserved tissue morphology, and generated high-resolution images with a voxel size of 5.4 µm. Various components of the arterial wall were segmented using a combination of manual and automatic thresholding algorithms. CONCLUSIONS: Our approach allows for spatial mapping of human artery tissue samples that can guide targeted histologic analysis of smaller tissue segments, provide geometric data to inform finite element models, quantify degree of atherosclerosis, and help to evaluate the foreign body response to intravascular medical implants. (JVS-Vascular Science 2020;2:13-19.). CLINICAL RELEVANCE: In this article, we describe a powerful technique for whole artery analysis of pathologic human tissue specimens that provides high-resolution spatial detail regarding composition of the blood vessel wall. The protocol described here is a valuable adjunct that can be used as a research tool to inform finite element modeling of arteries, quantify pathologic response (ie, neointimal hyperplasia and vascular calcification), and evaluate the tissue/device interface of implanted medical devices.

The Foreign Body Response to an Implantable Therapeutic Reservoir in a Diabetic Rodent Model.

Advancements in type 1 diabetes mellitus treatments have vastly improved in recent years. The move toward a bioartificial pancreas and other fully implantable systems could help restore patient's glycemic control. However, the long-term success of implantable medical devices is often hindered by the foreign body response. Fibrous encapsulation "walls off" the implant to the surrounding tissue, impairing its functionality. In this study we aim to examine how streptozotocin-induced diabetes affects fibrous capsule formation and composition surrounding implantable drug delivery devices following subcutaneous implantation in a rodent model. After 2 weeks of implantation, the fibrous capsule surrounding the devices were examined by means of Raman spectroscopy, micro-computed tomography (µCT), and histological analysis. Results revealed no change in mean fibrotic capsule thickness between diabetic and healthy animals as measured by µCT. Macrophage numbers (CCR7 and CD163 positive) remained similar across all groups. True component analysis also showed no quantitative difference in the alpha-smooth muscle actin and extracellular matrix proteins. Although principal component analysis revealed significant secondary structural difference in collagen I in the diabetic group, no evidence indicates an influence on fibrous capsule composition surrounding the device. This study confirms that diabetes did not have an effect on the fibrous capsule thickness or composition surrounding our implantable drug delivery device. Impact Statement Understanding the impact diabetes has on the foreign body response (FBR) to our implanted material is essential for developing an effective drug delivery device. We used several approaches (Raman spectroscopy and micro-computed tomography imaging) to demonstrate a well-rounded understanding of the diabetic impact on the FBR to our devices, which is imperative for its clinical translation.

Additive Manufacturing of Multi-Scale Porous Soft Tissue Implants That Encourage Vascularization and Tissue Ingrowth.

Medical devices, such as silicone-based prostheses designed for soft tissue implantation, often induce a suboptimal foreign-body response which results in a hardened avascular fibrotic capsule around the device, often leading to patient discomfort or implant failure. Here, it is proposed that additive manufacturing techniques can be used to deposit durable coatings with multiscale porosity on soft tissue implant surfaces to promote optimal tissue integration. Specifically, the "liquid rope coil effect", is exploited via direct ink writing, to create a controlled macro open-pore architecture, including over highly curved surfaces, while adapting atomizing spray deposition of a silicone ink to create a microporous texture. The potential to tailor the degree of tissue integration and vascularization using these fabrication techniques is demonstrated through subdermal and submuscular implantation studies in rodent and porcine models respectively, illustrating the implant coating's potential applications in both traditional soft tissue prosthetics and active drug-eluting devices.

Implantable Therapeutic Reservoir Systems for Diverse Clinical Applications in Large Animal Models.

Regenerative medicine approaches, specifically stem cell technologies, have demonstrated significant potential to treat a diverse array of pathologies. However, such approaches have resulted in a modest clinical benefit, which may be attributed to poor cell retention/survival at the disease site. A delivery system that facilitates regional and repeated delivery to target tissues can provide enhanced clinical efficacy of cell therapies when localized delivery of high doses of cells is required. In this study, a new regenerative reservoir platform (Regenervoir) is described for use in large animal models, with relevance to cardiac, abdominal, and soft tissue pathologies. Regenervoir incorporates multiple novel design features essential for clinical translation, with a focus on scalability, mechanism of delivery, fixation to target tissue, and filling/refilling with a therapeutic cargo, and is demonstrated in an array of clinical applications that are easily translated to human studies. Regenervoir consists of a porous reservoir fabricated from a single material, a flexible thermoplastic polymer, capable of delivering cargo via fill lines to target tissues. A radiopaque shear thinning hydrogel can be delivered to the therapy reservoir and multiple fixation methods (laparoscopic tacks and cyanoacrylate bioadhesive) can be used to secure Regenervoir to target tissues through a minimally invasive approach.