Surface modification of poly-L-lactide by photografting of hydrophilic polymers towards improving its hydrophilicity

The Role of Calcium Hydroxylapatite (Radiesse) as a Regenerative Aesthetic Treatment: A Narrative Review

For decades, a wide variety of natural and synthetic materials have been used to augment human tissue to improve aesthetic outcomes. Dermal fillers are some of the most widely used aesthetic treatments throughout the body. Initially, the primary function of dermal fillers was to restore depleted volume. As biomaterial research has advanced, however, a variety of biostimulatory fillers have become staples in aesthetic medicine. Such fillers often contain a carrying vehicle and a biostimulatory material that induces de novo synthesis of major structural components of the extracellular matrix. One such filler, Radiesse (Merz Aesthetics, Raleigh, NC), is composed of calcium hydroxylapatite microspheres suspended in a carboxymethylcellulose gel. In addition to immediate volumization, Radiesse treatment results in increases of collagen, elastin, vasculature, proteoglycans, and fibroblast populations via a cell-biomaterial-mediated interaction. When injected, Radiesse acts as a cell scaffold and clinically manifests as immediate restoration of depleted volume, improvements in skin quality and appearance, and regeneration of endogenous extracellular matrices. This narrative review contextualizes Radiesse as a regenerative aesthetic treatment, summarizes its unique use cases, reviews its rheological, material, and regenerative properties, and hypothesizes future combination treatments in the age of regenerative aesthetics.

LEVEL OF EVIDENCE: 5

Fabrication of silk fibroin film enhanced by acid hydrolyzed silk fibroin nanowhiskers to improve bacterial inhibition and biocompatibility efficacy

In this study, silk fibroin nanowhiskers (SNWs) were extracted from natural silk fiber by sulfuric acid hydrolysis with the assistance of ultrasonic wave treatment. The obtained SNWs were mixed with regenerated silk fibroin (RSF) solution to fabricate the SNWs/RSF films. The fabricating SNWs were systematically characterized by using SEM, FTIR, and the SNWs/RSF films were observed by digital camera, PM, etc. The results show that the monodisperse SNWs are evenly distributed in the RSF film. The presence of SNWs in RSF film significantly improves the performances of the film, including the swelling ability, mechanical properties, hydrophilicity, antibacterial efficacy, cytocompatibility. Meanwhile, the SNWs/RSF film can endorse the wound healing efficiency in vivo mice wound site. The proposed techniques for extracting SNWs and fabricating silk fibroin composite film may provide a valuable method for creating an ideal silk-based material for biomedical applications.

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.

Surface modification of PdlLGA microspheres with gelatine methacrylate: Evaluation of adsorption, entrapment, and oxygen plasma treatment approaches

Injectable poly (dl-lactic-co-glycolic acid) (PdlLGA) microspheres are promising candidates as biodegradable controlled release carriers for drug and cell delivery applications; however, they have limited functional groups on the surface to enable dense grafting of tissue specific biocompatible molecules. In this study we have evaluated surface adsorption, entrapment and oxygen plasma treatment as three approaches to modify the surfaces of PdlLGA microspheres with gelatine methacrylate (gel-MA) as a biocompatible and photo cross-linkable macromolecule. Time of flight secondary ion mass spectroscopy (TOF SIMS) and X-ray photoelectron spectroscopy (XPS) were used to detect and quantify gel-MA on the surfaces. Fluorescent and scanning electron microscopies (SEM) were used to image the topographical changes. Human mesenchymal stem cells (hMSCs) of immortalised cell line were cultured on the surface of gel-MA modified PdlLGA microspheres and Presto-Blue assay was used to study the effect of different surface modifications on cell proliferation. Data analysis showed that the oxygen plasma treatment approach resulted in the highest density of gel-MA deposition. This study supports oxygen plasma treatment as a facile approach to modify the surface of injectable PdlLGA microspheres with macromolecules such as gel-MA to enhance proliferation rate of injected cells and potentially enable further grafting of tissue specific molecules.

Statement of Significance

Poly (dl lactic-co-glycolic) acid (PdlLGA) microspheres offer limited functional groups on their surface to enable proper grafting of tissue specific bioactive molecules. To overcome this limitation, previous approaches have suggested using alkaline solutions to introduce active groups to the surface; however, they may compromise surface topography and lose any potential surface patterns. Plasma polymerisation of bioactive monomers has been suggested to enhance surface biocompatibility; however, it is not applicable on low vapour pressure macromolecules such as most extracellular matrix (ECM) proteins and growth factors. This study aims to evaluate three different approaches to modify the surface of PdlLGA microspheres with gelatine-methacrylate (gel-MA) to enable further grafting of cross-linkable biomolecules without compromising the surface topography or the biocompatibility of the system.

Multifunctional REDV-conjugated zwitterionic polycarboxybetaine–polycaprolactone hybrid surfaces for enhanced antibacterial activity, anti-thrombogenicity and endothelial cell proliferation

Multifunctional PCL hybrid surfaces are developed by grafting of REDV–zwitterionic polycarboxybetaine conjugates via surface-initiated ATRP.

In vitro degradation, hemolysis, and cytocompatibility of PEO/PLLA composite coating on biodegradable AZ31 alloy

Magnesium and its alloys have large potential as degradable and absorbable biomaterials because of their mechanical properties and biocompatibility. However, their corrosion resistance is usually inadequate especially in physiological environment, which limits their broad applications in biomedical areas. In this work, plasma electrolytic oxidized/poly(l-lactide) (PEO/PLLA) composite coating was successfully fabricated on biodegradable AZ31 alloy by combing PEO process and sealing with PLLA. The microstructure, elemental composition, and phase composition of the PEO/PLLA composite coating were investigated. The in vitro degradation of the PEO/PLLA composite coating in simulated body fluid (SBF) was also systematically evaluated. The results revealed that the PEO/PLLA composite coating improved the corrosion resistance of AZ31 alloy significantly. The corrosion potential shifted from -1.663V to more positive position -1.317 V and the corrosion current density was reduced with six-order of magnitude. The Mg(2+) ions, hydrogen release, and pH value change of solution caused by degradation were all decreased significantly. Moreover, the PEO process played a critical role in sustaining the integrity of the implant in long-term service. The result of hemolysis test showed that the PEO/PLLA composite coating vested AZ31 alloy a low hemolysis ratio (0.806 ± 0.771)%, which is much lower than the safe value of 5% according to ISO 10993-4. For the cytocompatibility test, compared with bare AZ31 alloy and PEO coating, MC3T3-E1 cells showed much better adhesion and proliferation on the PEO/PLLA composite coating with nearly 4-fold increase of cells after 7-day cultivation, indicating that the PEO/PLLA composite coating has good biocompatibility for biomedical applications.

Degradable polyester scaffolds with controlled surface chemistry combining minimal protein adsorption with specific bioactivation

Advanced biomaterials and scaffolds for tissue engineering place high demands on materials and exceed the passive biocompatibility requirements previously considered acceptable for biomedical implants. Together with degradability, the activation of specific cell–material interactions and a three-dimensional environment that mimics the extracellular matrix are core challenges and prerequisites for the organization of living cells to functional tissue. Moreover, although bioactive signalling combined with minimization of non-specific protein adsorption is an advanced modification technique for flat surfaces, it is usually not accomplished for three-dimensional fibrous scaffolds used in tissue engineering. Here, we present a one-step preparation of fully synthetic, bioactive and degradable extracellular matrix-mimetic scaffolds by electrospinning, using poly(D,L-lactide-co-glycolide) as the matrix polymer. Addition of a functional, amphiphilic macromolecule based on star-shaped poly(ethylene oxide) transforms current biomedically used degradable polyesters into hydrophilic fibres, which causes the suppression of non-specific protein adsorption on the fibres’ surface. The subsequent covalent attachment of cell-adhesion-mediating peptides to the hydrophilic fibres promotes specific bioactivation and enables adhesion of cells through exclusive recognition of the immobilized binding motifs. This approach permits synthetic materials to directly control cell behaviour, for example, resembling the binding of cells to fibronectin immobilized on collagen fibres in the extracellular matrix of connective tissue.

Characterization and cytocompatibility of surface modified polyamide66

The chemical modification of polyamide66 (PA66) membrane by graft polymerization with methacrylic acid (MAA) was initiated under ultraviolet light. Subsequently, covalent immobilization of bioactive surface was obtained by coupling gelatin to the MAA graft chains with the aid of a water-soluble carbodiimide (WSC). The existence of carboxyl groups grafted on PA66 surface was verified quantitatively by UV-vis spectroscopy. The chemical composition, surface topography, and wettability were investigated by Fourier transform infrared (FTIR) technique, X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle (WCA) measurement. Results showed that the WCA changed from the original value of 67.5 degrees to the minimum value of 30 degrees after grafting with PMAA. Original PA66 displayed a smooth surface morphology [root mean square (RMS) roughness was around 16 nm]. The modified PA66 surface exhibited an increase in roughness (RMS roughness around 21 nm). Simultaneously, the original and modified PA66 membranes were cultured with MG63 cells to investigate their cytocompatibility. The in vitro biological evaluation demonstrated that the immobilization of gelatin on PA66 membrane acted as a good template for the attachment and proliferation of cells. Also, the less toxic reagents and the moderate reaction conditions involved will be very helpful for the introduction of functional groups onto polymer surface.

Alkali etching of a poly(lactide) fiber

Alkali etching of a poly(l-lactic acid) fiber was studied by exposing the fiber surface to sodium hydroxide solutions. The factors examined included the etching time (0-1.5 h), alkali concentration (0.25-3 mol/L), and etching temperature (25-80 degrees C). The extent of etching was determined gravimetrically. Both weight loss and mechanical testing results suggest that alkali etching is strictly a surface hydrolysis reaction, as opposed to a bulk reaction, and thus the weight loss rate decreases with a shrinking fiber radius. A slight increase in the fiber crystallinity observed from thermal analysis was interpreted as a result of surface-limited etching on a sheath-core fiber microstructure. The dependence of the rate on the alkali concentration is nonlinear, suggesting that the fiber weight loss rate is subject to both chemical hydrolysis and transport limitations. The dependence of the rate on the temperature follows the Arrhenius equation. The fiber weight after etching can thus be predicted by an overall expression combining all factors: time, temperature, concentration, and fiber diameter.

Surface modified electrospun nanofibrous scaffolds for nerve tissue engineering

The development of biodegradable polymeric scaffolds with surface properties that dominate interactions between the material and biological environment is of great interest in biomedical applications. In this regard, poly-ε-caprolactone (PCL) nanofibrous scaffolds were fabricated by an electrospinning process and surface modified by a simple plasma treatment process for enhancing the Schwann cell adhesion, proliferation and interactions with nanofibers necessary for nerve tissue formation. The hydrophilicity of surface modified PCL nanofibrous scaffolds (p-PCL) was evaluated by contact angle and x-ray photoelectron spectroscopy studies. Naturally derived polymers such as collagen are frequently used for the fabrication of biocomposite PCL/collagen scaffolds, though the feasibility of procuring large amounts of natural materials for clinical applications remains a concern, along with their cost and mechanical stability. The proliferation of Schwann cells on p-PCL nanofibrous scaffolds showed a 17% increase in cell proliferation compared to those on PCL/collagen nanofibrous scaffolds after 8 days of cell culture. Schwann cells were found to attach and proliferate on surface modified PCL nanofibrous scaffolds expressing bipolar elongations, retaining their normal morphology. The results of our study showed that plasma treated PCL nanofibrous scaffolds are a cost-effective material compared to PCL/collagen scaffolds, and can potentially serve as an ideal tissue engineered scaffold, especially for peripheral nerve regeneration.

Beneficial effect of hydrophilized porous polymer scaffolds in tissue-engineered cartilage formation

Three dimensional (3D) porous poly(L-lactic acid) (PLLA) scaffolds were fabricated using a modified gas foaming method whose effervescent porogens were a mixture of sodium bicarbonate and citric acid. To improve chondrocyte adhesion, the scaffolds were then hydrophilized through oxygen plasma treatment and in situ graft polymerization of acrylic acid (AA). When the physical properties of AA-grafted scaffolds were examined, the porosity and pore size were 87 approximately 93% and 100 approximately 300 microm, respectively. The pore sizes were highly dependent on the varying ratios (w/w) between porogen and polymer solution. Influenced by their pore sizes, the compressive moduli of scaffolds significantly decreased with increasing pore size. The altered surface characteristics were clearly reflected in the reduced water contact angles that meant a significant hydrophilization with the modified polymer surface. Electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometer (ToF-SIMS) also confirmed the altered surface chemistry. When chondrocytes were seeded onto the AA-grafted PLLA scaffolds, cell adhesion and proliferation were substantially improved as compared to the unmodified scaffolds. The benefit of the modified scaffolds was clear in the gene expressions of collagen type II that was significantly upregulated after 4-week culture. Safranin-O staining also identified greater glycosaminoglycan (GAG) deposition in the modified scaffold. The AA-grafted porous polymer scaffolds were effective for cell adhesion and differentiation, making them a suitable platform for tissue-engineered cartilage.

Controlling protein release from scaffolds using polymer blends and composites

We report the development of three protein loaded polymer blend and composite materials that modify the release kinetics of the protein from poly(dl-lactic acid) (P(dl)LA) scaffolds. P(dl)LA has been combined with either poly(ethylene glycol) (PEG), poly(caprolactone) (PCL) microparticles or calcium alginate fibres using supercritical CO(2) (scCO(2)) processing to form single and dual protein release scaffolds. P(dl)LA was blended with the hydrophilic polymer PEG using scCO(2) to increase the water uptake of the resultant scaffold and modify the release kinetics of an encapsulated protein. This was demonstrated by the more rapid release of the protein when compared to the release rate from P(dl)LA only scaffolds. For the P(dl)LA/alginate scaffolds, the protein loaded alginate fibres were processed into porous protein loaded P(dl)LA scaffolds using scCO(2) to produce dual release kinetics from the scaffolds. Protein release from the hydrophilic alginate fibres was more rapid in the initial stages, complementing the slower release from the slower degrading P(dl)LA scaffolds. In contrast, when protein loaded PCL particles were loaded into P(dl)LA scaffolds, the rate of protein release was retarded from the slow degrading PCL phase.

Layer-by-layer assembly of chondroitin sulfate and collagen on aminolyzed poly(L-lactic acid) porous scaffolds to enhance their chondrogenesis

Layer-by-layer (LBL) assembly of cytocompatible chondroitin sulfate (CS) and collagen type I (Col) onto PLLA scaffolds were implemented to enhance the cell-material interaction. To introduce charges onto the hydrophobic and neutral PLLA surface so that the electronic assembly can be processed, the PLLA was aminolyzed in hexane diamine solution to obtain free amino groups that are positively charged at neutral pH. Ultaviolet-visible spectroscopy and ninhydrin analysis verified the consecutive deposition of CS/Col multilayers on the aminolyzed PLLA membranes. Confocal laser scanning microscopy (CLSM) observation and hydroxyproline quantification revealed the process of LBL assembly of CS/Col multilayers in the interior of PLLA porous scaffolds. In vitro chondrocyte culture found that the presence of CS and Col greatly improved the cytocompatibility of the PLLA scaffolds in terms of cell attachment, proliferation, cytoviability and GAG secretion.

Surface modification and property analysis of biomedical polymers used for tissue engineering

The response of host organism in macroscopic, cellular and protein levels to biomaterials is, in most cases, closely associated with the materials' surface properties. In tissue engineering, regenerative medicine and many other biomedical fields, surface engineering of the bio-inert synthetic polymers is often required to introduce bioactive species that can promote cell adhesion, proliferation, viability and enhanced ECM-secretion functions. Up to present, a large number of surface engineering techniques for improving biocompatibility have been well established, the work of which generally contains three main steps: (1) surface modification of the polymeric materials; (2) chemical and physical characterizations; and (3) biocompatibility assessment through cell culture. This review focuses on the principles and practices of surface engineering of biomedical polymers with regards to particular aspects depending on the authors' research background and opinions. The review starts with an introduction of principles in designing polymeric biomaterial surfaces, followed by introduction of surface modification techniques to improve hydrophilicity, to introduce reactive functional groups and to immobilize functional protein molecules. The chemical and physical characterizations of the modified biomaterials are then discussed with emphasis on several important issues such as surface functional group density, functional layer thickness, protein surface density and bioactivity. Three most commonly used surface composition characterization techniques, i.e. ATR-FTIR, XPS, SIMS, are compared in terms of their penetration depth. Ellipsometry, CD, EPR, SPR and QCM's principles and applications in analyzing surface proteins are introduced. Finally discussed are frequently applied methods and their principles to evaluate biocompatibility of biomaterials via cell culture. In this section, current techniques and their developments to measure cell adhesion, proliferation, morphology, viability, migration and gene expression are reviewed.

Grafting amine-terminated branched architectures from poly(L-lactide) film surfaces for improved cell attachment

Poly(L-lactide) (PLL) has been used as a bioabsorbable material in the medical and pharmaceutical fields. The unmodified hydrophobic PLL surface generally has low cell affinity; thus, modification of PLL film surface properties is necessary to improve its use as a biomaterial. Our surface modification method involved the use of photografting and typical wet chemistry to create branched architectures containing amine functionalities on the periphery of the grafted layers. Amine (-NH2) groups were first introduced on the PLL film surface by photoinduced grafting of 4,4'-diaminobenzophenone and the grafted branched architectures were created by subsequent reactions with succinic acid and tris(2-aminoethyl) amine. The resulting film surface was analyzed using contact angle goniometry and X-ray photoelectron spectroscopy. MC3T3 fibroblasts were cultured on unmodified PLL film and PLL films grafted with the branched structures and the films were subsequently analyzed by optical microscopy. The contact angle goniometry results showed an initial decrease and subsequent plateau in the water contact angles for the PLL films with each successive generation of the branched architectures. The X-ray photoelectron spectroscopy data provided insight into the structure of the grafted layer and revealed an increase in the nitrogen content with each generation. Optical micrographs showed enhanced cell attachment and viability on the surface-modified PLL films.

Fabrication and Characterization of Polysulfone-Dicalcium Silicate Composite Films

Polysulfone (PSU) composite films filled with β-dicalcium silicate (-Ca2SiO4) particles are prepared by the solvent casting-evaporation method. The surface morphologies and mechanical properties of the films are determined. The bioactivity of the composite films is evaluated by soaking them in simulated body fluid (SBF) and the results show that the composites are bioactive as they induce the formation of hydroxyapatite (HAp) on the surface of the composite films. The measurement of the water contact angles suggests that the incorporation of -Ca2SiO4 particles into PSU matrix can improve the hydrophilicity of the composite. PSU composite films filled with modified -dicalcium silicate (-mCa2SiO4) particles are also prepared after -Ca2SiO4 particles are treated with dodecyl alcohol through surface esterification reactions. The infrared spectra of the -mCa2SiO4 particles before and after aging in water indicate that the surface modification is reversible. The scanning electron microscope (SEM) images (micrographs) of both composites show that the dispersion of inorganic particles in the polymer matrix improves after surface modification. The PSU- -mCa2SiO4 composite is still bioactive and exhibits the same water contact angle after aging in water as compared to that of the PSU- -Ca2SiO4 composite. All these results suggest that the incorporation of -Ca2SiO4 particles is a useful method to prepare composites with improved bioactivity and hydrophilicity, and the surface modification of -Ca2SiO4 particles can improve the dispersion while retaining the bioactivity and hydrophilicity.

Poly(ethylene glycol) micro-patterns as environmentally sensitive template for selective or non-selective adsorption

Poly(ethylene glycol) (PEG), a hydrophilic and repulsive polymer to non-specific adsorption, was stamped onto carboxylic acid-enriched polymer surfaces using the micro-contact printing technique. The patterns are stabilized via hydrogen bonds. Areas printed with PEG were then shown to be non-adsorbed with fluorescein isothiocyanate (FITC)-labeled dextran, while the poly(methacrylic acid) (PMAA) regions could via hydrogen bonding. Due to this contrast, well defined dextran patterns were obtained. Tuned with pH and temperature, the PEG molecules could be detached from the surfaces, erasing the template. Moreover, ionization of PMAA at higher pH induced an abrupt transition to an extended conformation, weakening the interactions between PMAA and dextran. Not only the dextran patterns lose their spatial selectivity, but also the overall adsorption amount is much lower. The pH sensitivity was in a quite narrow range, i.e. around pH 5. As the hydrogen bonds are also temperature sensitive, the attach points of PEG molecules on the surfaces disappeared at higher temperature. For poly(acrylic acid) (PAA) photografted surfaces, the pH sensitivity was more complicated due to the formation of the compact complexes of PEG and PAA molecules.

Immobilization of Biomacromolecules onto Aminolyzed Poly(L-lactic acid) toward Acceleration of Endothelium Regeneration

By reaction of poly(L-lactic acid) (PLLA) membrane with 1,6-hexanediamine, free amino groups were introduced onto a PLLA surface, through which biocompatible macromolecules such as gelatin, chitosan, or collagen were covalently immobilized by employing glutaraldehyde as a coupling agent. The existence of free amino groups on the aminolyzed PLLA surface was verified quantitatively by the ninhydrin analysis method, which revealed that surface NH(2) density increased with 1,6-hexanediamine concentration or aminolyzing time. Scanning force microscopy measurements detected an increase in surface roughness after aminolysis. The culture of human umbilical vein endothelial cells (HUVECs) in vitro proved that the cell proliferation rate and cell activity of both aminolyzed and biomacromolecule-immobilized PLLAs were improved compared with control PLLA. Scanning electron microscopy observation showed more spreading and flat cell morphology after HUVECs were cultured for 4 days on either aminolyzed or biomacromolecule-immobilized PLLA membranes. Confluent cell layers were observed on the modified PLLA. Measurement of von Willebrand factor secreted by these HUVECs confirmed that endothelium function was maintained. Therefore, aminolysis and biomacromolecule immobilization are promising ways to accelerate endothelium regeneration, which is crucial for blood vessel tissue engineering.

Endothelial cell functionsin vitro cultured on poly(L-lactic acid) membranes modified with different methods

We recently developed several methods to enhance the cell-polymer interactions. Optimal conditions for each method have been revealed separately by in vitro cell culture. As a practical consideration for construction of tissue-engineered organs, it is necessary to consider which is the most suitable and convenient in clinical applications. To compare the efficiency of these methods with respect to cell functions, poly-L-lactic acid (PLLA) was selected as matrix being modified by 1) aminolysis (PLLA-NH(2)), 2) collagen immobilization with GA (PLLA-GA-Col), 3) chondroitin sulfate (CS)/collagen layer-by-layer (LBL) assembly (PLLA-CS/Col), 4) photo-induced grafting copolymerization of hydrophilic methacrylic acid (MAA) (PLLA-g-PMAA), and 5) further immobilization of collagen with 1-ethyl-3-(3-dimethylamino propyl) carbodiimide hydrochloride (EDAC) (PLLA-g-PMAA-Col). The surface wettability of the modified PLLA was determined by water contact angle measurements. The cell response to the modified PLLA was quantitatively assessed and compared by using human umbilical endothelial cells (HUVECs) culture. Our results indicate that all the modifications can improve the cytocompatibility of PLLA (e.g., cells can attach with spreading morphology, proliferate and secret vWF and 6-keto-PGF(1 alpha)). All the collagen-modified PLLA showed more positive cell response than those purely aminolyzed or PMAA grafted. Among all the methods, collagen immobilization by LBL assembly or GA bridging after aminolysis is more acceptable for the convenience and applicability to scaffolds.

Surface modification of poly-L-lactic acid (PLLA) membrane by grafting acrylamide: an effective way to improve cytocompatibility for chondrocytes

Poly-L-lactic acid (PLLA) membranes were photo-oxidized in hydrogen peroxide solution under ultraviolet light (UV) to introduce hydroperoxide groups onto the PLLA membrane surfaces. The photo-oxidized membranes were then immersed in acrylamide (AAm) solution containing Fe2+ to graft polyacrylamide (PAAm) onto the PLLA membrane surfaces. The density of the hydroperoxide groups introduced on the PLLA membrane surfaces varied with the temperature and the photo-oxidization time. The occurrence of grafting was verified by X-ray photoelectron spectroscopy (XPS). The degree of grafting increased with the monomer concentration and the polymerization time. Water contact angle measurements showed that the wettability of the modified PLLA membranes had improved. Chondrocytes proliferated more rapidly and were more spread out on the modified membrane than on the control PLLA membrane, indicating that the PAAm-grafted PLLA membrane has better cytocompatibility for chondrocytes.

Chondrocyte behaviors on poly-L-lactic acid (PLLA) membranes containing hydroxyl, amide or carboxyl groups

Hydrophilic groups, i.e. hydroxyl (-OH), carboxyl (-COOH) or amide (-CONH(2)) were introduced onto the poly-L-lactic acid (PLLA) membrane surfaces via the photo-induced grafting copolymerization of the corresponding monomers, i.e. hydroxyethyl methacrylate, methacrylic acid or acrylamide, respectively. Chondrocyte culture was used to study the correlation between the cell behaviors and the hydrophilic functional groups. The results showed that the cytocompatibility of the PLLA membranes with hydroxyl or amide groups on the surface was greatly improved compared to that of the original PLLA membrane. However, the PLLA membrane with carboxyl groups on the surface had even worse cytocompatibility though possessed a similar hydrophilicity.

Layer-by-layer assembly to modify poly(l-lactic acid) surface toward improving its cytocompatibility to human endothelial cells

A novel technique to introduce free amino groups onto polyester scaffolds via aminolyzing the ester groups with diamine has been developed recently. Positively charged chitosan was then deposited onto the aminolyzed poly(l-lactic acid) (PLLA) membrane surface in a layer-by-layer assembly manner using poly(styrene sulfonate, sodium salt) (PSS) as a negatively charged polyelectrolyte. The layer-by-layer deposition process of PSS and chitosan was monitored by UV-vis absorbance spectroscopy, energy transfer by fluorescence spectroscopy, and advancing contact angle measurements. The existed chitosan obviously improved the cytocompatibility of PLLA to human endothelial cells. The cell attachment, activity, and proliferation on the PLLA membranes assembled with three or five bilayers of PSS/chitosan with chitosan as the outermost layer were better than those with one bilayer of PSS/chitosan or the control PLLA. The cells also showed morphology of an elongated shape with abundant cytoplasm, and a confluent cell layer was reached after being cultured for 4 days. Measurement of von Willebrand factor secreted by these endothelial cells (ECs) verified the endothelial function. Hence, better ECs compatible PLLA were produced.