New polymers for drug delivery systems in orthopaedics: in vivo biocompatibility evaluation

Medical Adhesives and Their Role in Laparoscopic Surgery—A Review of Literature

Laparoscopic surgery is undergoing rapid development. Replacing the traditional method of joining cut tissues with sutures or staples could greatly simplify and speed up laparoscopic procedures. This alternative could undoubtedly be adhesives. For decades, scientists have been working on a material to bond tissues together to create the best possible conditions for tissue regeneration. The results of research on tissue adhesives achieved over the past years show comparable treatment effects to traditional methods. Tissue adhesives are a good alternative to surgical sutures in wound closure. This article is a review of the most important groups of tissue adhesives including their properties and possible applications. Recent reports on the development of biological adhesives are also discussed.

Fabrication of conductive fibrous scaffold for photoreceptor differentiation of mesenchymal stem cell

Conductive nanofibrous scaffolds with that can conduct electrical current have a great potential in neural tissue engineering. The purpose of this study was to survey effects of electrical stimulation and polycaprolactone/polypyrrole/multiwall carbon nanotube (PCL/PPY/MWCNTs) fibrous scaffold on photoreceptor differentiation of trabecular meshwork mesenchymal stem cells (TM-MSCs). PCL/PPY/MWCNTs scaffold was made by electrospinning method. TM-MSCs were seeded on PCL/PPY/MWCNTs scaffold and stimulated with a potential of 115 V/m. Scanning electron microscopy, transmission electron microscopy, and FT-IR were used to evaluate the fabricated scaffold. Immunofluorescence and quantitative real-time polymerase chain reaction were used to examine differentiated cells. Scanning electron microscopy, transmitting electron microscopy, and FT-IR confirmed the creation of the composite structure of fibers. RT-qPCR analysis showed that the expression of rhodopsin and peripherin genes in electrically stimulated cells were significantly higher (5.7- and 6.23-fold, respectively; p ≤ 0.05) than those with no electrical stimulation. Collectively, it seems that the combination of PCL/PPY/MWCNTs scaffold, as a suitable conductive scaffold, and electrical stimulation could be an effective approach in the differentiation of stem cells in retinal tissue engineering.

Conjugation with RGD Peptides and Incorporation of Vascular Endothelial Growth Factor Are Equally Efficient for Biofunctionalization of Tissue-Engineered Vascular Grafts

The blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL) has recently been considered promising for vascular tissue engineering. However, it was shown that PHBV/PCL grafts require biofunctionalization to achieve high primary patency rate. Here we compared immobilization of arginine-glycine-aspartic acid (RGD)-containing peptides and the incorporation of vascular endothelial growth factor (VEGF) as two widely established biofunctionalization approaches. Electrospun PHBV/PCL small-diameter grafts with either RGD peptides or VEGF, as well as unmodified grafts were implanted into rat abdominal aortas for 1, 3, 6, and 12 months following histological and immunofluorescence assessment. We detected CD31⁺/CD34⁺/vWF⁺ cells 1 and 3 months postimplantation at the luminal surface of PHBV/PCL/RGD and PHBV/PCL/VEGF, but not in unmodified grafts, with the further observation of CD31⁺CD34-vWF⁺ phenotype. These cells were considered as endothelial and produced a collagen-positive layer resembling a basement membrane. Detection of CD31⁺/CD34⁺ cells at the early stages with subsequent loss of CD34 indicated cell adhesion from the bloodstream. Therefore, either conjugation with RGD peptides or the incorporation of VEGF promoted the formation of a functional endothelial cell layer. Furthermore, both modifications increased primary patency rate three-fold. In conclusion, both of these biofunctionalization approaches can be considered as equally efficient for the modification of tissue-engineered vascular grafts.

Prevention of lung cancer recurrence using cisplatin-loaded superhydrophobic nanofiber meshes

For early stage lung cancer patients, local cancer recurrence after surgical resection is a significant concern and stems from microscopic disease left behind after surgery. Here we apply a local drug delivery strategy to combat local lung cancer recurrence after resection using non-woven, biodegradable nanofiber meshes loaded with cisplatin. The meshes are fabricated using a scalable electrospinning process from two biocompatible polymers--polycaprolactone and poly(glycerol monostearate-co-caprolactone)--to afford favorable mechanical properties for use in a dynamic tissue such as the lung. Owing to their rough nanostructure and hydrophobic polymer composition, these meshes exhibit superhydrophobicity, and it is this non-wetting nature that sustains the release of cisplatin in a linear fashion over ∼90 days, with anti-cancer efficacy demonstrated using an in vitro Lewis Lung carcinoma (LLC) cell assay. The in vivo evaluation of cisplatin-loaded superhydrophobic meshes in the prevention of local cancer recurrence in a murine model of LLC surgical resection demonstrated a statistically significant increase (p = 0.0006) in median recurrence-free survival to >23 days, compared to standard intraperitoneal cisplatin therapy of equivalent dose. These results emphasize the importance of supplementing cytoreductive surgery with local drug delivery strategies to improve prognosis for lung cancer patients undergoing tumor resection.

Phosphorous-containing polymers for regenerative medicine

Disease and injury have resulted in a large, unmet need for functional tissue replacements. Polymeric scaffolds can be used to deliver cells and bioactive signals to address this need for regenerating damaged tissue. Phosphorous-containing polymers have been implemented to improve and accelerate the formation of native tissue both by mimicking the native role of phosphorous groups in the body and by attachment of other bioactive molecules. This manuscript reviews the synthesis, properties, and performance of phosphorous-containing polymers that can be useful in regenerative medicine applications.

Polímeros usados como sistemas de transporte de princípios ativos

Os diferentes sistemas de transporte têm evidenciado potencial terapêutico para uma grande variedade de princípios ativos, satisfazendo vários requisitos, como a prevenção da sua eliminação rápida do organismo, a redução da sua toxicidade sistêmica, a estabilização e a otimização do seu metabolismo, e o direcionamento específico ao local alvo e os mecanismos de defesa. No entanto, têm sido reconhecidos vários outros desafios associados à liberação específica do princípio ativo ao local alvo, pelo que, para ultrapassar os obstáculos químicos e biológicos, a seleção do polímero utilizado para a preparação do sistema de transporte é de importância crucial. O presente trabalho apresenta um relato sobre os principais polímeros naturais e sintéticos utilizados para a preparação de sistemas de transporte de princípios ativos in vivo.

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.

Enhanced differentiation of retinal progenitor cells using microfabricated topographical cues

Due to the retina’s inability to replace photoreceptors lost during retinal degeneration, significant interest has been placed in methods to implant replacement cells. Polymer scaffolds are increasingly being studied as vehicles for cellular delivery to degenerated retinas. Previously, we fabricated poly(methyl methacrylate) thin film scaffolds that increased survival and integration of implanted retinal progenitor cells (RPCs). Additionally, these scaffolds minimized the trauma and cellular response associated with implantation of foreign bodies into mouse eyes. Here, we demonstrate that biodegradable polycaprolactone (PCL) thin film scaffolds can be fabricated with integrated microtopography. Microfabricated topography in a PCL thin film enhanced the attachment and organization of RPCs compared to unstructured surfaces. Using real-time quantitative polymerase chain reaction we also observed that attachment to microtopography induced cellular differentiation. RPCs grown on PCL thin films exhibited an increase in gene expression for the photoreceptor markers recoverin and rhodopsin, an increase in the glial and Müller cell marker GFAP, and a decrease in SOX2 gene expression (a marker for undifferentiated progenitor cells) compared to cells grown on unmodified tissue culture polystyrene (TCPS).

Indentation creep reservoirs for drug-eluting poly(L-lactic acid) scaffolds

The indentation creep behavior of poly(L-lactic acid) (PLLA) thin and thick films was examined. The creep rate was found to be strongly dependent on applied stress, as well as on the thickness of the PLLA film with creep rates being much larger in thin films compared to thick ones at lower stresses, but the difference was minimal at high stresses. The indentation creep approach was used to create a drug-delivery device with multiple reservoirs. Managing the thickness of the diffusion barrier that was a low-molecular-weight PLLA controlled the rate of drug release and it is shown that transport of drug through the barrier is diffusion controlled and the rate of dissolution of the PLLA is slower than the rate of transport of drug. A stable release rate together with periodic pulsed release was achieved over a period of 28 days with complete transport of the drug achieved over this time frame.

Synthesis and characterization of chalcone-substituted phosphazenes

A series of mono[(E)-1-(4-alkyloxyphenyl)-3-(4-hydroxy-phenyl)prop-2-en-1-one]cyclotriphosphazenes and hexakis[(E)-1-(4-alkyloxy-phenyl)-3-(4-hydroxy-phenyl) prop-2-en-1-one]cylotriphosphazenes have been synthesized. A convenient synthetic method was performed from the reaction of hexachlorocyclotriphosphazenes with 1 and 6 equiv. of (E)-1-(4-alkyloxyphenyl)-3-(4-hydroxy-phenyl)prop-2-en-1-one (2a–2c) to afford (3a–3c) in 17%–19% and (4a–4c) in 70%–82%, respectively. The compounds differ in the length of alkyl groups, CnH2n+1, where n = 10, 12, and 14.

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.

Genome-scale reconstruction and analysis of the Pseudomonas putida KT2440 metabolic network facilitates applications in biotechnology

A cornerstone of biotechnology is the use of microorganisms for the efficient production of chemicals and the elimination of harmful waste. Pseudomonas putida is an archetype of such microbes due to its metabolic versatility, stress resistance, amenability to genetic modifications, and vast potential for environmental and industrial applications. To address both the elucidation of the metabolic wiring in P. putida and its uses in biocatalysis, in particular for the production of non-growth-related biochemicals, we developed and present here a genome-scale constraint-based model of the metabolism of P. putida KT2440. Network reconstruction and flux balance analysis (FBA) enabled definition of the structure of the metabolic network, identification of knowledge gaps, and pin-pointing of essential metabolic functions, facilitating thereby the refinement of gene annotations. FBA and flux variability analysis were used to analyze the properties, potential, and limits of the model. These analyses allowed identification, under various conditions, of key features of metabolism such as growth yield, resource distribution, network robustness, and gene essentiality. The model was validated with data from continuous cell cultures, high-throughput phenotyping data, ¹³C-measurement of internal flux distributions, and specifically generated knock-out mutants. Auxotrophy was correctly predicted in 75% of the cases. These systematic analyses revealed that the metabolic network structure is the main factor determining the accuracy of predictions, whereas biomass composition has negligible influence. Finally, we drew on the model to devise metabolic engineering strategies to improve production of polyhydroxyalkanoates, a class of biotechnologically useful compounds whose synthesis is not coupled to cell survival. The solidly validated model yields valuable insights into genotype–phenotype relationships and provides a sound framework to explore this versatile bacterium and to capitalize on its vast biotechnological potential.

The pseudomonads include a diverse set of bacteria whose metabolic versatility and genetic plasticity have enabled their survival in a broad range of environments. Many members of this family are able to either degrade toxic compounds or to efficiently produce high value compounds and are therefore of interest for both bioremediation and bulk chemical production. To better understand the growth and metabolism of these bacteria, we developed a large-scale mathematical model of the metabolism of Pseudomonas putida, a representative of the industrially relevant pseudomonads. The model was initially expanded and validated with substrate utilization data and carbon-tracking data. Next, the model was used to identify key features of metabolism such as growth yield, internal distribution of resources, and network robustness. We then used the model to predict novel strategies for the production of precursors for bioplastics of medical and industrial relevance. Such an integrated computational and experimental approach can be used to study its metabolism and to explore the potential of other industrially and environmentally important microorganisms.

Species and density of implant surface chemistry affect the extent of foreign body reactions

Implant-associated fibrotic capsule formation presents a major challenge for the development of long-term drug release microspheres and implantable sensors. Since material properties have been shown to affect in vitro cellular responses and also to influence short-term in vivo tissue responses, we have thus assumed that the type and density of surface chemical groups would affect the degree of tissue responses to microsphere implants. To test this hypothesis, polypropylene particles with different surface densities of -OH and -COOH groups, along with the polypropylene control (-CH2 groups) were utilized. The influence of functional groups and their surface densities on fibrotic reactions were analyzed using a mice subcutaneous implantation model. Our comparative studies included determination and correlation of the extents of fibrotic capsule formation, cell infiltration into the particles, and recruitment of CD11b+ inflammatory cells for all of the substrates employed. We have observed major differences among microspheres coated with different surface functionalities. Surfaces with -OH surface groups trigger the strongest responses, while -COOH-rich surfaces prompt the least tissue reactions. However, variation of the surface density of either functional group has a relatively minor influence on the extent of fibrotic tissue reactions. The present results show that surface functionality can be used as a powerful tool to alter implant-associated fibrotic reactions and, potentially, to improve the efficacy and function of drug-delivery microspheres, implantable sensors, and tissue-engineering scaffolds.

Proliferation and osteogenic differentiation of mesenchymal stem cells cultured onto three different polymers in vitro

In this study, the osteoinductive and cell-binding properties of three different resorbable polymers were evaluated by human mesenchymal stem cells (MSCs). MSCs were isolated, expanded, and cultivated onto resorbable D,D,L,L-polylactide (PLLA), collagen I/III, and polygalactin-910/polydioxanone (PGPD) scaffolds in vitro. To evaluate the influence of dexamethasone, ascorbic acid, and beta-glycerolphosphate (DAG) on osteoblast differentiation, MSCs were incubated in a DAG-enriched medium. After a 28-day period in vitro, the cellular loaded polymers were digested enzymatically by papain and HCl. The Ca(2+) content of the biomembranes was evaluated by an o-kresolphthalein-complexon reaction via photometer. A PicoGreen assay was performed for dsDNA quantification. Significant differences between the number of adherent MSCs were documented (collagen > PLLA > PGPD). Compared to the initial number of adherent cells, all biomaterials induced a significant decrease in cellular adherence after 28 days in vitro. The presence of DAG-enriched culture medium stimulated the cellular proliferation for PLLA and slightly for PGPD, whereas cell proliferation was inhibited when MSCs were cultivated onto collagen I/III. In comparison with the control groups, all biomaterials (PLLA, PGPD, and collagen I/III) showed a significant increase in local Ca(2+) accumulation under DAG stimulation after 28 days in vitro. Furthermore, collagen I/III and PLLA scaffolds showed osteoinductive properties without DAG stimulation. These results were verified by immunocytochemical stainings against osteoblast-typical markers (osteopontin and alkaline phosphatase) and completed by calcified matrix detection (von Kossa staining). MSCs were identified by CD105 and CD13 antigen expression. Corresponding to an absence of CD34, CD45, and collagen II expression, we found no chondrogenic or hematopoietic cell differentiation. The results indicate significant differences for the proliferation, differentiation, adherence, and Ca(2+) accumulation between the tested polymers in a MSC culture.

Synthesis and characterization of alkyl- and acyl-substituted oxime–phosphazenes

Two oxime–cyclophosphazenes were prepared from the hexakis(4-formylphenoxy)cyclotriphosphazene (2) and hexakis(4-acetylphenoxy)cyclotriphosphazene (8). The reactions of these oximes with ethyl bromide, allyl bromide, propanoyl chloride, and acriloyl chloride were studied. Hexasubstituted compounds were obtained from the reactions of hexakis{4-[(hydroxyimino)methyl]phenoxy}cyclotriphosphazene (3) with ethyl bromide (4), allyl bromide (5), and propanoyl chloride (6), however, the oxime groups on 3 rearranged to nitrile (7) in the reaction of 3 with acriloyl chloride. Hexasubstituted compounds were also obtained from the reactions of hexakis{4-[(1)-N-hydroxyethaneimidoyl]phenoxy}cyclotriphosphazene (9) with allyl bromide (11) and propanoyl chloride (12). Tetra- and penta-substituted products were obtained from the reactions of 9 with ethyl bromide (10) and acriloyl chloride (13), respectively. All products were generally obtained in high yields. The structures of the compounds were defined by elemental analysis, IR, 1H, 13C, and 31P NMR spectroscopy. Key words: hexachlorocyclotriphosphazene, phosphazene, oxime, oxime derivatives, oxime–phosphazenes.