Three-Dimensional Bioprinted MR-Trackable Regenerative Scaffold for Postimplantation Monitoring on T1-Weighted MRI

Abstract

Background: A three-dimensional (3D) bioprinted tissue scaffold is a promising therapeutic that goes beyond providing physical support for tissue regeneration by enabling precise spatial control over scaffold geometry and integration of different materials/cells. Critically important is in vivo confirmation of correct scaffold placement and retention during the initial 24 hours postimplantation, to detect unwanted implant migration.

Purpose: To incorporate a safe, efficient MR contrast agent into a bioprinting workflow, and to achieve bright-contrast scaffold monitoring in vivo postimplantation.

Study type: In vitro and animal in vivo longitudinal study.

Animal model: Two female Sprague Dawley rats (~200 g) for labeled and unlabeled scaffold implantation in the subcutaneous dorsal space flanking the vertebral column.

Field strength/sequence: A 7.0 T/T₁ -weighted spin echo (SE) sequence and T₁ mapping using turbo SE with variable repetition times (TRs).

Assessment: Cell viability and proliferation were assessed over 2 weeks after labeling bioprinted gelatin/alginate scaffolds with MnPNH₂ (0.5 mM, 24 hours). In vitro MRI was performed 0, 12, and 24 hours postlabeling in nine labeled and three unlabeled (control) scaffolds to monitor T₁ evolution. In vivo MRI was performed immediately and 24 hours postimplantation to assess T₁ . Acute inflammation near surgical site was monitored in one rat to 3 days.

Statistical tests: One-way analysis of variance with Tukey-Kramer post hoc analysis (P < 0.01).

Results: Cell viability was unaffected by bioprinting/labeling: viability exceeded 90% in all scaffolds after 1 week. In vitro T₁ 's were significantly lower in labeled scaffolds compared to control (207 msec vs. 2257 msec) immediately postlabeling and 24 hours later (1227 msec vs. 2257 msec). In vivo T₁ 's were significantly different (243.6 msec vs. 2414.6 msec) immediately postimplantation, and no differences emerged compared to respective in vitro control/labeled counterparts. The 24-hours imaging and gross pathology confirmed migration of scaffolds beyond the imaging field.

Data conclusion: We report an MR-detectable, cell-compatible bioprinted scaffold, utilizing a T₁ -weighting contrast agent for high-resolution, postimplantation scaffold tracking.

Evidence level: 2 TECHNICAL EFFICACY: Stage 1.

Keywords: 3D bioprinting; T1-weighted imaging; gelatin/alginate; in vivo tracking; manganese porphyrin; scaffolds.