6.Sustainability

Over 200,000 ICDs are implanted worldwide every year (Ganesh, 2011). From material acquisition (i.e. mining) to manufacturing, implantation and disposal, ICD production will have environmental consequences.

Mainly, environmental concerns arise from the Material Acquisition and Manufacturing Phase, and the Waste Management that follows.

6.1.2 Material Acquisiton and Manufacturing

ICDs contain metals like titanium, lithium for batteries and many polymers.
Extraction and processing of these metals have environmental implications e.g. mining and refining processes.
Lithium-ion batteries are potential fire hazard and cause for contamination due to their chemical reactivity.
Lithium-ion batteries are hazard waste; US EPA classifies them as “universal waste”.

6.1.3 Waste Management

Domestic Processing by US and European nations on metal recovery like cobalt, lithium and nickel.
Europe and US send to nations like Belgium and Germany which have proper battery recycling.
Belgium (Umicore), Germany, South Korea host facilities specializing in recycling of lithium-ion batteries and complex electronic waste.

6.2 How can we make ICDs more sustainable

6.2.1 Introduction

From 'Principles' under section '2.5 Materials in ICD Manufacturing', the following materials have been outlined:

Titanium
Silicon and derived polymers
Conductive Metals (Platinum, Gold)
Polyurethane

In this section, the table below outlines why these materials are problematic to the environment and hence have to be modified.

6.2.2 Problem with Materials of Current-Day ICDs

Table 8 - Environmental Concerns for Titanium and Silicon and derived polymers

Table 9 - Environmental Concerns for Conductive Metals and Polyurethane

6.3 Overview of the 'green' next-generation ICD

Figure 39: AI generated image of a hybrid next-gen ICD with wearable charging pad on the body .

While integration of Artificial Intelligence (AI) into ICDs is the most probable up-and-coming solution at this current age, AI is not exactly environmentally sustainable as AI consume a lot of energy to run consistently and requires more energy than renewable energy can provide (Earth.org, 2023)
ICDs can be more sustainable through the research of durable biocompatible biomaterials to not only improve device functionality but to also design sustainability. To achieve this, our group is going to tap on biological process and mechanisms and implement them onto the next-gen of ICDs.

Figure 40 - A Venn diagram that underscores the three important aspects of the next-generation of ICDs

6.4 In-Depth: Sustainabiliy Modifications and Biological Processes

6.4.1 Bio-inspired Energy Harvesting Method

Details

Using Bio-energy harvesting methods by tapping into body’s natural electrical/kinetic energy.
Cardiac motion or blood flow kinetic energy can be utilised.
Piezoelectric materials (PMs) are those that generate electricity when bent or compressed.
Using PMs, we can use heartbeats or blood flow to generate power.

Intended Outcomes

Biological sources of energy reduces reliance on traditional batteries, thereby extending device life.

It also reduces environmental impact by reducing battery waste in landfills.

Figure 41 - PMs mechanism

Figure 42 - PM implantation in an artery (Joseph Allen, 2008)

6.4.2 Self-Healing Polymers for Durability

Figure 43 - Self-healing polymer mechanism diagram (MDPI, n.d.)

Details

Incorporating self-healing materials to extend ICD functionality and lifespan.

Can be applied to the leads manufacturing which prevents lead fracturing in the long run by self-healing of micro-fractures, hence reducing risks for surgical interventions.

Intended Outcome

Reduced environmental impact of disposed ICDs and lead replacement in the long run.

Biological Background

Self-healing polymers can mimic these regenerative properties, allowing for the autonomous repair of micro-fractures in ICD leads, integrating with surrounding cardiac tissue to minimise inflammation and enhance durability. Relevant genes include MMPs (Matrix Metalloproteinases) for extracellular matrix remodelling and VEGF (Vascular Endothelial Growth Factor) for promoting angiogenesis.

6.4.3 Genetic Engineering for Non-invasive tissue Stimulation

Details

Exploring genetic engineering to enable cardiac cells to respond to light or ultrasound instead of electrical stimulation.
Using a bandwidth of sound frequency and certain infrared light, can be coordinately used as stimuli for cardiac cells.
This can help circumvent for invasive implantation.
A waterproof, rechargeable wearable device instead can be worn under clothes to produce the specific bandwidth of ultrasound and infrared light.
-Alternatively, these technology can be used to instead recharge pacer in the body, instead of genetically engineering cardiac cells.

Intended Outcome

Reduced landfill waste from acquisition of raw materials, manufacturing nad transport of ICDs.

Figure 44 - Mechanism of Optogenetic Proteins in the development of ion potential (Rappleye et al.,2019)

Biological Background

Optogenetics and Channelrhodopsin Genes

The use of optogenetic proteins (e.g., channelrhodopsins, halorhodopsins) that enable cells to respond to light. Genes like ChR2 (channelrhodopsin-2) can be introduced to cardiac cells to make them light-sensitive, allowing non-invasive stimulation.

Mechano-transduction in Cardiac Tissue

The response of cardiac myocytes to mechanical forces and how they could potentially be engineered to respond to specific ultrasound frequencies. Genes involved in mechano-sensitive ion channels, such as Piezo1, are relevant for this aspect (Zhu et al, 2023).

Cardiac Cell Gene Expression and Responsiveness

Modifying specific cardiac cells to express proteins that can react to non-electrical stimuli, focusing on heart-specific genes like MYH6 (myosin heavy chain 6, found in atrial muscle) for targeted responses to light or sound waves.

Involvement of MYH6 in modification to make cardiac cells reactive to light or ultrasound (Chen et al., 2021).

Challenges and Risks

There is always a risk of cancer.

Genetic engineering is heavy regulated in multiple countries. Carrying out such experiments may not even be permissible and might be unethical for some countries. Genetic engineering of organisms have to be well assessed for their short, medium and long term effects on the organism. Multiple animal trials have to be carried out even before human embryo trials are carried out. It is almost impossible to do this with the current stance globally towards “designer babies”.

Europe: laws prohibiting germ-line genetic modification.

United States: not approved by regulatory bodies like the FDA

Japan: permits gene-editing research under strict conditions but ban its use in human reproduction.

6.4.4 Self-Regulating Temperature Control Using Thermoregulatory Proteins

Details

Thermoregulatory proteins similar to those regulating temperature in cells can be integrated into ICD to manage heat production and prevent tissue damage from overheating.
Heat Shock Proteins (HSPs) presence can activate heat shock factor (HSFs). Presence of HSF triggers HSE to increase HSP genes transcription.
Coating ICD with HSF

Intended Outcome

Cellular damage due to overheating in the long run can be reduced. Increases ICD lifespan hence reducing landfill waste.

Challenges

Long term studies have to be carried out as perpetual activation of HSEs may result in rouge cells i.e. Cancer.

Biological Background

HSPs have multiple mechanisms to protect cells from heat stress. Two of them are listed below:

1. As Molecular Chaperones

Elevated temperatures can cause proteins to lose their native structure and aggregate.
Assists in proper protein folding of nascent proteins, refold partially unfolded or misfolded proteins.
Prevents aggregation of misfolded proteins that may be toxic to the cell.

2. Protein Stabilization and Cellular Structures

HSPs interact with cellular proteins to protect them form irreversible damage by heat.

Thermoregulatory Proteins

Thermoregulatory proteins, similar to those found in cells, can be integrated into ICDs to manage heat production and prevent overheating, thereby protecting surrounding tissues from damage. These proteins can help maintain optimal temperature ranges for device operation

Coating ICD with HSF

Coating ICDs with HSF can enhance the device's ability to regulate temperature by promoting the expression of HSP genes in response to thermal stress. This adaptation can help mitigate the risks of tissue damage due to excessive heat during device operation.

Figure 45 - Multiple mechanisms of HSPs to thermoregulate at a cellular level (Saadeldin, n.d.)

6.4.5 Synthetic Biomimetic Nerve Networks for Signal Transmission

Details

Biomimetic networks mimic the nervous system to transmit signals without traditional wiring and leads.
Mimic function of neural networks using bio-inspired conductive proteins or synthetic neuron-like structures.
Replace traditional metal wiring with softer, more biocompatible materials.
Reduces risk of corrosion and fracturing, device is more compatible with tissue.
Rigidity is circumvented hence making it more comfortable for patients.

Intended Outcome

CD Patients will be able to do more physical activities and are less restricted by their ICDs.

Challenges

Surgical operations may be more invasive compared to intravenous lead insertion. This may lead to more complications and potential risk of infection.

Biological Background

Biomimetic Networks

Current research focuses on creating neural-inspired architectures that facilitate effective signal processing, such as using hydrogels that mimic the extracellular matrix for neuronal growth and connectivity.

Bio-inspired Conductive Proteins

Researchers are exploring the use of conductive proteins, like neurofilament proteins (e.g., NF-L - neurofilament light chain), which play critical roles in the structural integrity and signal transmission in neurons (Zhao et al., 2021).

Synthetic neuron-like structures, often made from conductive polymers such as polypyrrole and PEDOT are being developed to enhance electrical conductivity while mimicking biological signal propagation

6.4.6 Photosynthetic Power Source Using Light-Sensitive Pigments

Details

Power ICDs with energy harvested from light-sensitive pigments mimicking photosynthesis.
Light-sensitive pigments can be embedded on the epithelial layer of the skin connected to a subcutaneous ICD implant.
Hence the ICD could generate energy on light exposure, helping fulfil energy needs of the ICD or even store this energy for future need.
Suitable for patients who spend a lot of time outdoors and engage in physical activities.
These pigments can be placed somewhere near the chest and can only be visible under infrared light, for patients who do not want to see the pigments.

Intended Outcome

Reduced reliance on traditional batteries hence reducing need for ICD battery replacement. In the long run, it negates need for manufacturing of ICD batteries hence reducing manufacturing waste.

Biological Background

Phytochrome genes (e.g., PHYA and PHYB), could provide insights into optimising the efficiency of light-sensitive pigments. Understanding the mechanisms of photosynthetic efficiency at the molecular level can lead to advancements in pigment design and integration strategies.
Phytochrome A is (phyA) can reverse its conformational change (Chen et al., 2002) in the absence or presence of light. Downstream they possess kinase activity (Shinomura et al., 2000).

Epithelial Layer Integration

Studies are being conducted on transdermal delivery systems to ensure efficient embedding and integration of these pigments, which could help meet the energy demands of the ICD.

6.4.7 Enzyme-Powered Energy Cells using Body Fluids

Details

- Enzyme-based energy cells drawing power from blood or interstitial fluids.

- Conversion of glucose and oxygen from blood into electrical energy.

- Makes device self-sustaining, reducing need for conventional batteries

- There will be enzyme-linked bio-sensors and flow channels that detects and bind to glucose (Asrami et al., 2020) and reduces it, producing energy for the energy cells.

Intended Outcome

Reduced reliance on traditional batteries hence reducing need for ICD battery replacement. In the long run, it negates need for manufacturing of ICD batteries hence reducing manufacturing waste.

Challenges

Energy consumption of patient has to increase. There may be a risk of hypoglycemia, as patient has to continue consuming glucose, unsuitable for Type 1 diabetes patients that need continuous sugar source

Biological Background

Enzyme-Based Energy Cells

Current research focuses on using glucose oxidase (GOx) and lactate oxidase to facilitate the conversion of glucose and oxygen into electrical energy, which enhances the sustainability of medical devices.

Self-Sustaining Devices

Studies on integrating enzyme electrodes within devices aim to create a seamless energy generation system, improving device longevity and reliability.

ELBS and Flow Channels

biosensors can utilise glucose transporter proteins (such as GLUT1 and GLUT4) to enhance the uptake of glucose from blood or interstitial fluids. Flow channels designed to optimise the interaction between enzymes and substrates are being developed to maximise energy production. Research is being conducted on microfluidic devices that can enhance the detection and binding of glucose, enabling efficient energy conversion.

6.4.8 Genetically Encoded Protein-Based Power Generator

Details

- Utilise genetically encoded proteins generating energy when exposed to certain chemical signals within the body.

- Protein that respond to cellular metabolites could power specific ICD functions when sensing metabolic byproducts in the blood stream (cardiac arrest biomarkers if any)

- Possibly use ATP synthase on this one using ATP as a source of energy.

Intended Outcome
Reduced reliance on traditional batteries hence reducing need for ICD battery replacement. In the long run, it negates need for manufacturing of ICD batteries hence reducing manufacturing waste.

Challenges

Protein are heat sensitive, we need to engineer proteins that have high heat threshold. Also, this would mean energy production will be dependent on body heat i.e. during prolonged exercise, body heat produced can make energy production faster as more useful collision between substrate and protein. Tissue rejection, inflammation may be a biological hurdle.

Figure 46 - Tyrosine Kinase Receptor ((Tomulesa et al., 2024)

Biological Background

ATPase-linked Tyrosine Kinase Receptor only activated by HSFs at the extracellular region. Continuous ATP phosphorylation-dephosphorylation in the self-sustaining bio-ICD.

6.4.9 Harnessing ATP for Power for Next-gen ICDs

Details

Using bio-nanotechnology ATP can be harnessed or making use of ATP-drive enzymatic reactions to generate electric currents.
Using bio electrodes coated with ATP-hydrolysing enzymes.
Biocompatible sensors could interface with cellular ATP-producing mechanisms like mitochondrial activity.
ATPase can convert ATP into usable electrical power through redox reactions, ensuring a continuous energy supply.
Bioengineering a protein that is modelled after the ATPase to produce a gradient potential across the internal ICD system and the interstitial fluid. The gradient potential can be somewhat utilised to produce stored chemical energy that the ICD can use.

Intended Outcome

Lesser reliance on traditional batter, increase device lifespan.

Challenges

ATP production heavily depends on metabolic conditions that may fluctuate based on patient health and activity level. It may not meet high-energy demands of advanced ICDs.

Figure 47,48- ATPase and intermitochondrial membranes and space (image from BG1141 slides)

6.4.10 Body Heat to Power Next-Gen ICDs

Details

Heat is a byproduct of metabolism and can be harnessed using thermoelectric generators (TEGs) converting temperature gradients between body and environment into electrical energy via Seebeck effect.
Made of materials generating a voltage when there is temperature difference.

Challenges

The human body’s natural heat gradient is just a few degrees, providing limited energy. Generating enough electrical power for a reliable ICD means low efficiency of thermoelectric material.

Biological Background

Advanced biocompatible thermoelectric materials like doped semiconductors or nanomaterials can be implanted in the body, integrated with the ICD, creating a continuous power source.

Placement near large blood vessels or organs with high metabolic rate like liver or heart with substantial and heat consistent heat generation.
Generated power would be stored in micro-batteries or supercapacitors within ICD, with a power management system designed to handle the relatively low continuous energy flow, ensuring steady device functionality.

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