Effects of polycaprolactone-based scaffolds on the blood-brain barrier and cerebral inflammation

Abstract

Severe pathoanatomical and mechanical injuries compromise patient recovery and survival following penetrating brain injury (PBI). The realization that the blood-brain barrier (BBB) plays a major role in dictating post-PBI events has led to rising interests in possible therapeutic interventions through the BBB. Recently, the choroid plexus has also been suggested as a potential therapeutic target. The use of biocompatible scaffolds for the delivery of therapeutic agents, but little is known about their interaction with cerebral tissue, which has important clinical implications. Therefore, the authors have sought to investigate the effect of polycaprolactone (PCL) and PCL/tricalcium phosphate (PCL/TCP) scaffolds on the maintenance of BBB phenotype posttraumatic brain injury. Cranial defects of 3 mm depth were created in Sprague Dawley rats, and PCL and PCL/TCP scaffolds were subsequently implanted in predetermined locations for a period of 1 week and 1 month. Higher endothelial barrier antigen (EBA) expressions from PCL-based scaffold groups (p>0.05) were found, suggesting slight advantages over the sham group (no scaffold implantation). PCL/TCP scaffold group also expressed EBA to a higher degree (p>0.05) than PCL scaffolds. Importantly, higher capillary count and area as early as 1 week postimplantation suggested lowered ischemia from the PCL/TCP scaffold group as compared with PCL and sham. Evaluation of interlukin-1β expression suggested that the PCL and PCL/TCP scaffolds did not cause prolonged inflammation. BBB transport selectivity was evaluated by the expression of aquaporin-4 (AQP-4). Attenuated expression of AQP-4 in the PCL/TCP group (p<0.05) suggested that PCL/TCP scaffolds altered BBB selectivity to a lower degree as compared with sham and PCL groups, pointing to potential clinical implications in reducing cerebral edema. Taken together, the responses of PCL-based scaffolds with brain tissue suggested safety, and encourages further preclinical evaluation in PBI management with these scaffolds.

FIG. 1.

(A) Visualization of the morphology of the implanted PCL-based scaffolds taken by scanning electron microscopy, at 100× magnification. TCP particles (white arrows) were observed distributed within each PCL filament. (B) Representative image of a harvested Sprague Dawley rat brain with the locations of the scaffolds and sham (control) clearly indicated. PCL, polycaprolactone; TCP, tricalcium phosphate. Color images available online at www.liebertpub.com/tea

FIG. 2.

Illustration of the selected regions used: R1 indicating the defect region; R2 refers to the periphery (scale bar represents 1 mm). Color images available online at www.liebertpub.com/tea

FIG. 3.

(A) SMI-71 immunohistochemistry and (B) ImageJ quantification of total capillary number and average capillary area. SMI-71 was clearly expressed in the peripheral region of all groups. In the defect region (dark circled), morphological observations that the capillary count and area were superior in the PCL/TCP group as compared with the PCL group was confirmed by ImageJ analysis, with the results presented in (B). Notable superiority in total capillary count and average capillary area in PCL/TCP could be observed. Scale bar represents 500 μm. Color images available online at www.liebertpub.com/tea

FIG. 4.

(A) IL-1β expression over 1 week and 1 month and (B) ImageJ analysis of stain intensity. Scale bar represents 1 mm. Color images available online at www.liebertpub.com/tea

FIG. 5.

AQP-4 immunohistochemistry. Expression of AQP-4 in PCL/TCP scaffold group appeared to be lower than that of PCL and sham, and was confirmed by ImageJ analysis for stain intensity in the selected regions (white dotted squares). Scale bar represents 1 mm. Color images available online at www.liebertpub.com/tea