A new study published in PNAS Nexus suggests that painful neuromas are not simply bundles of misdirected nerve fibers. Instead, their axons appear to undergo a distinct molecular transformation that makes them unusually excitable and responsive to mechanical stimulation. Kyle Eberlin and colleagues examined the molecular architecture of ten painful neuromas removed during surgery and compared them with six healthy peripheral nerves obtained from lower-leg amputations performed for unrelated medical reasons. The comparison revealed a sharp shift in the identity and behavior of the nerve fibers inside the neuromas.

The researchers used immunofluorescent confocal microscopy, a technique that allows specific proteins and cellular structures to be labeled with fluorescent molecular markers and visualized in three dimensions. Neuroma and healthy-nerve samples were processed into sections 50 micrometers thick before staining. This approach enabled the team to map proteins associated with axonal regeneration, pain signaling, mechanical sensation, electrical excitability, and sympathetic innervation—the network of nerves involved in involuntary functions such as blood-vessel control.

Under the microscope, the axons within painful neuromas lacked the orderly organization seen in healthy nerves. Rather than running in aligned bundles toward a defined destination, the regenerating fibers formed irregular, densely packed structures. They also displayed high levels of markers associated with active growth and repair, indicating that the axons remained in a regenerative state even though they had failed to establish a functional connection with their target tissue.

One of the most striking findings involved calcitonin gene-related peptide, or CGRP. This neuropeptide is released by sensory neurons and plays a major role in transmitting and amplifying pain. CGRP can also contribute to inflammation and heightened sensitivity in injured tissues. In the neuroma samples, 84 percent of axons expressed CGRP, compared with only 3 percent of axons in healthy nerves. The difference suggests that a large proportion of the fibers in painful neuromas may be molecularly primed to detect and transmit nociceptive signals—the signals the nervous system interprets as potentially damaging or painful.

The neuromas also showed increased expression of Piezo2, a mechanically activated ion channel. Piezo2 opens when the cell membrane is deformed, allowing positively charged ions to enter the nerve cell and initiate electrical activity. In normal sensory neurons, this mechanism helps detect light touch, pressure, vibration, and body position. Within a disorganized neuroma, however, mechanical forces such as contact, stretching, or pressure may activate abnormal axonal endings. This could explain why even minor pressure against a scar or amputation site can trigger severe, shock-like pain.

Another important marker was Nav1.3, a voltage-gated sodium channel involved in the initiation and propagation of electrical impulses. Sodium channels are essential for nerve signaling, but their expression changes after injury. Elevated Nav1.3 can make damaged neurons more likely to fire spontaneously or respond excessively to weak stimuli. The researchers found that Nav1.3 was upregulated in the neuromas, adding another molecular indication that these nerve fibers had become hyperexcitable. Together, increased CGRP, Piezo2, and Nav1.3 point to a nerve structure simultaneously tuned for pain detection, mechanical sensitivity, and rapid electrical activation.

The study also identified an abundance of sympathetic nerve fibers within the painful neuromas. Sympathetic nerves are not traditionally considered the primary conductors of pain, yet growing evidence indicates that they can interact with injured sensory fibers and influence chronic pain. Chemical communication between sympathetic and sensory neurons may intensify inflammation or promote spontaneous activity in damaged axons. Their presence in the neuromas raises the possibility that the local nerve environment, rather than the sensory axons alone, contributes to persistent pain after nerve injury.

The findings may help explain why painful neuromas are difficult to treat and why conventional pain medicines do not always provide lasting relief. Current surgical approaches attempt to remove the abnormal tissue or redirect regenerating axons into muscle, bone, or other protective targets. The molecular profile described in this study suggests additional possibilities, including therapies designed to reduce CGRP signaling, inhibit abnormal Piezo2-mediated mechanosensation, or normalize Nav1.3 activity. Treatments that disrupt interactions between sympathetic and sensory fibers could represent another avenue. These possibilities remain experimental, and the study does not establish that any single marker causes neuroma pain.

The researchers emphasize that their work is based on a relatively small collection of human specimens, and the comparison between amputated nerves and surgically removed neuromas cannot capture every biological difference between patients. Nevertheless, studying human tissue directly provides a valuable view of the condition that animal models may not fully reproduce. Axonal regeneration is widespread across the animal kingdom, but the formation of painful neuromas appears to be a comparatively recent evolutionary development, emerging in birds and mammals. Understanding why regeneration becomes maladaptive in these species may ultimately reveal how healing turns into chronic pain—and how that process can be interrupted.

Subject of Research: Molecular characteristics and pain mechanisms of human painful neuromas.

Article Title: Painful neuromas exhibit axonal phenotypic shift via nociceptive and mechanosensitive marker up-regulation

News Publication Date: 11-Aug-2026

Web References: https://mediasvc.eurekalert.org/Api/v1/Multimedia/ffe0045b-cc00-42e9-ad96-94911df62e49/Rendition/low-res/Content/Public

References: PNAS Nexus, “Painful neuromas exhibit axonal phenotypic shift via nociceptive and mechanosensitive marker up-regulation.”

Image Credits: Aron Cserveny

Keywords: painful neuroma, peripheral nerve injury, chronic pain, axonal regeneration, CGRP, Piezo2, Nav1.3, mechanosensitivity, nociception, sympathetic nerve fibers, immunofluorescence, nerve amputation

Addressing these critical limitations, a pioneering study led by Xiaolei Guo and colleagues from Sichuan University introduces an innovative nerve repair conduit inspired by the adaptive closing mechanism of pinecone scales in response to moisture. This breakthrough device autonomously curls upon exposure to aqueous environments and simultaneously achieves adhesive fixation, enabling it to wrap and stably attach to severed nerves without the need for suturing. The conduit’s core design involves a bilayer film fabricated through the combination of hydrophilic γ-polyglutamic acid (PGA) with hydrophobic polyurethane (PU), processed via rapid drying to induce an asymmetric distribution of hydrophilicity and hydrophobicity across its two faces. This compositional dichotomy facilitates differential swelling when immersed in water, triggering a spontaneous rolling into a tubular form.

Crucially, the researchers further enhanced the material by applying a polyurethane-based adhesive layer onto the film surface, ensuring robust and persistent attachment to the native nerve tissue. This adhesive property obviates the reliance on microsuturing, substantially simplifying the surgical procedure and reducing potential iatrogenic complications. Through rigorous characterization, the team evaluated key parameters including curling kinetics, the influence of film thickness and compositional ratios on bending curvature, adhesive strength, and conformability to tubular structures of varying diameters. This thorough investigation enabled precise tuning of the material properties to optimize performance for peripheral nerve repair.

Biocompatibility and biological efficacy constituted essential components of the study’s evaluation framework. In vitro assays demonstrated that the self-curling film exhibited excellent Schwann-cell compatibility, promoting cell viability and significantly enhancing migration capabilities, thereby fostering a regenerative microenvironment conducive to nerve repair. Furthermore, macrophage polarization assays revealed that the conduit’s material composition actively modulated inflammatory responses, shifting macrophage phenotypes toward the pro-repair M2 phenotype, both in vitro and in vivo. Such immunomodulatory effects are critical in minimizing scar formation and facilitating effective axonal regeneration.

The team validated the therapeutic potential of this pinecone-inspired adhesive conduit using a rat model featuring an 8-mm sciatic nerve defect. Comparative analyses against a standard non-adhesive polyurethane conduit, autografts, and untreated controls underscored the superior regenerative performance of the self-curling conduit. This novel material facilitated more robust nerve bridging, evidenced by greater axon diameters, enhanced myelin sheath thickness, increased expression of regeneration markers, and improved vascularization. Functionally, rats treated with the adhesive conduit exhibited superior motor recovery and reduced muscle atrophy relative to those receiving conventional conduit repairs.

One of the most striking features of this innovation is its capacity for rapid and spontaneous transformation in physiological saline; the PU/PGA10 formulation demonstrated the fastest curling speed alongside the highest bending curvature among tested variants, enabling swift tubular formation. Importantly, the adhesive layer maintained stable fixation across a broad range of diameters (3 to 10 mm), indicating adaptability to diverse nerve sizes and geometries. This property addresses a longstanding challenge in nerve conduit design, offering a flexible, conformal, and suture-free solution for conduits that need to adapt intraoperatively to variable anatomical conditions.

Beyond surgical convenience, this design distinctly improves the biological milieu at the repair site through material-driven modulation of the cellular and immune environment. By integrating responsive materials with bioadhesive capability, the conduit not only secures the nerve ends but actively participates in enhancing axonal regeneration and functional recovery. This dual functionality marks a conceptual advance over existing nerve guidance conduits that primarily offer passive structural support without influencing the biological healing processes.

Despite these promising results, the researchers acknowledge that further refinement is necessary to achieve precise control over curling dynamics and curvature parameters. Future work will focus on combining advanced structural design, computational simulations, and extensive in vivo verification to customize the behavior of the material for clinical translation. Such advancements aim to realize clinically viable, patient-specific solutions capable of addressing complex peripheral nerve injuries within constrained and irregular operative fields.

This study exemplifies how bioinspired engineering, informed by natural mechanisms such as pinecone hygroscopic movement, can revolutionize biomedical devices. The self-curling adhesive conduit represents a paradigm shift in peripheral nerve repair technologies, introducing a smart, stimuli-responsive platform that brings nerve repair closer to the efficacy of autografts while significantly simplifying surgical protocols. Its development opens new avenues for suture-free, adaptive tissue-repair devices beyond nerve regeneration, with potential applications across a broad spectrum of regenerative medicine.

The authors of this research include Xiaolei Guo, Jinwei Li, Hongyu Xu, Shengrong Long, Junhong Li, Ao Wang, Wenkai Liu, Fan Zhang, Zhen Li, Feng Luo, Jiehua Li, Yanchao Wang, Hong Tan, and Ting Lan. Their collaborative effort reflects interdisciplinary expertise spanning polymer engineering, biomaterials science, and regenerative medicine.

This groundbreaking study received financial support from multiple grants provided by the National Natural Science Foundation of China (Grant Nos. 52433015, 52373296, 52473138, and 52173287), funding from the State Key Laboratory of Polymer Materials Engineering (sklpme2022-2-07), and the Outstanding Youth Foundation of Sichuan Cancer Hospital & Institute (Grant no. YB2025004). These sources underscore the strategic national prioritization of innovation in biomaterials and regenerative technologies.

Published in the journal Cyborg and Bionic Systems on March 27, 2026, the paper titled “Pinecone-Inspired Water-Responsive Curling Adhesive Conduit for Peripheral Nerve Repair” presents a comprehensive and rigorous investigation of this novel conduit from material synthesis and characterization through to rigorous biological and functional testing in animal models. Its reported outcomes signify a robust preclinical foundation for future clinical development.

This advancement holds tremendous promise not only for peripheral nerve repair but also as a versatile platform for engineering smart, responsive, and adhesive devices tailored for complex tissue interfaces. By bridging the gap between biomimicry and clinical utility, this research sets a precedent for next-generation biomaterials that dynamically interact with their environment to promote tissue regeneration with minimal surgical intervention.

Subject of Research: Development of a bioinspired, water-responsive, self-curling adhesive conduit for peripheral nerve repair.

Article Title: Pinecone-Inspired Water-Responsive Curling Adhesive Conduit for Peripheral Nerve Repair

News Publication Date: March 27, 2026

Image Credits: Xiaolei Guo, Sichuan University

Keywords

Peripheral nerve injury, nerve repair, self-curling conduit, polyurethane, γ-polyglutamic acid, bioadhesive, tissue engineering, regenerative medicine, Schwann cells, macrophage polarization, stimuli-responsive materials, biomimicry