Clinical potential of plasma-functionalized graphene oxide ultrathin sheets for bone and blood vessel regeneration: Insights from cellular and animal models

Graphene and graphene oxide (GO), due to their unique chemical and physical properties, possess biochemical characteristics that can trigger intercellular signals promoting tissue regeneration. Clinical applications of thin GO-derived sheets have inspired the development of various tissue regeneration and repair approaches. In this study, we demonstrate that ultrathin sheets of plasma-functionalized and reduced GO, with the oxygen content ranging from 3.2 % to 22 % and the nitrogen content from 0 % to 8.3 %, retain their essential mechanical and molecular integrity, and exhibit robust potential for regenerating bone tissue and blood vessels across multiple cellular and animal models. Initially, we observed the growth of blood vessels and bone tissue in vitro using these functionalized GO sheets on human adipose-derived mesenchymal stem cells and umbilical vein endothelial cells. Remarkably, our study indicates a 2.5-fold increase in mineralization and two-fold increase in tubule formation even in media lacking osteogenic and angiogenic supplements. Subsequently, we observed the initiation, conduction, and formation of bone and blood vessels in a rat tibial osteotomy model, evident from a marked 4-fold increase in the volume of low radio-opacity bone tissue and a significant elevation in connectivity density, all without the use of stem cells or growth factors. Finally, we validated these findings in a mouse critical-size calvarial defect model (33 % higher healing rate) and a rat skin lesion model (up to 2.5-fold increase in the number of blood vessels, and 35 % increase in blood vessels diameter). This study elucidates the pro-osteogenic and pro-angiogenic properties of both pristine and plasma-treated GO ultrathin films. These properties suggest their significant potential for clinical applications, and as valuable biomaterials for investigating fundamental aspects of bone and blood vessel regeneration.

3D-printed gelatin methacrylate (GelMA)/silanated silica scaffold assisted by two-stage cooling system for hard tissue regeneration

Among many biomaterials, gelatin methacrylate (GelMA), a photocurable protein, has been widely used in 3D bioprinting process owing to its excellent cellular responses, biocompatibility and biodegradability. However, GelMA still shows a low processability due to the severe temperature dependence of viscosity. To overcome this obstacle, we propose a two-stage temperature control system to effectively control the viscosity of GelMA. To optimize the process conditions, we evaluated the temperature of the cooling system (jacket and stage). Using the established system, three GelMA scaffolds were fabricated in which different concentrations (0, 3 and 10 wt%) of silanated silica particles were embedded. To evaluate the performances of the prepared scaffolds suitable for hard tissue regeneration, we analyzed the physical (viscoelasticity, surface roughness, compressive modulus and wettability) and biological (human mesenchymal stem cells growth, western blotting and osteogenic differentiation) properties. Consequently, the composite scaffold with greater silica contents (10 wt%) showed enhanced physical and biological performances including mechanical strength, cell initial attachment, cell proliferation and osteogenic differentiation compared with those of the controls. Our results indicate that the GelMA/silanated silica composite scaffold can be potentially used for hard tissue regeneration.

Characterization and Cytotoxicity Evaluation of a Marine Sponge Biosilica

Bone fractures characterize an important event in the medical healthcare, being related to traumas, aging, and diseases. In critical conditions, such as extensive bone loss and osteoporosis, the tissue restoration may be compromised and culminate in a non-union consolidation. In this context, the osteogenic properties of biomaterials with a natural origin have gained prominence. Particularly, marine sponges are promising organisms that can be exploited as biomaterials for bone grafts. Thus, the objectives of this study were to study the physicochemical and morphological properties of biosilica (BS) from sponges by using scanning electron microscopy, Fourier-transform infrared, X-ray diffraction (SEM, FTIR and XRD respectively), mineralization, and pH. In addition, tests on an osteoblast precursor cell line (MC3T3-E1) were performed to investigate its cytotoxicity and proliferation in presence of BS. Bioglass (BG) was used as gold standard material for comparison purposes. Sponge BS was obtained, and this fact was proven by SEM, FTIR, and XRD analysis. Calcium assay showed a progressive release of this ion from day 7 and a more balanced pH for BS was maintained compared to BG. Cytotoxicity assay indicated that BS had a positive influence on MC3T3-E1 cells viability and qRT-PCR showed that this material stimulated Runx2 and BMP4 gene expressions. Taken together, the results indicate a potential use of sponge biosilica for tissue engineering applications.

The Effect and Osteoblast Signaling Response of Trace Silicon Doping Hydroxyapatite

It is commonly accepted that silicon-doped hydroxyapatite (HAp) can achieve good repair effects for both spinal fusion and bone defect filling. However, the underlying mechanism by which silicon aids such beneficial effects is still not fully understood. Herein, we report on silicon-doped hydroxyapatites with excellent biocompatibility to osteoblast cells and suggest the signaling pathway involved. Non-doped HAp and trace Si-doped HAp (Si/HAp) with Si concentration close to and higher than natural bones were synthesized (i.e., 32, 260, and 2000 ppm Si). The composition, crystal lattice vibration pattern, and morphology of these samples are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and SEM, respectively. Positive biological activities of these Si-doped HAp materials were demonstrated through a cytotoxicity study and with the MTT and alkaline phosphatase (ALP) activity assays. The Si-doped samples were not toxic to MC3T3-E1 cells. Indeed, osteoblast proliferation measurement illustrated that 2000 ppm Si-doped HAp increased osteoblast proliferation by about 1.6 times compared to non-doped HAp. The ALP assay also proves that the trace Si doping has the function to enhance cell proliferation and differentiation. The ALP assay showed that Si doping also enhanced cell differentiation. QRT-PCR results revealed that Si-doped HAp enhanced osteogenic differentiation of osteoblast cells by upregulating genes such as MAPK3, Fzd1, Wnt1, Lrp6, and BMP2. In conclusion, Si-doped HAp promotes osteoblast proliferation and differentiation by activating the Wnt/β-catenin and MAPK signaling pathways. This work could provide useful information of the beneficial effects of silicon in human bones and provide clues as to the molecular mechanism of the promotive effect of Si-doped HAp biomaterials.

A cyclo-trimer of acetonitrile combining fluorescent property with ability to induce osteogenesis and its potential as multifunctional biomaterial

A biomaterial combining fluorescent property with ability to induce osteogenesis can serve as an ideal multifunctional scaffold in bone tissue engineering. However, the frequently used fluorescent agents can only serve as imaging probes. The polymer or oligomer with a conjugated system containing nitrogen atoms will fulfill these criteria. In this study, a cyclo-trimer of acetonitrile is synthesized using a facile method, which is proved to be 4-amino-2,6-dimethylpyrimidine. The cyclo-trimer of acetonitrile demonstrates strong intrinsic photoluminescence and has the potential for in vivo imaging. The cyclo-trimer of acetonitrile shows no toxicity both in vitro and in vivo. Moreover, the cyclo-trimer of acetonitrile significantly promotes the osteogenesis of SaOS-2 cells by improving alkaline phosphatase activity, collagen type I and osteocalcin expression, as well as expressions of osteoblastic genes, and enhances the matrix mineralization of rBMSCs. Thus, the cyclo-trimer of acetonitrile synthesized in present study illustrates the employment of this kind multifunctional biomaterial in bone tissue engineering and may offer great potential in biomedical applications where bioimaging and osteogenesis are both required.

STATEMENT OF SIGNIFICANCE

A conjugated cyclo-trimer of acetonitrile combining intrinsic fluorescent property with ability to induce osteogenesis was reported. Different from the traditional fluorescent dye or quantum dots, which are just "imaging agents", the cyclo-trimer of acetonitrile can serve as a multifunctional biomaterial and offer great potential in biomedical applications where bioimaging and osteogenesis are both required. To our best knowledge, the fluorescent property, especially fluorescent property in vivo and the ability of this molecule to induce osteogenesis have not been reported before. Our work illustrates the employment of this kind multifunctional biomaterial in bone tissue engineering and will highlight the importance of multifunctional biomaterial in biomedical applications.

Bio-templated silica composites for next-generation biomedical applications

Silica-based materials have extensive biomedical applications owing to their unique physical, chemical, and biological properties. Recently, increasing studies have examined the mechanisms involved in biosilicification to develop novel, fine-tunable, eco-friendly materials and/or technologies. In this review, we focus on recent developments in bio-templated silica synthesis and relevant applications in drug delivery systems, tissue engineering, and biosensing.

New Target Sites for Treatment of Osteoporosis

In the last few years, much progress has been achieved in the discovery of new drug target sites for treatment of osteoporotic disorders, one of the main challenging diseases with a large burden for the public health systems. Among these new agents promoting bone formation, shifting the impaired equilibrium between bone anabolism and bone catabolism in the direction of bone synthesis are inorganic polymers, in particular inorganic polyphosphates that show strong stimulatory effects on the expression of bone anabolic marker proteins and hydroxyapatite formation. The bone-forming activity of these polymers can even be enhanced by combination with certain small molecules like quercetin, or if given as functionally active particles with certain divalent cations like strontium ions even showing by itself biological activity. This chapter summarizes recent developments in the search and development of novel anti-osteoporotic agents, with a particular focus on therapeutic approaches based on the potential application of inorganic polymers and combinations.

Synthesis, characterization, and in-vitro cytocompatibility of amorphous β-tri-calcium magnesium phosphate ceramics

Biphasic mixtures of crystalline β-tricalcium magnesium phosphate (β-TCMP) and an amorphous calcium magnesium phosphate have been synthesized and reported to support enhanced hMSC differentiation in comparison to β-tricalcium phosphate (β-TCP) due to the release of increased amounts of bioactive ions. In the current study, completely amorphous β-TCMP has been synthesized which is capable of releasing increased amounts of Mg(2+) and PO4(3-) ions, rather than a biphasic mixture as earlier reported. The amorphous phase formed was observed to crystallize between temperatures of 400-600°C. The scaffolds prepared with amorphous β-TCMP were capable of supporting enhanced hMSC proliferation and differentiation in comparison to commercially available β-TCP. However, a similar gene expression of mature osteoblast markers, OCN and COL-1, in comparison to biphasic β-TCMP was observed. To further study the role of Mg(2+) and PO4(3-) ions in regulating hMSC osteogenic differentiation, the capability of hMSCs to mineralize in growth media supplemented with Mg(2+) and PO4(3-) ions was studied. Interestingly, 5mM PO4(3-) supported mineralization while the addition of 5mM Mg(2+) to 5mM PO4(3-) inhibited mineralization. It was therefore concluded that the release of Ca(2+) ions from β-TCMP scaffolds also plays a role in regulating osteogenic differentiation on these scaffolds and it is noted that further work is required to more accurately determine the exact role of Mg(2+) in regulating hMSC osteogenic differentiation.

Surface Chemical Gradient Affects the Differentiation of Human Adipose-Derived Stem Cells via ERK1/2 Signaling Pathway

To understand the role of surface chemistry on cell behavior and the associated molecular mechanisms, we developed and utilized a surface chemical gradient of amine functional groups by carefully adjusting the gas composition of 1,7-octadiene (OD) and allylamine (AA) of the plasma phase above a moving substrate. The chemical gradient surface used in the present work shows an increasing N/C ratio and wettability from the OD side toward the AA side with no change in surface topography. Under standard culture conditions (with serum), human adipose-derived stem cells (hASCs) adhesion and spreading area increased toward the AA side of the gradient. However, there were no differences in cell behavior in the absence of serum. These results, supported by the trends in proteins adsorption on the gradient surface, demonstrated that surface chemistry affects the response of hASCs through cell-adhesive serum proteins, rather than interacting directly with the cells. The expression of p-ERK and the osteogenic differentiation increased toward the AA side of the gradient, while adipogenic differentiation decreased in the same direction; however, when the activation of ERK1/2 was blocked by PD98059, the levels of osteogenic or adipogenic differentiation on different regions of the chemical gradient were the same. This indicates that ERK1/2 may be an important downstream signaling pathway of surface chemistry directed stem cell fate.

Modular Small Diameter Vascular Grafts with Bioactive Functionalities

We report the fabrication of a novel type of artificial small diameter blood vessels, termed biomimetic tissue-engineered blood vessels (bTEBV), with a modular composition. They are composed of a hydrogel scaffold consisting of two negatively charged natural polymers, alginate and a modified chitosan, N,O-carboxymethyl chitosan (N,O-CMC). Into this biologically inert scaffold two biofunctionally active biopolymers are embedded, inorganic polyphosphate (polyP) and silica, as well as gelatin which exposes the cell recognition signal, Arg-Gly-Asp (RGD). These materials can be hardened by exposure to Ca(2+) through formation of Ca(2+) bridges between the polyanions, alginate, N,O-CMC, and polyP (alginate-Ca(2+)-N,O-CMC-polyP). The bTEBV are formed by pressing the hydrogel through an extruder into a hardening solution, containing Ca(2+). In this universal scaffold of the bTEBV biomaterial, polycations such as poly(L-Lys), poly(D-Lys) or a His/Gly-tagged RGD peptide (three RGD units) were incorporated, which promote the adhesion of endothelial cells to the vessel surface. The mechanical properties of the biopolymer material (alginate-Ca(2+)-N,O-CMC-polyP-silica) revealed a hardness (elastic modulus) of 475 kPa even after a short incubation period in CaCl2 solution. The material of the artificial vascular grafts (bTEBVs with an outer size 6 mm and 1.8 mm, and an inner diameter 4 mm and 0.8 mm, respectively) turned out to be durable in 4-week pulsatile flow experiments at an alternating pressure between 25 and 100 mbar (18.7 and 75.0 mm Hg). The burst pressure of the larger (smaller) vessels was 850 mbar (145 mbar). Incorporation of polycationic poly(L-Lys), poly(D-Lys), and especially the His/Gly-tagged RGD peptide, markedly increased the adhesion of human, umbilical vein/vascular endothelial cells, EA.HY926 cells, to the surface of the hydrogel. No significant effect of the polyP samples on the clotting of human plasma is measured. We propose that the metabolically degradable polymeric scaffold bTEBV is a promising biomaterial for future prosthetic vascular grafts.

Surface modification of nano-silica on the ligament advanced reinforcement system for accelerated bone formation: primary human osteoblasts testing in vitro and animal testing in vivo

The Ligament Advanced Reinforcement System (LARS) has been considered as a promising graft for ligament reconstruction. To improve its biocompatibility and effectiveness on new bone formation, we modified the surface of a polyethylene terephthalate (PET) ligament with nanoscale silica using atom transfer radical polymerization (ATRP) and silica polymerization. The modified ligament is tested by both in vitro and in vivo experiments. Human osteoblast testing in vitro exhibits an ∼21% higher value in cell viability for silica-modified grafts compared with original grafts. Animal testing in vivo shows that there is new formed bone in the case of a nanoscale silica-coated ligament. These results demonstrate that our approach for nanoscale silica surface modification on LARS could be potentially applied for ligament reconstruction.

Retinol encapsulated into amorphous Ca(2+) polyphosphate nanospheres acts synergistically in MC3T3-E1 cells

Both the quality and quantity of collagen, the major structural component of the skin, decrease in aging skin. We succeeded to encapsulate retinol into amorphous inorganic polyphosphate (polyP) nanoparticles together with calcium ions ("aCa-polyP-NP"), under formation of amorphous Ca-polyP/retinol nanospheres ("retinol/aCa-polyP-NS"). The globular nanospheres are not cytotoxic, show an almost uniform size of ≈ 45 nm and have a retinol content of around 25%. Both components of those nanospheres, retinol and the aCa-polyP-NP, if administered together, caused a strong increase in proliferation of mouse calvaria MC3T3 cells. The expressions of collagen types I, II and III genes, but not the expression of collagen type V gene, were significantly enhanced if retinol is added together with aCa-polyP-NP. This synergistic effect was especially pronounced for the expression of the collagen type III gene. We propose that the synergistic effect of the retinol/aCa-polyP-NS on cell growth and collagen type III expression is induced via two routes, first through cellular uptake of the 45 nm nanospheres by clathrin-mediated endocytosis and second through extracellular disintegration of the nanospheres resulting in the release of retinol which is then taken up into the cells after binding to the retinal binding protein receptor.

Co(II)-mediated effects of plain and plasma immersion ion implanted cobalt-chromium alloys on the osteogenic differentiation of human mesenchymal stem cells

Medical CoCr is one of the main alloys used for metal-on-metal prosthesis in patients with total hip arthroplasty. CoCr surfaces modified by nitrogen plasma immersion ion implantation (PIII) are characterized by improved wear resistance but also showed increased Co(II) ion release under in vitro conditions. For the first time, CoCr modified by nitrogen PIII was evaluated with regard to its effect on the osteogenic differentiation of MSC. The activity of alkaline phosphatase, the expression of the osteogenic genes Runt-related transcription factor 2, osteopontin as well as integrin-binding bone sialoprotein and the production of osteocalcin and hydroxyapatite were determined. The results of our study demonstrate that Co(II) ions released from the alloy affected the osteogenic differentiation of MSC. Distinct differences in differentiation markers were found between pristine and modified alloys for osteocalcin but not for integrin-binding sialoprotein and hydroxyapatite. Interestingly, osteopontin was upregulated in naive and differentiated MSC by Co(II) ions and modified CoCr, likely through the induction of a cellular hypoxic response. The findings of this study contribute to a better understanding of possible risk factors with regard to a clinical applicability of surface modified CoCr implant materials.

Biologizing titanium alloy implant material with morphogenetically active polyphosphate

As a further step towards a new generation of bone implant materials, we developed a procedure for biological functionalization of titanium alloy surfaces with inorganic calcium polyphosphate (Ca-polyP).

A new printable and durable N,O-carboxymethyl chitosan–Ca2+–polyphosphate complex with morphogenetic activity

In the absence of Ca²⁺ the polymers N,O-carboxymethyl chitosan, together with Na-polyphosphate and alginate, form random-coiled structures. Addition of Ca²⁺ transforms these polymers to durable implants.

Effect of bioglass on growth and biomineralization of SaOS-2 cells in hydrogel after 3D cell bioprinting

We investigated the effect of bioglass (bioactive glass) on growth and mineralization of bone-related SaOS-2 cells, encapsulated into a printable and biodegradable alginate/gelatine hydrogel. The hydrogel was supplemented either with polyphosphate (polyP), administered as polyP • Ca2+-complex, or silica, or as biosilica that had been enzymatically prepared from ortho-silicate by silicatein. These hydrogels, together with SaOS-2 cells, were bioprinted to computer-designed scaffolds. The results revealed that bioglass (nano)particles, with a size of 55 nm and a molar ratio of SiO2 : CaO : P2O5 of 55 : 40 : 5, did not affect the growth of the encapsulated cells. If silica, biosilica, or polyP • Ca2+-complex is co-added to the cell-containing alginate/gelatin hydrogel the growth behavior of the cells is not changed. Addition of 5 mg/ml of bioglass particles to this hydrogel significantly enhanced the potency of the entrapped SaOS-2 cells to mineralize. If compared with the extent of the cells to form mineral deposits in the absence of bioglass, the cells exposed to bioglass together with 100 µmoles/L polyP • Ca2+-complex increased their mineralization activity from 2.1- to 3.9-fold, or with 50 µmoles/L silica from 1.8- to 2.9-fold, or with 50 µmoles/L biosilica from 2.7- to 4.8-fold or with the two components together (100 µmoles/L polyP • Ca2+-complex and 50 µmoles/L biosilica) from 4.1- to 6.8-fold. Element analysis by EDX spectrometry of the mineral nodules formed by SaOS-2 revealed an accumulation of O, P, Ca and C, indicating that the mineral deposits contain, besides Ca-phosphate also Ca-carbonate. The results show that bioglass added to alginate/gelatin hydrogel increases the proliferation and mineralization of bioprinted SaOS-2 cells. We conclude that the development of cell-containing scaffolds consisting of a bioprintable, solid and cell-compatible inner matrix surrounded by a printable hard and flexible outer matrix containing bioglass, provide a suitable strategy for the fabrication of morphogenetically active and biodegradable implants.

Bioactive and biodegradable silica biomaterial for bone regeneration

Biosilica, a biocompatible, natural inorganic polymer that is formed by an enzymatic, silicatein-mediated reaction in siliceous sponges to build up their inorganic skeleton, has been shown to be morphogenetically active and to induce mineralization of human osteoblast-like cells (SaOS-2) in vitro. In the present study, we prepared beads (microspheres) by encapsulation of β-tricalcium phosphate [β-TCP], either alone (control) or supplemented with silica or silicatein, into the biodegradable copolymer poly(d,l-lactide-co-glycolide) [PLGA]. Under the conditions used, ≈5% β-TCP, ≈9% silica, and 0.32μg/mg of silicatein were entrapped into the PLGA microspheres (diameter≈800μm). Determination of the biocompatibility of the β-TCP microspheres, supplemented with silica or silicatein, revealed no toxicity in the MTT based cell viability assay using SaOS-2 cells. The adherence of SaOS-2 cells to the surface of silica-containing microspheres was higher than for microspheres, containing only β-TCP. In addition, the silica-containing β-TCP microspheres and even more pronounced, a 1:1 mixture of microspheres containing β-TCP and silica, and β-TCP and silicatein, were found to strongly enhance the mineral deposition by SaOS-2 cells. Using these microspheres, first animal experiments with silica/biosilica were performed in female, adult New Zealand White rabbits to study the effect of the inorganic polymer on bone regeneration in vivo. The microspheres were implanted into 5mm thick holes, drilled into the femur of the animals, applying a bilateral comparison study design (3 test groups with 4-8 animals each). The control implant on one of the two hind legs contained microspheres with only β-TCP, while the test implant on the corresponding leg consisted either of microspheres containing β-TCP and silica, or a 1:1 mixture of microspheres, supplemented with β-TCP and silica, and β-TCP and silicatein. The results revealed that tissue/bone sections of silica containing implants and implants, composed of a 1:1 mixture of silica-containing microspheres and silicatein-containing microspheres, show an enhanced regeneration of bone tissue around the microspheres, compared to the control implants containing only β-TCP. The formation of new bone induced by the microspheres is also evident from measurements of the stiffness/reduced Young's modulus of the regenerated bone tissue. The reduced Young's modulus of the regenerating bone tissue around the implants was markedly higher for the silica-containing microspheres (1.1MPa), and even more for the 1:1 mixture of the silica- and silicatein-containing microspheres (1.4MPa), compared to the β-TCP microsphere controls (0.4MPa). We propose that based on their morphogenetic activity on bone-forming cells in vitro and the results of the animal experiments presented here, silica/biosilica-based scaffolds are promising materials for bone repair/regeneration.

Engineering a morphogenetically active hydrogel for bioprinting of bioartificial tissue derived from human osteoblast-like SaOS-2 cells

Sodium alginate hydrogel, stabilized with gelatin, is a suitable, biologically inert matrix that can be used for encapsulating and 3D bioprinting of bone-related SaOS-2 cells. However, the cells, embedded in this matrix, remain in a non-proliferating state. Here we show that addition of an overlay onto the bioprinted alginate/gelatine/SaOS-2 cell scaffold, consisting of agarose and the calcium salt of polyphosphate [polyP·Ca(2+)-complex], resulted in a marked increase in cell proliferation. In the presence of 100 μm polyP·Ca(2+)-complex, the cells proliferate with a generation time of approximately 47-55 h. In addition, the hardness of the alginate/gelatin hydrogel substantially increases in the presence of the polymer. The reduced Young's modulus for the alginate/gelatin hydrogel is approximately 13-14 kPa, and this value drops to approximately 0.5 kPa after incubation of the cell containing scaffolds for 5 d. In the presence of 100 μm polyP·Ca(2+)-complex, the reduced Young's modulus increases to about 22 kPa. The hardness of the polyP·Ca(2+)-complex containing hydrogel remains essentially constant if cells are absent in the matrix, but it drops to 3.2 kPa after a 5 d incubation period in the presence of SaOS-2 cells, indicating that polyP·Ca(2+)-complex becomes metabolized, degraded, by the cells. The alginate/gelatine-agarose system with polyP·Ca(2+)-complex cause a significant increase in the mineralization of the cells. SEM analyses revealed that the morphology of the mineral nodules formed on the surface of the cells embedded in the alginate/gelatin hydrogel do not significantly differ from the nodules on cells growing in monolayer cultures. The newly developed technique, using cells encapsulated into an alginate/gelatin hydrogel and a secondary layer containing the morphogenetically active, growth promoting polymer polyP·Ca(2+)-complex opens new possibilities for the application of 3D bioprinting in bone tissue engineering.

Surface modification by allylamine plasma polymerization promotes osteogenic differentiation of human adipose-derived stem cells

Tuning the material properties in order to control the cellular behavior is an important issue in tissue engineering. It is now well-established that the surface chemistry can affect cell adhesion, proliferation, and differentiation. In this study, plasma polymerization, which is an appealing method for surface modification, was employed to generate surfaces with different chemical compositions. Allylamine (AAm), acrylic acid (AAc), 1,7-octadiene (OD), and ethanol (ET) were used as precursors for plasma polymerization in order to generate thin films rich in amine (-NH2), carboxyl (-COOH), methyl (-CH3), and hydroxyl (-OH) functional groups, respectively. The surface chemistry was characterized by X-ray photoelectron spectroscopy (XPS), the wettability was determined by measuring the water contact angles (WCA) and the surface topography was imaged by atomic force microscopy (AFM). The effects of surface chemical compositions on the behavior of human adipose-derive stem cells (hASCs) were evaluated in vitro: Cell Count Kit-8 (CCK-8) analysis for cell proliferation, F-actin staining for cell morphology, alkaline phosphatase (ALP) activity analysis, and Alizarin Red S staining for osteogenic differentiation. The results show that AAm-based plasma-polymerized coatings can promote the attachment, spreading, and, in turn, proliferation of hASCs, as well as promote the osteogenic differentiation of hASCs, suggesting that plasma polymerization is an appealing method for the surface modification of scaffolds used in bone tissue engineering.

Biocalcite, a multifunctional inorganic polymer: Building block for calcareous sponge spicules and bioseed for the synthesis of calcium phosphate-based bone

Calcium carbonate is the material that builds up the spicules of the calcareous sponges. Recent results revealed that the calcium carbonate/biocalcite-based spicular skeleton of these animals is formed through an enzymatic mechanism, such as the skeleton of the siliceous sponges, evolutionarily the oldest animals that consist of biosilica. The enzyme that mediates the calcium carbonate deposition has been identified as a carbonic anhydrase (CA) and has been cloned from the calcareous sponge species Sycon raphanus. Calcium carbonate deposits are also found in vertebrate bones besides the main constituent, calcium phosphate/hydroxyapatite (HA). Evidence has been presented that during the initial phase of HA synthesis poorly crystalline carbonated apatite is deposited. Recent data summarized here indicate that during early bone formation calcium carbonate deposits enzymatically formed by CA, act as potential bioseeds for the precipitation of calcium phosphate mineral onto bone-forming osteoblasts. Two different calcium carbonate phases have been found during CA-driven enzymatic calcium carbonate deposition in in vitro assays: calcite crystals and round-shaped vaterite deposits. The CA provides a new target of potential anabolic agents for treatment of bone diseases; a first CA activator stimulating the CA-driven calcium carbonate deposition has been identified. In addition, the CA-driven calcium carbonate crystal formation can be frozen at the vaterite state in the presence of silintaphin-2, an aspartic acid/glutamic acid-rich sponge-specific protein. The discovery that calcium carbonate crystals act as bioseeds in human bone formation may allow the development of novel biomimetic scaffolds for bone tissue engineering. Na-alginate hydrogels, enriched with biosilica, have recently been demonstrated as a suitable matrix to embed bone forming cells for rapid prototyping bioprinting/3D cell printing applications.

Isoquercitrin and polyphosphate co-enhance mineralization of human osteoblast-like SaOS-2 cells via separate activation of two RUNX2 cofactors AFT6 and Ets1

Isoquercitrin, a dietary phytoestrogen, is a potential stimulator of bone mineralization used for prophylaxis of osteoporotic disorders. Here we studied the combined effects of isoquercitrin, a cell membrane permeable 3-O-glucoside of quercetin, and polyphosphate [polyP], a naturally occurring inorganic polymer inducing bone formation, on mineralization of human osteoblast-like SaOS-2 cells. Both compounds isoquercitrin and polyP induce at non-toxic concentrations the mineralization process of SaOS-2 cells. Co-incubation experiments revealed that isoquercitrin (at 0.1 and 0.3μM), if given simultaneously with polyP (as Ca(2+) salt; at 3, 10, 30 and 100μM) amplifies the mineralization-enhancing effect of the inorganic polymer. The biomineralization process induced by isoquercitrin and polyP is based on two different modes of action. After incubation of the cells with isoquercitrin or polyP the expression of the Runt-related transcription factor 2 [RUNX2] is significantly upregulated. In addition, isoquercitrin causes a strong increase of the steady-state-levels of the two co-activators of RUNX2, the activating transcription factor 6 [ATF6] and the Ets oncogene homolog 1 [Ets1]. The activating effect of isoquercitrin occurs via a signal transduction pathway involving ATF6, and by that, is independent from the induction cascade initiated by polyP. This conclusion is supported by the finding that isoquercitrin upregulates the expression of the gene encoding for osteocalcin, while polyP strongly increases the expression of the Ets1 gene and of the alkaline phosphatase. We show that the two compounds, polyP and isoquercitrin, have a co-enhancing effect on bone mineral formation and in turn might be of potential therapeutic value for prevention/treatment of osteoporosis.

The marine sponge-derived inorganic polymers, biosilica and polyphosphate, as morphogenetically active matrices/scaffolds for the differentiation of human multipotent stromal cells: potential application in 3D printing and distraction osteogenesis

The two marine inorganic polymers, biosilica (BS), enzymatically synthesized from ortho-silicate, and polyphosphate (polyP), a likewise enzymatically synthesized polymer consisting of 10 to >100 phosphate residues linked by high-energy phosphoanhydride bonds, have previously been shown to display a morphogenetic effect on osteoblasts. In the present study, the effect of these polymers on the differential differentiation of human multipotent stromal cells (hMSC), mesenchymal stem cells, that had been encapsulated into beads of the biocompatible plant polymer alginate, was studied. The differentiation of the hMSCs in the alginate beads was directed either to the osteogenic cell lineage by exposure to an osteogenic medium (mineralization activation cocktail; differentiation into osteoblasts) or to the chondrogenic cell lineage by incubating in chondrocyte differentiation medium (triggering chondrocyte maturation). Both biosilica and polyP, applied as Ca²⁺ salts, were found to induce an increased mineralization in osteogenic cells; these inorganic polymers display also morphogenetic potential. The effects were substantiated by gene expression studies, which revealed that biosilica and polyP strongly and significantly increase the expression of bone morphogenetic protein 2 (BMP-2) and alkaline phosphatase (ALP) in osteogenic cells, which was significantly more pronounced in osteogenic versus chondrogenic cells. A differential effect of the two polymers was seen on the expression of the two collagen types, I and II. While collagen Type I is highly expressed in osteogenic cells, but not in chondrogenic cells after exposure to biosilica or polyP, the upregulation of the steady-state level of collagen Type II transcripts in chondrogenic cells is comparably stronger than in osteogenic cells. It is concluded that the two polymers, biosilica and polyP, are morphogenetically active additives for the otherwise biologically inert alginate polymer. It is proposed that alginate, supplemented with polyP and/or biosilica, is a suitable biomaterial that promotes the growth and differentiation of hMSCs and might be beneficial for application in 3D tissue printing of hMSCs and for the delivery of hMSCs in fractures, surgically created during distraction osteogenesis.

Incorporation of silica particles into decellularized tissue biomaterial and its effect on macrophage activation

Secretion of signaling molecules by macrophages is induced by silica particles deposited onto decellularized tissue derived biomaterials.