Regulating proliferation and differentiation of osteoblasts on poly(l-lactide)/gelatin composite nanofibers via timed biomineralization

Clinical application of polylactic acid/gelatin nanofibre membrane in hard-to-heal lower extremity venous ulcers

Objective:

To evaluate the safety and effectiveness of polylactic acid/gelatin nanofibre membranes (PGNMs) in treating hard-to-heal lower extremity venous ulcer wounds.

Method:

In this prospective study, patients with venous leg ulcers (VLUs) were treated with PGNMs or standard of care. Wounds were assessed once a week until the wound was fully healed.

Results:

The treatment group was comprised of 10 patients with VLUs, aged between 47–64 years, with an average age of 56.58±6.19 years. The wounds were located in the lower leg and/or ankle. Average wound area was 8.91±13.57cm2 (range: 1.5–52.5cm2). Average wound healing time was 18.75±16.36 days. Of the patients, nine (90%) rated their pain as lighter when removing the dressing, with an average pain value of 2.0±1.0 points. There was less secondary trauma to the wound surface, and less bleeding. At six months after the wound healing, the scar evaluation (using the Vancouver Scar Scale) result was 3.75±1.96 points.

Conclusion:

In this study, the PGNMs were safe and effective in treating hard-to-heal lower extremity VLUs.

A polydopamine-assisted strontium-substituted apatite coating for titanium promotes osteogenesis and angiogenesis via FAK/MAPK and PI3K/AKT signaling pathways

Early osteointegration is essential for biomedical implants. Surface modifications can significantly compensate for an implant's lack of biocompatibility and osteo-differentiation. They can also be designed to promote angiogenesis in order to assist osteogenesis and ultimately facilitate bone regeneration. In this study, a polydopamine-assisted strontium-substituted apatite coating (Ti@PDA + SrHA) was fabricated on a multifunctional titanium implant to induce both angiogenic and osteogenic abilities for rapid osseointegration. Polydopamine and Sr-substituted hydroxyapatite were coated on the implant through biomineralization. The in vitro results showed that Ti@PDA + SrHA improved cell adhesion and increased the proliferation of rat bone marrow-derived mesenchymal stem cells (rBMSCs) and human umbilical vein endothelial cells (HUVECs). Ti@PDA + SrHA upregulated the expression of ALP activity and osteogenic genes in rBMSCs and elevated angiogenic genes in both rBMSCs and HUVECs. Mechanically, the FAK/MAPK signaling pathway was activated in rBMSCs, and the PI3K/AKT signaling pathway was activated in both rBMSCs and HUVECs. Consistent with these findings, Ti@PDA + SrHA accelerated new bone formation and rapid osseointegration in the femoral condyle implantation study with good stability. Overall, we fabricated a multifunctional biocompatible implant with better angiogenic and osteogenic performance compared to the non-coated implant.

Osteogenic Effect of a Biodegradable BMP-2 Hydrogel Injected into a Cannulated Mg Screw

Cannulated screws, containing an internal hole for inserting a guide pin, are commonly used in the management of bone fractures. Cannulated Mg screws can be biodegraded easily because their increased surface area including that of the inner hole rapidly reacts with body fluids. To delay biodegradation of cannulated Mg screws and improve bone regeneration, we developed a specific type of screw by injecting it with gelatin hydrogels [10 wt % gelatin_(gel) with 0.09 v/v % glutaraldehyde (cross-linker)] containing different concentrations (5, 10, or 25 μg/mL) of bone morphogenic proteins (BMPs). We analyzed the properties and biocompatibility of the screws with and without BMP-2 and found that the release rate of BMP-2 in the hydrogel changed proportionately with the degradation rate of the cross-linked hydrogel. Loading BMP-2 in the hydrogel resulted in sustained release of BMP-2 for 25 to 40 days or more. The degradation rate of BMP-2 hydrogels was inversely proportional to the concentration of BMP-2. The injection of the hydrogels in the cannulated screw delayed biodegradation inside of the screw by simulated body fluid. It also induced uniform corrosion and the precipitation of bioactive compounds onto the surface of the screw. In addition, osteoblast proliferation was very active near the BMP-2 hydrogels, depending on the BMP-2 concentration. The BMP-2 in the hydrogel improved cell differentiation. The cannulated screw injected with 10 μL/mL BMP-2 hydrogel prevented implant biodegradation and enhanced osteoconduction and osteointegration inside and outside the screw. In addition, the properties of BMP-2-loaded hydrogels can be changed by controlling the amount of the cross-linker and protein, which could be useful for tissue regeneration in other fields.

Osteoconductive and osteoinductive biodegradable microspheres serving as injectable micro-scaffolds for bone regeneration

There are intensive needs for scaffolds with new designs to meet the diverse requirements of bone repairing. Biodegradable microspheres are highlighted as injectable micro-scaffolds thanks to their advantages in filling irregular defects via a minimally invasive surgery. In this study, microspheres with surface micropores were made via the W1/O/W2 double emulsion method using amphiphilic triblock copolymers (PLLA-PEG-PLLA) composed of poly(L-lactide) (PLLA) and poly(ethylene glycol) (PEG) segments. When the PEG fraction was controlled as 10 wt.%, the microspheres demonstrated higher cell affinity than the smooth-surfaced PLLA microspheres. After being further functionalized with polydopamine coating and apatite deposition, the PLLA-PEG-PLLA microspheres could up-regulate the osteogenic differentiation of bone marrow mesenchymal stromal cells (BMSCs) significantly. Before subcutaneous implantation, bone morphogenetic protein-2 (BMP-2) was adsorbed onto the biomineralized microspheres by taking advantages of the strong affinity of apatite to BMP-2. The resulted microspheres induced ectopic osteogenesis efficiently without causing biocompatibility problems. In summary, this study provided a simple strategy to prepare functionalized microspheres with osteoconductivity and osteoinductivity, which showed great potential in promoting bone regeneration as injectable micro-scaffolds.

Comparison of Different Approaches to Surface Functionalization of Biodegradable Polycaprolactone Scaffolds

Due to their good mechanical stability compared to gelatin, collagen or polyethylene glycol nanofibers and slow degradation rate, biodegradable poly-ε-caprolactone (PCL) nanofibers are promising material as scaffolds for bone and soft-tissue engineering. Here, PCL nanofibers were prepared by the electrospinning method and then subjected to surface functionalization aimed at improving their biocompatibility and bioactivity. For surface modification, two approaches were used: (i) COOH-containing polymer was deposited on the PCL surface using atmospheric pressure plasma copolymerization of CO₂ and C₂H₄, and (ii) PCL nanofibers were coated with multifunctional bioactive nanostructured TiCaPCON film by magnetron sputtering of TiC–CaO–Ti₃PO_x target. To evaluate bone regeneration ability in vitro, the surface-modified PCL nanofibers were immersed in simulated body fluid (SBF, 1×) for 21 days. The results obtained indicate different osteoblastic and epithelial cell response depending on the modification method. The TiCaPCON-coated PCL nanofibers exhibited enhanced adhesion and proliferation of MC3T3-E1 cells, promoted the formation of Ca-based mineralized layer in SBF and, therefore, can be considered as promising material for bone tissue regeneration. The PCL–COOH nanofibers demonstrated improved adhesion and proliferation of IAR-2 cells, which shows their high potential for skin reparation and wound dressing.

Hydroxyapatite nanowire composited gelatin cryogel with improved mechanical properties and cell migration for bone regeneration

Hydrogels are normally not robust enough to meet the repairing requirements of bone defects, therefore, cryogels of higher mechanical properties are developed as the more proper candidates for the purpose. In view of the organic-inorganic composition of natural bone tissues, hydroxyapatite (HA) is envisioned as a good additive for protein cryogels to achieve biomimetic compositions, additionally, as an excellent reinforcement to increase the mechanical properties of cryogels. In this study, methacrylated gelatin (GelMA) was synthesized and corresponding 3D-structured cryogel was fabricated, followed by the incorporation of HA nanowires (HANWs) at different amounts as reinforcements. The results showed that the GelMA/HANW composite cryogels possessed highly porous structure with HANWs being homogeneously distributed. The compressive strengths and mechanical stability of the composite cryogels were improved alongside the increasing contents of HANWs. These composite cryogels were proven non-cytotoxic, able to support cell proliferation and promote osteogenic differentiation of bone mesenchymal stromal cells. More importantly, their porous structure allowed cell migration within the matrix, which was normally hard to be achieved in GelMA hydrogel. With improved performance, GelMA/HANW composite cryogels were thus possibly serving as a new type of bone repair materials.

Biomineralization improves mechanical and osteogenic properties of multilayer-modified PLGA porous scaffolds

Poly-(lactide-co-glycolide acid) (PLGA) has been widely investigated as scaffold material for bone tissue engineering owing to its biosafety, biodegradability, and biocompatibility. However, the bioinert surface of PLGA may fail in regulating cellular behavior and directing osteointegration between the scaffold and the host tissue. In this article, oxidized chondroitin sulfate (oCS) and type I collagen (Col I) were assembled onto PLGA surface via layer by layer technique (LbL) as an adhesive coating for the attachment of inorganic minerals. The multilayer-modified PLGA scaffold was mineralized in vitro to ensure the deposition of nanohydroxyapatite (nHAP). It was found that nHAP crystals were more uniformly and firmly attached on the multilayer-modified PLGA as compared with the pure PLGA scaffold, which remarkably improved PLGA surface and mechanical properties. Additionally, in vitro biocompatibility of PLGA scaffold, in terms of bone mesenchymal stem cells (BMSCs) attachment, spreading and proliferation was greatly enhanced by nHAP coating and multilayer deposition. Furthermore, the fabricated composite scaffold also shows the ability to promote the osteogenic differentiation of BMSCs through the up-regulation of osteogenic marker genes. Thus, this novel biomimetic composite scaffold might achieve a desirable therapeutic result for bone tissue regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2714-2725, 2018.

Surface modification of titanium with hydroxyapatite layer induced by phase-transited lysozyme coating

Surface modification of titanium with a hydroxyapatite (HAP) coating can improve the bioactivity of pristine titanium. The traditional techniques for coating HAP on titanium involve nonmild treatments using strong bases or acids or high temperatures. In this study, the coating of HAP was carried out by a novel methodology called phase-transited lysozyme-assisted hydroxyapatite formation (PAH); in this process of biomimetic mineralization, the abundant functional carboxyl groups of phase-transited lysozyme (PTL) were responsible for the nucleation of HAP crystals by concentrating Ca²⁺ ions at the interface between PTL and CaCl₂ solution and for the subsequent growth of HAP crystals occurring in simulated body fluid (SBF). In vitro and in vivo experiments verified that the surface of titanium modified with the HAP/PTL-Ti multilayer was endowed with improved biocompatibility and osteoinductivity compared with those of pristine titanium. Therefore, PAH is a simple, rapid, low-cost and green process for the surface modification of titanium with an HAP coating and thus will be a promising methodology for the surface modification of titanium implants.

Biomimetic Mineralization of Biomaterials Using Simulated Body Fluids for Bone Tissue Engineering and Regenerative Medicine<sup/>

Development of synthetic biomaterials imbued with inorganic and organic characteristics of natural bone that are capable of promoting effective bone tissue regeneration is an ongoing goal of regenerative medicine. Calcium phosphate (CaP) has been predominantly utilized to mimic the inorganic components of bone, such as calcium hydroxyapatite, due to its intrinsic bioactivity and osteoconductivity. CaP-based materials can be further engineered to promote osteoinductivity through the incorporation of osteogenic biomolecules. In this study, we briefly describe the microstructure and the process of natural bone mineralization and introduce various methods for coating CaP onto biomaterial surfaces. In particular, we summarize the advantages and current progress of biomimetic surface-mineralizing processes using simulated body fluids for coating bone-like carbonated apatite onto various material surfaces such as metals, ceramics, and polymers. The osteoinductive effects of integrating biomolecules such as proteins, growth factors, and genes into the mineral coatings are also discussed.

Multifunctional PLLA-ceramic fiber membranes for bone regeneration applications

A novel method to process electrospun poly(l-lactic acid) (PLLA) membranes incorporating glass reinforced hydroxyapatite granules (gHA) interspacially between the polymeric fibers is reported, thus increasing the surface area for cellular interactions. gHA granules (≤150μm) electrospun together with the polymer solution, lead to an average fiber diameter of 550±150nm for pristine PLLA and 440±170nm for the composite samples. An increase of the overall porosity was observed, from 79±3% for the PLLA up to 88±5% for the hybrid samples, keeping material's wettability and mechanical properties. Bone-bonding ability showed that both samples induced HA crystal nucleation, but with a distinct pattern of mineral deposition. gHA microcomposite allows a better F-actin cytoskeleton organization during the initial adhesion and spreading, favoring cell-fibers and cell-to-cell interactions and enhanced alkaline phosphatase activity, making them potential candidates for bone healing strategies.