Fumed Silica Nanoparticle Mediated Biomimicry for Optimal Cell-Material Interactions for Artificial Organ Development

Development of mechano-responsive polymeric scaffolds using functionalized silica nano-fillers for the control of cellular functions

We demonstrate an efficient method to produce mechano-responsive polymeric scaffolds which can alter cellular functions using two different functionalized (OH and NH2) silica nano-fillers. Fumed silica-hydroxyl and fumed silica-amine nano-fillers were mixed with a biocompatible polymer (POSS-PCU) at various wt% to produce scaffolds. XPS and mechanical testing demonstrate that bulk mechanical properties are modified without changing the scaffold's surface chemistry. Mechanical testing showed significant change in bulk properties of POSS-PCU scaffolds with an addition of silica nanofillers as low as 1% (P<0.01). Scaffolds modified with NH2 silica showed significantly higher bulk mechanical properties compared to the one modified with the OH group. Enhanced cell adhesion, proliferation and collagen production over 14days were observed on scaffolds with higher bulk mechanical properties (NH2) compared to those with lower ones (unmodified and OH modified) (P<0.05) during in vitro analysis. This study provides an effective method of manufacturing mechano-responsive polymeric scaffolds, which can help to customize cellular responses for biomaterial applications.

A Material Conferring Hemocompatibility

There is a need for biomimetic materials for use in blood-contacting devices. Blood contacting surfaces maintain their patency through physico-chemical properties of a functional endothelium. A poly(carbonate-urea) urethane (PCU) is used as a base material to examine the feasibility of L-Arginine methyl ester (L-AME) functionalized material for use in implants and coatings. The study hypothesizes that L-AME, incorporated into PCU, functions as a bioactive porogen, releasing upon contact with blood to interact with endothelial nitric oxide synthase (eNOS) present in blood. Endothelial progenitor cells (EPC) were successfully cultured on L-AME functionalized material, indicating that L-AME -increases cell viability. L-AME functionalized material potentially has broad applications in blood-contacting medical devices, as well as various other applications requiring endogenous up-regulation of nitric oxide, such as wound healing. This study presents an in-vitro investigation to demonstrate the novel anti-thrombogenic properties of L-AME, when in solution and when present within a polyurethane-based polymer.

Bioabsorbable Bypass Grafts Biofunctionalised with RGD Have Enhanced Biophysical Properties and Endothelialisation Tested In vivo

Small diameter arterial bypass grafts are considered as unmet clinical need since the current grafts have poor patency of 25% within 5 years. We have developed a 3D scaffold manufactured from natural and synthetic biodegradable polymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(𝜀-caprolactone) (PCL), respectively. Further to improve the biophysical properties as well as endothelialisation, the grafts were covalently conjugated with arginine-glycine-aspartic acid (RGD) bioactive peptides. The biophysical properties as well as endothelialisation of PHBV/PCL and PCL 2 mm diameter bypass grafts were assessed with and without biofunctionalisation with RGD peptides in vitro and in vivo. Morphology of the grafts was assessed by scanning electron microscopy, whereas physico-mechanical properties were evaluated using a physiological circulating system equipped with a state of art ultrasound vascular wall tracking system. Endothelialisation of the grafts in vitro and in vivo were assessed using a cell viability assay and rat abdominal aorta replacement model, respectively. The biofunctionalisation with RGD bioactive peptides decreased mean fiber diameter and mean pore area in PHBV/PCL grafts; however, this was not the case for PCL grafts. Both PHBV/PCL and PCL grafts with RGD peptides had lower durability compared to those without; these durability values were similar to those of internal mammary artery. Modification of PHBV/PCL and PCL grafts with RGD peptides increased endothelial cell viability in vitro by a factor of eight and enhanced the formation of an endothelial cell monolayer in vivo 1 month postimplantation. In conclusion, PHBV/PCL small-caliber graft can be a suitable 3D scaffold for the development of a tissue engineering arterial bypass graft.

Evaluation of experimental methods for nitric oxide release from cardiovascular implants; bypass grafts as an exemplar

BACKGROUND

There is a great potential for nitric oxide (NO) eluting biomaterials in biomedical applications. These include the development of cardiovascular implants, wound healing products, or applications in cancer and respiratory therapy. While the potential of these materials as a therapy is becoming clearer, the real-time monitoring of NO is not easy and the success in the development of such materials depends on the accurate quantification of NO release.

METHOD

To emphasize on the importance of a measurement technique on the outcome of an experiment, we compared total NO released from S-nitroso-N-acetyl-d-penicillamine (SNAP) incorporated nanocomposite polymer in the form of bypass grafts under simulated physiological conditions using amperometric and chemiluminescence techniques.

RESULTS

We found that the total amount of NO measured by the amperometric technique was 35.8% of the theoretical amount. Similarly, on measuring NO release from the bypass grafts, we demonstrated that the chemiluminesence technique detected NO at a relatively higher level.

CONCLUSIONS

The results of this study clearly demonstrate the relative difference between analysis techniques for accurate NO detection that can be applied to distinct experimental models associated with NO-eluting cardiovascular implants.

A potential platform for developing 3D tubular scaffolds for paediatric organ development

Children suffer from damaged or loss of hollow organs i.e. trachea, oesophagus or arteries from birth defects or diseases. Generally these organs possess an outer matrix consisting of collagen, elastin, and cells such as smooth muscle cells (SMC) and a luminal layer consisting of endothelial or epithelial cells, whilst presenting a barrier to luminal content. Tissue engineering research enables the construction of such organs and this study explores this possibility with a bioabsorbable nanocomposite biomaterial, polyhedral oligomeric silsesquioxane poly(ε-caprolactone) urea urethane (POSS-PCL).Our established methods of tubular graft extrusion were modified using a porogen-incorporated POSS-PCL and a new lamination method was explored. Porogen (40, 60 or 105 µm) were introduced to POSS-PCL, which were fabricated into a bilayered, dual topography matching the exterior and luminal interior of tubular organs. POSS-PCL with different amounts of porogen were tested for their suitability as a SMC layer by measuring optimal interactions with human adipose derived stem cells. Angiogenesis potential was tested with the chorioallantoic membrane assay. Tensile strength and burst pressures of bilayared tubular grafts were determined. Scaffolds made with 40 µm porogen demonstrated optimal adipose derived stem cell integration and the scaffolds were able to accommodate angiogenesis. Mechanical properties of the grafts confirmed their potential to match the relevant physiological and biophysical parameters. This study presents a platform for the development of hollow organs for transplantation based on POSS-PCL. These bilayered-tubular structures can be tailor-made for cellular integration and match physico-mechanical properties of physiological systems of interest. More specific luminal cell integration and sources of SMC for the external layer could be further explored.