In Vivo Implantation of Five Different Compositions of Tissue-Engineered Intervertebral Disks in a Rat Tail Model: Preliminary Results

Abstract

IntroductionDegenerative disk disease is a leading cause of disability in the developed countries and over the past few decades, has become a major public health problem worldwide due to the significant improvement of life expectancy. Current medical and surgical treatment strategies for DDD mainly focus on pain and symptom relief, and do not necessarily address the underlying pathology of the disease. In recent years, there has been an increasing interest in developing biological based implants as an alternative, which could restore function and mobility of the spine. Here, we present the preliminary results of our study, in which five different compositions of tissue-engineered intervertebral disks were implanted into the rat caudal spine, and radiographic studies were used to evaluate the results. Materials and MethodsBased on MRI and micro-computed tomography imaging of the rat spine, compound tissue-engineered total disk replacement implants (TE-TDR) were designed to a high degree of geometric accuracy. TE-TDRs were composed of a gelatinous nucleus pulposus (NP) surrounded by an aligned collagenous annulus fibrosus. Five different compositions of the TE-TDR were designed, containing different concentrations of collagen in the AF and different concentrations of sheep chondrocytes seeded in their NP. TE-TDR implants were then inserted into the S3/S4 caudal disk space of 37 mature athymic nude rats (RNU) and were maintained on average for 15 weeks. In group 1 (four rats), TE-TDRs contained 10 million sheep cells/mL in their NP and 1 mg/mL collagen in their AF; in a similar way group 2 (four rats) received TE-TDRs with 10 million cells/mL NP and 2 mg/mL collagen AF; group 3 (eight rats) received TE-TDRs with 1 million cells/mL NP and 2 mg/mL collagen AF; in groups 4 and 5, the TE-TDRs' cell and collagen concentrations were similar to those of group 3, however in group 4 (14 rats), the disks were additionally photo cross-linked and cultured in riboflavin within their development process; and in group 5 (seven rats), an additional layer of collagen gel was pipetted around each disk to produce a second lamella. X-rays were performed both after surgery and at the latest follow-up time. Disk height changes were evaluated by calculating the Disk Height Indices (DHI) on X-rays. Based on the rostral healthy disk, a baseline DHI was also calculated for each animal. The results were then presented as percentages, comparing the disk height of the level of interest to the rostral healthy disk height. Statistical analyses were performed comparing the implanted rats with a control group in the previously published data; comparisons were also been made between the different groups of implanted rats. ResultsFive different compositions of the TE-TDR with differences in their collagen and cell contents were designed and implanted in the S3/S4 caudal disk space of 37 rats; The radiographic results of these five groups were then compared to the previously published data on a control group (six rats), on which simple discectomies were performed. Both after the operation and at the latest follow-up, the mean disk height in implanted animals was significantly higher than the control group (51% and 61% compared to 37%). Interestingly, the disk height in the implanted group at the latest follow-up also showed a significant increase, compared to the postoperative disk height. Comparisons between different implanted groups, showed that group 3 (1 million cells/mL and 2 mg/mL collagen) was associated with best results both postoperatively and at the latest follow-up; also, the worst outcome were observed in group 5 (multilamellar) postoperatively, and in group 4 (cross-linked) at latest follow-up; nonetheless no statistical significance was detected. ConclusionThe findings of the present study, while preliminary, suggest that TE-TDR may yield a clinically feasible and efficacious treatment for intervertebral disk disease. Although limited by the sample size, this research will serve as a base for further future studies on biological disk replacement.I confirm having declared any potential conflict of interest for all authors listed on this abstractYesDisclosure of InterestNone declared