Fast in-situ formation of dextran-tyramine hydrogels for in vitro chondrocyte culturing

Emulsion Template Method for the Fabrication of Gelatin-Based Scaffold with a Controllable Pore Structure

The porous microstructure of scaffolds is an essential consideration for tissue engineering, which plays an important role for cell adhesion, migration, and proliferation. It is crucial to choose optimum pore sizes of scaffolds for the treatment of various damaged tissues. Therefore, the proper porosity is the significant factor that should be considered when designing tissue scaffolds. Herein, we develop an improved emulsion template method to fabricate gelatin-based scaffolds with controllable pore structure. Gelatin droplets were first prepared by emulsification and then solidified by genipin to prepare gelatin microspheres. The microspheres were used as a template for the fabrication of porous scaffolds, which were gathered and tightened together by dialdehyde amylose. The results showed that emulsification can produce gelatin microspheres with narrow size distribution. The size of gelatin microspheres was easily controlled by adjusting the concentration of gelatin and the speed of mechanical agitation. The gelatin-based scaffolds presented macroporous and interconnected structure. It is interesting that the pore size of scaffolds was directly related to the size of gelatin microspheres, displaying the same trend of change in size. It indicated that the gelatin microspheres can be used as the proper template to fabricate gelatin-based scaffold with a desired pore structure. In addition, the gelatin-based scaffolds possessed good blood compatibility and cytocompatibility. Overall, the gelatin-based scaffolds exhibited great potential in tissue engineering.

Injectable and 3D Bioprinted Polysaccharide Hydrogels: From Cartilage to Osteochondral Tissue Engineering

Biomechanical performance of functional cartilage is executed by the exclusive anisotropic composition and spatially varying intricate architecture in articulating ends of diarthrodial joint. Osteochondral tissue constituting the articulating ends comprise superfical soft cartilage over hard subchondral bone sandwiching interfacial soft-hard tissue. The shock-absorbent, lubricating property of cartilage and mechanical stability of subchondral bone regions are rendered by extended chemical structure of glycosaminoglycans and mineral deposition, respectively. Extracellular matrix glycosaminoglycans analogous polysaccharides are major class of hydrogels investigated for restoration of functional cartilage. Recently, injectable hydrogels have gained momentum as it offers patient compliance, tunable mechanical properties, cell deliverability, and facile administration at physiological condition with long-term functionality and hyaline cartilage construction. Interestingly, facile modifiable functional groups in carbohydrate polymers impart tailorability of desired physicochemical properties and versatile injectable chemistry for the development of highly potent biomimetic in situ forming scaffold. The scaffold design strategies have also evolved from single component to bi- or multilayered and graded constructs with osteogenic properties for deep subchondral regeneration. This review highlights the significance of polysaccharide structure-based functions in engineering cartilage tissue, injectable chemistries, strategies for combining analogous matrices with cells/stem cells and biomolecules and multicomponent approaches for osteochondral mimetic constructs. Further, the rheology and precise spatiotemporal positioning of cells in hydrogel bioink for rapid prototyping of complex three-dimensional anisotropic cartilage have also been discussed.

Microfluidic Foaming: A Powerful Tool for Tailoring the Morphological and Permeability Properties of Sponge-like Biopolymeric Scaffolds

Ordered porous polymeric materials can be engineered to present highly ordered pore arrays and uniform and tunable pore size. These features prompted a number of applications in tissue engineering, generation of meta materials, and separation and purification of biomolecules and cells. Designing new and efficient vistas for the generation of ordered porous materials is an active area of research. Here we investigate the potential of microfluidic foaming within a flow-focusing (FF) geometry in producing 3D regular sponge-like polymeric matrices with tailored morphological and permeability properties. The challenge in using microfluidic systems for the generation of polymeric foams is in the high viscosity of the continuous phase. We demonstrate that as the viscosity of the aqueous solution increases, the accessible range of foam bubble fraction (Φb) and bubble diameter (Db) inside the microfluidic chip tend to narrow progressively. This effect limits the accessible range of geometric properties of the resulting materials. We further show that this problem can be rationally tackled by appropriate choice of the concentration of the polymer. We demonstrate that via such optimization, the microfluidic assisted synthesis of porous materials becomes a facile and versatile tool for generation of porous materials with a wide range of pore size and pore volume. Moreover, we demonstrate that the size of interconnects among pores-for a given value of the gas fraction-can be tailored through the variation of surfactant concentration. This, in turn, affects the permeability of the materials, a factor of key importance in flow-through applications and in tissue engineering.

An injectable hyaluronic acid/PEG hydrogel for cartilage tissue engineering formed by integrating enzymatic crosslinking and Diels–Alder “click chemistry”

Injectable HA/PEG hydrogel was crosslinked by integrating the enzymatic crosslinking and Diels–Alder click chemistry and showed excellent shape recovery and anti-fatigue properties at a high compressive stress.

3D ingrowth of bovine articular chondrocytes in biodegradable cryogel scaffolds for cartilage tissue engineering

A feasibility study was undertaken to examine the potential of biodegradable HEMA-lactate-dextran (HEMA-LLA-D)-based cryogels as scaffolds for cartilage tissue engineering. This was a preliminary in vitro study giving essential information on the biocompatibility of cryogels with cartilage cells. HEMA-lactate (HEMA-LLA) and HEMA-LLA-D were synthesized and characterized by different techniques. Cryogel scaffolds with supermacroporous structures were produced by cryogenic treatment of these macromers. Chondrocytes obtained from bovine articular cartilage were seeded onto cylindrical cryogels and cultured. The samples were examined by several microcopical techniques for cell viability and morphological analyses were performed at two culture points. Histological study of the constructs revealed the cells' growth on the surface and within the scaffolds. Confocal microscopical images demonstrated that the majority of live vs. dead cells had been attached to and integrated with the pores of the scaffold. SEM analysis showed round to oval-shaped chondrocytic cells interconnected with each other by communicating junctions. The chondrocytes rapidly proliferated in the cryogels, manifesting that they fully covered the scaffold surface after 9 days and almost filled the spaces in the pores of the scaffold after 15 days of culture. Chondrocytes secreted significant amount of extracellular matrix in the scaffolds and exhibited highly interconnective morphology. Light and transmission electron microscopy revealed groups of active cartilage cells closely apposed to the cryogel. We concluded that cryogel scaffolds could be excellent candidates for cartilage tissue regeneration with their extraordinary properties, including soft, elastic nature, highly open interconnected pore structure and very rapid, controllable swellability.

Controlling the porosity and microarchitecture of hydrogels for tissue engineering

Tissue engineering holds great promise for regeneration and repair of diseased tissues, making the development of tissue engineering scaffolds a topic of great interest in biomedical research. Because of their biocompatibility and similarities to native extracellular matrix, hydrogels have emerged as leading candidates for engineered tissue scaffolds. However, precise control of hydrogel properties, such as porosity, remains a challenge. Traditional techniques for creating bulk porosity in polymers have demonstrated success in hydrogels for tissue engineering; however, often the conditions are incompatible with direct cell encapsulation. Emerging technologies have demonstrated the ability to control porosity and the microarchitectural features in hydrogels, creating engineered tissues with structure and function similar to native tissues. In this review, we explore the various technologies for controlling the porosity and microarchitecture within hydrogels, and demonstrate successful applications of combining these techniques.