Tissue engineering technology that adopts mesenchymal stem cells combined with scaffolds presents a promising strategy for tissue regeneration. Human adipose-derived stem cells (hADSCs) have attracted considerable attention in bone engineering for their osteogenic potential. The extracellular matrix (ECM) is critical for the stem cell niche as a physical support and is known to be able to maintain stem cell properties. In this study, the ECM derived from ADSCs was produced and termed the ADM. The ADM was demonstrated to markedly promote proliferation of bone marrow derived stem cells (BMSCs) and exhibited strongly osteogenic simulative effects in vitro. The results showed that alkaline phosphatase (ALP) activity, Alizarin red S (ARS) staining, osteogenic gene markers and proteins were significantly up-regulated. Next, we developed a poly(sebacoyl diglyceride) (PSeD) mesh scaffold coated with the ADM and evaluated its capacity to create an osteogenic microenvironment. BMSCs were cultured on the composite scaffolds and subjected to osteogenic differentiation in vitro. The results showed that the composite scaffolds facilitated the osteogenesis more than a simple PSeD scaffold. Then the PSeD/ADM scaffold seeded with BMSCs was used to repair critical-sized calvarial defects in rats, which significantly enhanced the reparative effects as confirmed via micro-CT, sequential fluorescent labeling and histological observation. In conclusion, we demonstrated that the ADM could promote both proliferation and osteogenesis of BMSCs, and the combination of ADM and PSeD synergistically stimulated bone formation, which may provide a novel scheme for bone regeneration.

Phosphorylated polymers are promising for bone regeneration because they may recapitulate the essence of the phosphorylated bone extracellular matrix (ECM) to build an instructive environment for bone formation. However, most of the existing synthetic phosphorylated polymers are not fully biodegradable; thus, they are not ideal for tissue engineering. Here, we designed and synthesized a new phosphorylated polymer, poly(sebacoyl diglyceride) phosphate (PSeD-P), based on the biodegradable osteoconductive backbone PSeD. To our knowledge, PSeD-P is the first polymer to integrate the osteoinductive moiety β-glycerol phosphate (β-GP). PSeD-P shows good biodegradability and can be readily fabricated on 3D porous scaffolds. It has a porous structure with interconnected macropores (75–150 μm) and extensive micropores (several microns). PSeD-P promotes the adhesion, proliferation, and maturation of osteoblasts more effectively than poly(lactic-co-glycolic acid) (PLGA). Furthermore, PSeD-P induces a significantly higher expression of osteogenic biomarkers and ALP activity in mesenchymal stem cells (MSCs) compared to its non-phosphorylated precursor, PSeD. The level of improvement is comparable to free β-GP in culture medium. More importantly, without using β-GP, the typical mineralization promoter in osteogenic culture media, PSeD-P substantially induces the mineralization of the ECM in MSCs, which is totally absent using PSeD under identical culture conditions. PSeD-P provides a new strategy to integrate bioactive phosphates via β-GP into biomaterial, and has promise for bone regeneration applications. In addition, the synthetic method is versatile; both the backbone and the side phosphate groups could be readily tailored to generate a family of phosphorylated polymers for a wide range of biomedical applications.

Successful regeneration of nerves can benefit from biomaterials that provide a supportive biochemical and mechanical environment while also degrading with controlled inflammation and minimal scar formation. Herein, we report a neuroactive polymer functionalized by covalent attachment of the neurotransmitter acetylcholine (Ach). The polymer was readily synthesized in two steps from poly(sebacoyl diglyceride) (PSeD), which previously demonstrated biocompatibility and biodegradation in vivo. Distinct from prior acetylcholine-biomimetic polymers, PSeD-Ach contains both quaternary ammonium and free acetyl moieties, closely resembling native acetylcholine structure. The polymer structure was confirmed via 1H nuclear magnetic resonance and Fourier-transform infrared spectroscopy. Hydrophilicity, charge, and thermal properties of PSeD-Ach were determined by tensiometer, zetasizer, differential scanning calorimetry, and thermal gravimetric analysis, respectively. PC12 cells exhibited the greatest proliferation and neurite outgrowth on PSeD-Ach and laminin substrates, with no significant difference between these groups. PSeD-Ach yielded much longer neurite outgrowth than the control polymer containing ammonium but no the acetyl group, confirming the importance of the entire acetylcholine-like moiety. Furthermore, PSeD-Ach supports adhesion of primary rat dorsal root ganglions and subsequent neurite sprouting and extension. The sprouting rate is comparable to the best conditions from previous report. Our findings are significant in that they were obtained with acetylcholine-like functionalities in 100% repeating units, a condition shown to yield significant toxicity in prior publications. Moreover, PSeD-Ach exhibited favorable mechanical and degradation properties for nerve tissue engineering application. Humidified PSeD-Ach had an elastic modulus of 76.9 kPa, close to native neural tissue, and could well recover from cyclic dynamic compression. PSeD-Ach showed a gradual in vitro degradation under physiologic conditions with a mass loss of 60% within 4 weeks. Overall, this simple and versatile synthesis provides a useful tool to produce biomaterials for creating the appropriate stimulatory environment for nerve regeneration.Keywords: acetylcholine; biomimetic material; dorsal root ganglion; nerve regeneration; neurite extension; neuron; neurotransmitter; poly(glycerol sebacate)

Biodegradable and biocompatible elastomers (bioelastomers) could resemble the mechanical properties of extracellular matrix and soft tissues and, thus, are very useful for many biomedical applications. Despite significant advances, tunable bioelastomers with easy processing, facile biofunctionalization, and the ability to withstand a mechanically dynamic environment have remained elusive. Here, we reported new dynamic hydrogen-bond cross-linked PSeD-U bioelastomers possessing the aforementioned features by grafting 2-ureido-4[1H]-pyrimidinones (UPy) units with strong self-complementary quadruple hydrogen bonds to poly(sebacoyl diglyceride) (PSeD), a refined version of a widely used bioelastomer poly(glycerol sebacate) (PGS). PSeD-U polymers exhibited stronger mechanical strength than their counterparts of chemically cross-linked PSeD and tunable elasticity by simply varying the content of UPy units. In addition to the good biocompatibility and biodegradability as seen in PSeD, PSeD-U showed fast self-healing (within 30 min) at mild conditions (60 °C) and could be readily processed at moderate temperature (90–100 °C) or with use of solvent casting at room temperature. Furthermore, the free hydroxyl groups of PSeD-U enabled facile functionalization, which was demonstrated by the modification of PSeD-U film with FITC as a model functional molecule.Keywords: bioelastomer; dynamic polymer; functionalization; hydrogen bonds; self-healing

Small-diameter vascular grafts (SDVGs) (D < 6 mm) are increasingly needed in clinical settings for cardiovascular disease, including coronary artery and peripheral vascular pathologies. Vessels made from synthetic polymers have shortcomings such as thrombosis, intimal hyperplasia, calcification, chronic inflammation and no growth potential. Decellularized xenografts are commonly used as a tissue-engineering substitute for vascular reconstructive procedures. Although acellular allogeneic vascular grafts have good histocompatibility and antithrombotic properties, the decellularization process may damage the biomechanics and accelerate the elastin deformation and degradation, finally resulting in vascular graft expansion and even aneurysm formation. Here, to address these problems, we combine synthetic polymers with natural decellularized small-diameter vessels to fabricate hybrid tissue-engineered vascular grafts (HTEV). The donor aortic vessels were decellularized with a combination of different detergents and dehydrated under a vacuum freeze-drying process. Polycaprolactone (PCL) nanofibers were electrospun (ES) outside the acellular aortic vascular grafts to strengthen the decellularized matrix. The intimal surfaces of the hybrid small-diameter vascular grafts were coated with heparin before the allograft transplantation. Histopathology and scanning electron microscope revealed that the media of the decellularized vessels were severely injured. Mechanical testing of scaffolds showed that ES-PCL significantly enhanced the biomechanics of decellularized vessels. Vascular ultrasound and micro-CT angiography showed that all grafts after implantation in a rat model were satisfactorily patent for up to 6 weeks. ES-PCL successfully prevented the occurrence of vasodilation and aneurysm formation after transplantation and reduced the cell inflammatory infiltration. In conclusion, the HTEV with perfect histocompatibility and biomechanics provide a facile and useful technique for the development of SDVGs.

Phosphorylated polymers are promising for bone regeneration because they may recapitulate the essence of the phosphorylated bone extracellular matrix (ECM) to build an instructive environment for bone formation. However, most of the existing synthetic phosphorylated polymers are not fully biodegradable; thus, they are not ideal for tissue engineering. Here, we designed and synthesized a new phosphorylated polymer, poly(sebacoyl diglyceride) phosphate (PSeD-P), based on the biodegradable osteoconductive backbone PSeD. To our knowledge, PSeD-P is the first polymer to integrate the osteoinductive moiety β-glycerol phosphate (β-GP). PSeD-P shows good biodegradability and can be readily fabricated on 3D porous scaffolds. It has a porous structure with interconnected macropores (75–150 μm) and extensive micropores (several microns). PSeD-P promotes the adhesion, proliferation, and maturation of osteoblasts more effectively than poly(lactic-co-glycolic acid) (PLGA). Furthermore, PSeD-P induces a significantly higher expression of osteogenic biomarkers and ALP activity in mesenchymal stem cells (MSCs) compared to its non-phosphorylated precursor, PSeD. The level of improvement is comparable to free β-GP in culture medium. More importantly, without using β-GP, the typical mineralization promoter in osteogenic culture media, PSeD-P substantially induces the mineralization of the ECM in MSCs, which is totally absent using PSeD under identical culture conditions. PSeD-P provides a new strategy to integrate bioactive phosphates via β-GP into biomaterial, and has promise for bone regeneration applications. In addition, the synthetic method is versatile; both the backbone and the side phosphate groups could be readily tailored to generate a family of phosphorylated polymers for a wide range of biomedical applications.

Tissue engineering technology that adopts mesenchymal stem cells combined with scaffolds presents a promising strategy for tissue regeneration. Human adipose-derived stem cells (hADSCs) have attracted considerable attention in bone engineering for their osteogenic potential. The extracellular matrix (ECM) is critical for the stem cell niche as a physical support and is known to be able to maintain stem cell properties. In this study, the ECM derived from ADSCs was produced and termed the ADM. The ADM was demonstrated to markedly promote proliferation of bone marrow derived stem cells (BMSCs) and exhibited strongly osteogenic simulative effects in vitro. The results showed that alkaline phosphatase (ALP) activity, Alizarin red S (ARS) staining, osteogenic gene markers and proteins were significantly up-regulated. Next, we developed a poly(sebacoyl diglyceride) (PSeD) mesh scaffold coated with the ADM and evaluated its capacity to create an osteogenic microenvironment. BMSCs were cultured on the composite scaffolds and subjected to osteogenic differentiation in vitro. The results showed that the composite scaffolds facilitated the osteogenesis more than a simple PSeD scaffold. Then the PSeD/ADM scaffold seeded with BMSCs was used to repair critical-sized calvarial defects in rats, which significantly enhanced the reparative effects as confirmed via micro-CT, sequential fluorescent labeling and histological observation. In conclusion, we demonstrated that the ADM could promote both proliferation and osteogenesis of BMSCs, and the combination of ADM and PSeD synergistically stimulated bone formation, which may provide a novel scheme for bone regeneration.