Does seeding density affectin vitro mineral nodules formation in novel composite scaffolds?

Effect of inoculation density of bone marrow mesenchymal stem cells cultured on calcium phosphate cement scaffold on osteogenic differentiation

BACKGROUND

Calcium phosphate cements (CPCs) are biocompatible materials that have been evaluated as scaffolds in bone tissue engineering. At present, the stem cell density of inoculation on CPC scaffold varies.

OBJECTIVE

The aim of this study is to analyze the effect of seeding densities on cell growth and osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs) on a calcium phosphate cements (CPCs) scaffold.

METHODS

BMMSCs derived from minipigs were seeded onto a CPC scaffold at three densities [1 million/mL (1M), 5 million/mL (5M) and 25 million/mL 25M)], and cultured for osteogenic induction for 1, 4 and 8 days.

RESULTS

Well adhered and extended BMMSCs on the CPC scaffold showed significantly different proliferation rates within each seeding density group at different time points (P < 0.05). The number of live cells per unit area in 1M, 5M and 25M increased by 3.5, 3.9 and 2.5 folds respectively. The expression of ALP peaked at 4 days post inoculation with the fold-change being 2.6 and 2.8 times higher in 5M and 25M respectively as compared to 1M. The expression levels of OC, Coll-1 and Runx-2 peaked at 8 days post inoculation.

CONCLUSIONS

An optimal seeding density may be more conducive for cell proliferation, differentiation, and extracellular matrix synthesis on scaffolds. We suggest the optimal seeding density should be 5 million/mL.

Improving cell distribution on 3D additive manufactured scaffolds through engineered seeding media density and viscosity

In order to ensure the long-term in vitro and in vivo functionality of cell-seeded 3D scaffolds, an effective and reliable method to control cell seeding efficiency and distribution is crucial. Static seeding on 3D additive manufactured scaffolds made of synthetic polymers still remains challenging, as it often results in poor cell attachment, high cell sedimentation and non-uniform cell distribution, due to gravity and to the intrinsic macroporosity and surface chemical properties of the scaffolds. In this study, the biocompatible macromolecules dextran and Ficoll (Ficoll-Paque) were used for the first time as temporary supplements to alter the viscosity and density of the seeding media, respectively, and improve the static seeding output. The addition of these macromolecules drastically reduced the cell sedimentation velocities, allowing for homogeneous cell attachment to the scaffold filaments. Both dextran and Ficoll-Paque -based seeding methods supported human mesenchymal stromal cells viability and osteogenic differentiation post-seeding. Interestingly, the improved cell distribution led to increased matrix production and mineralization compared to scaffolds seeded by conventional static method. These results suggest a simple and universal method for an efficient seeding of 3D additive manufactured scaffolds, independent of their material and geometrical properties, and applicable for bone and various other tissue regeneration. STATEMENT OF SIGNIFICANCE: Additive manufacturing has emerged as one of the desired technologies to fabricate complex and patient-specific 3D scaffolds for bone regeneration. Along with the technology, new synthetic polymeric materials have been developed to meet processability requirements, as well as the mechanical properties and biocompatibility necessary for the application. Yet, there is still lack of methodology for a universal cell seeding method applicable to all additive manufactured 3D scaffolds regardless of their characteristics. We believe that our simple and reliable method, which is based on adjusting the cell settling velocity to aid cell attachment, could potentially help to maximize the efficiency, and therefore, functionality of cell-seeded constructs. This is of great importance when aiming for both in vitro and future clinical applications.

Anti-Disuse Osteoporosis Activity of a Complex of Calcium-Binding Peptide from Auricularia auricula Protein Hydrolysates

Osteoporosis is a common metabolic bone disease that is often seen in bedridden patients and astronauts. Long-term bed rest and nonweight bearing tend to induce disuse osteoporosis. Calcium supplements are commonly used to help treat disuse osteoporosis along with medications, most of which are calcium carbonate based, but they have poor absorption effects. In this study, we prepared a novel Auricularia auricula peptide-calcium complex (AP-Ca) and evaluated its protective effects on disuse osteoporosis. In vitro assays showed that AP-Ca significantly increased the contents of calcium (P < 0.05) and the activity of alkaline phosphatase (AKP; P < 0.05) of osteoblasts cultured in a two-dimensional-rotating wall vessel. Meanwhile, supplementation with AP-Ca also inhibited the production of pro-inflammatory factors induced by the loss of stress, especially TNF-α (P < 0.05). In vivo, a mouse tail suspension (TS) model was established, and the results showed that AP-Ca helped to improve bone mineral density, bone mineral content, and bone organic content in TS mice and effectively alleviated the alteration of enzymes related to bone metabolism, including AKP (P < 0.05) and serum tartrate-resistant acid phosphatase (P < 0.05), to avoid more serious bone loss induced by TS. Furthermore, we found that AP-Ca downregulated the bone resorption-associated pro-inflammatory genes interleukin-1 (IL-1), tumor necrosis factor-α, and IL-6 by 59.53 ± 3.55%, 48.01 ± 5.68%, and 40.00 ± 5.89%, respectively (P < 0.05). In conclusion, AP-Ca showed potential to suppress bone loss induced by disuse and might be considered a new alternative to reduce the risk of disuse osteoporosis. PRACTICAL APPLICATION: This peptide-calcium complex supplement exhibited protective effects on the bone loss induced by disuse, which provided a new alternative for patients and astronauts to reduce the risk of disuse osteoporosis.

Characterization and Optimization of the Seeding Process of Adipose Stem Cells on the Polycaprolactone Scaffolds

The purpose of the current study was to evaluate the usefulness of adipose-derived stem cells (ASCs) for bone injury therapy. Lipoaspirates were collected from the abdomen regions of 17 healthy female donors (mean age 49 ± 6 years) using Coleman technique or Body-jet liposuction. In the present study, the primary objective was the in vitro characteristics of human ASCs. The secondary objective was the optimization of the cell seeding process on 3D-printed scaffolds using polycaprolactone (PCL) or polycaprolactone covered with tricalcium phosphate (PCL + 5% TCP). Biological evaluation of human ASC showed high efficiency of isolation obtaining a satisfying amount of homogeneous cell populations. Results suggest that ASCs can be cultured in vitro for a long time without impairing their proliferative capacity. Growth kinetics shows that the highest number of cells can be achieved in passage 5 and after the 16^th passage; there is a significant decrease of cell numbers and their proliferative potential. The percentage of colony forming units from the adipose stem cells is 8% ± 0.63% (p < 0.05). It was observed that the accumulation of calcium phosphate in the cells in vitro, marked with Alizarin Red S, was increased along with the next passage. Analysis of key parameters critically related to the cell seeding process shows that volume of cell suspension and propagation time greatly improve the efficiency of seeding both in PCL and PCL + 5% TCP scaffolds. The cell seeding efficiency did differ significantly between scaffold materials and cell seeding methods (p < 0.001). Increased seeding efficiency was observed when using the saturation of cell suspension into scaffolds with additional incubation. Alkaline phosphatase level production in PCL + 5% TCP scaffold was better than in PCL-only scaffold. The study results can be used for the optimization of the seeding process and quantification methods determining the successful implementation of the preclinical model study in the future tissue engineering strategies.

Microscale roughness regulates laminin-5 secretion of bone marrow mesenchymal stem cells

Laminin-5 (Ln-5), an important extracellular matrix (ECM) protein, plays a critical role in regulating the growth and differentiation of mesodermal tissues, including bone. Ln-5 can be secreted by the mesenchymal stem cells (MSCs), and Ln-5 promotes MSCs osteogenic differentiation. It has been demonstrated that a substrate's surface topography could regulate MSC secretion and differentiation. A better understanding of the mechanism of how Ln-5 and surface roughness regulate MSC osteogenic differentiation would guide the design of surface topography and coatings of orthopedic implants and cell culture substrates. However, few studies have investigated the relationship between surface roughness and the secretion of Ln-5 in MSC osteogenic differentiation. Whether substrate surface topography regulates MSC differentiation via regulating Ln-5 secretion and how surface topography contributes to the secretion of Ln-5 are still not known. In this study, the influence of microscale roughness at different levels (R0, R1 and R2) on the secretion of Ln-5 of human bone marrow MSCs (hBMSCs) and subsequent osteogenic differentiation were examined. hBMSCs spreading, distribution and morphology were greatly affected by different roughness levels. A significantly higher level of Ln-5 secretion was detected on R2, which correlated to the local cell density regulated by the rough surface. Ln-5 binding integrins (α2 and α3) were strongly activated on R2. In addition, the results from hBMSCs on R0 inserts with different cell densities further confirmed that local cell density regulated Ln-5 secretion and cell surface integrin activation. In addition, the mineralization level of MSCs on R2 was remarkably higher than that on R0 and R1. These results suggest that hBMSC osteogenic differentiation level on R2 roughness was enhanced via increased Ln-5 secretion that was attributed to rough surface regulated local cell density. Thus, the microroughness could serve as effective topographical stimulus in cell culture devices and bone implant materials.

Advantages of creation of holes and removal of air in artificial bone for early bone formation when used artificial bone as a gap filler in open wedge high tibial osteotomy

Recently, many facilities perform open wedge high tibial osteotomy (OWHTO) using artificial bone as a gap filler. However, there are many cases in which artificial bone is used without a clear purpose. We recommend a surgical technique to promote early synostosis between artificial bone and recipient bone due to mechanical support especially in the early stage after OWHTO. At our hospital, beta-tricalcium phosphate (β-TCP) with 60% porosity is used in OWHTO. Initially, a wedge-shaped block-type β-TCP, as large as possible, was inserted into the gap. However, from the standpoint of initial mechanical support, we changed the artificial bone size and created intentional holes. Furthermore, we removed air bubbles from β-TCP. We evaluated the synostosis on the basis of clinical results and diagnostic imaging. As a result of creating holes and removing air from the artificial bone, a trend toward faster synostosis was noted, especially at the early stage. No adverse events such as tibial plateau fracture, lateral cortical fracture, plate and screw failure and correction loss due to reducing the size of the artificial bone occurred, but placement of the artificial bone in contact with cortical bone and surface contact installation with the recipient bone tissue was important. When using artificial bone in OWHTO, holes formation and removal of air from the artificial bone are recommended for faster synostosis between artificial bone and recipient bone in the early stage after surgery. Artificial bone should be used, with attention to its positioning and shape, for efficient mechanical support.

Influence of highly porous electrospun PLGA/PCL/nHA fibrous scaffolds on the differentiation of tooth bud cells in vitro

In this study, we investigated the use of three-dimensional electrospun poly(lactic-co-glycolic acid)/poly(ε-caprolactone) (PLGA/PCL) scaffolds seeded and cultured with postnatal dental cells, for improved dental tissue regeneration. Wet-electrospinning combined with ultrasonic treatment was studied as a method to enhance scaffold porosity and to promote cell-cell interactions. We also investigated whether nano-hydroxyapatite (nHA) incorporation could enhance dental cell differentiation. All scaffolds were seeded with human tooth pulp-derived dental mesenchymal (hDM) cells, or a combination of hDM and pig dental epithelial (pDE) cells, cultured for up to 28 days. Developmentally staged samples were assessed using scanning electron microscopy, histological, immunohistochemical, DNA and alkaline phosphatase activity assays, and quantitative-PCR for ameloblastic, odontoblastic, and osteogenic related gene expression. Results showed that electrospun scaffolds exhibited sufficient porosity to support robust cell ingrowth. Additional ultrasonic treatment led to a less homogeneous scaffold porosity, resulting in evident cell clustering and enhanced hDM-pDE cell-cell interactions. Finally, nHA incorporation was found to enhance dental cell differentiation. However, it also resulted in smaller fiber diameter and reduced scaffold porosity, and inhibited cell ingrowth and proliferation. In conclusion, ultrasonically treated wet-electrospun PLGA/PCL scaffolds are a suitable material for dental tissue engineering, and support future in vivo evaluations of this model. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2597-2607, 2017.

Three-Dimensional Printed Scaffolds with Multipotent Mesenchymal Stromal Cells for Rabbit Mandibular Reconstruction and Engineering

Multipotent mesenchymal stromal cells (MSC) derived from both the bone marrow and adipose tissue possess the ability to differentiate into multiple cell lineages, regulate the immune function by secreting numerous bioactive paracrine factors, and hold great potential in cell therapy and tissue engineering. When combined with three-dimensional (3D) scaffolds, MSC can be used for bone defect reconstruction and engineering. This protocol describes the isolation of bone marrow mesenchymal stromal cells (BMMSC) and adipose-tissue derived stem cells (ADSC) from rabbits for subsequent seeding on tissue-engineered 3D-printed scaffolds and transplantation into a rabbit-model with the goal of repairing large osseous mandibular defects (one quarter of the lower jaw is removed surgically). Steps to demonstrate the three cell differentiation lineage potentials of BMMSC and ADSC into osteocytes, adipocytes, and chondrocytes are described. A modified cell seeding method using syringes on scaffold is detailed. Creating a large mandibular bone defect, the rapid prototyping method to print a customized 3D-scaffold, the scaffold implantation procedure in rabbits, and microcomputed tomography (micro-CT) analysis are also described.

Do Surface Porosity and Pore Size Influence Mechanical Properties and Cellular Response to PEEK?

BACKGROUND

Despite its widespread use in orthopaedic implants such as soft tissue fasteners and spinal intervertebral implants, polyetheretherketone (PEEK) often suffers from poor osseointegration. Introducing porosity can overcome this limitation by encouraging bone ingrowth; however, the corresponding decrease in implant strength can potentially reduce the implant's ability to bear physiologic loads. We have previously shown, using a single pore size, that limiting porosity to the surface of PEEK implants preserves strength while supporting in vivo osseointegration. However, additional work is needed to investigate the effect of pore size on both the mechanical properties and cellular response to PEEK.

QUESTIONS/PURPOSES

(1) Can surface porous PEEK (PEEK-SP) microstructure be reliably controlled? (2) What is the effect of pore size on the mechanical properties of PEEK-SP? (3) Do surface porosity and pore size influence the cellular response to PEEK?

METHODS

PEEK-SP was created by extruding PEEK through NaCl crystals of three controlled ranges: 200 to 312, 312 to 425, and 425 to 508 µm. Micro-CT was used to characterize the microstructure of PEEK-SP. Tensile, fatigue, and interfacial shear tests were performed to compare the mechanical properties of PEEK-SP with injection-molded PEEK (PEEK-IM). The cellular response to PEEK-SP, assessed by proliferation, alkaline phosphatase activity, vascular endothelial growth factor production, and calcium content of osteoblast, mesenchymal stem cell, and preosteoblast (MC3T3-E1) cultures, was compared with that of machined smooth PEEK and Ti6Al4V.

RESULTS

Micro-CT analysis showed that PEEK-SP layers possessed pores that were 284 ± 35 µm, 341 ± 49 µm, and 416 ± 54 µm for each pore size group. Porosity and pore layer depth ranged from 61% to 69% and 303 to 391 µm, respectively. Mechanical testing revealed tensile strengths > 67 MPa and interfacial shear strengths > 20 MPa for all three pore size groups. All PEEK-SP groups exhibited > 50% decrease in ductility compared with PEEK-IM and demonstrated fatigue strength > 38 MPa at one million cycles. All PEEK-SP groups also supported greater proliferation and cell-mediated mineralization compared with smooth PEEK and Ti6Al4V.

CONCLUSIONS

The PEEK-SP formulations evaluated in this study maintained favorable mechanical properties that merit further investigation into their use in load-bearing orthopaedic applications and supported greater in vitro osteogenic differentiation compared with smooth PEEK and Ti6Al4V. These results are independent of pore sizes ranging 200 µm to 508 µm.

CLINICAL RELEVANCE

PEEK-SP may provide enhanced osseointegration compared with current implants while maintaining the structural integrity to be considered for several load-bearing orthopaedic applications such as spinal fusion or soft tissue repair.

Cell seeding density is a critical determinant for copolymer scaffolds-induced bone regeneration

Constructs intended for bone tissue engineering (TE) are influenced by the initial cell seeding density. Therefore, the objective of this study was to determine the effect of bone marrow stromal stem cells (BMSCs) density loaded onto copolymer scaffolds on bone regeneration. BMSCs were harvested from rat's bone marrow and cultured in media with or without osteogenic supplements. Cells were seeded onto poly(l‐lactide‐co‐ε‐caprolactone) [poly(LLA‐co‐CL)] scaffolds at two different densities: low density (1 × 10⁶ cells/scaffold) or high density (2 × 10⁶ cells/scaffold) using spinner modified flasks and examined after 1 and 3 weeks. Initial attachment and spread of BMSC onto the scaffolds was recorded by scanning electron microscopy. Cell proliferation was assessed by DNA quantification and cell differentiation by quantitative real‐time reverse transcriptase‐polymerized chain reaction analysis (qRT‐PCR). Five‐millimeter rat calvarial defects (24 defects in 12 rats) were implanted with scaffolds seeded with either low or high density expanded with or without osteogenic supplements. Osteogenic supplements significantly increased cell proliferation (p < 0.001). Scaffolds seeded at high cell density exhibited higher mRNA expressions of Runx2 p = 0.001, Col1 p = 0.001, BMP2 p < 0.001, BSP p < 0.001, and OC p = 0.013. More bone was formed in response to high cell seeding density (p = 0.023) and high seeding density with osteogenic medium (p = 0.038). Poly (LLA‐co‐CL) scaffolds could be appropriate candidates for bone TE. The optimal number of cells to be loaded onto scaffolds is critical for promoting Extracellular matrix synthesis and bone formation. Cell seeding density and osteogenic supplements may have a synergistic effect on the induction of new bone. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 3649–3658, 2015.

Bone regeneration in critical-size calvarial defects using human dental pulp cells in an extracellular matrix-based scaffold

The rat calvarial defect is an established model to evaluate craniofacial bone regeneration using cell-scaffold biocomplexes. Dental pulp harbors stem cells with significant osteogenic properties. Extracellular matrix (ECM)-like scaffolds simulate the environment that cells observe in vivo. In the present study, we evaluated the osteogenic effect of a biocomplex of human dental pulp cells and a hyaluronic-based hydrogel scaffold in calvarial defects of immunocompetent rats. Dental pulp cells at the 2nd passage were characterized by flow cytometry, osteodifferentiated ex vivo for 4 days and the whole population was encapsulated in the synthetic ECM matrix. Cell vitality was verified 24 h upon encapsulation. 5 mm calvarial defects were created in 30 male rats and filled with the biocomplex, the scaffold alone, or left untreated. Histological evaluation at 8 weeks showed incomplete bone regeneration in all groups. The scaffold was not fully degraded and entrapped cells were detected in it. Histomorphometry showed statistically significant superior new bone formation in the biocomplex-treated group, compared to the two other groups. The present study provides evidence that the whole population of human dental pulp cells can advance bone healing when transplanted in immunocompetent animals and highlights the importance of proper scaffold degradation in cell-driven bioengineering treatments.

The Dose-Effect Relationship Between the Seeding Quantity of Human Marrow Mesenchymal Stem Cells and In Vivo Tissue-Engineered Bone Yield

Although the feasibility of human bone marrow mesenchymal stem cell (hBMMSC)-based tissue-engineered bone (TEB) has been proven in a number of studies, reaching a high positive fraction and bone yield of TEB still remains a challenge. Here we report a dose-effect relationship of the quantity of seeded cells with in vivo bone yield and the required quantity of hBMMSCs for the effective, stable bone formation of TEB. In our study, TEB was constructed using the static seeding technique with the gradient of seeding densities and volumes of passage 3 hBMMSCs. The in vitro characteristics of seeding efficiency, proliferation, viability, distribution, and osteogenic differentiation of hBMMSCs seeded on two commercial scaffolds of β-TCP and CHA were investigated using alamarBlue assay, live/dead staining, confocal laser scanning microscope, scanning electronic microscopy examination, and mRNA expression analysis of osteogenic differentiation markers. After 3 months of ectopic implantation, in vivo bone regeneration was examined by quantitative analysis of histology and micro-CT. The results showed that 10 × 10(6) cells/ml was the minimum cell seeding density for CHA and β-TCP to generate new bone in vivo. In addition, 20 × 10(6) cells/ml and 30 × 10(6) cells/ml were the saturating seeding densities for CHA and β-TCP to produce new bone effectively and stably, respectively. Thus, for different scaffolds, the saturating seeding density should be investigated first to ensure the effectiveness and stability of TEB construction with minimum donor injury, which is essential for the clinical application of TEB.

Static versus vacuum cell seeding on high and low porosity ceramic scaffolds

An adequate cell seeding technique is essential for effective bone regeneration on cell seeded constructs of porous tricalcium phosphates. In previous studies, dynamic cell seeding, in which an external force is applied to seed cells on a biomaterial, resulted in more homogeneous cell seeding in low porosity scaffolds than static seeding. The optimal cell seeding technique for high porosity scaffolds has not been defined yet. Human mesenchymal stem cells were isolated from bone marrow and characterized. The cells were seeded on low porosity (45%) and high porosity (90%) tricalcium phosphate scaffolds using a static and a vacuum seeding technique. LIVE/DEAD® staining of the cell-scaffold complexes followed by confocal laser scanning microscopy was used to measure cell proliferation, cell distribution and cell viability one, three and seven days after seeding. Cell proliferation was also quantified using a DNA quantification assay. Neither static nor vacuum seeding resulted in homogeneous cell seeding on both low and high porosity scaffolds. Cell density was lower on the inside than on the outside of the scaffolds. On low porosity scaffolds, the vacuum method yielded the highest numbers of cells compared to the static method. Low porosity scaffolds were seeded most homogeneously using the static seeding method. Seven days after seeding, numbers of adherent cells were comparable for both scaffold types and independent of the cell seeding technique used. In conclusion, on high porosity scaffolds, static seeding results in more homogeneous cell seeding and it is easier to use than a vacuum seeding technique.

Noninvasive real-time monitoring by alamarBlue(®) during in vitro culture of three-dimensional tissue-engineered bone constructs

Bone tissue engineering (TE) aims to develop reproducible and predictive three-dimensional (3D) TE constructs, defined as cell-seeded scaffolds produced by a controlled in vitro process, to heal or replace damaged and nonfunctional bone. To control and assure the quality of the bone TE constructs, a prerequisite for regulatory authorization, there is a need to develop noninvasive analysis techniques to evaluate TE constructs and to monitor their behavior in real time during in vitro culturing. Most analysis techniques, however, are limited to destructive end-point analyses. This study investigates the use of the nontoxic alamarBlue(®) (AB) reagent, which is an indicator for metabolic cell activity, for monitoring the cellularity of 3D TE constructs in vitro as part of a bioreactor culturing processes. Within the field of TE, bioreactors have a huge potential in the translation of TE concepts to the clinic. Hence, the use of the AB reagent was evaluated not only in static cultures, but also in dynamic cultures in a perfusion bioreactor setup. Hereto, the AB assay was successfully integrated in the bioreactor-driven TE construct culture process in a noninvasive way. The obtained results indicate a linear correlation between the overall metabolic activity and the total DNA content of a scaffold upon seeding as well as during the initial stages of cell proliferation. This makes the AB reagent a powerful tool to follow-up bone TE constructs in real-time during static as well as dynamic 3D cultures. Hence, the AB reagent can be successfully used to monitor and predict cell confluence in a growing 3D TE construct.

The application of super paramagnetic iron oxide-labeled mesenchymal stem cells in cell-based therapy

Mesenchymal stem cell (MSC)-based therapy has great potential for tissue regeneration. However, being able to monitor the in vivo behavior of implanted MSCs and understand the fate of these cells is necessary for further development of successful therapies and requires an effective, non-invasive and non-toxic technique for cell tracking. Super paramagnetic iron oxide (SPIO) is an idea label and tracer of MSCs. MRI can be used to follow SPIO-labeled MSCs and has been proposed as a gold standard for monitoring the in vivo biodistribution and migration of implanted SPIO-labeled MSCs. This review discusses the biological effects of SPIO labeling on MSCs and the therapeutic applications of local or systemic delivery of these labeled cells.

Enhancing the biological performance of synthetic polymeric materials by decoration with engineered, decellularized extracellular matrix

Materials based on synthetic polymers can be extensively tailored in their physical properties but often suffer from limited biological functionality. Here we tested the hypothesis that the biological performance of 3D synthetic polymer-based scaffolds can be enhanced by extracellular matrix (ECM) deposited by cells in vitro and subsequently decellularized. The hypothesis was tested in the context of bone graft substitutes, using polyesterurethane (PEU) foams and mineralized ECM laid by human mesenchymal stromal cells (hMSC). A perfusion-based bioreactor system was critically employed to uniformly seed and culture hMSC in the scaffolds and to efficiently decellularize (94% DNA reduction) the resulting ECM while preserving its main organic and inorganic components. As compared to plain PEU, the decellularized ECM-polymer hybrids supported the osteoblastic differentiation of newly seeded hMSC by up-regulating the mRNA expression of typical osteoblastic genes (6-fold higher bone sialoprotein; 4-fold higher osteocalcin and osteopontin) and increasing calcium deposition (6-fold higher), approaching the performance of ceramic-based materials. After ectopic implantation in nude mice, the decellularized hybrids induced the formation of a mineralized matrix positively immunostained for bone sialoprotein and resembling an immature osteoid tissue. Our findings consolidate the perspective of bioreactor-based production of ECM-decorated polymeric scaffolds as off-the-shelf materials combining tunable physical properties with the physiological presentation of instructive biological signals.

Characterization and optimization of cell seeding in scaffolds by factorial design: quality by design approach for skeletal tissue engineering

Cell seeding into scaffolds plays a crucial role in the development of efficient bone tissue engineering constructs. Hence, it becomes imperative to identify the key factors that quantitatively predict reproducible and efficient seeding protocols. In this study, the optimization of a cell seeding process was investigated using design of experiments (DOE) statistical methods. Five seeding factors (cell type, scaffold type, seeding volume, seeding density, and seeding time) were selected and investigated by means of two response parameters, critically related to the cell seeding process: cell seeding efficiency (CSE) and cell-specific viability (CSV). In addition, cell spatial distribution (CSD) was analyzed by Live/Dead staining assays. Analysis identified a number of statistically significant main factor effects and interactions. Among the five seeding factors, only seeding volume and seeding time significantly affected CSE and CSV. Also, cell and scaffold type were involved in the interactions with other seeding factors. Within the investigated ranges, optimal conditions in terms of CSV and CSD were obtained when seeding cells in a regular scaffold with an excess of medium. The results of this case study contribute to a better understanding and definition of optimal process parameters for cell seeding. A DOE strategy can identify and optimize critical process variables to reduce the variability and assists in determining which variables should be carefully controlled during good manufacturing practice production to enable a clinically relevant implant.

Effect of cell seeding density on proliferation and osteodifferentiation of umbilical cord stem cells on calcium phosphate cement-fiber scaffold

Calcium phosphate cement (CPC) can fill complex-shaped bone defects and set in situ to form a scaffold with intimate adaptation to neighboring bone. The objectives of this study were to determine (1) the effects of fiber length and alginate microbead volume fraction on CPC mechanical properties, and (2) the effect of cell seeding density of human umbilical cord mesenchymal stem cells (hUCMSCs) on their proliferation and osteodifferentiation on CPC. Adding microbeads to CPC degraded the strength. However, increasing the fiber length improved the mechanical properties. Strength and elastic modulus of CPC-microbead-fiber scaffold matched those reported for cancellous bone. When the cell seeding density was increased from 50k to 300k, the cell viability, osteodifferentiation, and bone mineral synthesis also increased. When the seeding density was further increased to 500k, the osteodifferentiation and mineralization decreased. Hence, the 300k seeding density was optimal for CPC-microbead-fiber under the specified conditions. At day 8, alkaline phosphatase (ALP) gene expression of hUCMSCs with seeding density of 300k was threefold the ALP at 150k, and 200-fold the ALP at 50k. At day 14, osteocalcin and runt-related transcription factor 2 with cell seeding density of 300k was fourfold those at 50k. At day 14, mineralization by hUCMSCs at seeding density of 300k was 5-fold the mineralization at 150k, and 25-fold that at 50k. In conclusion, the effect of stem cell seeding density on CPC was determined for the first time. At low cell densities, cell viability and mineralization increased with seeding density. However, a higher seeding density was not necessarily better, and an optimal seeding density on CPC resulted in the best osteodifferentiation and mineralization. The stem cell-seeded CPC-fiber scaffold with excellent osteodifferentiation and mineralization is promising for orthopedic and craniofacial applications.

Efficient Cell-seeding into Scaffolds Improves Bone Formation

Bone marrow stromal cells (BMSCs)/β-tricalcium phosphate (β-TCP) composites have attracted a great deal of attention in bone tissue engineering. If more effective bone regeneration is to be achieved, efficient cell-seeding systems need to be clarified. In this study, we investigated the number of cells contained in composites, and the in vitro/vivo osteogenic differentiation capacity of composites using 4 conventional systems of seeding rat BMSCs into β-TCP: soak, low-pressure, pipette, and syringe systems. The highest number of cells was contained in the composites from the syringe group. Moreover, after two-week osteogenic induction in vitro, the composites in the syringe group exhibited the highest osteogenic potential, which continued at 8 weeks after subcutaneous implantation in vivo. Our results indicated that efficient and appropriate cell-seeding could improve in vitro/vivo bone formation in composites and thus make a potential clinical contribution to successful bone tissue engineering. Abbreviations: BMSCs, bone marrow stromal cells; β-TCP, β-tricalcium phosphate; S-D, Sprague-Dawley; kPa, kilopascal; ALP, alkaline phosphatase; N, Newton; DNA, deoxyribonucleic acid; OCN, osteocalcin; ANOVA, analysis of variance; PLSD, protected least-significant difference; and HE, hematoxylin and eosin.

Bone grafts engineered from human adipose-derived stem cells in perfusion bioreactor culture

We report engineering of half-centimeter-sized bone constructs created in vitro using human adipose-derived stem cells (hASCs), decellularized bone scaffolds, and perfusion bioreactors. The hASCs are easily accessible, can be used in an autologous fashion, are rapidly expanded in culture, and are capable of osteogenic differentiation. hASCs from four donors were characterized for their osteogenic capacity, and one representative cell population was used for tissue engineering experiments. Culture-expanded hASCs were seeded on fully decellularized native bone scaffolds (4 mm diameter x 4 mm thick), providing the necessary structural and mechanical environment for osteogenic differentiation, and cultured in bioreactors with medium perfusion. The interstitial flow velocity was set to a level necessary to maintain cell viability and function throughout the construct volume (400 microm/s), via enhanced mass transport. After 5 weeks of cultivation, the addition of osteogenic supplements (dexamethasone, sodium-beta-glycerophosphate, and ascorbic acid-2-phosphate) to culture medium significantly increased the construct cellularity and the amounts of bone matrix components (collagen, bone sialoprotein, and bone osteopontin). Medium perfusion markedly improved the distribution of cells and bone matrix in engineered constructs. In summary, a combination of hASCs, decellularized bone scaffold, perfusion culture, and osteogenic supplements resulted in the formation of compact and viable bone tissue constructs.

Micropatterned matrix directs differentiation of human mesenchymal stem cells towards myocardial lineage

Stem cell response can be influenced by a multitude of chemical, topological and mechanical physiochemical cues. While extensive studies have been focused on the use of soluble factors to direct stem cell differentiation, there are growing evidences illustrating the potential to modulate stem cell differentiation via precise engineering of cell shape. Fibronectin were printed on poly(lactic-co-glycolic acid) (PLGA) thin film forming spatially defined geometries as a means to control the morphology of bone marrow derived human mesenchymal stem cells (hMSCs). hMSCs that were cultured on unpatterned substrata adhered and flattened extensively (approximately 10,000 microm(2)) while cells grown on 20 microm micropatterend wide adhesive strips were highly elongated with much smaller area coverage of approximately 2000 microm(2). Gene expression analysis revealed up-regulation of several hallmark markers associated to neurogenesis and myogenesis for cells that were highly elongated while osteogenic markers were specifically down-regulated or remained at its nominal level. Even though there is clearly upregulated levels of both neuronal and myogenic lineages but at the functionally relevant level of protein expression, the myogenic lineage is dominant within the time scale studied as determined by the exclusive expression of cardiac myosin heavy chain for the micropatterned cells. Enforced cell shape distortion resulting in large scale rearrangement of cytoskeletal network and altered nucleus shape has been proposed as a physical impetus by which mechanical deformation is translated into biochemical response. These results demonstrated for the first time that cellular shape modulation in the absence of any induction factors may be a viable strategy to coax lineage-specific differentiation of stem cells.

Effect of initial cell seeding density on early osteogenic signal expression of rat bone marrow stromal cells cultured on cross-linked poly(propylene fumarate) disks

The intercellular signaling mechanisms among a transplanted cell population are largely determined by the cell population itself as well as the surrounding environment. Changes in cell-to-cell paracrine signaling distance can be obtained by altering cell density, and signal expression of growth factors can be enhanced by auto/paracrine signal transduction. To examine these relationships, we investigated the effect of cell seeding density on viability, proliferation, differentiation, and the endogenous osteogenic signal expression among rat bone marrow stromal cells (BMSCs) cultured on a 2D disk. Rat BMSCs were isolated from rats and then cultured for 8 days on biodegradable poly(propylene fumarate) disks with three different seeding densities (0.06, 0.15, and 0.30 million cells/disk). At days 1, 4, and 8, viability by live/dead fluorescent staining, DNA amount, osteogenic differentiation by alkaline phosphatase and osteocalcin mRNA expression, calcium deposition, and osteogenic growth factor mRNA expression were assayed. Osteogenic signal expression was evaluated using quantitative reverse transcriptase-polymerase chain reaction, and signals of interest include bone morphogenetic protein-2, transforming growth factor-β(1), fibroblast growth factor-2, and platelet-derived growth factor-A. The results from this study demonstrate that rat BMSCs were viable over 8 days without being affected by cell density and that both cell proliferation rate and early osteogenic differentiation were stimulated by lower cell seeding density. Most importantly, this study has demonstrated for the first time that the temporal gene expression profiles of endogenous growth factors can be controlled by altering the initial cell seeding density on poly(propylene fumarate) disks. Therefore, our results suggest that changes in the paracrine signal distance by altering cell seeding density may be a useful strategy to optimize the cell-biomaterial construct microenvironments to enhance the osteogenic signal expression.

Cultivation of human bone marrow stromal cells on three-dimensional scaffolds of mineralized collagen: influence of seeding density on colonization, proliferation and osteogenic differentiation

In this study human bone marrow stromal cells (hBMSCs) were cultured on three-dimensional porous scaffolds of biomimetically mineralized collagen type I developed for bone engineering. Three different cell numbers were used for seeding of the nanocomposites, and the impact of the seeding density on proliferation and osteogenic differentiation of hBMSCs was investigated. In addition, the effect of the seeding cell number on seeding efficiency and distribution of the cells within the scaffolds was studied. Our data revealed that the open and interconnecting porosity of the mineralized collagen scaffolds allows a very efficient seeding for all seeding densities tested. Although penetration of the cells into the interior of the scaffolds was demonstrated for all seeding densities, the application of higher cell numbers resulted in a better colonization also of the deeper scaffold regions. A substantial influence of the seeding density was observed on proliferation and osteogenic differentiation of hBMSCs. Thus, the highest proliferation rate and specific alkaline phosphatase activity was found for the cell matrix constructs seeded with the lowest density. RT-PCR analyses revealed a higher expression of alkaline phosphatase and bone sialoprotein II at lower seeding densities; however, expression of osteopontin was unaffected by the seeding cell number. Our results demonstrated that the seeding density might be an important factor for the development of optimal cell matrix constructs for bone tissue engineering.

A mesoporous bioactive glass/polycaprolactone composite scaffold and its bioactivity behavior

Composite scaffolds of mesoporous bioactive glass (MBG)/polycaprolactone (PCL) and conventional bioactive glass (BG)/PCL were fabricated by a solvent casting-particulate leaching method, and the structure and properties of the composite scaffolds were characterized. The measurements of the water contact angles suggest that the incorporation of either MBG or BG into PCL can improve the hydrophilicity of the composites, and the former is more effective than the later. The bioactivity of the composite scaffold is evaluated by soaking the scaffolds in a simulated body fluid (SBF) and the results show that the MBG/PCL composite scaffolds can induce a dense and continuous layer of apatite after soaking in SBF for 3 weeks, as compared with the scattered and discrete apatite particles on the BG/PCL composite scaffolds. Such improvements (improvements of the hydrophilicity and apatite forming ability) should be helpful for the extensive applications of PCL scaffold in tissue engineering.

Mag-seeding of rat bone marrow stromal cells into porous hydroxyapatite scaffolds for bone tissue engineering

Bone tissue engineering has been investigated as an alternative strategy for autograft transplantation. In the process of tissue engineering, cell seeding into three-dimensional (3-D) scaffolds is the first step for constructing 3-D tissues. We have proposed a methodology of cell seeding into 3-D porous scaffolds using magnetic force and magnetite nanoparticles, which we term Mag-seeding. In this study, we applied this Mag-seeding technique to bone tissue engineering using bone marrow stromal cells (BMSCs) and 3-D hydroxyapatite (HA) scaffolds. BMSCs were magnetically labeled with our original magnetite cationic liposomes (MCLs) having a positive surface charge to improve adsorption to cell surface. Magnetically labeled BMSCs were seeded onto a scaffold, and a 1-T magnet was placed under the scaffold. By using Mag-seeding, the cells were successfully seeded into the internal space of scaffolds with a high cell density. The cell seeding efficiency into HA scaffolds by Mag-seeding was approximately threefold larger than that by static-seeding (conventional method, without a magnet). After a 14-d cultivation period using the osteogenic induction medium by Mag-seeding, the level of two representative osteogenic markers (alkaline phosphatase and osteocalcin) were significantly higher than those by static-seeding. These results indicated that Mag-seeding of BMSCs into HA scaffolds is an effective approach to bone tissue engineering.

Concepts of scaffold-based tissue engineering--the rationale to use solid free-form fabrication techniques

A paradigm shift is taking place in orthopaedic and reconstructive surgery from using medical devices and tissue grafts to a tissue engineering approach that uses biodegradable scaffolds combined with cells or biological molecules to repair and/or regenerate tissues. One of the potential benefits offered by solid free-form fabrication technology (SFF) is the ability to create scaffolds with highly reproducible architecture and compositional variation across the entire scaffold, due to its tightly controlled computer-driven fabrication. In this review, we define scaffold properties and attempt to provide some broad criteria and constraints for scaffold design in bone engineering.We also discuss the application-specific modifications driven by surgeon's requirements in vitro and/or in vivo. Next, we review the current use of SFF techniques in scaffold fabrication in the context of their clinical use in bone regeneration. Lastly, we comment on future developments in our groups, such as the functionalization of novel composite scaffolds with combinations of growth factors; and more specifically the promising area of heparan sulphate polysaccaride immobilization within the bone tissue engineering arena.

Effect of Collagen-I Modified Composites on Proliferation and Differentiation of Human Alveolar Osteoblasts

Collagen modification of scaffolds has been reported to promote matrix mineralization as an effective way to increase osseointegration of implants. The aim of this study was to investigate in vitro proliferation and differentiation of human alveolar osteoblasts (AOs) on medical-grade polycaprolactone–tricalcium phosphate (mPCL-TCP 80:20) scaffolds after collagen modification (mPCL-TCP-c) for 28 days. Collagen modification significantly increased the scaffold’s protein adsorption ability, and improved the initial seeding efficiency and cell attachment at day 1, compared with non-collagen-modified scaffolds. However, the total DNA content of both groups reached similar levels with no significant difference at 28 days’ culture. AOs were observed to spread along the collagen fibres and form extensive collagenous fibres with mineral nodules embedded, while multilayered cell sheets were formed in mPCL-TCP scaffolds. During culture, alkaline phosphatase (ALP) activity increased three- to five-fold in both groups, and collagen modification did not significantly affect either the metabolic rate or ALP activity kinetics of AOs. During osteogenic differentiation, similar gene expression of collagen type-I, osterix, osteopontin, and osteocalcin were detected in both groups. The mPCL-TCP group showed better organized mineralized tissue, but the mPCL-TCP-c showed more scattered and unorganized tissue. These results indicate that collagen modification improved the scaffold’s protein adsorption ability and encouraged initial cell attachment and distribution, but promoted fibrous-like tissue formation rather than mineralized tissue.