Case Examples
The same pattern repeats across different clinical domains: a problem arrives, a solution emerges, practice changes.
Pebble’s solutions now reach hundreds of thousands of patients across the world. Our portfolio spans molecular immunology to nutritional intervention, from refinements in surgical technique to the application of advanced nanomaterials. What unifies this work is not any particular scientific domain but rather an unwavering commitment to a single principle.
The answer must ultimately benefit patients.
The case examples below are a small selection of our work that is not confidential.
Vein Harvesting & Patient Deaths
A landmark study in the New England Journal of Medicine reported that minimally invasive vein harvesting for coronary artery bypass surgery was killing patients. Surgical centres across the UK and US abandoned the technique virtually overnight. They returned to traditional open harvesting: a continuous ankle to groin incision, causing prolonged pain, impaired mobility and high infection rates.
Were the reported harms real, or had confounding factors distorted the findings?
We provided the definitive answer via a combination of preclinical and clinical trials. Minimally invasive harvesting is safe, produces better patient outcomes, and reduces healthcare costs by more than £2,000 per procedure. Centres resumed the technique which is now standard care for more than 400,000 coronary bypass operations worldwide annually.
Cardiac MRI & DNA Damage
Published studies reported that cardiac MRI induces DNA damage in circulating immune cells. A diagnostic technology used on millions of patients annually might be causing immunological harm. Some researchers called for restrictions analogous to ionising radiation.
Does MRI genuinely cause such damage?
We ran the largest and most comprehensive investigation to date, combining in vitro exposures with in vivo sampling of patients undergoing cardiac MRI. We conclusively proved that clinical cardiac MRI does not induce DNA double-strand breaks, nor does it compromise immune cell viability or function. We also discovered why the smaller studies got it wrong: the biomarker they relied upon has such pronounced inter-individual variability that underpowered studies were detecting noise, not signal.
The technology is safe. Millions of patients continue to benefit from it.
Ex Vivo Lung Perfusion (EVLP)
Approximately 80% of donated lungs are deemed unsuitable and discarded, while patients on waiting lists die. Ex vivo lung perfusion (EVLP), developed by Prof Stig Steen at Igelösa, offered a way to evaluate marginal lungs outside the body before deciding whether to transplant.
But could EVLP do more than assess? Would it actively improve the donor lung?
We demonstrated for the first time that it does. EVLP depletes passenger leukocytes from the donor lung, stripping out the inflammatory cells that drive rejection. It upregulates cell survival pathways and downregulates those that induce cell death, meaning the lung that comes out of perfusion is fundamentally better than the lung that went in.
This understanding gave clinicians confidence in the technology. We then performed a multicentre clinical trial, confirming EVLP-reconditioned marginal lungs were comparable to standard transplants. Following FDA approval in 2018 and 2019, organs that would have been discarded are now routinely saving lives.
Cardiac Immunodepletion & Xenotransplantation
Hearts undergoing non-ischaemic perfusion were generating immunological responses that would cause severe rejection post-transplantation. What was perfusion actually doing to donor hearts?
Using flow cytometry, cytokine profiling, and targeted proteomics, we discovered something unexpected. Perfusion was progressively depleting the heart of its resident leukocyte populations. What looked like an inflammatory storm was actually therapeutic: it was exhausting the donor organ's capacity to attack its future recipient. We confirmed it in transplantation experiments, where immunodepleted hearts exhibited markedly reduced graft infiltration compared with conventional cold storage.
This understanding informed what came next. On 7 January 2022, surgeons at the University of Maryland transplanted a genetically modified pig heart into a 57-year-old man with terminal cardiac disease using this device.
Drug Monitoring in Transplant Patients
Transplant patients on immunosuppression need regular blood tests to ensure drug levels are correct: too low, the organ rejects, too high, toxicity causes harm. This means frequent trips to outpatient departments, often for years after transplantation.
The clinical team asked us: could we reduce this burden?
We tested how long cyclosporine and tacrolimus remain stable in dried blood spots. Both drugs can be accurately measured from a simple fingerprick sample posted to the laboratory, meaning patients no longer need to travel for routine monitoring. They take the sample at home, post the card, and the results come back.
Fewer hospital visits. Less disruption to patients' lives. The same clinical accuracy.
Wound Closure After Cardiac Surgery
Post-operative wound complications affect over 20% of cardiac surgery patients, yet the leg incisions required for vein harvesting had received surprisingly little rigorous evaluation. Technologies existed that might help, tissue adhesives and barbed sutures among them, but nobody had tested them in this context.
So we did. In the tissue adhesive study, every patient in the treatment group achieved optimal cosmesis. No patient in the conventional suture group did. Patient satisfaction was substantially higher. We then demonstrated that barbed sutures reduced closure times and healing complications.
This was the first evaluation in cardiac surgery. Both are now widely adopted.
Diet & Cardiovascular Risk in Transplant Patients
Cardiovascular disease is the leading killer of heart and lung transplant recipients. The clinical team asked us: could we improve outcomes without adding yet another pill to patients already burdened with complex medication regimes?
We designed a 12-month dietary intervention comparing Mediterranean and low-fat diets. 95% of patients completed the programme, all of them adhered to their diet, and both intervention groups reduced body mass index, fasting glucose, and total cholesterol. Those who continued with standard diet went in the opposite direction on every measure.
We can identify molecular mechanisms of immunological tolerance. We can also run a dietary study with patients and their families. Problems worth solving exist at every scale.
Extended Kidney Preservation
Kidney preservation by static cold storage is a race against time. Current guidelines permit 3-6 hours; beyond that, cumulative injury makes organs progressively less viable. In the United States, roughly a quarter of retrieved kidneys are discarded, in the UK, roughly 100 kidneys per year are deemed unsuitable after retrieval.
Could genuinely physiological perfusion substantially extend safe preservation?
We developed a protocol and tested it head-to-head against the clinical standard. Kidneys on our protocol maintained healthy blood flow, produced urine at normal adult rates, and showed no macroscopic injury. Kidneys on the clinical protocol reperfused poorly, produced grossly abnormal urine volumes indicating tubular injury, and developed multiple infarcts. Every clinical protocol kidney was unsuitable for transplantation. Every one of ours was suitable.
A first-in-human transplantation is now planned. If it works: no more emergency overnight surgery, adequate time for organ assessment, resulting in more kidneys reaching patients who need them.
Nanoparticle Protection of Transplanted Organs
Ischaemia-reperfusion injury is paradoxical: restoring blood flow to oxygen-starved tissue causes additional damage through cascading reactive oxygen species (ROS) - it is a fundamental transplantation challenge. Biological antioxidants do not help much because they denature and degrade too quickly.
Could synthetic nanoparticles engineered to scavenge ROS protect organs during preservation and reperfusion?
Working with nanoparticles that target the reactive species most implicated in reperfusion injury, we demonstrated striking protective effects: more than fivefold reduction in oxidised DNA, substantial drops in inflammatory markers, and stable haemodynamics while untreated organs became acidotic and required rescue.
This is the first therapeutic application of nanomedicine-augmented normothermic machine perfusion. It is proof of concept for an entirely new approach to protecting transplanted organs.
Limb Preservation
Reconstructive surgeons came to us with a scenario that had no solution: polytrauma with traumatic amputation. A patient arrives with head and chest injuries and a severed limb. You stabilise the patient first, but while the team saves the life, the limb is dying on a side table. By the time the patient is stable, it is too late.
They challenged us to build a system that maintains a limb outside the body long enough for life-saving surgery and reattachment.
We built it. The system now maintains an entire human limb for more than 24 hours with no detectable injury.
The technology is moving into another application: transplantation of limbs from deceased donors. A VCA transplant team is now working with our system, with the first transplant planned for 2026.
Gene Therapy Delivery to the Kidney
A gene therapy company developing AAV vectors for kidney disease had conducted preclinical studies in mice showing no obvious injury. They came to us to evaluate safety before moving toward clinical trials.
The problem was that mice are poor predictors of human AAV response. Their vasculature is too different, and immune responses not comparable. We designed a delivery protocol that could be replicated clinically: a single pass of the vector across the renal vasculature, followed by 24 hours of perfusion monitoring.
The result was unexpected. The treated kidney developed visible cortex necrosis and calyceal clot formation. The control kidney showed no injury. This was not visible in mice. It would have been visible in patients.
The company now had critical information: at this dose, their vector causes acute renal injury via this delivery route. They could adjust dose, modify delivery, or reformulate before reaching the clinic.
Lipid Nanoparticle Safety for Gene Editing
A company developing lipid nanoparticle therapeutics for liver-targeted gene editing needed comprehensive safety evaluation beyond what conventional models could provide.
We ran 30-hour perfusions comparing their LNP formulation against controls, monitoring haemodynamics, metabolic function, liver enzymes, and inflammatory responses across 17 mediators. The extended timeframe allowed us to distinguish immediate treatment effects from delayed responses, and therapy-specific changes from perfusion duration effects.
The company received a complete safety profile: which parameters changed, when, by how much, and whether changes were transient or sustained. Data to support their regulatory submissions and inform clinical development.
Liver Safety of a Novel Anti-Cancer Compound
A biotech company isolated a PKC activator from a tropical plant with potent anti-tumour activity. They wanted to use it for hepatic malignancies, but needed to understand how the liver would respond to direct injection.
We evaluated three doses against vehicle control over 24-hour perfusions in our LIVING-LIVER system. The study revealed something important: the drug's effects remained localised to the injection site, while the vehicle formulation caused diffuse injury throughout all lobes. This distinction, invisible in conventional testing, indicated the drug itself was not the problem. The formulation was.
The liver maintained global metabolic function throughout, with complete drug clearance by 6 hours at lower doses. The company now has safety data to guide reformulation and identify therapeutic windows for clinical development.
Extracellular Vesicle Biodistribution in the Kidney
A regenerative medicine company developing therapeutic extracellular vesicles needed to know where their EVs travel to when delivered to a kidney, and whether they cause harm.
We perfused kidneys with fluorescently labelled EVs and tracked their distribution. Histological analysis indicated EV deposits within glomeruli, inside vessel walls, and in intracellular spaces. Critically, we found no adverse effects: no biochemical derangement, no change in metabolic performance or difference in haemodynamics between treated and control kidneys.
This was the first time the company had observed exactly where their therapy localises in a functioning organ. They also had confirmation of safety across every measured parameter.
These are just examples. Most of what we solve remains confidential, reaching patients under our partners' names.