PRESSURE-INDICATING MATERIAL

Introduction

[0001] This application claims benefit of priority to U.S.

Provisional Patent Application Serial No. 63/142,667, filed

January 28, 2021, the content of which is incorporated herein by reference in its entirety.

Background

[0002] A medical device-related pressure injury (MDRPI) can arise due to the pressure/strain of devices applied to monitor or treat a patient's condition. Current preventative measures that are used to prevent and treat MDRPIs include frequent visual assessments during a nursing shift, and/or skin protection, such as foam padding, etc. MDRPIs impact at least

2,500,000 people annually in acute and long-term care settings. MDRPIs cause infection, pain, and other medical issues leading to longer hospitalizations. Such injuries can cause comorbidities and longer hospitalizations, which significantly increase the healthcare costs.

[0003] Approaches for sensing pressure in the biomedical field have been suggested. For example, a biocompatible implantable intraocular pressure sensor has been described based on deformation of a periodically nanostructured Bragg grating waveguide on a flexible 50 μm polydimethylsiloxane membrane and remote optical read out (Karrock & Gerken (2015)

Biomedical Optics Express 6(12):4901). Furthermore, WO

2020/170247 A1 describes a patch comprising at least one pressure-absorbing member, the pressure-absorbing member formed of a resilient material and configured with a plurality of projections and a plurality of channels and reservoirs, wherein the reservoirs may include colored capsules that rupture, burst, or tear when the fluid reservoir sites are subjected to pressure. However, the patch described in that approach is not reusable.

Summary of the Invention

[0004] This invention provides a medical device including a color-changing material, the color-changing material being transparent and configured to reversibly change color in response to pressure or strain at a patient-engaging surface of the medical device. In one aspect, the color-changing material has a smooth surface at the patient-engaging surface. In other aspects, the color-changing material changes color when pressure or strain exceeds 67 mmHg or when pressure or strain is 240 mmHg. In certain aspects, the color- changing material is an opalescent photonic-crystal elastomer composed of arrays of silica particles embedded in a transparent material, e.g., polydimethylsiloxane. In particular aspects, the color-changing material is adhered to the surface of the medical device or is embedded in the medical device. Medical devices embraced by this invention include an endotracheal tube, endotracheal tube holder, laryngeal mask, bag-valve-mask, nasal catheter, nasal cannula, nasopharyngeal airway or nasal trumpet, noninvasive ventilation mask, bilevel or two-level positive airway pressure (BiPAP) mask, oropharyngeal airway, venturi mask, oxygen mask, oxygen prong, oxygen tubing, intercostal catheter (ICC) or chest tube, elastic or compressive bandage, wrap or securement device, compression stocking, foley catheter, intravenous line, brace, splint, cast, spine board, restraint, cervical collar, pulse oximeter, external fixator, electrocardiogram, encephalogram electrodes, encephalogram wires, wireless medical device, wearable medical device, band or bandage, or fecal containment device. A method for preventing a medical device-related pressure injury or ulcer by embedding or adhering a color-changing material to a patient-engaging surface of a medical device is also provided.

Detailed Description of the Invention

[0005] There are a number of medical devices that frequently cause medical device-related pressure injuries. Accordingly, this invention provides for the surface of these devices to be covered with or be composed of one or more layers or lean on pressure-indicating material, such as films or polymers that change color when excessive pressure/strain/stress is exerted, thereby alerting the patient, medical staff, or healthcare provider of the overpressure/strain condition. In particular, the present invention provides a medical device including a pressure- or strain-sensing interface composed of a color-changing material that is transparent and configured to reversibly change color in response to pressure or strain at a patient-engaging surface of a medical device.

Advantageously, the present color-changing material allows healthcare providers to readily detect medical device-induced pressure that can damage the skin surface of patients.

[0006] As used herein, medical device-related pressure injuries (MDRPIs) or medical device-related pressure ulcers

(MDRPUs) are injuries that can be caused by devices designed and applied mostly for diagnostic or therapeutic purposes.

In MDRPIs, the forces are applied externally by a medical or other device that contacts the skin of a patient and potentially applies pressure and/or shear on the skin at the contact surfaces. MDRPIs are typically caused by mechanical forces applied by the device or that are associated with use of the device. Such forces include, but are not limited to pressure, shear stress, strain, normal pressure, tangential pressure, and the like. Endotracheal tubes, endotracheal tube holders, laryngeal masks, bag-valve-masks, nasal catheters, nasal cannulas, nasopharyngeal airways or nasal trumpets, noninvasive ventilation masks, bilevel or two-level positive airway pressure (BiPAP) masks, oropharyngeal airways, venturi masks, oxygen masks, oxygen prongs, oxygen tubing, intercostal catheters (ICC) or chest tubes, elastic or compressive bandage, wrap or securement device, compression stockings, foley catheters, intravenous lines, braces, splints, casts, spine boards, restraints, cervical collars, pulse oximeters, external fixators such as bone fixators, electrocardiogram and encephalogram electrodes and wires, wireless devices, wearable devices (e.g., devices for monitoring patient movements in bed, repositioning, or events of patients leaving the bed or returning to bed in hospitals or long-term care, etc.), bands and bandages, and fecal containment devices are a few examples of medical devices which can cause MDRPIs through application of mechanical forces via contact with the skin (including the lips, mucosal tissues of the nose etc.) or when placed between the body and a support surface (e.g., objects located between the body and mattress or cushion or spine board) which causes tissue distortion and/or reduced blood flow at and around the site of contact with the device or object. A positioner for a body part, for example, a head positioner on a wheelchair, could also be considered a medical device liable to present the risk of a pressure injury to a body part which it is designed to hold in place. Similarly, an elastic bandage or compression wrap may be considered a medical device that presents the risk of pressure injury. Although the color-changing material can be removably or integrally formed into any interfacing medical device or component in accordance with the principles herein, certain medical devices are more prone to cause severe MDRPIs including. Accordingly, in certain aspects, the instant color-changing material is used in connection with elastic or compressive bandages, wraps or securement devices, neck collars, oxygen masks, and endotracheal tubes material to reduce skin pressure/strain at vulnerable skin contact points of the elastic or compressive bandages, wraps or securement devices, neck collar, oxygen mask, or endotracheal tube.

[0007] As used herein, the term "skin" denotes skin, subdermal and deeper soft tissues of a body, including but not limiting the micro- and macro- vascular structure that may be prone to damage as a result of circumferential compressive forces, such as the body of a patient. It is noted that the body could be the body of a human or of an animal upon which pressure from an external source can be applied.

The term "pressure injury" is used to denote any type of pressure-related ulcer or injury, including MDRPU and MDRPI.

The term "pressure" denotes any kind of pressure, including focal pressure, shear stress, and tangential and normal pressure caused by any directly or indirectly exerted forces, e.g., normal forces, shear forces, frictional forces, etc. that generally have a component perpendicular to a unit area of the body. "Shear" refers to the situation when the skin and the subcutaneous tissue remain stationary and there is a differential movement of the underlying soft tissue like muscle and fascia. This forceful inter-tissue plane movement causes stretching and tearing of blood vessels, reduced blood flow, stasis, and ischemic tissue necrosis. While shear causes tissue damage differently than pressure, the damage is produced concomitant with pressure.

[0008] Pressure-induced vasodilatation leads to an increase in blood flow and is thought to entail the protection of the tissue from ischemia during mechanical loading when the applied pressure is below the level at which blood vessels become occluded. There are indications that the underlying myogenic response is most dominant between 15 and 20 mmHg of loading. However, external pressure of more than 33 mmHg occludes blood vessels so that the underlying and surrounding tissues become anoxic and if the pressure continues for a critical duration, cell death will occur, resulting in soft tissue necrosis and eventual ulceration. A number of studies have evaluated histopathological changes in tissue exposed to excessive pressure, using animal models including rodents and pigs, as well as engineered epidermis. These studies have shown that with pressure exposure between 15 minutes and one hour, a pressure over 32 kPa (240 mmHg) causes cell death in muscle, and with exposure for two hours or longer, a pressure over 9 kPa (67 mmHg) always causes muscle damage (Linder-Ganz et al. (2004) J. Appl. Physiol. 96(6):2034-49). Accordingly, in some aspects, the color-changing material is capable of detecting an applied pressure in the range of 0.5 to 300 MPa. of at least 33 mmHg, or more preferably greater than or equal to 67 mmHg, or most preferably 240 mmHg.

[0009] Depending upon the medical device and/or intended purpose or use of the medical device, the color-changing material may be provided in a kit for use with a medical device or embedded or integrated as a component of the device.

When adhered to the surface, the color-changing material may be adhered by any suitable medical-grade adhesive or in the case of certain color-changing materials may be adhered by molding the material to the surface of the medical device.

When embedded or integrated as a component of the device, the one or more layers of color-changing material may be integrated into the device during manufacture of the device.

By way of illustration a laminate material may be used to mold a device, wherein one or more outer layers of the laminate are composed of a color-changing material.

[0010] Independent of whether the color-changing material is embedded or adhered to the surface of the medical device, advantageously the color-changing material is located at a patient-engaging surface of the medical device so that excessive pressure or strain at the point of contact with a patient's skin can be detected. In this respect, the "patient- engaging surface" or "skin-engaging surface" refers to the interface between the patient 's skin and an external pressure-producing source, e.g., an element of a medical device, equipment, or consumable which can be in contact with the body of a patient, e.g., oxygen masks, any ventilation, feeding or urinary equipment and tubing, electrodes of any type and their wiring, stoma care devices, orthoLies and prosthetics, bone fixators, orthopedic equipment, sensors and monitoring equipment, e.g., pulse oximeters or glucose monitors, wireless devices and wearable devices, etc.

Wireless devices and wearable devices can be, for example, such as those used for monitoring patient movements in bed, repositioning, or events of patients leaving the bed or returning to bed in hospitals or long-term care.

[0011] It will be appreciated that the patient-engaging surface can be applied directly over the skin of an individual, or over a layer of clothing. For example, the patient-engaging surface can be applied to a heel of an individual wearing a sock, over the sock. Another example could be applying a pad under a shoulder strap of a backpack wherein the patient-engaging surface would bear over a garment (e.g., a shirt).

[0012] The color-changing material can have any shape, for example, a shape that can be described or roughly described by two dimensions, for example, a length and a width. In another aspect, the color-changing material can have a shape that can be described or roughly described by a single dimension, for example, a diameter. The color-changing material can have a shape of a rectangle, a shape approximating a rectangle, non-regular or regular polygon, any curved shape, or any combination thereof. The color- changing material can take the form of a pad, foam pad, patch, or film. The color-changing material ccaann be configured to have a particular size and shape, or it can be configured to be cut into a desired shape by a user of the color-changing material or by a caregiver.

[0013] The color-changing material can be flexible and can be configured to be laid along, or secured to, a curved shape, for example, a concave shape or a convex shape, of a medical device or any other object that is in the patient's surroundings and with which the patient may come into contact.

For example, a protective pad composed of the color-changing material can be wrapped around a tube such as a nasogastric tube or endotracheal tube to form a pad in the shape of a tube. In another example, a protective pad composed of the color-changing material can be shaped so as to fit along a portion of an oxygen mask which comes into contact with a patient's face, and it can be secured thereto, or alternatively formed as an integral part of the oxygen mask.

In other aspects, the composed of the color-changing material can have the shape of segments of a cervical collar or a spine board or be applied to cover the complete surfaces of these devices which may come into contact with a patient. In so far as the color-changing material is at least located at the patient-engaging surface of the medical device, it preferably provides a smooth surface and most preferably does not include any protrusions, filaments or other structures extending beyond the surface plane of the device, which would come into contact with the patient's skin. Moreover, because the instant invention provides a visual means for sensing pressure/strain, sending circuitry or alarms are avoided.

[0014] Ideally, all or a portion of the color-changing material is transparent. The term "transparent" will be used to describe a material, which can be completely transparent, partially transparent, semitransparent, or translucent, such that changes of color of the material can be observed in response to pressure/strain. In addition, the material's transparency allows visualization of any skin trauma without removal of medical devices, thus avoiding skin irritation. These features allow healthcare providers to easily detect Impending pressure/strain injury and take action to prevent an injury.

[0015] The color-changing material is configured to provide a visual indication regarding a measure of pressure/strain applied to it. The color-changing material may be composed of one or more layers. In some aspects, the color-changing material may be composed more than one layer. In aspects wherein the color-changing material is composed of more than one layer, at least one layer changes color in response to pressure/strain. In some aspects, the color-changing material may be composed more than one layer, where each layer is responsive to a different amount of pressure and indicates the changes in pressure with a color unique to that layer.

The color-changing material thus can be configured to provide an attention-grabbing visual indication, e.g., through the use of one or more bright colors, e.g., pink, red, green, white or blue, that a medical device is exerting a dangerous pressure on the body of a patient. In alternative aspect, the color-changing material can change from transparent to opaque

(i.e., milky, white, or cloudy) as an indication of applied pressure/strain. The change in color can indicate to a caregiver that the medical device must be adjusted immediately in order to prevent harm from being caused to the patient. By way of illustration, when pressure or strain is applied to the color-changing material, the color changes from transparent to opaque, pink, green, blue, white or other color depending on the amount of pressure/strain. The colorization can be controlled in a number of ways by adjusting the film thickness of the color-changing material by selecting polymer mixing ratios, particle coating methods, particle sizes, or fabrication process, for example. However, the more sensitive the elastomer, the thinner and more fragile it may become. Given that sensor durability must be maintained, the elastomer's balance of pressure/strain sensitivity and durability can be assessed and optimized by adjusting the mixing ratio of polymer cure gel, polymer ratio in a blend, drying temperature, and drying time.

[0016] The color-changing material and medical devices herein allow clinicians to obtain optimal pressure/strain interfaces between a patient's skin and a medical device due to the adjustable, customizable sensor colorization, sensitivity and durability of the color—changing material.

Successful parameters of the color-changing material can include, but are not limited to, slight colorization, preselected colors based on the particle size (e.g., pink begins at 67 mmHg and green at 240 mmHg), a stress-strain curve, and transparency of observable stage 1 pressure/strain injury beneath the medical device at the unloaded state.

[0017] Advantageously, changes in color of the color- changing material are reversible. A "reversible" change in color refers to the appearance of color in the color-changing material upon application of pressure or strain, wherein removal of said pressure or strain returns the color—changing material back to its original color. In this respect, color- changing material is reusable. Moreover, reversal of color can be used as a guide to aid clinicians in determining whether intervention for the overpressure/strain condition has been successful.

[0018] Examples of materials that provide a reversible change in color upon application of pressure and/or strain Include but are not limited to opalescent photonic-crystal-containing elastomers including arrays of silica particles or polystyrene particles embedded in a transparent material, e.g., an elastomer or silicone such as transparent room temperature vulcanizing (RTV) silicone rubber, polydimethylsiloxane (PDMS), vinyl methyl (VMQ) silicone rubber, soft silicone rubber transparent gel (e.g.,

Ecoflex™), or combinations thereof. See, e.g., Sitpathom et al. (2020) Optics Express 28(11); and Karrock & Gerken (2015)

Biomedical Optics Express 6(12):4901). Preferably, the elastomer has a Young's modulus of 2 MPa or less, 1.9 MPa or less, 1.8 MPa or less, 1.8 MPa or less, 1.7 MPa or less, 1.5

MPa or less, MPa or less, 1.3 MPa or less, 1.2 MPa or less, 1.1 MPa or less, 1.0 MPa or less. Preferably, the elastomer has a Young's modulus of at least 0.5 MPa, 0.6 MPa,

0.7 MPa, 0.8 MPa, 0.9 MPa or 1.0 MPa. In some aspects, the elastomer is a blend of PDMS and soft silicone rubber transparent gel. In certain aspects, blends of two elastomers can be in a ratio in the range of 5:1, 4:1, 3:1, 2:1 or 1:1.

[0019] Notably, elastomers can contain transparent colloidal particle arrays that visibly change color when subjected to strain or excessive pressure/strain, thus alerting clinicians to the potential MDRPI. The colors of such films can be tuned by varying the size of the particles (e.g., using particles with an average diameter in the range of 1 nm to 1 μm), changing the spacing of the planes (e.g., by using particles at a concentration in the range of 1% to 99% of the material in which they are embedded in), or changing the refractive indices of the components. In some aspects, silica particles having an average diameter in the range of 150 nm to 500 nm are used. In other aspects, silica particles are used at a concentration in the range of 1% to 20%, or more preferably

5% to 10%, of the material in which they are embedded. The colorization of the material can occur because the separation between inelastic particles enables color tuning without significant particle rearrangement, which is associated with elastic deformation of color-changing material and reversible color change. While not wishing to be bound by theory, lower concentrations of particles (i.e., greater spacing) may allow for detection of lower threshold pressures, while high concentrations of particles may allow for higher contrast when it the color change sets in, which means that the color will be clearer. Further, opal structures can reflect color as explained by Bragg's equation:n = 2dsinθ. When strain or pressure/strain is removed, the colorization gradually deactivates due to particle rearrangement, causing a reverse color change, and the elastomer reverts to its original shape.

[0020] Because elastomeric materials may be liquid before they dry, they can be molded into limitless shapes and thicknesses. Thus, the color-changing material can be readily applied to medical device surfaces, or integrally formed therein, where bulky materials cannot be used. Moreover, the elastic and soft nature of elastomeric polymers provides for optimization of skin sensation, comfort, and best fit.

Contrast color coordination, subject skin color and product colorization, size of device, air leakage (oxygen mask) can be considered in customizing and refining the color-changing material and integrated products.

[0021] In a further aspect, the color-changing material may be prepared in layers using a three-dimensional (3D) printer, e.g., via direct ink-writing, wherein layers of material are ejected through nozzles at a controlled flow rate and deposited along digitally defined paths to create 3D structures in a layer-by-layer fashion. In general, extrusion in 3D printing processes can be pneumatic (air pressure- driven) or mechanical (piston-driven). The printer can precisely manipulate the squeezing of an ink through the needles to print a required design. By way of illustration, a color-changing material may be prepared wherein a layer of silica particles are sandwiched between two layers of elastomeric material to create a composite, three-layer sandwich material (i.e., elastomer/SiO ₂ /elastomer film).

[0022] In a certain aspect of this invention, the color- changing material changes from transparent to pink to green or white with increasing pressure/strain, a phenomenon resembling a chameleon's changing color for example. In another aspect, pressure/strain can be revealed via interference, light scattering, stress-optical phenomenon, or chemistry related color change, for example as in Belousov-Zhabotinsky (BZ) or spiropyran polymer reactions.

[0023] In a further aspect of this invention, a method for preventing a medical device-related pressure injury or ulcer is provided. In accordance with this method of the invention, a color-changing material, which is transparent and configured to reversibly change color in response to pressure or strain, is embedded or adhered to a patient-engaging surface of a medical device so that changes in pressure upon use of the medical device are detected and a medical device- related pressure injury or ulcer is prevented.