Yuhua Yan

Conductive PPY/PDLLA conduit for peripheral nerve regeneration

The significant drawbacks and lack of success associated with current methods to treat critically sized nerve defects have led to increased interest in neural tissue engineering. Conducting polymers show great promise due to their electrical properties, and in the case of polypyrrole (PPY), its cell compatibility as well. Thus, the goal of this study is to synthesize a conducting composite nerve conduit with PPY and poly(d, l-lactic acid) (PDLLA), assess its ability to support the differentiation of rat pheochromocytoma 12 (PC12) cells in vitro, and determine its ability to promote nerve regeneration in vivo. Different amounts of PPY (5%, 10%, and 15%) are used to synthesize the conduits resulting in different conductivities (5.65, 10.40, and 15.56 ms/cm, respectively). When PC12 cells are seeded on these conduits and stimulated with 100 mV for 2 h, there is a marked increase in both the percentage of neurite-bearing cells and the median neurite length as the content of PPY increased. More importantly, when the PPY/PDLLA nerve conduit was used to repair a rat sciatic nerve defect it performed similarly to the gold standard autologous graft. These promising results illustrate the potential that this PPY/PDLLA conducting composite conduit has for neural tissue engineering.

PDLLA/chondroitin sulfate/chitosan/NGF conduits for peripheral nerve regeneration.

Biodegradable PDLLA/Chondroitin sulfate/Chitosan(PDLLA/CS/CHS) nerve conduits with potentially good biocompatibility and good mechanical property feasible for surgical manipulation have been developed in our previous work. The purpose of this study was to investigate their possible application in repairing damaged nerves and the effect of nerve growth factor (NGF). The PDLLA/CS/CHS/NGF nerve conduits were prepared by immobilizing NGF onto the PDLLA/CS/CHS nerve conduits with carbodiimide. Adult Sprague-Dawley (SD) rats weighing 200-250 g were used as the animal model. The conduits were employed to bridge the 10 mm defects in the sciatic nerve of the SD rats. Nerve conduction velocities (NCVs) were clearly detected in both nerve conduits after 3 months of implantation, indicating a rapid functional recovery for the disrupted nerves. The results of histological sections showed that the internal sides of the conduits were compact enough to prevent the connective tissues from ingrowth. Combined with the strong mechanical properties, good nerve regeneration ability and non-toxicity of its degradation products, PDLLA/CS/CHS nerve conduits would be expected to be useful materials to repair nerve damage and NGF can effectively promote the regeneration of peripheral nerve defect.

Dissolution behavior of hydroxyapatite powder in hydrothermal solution

Abstract The dissolution behavior of hydroxyapatite (HA) in a hydrothermal solution was investigated using a Morey-type autoclave over a range of 150–350°C and a pH value range of 5–9. The results showed that the dissolubility of HA powder was determined as a function of temperature and time under constant pressure, and the temperature coefficient for the solubility of HA powder was positive. The rate of dissolution of HA in the hydrothermal aqueous solution was mainly controlled by a polynuclear mechanism. The dissolution behavior of HA was affected mainly by the hydrothermal temperature and the dissolving activation energy. The effect of temperature was obviously more than that of the pH value of the solution.

Synthesis of a novel biodegradable and electroactive polyphosphazene for biomedical application

To prepare one electroactive and biodegradable biomaterial for biomedical application, a new synthetic strategy was developed to synthesize a novel electrically conductive biodegradable polyphosphazene polymer containing parent aniline pentamer (PAP) and glycine ethyl ester (GEE) as side chains by a nucleophilic substitution reaction. The electrical conductivity of the polymer is approximately 2 x 10(-5) S cm(-1) in the semiconducting region upon preliminarily protonic-doped experiment. The degradation and RSC96 Schwann cells experiments in vitro prove that the polymer is biodegradable and beneficial to the cell adhesion and proliferation. The as-synthesized polymer also shows good solubility in common organic solvent and good film-forming properties. This new type of polymer has potential applications as scaffolds for neuronal and cardiovascular tissue engineering or other biomedical devices that require electroactivity.

Degradation properties of the electrostatic assembly PDLLA/CS/CHS nerve conduit.

A poly(d,l-lactic acid)/chondroitin sulfate/chitosan (PDLLA/CS/CHS) nerve conduit for repairing nerve defects was prepared by electrostatic assembly and the thermally induced phase separation technique. The hydrophilic characteristics of the PDLLA/CS/CHS assembly nerve conduits were improved markedly. The degradation behavior of the nerve conduit with various assembly layers was evaluated by a pH change, weight loss rate and molecular weight change. The pH of the solution of the nerve conduit could be effectively adjusted by varying the layer numbers and overcoming the acidity-caused auto-acceleration of PDLLA; the nerve conduit can retain its integrity in a phosphate buffer solution after being degraded for 3 months. After such a conduit was implanted in the rat for 3 months, obvious degradation occurred, but the regenerated nerve was integrated and it grew successfully from the proximal to distal nerve stump. All these results implied that the degradation rate of the prepared conduit can adapt to the regeneration of the peripheral nerve, which might be a new derivative of PDLLA-based biodegradable materials for repairing nerve injuries without acidity-caused irritations and acidity-induced auto-accelerating degradation behavior as shown by PDLLA.

Preparation and drug-release behavior of β-TCP ceramics drug carrier in vitro

Abstractβ-TCP ceramics drug carrier was first prepared and characterized. SEM showed that β-TCP carrier was in porous amorphous structure with diameters around 10 μm. The physical properties including apparent porosity, volume-weight, tensile strength and the permeability were measured and the results indicated those properties fit the clinical usage of β-TCP drug carrier. Furthermore, drug release experiment in vitro showed that the carrier could prolong drug release in simulated body fluid which provides basis for the clinical use of β-TCP ceramics as drug carrier.