Sydney M. Caparaso

Chronic low back pain (LBP), often correlated with intervertebral disc degeneration, is a leading source of disability worldwide yet remains poorly understood. Current treatments often fail to provide sustained relief, highlighting the need to better understand the mechanisms driving discogenic LBP. During disc degeneration, the extracellular matrix degrades, allowing nociceptive nerve fibers to innervate previously aneural disc regions. Persistent mechanical and inflammatory stimulation of nociceptors can induce plastic changes within dorsal root ganglia (DRG) neurons, characterized by altered gene expression, enhanced excitability, and lowered activation thresholds. Although these transcriptional changes have been described in other pain states, including osteoarthritis, they remain underexplored in discogenic LBP. To address this gap, this study represents the first application of comprehensive single-nuclei RNA sequencing of DRG neurons in a rat model of chronic discogenic LBP. Eighteen distinct DRG subpopulations were identified and mapped to existing mouse and cross-species atlases revealing strong similarities in neuronal populations with the mouse. Differential expression analysis revealed increased expression of pain-associated genes, including Scn9a and Piezo2 , and neuroinflammatory mediators such as Fstl1 and Ngfr , in LBP animals. Axial hypersensitivity, measured using grip strength, significantly correlated with increased expression of Scn9a, Fstl1, and Ngfr, which suggests their role in maintaining axial hypersensitivity in this model. These findings establish a relationship between DRG transcriptomic changes and axial hypersensitivity in a discogenic LBP model, identifying potential molecular targets for non-opioid treatments and advancing understanding of discogenic LBP mechanisms.

Despite the significant global prevalence of chronic pain, current methods to identify pain therapeutics often fail translation to the clinic. Phenotypic screening platforms rely on modeling and assessing key pathologies relevant to chronic pain, improving predictive capability. Patients with chronic pain often present with sensitization of primary sensory neurons (that extend from dorsal root ganglia [DRG]). During neuronal sensitization, painful nociceptors display lowered stimulation thresholds. To model neuronal excitability, it is necessary to maintain three key anatomical features of DRGs to have a physiologically relevant platform: (1) isolation between DRG cell bodies and neurons, (2) 3D platform to preserve cell–cell and cell‐matrix interactions, and (3) presence of native non‐neuronal support cells, including Schwann cells and satellite glial cells. Currently, no culture platforms maintain the three anatomical features of DRGs. Herein, we demonstrate an engineered 3D multicompartment device that isolates DRG cell bodies and neurites and maintains native support cells. We observed neurite growth into isolated compartments from the DRG using two formulations of collagen, hyaluronic acid, and laminin‐based hydrogels. Further, we characterized the rheological, gelation and diffusivity properties of the two hydrogel formulations and found the mechanical properties mimic native neuronal tissue. Importantly, we successfully limited fluidic diffusion between the DRG and neurite compartment for up to 72 h, suggesting physiological relevance. Lastly, we developed a platform with the capability of phenotypic assessment of neuronal excitability using calcium imaging. Ultimately, our culture platform can screen neuronal excitability, providing a more translational and predictive system to identify novel pain therapeutics to treat chronic pain.

The diagnosis of fracture nonunion following plate osteosynthesis is subjective and frequently ambiguous. Initially following osteosynthesis, loads applied to the bone are primarily transmitted through the plate. However, as callus stiffness increases, the callus is able to bear load proportional to its stiffness while forces through the plate decrease. The purpose of this study was to use a “smart” fracture plate to distinguish between phases of fracture healing by measuring forces transmitted through the plate. A wireless force sensor and small adapter were placed on the outside of a distal femoral locking plate. The adapter converts the slight bending of the plate under axial load into a transverse force which is measurable by the sensor. An osteotomy was created and then plated in the distal femur of biomechanical Sawbones. Specimens were loaded to simulate single‐leg stance first with the osteotomy defect empty (acute healing), then sequentially filled with silicone (early callus) and then polymethyl methacrylate (hard callus). There was a strong correlation between applied axial load and force measured by the “smart” plate. Data demonstrate statistically significant differences between each phase of healing with as little as 150 N of axial load applied to the femur. Forces measured in the plate were significantly different between acute (100%), early callus (66.4%), and hard callus (29.5%). This study demonstrates the potential of a “smart” fracture plate to distinguish between phases of healing. These objective data may enable early diagnosis of nonunion and enhance outcomes for patients.