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Culture of three-dimensional (3D) constructs in hypoxic conditions (1-5% O) has been shown to increase production of extracellular matrix components in primary intervertebral disc (IVD) cells and drive chondrogenesis of human mesenchymal stem cells (hMSCs). Growing evidence suggests that two-dimensional (2D) expansion under hypoxic conditions may have an even greater influence on chondrogenesis in MSCs. This study aims to determine the effects of hypoxia during 2D expansion and subsequent 3D culture on the in vitro maturation of tissue-engineered IVDs (TE-IVDs) made with hMSCs, using a previously developed TE-IVD system. hMSCs were expanded in either hypoxic (5% O) or normoxic (21% O) conditions before construction of TE-IVDs. Discs were cultured in 3D in either hypoxic or normoxic conditions to create four experimental groups. Discs made from MSCs expanded in hypoxia were up to 141% stiffer than those made with normoxia-expanded MSCs. Similar patterns were seen in all mechanical properties. Increases in glycosaminoglycan content and collagen content in the nucleus pulposus (NP) were associated with 3D hypoxic culture. A boundary region between the manufactured fibrosus and NP regions developed by 2 weeks and mimicked the organization of the native disc. Hypoxic conditions in both 2D expansion and subsequent 3D culture improved the maturation of TE-IVDs made with hMSCs.

Study design Animal experimental study Objective To evaluate a novel quantitative imaging technique for assessing disc degeneration. Summary of Background Data T2-relaxation time (T2-RT) measurements have been used to quantitatively assess disc degeneration. T2 values correlate with the water content of inter vertebral disc tissue and thereby allow for the indirect measurement of nucleus pulposus (NP) hydration. Methods We developed an algorithm to subtract out MRI voxels not representing NP tissue based on T2-RT values. Filtered NP voxels were used to measure nuclear size by their amount and nuclear hydration by their mean T2-RT. This technique was applied to 24 rat-tail intervertebral discs’ (IVDs), which had been punctured with an 18-gauge needle according to different techniques to induce varying degrees of degeneration. NP voxel count and average T2-RT were used as parameters to assess the degeneration process at 1 and 3 months post puncture. NP voxel counts were evaluated against X-ray disc height measurements and qualitative MRI studies based on the Pfirrmann grading system. Tails were collected for histology to correlate NP voxel counts to histological disc degeneration grades and to NP cross-sectional area measurements. Results NP voxel count measurements showed strong correlations to qualitative MRI analyses (R2=0.79, p<0.0001), histological degeneration grades (R2=0.902, p<0.0001) and histological NP cross-sectional area measurements (R2=0.887, p<0.0001). In contrast to NP voxel counts, the mean T2-RT for each punctured group remained constant between months 1 and 3. The mean T2-RTs for the punctured groups did not show a statistically significant difference from those of healthy IVDs (63.55ms ±5.88ms month 1 and 62.61ms ±5.02ms) at either time point. Conclusion The NP voxel count proved to be a valid parameter to quantitatively assess disc degeneration in a needle puncture model. The mean NP T2-RT does not change significantly in needle-puncture induced degenerated IVDs. IVDs can be segmented into different tissue components according to their innate T2-RT.

Because of the limitations of current surgical methods in the treatment of degenerative disc disease, tissue-engineered intervertebral discs (TE-IVDs) have become an important target. This study investigated the biochemical and mechanical responses of composite TE-IVDs to dynamic unconfined compression. TE-IVDs were manufactured by floating an injection molded alginate nucleus pulposus (NP) in a type I collagen annulus fibrosus (AF) that was allowed to contract for 2 weeks before loading. The discs were mechanically stimulated at a range of strain amplitude (1-10%) for 2 weeks with a duty cycle of 1 h on-1 h off-1 h on before being evaluated for their biochemical and mechanical properties. Mechanical loading increased all properties in a dose-dependent manner. Glycosaminoglycans (GAGs) increased between 2.8 and 2.2 fold in the AF and NP regions, respectively, whereas the hydroxyproline content increased between 1.2 and 1.8 fold. The discs also experienced a 2-fold increase in the equilibrium modulus and a 4.3-fold increase in the instantaneous modulus. Full effects for all properties were seen by 5% strain amplitude. These data suggest that dynamic loading increases the functionality of our TE-IVDs with region-dependent responses using a method that may be scaled up to larger disc models to expedite maturation for implantation.

Introduction Disc degeneration in the cervical spine is a prevalent clinical predicament often requiring surgery. Anterior cervical decompression and fusion (ACDF), the most commonly performed procedure, poses risks of pseudoarthrosis, and adjacent segment disease (ASD).1,2 An emerging alternative treatment option is prosthetic total disc replacement (TDR),3 which preserves segmental mobility. Our group previously developed a biological TDR device using composite AF/NP disc-like construct with viable cells and mechanical properties analogous to the native discs in a rat tail model.4 In this study, we evaluated the in vivo efficacy of this tissue-engineered intervertebral disc (TE–IVD) in a beagle cervical model assessing radiological and histological parameters. Material and Methods TE-IVD construction: Canine-sized TE–IVDs were constructed as previously described.4 Cervical IVDs from skeletally mature beagles were separated into AF and NP tissues; component cells were isolated and cultured in vitro. Cultured NP cells were seeded with alginate, injected into a predesigned mold, and encircled with two layers of an AF cell laden collagen gel. The combined construct was kept in media for 2 weeks as the surrounding annulus fibrous aligned and contracted until required TE–IVD diameter was attained. Experimental Protocol: Overall, eight skeletally mature beagles were divided into the following two groups: the control group ( n = 2) underwent discectomy with fully resected IVDs, and the experimental group ( n = 6) underwent TE–IVD implantation postdiscectomy. Adjacent proximal segments served as internal healthy controls. Postoperative X-ray and MRI were taken at 2 and 4 weeks; disc height indices5 and NP hydration using a pre-established algorithm6 were analyzed. Beagles were humanely killed at 4 weeks for histological assessment. Results TE–IVDs were successfully implanted postdiscectomy ( Fig. 1A , B). At 2 weeks, MRIs of TE–IVDs revealed T2 high intensity with acute outer inflammation because of the surgical invasion, which faded by 4 weeks. At 4 weeks, TE–IVDs maintained position in the disc space with relatively increased T2 intensity, whereas discectomized segments manifested as black discs ( Fig. 1C , D). These findings suggest that the implanted TE–IVDs engraft in the disc space despite significant biomechanical demands of the beagle cervical environment. In fact, disc height indices of the TE–IVDs and discectomized discs were 71 and 49%, respectively, of that of healthy control discs. Likewise, MRIs revealed that NP hydration of the implanted TE–IVDs was over 70% of that of healthy discs. Histological assessments further demonstrated chondrocyte-like cell viability in the TE–IVD, abundant proteoglycan content in the extracellular matrices, and substantial integration into host tissues without signs of immune reactions. [Figure: see text] Conclusion Despite the severe local milieu of the beagle cervical spine owing to mechanical loading, our in vivo TE–IVDs when appropriately implanted, maintained their position and structure at 4 weeks. The TE–IVDs displayed dynamic adaptation to the host environment, with extracellular matrix production and cell proliferation. They further maintained disc height as well as NP hydration at 4 weeks with up to 70% viability as the normal healthy discs. References Nesterenko SO, Riley LH III, Skolasky RL. Anterior cervical discectomy and fusion versus cervical disc arthroplasty: current state and trends in treatment for cervical disc pathology. Spine 2012;37(17):1470–1474 Sugawara T, Itoh Y, Hirano Y, Higashiyama N, Mizoi K. Long term outcome and adjacent disc degeneration after anterior cervical discectomy and fusion with titanium cylindrical cages. Acta Neurochir (Wien) 2009;151(4):303–309, discussion 309 Kelly MP, Mok JM, Frisch RF, Tay BK. Adjacent segment motion after anterior cervical discectomy and fusion versus Prodisc-c cervical total disk arthroplasty: analysis from a randomized, controlled trial. Spine 2011;36(15):1171–1179 Bowles RD, Gebhard HH, Härtl R, Bonassar LJ. Tissue-engineered intervertebral discs produce new matrix, maintain disc height, and restore biomechanical function to the rodent spine. Proc Natl Acad Sci U S A 2011;108(32):13106–13111 Kim JS, Kroin JS, Li X, et al. The rat intervertebral disk degeneration pain model: relationships between biological and structural alterations and pain. Arthritis Res Ther 2011;13(5):R165 Grunert P, Hudson KD, Macielak MR, et al. Assessment of intervertebral disc degeneration based on quantitative magnetic resonance imaging analysis: an in vivo study. Spine 2014;39(6):E369–E378

Object Tissue-engineered intervertebral discs (TE-IVDs) represent a new experimental approach for the treatment of degenerative disc disease. Compared with mechanical implants, TE-IVDs may better mimic the properties of native discs. The authors conducted a study to evaluate the outcome of TE-IVDs implanted into the rat-tail spine using radiological parameters and histology. Methods Tissue-engineered intervertebral discs consist of a distinct nucleus pulposus (NP) and anulus fibrosus (AF) that are engineered in vitro from sheep IVD chondrocytes. In 10 athymic rats a discectomy in the caudal spine was performed. The discs were replaced with TE-IVDs. Animals were kept alive for 8 months and were killed for histological evaluation. At 1, 5, and 8 months, MR images were obtained; T1-weighted sequences were used for disc height measurements, and T2-weighted sequences were used for morphological analysis. Quantitative T2 relaxation time analysis was used to assess the water content and T1ρ-relaxation time to assess the proteoglycan content of TE-IVDs. Results Disc height of the transplanted segments remained constant between 68% and 74% of healthy discs. Examination of TE-IVDs on MR images revealed morphology similar to that of native discs. T2-relaxation time did not differ between implanted and healthy discs, indicating similar water content of the NP tissue. The size of the NP decreased in TE-IVDs. Proteoglycan content in the NP was lower than it was in control discs. Ossification of the implanted segment was not observed. Histological examination revealed an AF consisting of an organized parallel-aligned fiber structure. The NP matrix appeared amorphous and contained cells that resembled chondrocytes. Conclusions The TE-IVDs remained viable over 8 months in vivo and maintained a structure similar to that of native discs. Tissue-engineered intervertebral discs should be explored further as an option for the potential treatment of degenerative disc disease.