In vivo evaluation of skin integration with ventricular assist device drivelines.

BACKGROUND: Ventricular assist device (VAD) driveline exit site infection is a common complication. 3D scaffolds manufactured with highly homogeneous pores via melt electro-writing (MEW) may generate an improved skin-driveline interface which permits cellular in-growth and creates a barrier to prevent bacterial migration along the driveline tissue tunnel. This study investigated skin integration on segments of Heartmate 3 driveline: smooth polyurethane, velour, and on a custom MEW scaffold in a small animal model. METHODS: Drivelines with surfaces consisting of smooth polyurethane, velour bonded to smooth polyurethane, and smooth polyurethane with a MEW scaffold sleeve were implanted percutaneously in the dorsum of 42 rats. Each rat was implanted with 2 pieces of driveline of 2 cm in length. Skin integration was assessed after 7 and 14 days. RESULTS: Macroscopically, velour and MEW scaffold surfaces were anchored at the driveline-skin interface while smooth polyurethane samples were not attached. The histology analyses showed epidermal migration throughout the thickness of the velour and MEW scaffold groups. Evident tissue growth around single MEW scaffold fibers resulted in full coverage of the pores, while areas of compacted fibers were apparent in the velour group. Tissue ingrowth was significantly higher in the MEW group compared to the velour group after 7 (p < 0.0001) and 14 days (p < 0.0001). Marsupialization was observed in the smooth polyurethane samples. Mechanical pull-out forces were similar between velour and MEW scaffold groups at 7 and 14 days (p > 0.05). CONCLUSIONS: Velour and MEW scaffolds promoted epidermal integration while smooth polyurethane drivelines did not. Fine control of MEW scaffold structure production resulted in full cellular coverage and may reduce driveline infection.

Elastic Bioresorbable Polymeric Capsules for Osmosis-Driven Delayed Burst Delivery of Vaccines.

Single-administration vaccine delivery systems are intended to improve the efficiency and efficacy of immunisation programs in both human and veterinary medicine. In this work, an osmotically triggered delayed delivery device was developed that was able to release a payload after a delay of approximately 21 days, in a consistent and reproducible manner. The device was constructed out of a flexible poly(ε-caprolactone) photo-cured network fabricated into a hollow tubular shape, which expelled approximately 10% of its total payload within 2 days after bursting. Characterisation of the factors that control the delay of release demonstrated that it was advantageous to adjust material permeability and device wall thickness over manipulation of the osmogent concentration in order to maintain reproducibility in burst delay times. The photo-cured poly(ε-caprolactone) network was shown to be fully degradable in vitro, and there was no evidence of cytotoxicity after 11 days of direct contact with primary dermal fibroblasts. This study provides strong evidence to support further development of flexible biomaterials with the aim of continuing improvement of the device burst characteristics in order to provide the greatest chance of the devices succeeding with in vivo vaccine booster delivery.

Poly(2-allylamidopropyl-2-oxazoline)-Based Hydrogels: From Accelerated Gelation Kinetics to In Vivo Compatibility in a Murine Subdermal Implant Model.

A rapid photo-curing system based on poly(2-ethyl-2-oxazoline-co-2-allylamidopropyl-2-oxazoline) and its in vivo compatibility are presented. The base polymer was synthesized from the copolymerization of 2-ethyl-2-oxazoline (EtOx) and the methyl ester containing 2-methoxycarboxypropyl-2-oxazoline (C3MestOx) followed by amidation with allylamine to yield a highly water-soluble macromer. We showed that spherical hydrogels can be obtained by a simple water-in-oil gelation method using thiol-ene coupling and investigated the in vivo biocompatibility of these hydrogel spheres in a 28-day murine subdermal model. For comparison, hydrogel spheres prepared from poly(ethylene glycol) were also implanted. Both materials displayed mild, yet typical foreign body responses with little signs of fibrosis. This is the first report on the foreign body response of a poly(2-oxazoline) hydrogel, which paves the way for future investigations into how this highly tailorable class of materials can be used for implantable hydrogel devices.

Injectable biocompatible poly(2-oxazoline) hydrogels by strain promoted alkyne-azide cycloaddition.

Poly(2-alkyl-2-oxazoline) (PAOx) hydrogels are tailorable synthetic materials with demonstrated biomedical applications, thanks to their excellent biocompatibility and tunable properties. However, their use as injectable hydrogels is challenging as it requires invasive surgical procedures to insert the formed hydrogel into the body due to their nonsoluble 3D network structures. Herein, we introduce cyclooctyne and azide functional side chains to poly(2-oxazoline) copolymers to induce in situ gelation using strain promoted alkyne-azide cycloaddition. The gelation occurs rapidly, within 5 min, under physiological conditions when two polymer solutions are simply mixed. The influence of several parameters, such as temperature and different aqueous solutions, and stoichiometric ratios between the two polymers on the structural properties of the resultant hydrogels have been investigated. The gel formation within tissue samples was verified by subcutaneous injection of the polymer solution into an ex vivo model. The degradation study of the hydrogels in vitro showed that the degradation rate was highly dependent on the type of media, ranging from days to a month. This result opens up the potential uses of PAOx hydrogels in attempts to achieve optimal, injectable drug delivery systems and tissue engineering.

Production of Scaffolds Using Melt Electrospinning Writing and Cell Seeding.

Melt electrospinning writing (MEW) is a solvent-free fabrication method for making polymer fiber scaffolds with features which include large surface area, high porosity, and controlled deposition of the fibers. These scaffolds are ideal for tissue engineering applications. Here we describe how to produce scaffolds made from poly(ε-caprolactone) using MEW and the seeding of primary human-derived dermal fibroblasts to create cell-scaffold constructs. The same methodology could be used with any number of cell types and MEW scaffold designs.

Hydrogels with Cell Adhesion Peptide-Decorated Channel Walls for Cell Guidance.

A method is reported for making hollow channels within hydrogels decorated with cell-adhesion peptides exclusively at the channel surface. Sacrificial fibers of different diameters are used to introduce channels within poly(ethylene glycol) hydrogels crosslinked with maleimide-thiol chemistry, which are backfilled with a cysteine-containing peptide solution which is conjugated to the lumen with good spatial efficiency. This allows for peptide patterning in only the areas of the hydrogel where they are needed when used as cell-guides, reducing the amount of required peptide 20-fold when compared to bulk functionalization. The power of this approach is highlighted by successfully using these patterned hydrogels without active perfusion to guide fibroblasts and olfactory ensheathing cells-the latter having unique potential in neural repair therapies.

An in vitro Reconstructed Human Skin Equivalent Model to Study the Role of Skin Integration Around Percutaneous Devices Against Bacterial Infection.

Percutaneous devices are a key technology in clinical practice, used to connect internal organs to external medical devices. Examples include prosthesis, catheters and electrical drivelines. Percutaneous devices breach the skin's natural barrier and create an entry point for pathogens, making device infections a widespread problem. Modification of the percutaneous implant surface to increase skin integration with the aim to reduce subsequent infection is attracting a great deal of attention. While novel surfaces have been tested in various in vitro models used to study skin integration around percutaneous devices, no skin model has been reported, for the study of bacterial infection around percutaneous devices. Here, we report the establishment of an in vitro human skin equivalent model for driveline infections caused by Staphylococcus aureus, the most common cause of driveline-related infections. Three types of mock drivelines manufactured using melt electrowriting (smooth or porous un-seeded and porous pre-seeded with human fibroblasts) were implanted in human skin constructs and challenged with S. aureus. Our results show a high and stable load of S. aureus in association with the skin surface and no signs of S. aureus-induced tissue damage. Furthermore, our results demonstrate that bacterial migration along the driveline surface occurs in micro-gaps caused by insufficient skin integration between the driveline and the surrounding skin consistent with clinical reports from explanted patient drivelines. Thus, the human skin-driveline infection model presented here provides a clinically-relevant and versatile experimental platform for testing novel device surfaces and infection therapeutics.

Improving skin integration around long-term percutaneous devices using fibrous scaffolds in a reconstructed human skin equivalent model.

The interface between synthetic percutaneous devices and skin is a common area for bacterial infection, which may ultimately result in failure of the device. Better integration of percutaneous devices with skin may help reduce infection rates due to the creation of a dermal seal. However, the mismatch in material and chemical properties of devices and skin presents a challenge for closing the dermal gap at the skin-device interface. Here, we have used a tissue engineering approach to tissue integration by creating a highly fibrous poly(ε-caprolactone) scaffold using melt electrowriting and seeding this with dermal fibroblasts, followed by maturation and insertion into a full-thickness defect made in an ex vivo skin model. The integration of seeded scaffolds was compared with controls including a non-seeded scaffold and a polymer tube with a smooth surface. Dermal fibroblast inclusion in the scaffold and epidermal upgrowth versus downgrowth/marsupialization around the device were used as measures of integration. Based on these measures, almost all pre-seeded scaffolds performed better than both the non-seeded scaffolds and smooth tubes. The hypothesis is that the fibroblasts act as a barrier to epithelial downward migration, and provide healthy tissue for nascent epidermal development.