Injectable Particle Makes Surgery Safer for Newborns

It is, under a scanning electron microscope, a rather unremarkable-looking thing. Roughly a micron across, soft enough to deform on contact, studded with short chains of amino acids along its surface. You could fit thousands of them across the width of a human hair. What the particle does, though, is something quite specific to the biology of newborn infants, and something that conventional medicine has not, until now, been able to do cheaply or safely: it helps a premature or surgically compromised baby stop bleeding without triggering the dangerous overcorrection that adult blood products can cause.

The particle is called a BK-TriG, and a team of biomedical engineers at North Carolina State University and the University of North Carolina at Chapel Hill has just published evidence, in the journal Science Advances, that injecting it before a surgical procedure can reduce blood loss in a neonatal-like model by fifty to sixty percent. That number matters because neonates undergoing surgery face risks adults do not, and the gap in how their blood clots lie at the center of the problem.

Hemostasis, the process by which the body stops bleeding from a damaged vessel, is not a single fixed system. It changes as we age. In adults, the dominant mechanism for assembling fibrin (the stringy protein that forms the scaffolding of a blood clot) runs through what are called A-knob interactions: thrombin clips a small peptide from one end of fibrinogen molecules, exposing a sticky site that links the molecules into long protofibrils. In neonates, the molecular machinery is wired differently. Their fibrin polymerization depends more heavily on B-knob interactions, a separate set of molecular handshakes that promote lateral aggregation of those protofibrils into thicker, more branched fibres. The result is a clot that is softer, more porous, and more readily dissolved than an adult’s. Neonatal plasma clots, measured by imaging, have a porosity of roughly 96 percent; adult clots sit closer to 54 percent. They are, in effect, built from a looser weave.

That looseness is not a defect. It is a design feature of a developing system. The problem arises in the operating theater.

When a newborn requires surgery and loses blood, clinicians typically replace it with adult blood products: packed red cells, fresh frozen plasma, fibrinogen concentrate. These products carry adult fibrinogen, which forms stiffer, denser clots. In a neonate’s circulation, those stiffer clots can tip the balance toward thrombosis, where clots form in places they should not, including the lungs. A baby’s hemostatic system is essentially trying to absorb a foreign clotting architecture. Ashley Brown, co-corresponding author of the new paper and a biomedical engineer at NC State, has spent years on this specific problem. Her team wanted, as she has put it, to reduce the need for infants to receive adult blood transfusions during surgery altogether.

The BK-TriGs are the attempt at that reduction. Each particle is a hydrogel microgel, made from a polymer called pNIPAm, that can absorb water and become squishy. That squishiness is deliberate: deformable particles can spread between fibrin fibres and exert something like the mechanical force that platelets apply during clot contraction. The surface of each BK-TriG is conjugated with a peptide (the sequence AHRPYAAK) that mimics the B-knob of fibrin and binds specifically to hole b on adjacent fibrinogen molecules. Because neonatal clot formation runs preferentially through those B:b interactions, the particle is, in a sense, speaking the infant’s own molecular language.

In laboratory tests using neonatal plasma, BK-TriGs at their optimal concentration more than doubled clot density and nearly trebled the integrated measure of clot stability compared to untreated plasma. The particles BK-TriGs, Brown’s team reported, “outperformed any of the other options we tested at reducing blood loss.” In a mouse model engineered to carry neonatal fibrinogen rather than its own, the particles reduced blood loss from a liver laceration by fifty to sixty percent compared to saline controls. The same reduction had previously required antibody-based targeting systems, which are costly and complex to manufacture. The BK-TriGs achieve it with a short peptide instead.

There are complications, and they are worth taking seriously. The dose response is biphasic: at fifteen milligrams per kilogram, the particles perform well; push the dose to twenty mg/kg and blood loss actually increases, apparently because excess B-knob peptide starts competing with the body’s own fibrin machinery rather than supplementing it. That narrow therapeutic window will require careful characterisation before anything moves toward a clinic. The particles also need formal dose-escalation studies in actual neonatal animal models, not just adult mice carrying transplanted neonatal fibrinogen, a workaround that captures some aspects of neonatal clotting biology but almost certainly not all of them. “We are still far removed from clinical use,” Brown says.

What the study does establish, perhaps more clearly than any prior work, is the structural case for neonatal-specific hemostatic agents. Previous platelet-mimetic particles, designed primarily for adult physiology, targeted A-knob interactions. In neonates, those same particles were considerably less effective. BK-TriGs, targeting B-knob interactions, showed no meaningful effect in adult plasma at the concentrations that worked in neonatal plasma. The specificity goes both ways. It suggests the two populations probably need different tools, which is not how blood management in pediatric surgery currently operates.

The safety profile, from the mouse data at least, is encouraging. Immunohistochemical analysis of tissue from heart, kidney, spleen, and liver showed no significant off-target fibrin accumulation in uninjured areas after BK-TriG injection. In lung tissue specifically, animals treated with the particles actually showed less fibrin deposition than saline controls, which is the reverse of what a thrombogenic agent would produce. The particles appear, at this stage, to clot where clotting is needed and leave everything else alone.

The potential applications extend beyond surgical bleeding. Very low birth-weight infants are particularly vulnerable to intraventricular hemorrhage, bleeding into or around the brain’s ventricles, which is a leading cause of death and disability in premature neonates. Gastrointestinal hemorrhage is another serious neonatal complication, often linked to necrotizing enterocolitis. Both involve impaired fibrin formation in developing tissue where adult blood products could plausibly make things worse. Whether BK-TriGs could reach those locations effectively and safely remains an open question.

Peptide synthesis is considerably cheaper than manufacturing antibodies or single-domain antibody fragments, which is how earlier-generation hemostatic particles were built. If the safety data holds across larger animal models, cost would not be the obstacle it so often is in neonatal medicine. In a field where the patients are small, the procedures are technically demanding, and the blood volume to work with is tiny, that is not a minor consideration.

DOI / Source: https://doi.org/10.1126/sciadv.ady7698