Jonathan R. Slotkin

An injectable thiol-acrylate poly(ethylene glycol) hydrogel for sustained release of methylprednisolone sodium succinate.

Clinically available injectable hydrogels face technical challenges associated with swelling after injection and toxicity from unreacted constituents that impede their performance as surgical biomaterials. To overcome these challenges, we developed a system where chemical gelation was controlled by a conjugate Michael addition between thiol and acrylate in aqueous media, with 97% monomer conversion and 6 wt.% sol fraction. The hydrogel exhibited syneresis on equilibration, reducing to 59.7% of its initial volume. It had mechanical properties similar to soft human tissue with an elastic modulus of 189.8 kPa. Furthermore, a mesh size of 6.9 nm resulted in sustained release of methylprednisolone sodium succinate with a loading efficiency of 2 mg/mL. Functionalization with 50 μg/mL of an oligolysine peptide resulted in attachment of freshly isolated murine mesenchymal stem cells. The rational design of the physical, chemical and biological properties of the hydrogel makes it a potentially promising candidate for injectable applications.

Blockade of Peroxynitrite‐Induced Neural Stem Cell Death in the Acutely Injured Spinal Cord by Drug‐Releasing Polymer

Therapeutic impact of neural stem cells (NSCs) for acute spinal cord injury (SCI) has been limited by the rapid loss of donor cells. Neuroinflammation is likely the cause. As there are close temporal‐spatial correlations between the inducible nitric oxide (NO) synthase expression and the donor NSC death after neurotrauma, we reasoned that NO‐associated radical species might be the inflammatory effectors which eliminate NSC grafts and kill host neurons. To test this hypothesis, human NSCs (hNSCs: 5 × 104 to 2 × 106 per milliliter) were treated in vitro with “plain” medium, 20 μM glutamate, or donors of NO and peroxynitrite (ONOO−; 100 and 400 μM of spermine or DETA NONOate, and SIN‐1, respectively). hNSC apoptosis primarily resulted from SIN‐1 treatment, showing ONOO−‐triggered protein nitration and the activation of p38 MAPK, cytochrome c release, and caspases. Therefore, cell death following post‐SCI (p.i.) NO surge may be mediated through conversion of NO into ONOO−. We subsequently examined such causal relationship in a rat model of dual penetrating SCI using a retrievable design of poly‐lactic‐co‐glycolic acid (PLGA) scaffold seeded with hNSCs that was shielded by drug‐releasing polymer. Besides confirming the ONOO−‐induced cell death signaling, we demonstrated that cotransplantation of PLGA film embedded with ONOO− scavenger, manganese (III) tetrakis (4‐benzoic acid) porphyrin, or uric acid (1 μmol per film), markedly protected hNSCs 24 hours p.i. (total: n = 10). Our findings may provide a bioengineering approach for investigating mechanisms underlying the host microenvironment and donor NSC interaction and help formulate strategies for enhancing graft and host cell survival after SCI. Stem Cells 2009;27:1212–1222

Cellular Magnetic Resonance Imaging: Nanometer and Micrometer Size Particles for Noninvasive Cell Localization

SummaryThe use of nanometer and micrometer-sized superparamagnetic iron oxide particles as cellular contrast agents allows for the noninvasive detection of labeled cells on high-resolution magnetic resonance images. The development and application of these techniques to neurologic disorders is likely to accelerate the development of cell transplantation therapies and allow for the detailed study of in vivo cellular biology. This review summarizes the early development of iron oxide—based cellular contrast agents and the more recent application of this technology to noninvasive imaging of cellular transplants. The ability of this technique to allow for the noninvasive detection of in vivo transplants on the single-cell level is highlighted.

Establishing a model spinal cord injury in the African green monkey for the preclinical evaluation of biodegradable polymer scaffolds seeded with human neural stem cells

Given the involvement of post-mitotic neurons, long axonal tracts and incompletely elucidated injury and repair pathways, spinal cord injury (SCI) presents a particular challenge for the creation of preclinical models to robustly evaluate longitudinal changes in neuromotor function in the setting in the presence and absence of intervention. While rodent models exhibit high degrees of spontaneous recovery from SCI injury, animal care concerns preclude complete cord transections in non-human primates and other larger vertebrate models. To overcome such limitations a segmental thoracic (T9-T10) spinal cord hemisection was created and characterized in the African green monkey. Physiological tolerance of the model permitted behavioral analyses for a prolonged period post-injury, extending to predefined study termination points at which histological and immunohistochemical analyses were performed. Four monkeys were evaluated (one receiving no implant at the lesion site, one receiving a poly(lactide-co-glycolide) (PLGA) scaffold, and two receiving PLGA scaffolds seeded with human neural stem cells (hNSC)). All subjects exhibited Brown-Séquard syndrome 2 days post-injury consisting of ipsilateral hindlimb paralysis and contralateral hindlimb hypesthesia with preservation of bowel and bladder function. A 20-point observational behavioral scoring system allowed quantitative characterization of the levels of functional recovery. Histological endpoints including silver degenerative staining and Iba1 immunohistochemistry, for microglial and macrophage activation, were determined to reliably define lesion extent and correlate with neurobehavioral data, and justify invasive telemetered electromyographic and kinematic studies to more definitively address efficacy and mechanism.

Wound Complications Associated with the Use of Bovine Serum Albumin-glutaraldehyde Surgical Adhesive in Pediatric Patients

OBJECTIVE The use of dural sealants has become common in neurosurgery. Ten patients in whom a bovine albumin-glutaraldehyde combination (BioGlue; Cryolife, Inc., Kennesaw, GA) was implanted have had wound complications. The clinical experience of these patients is presented along with recommendations regarding the use of BioGlue. METHODS All clinical information was reviewed for the patients who had wound complications after implantation of BioGlue. Data collected included diagnosis, type of original surgery, clinical presentation of the wound complication, culture results, and management. RESULTS BioGlue was implanted in 75 patients during 77 procedures. Ten patients (13%) had wound complications. There were six boys and four girls with an average age of 5.2 years (range, 11 mo–16 yr). Three had undergone spinal procedures for detethering of the spinal cord and seven underwent craniotomies (five infratentorial, two supratentorial). Six patients presented with purulent drainage, two had periorbital cellulites, and two had swelling and fluctuance without drainage. All patients were managed operatively by washout, debridement, and removal of the BioGlue followed by a course of intravenous antibiotics. The average interval between the implantation and the debridement was 12.5 weeks (range, 2.5–28 wk). All patients had purulence around the BioGlue. Positive cultures were obtained in seven patients (Staphylococcus species in six and Streptococcus pneumoniae in one), including five who presented with wound drainage. CONCLUSION We have found a strong association between the use of BioGlue and postoperative wound complications in our pediatric neurosurgical practice and, thus, discourage its future use. BioGlue triggers an intense acute pyogenic and chronic granulomatous inflammatory response, which is an ideal environment for bacterial growth. The bacteria may arise from the BioGlue or other foreign bodies or, more likely, from the skin if the inflammation breaches the skin surface.

Biodegradable scaffolds promote tissue remodeling and functional improvement in non-human primates with acute spinal cord injury

Tissue loss significantly reduces the potential for functional recovery after spinal cord injury. We previously showed that implantation of porous scaffolds composed of a biodegradable and biocompatible block copolymer of Poly-lactic-co-glycolic acid and Poly-l-lysine improves functional recovery and reduces spinal cord tissue injury after spinal cord hemisection injury in rats. Here, we evaluated the safety and efficacy of porous scaffolds in non-human Old-World primates (Chlorocebus sabaeus) after a partial and complete lateral hemisection of the thoracic spinal cord. Detailed analyses of kinematics and muscle activity revealed that by twelve weeks after injury fully hemisected monkeys implanted with scaffolds exhibited significantly improved recovery of locomotion compared to non-implanted control animals. Twelve weeks after injury, histological analysis demonstrated that the spinal cords of monkeys with a hemisection injury implanted with scaffolds underwent appositional healing characterized by a significant increase in remodeled tissue in the region of the hemisection compared to non-implanted controls. The number of glial fibrillary acidic protein immunopositive astrocytes was diminished within the inner regions of the remodeled tissue layer in treated animals. Activated macrophage and microglia were present diffusely throughout the remodeled tissue and concentrated at the interface between the preserved spinal cord tissue and the remodeled tissue layer. Numerous unphosphorylated neurofilament H and neuronal growth associated protein positive fibers and myelin basic protein positive cells may indicate neural sprouting inside the remodeled tissue layer of treated monkeys. These results support the safety and efficacy of polymer scaffolds in a primate model of acute spinal cord injury. A device substantially similar to the device described here is the subject of an ongoing human clinical trial.

Ovarian Teratoma Masquerading as a CSF Pseudocyst in a Female with a Ventriculoperitoneal Shunt

Background. In todays fast-paced and high-acuity emergency departments, clinicians are often compelled to triage cases so rapidly that a differential diagnosis consistent with the history and physical examination is not comprehensive. Case Report. This case report describes the unexpected finding of a cystic ovarian neoplasm in a young female with an abdominal mass and a ventriculoperitoneal shunt, initially diagnosed as a cerebrospinal fluid pseudocyst. We use this case to illustrate that the astute clinician must always synthesize a diagnosis from all data sources and not to rely on initial radiographic evaluations. Conclusions. This remarkable case demonstrates that all differential diagnoses must be entertained in order to rapidly and accurately diagnose a patient with a cystic abdominal mass.