Development of chondrocyte-laden alginate hydrogels with modulated microstructure and properties for cartilage regeneration

Alginate hydrogel is an attractive biomaterial for cell microencapsulation. The microarchitecture of hydrogels can regulate cellular functions. This study aims to investigate the applicability of sodium citrate buffer (SCB) as a culture medium supplement for modulating the microstructure of alginate microbeads to provide a favorable microenvironment for chondrogenic induction. The chondrocyte-laden microbeads, with and without TGF-β3 incorporation, were produced through an encapsulator. The obtained small-sized microbeads (~300 μm) were exposed to a treatment medium containing SCB, composed of varied concentrations of sodium citrate (1.10-1.57 mM), sodium chloride (3.00-4.29 mM), and ethylenediaminetetraacetic acid (0.60-0.86 mM) to partially degrade their crosslinked structure for 3 days, followed by culture in a normal medium until day 21. Scanning electron microscope micrographs demonstrated a loose hydrogel network with an enhanced pore size in the SCB-treated microbeads. Increasing the concentration of SCB in the treatment medium reduced the calcium content of the microbeads via a Na⁺ /Ca²⁺ exchange process and improved the water absorption of the microbeads, resulting in a higher swelling ratio. All the tested SCB concentrations were non-cytotoxic. Increases in aggrecan and type II collagen gene expression and their corresponding extracellular matrix accumulation, glycosaminoglycans, and type II collagen were vividly detected in the TGF-β3-containing microbeads with increasing SCB concentrations in the treatment medium. Our findings highlighted that the combination of SCB treatment and TGF-β3 incorporation in the chondrocyte-laden microbeads is a promising strategy for enhancing cartilage regeneration, which may contribute to a versatile application in cell delivery and tissue engineering.

Chondrogenic phenotype in responses to poly(ɛ-caprolactone) scaffolds catalyzed by bioenzymes: effects of surface topography and chemistry

Biodegradable poly(ε-caprolactone) (PCL) has been increasingly investigated as a promising scaffolding material for articular cartilage tissue repair. However, its use can be limited due to its surface hydrophobicity and topography. In this study, 3D porous PCL scaffolds fabricated by a fused deposition modeling (FDM) machine were enzymatically hydrolyzed using two different biocatalysts, namely Novozyme®435 and Amano lipase PS, at varied treatment conditions in a pH 8.0 phosphate buffer solution. The improved surface topography and chemistry of the PCL scaffolds were anticipated to ultimately boost the growth of porcine articular chondrocytes and promote the chondrogenic phenotype during cell culture. Alterations in surface roughness, wettability, and chemistry of the PCL scaffolds after enzymatic treatment were thoroughly investigated using several techniques, e.g., SEM, AFM, contact angle and surface energy measurement, and XPS. With increasing enzyme content, incubation time, and incubation temperature, the surfaces of the PCL scaffolds became rougher and more hydrophilic. In addition, Novozyme®435 was found to have a higher enzyme activity than Amano lipase PS when both were used in the same enzymatic treatment condition. Interestingly, the enzymatic degradation process rarely induced the deterioration of compressive strength of the bulk porous PCL material and slightly reduced the molecular weight of the material at the filament surface. After 28 days of culture, both porous PCL scaffolds catalyzed by Novozyme®435 and Amano lipase PS could facilitate the chondrocytes to not only proliferate properly, but also function more effectively, compared with the non-modified porous PCL scaffold. Furthermore, the enzymatic treatments with 50 mg of Novozyme®435 at 25 °C from 10 min to 60 min were evidently proven to provide the optimally enhanced surface roughness and hydrophilicity most significantly favorable for induction of chondrogenic phenotype, indicated by the greatest expression level of cartilage-specific gene and the largest production of total glycosaminoglycans.

Recombinant Extracellular Matrix Protein Fragments Support Human Embryonic Stem Cell Chondrogenesis

We previously developed a 14-day culture protocol under potentially GMP, chemically defined conditions, to generate chondroprogenitors from human embryonic stem cells (hESCs). In vivo work has confirmed the cartilage repair capacity of these cells in a nude rat osteochondral defect model. Aiming to enhance hESC-chondrogenesis, we screened a range of extracellular matrix (ECM) molecules for their ability to support differentiation of hESCs toward chondrocytes. We identified two novel ECM protein fragments that supported hESC-chondrogenesis: Fibronectin III (fibronectin 7-14 protein fragments, including the RGD domain, syndecan-binding domain, and heparin-binding domain) and fibrillin-1 (FBN1) fragment PF8 (encoded by exons 30-38, residues 1238-1605, which contains the RGD motif but not heparin-binding site). These two protein fragments support hESC-chondrogenesis compared with the substrates routinely used previously (a mixture of fibronectin and gelatin) in our directed chondrogenic protocol. We have identified recombinant fibronectin fragment (FN III) and FBNI fragment (PF8) as alternative coating substrates to promote expression of genes known to regulate chondrocytes and code for chondrocyte ECM components. These recombinant protein fragments are likely to have better batch to batch stability than full-length molecules, especially where extracted from tissue/serum.

Biocompatibility of hydroxyapatite scaffolds processed by lithography-based additive manufacturing

The fabrication of hydroxyapatite scaffolds for bone tissue engineering applications by using lithography-based additive manufacturing techniques has been introduced due to the abilities to control porous structures with suitable resolutions. In this research, the use of hydroxyapatite cellular structures, which are processed by lithography-based additive manufacturing machine, as a bone tissue engineering scaffold was investigated. The utilization of digital light processing system for additive manufacturing machine in laboratory scale was performed in order to fabricate the hydroxyapatite scaffold, of which biocompatibilities were eventually evaluated by direct contact and cell-culturing tests. In addition, the density and compressive strength of the scaffolds were also characterized. The results show that the hydroxyapatite scaffold at 77% of porosity with 91% of theoretical density and 0.36 MPa of the compressive strength are able to be processed. In comparison with a conventionally sintered hydroxyapatite, the scaffold did not present any cytotoxic signs while the viability of cells at 95.1% was reported. After 14 days of cell-culturing tests, the scaffold was able to be attached by pre-osteoblasts (MC3T3-E1) leading to cell proliferation and differentiation. The hydroxyapatite scaffold for bone tissue engineering was able to be processed by the lithography-based additive manufacturing machine while the biocompatibilities were also confirmed.

Mechanical and biological properties of photocurable oligolactide-HA composites investigated under accelerated degradation

The major concern related to biodegradable bone substitute materials is the loss of mechanical strength which can be undesirable when occurring too quickly before new bone formation. In this study, the multifunctional lactide oligomers having 2, 3, and 4 arms end capped with methacrylate groups were synthesized with the aim of improving the degradation properties. Their composites with hydroxyapatite (HA) were photopolymerized and subjected to accelerated degradation at 60 °C. The results showed that increasing number of arms significantly improved thermal and mechanical properties as well as biocompatibility of the composites. All composites although varying in number of arms had similar levels of bone-specific gene expression and calcification indicating their equal bioactivity in supporting bone formation. The high HA content in the composites was proposed to be responsible for enhanced osteoblast response, and this tended to suppress the effects of polymeric structure.

Synthesis of GTMAC modified chitin-PAA gel and evaluation of its biological properties

The dressing prepared from GTMAC modified chitin-PAA was introduced with the aim of facilitating wound healing, particularly those effectively absorbing exudates, maintaining a moist wound environment and controlling bacterial proliferation. Chitin was chemically modified with acrylic acid to encourage a moist wound healing environment. The highly water-absorbable resulting product (chitin-PAA) was further reacted with glycidyltrimethylammonium chloride (GTMAC) to impart antibacterial activities. The final product, chitin-PAA-GTMAC was characterized by the techniques of Fourier Transform Infrared (FTIR), solid state (15) N NMR, and elemental analysis. Their cytotoxicity and antibacterial activities against S. epidermidis and E. coli were evaluated which found increasing effects in those properties with increasing degree substitution of GTMAC. All materials also showed good blood-clotting ability. The collagen gel contraction assay was used to analyze the behavior of fibroblasts after contact with the gels. The extent of the gel contraction as well as the examination of the secreted interleukin-8 (IL-8) and transforming growth factor-β1 (TGF-β1) were investigated. The results showed that chitin-PAA modified with GTMAC could stimulate the production of IL-8, but TGF-β1. Fibroblasts presented normal spreading and formation of cellular processes in the collagen gels with all of the modifications. Furthermore, all modified gels except for the highest GTMAC content gel [chitin-PAA-GTMAC (1:20)] were found a greater extent in gel contraction than the unmodified chitin-PAA. It suggested the promoting effect of GTMAC on cell proliferation if the GTMAC content in the gel was not too high, that is, the mole ratio of glucosamine to GTMAC of the gel should not greater than 1:10.

Fibroblast interaction with carboxymethylchitosan-based hydrogels

The interaction between L929 cells and carboxymethylchitosan (CM-chitosan)-based hydrogels, hydrogels from pure CM-chitosan and its blends, was examined in this study. Cytotoxicity of all materials was also assessed. The cellular morphology and behavior on the surfaces of the hydrogels were observed by scanning electron microscopy (SEM). The effects of various parameters, e.g., type and content of blended polymers, surface structure of hydrogels, and steaming condition used for the preparation of the hydrogels, on the cell-material response were investigated. The results of the cytotoxicity test revealed that all hydrogels were non-cytotoxic. The SEM micrographs demonstrated that the cells proliferated and spread onto a porous CM-chitosan sample. Better cell spreading was found on a flat surface of a CM-chitosan film. Rounded cells were observed when poly(vinyl alcohol) (PVA) was incorporated into CM-chitosan. Fewer cells were found when the content of PVA increased. Spherical clusters of the aggregated cells existed in the blends with ultra high viscosity carboxymethylcellulose (CM-cellulose). In contrast, with the use of low viscosity CM-cellulose, the cells appeared more spreading. The attached cells on the CM-chitosan film steamed at the highest temperature and longest period appeared to spread the most among all tested steaming conditions.