Radiopaque Implantable Biomaterials for Nerve Repair

Abstract

Repairing peripheral nerve injuries remains a clinical challenge. To enhance nerve regeneration and functional recovery, the use of auxiliary implantable biomaterial conduits has become widespread. After implantation, there is currently no way to assess the location or function of polymeric biomedical devices, as they cannot be easily differentiated from surrounding tissue using clinical imaging modalities. Adding nanoparticle contrast agents into polymer matrices can introduce radiopacity and enable imaging using computed tomography (CT), but radiopacity must be balanced with changes in material properties that impact device function and biological response. In this study radiopacity was introduced to porous films of polycaprolactone (PCL) and poly(lactide-co-glycolide) (PLGA) 50:50 and 85:15 with 0-40wt% biocompatible tantalum oxide (TaOx) nanoparticles. To achieve radiopacity, at least 5wt% TaOx was required, with more than or equal to 20wt% TaOx leading to reduced mechanical properties and increased nano-scale surface roughness of films. As polymers used for peripheral nerve injury devices, films facilitated nerve regeneration in an in vitro co-culture model of glia (Schwann cells) and dorsal root ganglion neurons (DRG), measured by expression markers for myelination. The ability of radiopaque films to support nerve regeneration was determined by the properties of the polymer matrix, with a range of 5-20wt% TaOx balancing both imaging functionality with biological response and proving that in situ monitoring of nerve repair devices is feasible.

In vivo Biomedical Imaging of Immune Tolerant, Radiopaque Nanoparticle-Embedded Polymeric Device Degradation

“…The femurs were placed in 70% ethanol and then kept on sterile ice-cold PBS. The ephiphyses of each bone was removed with scissors and the bone marrow was flushed with 5 ml PBS+1% Penicillin-Streptomycin (ThermoFisher Scientific, 15,140,122), by inserting a 22G needle into the bone shaft and collecting the hydrate in a sterile centrifuge tube. The collected cells were centrifuged for 5 min at 350g and resuspended in 500 μl of PBS.…”

“…Preparation of substrates: Disks of porous films were punched (13 mm diameter) and sterilized by immersion in 70% ethanol for 30 min, followed by two washes with sterile water. Sterile, hydrated films were placed into 24-well inserts (CellCrown™, Z681903-12 EA), as described previously [15]. Briefly, each sample consisted of two layers: a bottom layer of non-porous PCL (punched to 24mm diameter) and a top layer of porous film.…”

“…Therefore, the effects of nanoparticle addition were first studied in vitro with phantoms from PCL, PLGA 85:15 and PLGA 50:50, three biocompatible polymers covering the full range of predicted degradation behaviors from virtually non-degrading for PCL (years), slow degradation for PLGA 85:15 (months), and fast degradation PLGA 50:50 (weeks) [3,12]. The range of TaOx incorporation was chosen to represent the baseline (0wt%), a minimum incorporation for radiopacity (5wt%) and the maximum shown biocompatible for primary cell culture (20wt%) [15].…”

“…PLGA substrates had consistently up-regulated secretion of the pro-inflammatory marker TNFα with nanoparticle incorporation. The addition of nanoparticles corresponds to increases in surface roughness [15]. While macrophage polarization is known to be sensitive to changes in topography and pore size in 3D structures, in general, macrophages are more sensitive to micron scale changes in topography, as opposed to nanoscale changes, such as those caused by the nanoparticles [27].…”