Biomedical subjects

Antonios G Mikos

Publications and source records attributed to Antonios G Mikos.

At least 19 recordsLinked to original sources

PubMed2007

Nanobiomaterial applications in orthopedics.

Advancements in nanobiotechnology are revolutionizing our capability to understand biological intricacies and resolve biological and medical problems by developing subtle biomimetic techniques. Nanocomposites and nanostructured materials are believed to play a pivotal role in orthopedic research since bone itself is a typical example of a nanocomposite. This article reviews current strategies using nanobiomaterials to improve current orthopedic materials and examines their applications in bone tissue engineering. Preliminary investigations support the potential of nanobiomaterials in orthopedic applications; however, significant advancements are necessary to achieve clinical use. Overall, current trends in nanobiotechnology foreshadow a bright future through the use of nanobiomaterials in the orthopedic domain.

Biocompatible Materials↗

PubMed2006

Characterization of DNA release from composites of oligo(poly(ethylene glycol) fumarate) and cationized gelatin microspheres in vitro.

This research investigates the release of plasmid DNA from novel hydrogel composites of oligo(poly(ethylene glycol) fumarate) (OPF) and cationized gelatin microspheres (CGMS), as well as the swelling and degradation of these materials in vitro. The release of total DNA and of double-stranded DNA was measured fluorescently, and the swelling properties and polymer mass loss of the hydrogels were assessed. Further, the structural integrity of the released DNA was determined through electrophoresis. It was found that plasmid DNA can be released in a sustained fashion over the course of up to 49-140 days in vitro from hydrogels of OPF synthesized from poly(ethylene glycol) of nominal molecular weights of 10 kDa and 3 kDa, respectively, with the release kinetics depending upon the material composition and the method of DNA loading. Released DNA was predominately double-stranded DNA (dsDNA) in structure and of the open-circular conformation. The results suggest that DNA release from hydrogel composites of OPF and CGMS is dominated by the degradation of the OPF component of the gels. Electrophoresis results indicate that the released DNA retains suitable conformation for potential bioactivity over the course of at least 63 days of release. Thus, these studies demonstrate the potential of composites of OPF and CGMS in controlled gene delivery applications.

DNA↗

PubMed2006

Gene delivery strategies for cartilage tissue engineering.

Tissue engineering is a multifaceted technology developed with a purpose of regenerating complex tissues and organs. Cartilage regeneration continues to challenge engineers and a new wave of efforts focus on developing strategies that provide sustained stimulation to cells by growth factors and other biological molecules to promote their differentiation into chondrocytes. Though significant research is dedicated to developing controlled release systems that deliver growth factors directly, a simpler approach to resolving this dilemma involves converting cells into protein producing factories. This is done through gene delivery. Gene Therapy studies published for articular diseases such as rheumatoid and osteoarthritis provide valuable information regarding different types of cells, gene delivery vectors and genes that can potentially be used to regenerate cartilage. Tissue engineering approaches provide the opportunity to combine two or more strategies used for Gene Therapy thus far and create a cohesive system that addresses both cartilage degeneration and synthesis simultaneously. Adopting gene transfer techniques for tissue engineering is a relatively novel approach, as non-viral gene delivery vectors are continually optimized for therapeutic purposes, and reservations about viral vectors have increasingly dampened their appeal. However, every element involved in gene transfection (i.e., the cell, vector and gene) is a variable which decides the physiological and biomechanical properties of the cartilage produced, and significant work still needs to be done in understanding the contribution of each of these factors to cartilage regeneration.

Animals↗

PubMed2006

In vitro generated extracellular matrix and fluid shear stress synergistically enhance 3D osteoblastic differentiation.

This study instituted a unique approach to bone tissue engineering by combining effects of mechanical stimulation in the form of fluid shear stresses and the presence of bone-like extracellular matrix (ECM) on osteodifferentiation. Rat marrow stromal cells (MSCs) harvested from bone marrow were cultured on titanium (Ti) fiber mesh discs for 12 days in a flow perfusion system to generate constructs containing bone-like ECM. To observe osteodifferentiation and bone-like matrix deposition, these decellularized constructs and plain Ti fiber meshes were seeded with MSCs (Ti/ECM and Ti, respectively) and cultured in the presence of fluid shear stresses either with or without the osteogenic culture supplement dexamethasone. The calcium content, alkaline phosphatase activity, and osteopontin secretion were monitored as indicators of MSC differentiation. Ti/ECM constructs demonstrated a 75-fold increase in calcium content compared with their Ti counterparts after 16 days of culture. After 16 days, the presence of dexamethasone enhanced the effects of fluid shear stress and the bone-like ECM by increasing mineralization 50-fold for Ti/ECM constructs; even in the absence of dexamethasone, the Ti/ECM constructs exhibited approximately a 40-fold increase in mineralization compared with their Ti counterparts. Additionally, denatured Ti/ECM* constructs demonstrated a 60-fold decrease in calcium content compared with Ti/ECM constructs after 4 days of culture. These results indicate that the inherent osteoinductive potential of bone-like ECM along with fluid shear stresses synergistically enhance the osteodifferentiation of MSCs with profound implications on bone-tissue-engineering applications.

Alkaline Phosphatase↗

PubMed2006

Evaluation of bone regeneration by DNA release from composites of oligo(poly(ethylene glycol) fumarate) and cationized gelatin microspheres in a critical-sized calvarial defect.

This research examines the bone formation response to release of plasmid DNA encoding human Bone Morphogenetic Protein-2 from hydrogel composites consisting of cationized gelatin microspheres (CGMS) embedded within a crosslinked oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel network in a critical-sized rat cranial defect model after 30 days. Four composite groups were investigated: (1) composites with 10 microg DNA loaded into the CGMS phase, (2) composites with 10 microg DNA loaded into the OPF phase, (3) composites with 100 microg DNA loaded into the OPF phase, and (4) composites without DNA (material control). Light microscopy revealed no enhancement in bone formation for groups releasing plasmid DNA, relative to the material control group. Limited formation of new bone was observed from the defect margins and within the defect for some samples. The hydrogels swelled appreciably and fragmentation of the implants was noted to varying degrees among samples within groups, with a presence of inflammatory cells related to the degree of fragmentation. The lack of enhancement in bone formation indicates that the release of plasmid DNA from the composites was not sufficient to elicit a bone regeneration response.

Animals↗

PubMed2006

Modulation of cell differentiation in bone tissue engineering constructs cultured in a bioreactor.

In summary, many factors can influence the osteoblastic differentiation of marrow stromal cells when cultivated on three-dimensional tissue engineering scaffolds. In creating ideal bone tissue engineering constructs consisting of a combination of a scaffold, cells, and bioactive factors; a flow perfusion bioreactor is a much more suitable culture environment than static culture in well plates. The bioreactor eliminates mass transport limitations to the scaffold interior and provides mechanical stimulation to the seeded cells through fluid shear. Scaffold properties such as pore size impact cell differentiation, especially in flow perfusion culture. In addition, the bone-like extracellular matrix created by the in vitro culture of marrow stromal cells on porous scaffolds creates an osteoinductive environment for the differentiation of other marrow stromal cell populations. Therefore, bone tissue engineering constructs created by in vitro culture have excellent potential for bone regeneration applications in the clinic. However, more work is required to optimize this tissue engineering strategy. A biodegradable material with mechanical integrity similar to native bone and degradation properties similar to the rate of bone formation would be a more ideal scaffold material. It is also yet unclear what the optimum scaffold pore size and amount of in vitro generated extracellular matrix are to maximize bone formation. Finally, better characterization of the flow patterns within the flow perfusion bioreactor is needed to better understand the relationship between fluid shear and cell differentiation for creation of the ideal scaffold/culture combination.

Biocompatible Materials↗

PubMed2006

Biodegradable polymeric scaffolds. Improvements in bone tissue engineering through controlled drug delivery.

Recent advances in biology, medicine, and engineering have led to the discovery of new therapeutic agents and novel materials for the repair of large bone defects caused by trauma, congenital defects, or bone tumors. These repair strategies often utilize degradable polymeric scaffolds for the controlled localized delivery of bioactive molecules to stimulate bone ingrowth as the scaffold degrades. Polymer composition, hydrophobicity, crystallinity, and degradability will affect the rate of drug release from these scaffolds, as well as the rate of tissue ingrowth. Accordingly, this chapter examines the wide range of synthetic degradable polymers utilized for osteogenic drug delivery. Additionally, the therapeutic proteins involved in bone formation and in the stimulation of osteoblasts, osteoclasts, and progenitor cells are reviewed to direct attention to the many critical issues influencing effective scaffold design for bone repair.

Biocompatible Materials↗

PubMed2006

Injectable nanocomposites of single-walled carbon nanotubes and biodegradable polymers for bone tissue engineering.

We have investigated the dispersion of single-walled carbon nanotubes (SWNTs) and functionalized SWNTs (F-SWNTs) in the unsaturated, biodegradable polymer poly(propylene fumarate) (PPF) and examined the rheological properties of un-cross-linked nanocomposite formulations as well as the electrical and mechanical properties of cross-linked nanocomposites. F-SWNTs were produced from individual SWNTs by a diazonium-based method and dispersed better than unmodified SWNTs in both un-cross-linked and cross-linked PPF matrix. Cross-linked nanocomposites with F-SWNTs were superior to those with unmodified SWNTs in terms of their mechanical properties. Specifically, nanocomposites with 0.1 wt % F-SWNTs loading resulted in a 3-fold increase in both compressive modulus and flexural modulus and a 2-fold increase in both compressive offset yield strength and flexural strength when compared to pure PPF networks, whereas the use of 0.1 wt % SWNTs gained less than 37% mechanical reinforcement. These extraordinary mechanical enhancements considered together with Raman scattering and sol fraction measurements indicate strong SWNT-PPF interactions and increased cross-linking densities resulting in effective load transfer. With enhanced mechanical properties and capabilities of in situ injection and cross-linking, these SWNT/polymer nanocomposites hold significant implications for the fabrication of bone tissue engineering scaffolds.

Biocompatible Materials↗

PubMed2006

Electrospun poly(epsilon-caprolactone) microfiber and multilayer nanofiber/microfiber scaffolds: characterization of scaffolds and measurement of cellular infiltration.

The physical and spatial architectural geometries of electrospun scaffolds are important to their application in tissue engineering strategies. In this work, poly(epsilon-caprolactone) microfiber scaffolds with average fiber diameters ranging from 2 to 10 microm were individually electrospun to determine the parameters required for reproducibly fabricating scaffolds. As fiber diameter increased, the average pore size of the scaffolds, as measured by mercury porosimetry, increased (values ranging from 20 to 45 microm), while a constant porosity was observed. To capitalize on both the larger pore sizes of the microfiber layers and the nanoscale dimensions of the nanofiber layers, layered scaffolds were fabricated by sequential electrospinning. These scaffolds consisted of alternating layers of poly(epsilon-caprolactone) microfibers and poly(epsilon-caprolactone) nanofibers. By electrospinning the nanofiber layers for different lengths of time, the thickness of the nanofiber layers could be modulated. Bilayered constructs consisting of microfiber scaffolds with varying thicknesses of nanofibers on top were generated and evaluated for their potential to affect rat marrow stromal cell attachment, spreading, and infiltration. Cell attachment after 24 h did not increase with increasing number of nanofibers, but the presence of nanofibers enhanced cell spreading as evidenced by stronger F-actin staining. Additionally, increasing the thickness of the nanofiber layer reduced the infiltration of cells into the scaffolds under both static and flow perfusion culture for the specific conditions tested. The scaffold design presented in this study allows for cellular infiltration into the scaffolds while at the same time providing nanofibers as a physical mimicry of extracellular matrix.

Actins↗

PubMed2006

Electrospinning of polymeric nanofibers for tissue engineering applications: a review.

Interest in electrospinning has recently escalated due to the ability to produce materials with nanoscale properties. Electrospun fibers have been investigated as promising tissue engineering scaffolds since they mimic the nanoscale properties of native extracellular matrix. In this review, we examine electrospinning by providing a brief description of the theory behind the process, examining the effect of changing the process parameters on fiber morphology, and discussing the potential applications and impacts of electrospinning on the field of tissue engineering.

Animals↗

PubMed2006

In vitro localization of bone growth factors in constructs of biodegradable scaffolds seeded with marrow stromal cells and cultured in a flow perfusion bioreactor.

Tissue engineering strategies aim at controlling the behavior of individual cells to stimulate tissue formation. This control is achieved by mimicking signals that manage natural tissue development or repair. Flow perfusion bioreactors that create culture environments with minimal diffusion constraints and provide cells with mechanical stimulation may closely resemble in vivo conditions for bone formation. Therefore, these culturing systems, in conjunction with an appropriate scaffold and cell type, may provide significant insight towards the development of in vitro tissue engineering models leading to improved strategies for the construction of bone tissue substitutes. The objective of this study was to investigate the in vitro localization of several bone growth factors that are usually associated with bone formation in vivo by culturing rat bone marrow stromal cells seeded onto starch-based biodegradable fiber meshes in a flow perfusion bioreactor. The localization of several bone-related growth factors-namely, transforming growth factor-beta1, platelet-derived growth factor- A, fibroblast growth factor-2, vascular endothelial growth factor, and bone morphogenetic protein- 2-was determined at two different time points in scaffolds cultured under perfusion conditions at two different flow rates using an immunohistochemistry technique. The results show the presence of regions positively stained for all the growth factors considered, except platelet-derived growth factor-A. Furthermore, the images obtained from the positively stained sections suggest an increase in the immunohistochemically stained area at the higher flow rate and culture time. These observations demonstrate that flow perfusion augments the functionality of scaffold/cell constructs grown in vitro as it combines both biological and mechanical factors to enhance cell differentiation and cell organization within the construct. This study also shows that flow perfusion bioreactor culture of marrow stromal cells, combined with the use of appropriate biodegradable fiber meshes, may constitute a useful model to study bone formation and assess bone tissue engineering strategies in vitro.

Animals↗

PubMed2006

Trends in tissue engineering research.

For more than a decade, Tissue Engineering has been devoted to the reporting and discussion of scientific advances in the interdisciplinary field of tissue engineering. In this study, 779 original articles published in the journal since its inception were analyzed and classified according to different attributes, such as focus of research and tissue of interest, to reveal trends in tissue engineering research. In addition, the use of different biomaterials, scaffold architectures, surface and bulk modification agents, cells, differentiation factors, gene delivery vectors, and animal models was examined. The results of this survey show interesting trends over time and by continental origin.

Forecasting↗

PubMed2006

Porous poly(DL-lactic-co-glycolic acid)/calcium phosphate cement composite for reconstruction of bone defects.

Calcium phosphate (Ca-P) cements are injectable, self-setting ceramic pastes generally known for their favorable bone response. Ingrowth of bone and subsequent degradation rates can be enhanced by the inclusion of macropores. Initial porosity can be induced by CO(2) foaming during setting of the cement, whereas secondary porosity can develop after hydrolysis of incorporated poly(DL-lactic- co-glycolic acid) (PLGA) microparticles. In this study, we focused on the biological response to porous PLGA/Ca-P cement composites. Pre-set composite discs of four formulations (4 wt% or 15 wt% PLGA microparticles and low or high CO(2) induced porosity) were implanted subcutaneously and in cranial defects in rats for 12 weeks. Histological analysis of the explanted composites revealed that bone and fibrous tissue ingrowth was facilitated by addition of PLGA microparticles (number average diameter of 66 +/- 25 microm). No adverse tissue reaction was observed in any of the composites. Significant increases in composite density due to bone ingrowth in cranial implants were found in all formulations. The results suggest that the PLGA pores are suitable for bone ingrowth and may be sufficient to enable complete tissue ingrowth without initial CO(2) induced porosity. Finally, bone-like mineralization in subcutaneous implants suggests that, under appropriate conditions and architecture, porous PLGA/Ca-P cement composites can exhibit osteoinductive properties. These PLGA/Ca-P composites are a promising scaffolding material for bone regeneration and bone tissue engineering.

Absorbable Implants↗

PubMed2006

Influence of the porosity of starch-based fiber mesh scaffolds on the proliferation and osteogenic differentiation of bone marrow stromal cells cultured in a flow perfusion bioreactor.

This study investigates the influence of the porosity of fiber mesh scaffolds obtained from a blend of starch and poly(epsilon-caprolactone) on the proliferation and osteogenic differentiation of marrow stromal cells cultured under static and flow perfusion conditions. For this purpose, biodegradable scaffolds were fabricated by a fiber bonding method into mesh structures with two different porosities-- 50 and 75%. These scaffolds were then seeded with marrow stromal cells harvested from Wistar rats and cultured in a flow perfusion bioreactor or in 6-well plates for up to 15 days. Scaffolds of 75% porosity demonstrated significantly enhanced cell proliferation under both static and flow perfusion culture conditions. The expression of alkaline phosphatase activity was higher in flow cultures, but only for cells cultured onto the higher porosity scaffolds. Calcium deposition patterns were similar for both scaffolds, showing a significant enhancement of calcium deposition on cellscaffold constructs cultured under flow perfusion, as compared to static cultures. Calcium deposition was higher in scaffolds of 75% porosity, but this difference was not statistically significant. Observation by scanning electron microscopy showed the formation of pore-like structures within the extracellular matrix deposited on the higher porosity scaffolds. Fourier transformed infrared spectroscopy with attenuated total reflectance and thin-film X-ray diffraction analysis of the cell-scaffold constructs after 15 days of culture in a flow perfusion bioreactor revealed the presence of a mineralized matrix similar to bone. These findings indicate that starch-based scaffolds, in conjunction with fluid flow bioreactor culture, minimize diffusion constraints and provide mechanical stimulation to the marrow stromal cells, leading to enhancement of differentiation toward development of bone-like mineralized tissue. These results also demonstrate that the scaffold structure, namely, the porosity, influences the sequential development of osteoblastic cells and, in combination with the culture conditions, may affect the functionality of tissues formed in vitro.

Animals↗

PubMed2005

Gelatin as a delivery vehicle for the controlled release of bioactive molecules.

Gelatin is a commonly used natural polymer which is derived from collagen. The isoelectric point of gelatin can be modified during the fabrication process to yield either a negatively charged acidic gelatin, or a positively charged basic gelatin at physiological pH. This theoretically allows electrostatic interactions to take place between a charged biomolecule and gelatin of the opposite charge, forming polyion complexes. Various forms of gelatin carrier matrices can be fabricated for controlled-release studies, and characterization studies have been performed which show that gelatin carriers are able to sorb charged biomolecules such as proteins and plasmid DNA through polyion complexation. The crosslinking density of gelatin hydrogels has been shown to affect their degradation rate in vivo, and the rate of biomolecule release from gelatin carriers has been shown to have a similar profile, suggesting that complexed gelatin/biomolecule fragments are released by enzymatic degradation of the carrier in vivo. This review will emphasize how biomolecules released from gelatin controlled-release systems are able to retain their biological activity, allowing for their use in tissue engineering, therapeutic angiogenesis, gene therapy, and drug delivery applications.

Animals↗

PubMed2005

In vivo release of plasmid DNA from composites of oligo(poly(ethylene glycol)fumarate) and cationized gelatin microspheres.

Composites of cationized gelatin microspheres (CGMS), crosslinked with either 3 mM or 6 mM glutaraldehyde solution, and a novel hydrogel material, oligo(poly(ethylene glycol)fumarate) (OPF) were fabricated and investigated toward prolonging the release of plasmid DNA in vivo relative to the constituent materials. The composites and constituent materials were investigated in a subcutaneous murine model to assess the release of 125I-labeled plasmid DNA and 125I-labeled cationized gelatin in vivo. The time profiles of the radioactivity remaining were employed to compare the profiles of DNA release and cationized gelatin degradation. Both composite formulations (incorporating either 3 mM or 6 mM CGMS) prolonged the bioavailability of plasmid DNA relative to both injected plasmid DNA solution and the respective non-embedded cationized gelatin microspheres. Injected plasmid DNA solution persisted in the subject for only 7-10 days, whereas the persistence of DNA from composites of OPF and either 3 mM or 6 mM CGMS extended to at least day 42. The 3 mM and 6 mM CGMS each increased the persistence of DNA slightly, relative to injection of DNA solution, to between 28 and 35 days. Interestingly, the release profile of plasmid DNA from composites was not significantly different from the release of DNA from OPF alone. The release of plasmid DNA from the composites was in accord with the degradation of the microspheres within the OPF. These results show that composites of OPF and cationized gelatin microspheres are able to prolong the availability of plasmid DNA in vivo relative to cationized gelatin microspheres alone and provide a promising candidate material for the sustained, controlled release of plasmid DNA.

Cations↗

PubMed2005

Osteochondral repair in the rabbit model utilizing bilayered, degradable oligo(poly(ethylene glycol) fumarate) hydrogel scaffolds.

In this study, hydrogel scaffolds, based on the polymer oligo(poly(ethylene glycol) fumarate) (OPF), were implanted into osteochondral defects in the rabbit model. Scaffolds consisted of two layers-a bottom, bone forming layer and a top, cartilage forming layer. Three scaffold formulations were implanted to assess how material composition and transforming growth factor-beta1 (TGF-beta1) loading affected osteochondral repair. Critical histological evaluation and scoring of the quantity and quality of tissue in the chondral and subchondral regions of defects was performed at 4 and 14 weeks. At both time points, no evidence of prolonged inflammation was observed, and healthy tissue was seen to infiltrate the defect area. The quality of this tissue improved over time with hyaline cartilage filling the chondral region and a mixture of trabecular and compact bone filling the subchondral region at 14 weeks. A promising degree of Safranin O staining and chondrocyte organization was observed in the newly formed surface tissue, while the underlying subchondral bone was completely integrated with the surrounding bone at 14 weeks. Material composition within the bottom, bone-forming layer did not appear to affect the rate of scaffold degradation or tissue filling. However, no bone upgrowth into the chondral region was observed with any scaffold formulation. TGF-beta1 loading in the top layer of scaffolds appeared to exert some therapeutic affect on tissue quality, but further studies are necessary for scaffold optimization. Yet, the excellent tissue filling and integration resulting from osteochondral implantation of these OPF-based scaffolds demonstrates their potential in cartilage repair strategies.

Absorbable Implants↗

PubMed2005

Biocompatibility and degradation of poly(DL-lactic-co-glycolic acid)/calcium phosphate cement composites.

Injectable calcium phosphate (Ca-P) cement materials exhibit favorable osteocompatible behavior but are resorbed slowly because of a lack of a bone ingrowth-enabling macroporosity. In this study, poly(DL-lactic-co-glycolic acid) (PLGA) microparticles (average size 66 +/- 25 microm) were incorporated into Ca-P cement to obtain a macroporous Ca-P cement scaffold after PLGA hydrolysis in vivo. Preset PLGA/Ca-P cement composite discs of various weight ratios (0/100, 15/85, 30/70, and 50/50) were implanted subcutaneously and in cranial defects in rats for 12 weeks. Histological analysis revealed that all macropores in the PLGA-containing composites (average pore size 73 +/- 27 microm) were filled with fibrous tissue and blood vessels (subcutaneous implants) and/or bone (cranial implants). Histologically, bone formation appeared most abundant and most consistent in the 30/70 PLGA/Ca-P cement composites. Histomorphometrical evaluation revealed a significant increase in defect fill in the 15/85 and 30/70 PLGA/Ca-P cement composites. Finally, subcutaneous and cranial 50/50 PLGA/Ca-P cement composites had degraded to a large extent, without adequate replacement by bone in the cranial implants. Therefore, we conclude that PLGA/Ca-P cement composites enable tissue ingrowth and show excellent osteocompatibility in weight ratios of 15/85 and 30/70 PLGA/Ca-P cement. In this model, 30/70 PLGA/Ca-P cement composites showed the most favorable biological response.

Absorbable Implants↗