Reduction of protein adsorption and macrophage and astrocyte adhesion on ventricular catheters by polyethylene glycol and N-acetyl-L-cysteine

Nisin-based antibacterial and antiadhesive layer-by-layer coatings

Some removable medical devices such as catheters and cardiovascular biomaterials require antiadhesive properties towards both prokaryotic and eukaryotic cells in order to prevent the tissues from infections upon implantation and, from alteration upon removal. In order to inhibit cell adhesion, we developed ultrathin hydrated Layer-by-Layer (LbL) coatings composed of biocompatible polyelectrolytes, namely chondroitin sulfate A (CSA) and poly-l-lysine (PLL). The coatings were crosslinked with genipin (GnP), a natural and biocompatible crosslinking agent, to increase their resistance against environmental changes. In order to confer antibacterial activity to the coatings, we proceeded to the electrostatically-driven immobilization of nisin Z, an antimicrobial peptide (AMP) active against gram-positive bacteria. The nisin-enriched coatings had a significantly increased anti-proliferative impact on fibroblasts, as well as a strong contact-killing activity against Staphylococcus aureus in the short and long term.

Analysis of N-acetyl cysteine modified polydimethylsiloxane shunt for improved treatment of hydrocephalus

A major cause of hydrocephalus shunt failure is cell adhesion and obstruction of shunt catheter holes. An estimated 50% of pediatric shunts fail in the first 2 years of insertion, decreasing cell attachment and catheter obstruction can prolong the lifetime and effectiveness of the device. From previous studies, it was shown that treatment of the polydimethylsiloxane (PDMS) surface of a standard catheter with an N-acetyl-cysteine (NAC/1-ethyl-3-(3-dimethylanimopropyl)carbodiimide hydrochloride/N-hydroxysuccinimide) layer increases the wettability of the surface and has been shown to decrease cell adhesion. Other studies indicate that NAC's antioxidant behavior induces glutathione and in turn modulates cell inflammatory pathways. The current study explores the longevity of the NAC coating from the surface of the catheter over time and shows its effect on valve function. Using SEM imaging, contact angle testing, and nanodrop spectrophotometry, this release was quantified for shunt samples incubated for 0, 10, 30, 60, and 90 days. Contact angle showed a significant increase in wettability of the surface when shunts were treated with NAC, confirming successful surface modification. Pressure assays determined that if the coating is release it had no detrimental downstream effects, such as on the shunt valve mechanism. SEM imaging revealed slight deformations in surface coating indicative of salt deposition on the modified shunt samples, while nanodrop spectrophotometry and contact angle data trends suggested some discharge of the NAC coating from the catheter surfaces. The effects of NAC on cell activity may transform the way hydrocephalus is treated in the future by increasing the longevity of the shunt to protect from obstruction.

Controlling Experimental Parameters to Improve Characterization of Biomaterial Fouling

Uncontrolled protein adsorption and cell binding to biomaterial surfaces may lead to degradation, implant failure, infection, and deleterious inflammatory and immune responses. The accurate characterization of biofouling is therefore crucial for the optimization of biomaterials and devices that interface with complex biological environments composed of macromolecules, fluids, and cells. Currently, a diverse array of experimental conditions and characterization techniques are utilized, making it difficult to compare reported fouling values between similar or different biomaterials. This review aims to help scientists and engineers appreciate current limitations and conduct fouling experiments to facilitate the comparison of reported values and expedite the development of low-fouling materials. Recent advancements in the understanding of protein-interface interactions and fouling variability due to experiment conditions will be highlighted to discuss protein adsorption and cell adhesion and activation on biomaterial surfaces.

Switchable presentation of cytokines on electroactive polypyrrole surfaces for hematopoietic stem and progenitor cells

Hematopoietic stem cells are used in transplantations for patients with hematologic malignancies. Scarce sources require efficient strategies of expansion, including polymeric biomaterials mimicking architectures of bone marrow tissue. Tissue microenvironment and mode of cytokine presentation strongly influence cell fate. Although several cytokines with different functions as soluble or membrane-bound mediators have already been identified, their precise roles have not yet been clarified. A need exists for in vitro systems that mimic the in vivo situation to enable such studies. One way is to establish surfaces mimicking physiological presentation using protein-immobilization onto polymer films. However these films merely provide a static presentation of the immobilized proteins. It would be advantageous to also dynamically change protein presentation and functionality to better reflect the in vivo conditions. The electroactive polymer polypyrrole shows excellent biocompatibility and electrochemically alters its surface properties, becoming an interesting choice for such setups. Here, we present an in vitro system for switchable presentation of membrane-bound cytokines. We use interleukin IL-3, known to affect hematopoiesis, and show that when immobilized on polypyrrole films, IL-3 is bioavailable for the bone marrow-derived FDC-P1 progenitor cell line. Moreover, IL-3 presentation can be successfully altered by changing the redox state of the film, in turn influencing FDC-P1 cell viability. This novel in vitro system provides a valuable tool for stimuli-responsive switchable protein presentation allowing the dissection of relevant mediators in stem and progenitor cell behavior.

N-acetylcysteine-functionalized coating avoids bacterial adhesion and biofilm formation

N-acetyl cysteine (NAC) is an FDA-approved drug clinically applied on a broad range of pathologies. Further research has been conducted with this drug to benefit from its antimicrobial activity potential. However, NAC has a very short half-life and therefore strategies that accomplish high local concentrations would be beneficial. In this study, covalent immobilization of NAC was performed, in order to obtain long-lasting high local concentration of the drug onto a chitosan(Ch)-derived implant-related coating. For the development of NAC-functionalized Ch films, water-based carbodiimide chemistry was applied to avoid the use of toxic organic solvents. Here we report the optimization steps performed to immobilize NAC onto the surface of pre-prepared Ch coatings, to ensure full exposure of NAC. Surface characterization using ellipsometry, water contact angle measurements and X-ray photoelectron spectroscopy (XPS), demonstrated the success of NAC immobilization at 4 mg/mL. Quartz crystal microbalance with dissipation (QCM-D) demonstrated that surface immobilized NAC decreases protein adsorption to Ch coatings. Biological studies confirmed that immobilized NAC4 avoids methicillin-resistant Staphylococcus aureus adhesion to Ch coating, impairing biofilm formation, without inducing cytotoxic effects. This is particularly interesting towards further developments as a prevention coating.

Endoscopy in the treatment of slit ventricle syndrome

The present study aimed to investigate the efficacy of endoscopy in the treatment of post-shunt placement for slit ventricle syndrome (SVS). Endoscopic surgery was performed on 18 patients with SVS between October 2004 and December 2012. Sex, age, causes of the hydrocephalus, ventricular size and imaging data were collected and analyzed. All patients were divided into two groups according to ventricular size and underwent endoscopic surgeries, including endoscopic third ventriculostomy (ETV), endoscopic aqueductoplasty and cystocisternostomy. All treated patients were observed postoperatively for a period of 2 to 3 weeks, and outpatient follow-up was subsequently scheduled for >12 months. Clinical results, including catheter adherence, shunt removal and complications, were analyzed during the follow-up period. The success rate of endoscopic surgery was indicated to be 82.7%. Syndromes caused by aqueductal stenosis in 15 patients who underwent ETV were relieved; however, syndromes in the 3 patients with cerebral cysticercosis, suprasellar arachnoid cysts, pinea larea glioma and communicating hydrocephalus, respectively, were not relieved and underwent shunt placement again. Brain parenchyma, choroid plexus and ependymal tissue were the predominant causes for catheter obstruction and the obstruction rate was indicated to be 77.8% (14/18). Complications, such as pseudobulbar paralysis, infection and intraventricular hemorrhage arose in 3 patients. The present study indicates that endoscopic treatments are effective and ETV may be considered as a recommended option in the treatment of post-shunt placement SVS in hydrocephalus patients.

Reduced cell attachment to poly(2-hydroxyethyl methacrylate)-coated ventricular catheters in vitro

The majority of patients with hydrocephalus are dependent on ventriculoperitoneal shunts for diversion of excess cerebrospinal fluid. Unfortunately, these shunts are failure-prone and over half of all life-threatening pediatric failures are caused by obstruction of the ventricular catheter by the brain's resident immune cells, reactive microglia and astrocytes. Poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels are widely used for biomedical implants. The extreme hydrophilicity of PHEMA confers resistance to protein fouling, making it a strong candidate coating for ventricular catheters. With the advent of initiated chemical vapor deposition (iCVD), a solvent-free coating technology that creates a polymer in thin film form on a substrate surface by introducing gaseous reactant species into a vacuum reactor, it is now possible to apply uniform polymer coatings on complex three-dimensional substrate surfaces. iCVD was utilized to coat commercially available ventricular catheters with PHEMA. The chemical structure was confirmed on catheter surfaces using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. PHEMA coating morphology was characterized by scanning electron microscopy. Testing PHEMA-coated catheters against uncoated clinical-grade catheters in an in vitro hydrocephalus catheter bioreactor containing co-cultured astrocytes and microglia revealed significant reductions in cell attachment to PHEMA-coated catheters at both 17-day and 6-week time points. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1268-1279, 2018.

Cerebrospinal Fluid Shunting Complications in Children

Although cerebrospinal fluid (CSF) shunt placement is the most common procedure performed by pediatric neurosurgeons, shunts remain among the most failure-prone life-sustaining medical devices implanted in modern medical practice. This article provides an overview of the mechanisms of CSF shunt failure for the 3 most commonly employed definitive CSF shunts in the practice of pediatric neurosurgery: ventriculoperitoneal, ventriculopleural, and ventriculoatrial. The text has been partitioned into the broad modes of shunt failure: obstruction, infection, mechanical shunt failure, overdrainage, and distal catheter site-specific failures. Clinical management strategies for the various modes of shunt failure are discussed as are research efforts directed towards reducing shunt complication rates. As it is unlikely that CSF shunting will become an obsolete procedure in the foreseeable future, it is incumbent on the pediatric neurosurgery community to maintain focused efforts to improve our understanding of and management strategies for shunt failure and shunt-related morbidity.

Ventricular catheter development: past, present, and future

Cerebrospinal fluid diversion via ventricular shunting is the prevailing contemporary treatment for hydrocephalus. The CSF shunt appeared in its current form in the 1950s, and modern CSF shunts are the result of 6 decades of significant progress in neurosurgery and biomedical engineering. However, despite revolutionary advances in material science, computational design optimization, manufacturing, and sensors, the ventricular catheter (VC) component of CSF shunts today remains largely unchanged in its functionality and capabilities from its original design, even though VC obstruction remains a primary cause of shunt failure. The objective of this paper is to investigate the history of VCs, including successful and failed alterations in mechanical design and material composition, to better understand the challenges that hinder development of a more effective design.

Fabrication of three-dimensional hydrogel scaffolds for modeling shunt failure by tissue obstruction in hydrocephalus

Background

Shunt obstruction in the treatment of hydrocephalus is poorly understood, is multi-factorial, and in many cases is modeled ineffectively. Several mechanisms may be responsible, one of which involves shunt infiltration by reactive cells from the brain parenchyma. This has not been modeled in culture and cannot be consistently examined in vivo without a large sample size.

Methods

We have developed and tested a three-dimensional in vitro model of astrocyte migration and proliferation around clinical grade ventricular catheters and into catheter holes that mimics the development of cellular outgrowth from the parenchyma that may contribute to shunt obstruction.

Results

Cell attachment and growth was observed on shunt catheters for as long as 80 days with at least 77 % viability until 51 days. The model can be used to study cellular attachment to ventricular catheters under both static and pulsatile flow conditions, which better mimic physiological cerebrospinal fluid dynamics and shunt system flow rates (0.25 mL/min, 100 pulses/min). Pulsatile flow through the ventricular catheter decreased cell attachment/growth by 63 % after 18 h. Under both conditions it was possible to observe cells accumulating around and in shunt catheter holes.

Conclusions

Alone or in combination with previously-published culture models of shunt obstruction, this model serves as a relevant test bed to analyze mechanisms of shunt failure and to test catheter modifications that will prevent cell attachment and growth.

Basic cerebrospinal fluid flow patterns in ventricular catheters prototypes

OBJECT

A previous study by computational fluid dynamics (CFD) of the three-dimensional (3-D) flow in ventricular catheters (VC) disclosed that most of the total fluid mass flows through the catheter's most proximal holes in commercially available VC. The aim of the present study is to investigate basic flow patterns in VC prototypes.

METHODS

The general procedure for the development of a CFD model calls for transforming the physical dimensions of the system to be studied into a virtual wire-frame model which provides the coordinates for the virtual space of a CFD mesh, in this case, a VC. The incompressible Navier-Stokes equations, a system of strongly coupled, nonlinear, partial differential conservation equations governing the motion of the flow field, are then solved numerically. New designs of VC, e.g., with novel hole configurations, can then be readily modeled, and the corresponding flow pattern computed in an automated way. Specially modified VCs were used for benchmark experimental testing.

RESULTS

Three distinct types of flow pattern in prototype models of VC were obtained by varying specific parameters of the catheter design, like the number of holes in the drainage segments and the distance between them. Specifically, we show how to equalize and reverse the flow pattern through the different VC drainage segments by choosing appropriate parameters.

CONCLUSIONS

The flow pattern in prototype catheters is determined by the number of holes, the hole diameter, the ratio hole/segment, and the distance between hole segments. The application of basic design principles of VC may help to develop new catheters with better flow circulation, thus reducing the possibility of becoming occluded.

Fabrication of multi-well chips for spheroid cultures and implantable constructs through rapid prototyping techniques

Three-dimensional (3D) culture models are widely used in basic and translational research. In this study, to generate and culture multiple 3D cell spheroids, we exploited laser ablation and replica molding for the fabrication of polydimethylsiloxane (PDMS) multi-well chips, which were validated using articular chondrocytes (ACs). Multi-well ACs spheroids were comparable or superior to standard spheroids, as revealed by glycosaminoglycan and type-II collagen deposition. Moreover, the use of our multi-well chips significantly reduced the operation time for cell seeding and medium refresh. Exploiting a similar approach, we used clinical-grade fibrin to generate implantable multi-well constructs allowing for the precise distribution of multiple cell types. Multi-well fibrin constructs were seeded with ACs generating high cell density regions, as shown by histology and cell fluorescent staining. Multi-well constructs were compared to standard constructs with homogeneously distributed ACs. After 7 days in vitro, expression of SOX9, ACAN, COL2A1, and COMP was increased in both constructs, with multi-well constructs expressing significantly higher levels of chondrogenic genes than standard constructs. After 5 weeks in vivo, we found that despite a dramatic size reduction, the cell distribution pattern was maintained and glycosaminoglycan content per wet weight was significantly increased respect to pre-implantation samples. In conclusion, multi-well chips for the generation and culture of multiple cell spheroids can be fabricated by low-cost rapid prototyping techniques. Furthermore, these techniques can be used to generate implantable constructs with defined architecture and controlled cell distribution, allowing for in vitro and in vivo investigation of cell interactions in a 3D environment.

New designs of ventricular catheters for hydrocephalus by 3-D computational fluid dynamics

INTRODUCTION

Based on a landmark study by Lin et al. of the two-dimensional flow in ventricular catheters (VCs) via computational fluid dynamics (CFD), we studied in a previous paper the three-dimensional flow patterns of five commercially available VC. We found that the drainage of the cerebrospinal fluid (CSF) mostly occurs through the catheter's most proximal holes. In this paper, we design five VC prototypes with equalized flow characteristics.

METHODS

We study five prototypes of VC by means of CFD in three-dimensional (3-D) automated models and compare the fluid-mechanical results with our previous study of currently in use VC. The general procedure for the development of a CFD model calls for transforming the physical dimensions of the system to be studied into a virtual wire-frame model, which provides the coordinates for the virtual space of a CFD mesh. The incompressible Navier-Stokes equations, a system of strongly coupled, nonlinear, partial differential equations governing the motion of the flow field, are then solved numerically.

RESULTS

By varying the number of drainage holes and the ratio hole/segment, we improved flow characteristics in five prototypes of VC. Models 1, 2, and 3 have a distal to proximal decreasing flow. Model 4 has an inverse flow to the previous ones, that is, a distal to proximal increasing flow, while model 5 has a constant flow over the segments.

CONCLUSIONS

New catheter designs with variable hole diameter, number of holes, and ratio hole/segment along the catheter allow the fluid to enter the catheter more uniformly along its length, thus reducing the chance that the catheter becomes occluded.

Electrospun polyurethane as an alternative ventricular catheter and in vitro model of shunt obstruction

Intracranial pressure and volume vary considerably between hydrocephalic patients, and with age, health and haemodynamic status; if left untreated, intracranial pressure rises and the ventricular system expands to accommodate the excess cerebrospinal fluid, with significant morbidity and mortality. Cerebrospinal fluid shunts in use today have a high incidence of failure with shunt obstruction being the most serious. Conventional proximal shunt catheters are made from poly(dimethyl)siloxane, the walls of which are perforated with holes for the cerebrospinal fluid to pass through. The limited range of catheters, in terms of material selection and flow distribution, is responsible in large part for their poor performance.

In this study, we present an alternative design of proximal catheter made of electrospun polyether urethane, and evaluate its performance in the presence of glial cells, which are responsible for shunt blockage. The viability and growth of cells on catheter materials such as poly(dimethyl)siloxane and polyurethane in the form of cast films, microfibrous mats and porous sponges were studied in the presence of proteins present in cerebrospinal fluid after 48 h and 96 h in culture. The numbers of viable cells on each substrate were comparable to untreated poly(dimethyl)siloxane, both in the presence and absence of serum proteins found in cerebrospinal fluid. A cell culture model of shunt obstruction was developed in which cells on electrospun polyether urethane catheters were subjected to flow during culture in vitro, and the degree of obstruction quantified in terms of hydraulic permeability after static and perfusion culture. The results indicate that a catheter made of electrospun polyether urethane would be able to maintain cerebrospinal fluid flow even with the presence of cells for the time period chosen for this study. These findings have implications for the design and deployment of microporous shunt catheter systems for the treatment of hydrocephalus.

Building an antifouling zwitterionic coating on urinary catheters using an enzymatically triggered bottom-up approach

Catheter associated urinary tract infections are common during hospitalization due to the formation of bacterial biofilms on the indwelling device. In this study, we report an innovative biotechnology-based approach for the covalent functionalization of silicone catheters with antifouling zwitterionic moieties to prevent biofilm formation. Our approach combines the potential bioactivity of a natural phenolics layer biocatalytically conjugated to sulfobetaine-acrylic residues in an enzymatically initiated surface radical polymerization with laccase. To ensure sufficient coating stability in urine, the silicone catheter is plasma-activated. In contrast to industrial chemical methods, the methacrylate-containing zwitterionic monomers are polymerized at pH 5 and 50 °C using as an initiator the phenoxy radicals solely generated by laccase on the phenolics-coated catheter surface. The coated catheters are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FTIR) analysis, atomic force microscopy (AFM), and colorimetrically. Contact angle and protein adsorption measurements, coupled with in vitro tests with the Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus in static and dynamic conditions, mimicking the operational conditions to be faced by the catheters, demonstrate reduced biofilm formation by about 80% when compared to that of unmodified urinary catheters. The zwitterionic coating did not affect the viability of the human fibroblasts (BJ-5ta) over seven days, corresponding to the extended useful life of urinary catheters.

Computational fluid dynamics of ventricular catheters used for the treatment of hydrocephalus: a 3D analysis

INTRODUCTION

The most common treatment for hydrocephalus remains the ventriculoperitoneal shunt. Yet, the most frequent complication is ventricular catheter obstruction, which may account for 50-80 % of newly inserted shunts. Although many factors contribute to this, the main one is related to flow characteristics of the catheter within the hydrocephalic brain. A landmark study by Lin et al. addressed the problem of fluid characteristics in ventricular catheters using a two-dimensional simulation program of computational fluid dynamics (CFD).

METHODS

The authors have studied five current commercially available ventricular catheter designs using CFD in three-dimensional automated designs. The general procedure for the development of a CFD model involves incorporating the physical dimensions of the system to be studied into a virtual wire-frame model. The shape and features of the actual physical model are transformed into coordinates for the virtual space of the computer and a CFD computational grid (mesh) is generated. The fluid properties and motion are calculated at each of these grid points. After grid generation, flow field boundary conditions are applied, and the fluid's thermodynamic and transport properties are included. At the end, a system of strongly coupled, nonlinear, partial differential conservation equations governing the motion of the flow field are numerically solved. This numerical solution describes the fluid motion and properties.

RESULTS

The authors calculated that most of the total fluid mass flows into the catheter's most proximal holes. Fifty to 75 % flows into the two most proximal sets of inlets of current commercially available 12-32-hole catheters. Some flow uniformity was disclosed in Rivulet-type catheter.

CONCLUSIONS

Most commercially available ventricular catheters have an abnormally increase flow distribution pattern. New catheter designs with variable hole diameters along the catheter tip will allow the fluid to enter the catheter more uniformly along its length, thereby reducing the probability of its becoming occluded.

What We Should Know About the Cellular and Tissue Response Causing Catheter Obstruction in the Treatment of Hydrocephalus

The treatment of hydrocephalus by cerebrospinal fluid shunting is plagued by ventricular catheter obstruction. Shunts can become obstructed by cells originating from tissue normal to the brain or by pathological cells in the cerebrospinal fluid for a variety of reasons. In this review, the authors examine ventricular catheter obstruction and identify some of the modifications to the ventricular catheter that may alter the mechanical and chemical cues involved in obstruction, including alterations to the surgical strategy, modifications to the chemical surface of the catheter, and changes to the catheter architecture. It is likely a combination of catheter modifications that will improve the treatment of hydrocephalus by prolonging the life of ventricular catheters to improve patient outcome.