Cheol-Min Han

Biointerface control of electrospun fiber scaffolds for bone regeneration: Engineered protein link to mineralized surface

Control over the interface of biomaterials that favors the initial adhesion and subsequent differentiation of stem cells is one of the key strategies in bone tissue engineering. Here we engineer the interface of biopolymer electrospun fiber matrices with a fusion protein of fibronectin 9-10 domain (FNIII9-10) and osteocalcin (OCN), aiming to stimulate mesenchymal stem cell (MSC) functions, including initial adhesion, growth and osteogenic differentiation. In particular, a specific tethering of FNIII9-10-OCN protein was facilitated by the hydroxyapatite (HA) mineralization of the biopolymer surface through a molecular recognition of OCN to the HA crystal lattice. The FNIII9-10-OCN anchorage to the HA-mineralized fiber was observed to be highly specific and tightly bound to preserve stability over a long period. Initial cell adhesion levels, as well as the spreading shape and process, of MSCs within 24h were strikingly different between the fibers linked with and without fusion protein. Significant up-regulations in the mRNA expression of adhesion signaling molecules occurred with the fusion protein link, as analyzed by the reverse transcriptase polymerase chain reaction. The expression of a series of osteogenic-related genes at later stages, over 2-3weeks, was significantly improved in the fusion protein-tailored fiber, and the osteogenic protein levels were highly stimulated, as confirmed by immunofluorescence imaging and fluorescence-activated cell sorting analyses. In vivo study in a rat calvarium model confirmed a higher quantity of new bone formation in the fiber linked with fusion protein, and a further increase was noticed when the MSCs were tissue-engineered with the fusion protein-linked fiber. Collectively, these results indicate that FN-OCN fusion protein links via HA mineralization is a facile tool to generate a biointerface with cell-attractive and osteogenic potential, and that the engineered fibrous matrix is a potential bone regenerative scaffold.

Nanostructured Biointerfacing of Metals with Carbon Nanotube/Chitosan Hybrids by Electrodeposition for Cell Stimulation and Therapeutics Delivery

Exploring the biological interfaces of metallic implants has been an important issue in achieving biofunctional success. Here we develop a biointerface with nanotopological features and bioactive composition, comprising a carbon nanotube (CNT) and chitosan (Chi) hybrid, via an electrophoretic deposition (EPD). The physicochemical properties, in vitro biocompatibility, and protein delivering capacity of the decorated nanohybrid layer were investigated, to address its potential usefulness as bone regenerating implants. Over a wide compositional range, the nanostructured hybrid interfaces were successfully formed with varying thicknesses, depending on the electrodeposition parameters. CNT-Chi hybrid interfaces showed a time-sequenced degradation in saline water, and a rapid induction of hydroxyapatite mineral in a simulated body fluid. The nanostructured hybrid substrates stimulated the initial adhesion events of the osteoblastic cells, including cell adhesion rate, spreading behaviors, and expression of adhesive proteins. The nanostructured hybrid interfaces significantly improved the adsorption of protein molecules, which was enabled by the surface charge interaction, and increased surface area of the nanotopology. Furthermore, the incorporated protein was released at a highly sustained rate, profiling a diffusion-controlled pattern over a couple of weeks, suggesting the possible usefulness as a protein delivery device. Collectively, the nanostructured hybrid CNT-Chi layer, implemented by an electrodeposition, is considered a biocompatible, cell-stimulating, and protein-delivering biointerface of metallic implants.

Physically-strengthened collagen bioactive nanocomposite gels for bone: A feasibility study

Collagen hydrogel systems have been limited in their uses for hard tissue engineering due to their poor mechanical properties in spite of their excellent biocompatibility. Physical strengthening and incorporation of the inorganic substances are considered as promising ways to improve mechanical stability of the collagen gel, while providing effective biomimetic environment for cells. Here, we developed three-dimensional matrix by rolling up the plastically-compressed collagen hydrogel composites with mesoporous bioactive glass nanoparticle (BGn). Monodispersed BGn with a size of ~90 nm was well incorporated within the collagen matrix which has nanofibrillar structure. The mechanical properties of the composite hydrogels measured by dynamic mechanical analysis were significantly improved by the compression of the hydrogels and further improved by addition of BGn into hydrogels. Moreover, the proliferation rate and osteogenic differentiation of rat bone marrow derived mesenchymal stem cells cultured within the composite hydrogels were enhanced by incorporation of BGn. The results suggest that physically-strengthened nanocomposite collagen hydrogel would be useful in hard tissue engineering applications.

Fibronectin immobilization on to robotic-dispensed nanobioactive glass/polycaprolactone scaffolds for bone tissue engineering

Bioactive nanocomposite scaffolds with cell-adhesive surface have excellent bone regeneration capacities. Fibronectin (FN)-immobilized nanobioactive glass (nBG)/polycaprolactone (PCL) (FN-nBG/PCL) scaffolds with an open pore architecture were generated by a robotic-dispensing technique. The surface immobilization level of FN was significantly higher on the nBG/PCL scaffolds than on the PCL scaffolds, mainly due to the incorporated nBG that provided hydrophilic chemical-linking sites. FN-nBG/PCL scaffolds significantly improved cell responses, including initial anchorage and subsequent cell proliferation. Although further in-depth studies on cell differentiation and the in vivo animal responses are required, bioactive nanocomposite scaffolds with cell-favoring surface are considered to provide promising three-dimensional substrate for bone regeneration.

In vitro co-culture strategies to prevascularization for bone regeneration: A brief update

Vascularization is an important event that generates blood vessels for bone healing and regeneration processes. Vascularization of the engineered bone construct can keep the cells alive by sufficiently supplying nutrient and oxygen and delivering progenitor / stem cells and signaling molecules to the defect site. For this reason there have been extensive research efforts to develop new methodologies, which include development of scaffolds, controlled delivery of signaling molecules, and co-culture systems. Among these, the co-cultures of cells, which involve the cross-talks between vasculogenic cells and osteoprogenitor cells, have recently shown to be an effective prevascularization strategy. Here we briefly update recent key co-culture systems modeled with different culture components and the in vitro and in vivo findings of the prevascularized bone constructs.

Bioactive injectables based on calcium phosphates for hard tissues: A recent update

Self-gelling/setting injectable biomaterials hold great promise for the delivery of bioactive molecules and cells useful for tissue engineering and regenerative medicine. In the biopolymeric regime, a broad compositional spectrum has been developed, yet very limited compositional options have been developed for inorganic injectables. For example, calcium phosphate (CaP)-based injectables are considered to be one of the most promising classes of materials for bone repair and reconstruction. Here we present an update on the recent advancements in CaP-injectables, where significant efforts have been undertaken to improve the regenerative capacity by tailoring the chemical compositions and increasing the drug delivery potential.

Gelatin-apatite bone mimetic co-precipitates incorporated within biopolymer matrix to improve mechanical and biological properties useful for hard tissue repair.

Synthetic biopolymers are commonly used for the repair and regeneration of damaged tissues. Specifically targeting bone, the composite approach of utilizing inorganic components is considered promising in terms of improving mechanical and biological properties. We developed gelatin-apatite co-precipitates which mimic the native bone matrix composition within poly(lactide-co-caprolactone) (PLCL). Ionic reaction of calcium and phosphate with gelatin molecules enabled the co-precipitate formation of gelatin-apatite nanocrystals at varying ratios. The gelatin-apatite precipitates formed were carbonated apatite in nature, and were homogeneously distributed within the gelatin matrix. The incorporation of gelatin-apatite significantly improved the mechanical properties, including tensile strength, elastic modulus and elongation at break, and the improvement was more pronounced as the apatite content increased. Of note, the tensile strength increased to as high as 45 MPa (a four-fold increase vs. PLCL), the elastic modulus was increased up to 1500 MPa (a five-fold increase vs. PLCL), and the elongation rate was ∼240% (twice vs. PLCL). These results support the strengthening role of the gelatin-apatite precipitates within PLCL. The gelatin-apatite addition considerably enhanced the water affinity and the acellular mineral-forming ability in vitro in simulated body fluid; moreover, it stimulated cell proliferation and osteogenic differentiation. Taken together, the GAp-PLCL nanocomposite composition is considered to have excellent mechanical and biological properties, which hold great potential for use as bone regenerative matrices.

Recent update on implant surface tailoring to improve bone regenerative capacity

Metallic implants in dentistry and orthopedics are currently considered one of the most successful clinical devices. The bone regenerative ability at the interface of the implants is largely dominated by the surface properties and the complex events involved with biological ingredients such as ions, proteins and cells. Here we cast an opinion on how to improve the bone regenerative potential of metallic implants, particularly of Ti (alloys) by means of i) updating current technological advances, ii) focusing on the effects of tailored-surface nanostructures on in vitro osteoblasts/stem cells responses, and iii) outlining some in vivo findings. This short review will help spurring future works on advanced surface designs to simulate stem cell behaviors and in vivo outcomes for successful bone regeneration.