Upcycling plastic waste into fully recyclable composites through cold sintering

Plastics have substantial societal benefits, but their widespread use has led to a critical waste management challenge. While mechanical recycling dominates the reuse of post-consumer plastics, it is limited in efficacy, especially for composites. To address this, we propose a direct reprocessing approach that enables the creation of hybrid, long-lasting, and durable composites from difficult-to-recycle plastics. This approach utilizes cold sintering, a process that consolidates inorganic powders through fractional dissolution and precipitation at temperatures far below conventional sintering; these temperatures are compatible with plastic processing. We show that this process can create inorganic-matrix composites with significant enhancements in tensile strength and toughness over pure gypsum, which is commonly found in construction waste. These composites can be recycled multiple times through direct reprocessing with the addition of only water as a processing promoter. This approach to recycling leads to composites with orders of magnitude lower energy demand, global warming potential, and water demand, when compared against common construction products. Altogether, we demonstrate the potential for cold sintering to integrate waste into high-performance recyclable composites.

Accelerating Patterned Vascularization Using Granular Hydrogel Scaffolds and Surgical Micropuncture

Bulk hydrogel scaffolds are common in reconstructive surgery. They allow for the staged repair of soft tissue loss by providing a base for revascularization. Unfortunately, they are limited by both slow and random vascularization, which may manifest as treatment failure or suboptimal repair. Rapidly inducing patterned vascularization within biomaterials has profound translational implications for current clinical treatment paradigms and the scaleup of regenerative engineering platforms. To address this long-standing challenge, a novel microsurgical approach and granular hydrogel scaffold (GHS) technology are co-developed to hasten and pattern microvascular network formation. In surgical micropuncture (MP), targeted recipient blood vessels are perforated using a microneedle to accelerate cell extravasation and angiogenic outgrowth. By combining MP with an adjacent GHS with precisely tailored void space architecture, microvascular pattern formation as assessed by density, diameter, length, and intercapillary distance is rapidly guided. This work opens new translational opportunities for microvascular engineering, advancing reconstructive surgery, and regenerative medicine.

A245 A TERTIARY CENTRE REVIEW OF PORTO-SYSTEMIC SHUNTS: AN INCREASINGLY IMPORTANT TOOL IN LIVER DISEASE MANAGEMENT

Background

Portal hypertensive complications arising from chronic liver disease are increasingly prevalent. Radiologically placed porto-systemic shunts are used successfully to address complications such as ascites and recurrent variceal bleeding.

Purpose

We sought, with approval from ethics to electronically chart review the UHN experience for TIPSS (transjugular intrahepatic porto-systemic shunt) and DIPS (direct intrahepatic porto-caval shunt) over time.

Method

We employed a search strategy focused on radiologic databases, to identify UHN patients who had received a porto-systemic shunt insertion over three decades between January 1, 1990, to September 14, 2021. A total of 238 UHN patients that had a shunt imaged, re-assessed, or inserted were included in this retrospective electronic chart review. Demographic information was recorded at baseline. Data pertaining to clinical outcomes of portal hypertension such as refractory ascites, recurrent gastrointestinal bleeding and ESLD progression was recorded at baseline, 1 month, 3 months and 6 months post-shunt insertion. HVPG was recorded pre-shunt and post-shunt insertion. Transplant-free survival and post-operative complications was also assessed. Patients were followed until death or liver transplant.

Result(s)

Out of 238 patients confirmed, 219 had a TIPSS insertion and 19 a DIPS insertion. The average age at time of shunt was 55.1 ± 8.4 years. 53.7% (n=128) of patients were male. Indications for portosystemic shunt placement included refractory ascites (n=141), recurrent gastrointestinal bleeding (n=73), hydrothorax (n=10), hepatorenal syndrome (n=8), and portal vein thrombosis (n=4). Etiology of disease was categorized as alcohol-associated liver disease (n=107), non-alcohol associated fatty liver disease (n=36), viral hepatitis (n=27), autoimmune hepatitis (n=38) and vascular liver disease (n=20). Relevant events noted post procedure included hepatic encephalopathy (n=34), hydrothorax (n=17), vascular (including stent) thrombosis (n=17) and renal failure (n=4). 12 months post-shunt insertion 2.5% (n=6) of patients had died or received liver transplant; of these 1.7% (n=4) were transplanted. HPVG fell consistently post-procedure: 15.6 ± 1.5mmHg pre-shunt to 5.9 ± 1.2mmHg post-shunt. There was no observable increase in MELD-Na score in the first month post-shunt. Temporal trends showed that more patients aged 50 to 69, and more female patients, are now receiving shunt insertion than at the initiation of the chart review.

Image

Conclusion(s)

Portosystemic shunt placement in the form of TIPSS or DIPS insertion is an increasingly common and effective treatment for portal hypertension in patents with advanced liver disease at UHN.

Disclosure of Interest

None Declared

Gelatin Methacryloyl Granular Hydrogel Scaffolds: High-throughput Microgel Fabrication, Lyophilization, Chemical Assembly, and 3D Bioprinting

The emergence of granular hydrogel scaffolds (GHS), fabricated via assembling hydrogel microparticles (HMPs), has enabled microporous scaffold formation in situ. Unlike conventional bulk hydrogels, interconnected microscale pores in GHS facilitate degradation-independent cell infiltration as well as oxygen, nutrient, and cellular byproduct transfer. Methacryloyl-modified gelatin (GelMA), a (photo)chemically crosslinkable, protein-based biopolymer containing cell adhesive and biodegradable moieties, has widely been used as a cell-responsive/instructive biomaterial. Converting bulk GelMA to GHS may open a plethora of opportunities for tissue engineering and regeneration. In this article, we demonstrate the procedures of high-throughput GelMA microgel fabrication, conversion to resuspendable dry microgels (micro-aerogels), GHS formation via the chemical assembly of microgels, and granular bioink fabrication for extrusion bioprinting. We show how a sequential physicochemical treatment via cooling and photocrosslinking enables the formation of mechanically robust GHS. When light is inaccessible (e.g., during deep tissue injection), individually crosslinked GelMA HMPs may be bioorthogonally assembled via enzymatic crosslinking using transglutaminases. Finally, three-dimensional (3D) bioprinting of microporous GHS at low HMP packing density is demonstrated via the interfacial self-assembly of heterogeneously charged nanoparticles.

An equivalent circuit model for localized electroporation on porous substrates

In vitro intracellular delivery is a fundamental challenge with no widely adopted methods capable of both delivering to millions of cells and controlling that delivery to a high degree of accuracy. One promising method is porous substrate electroporation (PSEP), where cells are cultured on porous substrates and electric fields are used to permeabilize discrete portions of the cell membrane for delivery. A major obstacle to the widespread use of PSEP is a poor understanding of the various impedances that constitute the system, including the impedances of the porous substrate and the cell monolayer, and how these impedances are influenced by experimental parameters. In response, we used impedance measurements to develop an equivalent circuit model that closely mimics the behavior of each of the main components of the PSEP system. This circuit model reveals for the first time the distribution of voltage across the electrode-electrolyte interface impedances, the channels of the porous substrate, the cell monolayer, and the transmembrane potential during PSEP. We applied sample waveforms through our model to understand how waveforms can be improved for future studies. Our model was validated from intracellular delivery of protein using PSEP.

A228 WHEN ASCITES & VARICEAL BLEEDING ARE NOT FROM CIRRHOSIS: A CASE OF MUTIPLE ARTERIOPORTAL FISTULAE CAUSING PORTAL HYPERTENSION

Background

Portal hypertension is usually due to increased resistance from cirrhosis. However, pressures can also be elevated due to increased flow.

Aims

To describe a peculiar case of non-cirrhotic portal hypertension.

Methods

A case report and literature review was performed.

Results

A 47-year-old previously well man presented with a 6 month history of rapidly progressive weight loss, ascites and variceal bleed. Workup ruled out common causes of primary liver disease. Initial imaging demonstrated a heterogenous liver, splenomegaly, ascites, patent hepatic/portal veins and multiple poorly defined low-density hepatic lesions with the largest measuring 2.1 cm. Transient elastography was 7.3 kPa (F1-mild fibrosis). At transjugular liver biopsy, hepatic venogram ruled out Budd-Chiari and hepatic vein pressure gradient was normal at 3–4 mmHg. Histology unfortunately showed hemangioma. A percutaneous liver biopsy suggested nodular regenerative hyperplasia, minimal fibrosis and mild cholestasis. Given worsening ascites, hyponatremia and 7 months of rapidly progressive decline, transjugular intrahepatic portosystemic shunt (TIPSS) was inserted. Intra-procedure, portal vein pressure was noted to be 51 mmHg, with a portosystemic gradient of 42 mmHg. Although numerous abdominal CT and MRI did not show AV shunting, ultrasound post-TIPSS showed hepatic pseudoaneurysms & arterioportal fistulae (APF). Direct angiogram showed numerous hepatic pseudoaneurysms and intrahepatic fistulae making embolization impossible. CT showed no evidence of pseudoaneurysms or fistulae outside of the liver. Workup for autoimmune rheumatological diseases and congenital telangiectatic syndromes were negative. Given the high pressures being directed through the new TIPSS, right heart failure is an ongoing concern.

APF are rarely encountered causes of presinusoidal portal hypertension, with communications most commonly arising from the hepatic (65%) & splenic arteries (11%) & the portal vein. Causes include traumatic (28%), iatrogenic (16%), vascular/telangiectatic malformations (15%), tumors (15%), aneurysms (14%) & congenital disease. Endovascular embolization can be used to treat single lesions. In complex cases with mulitple APF, surgery and/or liver transplantation may be required.

Conclusions

We report a rare case of non-cirrhotic portal hypertension due to increased flow rather than increased resistance secondary to APF.

Funding Agencies

None

Comparison of transarterial bland and chemoembolization for neuroendocrine tumours: a systematic review and meta-analysis

Background

Treatment of hepatic metastases from neuroendocrine tumours improves survival and symptom relief. Hepatic arterial embolotherapy techniques include transarterial chemoembolization (tace) and bland embolization (tae). The relative efficacy of the techniques is controversial. The purpose of the present study was to use a meta-analysis and systematic review to compare tace with tae in the treatment of hepatic metastases.

Methods

A literature search identified studies comparing tace and tae for treatment of hepatic metastases. Outcomes of interest included overall survival (os), progression-free survival (pfs), radiographic response, complications, and symptom control. The hazard ratios (hrs) and odds ratios (ors) were estimated and pooled.

Results

Eight studies and 504 patients were included. No statistically significant differences between tace and tae were observed for os at 1, 2, and 5 years or for hrs [1-year or: 0.72; 95% confidence interval (ci): 0.27 to 1.94; p < 0.52; 2-year or: 0.69; 95% ci: 0.43 to 1.11; p < 0.12; 5-year or: 0.91; 95% ci: 0.37 to 2.24; p < 0.85; hr: 0.96; 95% ci: 0.73 to 1.24; p < 0.74]. No statistically significant differences between tace and tae were observed for pfs at 1, 2, and 5 years or for hrs (1-year or: 0.71; 95% ci: 0.38 to 1.55; p < 0.30; 2-year or: 0.83; 95% ci: 0.33 to 2.06; p < 0.69; 5-year or: 0. 91; 95% ci: 0.37 to 2.24; p < 0.85; hr: 0.99-1.74; 95% ci: 0.74 to 1.73; p < 0.97). Both techniques are safe and effective for symptom control.

Conclusions

No statistically significant differences between tace and tae were observed for os and pfs.

High Throughput and Highly Controllable Methods for In Vitro Intracellular Delivery

In vitro and ex vivo intracellular delivery methods hold the key for releasing the full potential of tissue engineering, drug development, and many other applications. In recent years, there has been significant progress in the design and implementation of intracellular delivery systems capable of delivery at the same scale as viral transfection and bulk electroporation but offering fewer adverse outcomes. This review strives to examine a variety of methods for in vitro and ex vivo intracellular delivery such as flow-through microfluidics, engineered substrates, and automated probe-based systems from the perspective of throughput and control. Special attention is paid to a particularly promising method of electroporation using micro/nanochannel based porous substrates, which expose small patches of cell membrane to permeabilizing electric field. Porous substrate electroporation parameters discussed include system design, cells and cargos used, transfection efficiency and cell viability, and the electric field and its effects on molecular transport. The review concludes with discussion of potential new innovations which can arise from specific aspects of porous substrate-based electroporation platforms and high throughput, high control methods in general.

Microfluidic Systems with Embedded Cell Culture Chambers for High-Throughput Biological Assays

The ability to generate chemical and mechanical gradients on chips is important for either creating biomimetic designs or enabling high-throughput assays. However, there is still a significant knowledge gap in the generation of mechanical and chemical gradients in a single device. In this study, we developed gradient-generating microfluidic circuits with integrated microchambers to allow cell culture and to introduce chemical and mechanical gradients to cultured cells. A chemical gradient is generated across the microchambers, exposing cells to a uniform concentration of drugs. The embedded microchamber also produces a mechanical gradient in the form of varied shear stresses induced upon cells among different chambers as well as within the same chamber. Cells seeded within the chambers remain viable and show a normal morphology throughout the culture time. To validate the effect of different drug concentrations and shear stresses, doxorubicin is flowed into chambers seeded with skin cancer cells at different flow rates (from 0 to 0.2 μL/min). The experimental results show that increasing doxorubicin concentration (from 0 to 30 μg/mL) within chambers not only prohibits cell growth but also induces cell death. In addition, the increased shear stress (0.005 Pa) at high flow rates poses a synergistic effect on cell viability by inducing cell damage and detachment. Moreover, the ability of the device to seed cells in a 3D microenvironment was also examined and confirmed. Collectively, the study demonstrates the potential of microchamber-embedded microfluidic gradient generators in 3D cell culture and high-throughput drug screening.

Microfluidic Device for Localized Electroporation

Electroporation is a common method of transfection due to its relatively low risk and high transfection efficiency. The most common method of electroporation is bulk electroporation which is easily performed on large quantities of cells yet results in variable levels of viability and transfection efficiency across the population. Localized electroporation is an alternative that can be administered on a similar scale but results in much more consistent with higher quality transfection and higher cell viability. This chapter discusses the creation and use of a simple and cost-effective device using porous membrane for performing localized electroporation.

3D-Printed Sugar-Based Stents Facilitating Vascular Anastomosis

Microvascular anastomosis is a common part of many reconstructive and transplant surgical procedures. While venous anastomosis can be achieved using microvascular anastomotic coupling devices, surgical suturing is the main method for arterial anastomosis. Suture-based microanastomosis is time-consuming and challenging. Here, dissolvable sugar-based stents are fabricated as an assistive tool for facilitating surgical anastomosis. The nonbrittle sugar-based stent holds the vessels together during the procedure and are dissolved upon the restoration of the blood flow. The incorporation of sodium citrate minimizes the chance of thrombosis. The dissolution rate and the mechanical properties of the sugar-based stent can be tailored between 4 and 8 min. To enable the fabrication of stents with desirable geometries and dimensions, 3D printing is utilized to fabricate the stents. The effectiveness of the printed sugar-based stent is assessed ex vivo. The fabrication procedure is fast and can be performed in the operating room.

Which G-Tube to Use in Pullers: Assessment of Pull Pressures on Skin Models to Determine Optimal Catheter Choice in Patients with Recurrent Pulled Gastrostomy Tubes

INTRODUCTION

Pulled or dislodged gastrostomy catheters represent a common complication associated with percutaneous gastrostomy and are a common cause of recurrent visits in patients with altered mental status. We intended to perform an experiment to compare the pull forces required to dislodge different commonly used gastrostomy catheters.

MATERIALS AND METHODS

We used a digital force gauge device to measure the pull forces required to dislodge three types of 20 French gastrostomy catheters in double-layer skin models. These included the Flow 20 Pull Method (Cook Medical, Bloomington, IN, USA), Entuit Gastrostomy BR Balloon Retention feeding tube (Cook Medical, Bloomington, IN, USA), and Ponsky Non-Balloon Replacement Gastrostomy Tube (CR Bard Inc, Salt Lake City, Utah, USA). The catheters were inserted into the skin model using the same technique as would be utilized in a patient.

RESULTS

The mean forces measured to dislodge the per-oral Flow 20 Pull Method, Entuit Thrive Balloon Retention, and button-type retention Ponsky replacement catheters were 35.6, 22.8, and 20.6 Newtons, respectively. The pull method per-oral gastrostomy catheter required significantly more pull force to dislodge than both the Ponsky button-type retention catheter and the Entuit balloon retention catheters. There was no significant difference in the pull force required to dislodge the Ponsky replacement catheter and the Entuit balloon retention catheter.

CONCLUSIONS

Per-oral image-guided gastrostomy with pull-method button-type retention catheters may be the ideal choice in patients at high risk of tube dislodgment.

Risk Factors for the Development of Cephalic Arch Stenosis

Purpose

The creation of a vascular access is necessary in hemodialysis patients, including those with marginal vessels. Upper arm fistulae are attractive due to the ease of creation and of achieving high access flow rates. Cephalic arch stenosis (CAS) can lead to failure of upper arm fistulae and is increasingly identified. We hypothesized that CAS is promoted by high blood flow rates, brachiocephalic fistulae, and an angle of cephalic vein insertion approaching 90 degrees.

Methods

All patients requiring a fistulogram between January 2004 and May 2006 had surveillance fluoroscopy of the central veins. Demographic, clinical and laboratory parameters were collected and the angle of the cephalic vein insertion measured by 3 blinded independent observers.

Results

Fifty-eight patients had fistulograms and CAS was detected in 18 subjects. Significant differences between the CAS and non-CAS groups were brachiocephalic fistula site (p=0.046), access flow (mL/min) (p=0.012), and absence of diabetes (p=0.03). Univariate predictors of CAS include access flow (per 100 mL/min) (p=0.042), platelet count (p=0.031) and calcium-phosphate product (p=0.026). The relationship of brachiocephalic site and CAS was confounded by access flow [(per 100 mL/min)*brachiocephalic fistula site (p=0.016)] and fistula age [brachiocephalic fistula site*fistula age (p=0.017)]. In multivariate analysis, renovascular disease, calcium-phosphate product, platelet count and access flow (per 100 mL/min)*brachiocephalic fistula predicted CAS (p<0.001, Negelkerke's R-Square= 0.55). The angle of insertion of the cephalic vein was not predictive for CAS.

Conclusions

CAS may be a long-term consequence of high blood flow rates. The interaction of access flow and brachiocephalic fistula supports the hypothesis that high flow through a brachiocephalic fistula promotes CAS. The multiple factors influencing cephalic arch remodeling require further research.

Risk factors for the development of cephalic arch stenosis

PURPOSE

The creation of a vascular access is necessary in hemodialysis patients, including those with marginal vessels. Upper arm fistulae are attractive due to the ease of creation and of achieving high access flow rates. Cephalic arch stenosis (CAS) can lead to failure of upper arm fistulae and is increasingly identified. We hypothesized that CAS is promoted by high blood flow rates, brachiocephalic fistulae, and an angle of cephalic vein insertion approaching 90 degrees.

METHODS

All patients requiring a fistulogram between January 2004 and May 2006 had surveillance fluoroscopy of the central veins. Demographic, clinical and laboratory parameters were collected and the angle of the cephalic vein insertion measured by 3 blinded independent observers.

RESULTS

Fifty-eight patients had fistulograms and CAS was detected in 18 subjects. Significant differences between the CAS and non-CAS groups were brachiocephalic fistula site (p = 0.046), access flow (mL/min) (p = 0.012), and absence of diabetes (p = 0.03). Univariate predictors of CAS include access flow (per 100 mL/min) (p = 0.042), platelet count (p = 0.031) and calcium-phosphate product (p = 0.026). The relationship of brachiocephalic site and CAS was confounded by access flow [(per 100 mL/min)*brachiocephalic fistula site (p = 0.016)] and fistula age [brachiocephalic fistula site*fistula age (p = 0.017)]. In multivariate analysis, renovascular disease, calcium-phosphate product, platelet count and access flow (per 100 mL/min)*brachiocephalic fistula predicted CAS (p < 0.001, Negelkerke's R-Square = 0.55). The angle of insertion of the cephalic vein was not predictive for CAS.

CONCLUSIONS

CAS may be a long-term consequence of high blood flow rates. The interaction of access flow and brachiocephalic fistula supports the hypothesis that high flow through a brachiocephalic fistula promotes CAS. The multiple factors influencing cephalic arch remodeling require further research.