Polymers For Tissue Engineering Research Articles

Poly(dopamine) coating to biodegradable polymers for bone tissue engineering

In this study, a technique based on poly(dopamine) deposition to promote cell adhesion was investigated for the application in bone tissue engineering. The adhesion and proliferation of rat osteoblasts were evaluated on poly(dopamine)-coated biodegradable polymer films, such as polycaprolactone, poly(l-lactide) and poly(lactic-co-glycolic acid), which are commonly used biodegradable polymers in tissue engineering. Cell adhesion was significantly increased to a plateau by merely 15 s of dopamine incubation, 2.2-4.0-folds of increase compared to the corresponding untreated substrates. Cell proliferation was also greatly enhanced by poly(dopamine) deposition, indicated by shortened cell doubling time. Mineralization was also increased on the poly(dopamine)-deposited surfaces. The potential of poly(dopamine) deposition in bone tissue engineering is demonstrated in this study.

Electrospun vascular graft properties following femtosecond laser ablation

AbstractFor polymers in tissue engineering to reach their full potential, the three‐dimensional integration of cells with scaffolds must become more complex. In vascular grafts this is particularly challenging as specific physical property requirements must be met. We apply a combination of polymer processing techniques—electrospinning and femtosecond laser ablation—to produce microchannels inside the walls of electrospun tubes providing for spatially‐controlled cell seeding. To determine if such a scaffold can provide the desired physical properties, a greater understanding of the relationship between manufacturing and mechanics is needed. As the strength of these scaffolds is an important functional component, the relative properties of single, bi‐ and tri‐layer combinations produced using different solvents were compared. The effect of fiber layer thickness was also investigated. The thickness of the hexafluorisopropanol‐derived layer dominated the overall scaffold properties regardless of the nature of the other two layers. Although laser‐machined microchannels had substantial effects on single layer and some of the bilayers, in the “final” trilayer scaffold, little effect on mechanical properties was observed. The concept of “vascular wall engineering” could successfully produce trilayer composite scaffolds that maintain the targeted mechanical properties while allowing intricate, three‐dimensional cell seeding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis of Polyurethane from Poly(3‐hydroxybutyrate) and Poly(p‐dioxanone): Molar Mass Reduction via Sodium Borohydrate

AbstractPoly(3‐hydroxybutyrate) PHB and poly(p‐dioxanone) PPD are examples of promising polymers in tissue engineering. The purpose of this work is to synthesize polyurethanes which combine stereoregular and rigid blocks of PHB with stereoregular and flexible blocks of PPD. In order to guarantee stereoregularity, polyols from PHB and PPD were obtained from mass reduction via sodium borohydrate. This route allows us to obtain bifuncional polyols. The polymer molar mass reduction using this strategy was effective, however secondary and non reactive products with diisocyanate like insaturated acid were formed as shown by mass spectroscopy data. The products of mass reduction were characterized by H1 NMR, FT‐IR, DSC and MALDI‐TOF/MS. The PU's were synthesized reacting the polyols with hexamethylene diisocyanate (HDI) and they were characterized by FT‐IR, H1 NMR, DSC and XRD.The PU obtained from PHB and PPD polyols presents two crystalline phases, corresponding to both polyester blocks. The introduction of flexible segments of PPD in polyurethane, affected the characteristics of crystalline phase formation of PHB, increasing the melting point of this block in comparison with the pure PHB polyol, probably by increasing the crystallization rate.

Plant Proteins for Medical Applications

Plant proteins show good potential for medical applications but offer considerable challenges in fabricating biomaterials. Despite substantial efforts, especially in the last decade, to develop polymeric biomaterials, there are no polymers that are ideally suited for tissue engineering, drug delivery and other medical applications. Therefore, the quest to find new sources for biomaterials continues. Natural proteins such as collagen and silk, carbohydrates such as chitosan and cellulose and synthetic biopolymers such as poly (lactic acid) have been extensively studied for potential medical applications. Biotechnology and nanotechnology have also been widely adopted to develop regenerated and recombinant polymers for medical applications. The advent of nanotechnology and its many advantages for medical applications have led to the development of nanofibers and nanoparticles from both the natural and synthetic polymers for tissue engineering, controlled release and other medical applications. However, both natural and synthetic polymers currently available have many limitations that restrict their use for medical applications. Biomaterials developed from natural polymers do not have the desired mechanical properties for medical applications. For instance, scaffolds developed from collagen have poor hydrolytic stability and efforts to crosslink and improve the properties have not been successful to provide cytocompatible biomaterials. Although silk has excellent mechanical properties and biocompatibility, silk has slow degradation rates and it is difficult to dissolve and process silk into various types of biomaterials. Biomaterials developed from most synthetic polymers have the biocompatibility and mechanical properties but their degradation into toxic substances in the body is a cause for concern. Similarly, metal and ceramic based biomaterials do not have the desired degradability and are difficult to process into different forms of biomaterials.

The Use of Natural Polymers in Tissue Engineering: A Focus on Electrospun Extracellular Matrix Analogues

Natural polymers such as collagens, elastin, and fibrinogen make up much of the body’s native extracellular matrix (ECM). This ECM provides structure and mechanical integrity to tissues, as well as communicating with the cellular components it supports to help facilitate and regulate daily cellular processes and wound healing. An ideal tissue engineering scaffold would not only replicate the structure of this ECM, but would also replicate the many functions that the ECM performs. In the past decade, the process of electrospinning has proven effective in creating non-woven ECM analogue scaffolds of micro to nanoscale diameter fibers from an array of synthetic and natural polymers. The ability of this fabrication technique to utilize the aforementioned natural polymers to create tissue engineering scaffolds has yielded promising results, both in vitro and in vivo, due in part to the enhanced bioactivity afforded by materials normally found within the human body. This review will present the process of electrospinning and describe the use of natural polymers in the creation of bioactive ECM analogues in tissue engineering.

Gelatin/PLLA Sponge‐Like Scaffolds Allow Proliferation and Osteogenic Differentiation of Human Mesenchymal Stromal Cells

Tissue engineering has the potential to supply constructs capable of restoring the normal function of native tissue following injury. Poly(L-lactic acid) (PLLA) scaffolds are amongst the most commonly used biodegradable polymers in tissue engineering and previous studies performed on ovine fibroblasts have showed that addition of gelatin creates a favorable hydrophilic microenvironment for the growth of these cells. The attractiveness of using mesenchymal stromal cells (MSCs) in tissue regeneration is that they are able to differentiate into several lines including osteoblasts. In this study, we investigated the ability of gelatin/PLLA sponges to support the adhesion, proliferation, and osteogenic differentiation of human MSCs isolated from the bone marrow of four donors. [Figure: see text].

Raman imaging for quantification of the volume fraction of biodegradable polymers in histological preparations

Postretrieval analysis of biodegradable polymeric constructs for degradation rates requires correct identification of the degradable polymer, de novo tissue and the confounding presence of a secondary polymer used for embedding. Similarities between the structures of many tissue engineering polymers may make them difficult to distinguish from the polymer used to embed explants prior to histological sectioning. In this study, we assessed the feasibility of a chemical imaging method, Raman microscopy, to discriminate between more than one polymer species. From the perspective of spectroscopy, this is not a straightforward process because of the emergence of multiple peaks, ubiquity of embedding medium, and presence of observations sourcing from points sampled at the interface of two phases. A multivariate K-means data clustering method was used to discriminate between different polymeric components. The method was able to classify 95% of the observations to the correct category. The remaining data displayed multiple memberships because of (1) the laser spot coinciding with the interfaces of more than one phase or (2) infiltration of histological embedding polymer. Combined with multivariate analysis methods, this technique may prove useful in the future for tissue engineering and biomaterials analysis of degradation rates of, and tissue ingrowth into, polymer scaffolds.

Effect of poly(lactic‐co‐glycolic acid) contact on maturation of murine bone marrow‐derived dendritic cells

Understanding of biomaterial adjuvant effect and its mechanisms is essential for the effective design and selection of appropriate materials for specific applications. We have previously shown that poly(lactic-co-glycolic acid) (PLGA), one of the most commonly studied polymers in tissue engineering, supports an adjuvant effect as measured by enhanced immune response against a co-delivered model antigen, which was dependent on the form of the biomaterial. Furthermore, we have shown that PLGA induces the maturation of human peripheral blood mononuclear cell-derived dendritic cells (DCs) in vitro. In this study, the effect of PLGA contact on the maturation of murine bone marrow-derived DCs was investigated in part to explain the biomaterial adjuvant effect observed. Treatment of bone marrow-derived DCs from C57BL6 mice with PLGA microparticles or films lead to maturation of these cells as exemplified by increased expression of co-stimulatory molecules CD80 and CD86 and production of proinflammatory cytokines TNF-alpha and IL-6. These results suggest that PLGA contact induces maturation of murine DCs, supporting our observations with human DCs. With the techniques developed in this study and given the results, our future goal is to utilize transgenic murine models to delineate the mechanisms of biomaterial-induced DC maturation.

Polymers for tissue engineering, medical devices, and regenerative medicine. Concise general review of recent studies

AbstractRecently investigated applications of polymeric materials for tissue engineering, regenerative medicine, implants, stents, and medical devices are described in the present review. Papers published during the last 2 years about polymeric materials used for preparation of various polymeric scaffolds, methods of fabrication of such scaffolds and their effectiveness in providing support for cell growth and development into various tissues and enhancing or mimicking an extracellular network (ECM's) have been cited. Papers describing the use of such polymeric materials for tissue engineering of cartilage and bones were cited. The exciting developments in the field of regenerative medicine, based on application of the self‐assembled biocompatible polymeric scaffolds for regeneration of tissues and organs are described in some detail. The use of the biocompatible and biodegradable collapsible polymeric stents, as well as the use of biocompatible, but not necessarily biodegradable polymeric materials for protective coatings of metallic stents and reservoirs of drugs, preventing restenosis and other post‐operative complications that may occur after insertion of a stent, have been reviewed. Clinical results pointing out the advantages of such treatments, as well as results indicating their limitations, have been cited. New formulas, for coating implants, stents, and other medical devices, have been discussed. Copyright © 2006 John Wiley & Sons, Ltd.

Polymers for Tissue Engineering

Polymers for Tissue Engineering

In vitro and in vivo comparison of bulk and surface hydrolysis in absorbable polymer scaffolds for tissue engineering

This article describes preliminary in vitro and in vivo studies comparing bulk and surface hydrolysis in absorbable polymer scaffolds proposed for tissue engineering of bone. The two polymers systems used were a bulk hydrolyzing 50:50 poly(DL-lactide-co-glycolide) (PLGA) and a surface hydrolyzing self-catalytic poly(ortho ester) (POE). Polymer scaffolds were exposed to physiological saline at body temperature and changes in polymer mass loss and inherent viscosity were monitored over time. New bone formation and local tissue response were evaluated by implanting scaffold disks of both polymer systems into non-critical-size calvarial defects in rabbits. New bone formation was determined by bone mineral density measurements, and local tissue response was determined by qualitative histology. Preliminary results confirmed that one of the main design characteristics for absorbable polymers in tissue engineering of bone, coordination of controlled polymer mass loss with new tissue formation, appeared to be achieved better using a surface hydrolyzing POE, rather than with a bulk hydrolyzing 50:50 PLGA. Bone mineral density at 6 and 12 weeks was an average 25% higher in the surface hydrolyzing scaffold. Unfortunately, the amount of bone formed was so inconsequential that this observation is of little relevance. Use of a water-soluble signaling factor such as basic fibroblast growth factor (bFGF) failed to increase bone formation. The histological response of these two polymer systems was similar and unaffected by the presence or absence of bFGF. The persistence of structural integrity for self-catalytic POE scaffolds after 6 and 12 weeks implantation, while 50:50 PLGA scaffolds had partially collapsed after 6 weeks, suggests surface hydrolyzing scaffolds may have some advantage over bulk hydrolyzing scaffolds in resisting normal in vivo stresses when used in a calvarial defect. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater;rpar; 48: 602–612, 1999

Polymers for tissue engineering

(1998). Polymers for tissue engineering. Journal of Biomaterials Science, Polymer Edition: Vol. 9, No. 5, pp. 405-406.

Resorbable polyesters in cartilage engineering: affinity and biocompatibility of polymer fiber structures to chondrocytes.

The resorbable polymers polyglycolic acid (PGA) and polylactic acid (PLA) are gaining increasing importance in tissue engineering and cell transplantation. The present investigation was focused on the biocompatibility and cell retaining behavior of PGA/poly-L-lactide (PLLA) (90/10) and PLLA nonwoven structures for the in vitro development of chondrocyte-polymer constructs. The effect of the relevant monomers to chondrocytes was analyzed. Type II collagen and poly-L-lysine were compared to improve loading of PGA/PLLA and PLLA polymer nonwovens with chondrocytes. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-zoliumbrom ide (MTT) test was applied for quantification. At concentrations above 2 mg/mL, glycolic acid was more cytotoxic than lactic acid. As shown by pH equilibration, the cytotoxic effect is not due merely to the acidity of the alpha-hydroxy acids. Regarding the degradation products, glycolic acid, and L(+) lactic acid, nonwovens of PLLA are more biocompatible with chondrocytes than nonwovens of polyglycolide. Collagen type II and poly-L-lysine generally improved cell seeding on resorbable polymers in tissue engineering; however, their efficiency varies depending on the type of fiber structure.