Publications & Presentations

The development of effective regenerative therapies for spinal cord injury is hindered by two major barriers: the lack of structurally optimized bridging scaffolds and the inability to monitor biological integration in real time. This thesis addresses both challenges through a dual-objective framework.

Three scaffold materials — polycaprolactone, poly(lactic-co-glycolic acid), and silicone — were evaluated through extrusion-based direct ink writing at channel widths of 200, 400, and 600 µm. PCL with a 400 µm pore size emerged as the strongest candidate, combining surgical toughness with strong in vitro support for neural progenitor cell viability. PLGA created cytotoxic acidic microenvironments through hydrolytic degradation.

Complementing the scaffold work, a chronic dorsal spinal imaging window was designed and surgically validated in a rat model. Inspired by surgical retractors, the device used 3D-printed teeth to hold tissue open and a flush-mounted PET optical film for stable, long-term in vivo visualization.

Spinal cord injury produces sensory and motor deficits from damage to the dorsal and ventral cord. Dorsal horn sensory circuitry remains understudied despite most SCI patients experiencing sensory dysfunction, and poor graft integration limits the benefit of cell transplantation. Regional specification and structural support are two levers for improving integration.

Human iPSC-derived dorsal spinal neural progenitor cells were 3D printed into scaffolds, matured, and transplanted at a complete T8/T9 transection in athymic nude rats. Behavioral recovery was compared across injury-only, empty-scaffold, and dorsal-sNPC-scaffold groups over 12 weeks using BBB and Von Frey testing. Mihir led the 3D bioprinting and scaffold fabrication for the study.

Cell replacement therapy using stem-cell-derived neural progenitor cells is a promising treatment for spinal cord injury, and 3D-cultured grafts better mimic the in vivo environment than 2D cultures. Protocols were developed to differentiate human iPSCs into spinal neural progenitor cells (sNPCs) in seven days and 3D print them into scaffolds.

sNPCs were cultured in 2D and in 3D-printed silicone scaffolds for 7, 27, and 77 days and assessed by RT-qPCR, immunocytochemistry, and patch-clamp electrophysiology. 3D-printed cultures showed reduced proliferation, greater neuronal maturation, and stronger spinal regional identity. Mihir contributed the 3D bioprinting of the sNPC scaffolds.

Achieving correct regional specification is essential for transplanted cells to integrate with the native spinal cord, yet dissociated cells often engraft poorly and scaffold–cell combinations create significant FDA regulatory hurdles. This work introduces a “print-to-release” approach that keeps the benefits of printed architecture while removing the implanted biomaterial.

Human iPSC-derived dorsal and ventral sNPCs were printed into dorsally–ventrally organized silicone scaffolds, matured, and released as scaffold-free assembloids for transplantation into a complete T7/T8 transection. Organoid-scaffold groups showed significant BBB and MEP improvements versus controls, informing future scaffold-free assembloid studies toward IND-enabling, first-in-human work. Mihir contributed the 3D bioprinting of the regional scaffolds.

This study evaluates the rate of tensile strength loss in sutures subjected to hydrolysis, giving surgeons data to predict wound-closure risks. Absorbable sutures degrade through hydrolysis in moisture-rich settings, and rapid degradation in spinal surgeries can contribute to wound reopening, delayed healing, and infection.

A custom degradation chamber replicated in vivo conditions using phosphate-buffered saline at 37°C with pre-tensioned loads for different suture sizes. Weekly tensile testing over five weeks followed ASTM D2256-02 standards with surgeon-prepared samples.

Peripheral intravenous insertion is a common clinical procedure, but failed attempts — especially in pediatric and small-vein patients — cause pain, anxiety, and delays. Manual techniques such as massage and warming are used but not standardized or validated.

This project developed a thermal massaging tourniquet combining a tourniquet cuff, targeted vibration motors, and a heating filament above the cubital fossa. Ultrasound imaging quantified cephalic vein cross-sectional area across conditions, while transient conduction simulation informed safe temperature targets and heating duration.

Extrusion-based 3D bioprinting of biodegradable polymers such as PCL and PLGA relies on solvent evaporation to generate the microporosity needed for cell infiltration and nutrient transport. This paper examines how coupled convective heat and mass transfer at the filament-air interface governs pore formation, and how that architecture influences effective thermal conductivity.

The analysis builds a coupled energy-mass balance framework in which the convective heat-transfer coefficient provides latent heat for vaporization and the mass-transfer coefficient governs vapor removal. Airflow velocity, ambient temperature, and solvent vapor concentration are identified as key process levers connecting manufacturing conditions to thermal performance.