Direct and indirect co-culture of chondrocytes and mesenchymal stem cells for the generation of polymer/extracellular matrix hybrid constructs

In this work, the influence of direct cell–cell contact in co-cultures of mesenchymal stem cells (MSCs) and chondrocytes for the improved deposition of cartilage-like extracellular matrix (ECM) within nonwoven fibrous poly(∊-caprolactone) (PCL) scaffolds was examined. To this end, chondrocytes and MSCs were either co-cultured in direct contact by mixing on a single PCL scaffold or produced via indirect co-culture, whereby the two cell types were seeded on separate scaffolds which were then cultured together in the same system either statically or under media perfusion in a bioreactor. In static cultures, the chondrocyte scaffold of an indirectly co-cultured group generated significantly greater amounts of glycosaminoglycan and collagen than the direct co-culture group initially seeded with the same number of chondrocytes. Furthermore, improved ECM production was linked to greater cellular proliferation and distribution throughout the scaffold in static culture. In perfusion cultures, flow had a significant effect on the proliferation of the chondrocytes. The ECM contents within the chondrocyte-containing scaffolds of the indirect co-culture groups either approximated or surpassed the amounts generated within the direct co-culture group. Additionally, within bioreactor culture there were indications that chondrocytes had an influence on the chondrogenesis of MSCs as evidenced by increases in cartilaginous ECM synthetic capacity. This work demonstrates that it is possible to generate PCL/ECM hybrid scaffolds for cartilage regeneration by utilizing the factors secreted by two different cell types, chondrocytes and MSCs, even in the absence of juxtacrine signaling

Flow Perfusion Co-culture of Human Mesenchymal Stem Cells and Endothelial Cells on Biodegradable Polymer Scaffolds

In this study, we investigated the effect of flow perfusion culture on the mineralization of co-cultures of human umbilical vein endothelial cells (HUVECs) and human mesenchymal stem cells (hMSCs). Osteogenically precultured hMSCs were seeded onto electrospun scaffolds in monoculture or a 1:1 ratio with HUVECs, cultured for 7 or 14 days in osteogenic medium under static or flow perfusion conditions, and the resulting constructs were analyzed for cellularity, alkaline phosphatase (ALP) activity and calcium content. In flow perfusion, constructs with monocultures of hMSCs demonstrated higher cellularity and calcium content, but lower ALP activity compared to corresponding static controls. ALP activity was enhanced in co-cultures under flow perfusion conditions, compared to hMSCs alone; however unlike the static controls, the calcium content of the co-cultures in flow perfusion was not different from the corresponding hMSC monocultures. The data suggest that co-cultures of hMSCs and HUVECs did not contribute to enhanced mineralization compared to hMSCs alone under the flow perfusion conditions investigated in this study. However, flow perfusion culture resulted in an enhanced spatial distribution of cells and matrix compared to static cultures, which were limited to a thin surface layer

Mesenchymal stem cell and gelatin microparticle encapsulation in thermally and chemically gelling injectable hydrogels for tissue engineering

In this work, we investigated the viability and osteogenic differentiation of mesenchymal stem cells encapsulated with gelatin microparticles (GMPs) in an injectable, chemically and thermally gelling hydrogel system combining poly(N-isopropylacrylamide)-based thermogelling macromers containing pendant epoxy rings with polyamidoamine-based hydrophilic and degradable diamine crosslinking macromers. Specifically, we studied how the parameters of GMP size and loading ratio affected the viability and differentiation of cells encapsulated within the hydrogel. We also examined the effects of cell and GMP co-encapsulation on hydrogel mineralization. Cells demonstrated long-term viability within the hydrogels, which was shown to depend on GMP size and loading ratio. In particular, increased interaction of cells and GMPs through greater available GMP surface area, use of an epoxy-based chemical gelation mechanism, and the tunable high water content of the thermogelled hydrogels led to favorable long-term cell viability. Compared with cellular hydrogels without GMPs, hydrogels co-encapsulating cells and GMPs demonstrated greater production of alkaline phosphatase by cells at all time-points and a transient early enhancement of hydrogel mineralization for larger GMPs at higher loading ratios. Such injectable, in situ forming hydrogels capable of delivering and maintaining populations of encapsulated mesenchymal stem cells and promoting mineralization in vitro offer promise as novel therapies for applications in tissue engineering and regenerative medicine

Responsive and In situ-forming chitosan scaffolds for bone tissue engineering applications : an overview of the last decade

The use of bioabsorbable polymeric scaffolds is being investigated for use in bone tissue engineering applications, as their properties can be tailored to allow them to degrade and integrate at optimal rates as bone remodelling is completed. The main goal of this review is to highlight the “intelligent” properties exhibited by chitosan scaffolds and their use in the bone tissue engineering field. To complement the fast evolution of the bone tissue engineering field, it is important to propose the use of responsive scaffolds and take advantage of bioinspired materials and their properties as emerging technologies. There is a growing interest and need for new biomaterials, such as “smart”/responsive materials with the capability to respond to changes in the in vivo environment. This review will provide an overview of strategies that can modulate bone tissue regeneration by using in situ-forming scaffolds

Design of a High-Throughput Flow Perfusion Bioreactor System for Tissue Engineering

Flow perfusion culture is used in many areas of tissue engineering and offers several key advantages. However, one challenge to these cultures is the relatively low-throughput nature of perfusion bioreactors. Here, a flow perfusion bioreactor with increased throughput was designed and built for tissue engineering. This design uses an integrated medium reservoir and flow chamber in order to increase the throughput, limit the volume of medium required to operate the system, and simplify the assembly and operation

A factorial analysis of the combined effects of hydrogel fabrication parameters on the in vitro swelling and degradation of oligo(poly(ethylene glycol) fumarate) hydrogels

In this study, a full factorial approach was used to investigate the effects of poly(ethylene glycol) (PEG) molecular weight (MW; 10,000 vs. 35,000 nominal MW), crosslinker-to-macromer carbon–carbon double bond ratio (DBR; 40 vs. 60), crosslinker type (PEG-diacrylate (PEGDA) vs. N,N′-methylene bisacrylamide (MB)), crosslinking extent of incorporated gelatin microparticles (low vs. high), and incubation medium composition (with or without collagenase) on the swelling and degradation characteristics of oligo[(poly(ethylene glycol) fumarate)] (OPF) hydrogel composites as indicated by the swelling ratio and the percentage of mass remaining, respectively. Each factor consisted of two levels, which were selected based on previous in vitro and in vivo studies utilizing these hydrogels for various tissue engineering applications. Fractional factorial analyses of the main effects indicated that the mean swelling ratio and the mean percentage of mass remaining of OPF composite hydrogels were significantly affected by every factor. In particular, increasing the PEG chain MW of OPF macromers significantly increased the mean swelling ratio and decreased the mean percentage of mass remaining by 5.7 ± 0.3 and 17.2 ± 0.6%, respectively. However, changing the crosslinker from MB to PEGDA reduced the mean swelling ratio and increased the mean percentage of mass remaining of OPF composite hydrogels by 4.9 ± 0.2 and 9.4 ± 0.9%, respectively. Additionally, it was found that the swelling characteristics of hydrogels fabricated with higher PEG chain MW or with MB were more sensitive to increases in DBR. Collectively, the main and cross effects observed between factors enables informed tuning of the swelling and degradation properties of OPF-based hydrogels for various tissue engineering applications

Articular chondrocytes and mesenchymal stem cells seeded on biodegradable scaffolds for the repair of cartilage in a rat osteochondral defect model

This work investigated the ability of co-cultures of articular chondrocytes and mesenchymal stem cells (MSCs) to repair articular cartilage in osteochondral defects. Bovine articular chondrocytes and rat MSCs were seeded in isolation or in co-culture onto electrospun poly(ɛ-caprolactone) (PCL) scaffolds and implanted into an osteochondral defect in the trochlear groove of 12-week old Lewis rats. Additionally, a blank PCL scaffold and untreated defect were investigated. After 12 weeks, the extent of cartilage repair was analyzed through histological analysis, and the extent of bone healing was assessed by quantifying the total volume of mineralized bone in the defect through microcomputed tomography. Histological analysis revealed that the articular chondrocytes and co-cultures led to repair tissue that consisted of more hyaline-like cartilage tissue that was thicker and possessed more intense Safranin O staining. The MSC, blank PCL scaffold, and empty treatment groups generally led to the formation of fibrocartilage repair tissue. Microcomputed tomography revealed that while there was an equivalent amount of mineralized bone formation in the MSC, blank PCL, and empty treatment groups, the defects treated with chondrocytes or co-cultures had negligible mineralized bone formation. Overall, even with a reduced number of chondrocytes, co-cultures led to an equal level of cartilage repair compared to the chondrocyte samples, thus demonstrating the potential for the use of co-cultures of articular chondrocytes and MSCs for the in vivo repair of cartilage defects

Synthetic biodegradable hydrogel delivery of demineralized bone matrix for bone augmentation in a rat model

There exists a strong clinical need for a more capable and robust method to achieve bone augmentation, and a system with fine-tuned delivery of demineralized bone matrix (DBM) has the potential to meet that need. As such, the objective of the present study was to investigate a synthetic biodegradable hydrogel for the delivery of DBM for bone augmentation in a rat model. Oligo(poly(ethylene glycol) fumarate) (OPF) constructs were designed and fabricated by varying the content of rat-derived DBM particles (either 1:3, 1:1 or 3:1 DBM:OPF weight ratio on a dry basis) and using two DBM particle size ranges (50–150 or 150–250 μm). The physical properties of the constructs and the bioactivity of the DBM were evaluated. Selected formulations (1:1 and 3:1 with 50–150 μm DBM) were evaluated in vivo compared to an empty control to investigate the effect of DBM dose and construct properties on bone augmentation. Overall, 3:1 constructs with higher DBM content achieved the greatest volume of bone augmentation, exceeding 1:1 constructs and empty implants by 3- and 5-fold, respectively. As such, we have established that a synthetic, biodegradable hydrogel can function as a carrier for DBM, and that the volume of bone augmentation achieved by the constructs correlates directly to the DBM dose

Enhanced osteogenesis in co-cultures with human mesenchymal stem cells and endothelial cells on polymeric microfiber scaffolds

In this work, human mesenchymal stem cells (hMSCs) and their osteogenically precultured derivatives were directly co-cultured with human umbilical vein endothelial cells (HUVECs) on electrospun 3D poly(-caprolactone) microfiber scaffolds in order to evaluate the co-culture’s effect on the generation of osteogenic constructs. Specifically, cells were cultured on scaffolds for up to three weeks, and the cellularity, alkaline phosphatase activity (ALP), and bone-like matrix formation were assessed. Constructs with co-cultures and monocultures had almost identical cellularity after the first week, however lower cellularity was observed in co-cultures compared to monocultures during the subsequent two weeks of culture. Scaffolds with co-cultures showed significantly higher ALP activity, glycosaminoglycan and collagen production, as well as greater calcium deposition over the course of study compared to monocultures of hMSCs. Furthermore, the osteogenic outcome was equally robust in co-cultures containing osteogenically precultured and non-precultured hMSCs. The results demonstrate that the combination of MSC and HUVEC populations within a porous scaffold material under osteogenic culture conditions is an effective strategy to promote osteogenesis