Biomaterials (v.27, #35)

Calendar (I).

Molecular basis of cell–biomaterial interaction: Insights gained from transcriptomic and proteomic studies by William M. Gallagher; Iseult Lynch; Lorcan T. Allen; Ian Miller; Stephen C. Penney; Darran P. O’Connor; Stephen Pennington; Alan K. Keenan; Kenneth A. Dawson (5871-5882).
With the growing interest in clinical interventions that involve medical devices, the role for new biomaterials in modern medicine is currently expanding at a phenomenal rate. Failure of most implant materials stems from an inability to predict and control biological phenomena, such as protein adsorption and cell interaction, resulting in an inappropriate host response to the materials. Contemporary advances in biological investigation are starting to shift focus in the biomaterials field, in particular with the advent of high-throughput methodologies for gene and protein expression profiling. Here, we examine the role that emerging transcriptomic and proteomic technologies could play in relation to biomaterial development and usage. Moreover, a number of studies are highlighted which have utilized such approaches in order to try to create a deeper understanding of cell–biomaterial interactions and, hence, improve our ability to predict and control the biocompatibility of new materials.
Keywords: Biocompatibility; Transcriptomics; DNA microarrays; Proteomics; Mass spectrometry; Cell interaction;

Biological functionalization and surface micropatterning of polyacrylamide hydrogels by Mary Rose Burnham; James N. Turner; Donald Szarowski; David L. Martin (5883-5891).
Hydrogels are useful for linking proteins to solid surfaces because their hydrophilic nature and porous structure help them to maintain these labile molecules in the native functional state. We have developed a method for creating surface-patterned, biofunctionalized hydrogels on glass or silicon, using polyacrylamide and the disulfide-containing polyacrylamide crosslinker, bis(acryloyl)cystamine. Treatment with a reducing agent created reactive sulfhydryl (–SH) groups throughout these hydrogels that were readily conjugated to iodoacetyl biotin and streptavidin (SA). Immobilization efficiency was approximately 1–2% of the total potential binding capacity of the hydrogel. Porosity of the hydrogel was not a limiting factor for SA immobilization, as determined using fluorescence confocal microscopy. Rather, steric hindrance due to the binding of SA decreased the effective porosity near the surface of the hydrogel, restricting access to the rest of the gel. Using microcontact printing, we indirectly patterned SA on the surface of the hydrogel, generating well-resolved feature sizes of 2 μm in width. Through repeated rounds of microcontact printing, multiple, adjacent protein patterns were generated on the surface of the hydrogel. Biotinylated immune complexes and lipid vesicles readily bound to SA-functionalized hydrogels, demonstrating the feasibility of using this hydrogel system to generate complex biofunctionalized surfaces.
Keywords: Hydrogel; Polyacrylamide; Bis(acryloyl)cystamine; Streptavidin; Microcontact printing;

A porous structure comprises pores and pore throats with a complex three-dimensional (3D) network structure, and many investigators have described the relationship between average pore size and the amount of bone ingrowth. However, the influence of network structure or pore throats for tissue ingrowth has rarely been discussed. Four types of bioactive porous titanium implants with different pore sizes and porosities (6 mm in diameter and 15 mm long) were analyzed using specific algorithms for 3D analysis of interconnectivity based on a micro focus X-ray computed tomography system. In vivo histomorphometric analysis was performed using the very same implants implanted into the femoral condyles of male rabbits for 6 and 12 weeks. This matching study revealed that more poorly differentiated pores tended to have narrow pore throats, especially in their shorter routes to the outside. In addition, for assessment of the entire implant, we proposed new two indices that represent the degree of bone and tissue ingrowth into an implant by considering the effect of narrow pore throats.Data obtained suggest that this sort of novel analysis is useful for evaluating bone and tissue ingrowth into porous biomaterials.
Keywords: Titanium; Porosity; Osseointegration; Interconnection; Micro-CT;

The influence of fetal bovine serum (FBS) adsorbed to poly(ethylene-co-vinyl alcohol) (EVAL) and polyvinyl alcohol (PVA) substrates (coated FBS) and FBS present in the culture medium (soluble FBS) on the behavior of embryonic rat cerebral cortical neural stem cells was studied at neurosphere level. When both coated FBS and soluble FBS were not present in the culture system, the fate and behavior of neurospheres were mediated mainly by the substrates used. When neurospheres were cultured either on FBS-coated EVAL or FBS-coated PVA substrates in the serum-free medium, the most striking morphological characteristic of neurospheres was that these neurosphere-forming cells attached and were induced to differentiate into process-bearing cell phenotypes predominantly; however, the differentiated cell phenotypes were dissimilar on these two substrates. On the contrary, when neurospheres were cultured in the medium containing 10% FBS, the neurosphere-forming cells were induced into protoplasmic cells typically but no difference in differentiated cell phenotypes on EVAL and PVA substrates was observed. Interestingly, instead of promoting process outgrowth under serum-free medium condition, coated FBS enhanced migration of differentiated protoplasmic cells when soluble FBS were present. These results inform that the substrates, coated serum, and soluble serum within the culture environment together can significantly alter cell behavior and morphological differentiation and will therefore be an important clue for the development of biomaterials to regulate the potential of the CNS neural stem cells.
Keywords: Poly(ethylene-co vinyl alcohol) (EVAL); Poly vinyl alcohol (PVA); Fetal bovine serum (FBS); Neural stem cells;

The effect of anisotropic architecture on cell and tissue infiltration into tissue engineering scaffolds by M.M.C.G. Silva; L.A. Cyster; J.J.A. Barry; X.B. Yang; R.O.C. Oreffo; D.M. Grant; C.A. Scotchford; S.M. Howdle; K.M. Shakesheff; F.R.A.J. Rose (5909-5917).
A common phenomenon in tissue engineering is rapid tissue formation on the outer edge of the scaffold which restricts cell penetration and nutrient exchange to the scaffold centre, resulting in a necrotic core. To address this problem, we generated scaffolds with both random and anisotropic open porous architectures to enhance cell and subsequent tissue infiltration throughout the scaffold for applications in bone and cartilage engineering. Hydroxyapatite (HA) and poly(d,l-lactic acid) (P dl LA) scaffolds with random open porosity were manufactured, using modified slip-casting and by supercritical fluid processing respectively, and subsequently characterised. An array of porous aligned channels (400 μm) was incorporated into both scaffold types and cell (human osteoblast sarcoma, for HA scaffolds; ovine meniscal fibrochondrocytes, for P dl LA scaffolds) and tissue infiltration into these modified scaffolds was assessed in vitro (cell penetration) and in vivo (tissue infiltration; HA scaffolds only). Scaffolds were shown to have an extensive random, open porous structure with an average porosity of 85%. Enhanced cell and tissue penetration was observed both in vitro and in vivo demonstrating that scaffold design alone can influence cell and tissue infiltration into the centre of tissue engineering scaffolds.
Keywords: Hydroxyapatite; Poly(lactic acid); Aligned macroarchitecture; Bone tissue engineering; Cartilage tissue engineering; Scaffold;

Polymer hollow fiber three-dimensional matrices with controllable cavity and shell thickness by Lorenzo Moroni; Roka Schotel; Jerome Sohier; Joost R. de Wijn; Clemens A. van Blitterswijk (5918-5926).
Hollow fibers find useful applications in different disciplines like fluid transport and purification, optical guidance, and composite reinforcement. In tissue engineering, they can be used to direct tissue in-growth or to serve as drug delivery depots. The fabrication techniques currently available, however, do not allow to simultaneously organize them into three-dimensional (3D) matrices, thus adding further functionality to approach more complicated or hierarchical structures. We report here the development of a novel technology to fabricate hollow fibers with controllable hollow cavity diameter and shell thickness. By exploiting viscous encapsulation, a rheological phenomenon often undesired in molten polymeric blends flowing through narrow ducts, fibers with a shell–core configuration can be extruded. Hollow fibers are then obtained by selective dissolution of the inner core polymer. The hollow cavity diameter and the shell thickness can be controlled by varying the polymers in the blend, the blend composition, and the extrusion nozzle diameter. Simultaneous with extrusion, the extrudates are organized into 3D matrices with different architectures and custom-made shapes by 3D fiber deposition, a rapid prototyping tool which has recently been applied for the production of scaffolds for tissue engineering purposes. Applications in tissue engineering and controlled drug delivery of these constructs are presented and discussed.
Keywords: Hollow fibers; Viscous encapsulation; Rapid prototyping; Tissue engineering; Drug delivery;

Use of hydrodynamic forces to engineer cartilaginous tissues resembling the non-uniform structure and function of meniscus by Anna Marsano; David Wendt; Roberto Raiteri; Riccardo Gottardi; Martin Stolz; Dieter Wirz; Alma U. Daniels; Donald Salter; Marcel Jakob; Thomas M. Quinn; Ivan Martin (5927-5934).
The aim of this study was to demonstrate that differences in the local composition of bi-zonal fibrocartilaginous tissues result in different local biomechanical properties in compression and tension. Bovine articular chondrocytes were loaded into hyaluronan-based meshes (HYAFF®-11) and cultured for 4 weeks in mixed flask, a rotary Cell Culture System (RCCS), or statically. Resulting tissues were assessed histologically, immunohistochemically, by scanning electron microscopy and mechanically in different regions. Local mechanical analyses in compression and tension were performed by indentation-type scanning force microscopy and by tensile tests on punched out concentric rings, respectively. Tissues cultured in mixed flask or RCCS displayed an outer region positively stained for versican and type I collagen, and an inner region positively stained for glycosaminoglycans and types I and II collagen. The outer fibrocartilaginous capsule included bundles (up to 2 μm diameter) of collagen fibers and was stiffer in tension (up to 3.6-fold higher elastic modulus), whereas the inner region was stiffer in compression (up to 3.8-fold higher elastic modulus). Instead, molecule distribution and mechanical properties were similar in the outer and inner regions of statically grown tissues. In conclusion, exposure of articular chondrocyte-based constructs to hydrodynamic flow generated tissues with locally different composition and mechanical properties, resembling some aspects of the complex structure and function of the outer and inner zones of native meniscus.
Keywords: Bioreactor; Shear; Cartilage tissue engineering; Chondrocyte;

Stimulation of in vivo angiogenesis using dual growth factor-loaded crosslinked glycosaminoglycan hydrogels by Celeste M. Riley; Peter W. Fuegy; Matthew A. Firpo; Xiao Zheng Shu; Glenn D. Prestwich; Robert A. Peattie (5935-5943).
Crosslinked, chemically modified hyaluronan (HA) hydrogels pre-loaded with two cytokine growth factors, vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), were employed to elicit new microvessel growth in vivo, in both the presence and absence of heparin (Hp) in the gels. HA hydrogel film samples were surgically implanted in the ear pinnae of mice, and the ears were harvested at 7 or 14 days post-implantation. Analysis of neovascularization showed that each of the treatment groups receiving an implant, except for HA/Hp at day 14, demonstrated significantly more microvessel density than control ears undergoing surgery but receiving no implant (p<0.015). Treatment groups receiving either Ang-1 alone, or aqueous co-delivery of both Ang-1 and VEGF, were statistically unchanged with time. In contrast, film delivery of both growth factors produced continuing increases in vascularization from day 7 to day 14 in the absence of Hp, but decreases in its presence. However, presentation of both VEGF and Ang-1 in crosslinked HA gels containing Hp generated intact microvessel beds with well-defined borders. The HA hydrogels containing Ang-1+VEGF produced the greatest angiogenic response of any treatment group tested at day 14 (NI=7.44 in the absence of Hp and 4.67 in its presence, where NI is a neovascularization index). Even in the presence of Hp, this had 29% greater vessel density than the next largest treatment group receiving HA/Hp+VEGF (NI=3.61, p = 0.04 ). New therapeutic approaches for numerous pathologies could be notably enhanced by the localized, sustained angiogenic response produced by release of both VEGF and Ang-1 from crosslinked HA films.
Keywords: Angiogenesis; Glycosaminoglycans; Growth factors; Cytokine; Vascular endothelial growth factor; Angiopoietin-1;

Platinum nanowire nanoelectrode array for the fabrication of biosensors by Minghui Yang; Fengli Qu; Yashuang Lu; Yan He; Guoli Shen; Ruqin Yu (5944-5950).
Platinum nanowire arrays can be grown by electrodeposition in polycarbonate membrane, with the average diameter of the nanowires about 250 nm and the height about 2 μm. The nanowire array prepared by the proposed method can be considered as nanoelectrode array (NEA) with nanoelectrode density of 5×108  cm−2. While the NEA can improve the signal-to-noise ratio and decrease the detection limit, the high surface area of the platinum NEA circumvents the problem of conventional platinum electrodes associated with the limited electroactive site. The platinum NEA can direct response to hydrogen peroxide at low potential of 0 V with wide linear range (1×10−7–6×10−2m) and sensitivity 50 times larger than that of the conventional platinum electrode. With the absorption of glucose oxidase onto the ordered NEA surface, the spatially patterned glucose oxidase improves greatly the resulting biosensor. The biosensor can achieve interference free determination of glucose with wide linear range (10−6–3×10−2m). The sensitivity of the glucose biosensor is one-fifth of the sensitivity toward hydrogen peroxide, indicating high efficiency of signal transduction. The biosensor was used to determine glucose in real blood samples, and the glucose contents determined by the present biosensor were in agreement with the results of existing method.
Keywords: Biosensor; Enzyme; Platinum nanowire; Polycarbonate membrane; Nanoelectrode array;

Delivery of dexamethasone, ascorbate, and growth factor (TGF β-3) in thermo-reversible hydrogel constructs embedded with rabbit chondrocytes by Kun Na; Ji Hyun Park; Sung Won Kim; Bo Kyung Sun; Dae Gyun Woo; Hyung-Min Chung; Keun-Hong Park (5951-5957).
The aim of this study was to assess the efficacy of poly(N-isopropylacrylamide-co-acrylic acid) (p(NiPAAm-co-AAc)) as an injectable drug delivery vehicle and a cell therapeutic agent in the form of a supporting matrix for the chondrogenic differentiation of rabbit chondrocytes. The p(NiPAAm-co-AAc) hydrogel itself without specific differentiation-inducing drugs was used as a control in order to determine the effects of these materials on chondrogenic differentiation. The level of cartilage associated extracellular matrix (ECM) proteins was examined by immunohistochemical staining for collagen type II as well as Safranin-O and Alcian blue (GAG) staining. These results highlight the potential of a thermo-reversible hydrogel mixed with chondrocytes and differentiation materials as an injectable delivery vehicle for use in neocartilage formation.
Keywords: Thermosensitive hydrogel; Dexamethasone; Transforming growth factor β-3 (TGF β-3); Chondrocytes; Cartilage;

Poly(γ,l-glutamic acid)–cisplatin conjugate effectively inhibits human breast tumor xenografted in nude mice by Haifeng Ye; Li Jin; Rongzhang Hu; Zhengfang Yi; Jing Li; Yelin Wu; Xuguang Xi; Zirong Wu (5958-5965).
An easily administered cis-dichlorodiammineplatinum (II) (CDDP) formulation with less toxicity and greater antitumor effect would be extremely valuable. We describe PGA–CDDP, a water-soluble CDDP derivative. The hydrolyzed γ-PGA has a molecular weight between 45 and 60 kDa, and is a water-soluble, biodegradable, and nontoxic polymer produced by microbial fermentation. CDDP can be released from the resulting conjugate in PBS: there was initially a burst release during the first 6 h, followed by sustained release. In vitro, PGA–CDDP was less potent than free CDDP at inhibiting cell growth in the Bcap-37 cell line. PGA–CDDP was given as 3 doses at an equivalent CDDP dose of 4 or 12 mg/kg with 2-day intervals between injections to Bcap-37-grafted mice. This treatment showed stronger antitumor activity and was less toxic than CDDP in vivo. Antitumor activity assays demonstrated that the PGA–CDDP conjugate treatment had significantly higher antitumor activity than control PBS treatment ( P < 0.01 ). PGA–CDDP also increased the survival of mice bearing Bcap-37 cells with reference to PBS treatment or free CDDP treatment. Furthermore, mice treated with PGA–CDDP (4 mg/kg, administered on day 0 and 5) showed no body weight loss ( P > 0.05 with respect to PBS treatment), whereas free CDDP treatment at the same dose caused a body weight loss of 20–30% ( P < 0.001 ). These findings suggest that PGA produced by microbial fermentation may be used as an effective drug carrier for CDDP and that PGA–CDDP may have potential applications in the treatment of human breast cancer.
Keywords: Cis-dichlorodiammineplatinum(II); Poly(γ-glutamic acid); Drug carriers; Antitumor efficacy;