Activation of osteoblast-like MC3T3-E1 cell responses by poly(lactide)

Differentiation behavior of iPS cells cultured on PLGA with osteoinduction medium

In the present report, we have generated osteoblast-like cells derived from mouse induced-pluripotent stem (iPS) cells on PLGA with osteoinduction medium in vitro and in vivo. The cell culture period was 2 weeks. At 2 weeks, mRNA level of type I collagen was significantly higher than at 1 week. Osteocalcin mRNA level at 2 weeks was tendency to increase compared with at 1 week. And the cells cultured on PLGA were positive for immunofluorescent staining of osteocalcin and alizarin red S staining. The scaffold and osteogenic-like cells induced in vitro were implanted subcutaneously into SCID mice. In resected teratoma, hard tissues resembling bone were observed mixed with other tissues on the scaffold. The sum of these findings suggests that PLGA does not disturb the osteogenesis of iPS cells.

Mechanical and biological properties of photocurable oligolactide-HA composites investigated under accelerated degradation

The major concern related to biodegradable bone substitute materials is the loss of mechanical strength which can be undesirable when occurring too quickly before new bone formation. In this study, the multifunctional lactide oligomers having 2, 3, and 4 arms end capped with methacrylate groups were synthesized with the aim of improving the degradation properties. Their composites with hydroxyapatite (HA) were photopolymerized and subjected to accelerated degradation at 60 °C. The results showed that increasing number of arms significantly improved thermal and mechanical properties as well as biocompatibility of the composites. All composites although varying in number of arms had similar levels of bone-specific gene expression and calcification indicating their equal bioactivity in supporting bone formation. The high HA content in the composites was proposed to be responsible for enhanced osteoblast response, and this tended to suppress the effects of polymeric structure.

Significance of nano- and microtopography for cell-surface interactions in orthopaedic implants

Cell-surface interactions play a crucial role for biomaterial application in orthopaedics. It is evident that not only the chemical composition of solid substances influence cellular adherence, migration, proliferation and differentiation but also the surface topography of a biomaterial. The progressive application of nanostructured surfaces in medicine has gained increasing interest to improve the cytocompatibility and osteointegration of orthopaedic implants. Therefore, the understanding of cell-surface interactions is of major interest for these substances. In this review, we elucidate the principle mechanisms of nano- and microscale cell-surface interactions in vitro for different cell types onto typical orthopaedic biomaterials such as titanium (Ti), cobalt-chrome-molybdenum (CoCrMo) alloys, stainless steel (SS), as well as synthetic polymers (UHMWPE, XLPE, PEEK, PLLA). In addition, effects of nano- and microscaled particles and their significance in orthopaedics were reviewed. The significance for the cytocompatibility of nanobiomaterials is discussed critically.

Pre-osteoblasts on poly(L-lactic acid) and silicon oxide: Influence of fibronectin and albumin adsorption

Cell adhesion and subsequent viability are critical initial steps in biomaterial-tissue integration and are strongly dependent on the material properties and the presence of matrix proteins. In the present study MC3T3-E1 osteoblast-like cell behavior on silicon oxide (SO) and poly(L-lactic acid) (PLLA) substrates has been examined, with a focus on the influence of the adhesive protein fibronectin and the non-adhesive protein albumin adsorbed on the substrates. Quartz crystal microgravimetry showed adsorption of fibronectin and albumin to be nearly identical on SO and PLLA. Subsequent exposure a previously adsorbed fibronectin layer to albumin decreased the rigidity of the adsorbed layer without any measurable increase in adsorbed mass. Cell adhesion and spreading were significantly enhanced on both SO and PLLA substrates coated with fibronectin or with fibronectin and albumin, compared with uncoated or albumin-coated substrates. The only statistically significant difference between the two substrates in these assays was increased spreading on PLLA compared with SO in the presence of fibronectin and albumin. Cell proliferation was significantly higher on SO compared with PLLA after 7 days culture, but depended on the presence of fibronectin only in the PLLA system. In contrast, mitochondrial activity was higher on PLLA than on SO, and was enhanced by fibronectin on both substrates. PLLA substrates coated with fibronectin and subsequently exposed to albumin exhibited the highest level of cell differentiation, as assayed via alkaline phosphatase activity. These results demonstrate the importance of adsorbed proteins on osteoblast-like cell-surface interactions.

Release kinetics of polymer-bound bone morphogenetic protein-2 and its effects on the osteogenic expression of MC3T3-E1 osteoprecursor cells

BACKGROUND

In an effort to augment scaffold performance, additives such as growth factors are under investigation for their ability to optimize the "osteopotential" of synthetic polymer scaffolds. In parallel research, bone morphogenetic protein-2 (BMP-2), a growth factor that initiates bone formation, has been locally delivered to augment fracture healing and spinal fusion. The authors hypothesize that BMP-2 can be covalently bound to a polymer substrate, increasing its concentration and bioavailability over longer periods, thus improving the efficacy of the growth factor and subsequently the bony matrix production. It would remain bound longer when compared with published controls. This prolonged binding would then increase the bioavailability of the growth factor and thus increase bony matrix production over a longer interval.

METHODS

Mouse preosteoblast MC3T3-E1 cells were cultured on poly(lactic-co-glycolic acid) and polycaprolactone polymer disks covalently bound with BMP-2 to assess the progression and quality of osteogenesis. Covalent binding of BMP-2 to each polymer was visualized by immunohistochemical analysis of polymer-coated microscope slides. The quantity of covalently bound BMP-2 was determined using enzyme-linked immunosorbent assay.

RESULTS

Polymerase chain reaction results showed elevated expression levels for alkaline phosphatase and osteocalcin genes. BMP-2 was released from polycaprolactone over 2 weeks, with 86 percent remaining covalently bound, in contrast to 93 percent retained by poly(lactic-co-glycolic acid).

CONCLUSIONS

BMP-2, proven to alter polymer osteogenicity, remained bound to poly(lactic-co-glycolic acid), which may render poly(lactic-co-glycolic acid) an ideal choice as a polymer for scaffold-based bone tissue engineering using growth factor delivery.

Functionalization of poly(L-lactide) nanofibrous scaffolds with bioactive collagen molecules

The utilization of electrospun biodegradable scaffolds by fine-tuning their biofunctionalities through a simple mixing method was demonstrated in this study. Poly(L-lactide) (PLLA)-based scaffolds containing small amounts of bioactive collagen type I molecules were investigated for enhancements in cellular behavior. Electron microscopy revealed no topological alterations of the fibers in the collagen/PLLA scaffolds when compared with pure PLLA scaffolds. Cell attachment after 24 h was robust on collagen/PLLA scaffolds, with cytoskeletal analysis showing that the attached cells were aligned along the fibers assuming a spindle-shape appearance. Despite these morphological differences, gene expression analyses revealed no apparent alterations in mRNA levels of four genes involved in cell attachment across the various scaffolds. Although cell proliferation was not adversely affected, there were clear differences in cell penetration; after 1 week, cells migrated through 32 and 85% of PLLA and collagen/PLLA scaffolds, respectively. Mineralization of primary calvaria osteoblasts provided further evidence that collagen-containing electrospun PLLA scaffolds could sustain cell differentiation. Overall, the inclusion of collagen type I in even miniscule amounts (<1 wt %) within electrospun PLLA scaffolds could effectively modulate certain aspects of cellular behavior.

In vitro evaluation of poly[bis(ethyl alanato)phosphazene] as a scaffold for bone tissue engineering

Polyphosphazenes with amino acid ester as side groups are biocompatible polymers that could provide valid scaffolds for cell growth. In the present study we investigate the adhesion and growth of osteoblasts obtained from rat bone marrow on matrices composed of thin fibers of poly[bis(ethyl alanato)phosphazene] (PAlaP), poly(d,l-lactic acid) (PDLLA), or PAlaP/PDLLA blend. Our data show that scaffolds of PAlaP or PAlaP/PDLLA blend enhanced the cell adhesion and growth in comparison with that observed in cultures seeded on polystyrene tissue culture plates. Although collagenase-digestible protein synthesis remained unchanged, all scaffolds induced a decrease in alkaline phosphatase activity, suggesting that osteoblasts are in the proliferation phase. Both PAlaP and PAlaP blended with PDLLA may represent a new and interesting substrate for bone tissue engineering.

Influence of Molecular Weight and Crystallinity of Poly(L-Lactic Acid) on the Adhesion and Proliferation of Human Osteoblast Like Cells

The molecular weight and crystallinity of systems based on poly(L-lactic acid) PLLA is an important issue as it can influence, besides the general physical properties of the polymer, the patterns of cell adhesion, proliferation and cell morphology. The objective of the present study was to evaluate how crystallinity and molecular weight of PLLA influence the referred parameters. Four conditions were tested: low molecular weight amorphous and semi-crystalline PLLA disks, and high molecular weight amorphous and semi-crystalline PLLA disks, obtained from hot press. The thermal properties of the studied materials were accessed by differential scanning calorimetry. For the cell culture studies a human osteosarcoma cell line (SaOS-2) was chosen. Disks were immersed in a cell suspension containing 5x104 cells/ml and kept in culture for periods up to two weeks. Cell viability and proliferation of SaOS-2 cells was assessed by MTS test and a total protein assay, respectively. The adhesion and morphology of SaOS-2 cells on PLLA disks was assessed by scanning electronic microscopy. Results showed that cell viability was not affected by the different tested conditions. However, cell proliferation was increased in the high molecular weight amorphous samples and cells seemed to have higher adhesion patterns on semi-crystalline samples. This is probably happening due to different rates of integrin interaction with the substrate leading to different patterns of focal adhesion points formation.

Regulation of Osteoblast Gene Expression and Phenotype by Polylactide-fatty Acid Surfaces

Cell function is influenced by surface structure and molecules. Molecules that enhance cellular differentiation can be applied to tissue scaffold surfaces to stimulate endogenous tissue regeneration. The application of this approach to bone implants yields surfaces coated with factors (proteins, peptides, etc...) that promote the differentiation of osteoblasts, the cells that make bone. Increased bone formation leads to increased healing and union of the implant with endogenous bone. To obtain better control over surface coating we developed PLLA copolymers with allyl (PLLA-co-DAG) and 3-hydroxypropyl (PLLA-co-HP) side chains to which we can attach functional groups. Given the potential of fatty acids being able to incorporate into lipid bilayers and/or influence gene expression, we grafted different fatty acid side chains to PLLA-co-HP by esterifying the corresponding fatty acids with the PLLA-co-HP 3-hydroxypropyl side chains. The effects of the polymer modifications on osteoblasts were then evaluated. While cellular morphology differed between surface coatings, they did not reflect changes in cellular phenotype. Changes in gene expression were most evident with arachidonate and 3-hydroxypropyl side-chains which exhibited osteoblast differentiating capabilities. Linoleate, myristate, oleate, and stearate ester side-chains did not have a significant influence on osteoblast phenotype. Growth characteristics of osteoblasts did not differ between the fatty acid copolymer films, although cells grown on PLLA-co-HP exhibited a trend toward increased growth. Taken together our findings demonstrate that surface fatty acid composition can impact osteoblast phenotype.

Combinatorial screening of cell proliferation on poly(l-lactic acid)/poly(d,l-lactic acid) blends

We have combined automated fluorescence microscopy with a combinatorial approach for creating polymer blend gradients to yield a rapid screening method for characterizing cell proliferation on polymer blends. A gradient in polymer blend composition of poly(L-lactic acid) (PLLA) and poly(D,L-lactic acid) (PDLLA) was created in the form of a strip-shaped film and was annealed to allow PLLA to crystallize. Fourier transform infrared (FTIR) microspectroscopy was used to determine the composition in the gradients and atomic force microscopy was used to characterize surface topography. Osteoblasts were cultured on the gradients and proliferation was assessed by automated counting of cells using fluorescence microscopy. Surface roughness varied with composition, was smooth on PDLLA-rich regions and was rough on the PLLA-rich regions. Cell adhesion was similar on all regions of the gradients while proliferation was faster on the smooth, PDLLA-rich end of the gradients than on the rough, PLLA-rich end of the gradients. These results demonstrate the feasibility of a new, combinatorial approach for evaluating cell proliferation on polymer blends.

Osteoblastic Phenotype Expression of MC3T3-E1 Cells Cultured on Polymer Surfaces

BACKGROUND

Current efforts in bone tissue engineering have as one focus the search for a scaffold material that will support osteoblast proliferation, matrix mineralization, and, ultimately, bone formation. The goal is to develop a bone substitute that is functionally equivalent to autograft bone. Previously published reports have shown that osteoblasts exhibit varying rates and degrees of proliferation and mineralization when grown on different surfaces.

METHODS

This study presents a histologic and biomolecular analysis of MC3T3-E1 murine preosteoblast cells grown on poly(lactide-co-glycolide) (PLGA) versus poly(-caprolactone) (PCL), two commonly studied scaffold polymers. MC3T3-E1 cells were cultured on slides coated with either PLGA or PCL, and on uncoated glass slides as control, with six slides in each group. After 6 weeks in culture, the cells were stained for osteocalcin, alkaline phosphatase activity, and matrix mineralization. In addition, to assess the effects of the surface material on phenotypic expression at the molecular level, MC3T3-E1 cells were cultured on polymer-coated 24-well plates for 4 days, and analyzed by reverse transcription polymerase chain reaction for the expression of osteocalcin and alkaline phosphatase.

RESULTS

The results showed that three groups of slides stained positively for osteocalcin at 6 weeks. However, markedly less alkaline phosphatase activity and mineralization were observed on the cells grown on PCL. Real-time polymerase chain reaction assays subsequently revealed decreased expression of both markers by cells cultured on PCL compared with PLGA.

CONCLUSIONS

These results suggest that PCL does not support the full expression of an osteoblastic phenotype by MC3T3-E1 cells. PCL, therefore, is less desirable as a scaffold polymer in bone tissue engineering in so far as supporting bone formation is concerned. However, because PCL has favorable handling characteristics and strength, modifications of PCL may prompt further investigation.

Interaction of cells withL-lactide/glycolide copolymers synthesized with the use of tin or zirconium compounds

Comparative studies have been carried out on the viability of cells culture and production of collagen on lactide/glycolide copolymers synthesized using zirconium or tin initiators. Cell response of various cell types: fibroblast-like cells, osteoblast-like cells, monocyte/macrophage-like cells has been examined. Cell response depends on the kind of cells and the initiator used during the synthesis of the polymer. In a number of cases the cells grown on materials containing zirconium have been reported to have better survival (for example, Saos2 cells). An enhanced collagen production on these copolymers has been also observed.

Biocompatibility and integrin-mediated adhesion of human osteoblasts to poly(DL-lactide-co-glycolide) copolymers

The biocompatibility of polylactic acid (PLA) and polyglycolic acid (PGA) copolymers, employed in manufacturing bone-graft substitutes, is affected by their chemical composition, molecular weight and cell environment, and by the methods of polymerization and processing. Their in vitro bioactivity on human osteoblasts has been investigated very little. We first evaluated the behavior of primary human osteoblasts cultured in close contact with 75:25 and 50:50 PLA-PGA copolymers for 14 days adopting a cell culture system that allowed us to evaluate the influence of direct contact, and of factors released from polymers. The copolymers had no negative influence on cell morphology, cell viability and proliferation. Alkaline phosphatase (ALP) activity and osteocalcin production were also not affected. The initial adhesion of osteoblasts on implant surfaces requires the contribution of integrins, acting as a primary mechanism regulating cell-extracellular matrix (ECM) interactions. We observed that adhesion of osteoblasts to PLA-PGA copolymers, 2h after plating, was reduced by approximately 70% by antibodies capable to block integrin beta(1) and alpha(5)beta(1) complex and only by approximately 30% by an anti-integrin alpha(v) antibody. Therefore, beta(1) integrins may represent a predominant adhesion receptor subfamily utilized by osteoblasts to adhere to PLA-PGA copolymers. These materials do not show any negative influence on cell proliferation and differentiation.

Enhancing effect of poly(L-lactide) on the differentiation of mouse osteoblast-like MC3T3-E1 cells

Poly(L-lactide) (PLLA) has bioabsorbability and biocompatibility, and it is used as biodegradable screws, pins and plates for internal bone fixation. The purpose of this study was to clarify the effects of low molecular weight (Mw) PLLA on the proliferation and differentiation of mouse osteoblast-like MC3T3-E1 cells. MC3T3-E1 cells were cultured with the concentration of 5-50 microg/ml of PLLA with weight average Mw of 5000 (PLLA-5k) and 10,000 (PLLA-10k) for 2 weeks using the micromass culture. Both PLLAs did not affect the proliferation of MC3T3-E1 cells. However, the calcifications of MC3T3-E1 cells were stimulated with increasing the concentration of the PLLAs. Then PLLA-5k increased the calcification of MC3T3-E1 cells more than PLLA-10k. Additionally, both PLLAs increased the alkaline phosphatase (ALP) activity and calcium content of MC3T3-E1 cells up to the similar level to the calcification. These results indicated that low Mw PLLA enhanced the differentiation of MC3T3-E1 cells with no effect on the proliferation. Moreover, it was suggested that the increase of the ALP activity was a key step to stimulate the calcification of MC3T3-E1 cells. The osteoconductivity of implanted PLLA would be based on the enhancing effect of low Mw PLLA on the differentiation of the osteoblasts.

IGF-I and TGF-beta 1 incorporated in a poly(D,L-lactide) implant coating stimulates osteoblast differentiation and collagen-1 production but reduces osteoblast proliferation in cell culture

Previous in vivo studies revealed a stimulating effect of locally applied IGF-I and TGF-beta1 released from poly(D,L-lactide)-coated titanium implants on rat and porcine fracture healing. The purpose of the present study was to evaluate the effect of IGF-I (5% w/w) and TGF-beta1 (1% w/w) and the carrier PDLLA on osteoblasts in cell culture to improve the understanding of these growth factors. The well-characterized human osteoblast cell line hFOB 1.19 was used in the study. The implants and cells were cocultured in a noncontact manner. The cells were incubated for 10 days in total, and the implants (n = 6 each group and time point) were added for 1 h, 12 h, 24 h, 2 d, 4 d, or 10 d. To analyze a possible effect of the growth factors or the coating, cell proliferation, metabolism, and differentiation were investigated. As an indicator for differentiation the production of collagen I was chosen. All experimental groups showed comparable cell vitality. No change in the pH of the medium was detectable between the analyzed groups. When the effect of the titanium implant and the PDLLA coating were compared with the control culture, no differences in proliferation, metabolic activity, and collagen I production were detectable. The osteoblasts treated with IGF-I and TGF-beta1 released from PDLLA revealed a significantly enhanced collagen I production with a decrease in proliferation and metabolic activity compared to the other groups. No significant differences in collagen I production were seen due to the incubation time points. None of the experimental groups evoked an immunological response on mouse macrophages. In conclusion, the PDLLA-carrier showed no negative effect on osteoblasts, whereas the incorporated growth factors stimulated osteoblast differentiation.

Effect of gamma-ray irradiated poly(L-lactide) on the differentiation of mouse osteoblast-like MC3T3-E1 cells

The purpose of this study was to clarify the effects of gamma-ray irradiated poly(L-lactide) (PLLA) on the proliferation and differentiation of mouse osteoblast-like MC3T3-E1 cells. The PLLA was y-irradiated at the dose of 10, 25 or 50 kGy, and the molecular weight of irradiated PLLA decreased with increasing irradiation dose. The proliferation and differentiation of MC3T3-E1 cells cultured on irradiated PLLA for 2 weeks were evaluated using micromass culture. The y-irradiation of PLLA did not affect the proliferation, but stimulated the differentiation of MC3T3-E1 cells cultured on irradiated PLLA. These results suggested that lower change in the molecular weight of PLLA was responsible for stimulation of the differentiation of MC3T3-E1 cells cultured on irradiated PLLA. Furthermore, the proliferation and calcification of MC3T3-E1 cells cultured in the medium containing low molecular weight PLLA for 2 weeks were evaluated. The low molecular weight PLLA also stimulated the calcification of MC3T3-E1 cells with no effect on the proliferation. The y-irradiation was suitable for PLLA on the differentiation of mouse osteoblasts.