Water absorption and surface properties of novel poly(ethylmethacrylate) polymer systems for use in bone and cartilage repair

A Versatile Strategy for the Fabrication of Poly(ethyl methacrylate) Composites

Poly(ethyl methacrylate) (PEMA) is dissolved in ethanol, known to be a non-solvent for PEMA, due to the solubilizing ability of an added bile acid biosurfactant, lithocholic acid (LA). The ability to avoid traditional toxic and carcinogenic solvents is important for the fabrication of composites for biomedical applications. The formation of concentrated solutions of high molecular weight PEMA is a key factor for the film deposition using the dip coating method. PEMA films provide corrosion protection for stainless steel. Composite films are prepared, containing bioceramics, such as hydroxyapatite and silica, for biomedical applications. LA facilitates dispersion of hydroxyapatite and silica in suspensions for film deposition. Ibuprofen and tetracycline are used as model drugs for the fabrication of composite films. PEMA-nanocellulose films are successfully prepared using the dip coating method. The microstructure and composition of the films are investigated. The conceptually new approach developed in this investigation represents a versatile strategy for the fabrication of composites for biomedical and other applications, using natural biosurfactants as solubilizing and dispersing agents.

Preparation and characterisation of highly alkaline hydrogels for the re-alkalisation of carbonated cementitious materials

Highly alkaline hydrogels that allow the restoration of alkaline buffer in cementitious materials can be obtained from diallyldimethylammonium hydroxide. The latter must be prepared in dilute solutions and polymerised at ambient temperatures in order to avoid decomposition. Using methacrylamide as a neutral co-monomer capable of forming hydrogen bonds, the rheological properties of the gels can be adjusted over a wide range; e.g. the viscosity increases a thousandfold from 0.35 Pa s to >350 Pa s by using 10 mol% methacrylamide. For the proof of principle experiments, gels with 9 mol% methacrylamide were used, which contain approx. 1.6 mol hydroxide ions per kg gel. Ion exchange between this and a neutral chloride containing gel provided an apparent diffusion coefficient of 4.12 × 10-7 m2 s-1 for the hydroxide ions and confirmed the transport of chloride ions into the alkaline gel. The re-alkalisation was tested on fully carbonated mortar prisms made from Portland cement. Re-alkalisation of the mortar was confirmed by the phenolphthalein test according to DIN EN 14630:2007-01 and by a control experiment with pure calcium carbonate using IR spectroscopy.

Tailoring Biomaterial Compatibility: In Vivo Tissue Response versus in Vitro Cell Behavior

Biocompatibility relies essentially on surface phenomena, represented by cell-cell, cell-material and material (polymer)-protein interactions. An in vivo and in vitro experimental investigation was carried out on the biomaterials of two different classes with a good potential for in situ utilisation. Non-resorbable (Polypyrrole, Polyaniline, Polyimide) and resorbable (PLLA-PDXO-PLLA) materials for tissue engineering were studied for their overall tissue tolerance and cellular interactions. These non-resorbable polymers conceived for biosensor applications and implantable drug-delivery systems are intrinsically conductive. The PLLA-PDXO-PLLA triblock copolymer showed interesting tensile properties for bone and cartilage tissue engineering due to the presence of 1,5-dioxepan-2-one. In vitro and in vivo parallel studies showed an interesting correspondence: a) the cells in contact with the resorbable material that appeared to be capable of migratory-regenerative aspects in vitro exhibited good compatibility in vivo; whereas b) the non-resorbable materials, which are designed to remain in situ in vivo, were seen to have the potential to represent an adverse factor (inflammation, fibrotic reactions) that correlated with some aspects of cell behaviour in vitro.

Natural and Synthetic Polyesters for Musculoskeletal Tissue Repair: Experimental in Vitro and in Vivo Evaluations

Two natural Biopol™ polyesters, containing 8% (D400G) and 12% (D600G) of hydroxyvalerate component, and a synthetic polyester based on 1,4 cyclohexanediol [Poly(cyclohexyl-sebacate) - PCS] were studied to investigate their in vitro and in vivo behavior for application in musculoskeletal tissue repair. The polyesters were placed in direct contact with L929 fibroblasts and cell proliferation (WST-1), cytotoxic effect (LDH), synthetic activity (total proteins) and cytokine production (IL-1β, IL-6, TNFα) were assessed after an incubation period of 72 hours and 7 days. Then, 12 Sprague-Dawley rats underwent dorsal subcutaneous implants of tested polyesters under general anesthesia. After 1 and 4 weeks from surgery, the animals were pharmacologically euthanized and the implants retrieved with surrounding tissue for histologic and histomorphometric investigations. In vitro results showed that D600G behaved a little worse in comparison to other tested polyesters in terms of cell proliferation and TNFα at 7 days. PCS presented the lowest total protein value at 7 days. In vivo results indicated that PCS implants produced a higher (p < 0.01) extent of inflammatory tissue in comparison to D600G at 1 week and to D400G at 4 weeks, and the lowest vascular densities at both experimental times. D400G seems to be the most suitable material for biomedical application when tested in fibroblast cultures and in the subcutaneous tissue of rats.

Loading of BMP-2-related peptide onto three-dimensional nano-hydroxyapatite scaffolds accelerates mineralization in critical-sized cranial bone defects

Extrusion free-forming, as a rapid prototyping technique, is extensively applied in fabricating ceramic material in bone tissue engineering. To improve the osteoinductivity of nano-hydroxyapatite (nHA) scaffold fabricated by extrusion free-forming, in this study, we incorporated a new peptide (P28) and optimized the superficial microstructure after shaping by controlling the sintering temperature. P28, a novel bone morphogenic protein 2 (BMP-2)-related peptide, was designed in this study. Analysis of the structure, physicochemical properties and release kinetics of P28 from nHA sintered at temperatures ranging from 1000 °C to 1400 °C revealed that nHA sintered at 1000 °C had higher porosity, preferable pore size and better capacity to control P28 release than that sintered at other temperatures. Moreover, the nHA scaffold sintered at 1000 °C with P28 showed improved adhesion, proliferation and osteogenic differentiation of MC3T3-E1 cells compared with scaffolds lacking P28 or BMP-2. In vivo, nHA scaffolds sintered at 1000 °C with P28 or BMP-2 induced greater bone regeneration in critical-sized rat cranial defects at 6 and 12 weeks post-implantation compared with scaffolds lacking P28 or BMP-2. Thus, nHA scaffolds sintered at 1000 °C and loaded with P28 may be excellent biomaterials for bone tissue engineering. Copyright © 2016 John Wiley & Sons, Ltd.

A defined synthetic substrate for serum-free culture of human stem cell derived cardiomyocytes with improved functional maturity identified using combinatorial materials microarrays

Cardiomyocytes from human stem cells have applications in regenerative medicine and can provide models for heart disease and toxicity screening. Soluble components of the culture system such as growth factors within serum and insoluble components such as the substrate on which cells adhere to are important variables controlling the biological activity of cells. Using a combinatorial materials approach we develop a synthetic, chemically defined cellular niche for the support of functional cardiomyocytes derived from human embryonic stem cells (hESC-CMs) in a serum-free fully defined culture system. Almost 700 polymers were synthesized and evaluated for their utility as growth substrates. From this group, 20 polymers were identified that supported cardiomyocyte adhesion and spreading. The most promising 3 polymers were scaled up for extended culture of hESC-CMs for 15 days and were characterized using patch clamp electrophysiology and myofibril analysis to find that functional and structural phenotype was maintained on these synthetic substrates without the need for coating with extracellular matrix protein. In addition, we found that hESC-CMs cultured on a co-polymer of isobornyl methacrylate and tert-butylamino-ethyl methacrylate exhibited significantly longer sarcomeres relative to gelatin control. The potential utility of increased structural integrity was demonstrated in an in vitro toxicity assay that found an increase in detection sensitivity of myofibril disruption by the anti-cancer drug doxorubicin at a concentration of 0.05 µM in cardiomyocytes cultured on the co-polymer compared to 0.5 µM on gelatin. The chemical moieties identified in this large-scale screen provide chemically defined conditions for the culture and manipulation of hESC-CMs, as well as a framework for the rational design of superior biomaterials.

Controlling whole blood activation and resultant clot properties by carboxyl and alkyl functional groups on material surfaces: a possible therapeutic approach for enhancing bone healing

Most research virtually ignores the important role of a blood clot in supporting bone healing.

Patterned polymer films via reactive silane infusion-induced wrinkling

A method for simultaneously patterning and functionalizing thin poly(2-hydroxyethyl methacrylate) films through a reactive silane infusion based wrinkling is developed. Wrinkled patterns with tunable wavelengths on submicrometer size are easily produced over large area surfaces and can express a wide variety of chemical functional groups on the surface. The characteristic wavelength of wrinkling scales linearly with initial film thickness, in agreement with a gradationally swollen film model. Results from X-ray photoelectron spectroscopy confirm that the wrinkled film is composed of two layers: a gradient cross-linked top layer and a uniform un-cross-linked bottom layer. The surface chemical properties of wrinkles can be easily tuned by infusion of different functional silanes. Hierarchical wrinkled patterns with micro/nano structure can be achieved by combining wrinkling with other simple lithography methods. Wrinkled nanopatterns can be used as a mold to transfer the topology to a variety of other materials using nanoimprint lithography.

Modulation of chondrocyte behavior through tailoring functional synthetic saccharide-peptide hydrogels

Tailoring three-dimensional (3D) biomaterial environments to provide specific cues in order to modulate function of encapsulated cells could potentially eliminate the need for addition of exogenous cues in cartilage tissue engineering. We recently developed saccharide-peptide copolymer hydrogels for cell culture and tissue engineering applications. In this study, we aim to tailor our saccharide-peptide hydrogel for encapsulating and culturing chondrocytes in 3D and examine the effects of changing single amino acid moieties differing in hydrophobicity/hydrophilicity (valine (V), cysteine (C), tyrosine (Y)) on modulation of chondrocyte function. Encapsulated chondrocytes remained viable over 21 days in vitro. Glycosaminoglycan and collagen content was significantly higher in Y-functionalized hydrogels compared to V-functionalized hydrogels. Extensive matrix accumulation and concomitant increase in mechanical properties was evident over time, particularly with the presence of Y amino acid. After 21 days in vitro, Y-functionalized hydrogels attained a modulus of 193 ± 46 kPa, compared to 44 ± 21 kPa for V-functionalized hydrogels. Remarkably, mechanical and biochemical properties of chondrocyte-laden hydrogels were modulated by change in a single amino acid moiety. This unique property, combined with the versatility and biocompatibility, makes our saccharide-peptide hydrogels promising candidates for further investigation of combinatorial effects of multiple functional groups on controlling chondrocyte and other cellular function and behavior.

Implantable polyimide cable for multichannel high-data-rate neural recording microsystems

To avoid or minimize postimplantation injury as a result of brain micromotion relative to the skull, a flexible multichannel polyimide (PI) cable was designed and microfabricated for data and power transmission between an intracranial IC recording from a neural probe array and an extracranial IC exchanging power and data wirelessly with an external unit. Surface characteristics, electrical properties, and cytocompatibility of the PI ribbon cable were investigated in this study. Scanning electron microscopic examination and atomic force microscopy analyses showed that the surface of the PI ribbon cable became significantly rougher due to the reactive oxygen ion etching process to open bonding pads. The enhanced surface roughness was also responsible for the increase in wettability and water absorption rate. However, water permeability measurement revealed that the micromachining fabrication process did not meaningfully affect the acceptable water vapor transmission rate of PI. Moreover, electrical properties, such as insertion loss, isolation between channels and data transmission capacity, were assessed for each channel of the PI ribbon cable on the basis of scattering parameter (S-parameter) measurement. Finally, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay and live/dead intracellular staining tests were carried out to evaluate cell behaviors on the PI ribbon cable, indicating that the PI ribbon cable did not have acute cytotoxicity and appeared to be as cytocompatible as blank PI foils.

Electrospun conducting polymer nanofibers and electrical stimulation of nerve stem cells

Tissue engineering of nerve grafts requires synergistic combination of scaffolds and techniques to promote and direct neurite outgrowth across the lesion for effective nerve regeneration. In this study, we fabricated a composite polymeric scaffold which is conductive in nature by electrospinning and further performed electrical stimulation of nerve stem cells seeded on the electrospun nanofibers. Poly-L-lactide (PLLA) was blended with polyaniline (PANi) at a ratio of 85:15 and electrospun to obtain PLLA/PANi nanofibers with fiber diameters of 195 ± 30 nm. The morphology, chemical and mechanical properties of the electrospun PLLA and PLLA/PANi scaffolds were carried out by scanning electron microscopy (SEM), X-ray photo electron spectroscopy (XPS) and tensile instrument. The electrospun PLLA/PANi fibers showed a conductance of 3 × 10⁻⁹ S by two-point probe measurement. In vitro electrical stimulation of the nerve stem cells cultured on PLLA/PANi scaffolds applied with an electric field of 100 mV/mm for a period of 60 min resulted in extended neurite outgrowth compared to the cells grown on non-stimulated scaffolds. Our studies further strengthen the implication of electrical stimulation of nerve stem cells on conducting polymeric scaffolds towards neurite elongation that could be effective for nerve tissue regeneration.

Hydrogels for the repair of articular cartilage defects

The repair of articular cartilage defects remains a significant challenge in orthopedic medicine. Hydrogels, three-dimensional polymer networks swollen in water, offer a unique opportunity to generate a functional cartilage substitute. Hydrogels can exhibit similar mechanical, swelling, and lubricating behavior to articular cartilage, and promote the chondrogenic phenotype by encapsulated cells. Hydrogels have been prepared from naturally derived and synthetic polymers, as cell-free implants and as tissue engineering scaffolds, and with controlled degradation profiles and release of stimulatory growth factors. Using hydrogels, cartilage tissue has been engineered in vitro that has similar mechanical properties to native cartilage. This review summarizes the advancements that have been made in determining the potential of hydrogels to replace damaged cartilage or support new tissue formation as a function of specific design parameters, such as the type of polymer, degradation profile, mechanical properties and loading regimen, source of cells, cell-seeding density, controlled release of growth factors, and strategies to cause integration with surrounding tissue. Some key challenges for clinical translation remain, including limited information on the mechanical properties of hydrogel implants or engineered tissue that are necessary to restore joint function, and the lack of emphasis on the ability of an implant to integrate in a stable way with the surrounding tissue. Future studies should address the factors that affect these issues, while using clinically relevant cell sources and rigorous models of repair.

The dependence of MG63 osteoblast responses to (meth)acrylate-based networks on chemical structure and stiffness

The cell response to an implant is regulated by the implant's surface properties including topography and chemistry, but less is known about how the mechanical properties affect cell behavior. The objective of this study was to evaluate how the surface stiffness and chemistry of acrylate-based copolymer networks affect the in vitro response of human MG63 pre-osteoblast cells. Networks comprised of poly(ethylene glycol) dimethacrylate (PEGDMA; Mn approximately 750) and diethylene glycol dimethacrylate (DEGDMA) were photopolymerized at different concentrations to produce three compositions with moduli ranging from 850 to 60 MPa. To further decouple chemistry and stiffness, three networks comprised of 2-hydroxyethyl methacrylate (2HEMA) and PEGDMA or DEGDMA were also designed that exhibited a range of moduli similar to the PEGDMA-DEGDMA networks. MG63 cells were cultured on each surface and tissue culture polystyrene (TCPS), and the effect of copolymer composition on cell number, osteogenic markers (alkaline phosphatase specific activity and osteocalcin), and local growth factor production (OPG, TGF-beta1, and VEGF-A) were assessed. Cells exhibited a more differentiated phenotype on the PEGDMA-DEGDMA copolymers compared to the 2HEMA-PEGDMA copolymers. On the PEGDMA-DEGDMA system, cells exhibited a more differentiated phenotype on the stiffest surface indicated by elevated osteocalcin compared with TCPS. Conversely, cells on 2HEMA-PEGDMA copolymers became more differentiated on the less stiff 2HEMA surface. Growth factors were regulated in a differential manner. These results indicate that copolymer chemistry is the primary regulator of osteoblast differentiation, and the effect of stiffness is secondary to the surface chemistry.

Biosensors for phenolic compounds by immobilization of tyrosinase in photocurable methacrylic-acrylic membranes of varying hydrophilicities

Electrochemical biosensors for phenolic compound determination were developed by immobilization of tyrosinase enzyme in a series of methacrylic-acrylic based biosensor membranes deposited directly using a photocuring method. By modifying the hydrophilicity of the membranes using different proportions of 2-hydroxyethyl methacrylate (HEMA) and butyl acrylate (nBA), we developed biosensor membranes of different hydrophilic characters. The differences in hydrophilicity of these membranes led to changes in the sensitivity of the biosensors towards different phenolic compounds. In general biosensors constructed from the methacrylic-acrylic based membranes showed the poorest response to catechol relative to other phenolic compounds, which is in contrast to many other biosensors based on tyrosinase. The decrease in hydrophilicity of the membrane also allowed better selectivity towards chlorophenols. However, phenol biosensors constructed from the more hydrophilic membrane materials demonstrated better analytical performance towards phenol compared with those made from less hydrophilic ones. For the detection of phenols, these biosensors with different membranes gave detection limits of 0.13-0.25 microM and linear response range from 6.2-54.2 microM phenol. The phenol biosensors also showed good phenol recovery from landfill leachate samples (82-117%).

Mechanical and morphological evaluation of osteochondral implants in dogs

The mechanical behavior of osteochondral defects was evaluated in this study with the intention of developing alternative procedures. Cylindrical pins (5.00 mm in diameter and in height) made of pHEMA hydrogel covered ultra-high molecular weight polyethylene (UHMWPE) or beta-tricalcium phosphate (beta-TCP) matrix were used. Ostoechondral defects were caused in the knees of adult dogs and the evaluation was carried out after a 9-month follow-up period. The mechanical behavior of the implants was evaluated by means of an indentation creep test that showed that the UHMWPE matrix maintained its viscoelastic behavior even after follow-up time, while the beta-TCP matrix osteochondral implants presented significant alterations. It is believed that the beta-TCP osteochondral implants were unable to withstand the load applied, causing an increase of complacency when compared to the UHMWPE osteochondral implants. Based on micro and macroscopic analysis, no significant wear was observed in either of the osteochondral implants when compared to the controls. However, morphological alterations, with fragmentation indices in the patella, were observed either due to friction with the hydrogel in the first postoperative months or due to forming of a dense conjunctive tissue. This wear mechanism caused on the counterface of the implant (patella) was observed, notwithstanding the osteochondral implant studied.

Structure and properties of methacrylate-endcapped caprolactone networks with modulated water uptake for biomedical applications

Methacrylate-endcapped caprolactone (CLMA) networks were synthesized and copolymerized with 2-hydroxyethyl acrylate (HEA) seeking to tailor the hydrophilicity of the system. The resulting structure of the copolymer network is investigated by differential scanning calorimetry, thermogravimetry, and Fourier transform infrared spectroscopy. The dynamic swelling behavior and the equilibrium water sorption is measured and correlated with the microstructure. The experimental results allow one to conclude that the new material is a random copolymer of both components, HEA and CLMA. The effect of cell attachment and proliferation on the new copolymer networks was observed by in vitro culture of human chondrocytes up to 8 days. Enhanced cellular adhesion, similar to that obtained with tissue culture polystyrene (TCPS), was obtained in the hydrophilized systems. The new copolymers are appropriate for the fabrication of scaffolds with controlled porosity for tissue engineering.

Porous poly(2-hydroxyethyl methacrylate) hydrogels synthesized within high internal phase emulsions

Hydrogels, such as those based on poly(2-hydroxyethyl methacrylate) (PHEMA), are hydrophilic three dimensional network structures that undergo extensive swelling in water. PolyHIPEs are highly porous, crosslinked polymers typically synthesized within high internal phase emulsions (HIPEs). This research describes materials with enhanced water absorption that combine hydrogel water absorption with capillary action by synthesizing PHEMA-based polyHIPEs within oil-in-water HIPEs. The variation in the ,-methylenebisacrylamide (MBAM) crosslinking comonomer content yields a narrow synthesis window in which water-swollen micro-gel particles phase separate, agglomerate, and form a heterogeneous polyHIPE wall structure with nanoscale porosity. Surprisingly, a hydrogel polyHIPE with a relatively high MBAM content also had the highest surface area and the highest water absorption. Ultimately, it is the influence of the MBAM content on the polymer hydrophilicity and on the porous structure that determines its effects on the properties.

Development of wollastonite-poly(ethylmethacrylate co-vinylpyrrolidone) based materials for multifunctional devices

The manufacturing of a composite made of a synthetic bioactive ceramic, pseudowollastonite (psW), and a bioresorbable copolymer ethylmethacrylate-vinylpyrrolidone (EMA/VP) is presented in this article. psW porous blocks were produced by dipping an open porous polyurethane foam in a psW containing slurry. A 40/60 wt % EMA/VP monomers mixture was poured on the blocks, and free radical polymerization initiated by azobis(isobutyronitrile) at 50 degrees C. Disks of 1 mm height were obtained by cutting the composite with a diamond saw, and bioresorption and bioactivity of the specimens were tested by immersion of the disks into SBF. A ceramic/polymer weight ratio of 72/28, greater than the usually achievable ratio by polymeric solidification of slurries of monomers charged with a powdered solid component, has been obtained. The system is bioactive and does not change the pH of the medium during the degradation test.

The wettability of intrasynovial and extrasynovial tendons

PURPOSE

The surface properties of biologic materials are important to their observed physiochemical responses, mechanical interactions, and compatibility with other materials. The purpose of this study was to characterize further the surface properties of canine tendons, specifically how they interface with fluids--that is, their wettability.

METHODS

Drop-shape analysis was used to study contact angles on intrasynovial and extrasynovial tendon surfaces. This standard goniometric method was used to estimate tendon-wettability properties.

RESULTS

This study showed that extrasynovial tendon portions (particularly the dorsal sides) are more wettable than intrasynovial tendons. We also showed that trypsin digestion of tendon surfaces increases their wettability.

CONCLUSIONS

The wettability differences between intrasynovial and extrasynovial canine tendons may help to explain known differences in the propensities of these 2 different tendon types to form adhesions after surgery.

Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects

OBJECTIVE

To review the basic scientific status of repair in articular cartilage tissue and to assess the efficiency of current clinical therapies instigated for the treatment of structural lesions generated therein as a result of trauma or during the course of various diseases, notably osteoarthritis (OA). Current scientific trends and possible directions for the future will also be discussed.

DESIGN

A systematic and critical analysis is undertaken, beginning with a description of the spontaneous repair responses in different types of lesion. Surgical interventions aimed at inducing repair without the use of active biologics will then be considered, followed by those involving active biologics and those drawing on autogenic and allogeneic tissue transplantation principles. Cell transplantation approaches, in particular novel tissue engineering concepts, will be critically presented. These will include growth-factor-based biological treatments and gene transfection protocols. A number of technical problems associated with repair interventions, such as tissue integration, tissue retention and the role of mechanical factors, will also be analysed.

RESULTS

A critical analysis of the literature reveals the existence of many novel and very promising biologically-based approaches for the induction of articular cartilage repair, the vast majority of which are still at an experimental phase of development. But prospective, double-blinded clinical trials comparing currently practiced surgical treatments have, unfortunately, not been undertaken.

CONCLUSION

The existence of many new and encouraging biological approaches to cartilage repair justifies the future investment of time and money in this research area, particularly given the extremely high socio-economic importance of such therapeutic strategies in the prevention and treatment of these common joint diseases and traumas. Clinical epidemiological and prospective trials are, moreover, urgently needed for an objective, scientific appraisal of current therapies and future novel approaches.