Assessment of a long-term in vitro model to characterize the mechanical behavior and macrophage-mediated degradation of a novel, degradable, electrospun poly-urethane vascular graft.

An assessment tool to evaluate the degradation of biodegradable materials in a more physiological environment is still needed. Macrophages are critical players in host response, remodeling and degradation. In this study, a cell culture model using monocyte-derived primary macrophages was established to study the degradation, macro-/micro-mechanical behavior and inflammatory behavior of a new designed, biodegradable thermoplastic polyurethane (TPU) scaffold, over an extended period of time in vitro. For in vivo study, the scaffolds were implanted subcutaneously in a rat model for up to 36 weeks. TPU scaffolds were fabricated via the electrospinning method. This technique provided a fibrous scaffold with an average fiber diameter of 1.39 ± 0.76 µm and an average pore size of 7.5 ± 1.1 µm. The results showed that TPU scaffolds supported the attachment and migration of macrophages throughout the three-dimensional matrix. Scaffold degradation could be detected in localized areas, emphasizing the role of adherent macrophages in scaffold degradation. Weight loss, molecular weight and biomechanical strength reduction were evident in the presence of the primary macrophage cells. TPU favored the switch from initial pro-inflammatory response of macrophages to an anti-inflammatory response over time both in vitro and in vivo. Expression of MMP-2 and MMP-9 (the key enzymes in tissue remodeling based on ECM modifications) was also evident in vitro and in vivo. This study showed that the primary monocyte-derived cell culture model represents a promising tool to characterize the degradation, mechanical behavior as well as biocompatibility of the scaffolds during an extended period of observation.

Long Term Evaluation of Nanofibrous, Bioabsorbable Polycarbonate Urethane Grafts for Small Diameter Vessel Replacement in Rodents.

OBJECTIVE: Biodegradable materials for in situ vascular tissue engineering could meet the increasing clinical demand for sufficient synthetic small diameter vascular substitutes in aortocoronary bypass and peripheral vascular surgery. The aim of this study was to design a new degradable thermoplastic polycarbonate urethane (dPCU) with improved biocompatibility and optimal biomechanical properties. Electrospun conduits made from dPCU were evaluated in short and long term follow up and compared with expanded polytetrafluoroethylene (ePTFE) controls. METHODS: Both conduits were investigated prior to implantation to assess their biocompatibility and inflammatory potential via real time polymerase chain reaction using a macrophage culture. dPCU grafts (n = 28) and ePTFE controls (n = 28) were then implanted into the infrarenal abdominal aorta of Sprague-Dawley rats. After seven days, one, six, and 12 months, grafts were analysed by histology and immunohistochemistry (IHC) and assessed biomechanically. RESULTS: Anti-inflammatory signalling was upregulated in dPCU conduits and increased significantly over time in vitro. dPCU and ePTFE grafts offered excellent long and short term patency rates (92.9% in both groups at 12 months) in the rat model without dilatation or aneurysm formation. In comparison to ePTFE, dPCU grafts showed transmural ingrowth of vascular specific cells resulting in a structured neovessel formation around the graft. The graft material was slowly reduced, while the compliance of the neovessel increased over time. CONCLUSION: The newly designed dPCU grafts have the potential to be safely applied for in situ vascular tissue engineering applications. The degradable substitutes showed good in vivo performance and revealed desirable characteristics such as biomechanical stability, non-thrombogenicity, and minimal inflammatory response after long term implantation.

Bi-directional cell-pericellular matrix interactions direct stem cell fate.

Modifiable hydrogels have revealed tremendous insight into how physical characteristics of cells' 3D environment drive stem cell lineage specification. However, in native tissues, cells do not passively receive signals from their niche. Instead they actively probe and modify their pericellular space to suit their needs, yet the dynamics of cells' reciprocal interactions with their pericellular environment when encapsulated within hydrogels remains relatively unexplored. Here, we show that human bone marrow stromal cells (hMSC) encapsulated within hyaluronic acid-based hydrogels modify their surroundings by synthesizing, secreting and arranging proteins pericellularly or by degrading the hydrogel. hMSC's interactions with this local environment have a role in regulating hMSC fate, with a secreted proteinaceous pericellular matrix associated with adipogenesis, and degradation with osteogenesis. Our observations suggest that hMSC participate in a bi-directional interplay between the properties of their 3D milieu and their own secreted pericellular matrix, and that this combination of interactions drives fate.

Biocompatibility Assessment of a New Biodegradable Vascular Graft via In Vitro Co-culture Approaches and In Vivo Model.

Following the implantation of biodegradable vascular grafts, macrophages and fibroblasts are the major two cell types recruited to the host-biomaterial interface. In-vitro biocompatibility assessment usually involves one cell type, predominantly macrophages. In this study, macrophage and fibroblast mono- and co-cultures, in paracrine and juxtacrine settings, were used to evaluate a new biodegradable thermoplastic polyurethane (TPU) vascular graft. Expanded-polytetrafluoroethylene (ePTFE) grafts served as controls. Pro/anti-inflammatory gene expression of macrophages and cytokines was assessed in vitro and compared to those of an in vivo rat model. Host cell infiltration and the type of proliferated cells was further studied in vivo. TPU grafts revealed superior support in cell attachment, infiltration and proliferation compared with ePTFE grafts. Expression of pro-inflammatory TNF-α/IL-1α cytokines was significantly higher in ePTFE, whereas the level of IL-10 was higher in TPU. Initial high expression of pro-inflammatory CCR7 macrophages was noted in TPU, however there was a clear transition from CCR7 to anti-inflammatory CD163 expression in vitro and in vivo only in TPU, confirming superior cell-biomaterial response. The co-culture models, especially the paracrine model, revealed higher fidelity to the immunomodulatory/biocompatibility behavior of degradable TPU grafts in vivo. This study established an exciting approach developing a co-culture model as a tool for biocompatibility evaluation of degradable biomaterials.

Modification of the release characteristics of estradiol encapsulated in PLGA particles via surface coating.

BACKGROUND: Drug-loaded poly(lactide-co-glycolide) particles (100-4500 nm in diameter) were prepared via the electrospraying method. An extensive study was then carried out to determine the parameters affecting the release profile of estradiol (the drug or active pharmaceutical ingredient) in order to facilitate minimum initial burst release of estradiol. RESULTS AND DISCUSSION: The three most important factors affecting estradiol release were identified as: particle size, coating of the particles with chitosan/gelatin and the concentration of the coating agent. It was shown that coating the particles with chitosan significantly reduced the burst and initial release without affecting the subsequent release profile. CONCLUSIONS: This work demonstrates a powerful method of generating drug-loaded polymeric particles with modified release behavior and control over the initial release phase. The surface-modified particles may be useful in controlled therapeutic delivery systems to minimize undesirable side effects.