Synthetic hydrogels with engineered, cell-mediated degradation sites are an important category of biomimetic materials. Here, hydrogels are synthesized by a step-growth reaction mechanism via a radically mediated thiol-norbornene (thiol-ene) photopolymerization. This reaction combines the advantages of ideal, homogeneous polymer network formation, facile incorporation of peptides without post-synthetic modification, and spatial and temporal control over the network evolution into a single system to produce proteolytically degradable poly(ethylene glycol) (PEG) peptide hydrogels. Using a thiol-ene photopolymerization, rapid gelation times are achieved, while maintaining high cell viability for cell encapsulation. The enzyme- and cellresponsive characteristics are demonstrated by tailoring the rate of spreading of human mesenchymal stem cells (hMSCs) through both the selection of proteolytically degradable crosslinkers and the density of the adhesion peptide RGDS. Furthermore, cellular function is manipulated spatially within the thiol-ene hydrogels through biochemical photopatterning. The high degree of spatial and temporal control over gelation, combined with robust material properties, makes thiol-ene hydrogels an excellent tool for a variety of medical and biological applications.

Introduction Neuroenhancing therapies are desired because repair of nerve injuries can fail to achieve recovery. We compared two neuroenhancing therapies, electrical stimulation (ES) and systemic tacrolimus (FK506), for their capabilities to enhance regeneration in the context of a rat model. Methods Rats were randomized to four groups: ES 0.5 mA, ES 2.0 mA, FK506, and repair alone. All groups underwent tibial nerve transection and repair, and outcomes were assessed by using twice per week walking track analysis, cold allodynia response, relative muscle mass, and nerve histology. Results Electrical stimulation and FK506 groups demonstrated improved functional recovery and myelinated axon counts distal to the repair compared with repair alone. Electrical stimulation provided improvements in nerve regeneration that were not different from optimized FK506 systemic administration. Discussion Providing ES after nerve repair improved regeneration and recovery in rats, with minimal differences in therapeutic efficacy to FK506, further demonstrating its clinical potential to improve management of nerve injuries.

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Peripheral sensory neurons located in dorsal root ganglia relay sensory information from the peripheral tissue to the brain. Satellite glial cells (SGC) are unique glial cells that form an envelope completely surrounding each sensory neuron soma. This organization allows for close bidirectional communication between the neuron and it surrounding glial coat. Morphological and molecular changes in SGC have been observed in multiple pathological conditions such as inflammation, chemotherapy-induced neuropathy, viral infection and nerve injuries. There is evidence that changes in SGC contribute to chronic pain by augmenting neuronal activity in various rodent pain models. SGC also play a critical role in axon regeneration. Whether findings made in rodent model systems are relevant to human physiology have not been investigated.Here we present a detailed characterization of the transcriptional profile of SGC in mouse, rat and human at the single cell level. Our findings suggest that key features of SGC in rodent models are conserved in human. Our study provides the potential to leverage on rodent SGC properties and identify potential targets for the treatment of nerve repair and alleviation of painful conditions.

Neurons of the PNS are able to regenerate injured axons, a process requiring significant cellular resources to establish and maintain long-distance growth. Genetic activation of mTORC1, a potent regulator of cellular metabolism and protein translation, improves axon regeneration of peripheral neurons by an unresolved mechanism. To gain insight into this process, we activated mTORC1 signaling in mouse nociceptors via genetic deletion of its negative regulator Tsc2. Perinatal deletion of Tsc2 in nociceptors enhanced initial axon growth after sciatic nerve crush, however by 3 d post-injury axon elongation rate became similar to controls. mTORC1 inhibition prior to nerve injury was required to suppress the enhanced axon growth. Gene expression analysis in purified nociceptors revealed that Tsc2-deficient nociceptors had increased activity of regeneration-associated transcription factors (RATFs), including cJun and Atf3, in the absence of injury. Additionally, nociceptor deletion of Tsc2 activated satellite glial cells and macrophages in the dorsal root ganglia (DRG) in a similar manner to nerve injury. Surprisingly, these changes improved axon length but not percentage of initiating axons in dissociated cultures. The pro-regenerative environment in naïve DRG was recapitulated by AAV8-mediated deletion of Tsc2 in adult mice, suggesting that this phenotype does not result from a developmental effect. Consistently, AAV8-mediated Tsc2 deletion did not improve behavioral recovery after a sciatic nerve crush injury despite initially enhanced axon growth. Together, these data show that neuronal mTORC1 activation induces an incomplete pro-regenerative environment in the DRG that improves initial but not later axon growth after nerve injury.

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The geriatric trauma population is unique. These patients are at risk of being discharged to rehabilitation or a skilled nursing facility, instead of being returned to their homes, placing a significant burden on both the patient families and society. This study evaluated which patient characteristics increase the likelihood of a previously independent geriatric blunt trauma becoming functionally dependent and being discharged to a location other than home. Data were extracted from the National Trauma Data Bank from 2012 to 2014 for blunt trauma patients ≥65 years old, admitted from home, with one or more rib fractures. Primary outcomes were discharge home versus a facility. Subgroup analysis evaluated disposition to acute short-term rehabilitation or subacute rehabilitation or skilled nursing facility. Multivariable analysis was used to calculate probabilities of disposition based on the above variables, controlling for comorbidities. Sixteen thousand six hundred thirty-two patients were included. Only 58 per cent were discharged home. Increased age, ≥4 rib fractures, white race, and female gender were found to increase the risk of discharge to a facility. In addition, patients with chronic renal failure, history of diabetes, obesity, or heart failure were less likely to be discharged home. This study shows that age, gender, race, and the number of rib fractures are statistically significant in predicting which patients are less likely to be discharged home. This reinforces the need for the development of triage and treatment protocols in this higher risk population, to decrease the social and financial burden of these injuries.

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