R. Marwan1, S. Williams1, J. Bardill2, D. Park2, N. Abd Aziz1, R. Marwan1 1University Of Colorado Denver,Pediatric Surgery,Aurora, CO, USA 2University Of Colorado Denver,Bioengineering,Aurora, CO, USA
Introduction: Neural tube defects (NTDs) are the leading cause of central nervous system malformation in humans & a devastating birth defect resulting in destruction of the developing spinal cord. Their sequelae are staggering & appear not only to have anatomical effects, but also functional, emotional & psychological morbidities including bladder & bowel incontinence, paralysis, musculoskeletal deformity, & shunt malfunctions & infections. Ultimately, its compound nature results in an immense financial burden amounting to $1,400,000. The morbidity & mortality associated with having a NTD is secondary not only to ongoing spinal cord injury as a result of prolonged mechanical trauma to the neural elements, but also chemical inflammation associated with exposure to amniotic fluid. Currently, pre-natal repair is performed relatively late, around 22-26 weeks of gestation & is associated with a 50% reduction in the need for ventriculoperitoneal shunting. However, it is associated with an increased risk to both mother & fetus including premature labor & prematurity among others. Reverse Thermal Gels are a group of biomimetic polymers that can undergo reversible phase transition from liquid to physical gel upon temperature change without the need for reactive species or outside energy sources making them suitable for biological use. We propose to test if an earlier repair using a bioengineering approach will result in better outcomes. This study focuses on the properties of our polymer
Methods: Surface ultrastructure of the polymer was studied using scanning electron microscopy of a 0.5cm3 mold of 3 different percent mass/volume (%m/v) freeze-dried polymer samples. Permeability to fluorescein and albumin was tested using 0.4mm pore polymer coated inserts in a 12 well plate. A micro-plate reader measured the absorbance of fluid in the bottom well. Degradation in both human & sheep amniotic fluid was studied using Gel Permeation Chromatography. Finally, proliferation of murine embryonic fibroblasts was measured using an MTT proliferation assay kit.
Results: Our polymer possesses a unique surface ultrastructure dictated by concentration and is tied to its biological properties. A 15% m/v sample has smaller pore sizes when compared to 10% & 13% samples. Permeability to fluorescein is predictable and depends on the pore sizes. At 1 day, 10% m/v polymer is more permeable to fluorescein than 13% & 15%. However, after 8 days, it is equivalent. There is minimal permeability to albumin. The polymer does not degrade in neither human nor sheep amniotic fluid for up to 30 days. Finally, compared to control media, murine embryonic fibroblasts possess a similar proliferation profile when subjected to polymer extract.
Conclusion: Our polymer is stable in amniotic fluid and possesses a unique ultrastructure and functional characteristics that supports its use as an innovative bioengineering approach to open fetal repair of NTDs.