Introduction: It is well known that the fate of biomaterials is determined by the distribution of proteins attached to the surface from the initial contact with blood or serum. This profile determines wether a material is inert, creates a foreign body response or is bioactive. Bioinert materials, such as polyethylene completely denature surface proteins, whilst materials inducing inflammatory responses are predisposed to complement protein attachment. Bioactive materials such autologous tissue grafts adsorb, but do not denature serum proteins such as fibronectin and Von Willebrand’s factor. This does not interfere with the healing cascade. This aim of this study is to prepare a synthetic bone graft substitute that activates the body’s autologous healing cascade by activating platelets, without activating a complement response through the controlled adsorption of serum proteins.

Methods: Polymers composed of varied concentration of acrylic acid (AA) and comonomers (methyl, ethyl and butyl methacrylates (MMA, EMA, BMA)) were prepared in glass vials by free radical polymerisation. Fresh blood was collected from a healthy donor and pipetted immediately into each chamber. Glass was used as a control. The chambers were incubated at 37o C for 2 hours. The surface morphology was examined using Scanning Electron Microscopy (SEM). Concentration of complement protein C5a and prothrombin fragments 1 and 2 were determined using commercial ELISA kits. Foreign body reaction (FBR) initiated by the biomaterial was estimated by counting leukocytes on clot sections using immunofluorescence.

Results: Extent of coagulation was correlated with plasma concentrations of Prothrombin fragments 1 and 2. These measurements show blood incubated with various polymers composed of different comonomers all promoted the formation of blood clots. It was found that the leukocyte population towards the interface of clot and polymer (AA:MMA) decreased with increasing surface acid concentration (65%AA:MMA 30 leukocytes/0.25mm2, glass 70 leukocytes/0.25mm2 (p< 0.05)). FBR is induced by the activation of complement system. The percentage of C5a concentration detected in blood incubated with various polymers composed of different comonomers relative to normal serum level of C5a (35ng/mL). No significant elevations of C5a were measured from polymer 65% AA:MMA and 65% AA:EMA. Glass induced vigorous complement response as expected. The synergistic combination of surface acid concentration and comonomers had a significant effect on extent of FBR. Increased acid concentration resulted in decreased C5a level with MMA and ET but increased level with BMA.

Discussion: The functional groups exposed on the surface of a material influence whether leukocyte or platelet activation is responsible for the subsequent physiological response. By modifying the combinations of surface acid concentrations and comonomers, we show that a biomaterial with an appropriate surface chemistry promotes the platelet plug formation and coagulation but down regulated foreign body reaction. This study shows that that a biomaterial with the appropriate surface chemistry to evoke the same coagulation response as damaged tissue, mediated through platelet activation and intrinsic and extrinsic coagulation, initiates the initial pathways of the bone healing cascade. This material is a realistic candidate for biomaterial induced bone regeneration.

Introduction: Acute neurological damage from spinal cord injuries is believed to be localised, however it initiates a cascade of secondary events which usually leads to extensive and permanent neurological deficit. The secondary damage begins with the disruption of the blood-spinal cord barrier which unleashes a protracted inflammatory response. This prolonged inflammatory response is the catalyst for the secondary neurodegeneration and limited repair response that occurs in the chronic phase of a spinal cord injury. In this study it was proposed that the acute delivery of the angiogenic growth factors vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) would mediate inflammation and restore the blood spinal cord barrier. This would minimise the formation of glial scar and reduce the extent of secondary degeneration caudal and cranial to the lesion site.

Methods: Adult male Wistar rats (400g) were anesthetised. Complete laminectomies were performed at T10 and the animals were subjected to T10 hemisection. Animals were randomised to a treatment group (Lesion Control (LC), Gel Control (GC) and Angiogenic Gel (AG)) after the spinal cord was cut. Each treatment group had 6 animals sacrificed 3 months post injury. Sections were stained with antibodies to neurofilament 200, glial fibrillary acidic protein, smooth muscle actin (SMA), and fluorescent secondary antibodies and mounted with DAPI. The lesion size was measured from horizontal histological sections of the midline from 5 animals in each group using Axiovision version 4.6.1.0 (Carl Zeiss Imaging Solutions, Germany).

Results: The mean lesion size for the lesion control group was 2.09mm2, 1.97mm2 for the gel control group and 0.45mm2 for the active gel group. A t-test was used to confirm that the differences between the active gel and the two control groups were statistically significant (AG vs LC p= 0.021 AG vs GC p= 0.026). Histology showed a marked improvement of the morphology of the astrocytes in the treatment group over the control groups indicating that the treatment affected the population of reactive astrocytes. SMA staining showed an increased level of revascularisation in the treated lesions.

Discussion: Spinal cords do not heal because of prolonged inflammation which leads to secondary necrotic events, scar formation and the inhibition of regeneration. In this study we present a method for regulating the post lesion inflammatory signals, significantly reducing post-lesion scar formation. We propose the delivery of VEGF/PDGF significantly increases the permeability of the blood spinal cord barrier to neutrophils and macrophages and promotes angiogenesis observed in the lesion site. This may have two major effects on the progression of the spinal cord injury. Firstly, by increasing the initial influx of inflammatory cells it enables the faster removal of damaged tissue and phagocytosis of apoptotic cells thereby restoring the balance in favour of regulated inflammation and results in a finite and reduced inflammation time. Secondly, combination of VEGF and PDGF provides a robust angiogenic response and reduces ischemia, the population of reactive astrocytes and the capacity to form glial scars. These growth factors appear to moderate the secondary degenerative changes that result from the prolonged inflammation and thus promote the inherent capacity for regeneration.