Electrospun Nanofibrous Composite Materials For Guided Tissue/Bone Regeneration

Electrospun nanofibers with ultrahigh surface area and high porosity which mimic the structure of natural extracellular matrix have been widely used in the preparation of biomedical materials such as tissue engineering scaffolds,wound dressings and drug delivery carriers.The electrospun nanofibrous materials used in guided tissue/bone regeneration therapy can not only isolate the damaged region from surrounding connective tissues,but also promote the generation of new alveoli and periodontal ligament tissues.Clinical studies have showed that single-component material cannot satisfy the complexity of dental surgery. Therefore,it calls for the adoption of multiple nanofibers with different composition and structures to improve the mechanical properties,to control the degradation rate more predictably and to induce periodontal functional reconstruction.By mimicking the natural woven bone,three dimensional nanofibrous composite scaffolds were also prepared to improving bone regeneration by providing enhanced mineralization and cell infiltration.The aim of this study was to fabricate nanofibrous composite materials by electrospinning for guided tissue/bone regeneration.To evaluate the feasibility and superiority of the new type of biomaterials for clinical use,the material composition,surface modification,mechanical properties and biocompatibility were all studied systematically.Firstly,the electrospinning of polylactic acid(PLLA) and polylactic acid/hydroxyapatite(HA) nanofibers were optimized by using mixture solutions.As a result,not only the fiber diameters decreased obviously, but also the process stability was improved.After hot stretching treatment, the fiber diameters,diameter distributions and porosity of PLLA parallel nanofibrous membranes were all reduced with the increase of stretch ratio, while the maximum tensile strength and modulus along the fibers reached 103 MPa and 1.83 GPa,respectively.Furthermore,the hydrophilicity of the PLLA and PLLA/HA nanofibrous membranes was improved by alkaline etching and gelatin coating.The water contact angle of the resultant nanofibrous membranes has fallen from 130°to 60°after the surface modification.Secondly,the electrospinning of gelatin aqueous solution was successfully carried out by elevating the spinning temperature.Gelatin nanofibers with different diameters were obtained by varying the spinning temperature,solution concentration and other parameters.In order to improve the stability and mechanical properties in moist state,the gelatin nanofibrous membranes were chemically crosslinked by 1-ethyl-3-dimethyl-aminopropyl carbo-diimide hydrochloride (EDC) and N-hydroxyl succinimide(NHS).Nanofibrous structure of the membrane was still retained after lyophilization,although the fibers were curled and conglutinated.Tensile test revealed that the hydrated membrane became pliable and provided predetermined mechanical properties,which was in favor of covering the damage region and avoiding breakage during the treatment.Gelatin/β-tricalcium phosphate (β-TCP) nanofibers with homogeneous dispersion ofβ-TCP were also electrospun from aqueous solution with the assistance of poloxamer F-68.In order to satisfy the clinical criteria of guided tissue/bone regeneration,composite membranes with layered structure had been designed and prepared with these resultant materials.The upper layer with dense PLLA nanofibers provided a physically compatible barrier to gingival fibroblasts.The layer in the middle was mainly constructed by parallel PLLA nanofibers to achieve high mechanical strength.The loose and porous gelatin/β-TCP nanofibers acted as the bottom layer that performed the function of guided bone regeneration.Bio-ceramic nanofibrous scaffolds were successfully prepared by combining electrospinning and sol-gel technique.A wovenβ-TCP scaffold with high purity and crystallinity was obtained by varying the Ca/P ratio,pH value,spinning solution component and sintering temperature.Collagen coating on the surface ofβ-TCP fibers,generated by impregnating method,could not only enhance the stability and toughness of the scaffold,but also promote the mineralization and cell infiltration.Finally,the biocompatibility test was prepared on the above mentioned nanofibrous composite membranes and nanofibrous scaffolds, such as cytotoxicity test(MTT test) and human periodontal ligament cells (hPDLCs) or osteoblast-like cells(MG-63) in vitro co-culture experiments.MTT test results indicated that the number of hPDLCs in PLLA/HA group were larger than that in PLLA group at 7th day.The crosslinked gelatin nanofibrous membrane could promote proliferation of hPDLCs significantly,and cell activity increased over time.The cells number ofβ-TCP/collagen nanofibrous scaffold group at 5th day was significantly higher thanβ-TCP group.The co-culture in vitro showed that all the resultant nanofibrous materials allow cells to achieve good adhesion and proliferation.On the optimized PLLA and PLLA/HA nanofibrous membranes,the PLLA/HA group was more conductive to the hPDLCs growth than the PLLA group.Paraffin sections showed that a large number of cells only gathered on the surface of hot-stretched PLLA parallel nanofibrous membrane,which revealed good cell occlusive ability.HPDLCs also distributed uniformly and grew well on the crosslinked gelatin nanofibrous membrane.MG-63 grew on the β-TCP/collagen nanofibrous scaffold after 24h superior to theβ-TCP group.Paraffin sections results showed that there was more cell infiltration into theβ-TCP/collagen nanofibrous scaffold.Therefore,the electrospun nanofibrous materials with good biocompatibility and mechanical properties can be used as promising biomaterials for GTR/GBR procedures.