Development and Characterization of a Benchtop Corneal Puncture Injury Model

The Projectile Perforation Resistance of Materials: Scaling the Impact Resistance of Thin Films to Macroscale Materials

From drug delivery to ballistic impact, the ability to control or mitigate the puncture of a fast-moving projectile through a material is critical. While puncture is a common occurrence, which can span many orders of magnitude in the size, speed, and energy of the projectile, there remains a need to connect our understanding of the perforation resistance of materials at the nano- and microscale to the actual behavior at the macroscale that is relevant for engineering applications. In this article, we address this challenge by combining a new dimensional analysis scheme with experimental data from micro- and macroscale impact tests to develop a relationship that connects the size-scale effects and materials properties during high-speed puncture events. By relating the minimum perforation velocity to fundamental material properties and geometric test conditions, we provide new insights and establish an alternative methodology for evaluating the performance of materials that is independent of the impact energy or the specific projectile puncture experiment type. Finally, we demonstrate the utility of this approach by assessing the relevance of novel materials, such as nanocomposites and graphene for real-world impact applications.

Development of a Modular Tissue Phantom for Evaluating Vascular Access Devices

Central vascular access (CVA) may be critical for trauma care and stabilizing the casualty. However, it requires skilled personnel, often unavailable during remote medical situations and combat casualty care scenarios. Automated CVA medical devices have the potential to make life-saving therapeutics available in these resource-limited scenarios, but they must be properly designed. Unfortunately, currently available tissue phantoms are inadequate for this use, resulting in delayed product development. Here, we present a tissue phantom that is modular in design, allowing for adjustable flow rate, circulating fluid pressure, vessel diameter, and vessel positions. The phantom consists of a gelatin cast using a 3D-printed mold with inserts representing vessels and bone locations. These removable inserts allow for tubing insertion which can mimic normal and hypovolemic flow, as well as pressure and vessel diameters. Trauma to the vessel wall is assessed using quantification of leak rates from the tubing after removal from the model. Lastly, the phantom can be adjusted to swine or human anatomy, including modeling the entire neurovascular bundle. Overall, this model can better recreate severe hypovolemic trauma cases and subject variability than commercial CVA trainers and may potentially accelerate automated CVA device development.

An image classification deep-learning algorithm for shrapnel detection from ultrasound images

Ultrasound imaging is essential for non-invasively diagnosing injuries where advanced diagnostics may not be possible. However, image interpretation remains a challenge as proper expertise may not be available. In response, artificial intelligence algorithms are being investigated to automate image analysis and diagnosis. Here, we highlight an image classification convolutional neural network for detecting shrapnel in ultrasound images. As an initial application, different shrapnel types and sizes were embedded first in a tissue mimicking phantom and then in swine thigh tissue. The algorithm architecture was optimized stepwise by minimizing validation loss and maximizing F1 score. The final algorithm design trained on tissue phantom image sets had an F1 score of 0.95 and an area under the ROC curve of 0.95. It maintained higher than a 90% accuracy for each of 8 shrapnel types. When trained only on swine image sets, the optimized algorithm format had even higher metrics: F1 and area under the ROC curve of 0.99. Overall, the algorithm developed resulted in strong classification accuracy for both the tissue phantom and animal tissue. This framework can be applied to other trauma relevant imaging applications such as internal bleeding to further simplify trauma medicine when resources and image interpretation are scarce.

Development and characterization of a hydrogel-based adhesive patch for sealing open-globe injuries

Full-thickness wounds to the eye can lead to serious vision impairment. Current standards of care (from suturing to tissue transplantation) usually require highly skilled surgeons and use of an operating theater. In this study, we report the synthesis, optimization, and in vitro and ex vivo testing of photocrosslinkable hydrogel-based adhesive patches that can easily be applied to globe injuries or corneal incisions. According to the type and concentration of polymers used in the adhesive formulations, we were able to finely tune the physical properties of the bioadhesive including viscosity, elastic modulus, extensibility, ultimate tensile strength, adhesion, transparency, water content, degradation time, and swellability. Our in vitro studies showed no sign of cytotoxicity of the hydrogels. Moreover, the hydrogel patches showed higher adhesion on freshly explanted pig eyeballs compared to a marketed ocular sealant. Finally, ex vivo feasibility studies showed that the hydrogel patches could seal complex open-globe injuries such as large incision, cruciform injury, and injury associated with tissue loss. These results suggest that our photocrosslinkable hydrogel patch could represent a promising solution for the sealing of open-globe injuries or surgical incisions. STATEMENT OF SIGNIFICANCE: Current management of severe ocular injuries require advanced surgical skills and access to an operating theater. To address the need for emergent management of wounds that cannot be handled in the operating room, surgical adhesives have gained popularity, but none of the currently available adhesives have optimal bioavailability, adhesive or mechanical properties. This study describes the development, optimization and testing of a light-sensitive adhesive patch that can easily be applied to the eye. After solidification using visible light, the patch shows no toxicity and is more adherent to the tissue than a marketed sealant. Thus this technology could represent a promising solution to stabilize ocular injuries in emergency settings before definitive surgical repair.

An Open-Globe Porcine Injury Platform for Assessing Therapeutics and Characterizing Biological Effects

Open-globe injuries can result in permanent vision loss, partly due to extended delays between injury and medical intervention. Even with early intervention, the management of open-globe injuries remains a challenge for ophthalmologists, mostly due to inadequate or suboptimal current therapies. To aid in the development of novel therapeutics and track toxicological and pathophysiological changes, this article details an open-globe injury platform capable of inducing injuries in enucleated porcine eyes. The injury platform relies on a high-speed solenoid device to mimic explosive injury scenarios, allowing for large, complex injury shapes and sizes that are often observed in casualties and are more difficult to treat. The system can be implemented with precise computer control of the injury mechanism to allow for more complex setups. Also, the system can make use of real-time intraocular pressure measurement to track changes during injury induction and to assess therapeutic efficacy for restoring intraocular pressure and the integrity of the eye. These protocols will assist with implementation of the injury model in prospective laboratories seeking to develop therapeutics or studying biological changes that occur from this type of traumatic injury. Published 2020. U.S. Government. Basic Protocol 1: Preparing gelatin molds and porcine eye tissue Basic Protocol 2: Creating an open-globe injury using a solenoid device Alternate Protocol 1: Constructing a computer-controlled system for open-globe injury Alternate Protocol 2: Constructing a pressure measurement system for tracking intraocular pressure Support Protocol 1: Assessing ocular compliance in porcine eyes Support Protocol 2: Assessing outflow rate from the anterior chamber Support Protocol 3: Assessing burst pressure in porcine eyes.

Assessment of Commercial Off-the-Shelf Tissue Adhesives for Sealing Military-Relevant Corneal Perforation Injuries

INTRODUCTION

Open-globe ocular injuries have increased in frequency in recent combat operations due to increased use of explosive weaponry. Unfortunately, open-globe injuries have one of the worst visual outcomes for the injured warfighter, often resulting in permanent loss of vision. To improve visual recovery, injuries need to be stabilized quickly following trauma, in order to restore intraocular pressure and create a watertight seal. Here, we assess four off-the-shelf (OTS), commercially available tissue adhesives for their ability to seal military-relevant corneal perforation injuries (CPIs).

MATERIALS AND METHODS

Adhesives were assessed using an anterior segment inflation platform and a previously developed high-speed benchtop corneal puncture model, to create injuries in porcine eyes. After injury, adhesives were applied and injury stabilization was assessed by measuring outflow rate, ocular compliance, and burst pressure, followed by histological analysis.

RESULTS

Tegaderm dressings and Dermabond skin adhesive most successfully sealed injuries in preliminary testing. Across a range of injury sizes and shapes, Tegaderm performed well in smaller injury sizes, less than 2 mm in diameter, but inadequately sealed large or complex injuries. Dermabond created a watertight seal capable of maintaining ocular tissue at physiological intraocular pressure for almost all injury shapes and sizes. However, application of the adhesive was inconsistent. Histologically, after removal of the Dermabond skin adhesive, the corneal epithelium was removed and oftentimes the epithelium surface penetrated into the wound and was adhered to inner stromal tissue.

CONCLUSIONS

Dermabond can stabilize a wide range of CPIs; however, application is variable, which may adversely impact the corneal tissue. Without addressing these limitations, no OTS adhesive tested herein can be directly translated to CPIs. This highlights the need for development of a biomaterial product to stabilize these injuries without causing ocular damage upon removal, thus improving the poor vision prognosis for the injured warfighter.

Characterization of an anterior segment organ culture model for open globe injuries

Open-globe injuries have poor visual outcomes and have increased in frequency. The current standard of care is inadequate, and a therapeutic is needed to stabilize the injury until an ophthalmic specialist is reached. Unfortunately, current models or test platforms for open-globe injuries are insufficient. Here, we develop and characterize an open-globe injury model using an anterior segment organ-culture platform that allows therapeutic assessment for up to 72 h post-injury. Anterior segments maintained in organ culture were kept at physiological intraocular pressure throughout, and puncture injuries were created using a novel pneumatic-powered system. This system can create high-speed, military-relevant injuries up to 4.5 mm in diameter through the cornea. From intraocular pressure readings, we confirmed a loss of pressure across the 72 h after open-globe injury. Proof-of-concept studies with a Dermabond tissue adhesive were performed to show how this model system could track therapeutic performance for 72 h. Overall, the organ-culture platform was found to be a suitable next step towards modeling open-globe injuries and assessing wound closure over the critical 72 h post-injury. With improved models such as this, novel biomaterial therapeutics development can be accelerated, improving care, and, thus, improving the prognosis for the patients.