Influence of nanofibers on the growth and osteogenic differentiation of stem cells: a comparison of biological collagen nanofibers and synthetic PLLA fibers

Three-Dimensional Modeling of the Structural Microenvironment in Post-Traumatic War Wounds

BACKGROUND:

The development of post-traumatic heterotopic ossification (HO) is a common, undesirable sequela in patients with high-energy (war-related) extremity injuries. While inflammatory and osteoinductive signaling pathways are known to be involved in the development and progression of post-traumatic HO, features of the structural microenvironment within which the ectopic bone begins to form remain poorly understood. Thus, increasing our knowledge of molecular and structural changes within the healing wound may help elucidate the pathogenesis of post-traumatic HO and aid in the development of specific treatment and/or prevention strategies.

METHODS:

In this study, we performed high-resolution microscopy and biochemical analysis of tissues obtained from traumatic war wounds to characterize changes in the structural microenvironment. In addition, using an electrospinning approach, we modeled this microenvironment to reconstitute a three-dimensional type I collagen scaffold with non-woven, randomly oriented nanofibers where we evaluated the performance of primary mesenchymal progenitor cells.

RESULTS:

We found that traumatic war wounds are characterized by a disorganized, densely fibrotic collagen I matrix that influences progenitor cells adhesion, proliferation and osteogenic differentiation potential.

CONCLUSION:

Altogether, these results suggest that the structural microenvironment present in traumatic war wounds has the potential to contribute to the development of post-traumatic HO. Our findings may support novel treatment strategies directed towards modifying the structural microenvironment after traumatic injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-021-00355-y.

Donepezil hydrochloride as a novel inducer for osteogenic differentiation of mesenchymal stem cells on PLLA scaffolds in vitro

Over the past decades, bone defects caused by illness or trauma have been the most common traumatic injuries in humans and treatment of orthopedic infections has always been a serious challenge to experts in the world. In this project, poly L-lactic acid (PLLA) nanofibrous scaffolds were synthesized as a nontoxic, eco-friendly, and cost-effective scaffold by the electrospinning technique. Then, the impact of PLLA on the cell proliferation and osteogenic differentiation of human mesenchymal stem cells (hMSCs) was assayed in the presence and absence of donepezil hydrochloride (DH) which was prescribed in patients with Alzheimer's disease. Also, hMSCs were seeded on PLLA scaffold in the presence (PLLA-DH) and absence of 1 μg mL^-1 of DH under osteogenic induction media. Osteogenic differentiation of hMSCs was assessed by specific bone-related tests including alkaline phosphatase (ALP) activity, Alizarin red and von Kossa staining, calcium content assay. Also, Osteocalcin and osteopontin were evaluated as osteogenic proteins as well as ALP, osteonectin, osteocalcin, collagen type I (Col-I) and Runx2 as osteogenic genes via immunocytochemistry (ICC) and Real-time PCR analyses. The obtained data showed the higher ALP enzyme activity and biomineralization, more intensity during von Kossa staining as well as the increase in the expression rate of osteogenic related gene and protein markers in differentiated hMSCs on PLLA-DH. In conclusion, the present study revealed that the combination of PLLA scaffold with DH provides a scope to develop a suitable matrix in bone tissue engineering applications.

Direct incorporation of mesenchymal stem cells into a Nanofiber scaffold - in vitro and in vivo analysis

Bony defects are a common problem in musculoskeletal surgery. Replacement with autologous bone grafts is limited by availability of transplant material. Sterilized cancellous bone, while being osteoconductive, has limited osteoinductivity. Nanofiber scaffolds are currently used for several purposes due to their capability of imitating the extracellular matrix. Furthermore, they allow modification to provide functional properties. Previously we showed that electrospun nanofiber scaffolds can be used for bone tissue regeneration. While aiming to use the osteoinductive capacities of collagen type-I nanofibers we saw reduced scaffold pore sizes that limited cellular migration and thus colonization of the scaffolds. Aim of the present study was the incorporation of mesenchymal stem cells into the electrospinning process of a nanofiber scaffold to produce cell-seeded nanofiber scaffolds for bone replacement. After construction of a suitable spinning apparatus for simultaneous electrospinning and spraying with independently controllable spinning and spraying devices and extensive optimization of the spinning process, in vitro and in vivo evaluation of the resulting scaffolds was conducted. Stem cells isolated from rat femora were incorporated into PLLA (poly-l-lactide acid) and PLLA-collagen type-I nanofiber scaffolds (PLLA Col I Blend) via simultaneous electrospinning and -spraying. Metabolic activity, proliferation and osteoblastic differentiation were assessed in vitro. For in vivo evaluation scaffolds were implanted into critical size defects of the rat scull. After 4 weeks, animals were sacrificed and bone healing was analyzed using CT-scans, histological, immunhistochemical and fluorescence evaluation. Successful integration of mesenchymal stem cells into the scaffolds was achieved by iteration of spinning and spraying conditions regarding polymer solvent, spinning distance, the use of a liquid counter-electrode, electrode voltage and spinning duration. In vivo formation of bone tissue was achieved. Using a PLLA scaffold, comparable results for the cell-free and cell-seeded scaffolds were found, while the cell-seeded PLLA-collagen scaffolds showed significantly better bone formation when compared to the cell-free PLLA-collagen scaffolds. These results provide support for the future use of cell-seeded nanofiber scaffolds for large bony defects.

Fabrication and Plasma Modification of Nanofibrous Tissue Engineering Scaffolds

This paper provides a comprehensive overview of nanofibrous structures for tissue engineering purposes and the role of non-thermal plasma technology (NTP) within this field. Special attention is first given to nanofiber fabrication strategies, including thermally-induced phase separation, molecular self-assembly, and electrospinning, highlighting their strengths, weaknesses, and potentials. The review then continues to discuss the biodegradable polyesters typically employed for nanofiber fabrication, while the primary focus lies on their applicability and limitations. From thereon, the reader is introduced to the concept of NTP and its application in plasma-assisted surface modification of nanofibrous scaffolds. The final part of the review discusses the available literature on NTP-modified nanofibers looking at the impact of plasma activation and polymerization treatments on nanofiber wettability, surface chemistry, cell adhesion/proliferation and protein grafting. As such, this review provides a complete introduction into NTP-modified nanofibers, while aiming to address the current unexplored potentials left within the field.

Poly-l/dl-lactic acid films functionalized with collagen IV as carrier substrata for corneal epithelial stem cells

Limbal epithelial stem cells (LESCs) are responsible for the renewal of corneal epithelium. Cultivated limbal epithelial transplantation is the current treatment of choice for restoring the loss or dysfunction of LESCs. To perform this procedure, a substratum is necessary for in vitro culturing of limbal epithelial cells and their subsequent transplantation onto the ocular surface. In this work, we evaluated poly-L/DL-lactic acid 70:30 (PLA) films functionalized with type IV collagen (col IV) as potential in vitro carrier substrata for LESCs. We first demonstrated that PLA-col IV films were biocompatible and suitable for the proliferation of human corneal epithelial cells. Subsequently, limbal epithelial cell suspensions, isolated from human limbal rings, were cultivated using culture medium that did not contain animal components. The cells adhered significantly faster to PLA-col IV films than to tissue culture plastic (TCP). The mRNA expression levels for the LESC specific markers, K15, P63α and ABCG2 were similar or greater (significantly in the case of K15) in limbal epithelial cells cultured on PLA-col IV films than limbal epithelial cells cultured on TCP. The percentage of cells expressing the corneal (K3, K12) and the LESC (P63α, ABCG2) specific markers was similar for both substrata. These results suggest that the PLA-col IV films promoted LESC attachment and helped to maintain their undifferentiated stem cell phenotype. Consequently, these substrata offer an alternative for the transplantation of limbal cells onto the ocular surface.

Tissue engineering; strategies, tissues, and biomaterials

Current tissue regenerative strategies rely mainly on tissue repair by transplantation of the synthetic/natural implants. However, limitations of the existing strategies have increased the demand for tissue engineering approaches. Appropriate cell source, effective cell modification, and proper supportive matrices are three bases of tissue engineering. Selection of appropriate methods for cell stimulation, scaffold synthesis, and tissue transplantation play a definitive role in successful tissue engineering. Although the variety of the players are available, but proper combination and functional synergism determine the practical efficacy. Hence, in this review, a comprehensive view of tissue engineering and its different aspects are investigated.

The performance of bone tissue engineering scaffolds in in vivo animal models: A systematic review

Bone tissue engineering is an excellent alternative for the regeneration of large bone defects caused by trauma or bone pathologies. Scaffolds, stem cells, and bioactive molecules are the three key components of bone regeneration. Although a wide range of biomaterials of various compositions and structures has been proposed in the literature, these materials are rarely used in clinical applications. Therefore, more standardized studies are required to design scaffolds that enable better bone regeneration and are suitable for clinical use. The aim of this systematic review was to compare the performance of scaffolds used in preclinical animal studies to determine which class of materials has achieved a higher rate of bone neoformation (osteoinduction and osteoconduction). The selected studies were divided into three groups according to the following experimental models: studies that used subcutaneous models, bone defects in calvaria, and bone defects in long bones. Despite the large number of parameters in the included studies, we generally concluded that biomaterials containing calcium phosphates had important osteoinductive effects and were essential for better performance of the materials. Furthermore, natural polymers generally had better performance than synthetic polymers did, especially when the materials were associated with stem cells. The combination of materials from different classes was the most promising strategy for bone tissue regeneration.

Hybrid Membranes of PLLA/Collagen for Bone Tissue Engineering: A Comparative Study of Scaffold Production Techniques for Optimal Mechanical Properties and Osteoinduction Ability

Synthetic and natural polymer association is a promising tool in tissue engineering. The aim of this study was to compare five methodologies for producing hybrid scaffolds for cell culture using poly-l-lactide (PLLA) and collagen: functionalization of PLLA electrospun by (1) dialkylamine and collagen immobilization with glutaraldehyde and by (2) hydrolysis and collagen immobilization with carbodiimide chemistry; (3) co-electrospinning of PLLA/chloroform and collagen/hexafluoropropanol (HFP) solutions; (4) co-electrospinning of PLLA/chloroform and collagen/acetic acid solutions and (5) electrospinning of a co-solution of PLLA and collagen using HFP. These materials were evaluated based on their morphology, mechanical properties, ability to induce cell proliferation and alkaline phosphatase activity upon submission of mesenchymal stem cells to basal or osteoblastic differentiation medium (ODM). Methods (1) and (2) resulted in a decrease in mechanical properties, whereas methods (3), (4) and (5) resulted in materials of higher tensile strength and osteogenic differentiation. Materials yielded by methods (2), (3) and (5) promoted osteoinduction even in the absence of ODM. The results indicate that the scaffold based on the PLLA/collagen blend exhibited optimal mechanical properties and the highest capacity for osteodifferentiation and was the best choice for collagen incorporation into PLLA in bone repair applications.

Influence of cyclical mechanical loading on osteogenic markers in an osteoblast-fibroblast co-culture in vitro: tendon-to-bone interface in anterior cruciate ligament reconstruction

PURPOSE

We aimed to evaluate the influence of cyclical mechanical loading on osteoblasts and fibroblasts, and co-cultures of both in vitro, simulating the conditions of the tendon-to-bone interface in anterior cruciate ligament reconstruction.

METHODS

Osteoblast-like cells (OBL) and tendon-derived rodent fibroblasts (TDF) were cultured alone or in co-culture to simulate the tendon-to-bone interface. Cyclical loading was applied for one hour twice a day for three days, with a frequency of 1 Hz and 3 % strain. Alkaline phosphatase (AP), osteocalcin (OC), collagen type 1 (COL1A1), and bone morphogenetic protein 2 (BMP-2) gene expression and protein deposition were detected by real-time polymerase chain reaction (qPCR) and immunocytochemical analysis.

RESULTS

Mechanical loading significantly decreased AP, OC, and COL1A1 gene expression in both OBL and TDF, compared to non-loaded culture. However, mechanical load increased gene expression of the same marker genes including BMP-2 during co-culture. Immunocytochemistry demonstrated increased deposition of corresponding proteins in the same range, independent of culture conditions. Higher depositions of BMP-2 were shown under loading conditions for osteoblast and TDF monocultures. Prolongation of mechanical loading resulted in cell detachment and spheroid formation.

CONCLUSION

Cyclical mechanical loading caused downregulation of genes involved in osteointegration and osteoinduction, such as OC, ALP, and COL1A1 in monocultures of osteoblasts and fibroblasts; co-cultures lacked this phenomenon. Immunocytochemistry and qPCR analysis showed slight upregulations of marker genes and corresponding proteins. This might be due to the potential stabilising effects of osteoblast-fibroblast cross talk in the co-culture environment, simulating fibrocartilage formation at the tendon-to-bone interface.

The activation of satellite cells by nanofibrous poly ε-caprolacton constructs

Nanoscale patterning of scaffolds provides broad surface for adhesion and differentiation of stem cells. As we know, the combination of tissue engineering with stem cells technology hold the key for regeneration of damaged tissues for example skeletal muscle tissues. On the other hand, the mechanical assessments of poly ε-caprolacton nanofibers determined the required features of biomedical scaffold for skeletal muscle tissue. In this study, skeletal muscle satellite cells as the main group of stem cells were cultivated on the electrospun poly ε-caprolacton nanofibers. Our results indicated that in comparison with tissue culture polystyrene, the nanoscale of scaffolds provided more induction to matured cells of skeletal muscle. Moreover, the immobilization of cells by collagen on poly ε-caprolacton nanofibers significantly improved the differential potency of satellite cells.

The guidance of stem cell differentiation by substrate alignment and mechanical stimulation

Mesenchymal stem cells (MSC) represent a promising and clinically relevant cell source for tissue engineering applications. As such, guiding MSCs toward specific lineages and maintaining these phenotypes have been particularly challenging as the contributions of mechanical, chemical and structural cues to the complex differentiation process are largely unknown. To fully harness the potential of MSCs for regenerative medicine, a systematic investigation into the individual and combined effects of these stimuli is needed. In addition, unlike chemical stimulation, for which temporal and concentration gradients are difficult to control, mechanical stimulation and scaffold-based cues may be relatively more biomimetic and can be applied with greater control to ensure fidelity in MSC differentiation. The objective of this study is to investigate the role of nanofiber matrix alignment and mechanical stimulation on MSC differentiation, focusing on elucidating the relative contribution of each parameter in guided regeneration of functional connective tissues. It is observed that nanofiber alignment directs MSC response to physiological loading and that fibroblastic differentiation requires a combination of physiologically-relevant cell-material interactions in conjunction with mechanical stimulation. Importantly, the results of this study reveal that systemic and readily controllable cues, such as scaffold alignment and optimized mechanical stimulation, are sufficient to drive MSC differentiation, without the need for additional chemical stimuli. Moreover, these findings yield a set of fundamental design rules that can be readily applied to connective tissue regeneration strategies.

Functionalisation of PLLA nanofiber scaffolds using a possible cooperative effect between collagen type I and BMP-2: impact on colonization and bone formation in vivo

The reconstruction of large bone defects after injury or tumor resection often requires the use of bone substitution. Artificial scaffolds based on synthetic biomaterials can overcome disadvantages of autologous bone grafts, like limited availability and donor side morbidity. Among them, scaffolds based on nanofibers offer great advantages. They mimic the extracellular matrix, can be used as a carrier for growth factors and allow the differentiation of human mesenchymal stem cells. Differentiation is triggered by a series of signaling processes, including integrin and bone morphogenetic protein (BMP), which act in a cooperative manner. The aim of this study was to analyze whether these processes can be remodeled in artificial poly-(l)-lactide acid (PLLA) based nanofiber scaffolds in vivo. Electrospun matrices composed of PLLA-collagen type I or BMP-2 incorporated PLLA-collagen type I were implanted in calvarial critical size defects in rats. Cranial CT-scans were taken 4, 8 and 12 weeks after implantation. Specimens obtained after euthanasia were processed for histology and immunostainings on osteocalcin, BMP-2 and Smad5. After implantation the scaffolds were inhomogeneously colonized and cells were only present in wrinkle- or channel-like structures. Ossification was detected only in focal areas of the scaffold. This was independent of whether BMP-2 was incorporated in the scaffold. However, cells that migrated into the scaffold showed an increased ratio of osteocalcin and Smad5 positive cells compared to empty defects. Furthermore, in case of BMP-2 incorporated PLLA-collagen type I scaffolds, 4 weeks after implantation approximately 40 % of the cells stained positive for BMP-2 indicating an autocrine process of the ingrown cells. These findings indicate that a cooperative effect between BMP-2 and collagen type I can be transferred to PLLA nanofibers and furthermore, that this effect is active in vivo. However, this had no effect on bone formation. The reason for this seems to be an unbalanced colonization of the scaffolds with cells, due to insufficient pore size.

Nanomaterial scaffolds for stem cell proliferation and differentiation in tissue engineering

Tissue engineering is a clinically driven field and has emerged as a potential alternative to organ transplantation. The cornerstone of successful tissue engineering rests upon two essential elements: cells and scaffolds. Recently, it was found that stem cells have unique capabilities of self-renewal and multilineage differentiation to serve as a versatile cell source, while nanomaterials have lately emerged as promising candidates in producing scaffolds able to better mimic the nanostructure in natural extracellular matrix and to efficiently replace defective tissues. This article, therefore, reviews the key developments in tissue engineering, where the combination of stem cells and nanomaterial scaffolds has been utilized over the past several years. We consider the high potential, as well as the main issues related to the application of stem cells and nanomaterial scaffolds for a range of tissues including bone, cartilage, nerve, liver, eye etc. Promising in vitro results such as efficient attachment, proliferation and differentiation of stem cells have been compiled in a series of examples involving different nanomaterials. Furthermore, the merits of the marriage of stem cells and nanomaterial scaffolds are also demonstrated in vivo, providing early successes to support subsequent clinical investigations. This progress simultaneously drives mechanistic research into the mechanotransduction process responsible for the observations in order to optimize the process further. Current understanding is chiefly reported to involve the interaction of stem cells and the anchoring nanomaterial scaffolds by activating various signaling pathways. Substrate surface characteristics and scaffold bulk properties are also reported to influence not only short term stem cell adhesion, spreading and proliferation, but also longer term lineage differentiation, functionalization and viability. It is expected that the combination of stem cells and nanomaterials will develop into an important tool in tissue engineering for the innovative treatment of many diseases.

Cell adhesion and proliferation enhancement by gelatin nanofiber scaffolds

Gelatin nanofibers (GNs) prepared by electrospinning were cross-linked with glutaraldehyde vapor to improve their water-resistant ability. After cross-linking treatment, the form of the fibers expressed no substantial change, but the average diameter of the fibers increased with increasing cross-linking time. The swelling induced by the moisture during the cross-linking process was moderated when the cross-linking time reached 45 min. The contact angle measurements confirmed that the electrospun gelatin fibers were more hydrophilic than the gelatin film (GF). Increasing the cross-linking time did not alter the hydrophilic properties of the gelatin fibers. The cell compatibility was evaluated based on 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay, scanning electron microscope and confocal microscope observations, and Western blot analysis by culturing MG-63 cells on the GFs and GNs. The nanofibrous structure fabricated by an electrospinning technique was found to enhance cell adhesion and proliferation. This process is a cost-effective simulation of GN structures’ promising applications on scaffold preparation for tissue engineering.

Electrospun PLLA nanofiber scaffolds and their use in combination with BMP-2 for reconstruction of bone defects

INTRODUCTION

Adequate migration and differentiation of mesenchymal stem cells is essential for regeneration of large bone defects. To achieve this, modern graft materials are becoming increasingly important. Among them, electrospun nanofiber scaffolds are a promising approach, because of their high physical porosity and potential to mimic the extracellular matrix (ECM).

MATERIALS AND METHODS

The objective of the present study was to examine the impact of electrospun PLLA nanofiber scaffolds on bone formation in vivo, using a critical size rat calvarial defect model. In addition we analyzed whether direct incorporation of bone morphogenetic protein 2 (BMP-2) into nanofibers could enhance the osteoinductivity of the scaffolds. Two critical size calvarial defects (5 mm) were created in the parietal bones of adult male Sprague-Dawley rats. Defects were either (1) left unfilled, or treated with (2) bovine spongiosa, (3) PLLA scaffolds alone or (4) PLLA/BMP-2 scaffolds. Cranial CT-scans were taken at fixed intervals in vivo. Specimens obtained after euthanasia were processed for histology, histomorphometry and immunostaining (Osteocalcin, BMP-2 and Smad5).

RESULTS

PLLA scaffolds were well colonized with cells after implantation, but only showed marginal ossification. PLLA/BMP-2 scaffolds showed much better bone regeneration and several ossification foci were observed throughout the defect. PLLA/BMP-2 scaffolds also stimulated significantly faster bone regeneration during the first eight weeks compared to bovine spongiosa. However, no significant differences between these two scaffolds could be observed after twelve weeks. Expression of osteogenic marker proteins in PLLA/BMP-2 scaffolds continuously increased throughout the observation period. After twelve weeks osteocalcin, BMP-2 and Smad5 were all significantly higher in the PLLA/BMP-2 group than in all other groups.

CONCLUSION

Electrospun PLLA nanofibers facilitate colonization of bone defects, while their use in combination with BMP-2 also increases bone regeneration in vivo and thus combines osteoconductivity of the scaffold with the ability to maintain an adequate osteogenic stimulus.

Functionalisation of PLLA nanofiber scaffolds using a possible cooperative effect between collagen type I and BMP-2: impact on growth and osteogenic differentiation of human mesenchymal stem cells

Mesenchymal stem cell differentiation of osteoblasts is triggered by a series of signaling processes including integrin and bone morphogenetic protein (BMP), which therefore act in a cooperative manner. The aim of this study was to analyze whether these processes can be remodeled in an artificial poly-(L)-lactide acid (PLLA) based nanofiber scaffold. Matrices composed of PLLA-collagen type I or BMP-2 incorporated PLLA-collagen type I were seeded with human mesenchymal stem cells (hMSC) and cultivated over a period of 22 days, either under growth or osteoinductive conditions. During the course of culture, gene expression of alkaline phosphatase (ALP), osteocalcin (OC) and collagen I (COL-I) as well as Smad5 and focal adhesion kinase (FAK), two signal transduction molecules involved in BMP-2 or integrin signaling were analyzed. Furthermore, calcium and collagen I deposition, as well as cell densities and proliferation, were determined using fluorescence microscopy. The incorporation of BMP-2 into PLLA-collagen type I nanofibers resulted in a decrease in diameter as well as pore sizes of the scaffold. Mesenchymal stem cells showed better adherence and a reduced proliferation on BMP-containing scaffolds. This was accompanied by an increase in gene expression of ALP, OC and COL-I. Furthermore the presence of BMP-2 resulted in an upregulation of FAK, while collagen had an impact on the gene expression of Smad5. Therefore these different strategies can be combined in order to enhance the osteoblast differentiation of hMSC on PLLA based nanofiber scaffold. By doing this, different signal transduction pathways seem to be up regulated.

RGD-functionalisation of PLLA nanofibers by surface coupling using plasma treatment: influence on stem cell differentiation

The aim of this study was to functionalize the surface of synthetic poly-(l-lactic) (PLLA) nanofibers with RGD peptide, in order to promote growth and osteogenic differentiation of human mesenchymal stem cells (hMSC) in vitro. The cRGD was coupled onto PLLA nanofibers using oxygen plasma combined with EDC/sulfo-NHS activation. Matrices were seeded with hMSC and cultivated over a period of 22 days under growth conditions and analyzed during the course of cultivation. The plasma activation of PLLA nanofibers resulted in a reduction of hydrophobicity as well as a formation of carboxyl groups on the surface of the fibers. Furthermore, maximum load, but not young's modulus was influenced by the treatment with oxygen plasma. When hMSC were cultured onto the cRGD functionalized scaffolds, cells showed no increased proliferation or cell density but an induction of genes associated with the osteoblast lineage. In brief, this study indicates that functional peptides of the extracellular matrix can be coupled onto PLLA nanofibers using plasma treatment in combination with EDC/sulfo-NHS treatment. These groups are accessible for the growing cell and mediate probably some osteoinductive properties of collagen nanofibers.

Influence of nanofibers on growth and gene expression of human tendon derived fibroblast

Background

Rotator cuff tears are a common and frequent lesion especially in older patients. The mechanisms of tendon repair are not fully understood. Common therapy options for tendon repair include mini-open or arthroscopic surgery. The use of growth factors in experimental studies is mentioned in the literature. Nanofiber scaffolds, which provide several criteria for the healing process, might be a suitable therapy option for operative treatment. The aim of this study was to explore the effects of nanofiber scaffolds on human tendon derived fibroblasts (TDF's), as well as the gene expression and matrix deposition of these fibroblasts.

Methods

Nanofibers composed of PLLA and PLLA/Col-I were seeded with human tendon derived fibroblasts and cultivated over a period of 22 days under growth-inductive conditions, and analyzed during the course of culture, with respect to gene expression of different extra cellular matrix components such as collagens, bigylcan and decorin. Furthermore, we measured cell densities and proliferation by using fluorescene microscopy.

Results

PLLA nanofibers possessed a growth inhibitory effect on TDF's. Furthermore, no meaningful influence on the gene expression of collagen I, collagen III and decorin could be observed, while the expression of collagen X increased during the course of cultivation. On the other hand, PLLA/Col-I blend nanofibers had no negative influence on the growth of TDF's. Furthermore, blending PLLA nanofibers with collagen had a positive effect on the gene expression of collagen I, III, X and decorin. Here, gene expression indicated that focal adherence kinases might be involved.

Conclusion

This study indicates that the use of nanofibers influence expression of genes associated with the extra cellular matrix formation. The composition of the nanofibers plays a critical role. While PLLA/Col-I blend nanofibers enhance the collagen I and III formation, their expression on PLLA nanofibers was more comparable to controls. However, irrespective of the chemical composition of the fibres, the collagen deposition was altered, an effect which might be associated with a decreased expression of biglycanes.

Effect of direct RGD incorporation in PLLA nanofibers on growth and osteogenic differentiation of human mesenchymal stem cells

The aim of this study was to functionalize synthetic poly-(L-lactic) (PLLA) nanofibers by direct incorporation of cRGD, in order to promote adhesion, growth and osteogenic differentiation of human mesenchymal stem cells (hMSC) in vitro. The cRGD was incorporated into PLLA nanofibers either by emulsion [PLLA-cRGD (d)] or suspension [PLLA-cRGD (s)]. Matrices were seeded with hMSC and cultivated over a period of 28 days under growth conditions and analyzed during the course. Although the mode of incorporation resulted in different distributions of the RGD peptide, it had no impact on the fiber characteristics when compared to corresponding unblended PLLA control fibers. However, hMSC showed better adherence on PLLA-cRGD (d). Nevertheless, this advantage was not reflected during the course of cultivation. Furthermore, the PLLA-cRGD (s) fibers mediated the osteogenic potential of collagen (determined as the expression and deposition of collagen and osteocalcin) to some extent. Further studies are needed in order to optimize the RGD distribution and concentration.