Multi-component hybrid hydrogels – understanding the extent of orthogonal assembly and its impact on controlled release

This paper reports self-assembled multi-component hybrid hydrogels including a range of nanoscale systems and characterizes the extent to which each component maintains its own unique functionality, demonstrating that multi-functionality can be achieved by simply mixing carefully-chosen constituents. Specifically, the individual components are: (i) pH-activated low-molecular-weight gelator (LMWG) 1,3;2,4-dibenzylidenesorbitol-4′,4′′-dicarboxylic acid (DBS–COOH), (ii) thermally-activated polymer gelator (PG) agarose, (iii) anionic biopolymer heparin, and (iv) cationic self-assembled multivalent (SAMul) micelles capable of binding heparin. The LMWG still self-assembles in the presence of PG agarose, is slightly modified on the nanoscale by heparin, but is totally disrupted by the micelles. However, if the SAMul micelles are bound to heparin, DBS–COOH self-assembly is largely unaffected. The LMWG endows hybrid materials with pH-responsive behavior, while the PG provides mechanical robustness. The rate of heparin release can be controlled through network density and composition, with the LMWG and PG behaving differently in this regard, while the presence of the heparin binder completely inhibits heparin release through complexation. This study demonstrates that a multi-component approach can yield exquisite control over self-assembled materials. We reason that controlling orthogonality in such systems will underpin further development of controlled release systems with biomedical applications

Living Bacterial Sacrificial Porogens to Engineer Decellularized Porous Scaffolds

Decellularization and cellularization of organs have emerged as disruptive methods in tissue engineering and regenerative medicine. Porous hydrogel scaffolds have widespread applications in tissue engineering, regenerative medicine and drug discovery as viable tissue mimics. However, the existing hydrogel fabrication techniques suffer from limited control over pore interconnectivity, density and size, which leads to inefficient nutrient and oxygen transport to cells embedded in the scaffolds. Here, we demonstrated an innovative approach to develop a new platform for tissue engineered constructs using live bacteria as sacrificial porogens. E.coli were patterned and cultured in an interconnected three-dimensional (3D) hydrogel network. The growing bacteria created interconnected micropores and microchannels. Then, the scafold was decellularized, and bacteria were eliminated from the scaffold through lysing and washing steps. This 3D porous network method combined with bioprinting has the potential to be broadly applicable and compatible with tissue specific applications allowing seeding of stem cells and other cell types

Clinical application of scaffolds for cartilage tissue engineering

The purpose of this paper is to review the basic science and clinical literature on scaffolds clinically available for the treatment of articular cartilage injuries. The use of tissue-engineered grafts based on scaffolds seems to be as effective as conventional ACI clinically. However, there is limited evidence that scaffold techniques result in homogeneous distribution of cells. Similarly, few studies exist on the maintenance of the chondrocyte phenotype in scaffolds. Both of which would be potential advantages over the first generation ACI. The mean clinical score in all of the clinical literature on scaffold techniques significantly improved compared with preoperative values. More than 80% of patients had an excellent or good outcome. None of the short- or mid-term clinical and histological results of these tissue-engineering techniques with scaffolds were reported to be better than conventional ACI. However, some studies suggest that these methods may reduce surgical time, morbidity, and risks of periosteal hypertrophy and post-operative adhesions. Based on the available literature, we were not able to rank the scaffolds available for clinical use. Firm recommendations on which cartilage repair procedure is to be preferred is currently not known on the basis of these studies. Randomized clinical trials and longer follow-up periods are needed for more widespread information regarding the clinical effectiveness of scaffold-based, tissue-engineered cartilage repair

Experimentelle Untersuchungen zur Reparatur von Gelenkknorpeldefekten durch Transplantation von stimulierten allogenen Chondrozyten Abschlussbericht

Available from TIB Hannover: DtF QN1(55,48) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Transplantation of allograft chondrocytes embedded in agarose gel into cartilage defects of rabbits

AbstractObjective: Durable healing of full-thickness articular cartilage defects has been considered for a long time as a highly desirable, but unlikely event to occur. In recent years, conflicting reports on the outcome ofin vitroandin vivostudies on chondrocyte and cartilage grafting into animal and human joints have raised new arguments for and against controlled repair of articular cartilage following injury. Some of the problems result from insufficient characterization of implant and repair tissue, and from too short follow up phases. Here we describe a new approach to repair articular cartilage defects in rabbit knees by allografting chondrocytes cultured in agarose gels.Design: The implants were monitored over 6–18 months and graded histologically, immunohistochemically, and electron microscopically, using a grading scale based on seven evaluation criteria. Control implants of pure agarose produced poor fibrous substitute tissue, insufficient healing and incomplete filling of the cartilage defects. After transplantation of allogenic chondrocytes embedded in agarose, the quality of the newly formed repair cartilage was superior with respect to type II collagen and proteoglycan content and cellular architecture when compared with untreated defects. Superficial fibrillation and degradation were significantly diminished or prevented.Results: New subchondral bone formed at the level of the previous subchondral bone. In most cases the repair tissue merged with the host articular cartilage; normal calcified cartilage was the only tissue zone that did not participate in the integration of the transplant. By gross evaluation 24% of grafts showed an extent of recovery never observed in controls. The best results were obtained after 18 months when 47% of the grafts (N=15) developed a morphologically stable hyaline cartilage.Conclusion: These studies demonstrate that agarose-embedded chondrocyte may prove a valuable tool for controlled repair of articular cartilage defects

Role of growth factors in rabbit articular cartilage repair by chondrocytes in agarose

AbstractObjective Novel approaches to intervention in joint diseases consist of the replacement of diseased cartilage by in vitro engineered, viable cells or graft tissues. Two major obstacles remain to be overcome: (1) Hyaline cartilage in vitro often loses differentiated traits. (2) Grafts frequently are not integrated satisfactorily into host cartilage and/or the tissue is remodelled in situ into functionally inferior fibrocartilage. Therefore, we have explored the possibility whether chondrocytes embedded into agarose gels provided better graft tissues in a repair model of full thickness defects in rabbit joint cartilage.Design Experimental defects of knee joint cartilage was filled with articular chondrocytes cultured in agarose gels. Chondrocytes in vitro either remained unstimulated or were treated with several growth factors. Repair of the defects was assessed by histology and was scored between 0 (no healing) and 1 (perfect healing) as judged by the follwing parameters: intensity of proteoglycan staining, organization of the superficial zone, ossification at the border between repair cartilage and subchondral bone, tidemark formation in the repaired area, arrangement of chondrocytes, and integration of repair cartilage into host.Results Treatment of chondrocyte cultures with bFGF had a stabilizing effect on the differentiated state of the cells in implanted grafts whereas bone morphogenetic proteins stimulated ingrowth of subchondral bone reducing repair cartilage thickness and preventing normal tide mark formation; TGF-β did not significantly affect evaluation parameters in comparison with untreated controls.Conclusion Growth factor treatment resulted in an ambiguous quality of graft development. Only FGF had a clear beneficial effect to the graft tissues after 1 month. Further studies are required to define the precise conditions and sequence of growth factor treatment of in vitro engineered cartilage which benefits graft quality