Combining adhesive and nonadhesive injectable hydrogels for intervertebral disc repair in an ovine discectomy model.

Background: Intervertebral disc (IVD) disorders (e.g., herniation) directly contribute to back pain, which is a leading cause of global disability. Next-generation treatments for IVD herniation need advanced preclinical testing to evaluate their ability to repair large defects, prevent reherniation, and limit progressive degeneration. This study tested whether experimental, injectable, and nonbioactive biomaterials could slow IVD degeneration in an ovine discectomy model. Methods: Ten skeletally mature sheep (4-5.5 years) experienced partial discectomy injury with cruciate-style annulus fibrosus (AF) defects and 0.1 g nucleus pulposus (NP) removal in the L1-L2, L2-L3, and L3-L4 lumbar IVDs. L4-L5 IVDs were Intact controls. IVD injury levels received: (1) no treatment (Injury), (2) poly (ethylene glycol) diacrylate (PEGDA), (3) genipin-crosslinked fibrin (FibGen), (4) carboxymethylcellulose-methylcellulose (C-MC), or (5) C-MC and FibGen (FibGen + C-MC). Animals healed for 12 weeks, then IVDs were assessed using computed tomography (CT), magnetic resonance (MR) imaging, and histopathology. Results: All repaired IVDs retained ~90% of their preoperative disc height and showed minor degenerative changes by Pfirrmann grading. All repairs had similar disc height loss and Pfirrmann grade as Injury IVDs. Adhesive AF sealants (i.e., PEGDA and FibGen) did not herniate, although repair caused local endplate (EP) changes and inflammation. NP repair biomaterials (i.e., C-MC) and combination repair (i.e., FibGen + C-MC) exhibited lower levels of degeneration, less EP damage, and less severe inflammation; however, C-MC showed signs of herniation via biomaterial expulsion. Conclusions: All repair IVDs were noninferior to Injury IVDs by IVD height loss and Pfirrmann grade. C-MC and FibGen + C-MC IVDs had the best outcomes, and may be appropriate for enhancement with bioactive factors (e.g., cells, growth factors, and miRNAs). Such bioactive factors appear to be necessary to prevent injury-induced IVD degeneration. Application of AF sealants alone (i.e., PEGDA and FibGen) resulted in EP damage and inflammation, particularly for PEGDA IVDs, suggesting further material refinements are needed.

Teaching Tissue Repair Through an Inquiry-Based Learning Bioadhesives Module.

Bioadhesives are an important class of biomaterials for wound healing, hemostasis, and tissue repair. To develop the next generation of bioadhesives, there is a societal need to teach trainees about their design, engineering, and testing. This study designed, implemented, and evaluated a hands-on, inquiry-based learning (IBL) module to teach bioadhesives to undergraduate, master's, and PhD/postdoctoral trainees. Approximately 30 trainees across three international institutions participated in this IBL bioadhesives module, which was designed to last approximately 3 h. This IBL module was designed to teach trainees about how bioadhesives are used for tissue repair, how to engineer bioadhesives for different biomedical applications, and how to assess the efficacy of bioadhesives. The IBL bioadhesives module resulted in significant learning gains for all cohorts; whereby, trainees scored an average of 45.5% on the pre-test assessment and 69.0% on the post-test assessment. The undergraduate cohort experienced the greatest learning gains of 34.2 points, which was expected since they had the least theoretical and applied knowledge about bioadhesives. Validated pre/post-survey assessments showed that trainees also experienced significant improvements in scientific literacy from completing this module. Similar to the pre/post-test, improvements in scientific literacy were most significant for the undergraduate cohort since they had the least amount of experience with scientific inquiry. Instructors can use this module, as described, to introduce undergraduate, master's, and PhD/postdoctoral trainees to principles of bioadhesives.

Wharton's jelly derived mesenchymal stem cells differentiate into oocyte like cells in vitro by follicular fluid and cumulus cells conditioned medium.

Wharton's jelly derived-mesenchymal stem cells (WJ-MSCs) have a same developmental origin with primordial germ cells. WJ-MSCs perhaps differentiate into oocyte and germ like-cells (OLCs/GLCs) in the presence of appropriate inducers. Human follicular fluid (FF) and cumulus cells conditioned medium (CCM) are naturally rich sources for oocyte development. The aim of this study was to evaluate WJ-MSCs potential for differentiating into OLCs and GLCs exposed to FF and CCM. WJ-MSCs were cultured in two different induction media (10% FF, 10% CCM) for 21 days. Morphological changes and expression of developmental genes were evaluated on days 0, 7, 14 and 21 of culture. Also, on 21st day of culture, the expression of oocyte and germ cell proteins investigated using immunofluorescence staining. Appearance of round shaped cells from 7th day onwards indicated that WJ-MSCs can differentiate into OLCs when exposed to FF and CCM. The size of produced OLCs and expression of oocyte specific genes and proteins were increased more positively in FF group rather than CCM group. Although, WJ-MSCs could differentiate into OLCs by FF and CCM, however, the induction potential of FF for producing OLCs was better than CCM.

Synthesis of Thermogelling Poly(N-isopropylacrylamide)-graft-chondroitin Sulfate Composites with Alginate Microparticles for Tissue Engineering.

Injectable biomaterials are defined as implantable materials that can be introduced into the body as a liquid and solidify in situ. Such materials offer the clinical advantages of being implanted minimally invasively and easily forming space-filling solids in irregularly shaped defects. Injectable biomaterials have been widely investigated as scaffolds for tissue engineering. However, for the repair of certain load-bearing areas in the body, such as the intervertebral disc, scaffolds should possess adhesive properties. This will minimize the risk of dislocation during motion and ensure intimate contact with the surrounding tissue, providing adequate transmission of forces. Here, we describe the preparation and characterization of a scaffold composed of thermally sensitive poly(N-isopropylacrylamide)-graft-chondroitin sulfate (PNIPAAM-g-CS) and alginate microparticles. The PNIPAAm-g-CS copolymer forms a viscous solution in water at RT, into which alginate particles are suspended to enhance adhesion. Above the lower critical solution temperature (LCST), around 30 °C, the copolymer forms a solid gel around the microparticles. We have adapted standard biomaterials characterization procedures to take into account the reversible phase transition of PNIPAAm-g-CS. Results indicate that the incorporation of 50 or 75 mg/ml alginate particles into 5% (w/v) PNIPAAm-g-CS solutions quadruple the adhesive tensile strength of PNIPAAm-gCS alone (p<0.05). The incorporation of alginate microparticles also significantly increases swelling capacity of PNIPAAm-g-CS (p<0.05), helping to maintain a space-filling gel within tissue defects. Finally, results of the in vitro toxicology assay kit, 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) and Live/Dead viability assay indicate that the adhesive is capable of supporting the survival and proliferation of encapsulated Human Embryonic Kidney (HEK) 293 cells over 5 days.

Evaluation of an injectable hydrogel and polymethyl methacrylate in restoring mechanics to compressively fractured spine motion segments.

BACKGROUND CONTEXT: Compressive fracture can produce profound changes to the mechanical profile of a spine segment. Minimally invasive repair has the potential to restore both function and structural integrity to an injured spine. Use of both hydrogels to address changes to the disc, combined with polymethyl methacrylate (PMMA) to address changes to the vertebral body, has the potential to facilitate repair. PURPOSE: The purpose of this investigation was to determine if the combined use of hydrogel injection and PMMA could restore the mechanical profile of an axially injured spinal motion segment. STUDY DESIGN: This is a basic science study evaluating a combination of hydrogel injection and vertebroplasty on restoring mechanics to compressively injured porcine spine motion segments. METHODS: Fourteen porcine spine motion segments were subject to axial compression until fracture using a dynamic servohydraulic testing apparatus. Rotational and compressive stiffness was measured for each specimen under the following conditions: initial undamaged, fractured, fatigue loading under compression, hydrogel injection, PMMA injection, and fatigue loading under compression. Group 1 received hydrogel injection followed by PMMA injection, whereas Group 2 received PMMA injection followed by hydrogel injection. This study was funded under a Natural Sciences and Engineering Research Council of Canada discovery grant. RESULTS: PMMA injection was found to alter the compressive stiffness properties of axially injured spine motion segments, restoring values from Groups 1 and 2 to 89.3%±29.3% and 81%±27.9% of initial values respectively. Hydrogel injection was found to alter the rotational stiffness properties, restoring specimens in Groups 1 and 2 to 151.5%±81% and 177.2%±54.9% of initial values respectively. Prolonged restoration of function was not possible, however, after further fatigue loading. CONCLUSIONS: Using this repair technique, replication of the mechanism of injury appears to cause a rapid deterioration in function of the motion segments. Containment of the hydrogel appears to be an issue with large breaches in the end plate, as it is posited to migrate into the cancellous bone of the vertebral body. Future work should attempt to evaluate methods in fully sealing the disc space.

Disc height loss and restoration via injectable hydrogel influences adjacent segment mechanics in-vitro.

BACKGROUND: Height loss can have a profound influence on the local mechanical environment of the disc. While disc height loss is incorporated into scales of degeneration, its direct influence on spine kinematics is unclear. Further, there is a need for minimally invasive techniques to restore disc height; injectable hydrogels are a potential solution. Tandem investigation of disc height loss and subsequent restoration will enhance understanding of spine dysfunction and aberrant movement. METHODS: Twenty porcine spine specimens with two functional segments were tested in repeated flexion and extension. Relative angular displacement of each segment was measured with full specimen disc height, disc height loss in one of the segments (superior or inferior), and disc height restoration via hydrogel injection. FINDINGS: Disc height loss decreased the range of motion at the affected segment and increased the range of motion at the adjacent segment. Relative angular displacement decreased at the affected segment by 13.8% (SD=5.3%) and 4.5% (SD=2.1%) for specimens with height loss in the superior and inferior discs respectively. Hydrogel injection was able to restore segmental kinematics to the pre-injury state, with 12.7% (SD=5.5%) and 6.4% (SD=4.2%) of motion regained at the affected segment for superior and inferior disc height loss specimens respectively. INTERPRETATION: Acute disc height loss reduces motion at an affected segment, while increasing motion at an adjacent segment in-vitro; relative motion appears to be governed by local stiffness. Injectable hydrogels show promise in their ability to restore kinematics to segments with disc height loss.