Abstract

Mg-, Zn- and Sr-doped hierarchically macroporous and mesoporous CaO–MO–SiO₂–P₂O₅ (M = Mg, Zn or Sr) bioactive glass (HMMBG) scaffolds were synthesized using the non-ionic block copolymer EO₂₀PO₇₀EO₂₀ and polyurethane sponges as cotemplates. The Mg-, Zn- or Sr-doped HMMBG scaffolds showed no distinct difference in phase composition, macroporous structure or pore volume from the HMMBG scaffolds without Mg, Zn or Sr. The Mg-, Zn- and Sr-doped HMMBG scaffolds showed no cytotoxicity. The gradual release of Ca, P, Si, Mg, Zn and Sr into the culture medium from these scaffolds contributed to the enhancement of the proliferation and ALP activity of mesenchymal stem cells (MSCs). The Mg-, Zn- and Sr-doped HMMBG scaffolds may be used as bone substitute materials.

Abstract

Biomaterials to be used for the production of endosseous devices in dental, orthopedic and maxillo-facial applications, might be designed to support, guide and enhance osteoblast adhesion. Cell recruitment onto biomaterial surface is a fundamental step within the complex process responsible for implant osseointegration; this process involves several proteins from the extra cellular matrix (ECM), cytoskeleton and cell membrane.

A new strategy to improve endosseous implant integration is based on preparing biomimetic surfaces able to present adhesive factors to cells. Osteoblast adhesion takes place by at least two different mechanisms: the most investigated one implies the interaction with RGD sequences via cell-membrane integrin receptors; a further mechanism concerns the interaction between cell-membrane heparan sulfate proteoglycans and heparin-binding sites of ECM proteins.

In the present study two different biomimetic surfaces were obtained by covalently grafting two adhesive peptides on oxidized titanium substrates after silanization: an RGD-containing peptide and a peptide mapped on human vitronectin. The two sequences are known to act via different adhesive mechanisms. The amount of human osteoblasts adhered onto peptide-enriched or not enriched titanium oxidized surfaces and the strength of cell binding were estimated, thus comparing the capacity of the bioactive substrates in promoting cell adhesion.

Abstract

The adhesive area is important to modulate cell behaviors on a substrate. This paper aims to semi-quantitatively examine the existence of the characteristic areas of cell adhesion on the level of individual cells. We prepared a series of micropatterned surfaces with adhesive microislands of various sizes on an adhesion-resistant background, and cultured cells of MC3T3-E1 (osteoblast), BMSC (bone mesenchymal stem cell) or NIH3T3 (fibroblast) on those modeled surfaces. We have defined seven characteristic areas of an adhesive microisland and confirmed that they are meaningful to describe cell adhesion behaviors. Those parameters are (1) the critical adhesion area from apoptosis to survival denoted as A^∗ or A_c1, (2) the critical area from adhesion of a single cell to adhesion of multiple cells (A_c2), (3) the basic area for one more cell to adhere (A_Δ), (4) and (5) the characteristic areas of a microisland most probably occupied by one cell (A_peak(1)) and two cells (A_peak(2)), (6) and (7) the characteristic areas of a microisland occupied by one cell (A_N(1)) or two cells (A_N(2)) on average. Besides the introduction of those basic parameters, the present paper demonstrates how to determine them experimentally. We further discussed the relationship between those characteristic areas and the spreading area on a non-patterned adhesive surface.

Abstract

This manuscript is part of a debate on the statement that “the use of short synthetic adhesion peptides, like RGD, is the best approach in the design of biomaterials that guide cell behavior for regenerative medicine and tissue engineering”. We take the position that although there are some acknowledged disadvantages of using short peptide ligands within biomaterials, it is not necessary to discard the notion of using peptides within biomaterials entirely, but rather to reinvent and evolve their use. Peptides possess advantageous chemical definition, access to non-native chemistries, amenability to de novo design, and applicability within parallel approaches. Biomaterials development programs that require such aspects may benefit from a peptide-based strategy.

Abstract

This paper constitutes the judgment on the four-paper debate in the same issue of this journal on the motion that ‘‘the use of short synthetic adhesion peptides, like RGD, is the best approach in the design of biomaterials that guide cell behavior for regenerative medicine and tissue engineering”. It is concluded that this motion is carried on the basis that the concept of installing multifunctionality and modularity in peptides is the more powerful concept, coupled with the potential attractiveness of retaining a chemically defined product, without any possibilities of disease transmission, and relative inexpensiveness and clearer regulatory pathways.

Abstract

Integrin-binding peptides increase cell adhesion to naive hydroxyapatite (HA), however, in the body, HA becomes rapidly modified by protein adsorption. Previously we reported that, when combined with an adsorbed protein layer, RGD peptides interfered with cell adhesion to HA. In the current study we evaluated mesenchymal stem cell (MSC) interactions with HA disks coated with the collagen-mimetic peptides, DGEA, P15 and GFOGER. MSCs adhered equally well to disks coated with DGEA, P15, or collagen I, and all three substrates, but not GFOGER, supported greater cell adhesion than uncoated HA. When peptide-coated disks were overcoated with proteins from serum or the tibial microenvironment, collagen mimetics did not inhibit MSC adhesion, as was observed with RGD, however neither did they enhance adhesion. Given that activation of collagen-selective integrins stimulates osteoblastic differentiation, we monitored osteocalcin secretion and alkaline phosphatase activity from MSCs adherent to DGEA or P15-coated disks. Both of these osteoblastic markers were upregulated by DGEA and P15, in the presence and absence of differentiation-inducing media. Finally, bone formation on HA tibial implants was increased by the collagen mimetics. Collectively these results suggest that collagen-mimetic peptides improve osseointegration of HA, most probably by stimulating osteoblastic differentiation, rather than adhesion, of MSCs.

Abstract

Metal-based scaffolds such as stents are the most preferred treatment methods for coronary artery disease. However, impaired endothelialization on the luminal surface of the stents is a major limitation occasionally leading to catastrophic consequences in the long term. Coating the stent surface with relevant bioactive molecules is considered to aid in recovery of endothelium around the wound site. However, this strategy remains challenging due to restrictions in availability of proper bioactive signals that will selectively promote growth of endothelium and the lack of convenience for immobilization of such signaling molecules on the metal surface. In this study, we developed self-assembled peptide nanofibers that mimic the native endothelium extracellular matrix and that are securely immobilized on stainless steel surface through mussel-inspired adhesion mechanism. We synthesized Dopa-conjugated peptide amphiphile and REDV-conjugated peptide amphiphile that are self-assembled at physiological pH. We report that Dopa conjugation enabled nanofiber coating on stainless steel surface, which is the most widely used backbone of the current stents. REDV functionalization provided selective growth of endothelial cells on the stainless steel surface. Our results revealed that adhesion, spreading, viability and proliferation rate of vascular endothelial cells are remarkably enhanced on peptide nanofiber coated stainless steel surface compared to uncoated surface. On the other hand, although vascular smooth muscle cells exhibited comparable adhesion and spreading profile on peptide nanofibers, their viability and proliferation significantly decreased. Our design strategy for surface bio-functionalization created a favorable microenvironment to promote endothelial cell growth on stainless steel surface, thereby providing an efficient platform for bioactive stent development for long term treatment of cardiovascular diseases.

Abstract

Immobilization of RGD peptides on titanium (Ti) surfaces enhances implant bone healing by promoting early osteoblastic cell attachment and subsequent differentiation by facilitating integrin binding. Our previous studies have demonstrated the efficacy of RGD peptide immobilization on Ti surfaces through the electrodeposition of poly(ethylene glycol) (PEG) (RGD/PEG/Ti), which exhibited good chemical stability and bonding. The RGD/PEG/Ti surface promoted differentiation and mineralization of pre-osteoblasts. This study investigated the in vivo bone healing capacity of the RGD/PEG/Ti surface for biomedical application as a more osteoconductive implant surface in dentistry. The RGD/PEG/Ti surface was produced on an osteoconductive implant surface, i.e. the grit blasted micro-rough surface of a commercial oral implant. The osteoconductivity of the RGD/PEG/Ti surface was compared by histomorphometric evaluation with an RGD peptide-coated surface obtained by simple adsorption in rabbit cancellous bone after 2 and 4 weeks healing. The RGD/PEG/Ti implants displayed a high degree of direct bone apposition in cancellous bone and achieved greater active bone apposition, even in areas of poor surrounding bone. Significant increases in the bone to implant contact percentage were observed for RGD/PEG/Ti implants compared with RGD-coated Ti implants obtained by simple adsorption both after 2 and 4 weeks healing (P < 0.05). These results demonstrate that RGD peptide immobilization on a Ti surface through electrodeposited PEG may be an effective method for enhancing bone healing with commercial micro-rough surface oral implants in cancellous bone by achieving rapid bone apposition on the implant surface.

Abstract

Although Bioglass® has existed for nearly half a century its ability to trigger bone formation and tuneable degradability is vastly superior to other bioceramics, such as SiO₂–CaO bioactive glasses. The sol–gel process of producing glass foams is well established for SiO₂–CaO compositions, but not yet established for 45S5 composites containing Na₂O. In this work the sol–gel derived 45S5 Bioglass® has for the first time been foamed into highly porous three-dimensional scaffolds using a surfactant, combined with vigorous mechanical stirring and subsequent sintering at 1000 °C for 2 h. It was found that the mechanical strength of the sintered sol–gel derived Bioglass® scaffolds was significantly improved, attributable to the small fraction of material on the pore walls. More importantly, the compressive strength of the three-dimensional scaffolds produced by this surfactant foaming method could be predicted using Gibson and Ashby’s closed cell model of porous networks. A comparative experiment revealed that ion release from the sol–gel derived Bioglass® foams was faster than that of counterparts produced by the replication technique. In vitro evaluation using osteoblast-like cells demonstrated that the sol–gel derived 45S5 Bioglass foams supported the proliferation of viable cell populations on the surface of the scaffolds, although few cells were observed to migrate into the virtually closed pores within the foams. Further work should be focused on modifications of the reaction conditions or alternative foaming techniques to improve pore interconnection.

Graphical abstract

The compressive strength of the sol-gel derived 45S5 Bioglass® 3D scaffolds can well be predicted using Gibson and Ashby’s closed-cell model of porous network. In vitro evaluation using osteoblast-like cells demonstrated that the sol–gel derived 45S5 Bioglass foams support cell attachment and proliferation on the surface of the scaffolds.

Abstract

In this paper we report on the metabolic response of human hepatocytes grown on polyethersulfone membranes surface modified with a plasma-deposited acrylic acid coating and RGD peptide covalently immobilized through a “spacer arm” molecule. The modified surfaces were characterized by means of X-ray photoelectron spectroscopy and water contact angle measurements.

The performance of modified and unmodified membranes was evaluated by assessing the expression of liver specific and biotransformation functions of human hepatocytes. Diclofenac, a non-steroidal anti-inflammatory drug, was used to investigate the biotransformation functions.

Surface-modified membranes elicit specific cellular responses and induce hepatocytes to enhance the synthesis rate of albumin and urea, particularly in the presence of diclofenac. Also the biotransformation functions were expressed at high levels.

Abstract

Plastically compressed dense collagen (DC) gels mimic the microstructural, mechanical, and biological properties of native osteoid. This study investigated the effect of hybridizing DC with osteoinductive nano-sized bioactive glass (nBG) particles in order to potentially produce readily implantable, and mineralizable, cell seeded hydrogel scaffolds for bone tissue engineering. Due to the high surface area of nBG and increased reactivity, calcium phosphate formation was immediately detected within as processed DC-nGB hybrid gel scaffolds. By day 3 in simulated body fluid, accelerated mineralization was confirmed through the homogeneous growth of carbonated hydroxylapatite on the nanofibrillar collagen framework. At day 7, there was a 13 fold increase in the hybrid gel scaffold compressive modulus. MC3T3-E1 pre-osteoblasts, three-dimensionally seeded at the point of nanocomposite self-assembly, were viable up to day 28 in culture. In the absence of osteogenic supplements, MC3T3-E1 metabolic activity and alkaline phosphatase production were affected by the presence of nBG, indicating accelerated osteogenic differentiation. Additionally, no cell-induced contraction of DC-nBG gel scaffolds was detected. The accelerated mineralization of rapidly produced DC-nBG hybrid gels indicates their potential suitability as osteoinductive cell delivery scaffolds for bone regenerative therapy.

Abstract

The present study investigates the influence of SrO on structure, apatite-forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with the composition (mol.%): (36.07 − x) CaO–xSrO–19.24MgO–5.61P₂O₅–38.49SiO₂–0.59CaF₂, where x varies between 0 and 10. The detailed structural analysis of the glasses is made by infrared spectroscopy and magic angle spinning–nuclear magnetic resonance spectroscopy. Silicon is predominantly present as Q² (Si) species, while phosphorus is found as orthophosphate in all the investigated glasses. The apatite-forming ability of glasses is investigated by immersion of glass powders in simulated body fluid for time durations varying between 1 h and 7 days. While increasing the Sr²⁺/Ca²⁺ ratio in the glasses does not affect their structure significantly, their apatite-forming ability is decreased considerably. Further, physico-chemical degradation of glasses is studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris–HCl and citric acid buffer, and the possible implications of the ion release profiles from the glasses in different solutions are discussed. The addition of strontium to the glasses leads to a sevenfold decrease in chemical degradation of glasses in Tris–HCl. The sintering of glass powders renders glass ceramics (GCs) with varying degrees of crystallinity and good flexural strength (98–131 MPa), where the mechanical properties depend on the nature and amount of crystalline phases present in the GCs.