Improvement of Smart Wound Diagnostics

Introduction to Smart wound dressings:

Chronic wounds afflict approximately 2 % of the worldwide population and cost billions of pounds to the healthcare sector. Microbial biofilms have been implicated in the persistence of chronic wounds and are thought to be responsible for nearly 80 % of all non-healing wounds. (Magee et. al)

A smart dressing fabricated from optimal material combinations oriented in a specific multi-layered architecture should have qualities that inhibit bacterial growth, manage excess exudate, and promote re-epithelialization, while simultaneously maintaining a moderately moist environment. Composites of natural and synthetic polymers can contribute a similar composition as ECM in addition to delivering antibiotics and growth factors. Fiber geometry and scaffold type can also affect antibiotic elution, mechanical strength, and porous structure for tissue growth. The aim of smart wound dressings is to create an advanced wound dressing technology that will detect wound infection and colonization by pathogenic bacteria producing a colour change, and then automatically triggering the release of antimicrobials /antibiotics into the wound area. (Gianino et. al)

A range of coloured indicator films containing dyes responsive to volatile substances in the wound were developed and tested against porcine skin inoculated with

Pseudomonas aeruginosa

. This study showed a CO

₂

-sensing film comprising of xylenol blue dye underwent a marked colour change from blue to yellow within 12 h of bacterial inoculation, whilst in uninoculated control skin the film remained blue (no colour change). (Phillips et al)

In addition,vAPCI-MS identified putrescine as an additional compound of interest, and responsive indicator films were developed for its detection. The marked colour change exhibited by each indicator film has potential to develop an early warning, point-of-care technology and is promising to combat the development of microbial biofilm in wounds. (Phillips et al)

Pathogenic bacteria responsible for wound infection secrete virulence factors that alter their host environment such as lipases, hyaluronidase which degrade healthy tissue, and toxins such as a-hemolysin, leukocidins , leukotoxins and cytotoxins which actively kill healthy cells. One of the ways smart wound dressing technology aims to enhance wound healing is by targeting these toxin producing bacteria using wound dressings impregnated with nanocapsules containing antibiotics/antimicrobials combined with a dye that on release changes colour. (Zhou et al)

Research has also focused on stabilizing the nanocapsules whilst retaining their sensitivity to bacterial virulence factors and investigating a range of methodologies for attachment into wound dressings or wound dressing components such as non-woven polypropylene. (Young et al)

Current wound dressings which slow or prevent wound infection primarily use silver as the antimicrobial component. Unfortunately, silver-containing dressings may be partially cytotoxic, reducing epithelialization and tissue growth, which in turn may lead to a significant increase in hospitalization time and healthcare costs. Moreover, silver-containing dressings continually expose the wound to the antimicrobial agent, which may increase the rate of bacteria evolving resistance (Poon et al)

Svendsen et al from Tromsø University in Norway discovered the antimicrobial peptide AMC-109 and recent research has aimed at incorporating this into a ‘smart’ wound dressing, in which the antimicrobial peptide will be covalently bound to a polymer hydrogel matrix, incorporating an enzyme cleavable ester linker with the peptide being released via the action of bacterially secreted esterase enzymes. The advantage of this approach is that the antimicrobial will be released only when it is needed, where it is needed. (Young and Jenkins)

Different types of wound dressings & nanoparticles:

There are several types of wounds, each having distinctive healing processes. This necessitates the utilization of a wide range of polymer based wound dressings (Mir et al, 2018). These include foams, films (polyurethane), hydrogels (glycerin, alginate), haemostatic agents (collagen), hydrofibers (cellulose), sealants (dimethicone) and composites with shape memory polyurethanes (SMPUs).

Effective wound care treatments need to tackle the problems of pain, inflammation, infection caused by multi-drug resistant bacteria, delayed healing and associated costs to the National Health Service (Das and Baker). Unlike traditional synthetic or natural polymer wound dressings, smart polymers can control material properties in response to external cues (Koetting et.al. 2015). By doing so, drug delivery can be controlled in response to environmental cues and ultimately stimulate faster healing.  (Gianino et.al,2018) Biomaterials based approaches for modulating gene expression provide the possibility to transiently alter protein levels locally within a wound(Castleberry et.al.2016; Nelson et. al. 2014; Martin et. al. 2016) This can be used to understand how specific biological changes affect key stages of wound repair.

Recent developments in biomaterial based wound dressings include different types such as:  1. Standalone biomaterials (Siloxysilane; Dextran; Urethane; Collagen; Synthetic); 2. Dressings with bioactive components (Fibrin; Hyaluronic acid) 3. Cell encapsulating (Poly Beta- Amino ester; Fibrin and PEG, PEG and RGD) 4. Nucleic acid delivering (Collagen; Hyaluronic acid; Polyurethene; Chitosan, Dextran Sulfate and Poly-2) 5. Animal product based (Small intestine, Submucosa, Amniotic membrane, Fibroin, Marine collagen) 6. Drug or antibiotic loaded dressings (Chitosan and PEG; Carrageenan, Polyox, HPMC; Polyurethene and Dextran; PEG and Chitosan; PEG) 7. Natural Product (Genipin, chitosan, PEG, and silver) (Das and Baker, 2016)

Recent developments in Nanoparticle – based wound therapies include several types such as:

1 Metal (Silver, MgF

₂

, Cerium oxide, Copper, Iron Oxide, Gold) 2. Antibiotic loaded (Polyacrylate; Folic acid- tagged Chitosan) 3. Nitric Oxide releasing (Tetramethyl Orthosilicate, PEG; and Chitosan; Silica) 4. Lipid based (Proteoliposomes in Alginate hydrogel; Solid lipid nanoparticles; Exosomes) 5. Polymer based (Chitosan, Pectin and Titanium dioxide; Hyaluronan) (Das and Baker, 2016).

Role of Biosensing:

Bio sensing helps in the real time quantitative evaluation of several parameters such as exudate levels, bacterial concentrations, skin pH, local temperature and tissue regeneration etc. which help to monitor wound healing. Developing a sensor embedded within a smart wound dressing could potentially solve problems associated with the need to frequently change dressings, as it will be possible to monitor the status of the wound with the smart dressing in place. (Gianino et.al)

Various sensing strategies (electrochemical, mass based, and optical) can be used for identification of a specific biomolecule using different measurement methods (conductometric, potentiometric, amperometric, impedimetric, surface charge, piezoelectric, megnetoelastic, surface acoustic wave, fiber optic, absorbance, and luminescence). Some of the sensors used to detect biomarkers in chronic wounds include Smart Bandage UA Sensor, Carbon Fiber sensor, Oxygen Bandage sensor, Wireless thermistor, Flexible Sensor array and Inkjet printed smart bandage, ELISA MMP Sensor, Wearable enzymatic Sensor, Flexible Hydrogel pH Sensor, Poly-tryptophan Carbnon fiber pH Sensor, Intelligent Hydrogel Dressing etc. (Gianino,2018).Polypyrrole, polyaniline, and poly(ethylenedioxy thiophene) are the most common conducting polymers used for conductive hydrogel fabrication (Tavakoli and Tang, 2017)

Electrospinning is a simple, cost-effective, and reproducible process that can utilize both synthetic and natural polymers to form polymer nanofibre meshes.These nanofibre meshes formed an effective scaffolding for wound dressings by providing high-surface area, micro-porosity, and the ability to load drugs or other biomolecules into the fibres. Abrigo et al utilised electrospinning technique and demonstrated its potential for enhancing wound healing in two ways. Firstly, these meshes have the potential to incorporate Antibacterial delivery (with responsive systems which trigger release of antibiotics only if infection occurs). Simultaneously, these meshes also stimulate cell proliferation in the wound and encourage healing.

There are many sensor types and potential target of biomarkers, but for them to be useful in sensing the wound environment they need to be economical, disposable, biocompatible, and able to detect clinically relevant parameters, conform to the shape of the wound / ulcer and have flexible properties similar to conventionally applied dressing. (Gianino et.al)

Biochemical sensors are highly sensitive but miniaturization and integration with a smart dressing is more difficult and these devices are typically limited with respect to shapes for fabrication. On the other hand, impedance and pressure sensors could be fabricated as an array that could be implanted into the dressing of choice. Further research and investigation needs to be done to assess the use of biological, impedance, or pressure sensors in the use of real-time detection of the chronic wound environment. (Gianino et.al)

Advanced integration of biosensors in smart dressing would help prevent ulcers and amputations and accelerate the healing process. Sensing the chronic wound environment in real-time and creating a feedback system would quantify and classify the healing process and equip clinicians with a valuable tool to quickly identify the worsening of a chronic wound.

Suggested Aims of the Project:

1. To develop novel biopolymers which can be used to improve smart wound dressings, improve healing rates and reduce healing times using methods which target multiple aspects of the repair process.

2. To develop, assess and integrate the use of biosensors (biological, biochemical, impedance, or pressure sensors) in the use of real-time detection of the chronic wound environment.

3.    Investigate the properties of hydrogels which will form part of the sensor system.

4.     Develop methods to covalently bind antibodies to the sensor surface and photo     functionalize the material, and make the patterns and optical structures which will eventually form the sensor.

Provisional Progress Plan

Year 1:

• I will start designing the research, make a timetable, consider ethical issues and iron out any potential problems and challenges as they occur. I will draft a review of literature with extensive references and identify the shortcomings of existing technology which would provide potential scope for improvement.
• Evaluation of hydrogel polymers for entrapment and release of antimicrobial peptide including measurement of release kinetics and efficacy in controlling Staphylococcus aureus infection in wound models.
• Network and liaise with infectious disease / research nurses from the NHS with a view to study the efficacy of antimicrobial peptides against bacteria obtained from infected patients.

Year 2:

• Construction of wound dressing with combined diagnostic and antimicrobial functionality via patterning of gel matrix with signaling or antimicrobial components. This will involve integrating biopolymers with biosensors.
• I will investigate the properties of hydrogels which will form part of the sensor system with a view of  testing on ex-vivo rat or porcine wound models.

Year 3:

• Develop Covalent attachment of antimicrobial peptide into hyaluronic acid hydrogel gel and incorporation into prototype wound dressing for evaluation of triggered antimicrobial release.
• Based on results, patenting and evaluation of potential for upscaling and technology transfer with industry partners (Smith & Nephew)
• Last six months would be devoted to papers and thesis writing

Abbreviations:

CO

₂

– Carbon Dioxide

(vAPCI-MS) – Volatile Atmospheric Pressure Chemical Ionization-Mass spectroscopy

ECM –  Extra Cellular Matrix

SMPU- Shape Memory Polyurethanes

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