Table of contents

This issue contains a selection of peer-reviewed articles that were presented during the 4th Korea–China Symposium on Biomaterials and Nano-Biotechnology held in the Seokwipo KAL Hotel, Jeju-Do, Korea on 19–24 October 2006. The symposium focused on the recent development of novel biomaterials and nano-biotechnologies related to medical industries with financial support from the Korea Science and Engineering Foundation (KOSEF) and the National Natural Science Foundation of China (NSFC).

With human health and welfare in mind, research on biomaterials and nano-biotechnology has been one of the fastest growing areas, combining interdisciplinary engineering and scientific bases underlying the development of new biomaterials, methodology and technology for clinical applications. In the near future, by developing novel biomaterials and biotechnology, the biomedical industries will be able to provide patients as well as medical doctors with more effective and safer devices and treatments for many clinical approaches. The newly emerging biomaterials and nano-biotechnologies will enable many engineers, scientists and clinicians to revolutionize medical devices and provide treatments specifically adapted to each individual disease.

At the 4th Korea–China Symposium, scientifically distinguished speakers from Korea, China, Japan and the USA shared their experiences and knowledge about these emerging fields of biomaterials and nano-biotechnology. The topics covered mainly the areas of biopolymers, bioceramics, biometals, modification of biomaterials, tissue engineering, drug delivery and nano-biotechnology. We are grateful to all the authors for submitting their work to this special issue as well as to Professors F-Z Cui, I-S Lee and M Spector, the Editors-in-Chief of Biomedical Materials, for their contributions to the symposium. Through these continuing symposia we hope that the participating scientists will take further steps forward in the development of advanced biomaterials and nano-biosciences and technologies for both Korea and China, as well as enhancing the partnership between the two countries.

A thin calcium phosphate film was synthesized on both commercially pure Ti and Si wafers by electron beam evaporation of hydroxyapatite as an evaporant with simultaneous Ar ion beam bombardments. Silver was introduced into an ion-beam-assisted deposition of a calcium phosphate thin film for antimicrobial effect. The amount of incorporated silver ions was controlled by immersing calcium-phosphate-coated samples in different AgNO₃ concentrations, and Rutherford backscattering spectrometry (RBS) was employed to measure the amounts of substituted silver. The higher concentration of silver in the calcium phosphate film was more effective in reducing the bacteria of Escherichia coli ATCC 8739 and Streptococcus mutans OMZ 65 on contact with respect to controls.

Chitosan has been investigated as a non-viral vector because it has several advantages such as biocompatibility, biodegradability and low toxicity with high cationic potential. However, the low specificity and low transfection efficiency of chitosan need to be solved prior to clinical application. In this paper, we focused on the galactose or mannose ligand modification of chitosan for enhancement of cell specificity and transfection efficiency via receptor-mediated endocytosis in vitro and in vivo.

The purpose of this study was to evaluate the effects of a chitosan membrane coated with polylactic and polyglycolic acid (PLGA) on bone regeneration in a rat calvarial defect. Surgical implantation of chitosan membranes resulted in enhanced local bone formation at both 2 and 8 weeks. In conclusion, the chitosan membrane coated with PLGA had a significant potential to induce bone formation in the rat calvarial defect model. Within the selected PLGA dose range and observation intervals, there appeared to be no meaningful differences in bone formation.

The purpose of this study was to evaluate the regenerative effects of a tetracycline blended polylactic and polyglycolic acid (TC-PLGA) and non-blended polylactic and polyglycolic acid (PLGA) barrier membrane on one-wall intrabony defects in beagle dogs. It can be concluded that when used for guided tissue regeneration TC-PLGA membranes show a beneficial effect on one-wall intrabony defects in beagle dogs.

Surface immobilization of bioactive molecules onto natural tissues has been interestingly studied for the development of new functional matrices for the replacement of lost or malfunctioning tissues. In this study, an acellular matrix of bovine pericardium (ABP) was chemically modified by the direct coupling of L-arginine after glutaraldehyde (GA) cross-linking. The effects of L-arginine coupling on durability and calcification were investigated and the biocompatibility was evaluated in vitro and in vivo. A four-step detergent and enzymatic extraction process has been utilized to remove cellular components from fresh bovine pericardium (BP). Microscopic observation confirmed that nearly all cellular constituents are removed. Thermal and mechanical properties showed that the durability of L-arginine-treated matrices increased as compared with control ABP and GA-treated ABP. Resistance to collagenase digestion revealed that modified matrices have greater resistance to enzyme digestion than control ABP and GA-treated ABP. The in vivo calcification study demonstrated much less calcium deposition on L-arginine-treated ABP than GA-treated one. In vitro cell viability results showed that ABP modified with L-arginine leads to a significant increase in attachment of human dermal fibroblasts. The obtained results attest to the usefulness of L-arginine-treated ABP matrices for cardiovascular bioprostheses.

This work attempts to understand the in vitro biocompatibility of ultrafine grained titanium prepared by the ECAP route. The results obtained from the mouse fibroblast cell line 3T3 showed a better cell adherence and cell proliferation on ECAP titanium specimen compared to the coarse grain Grade-2 Ti and Ti6Al4V alloy. This could be attributed to the increased surface energy and grain boundary energy and possibly the presence of a large number of nano-size conical groove-like structures (at triple point junctions of grain boundaries on the surface) in the ECAP Ti specimen compared to the coarse grain Grade-2 Ti and Ti6Al4V alloy.

An active artificial cornea which can perform the function of inducing new cornea generation in vivo but does not need culture cells in vitro and which has similar optical and mechanical properties to those of the human cornea was constructed. An animal keratoplasty experiment using the artificial cornea as the implant showed that the animals' corneas could keep smooth surface and clear stroma postoperatively, and that the repopulation of the host's keratocytes, the degradation of the implant and new corneal tissue generation were completed at 5–6 months after surgery. Such an artificial cornea has several advantages over other corneal equivalents constructed in the typical way of tissue engineering: in having similar mechanical and optical properties to those of the human cornea and with no exogenetic cells, it can be used universally in different implantation surgeries without immunoreaction; it is easy to prepare and process into different shapes and sizes on a large scale, and suitable for long-distance transportation and long-term storage. All these characteristics make it a new approach to cornea tissue engineering having potential in many clinical applications.

Nanosilver particles and microsilver particles were implanted into a rat's back muscle. The pathology and the local biocompatibility were observed and compared at days 7, 14, 30, 90 and 180 after implantation. A good biological effect was observed on days 7 and 14, both in rats treated with nanosilver particles and in rats treated with microsilver particles. A bad biological effect was observed at day 30, and the nanosilver-treated rats had more serious inflammation than the microsilver-treated rats.

The objective of this work was to find a new material or new technology to achieve satisfactory post-surgery anti-adhesion. An agarose/collagen composite sheet was developed to prevent mesenchymal cells and extracellular matrix from adhering on the lesion site, in which agarose formed uniaxial channels that hindered penetration and intercommunication of cells among pores in a 3D sheet. The tensile strength of the composite sheet in the designed ratio of agarose and collagen was over 17 MPa in dry and 2 MPa in wet, which was suitable and convenient to be sewed or operated on in other general surgery. In vitro and in vivo experimental results showed that fibroblasts, adult-derived adipose stem cells, could not penetrate into the sheet and formed a 3D tissue, and agarose did not degrade in three weeks. The demonstration that this sheet can prevent mesenchymal cells from penetrating in 3D and forming a tissue warrants the agarose-based composite for an anti-adhesive membrane.

Hyaluronic acid (HA), a principal matrix molecule in many tissues, is present in high amounts in articular cartilage. HA contributes in unique ways to the physical behavior of the tissue, and has been shown to have beneficial effects on chondrocyte activity. The goal of this study was to incorporate graduated amounts of HA into type I collagen scaffolds for the control of chondrocyte-mediated contraction and chondrogenesis in vitro. The results demonstrated that the amount of contraction of HA/collagen scaffolds by adult canine articular chondrocytes increased with the HA content of the scaffolds. The greatest amount of chondrogenesis after two weeks was found in the scaffolds which had undergone the most contraction. HA can play a useful role in adjusting the mechanical behavior of tissue engineering scaffolds and chondrogenesis in chondrocyte-seeded scaffolds.

A biocompatible hydrogel of hyaluronic acid with the neurite-promoting peptide sequence of IKVAV was synthesized. The characterization of the hydrogel shows an open porous structure and a large surface area available for cell interaction. Its ability to promote tissue repair and axonal regeneration in the lesioned rat cerebrum is also evaluated. After implantation, the polymer hydrogel repaired the tissue defect and formed a permissive interface with the host tissue. Axonal growth occurred within the microstructure of the network. Within 6 weeks the polymer implant was invaded by host-derived tissue, glial cells, blood vessels and axons. Such a hydrogel matrix showed the properties of neuron conduction. It has the potential to repair tissue defects in the central nervous system by promoting the formation of a tissue matrix and axonal growth by replacing the lost tissue.

A kind of novel biodegradable supramolecular hydrogel was synthesized via copolymerization of gelatin methacrylamide with photocurable and biodegradable polypseudorotaxanes under UV irradiation. These polypseudorotaxanes were prepared by supramolecular self-assemblies of α-cyclodextrins threaded onto amphiphilic LA-PEG-LA copolymers end-capped with methacryloyl groups. The hydrogels are injectable, and their structure was characterized in detail with FTIR, ¹H NMR, XRD, TG and DSC techniques. Their swelling behaviour and morphologies were also examined. The analytical results demonstrated that the channel-type crystalline structure of the polypseudorotaxanes remains in the as-obtained hydrogels. Moreover, the SEM pictures showed that the hydrogels having gelatin methacrylamide are more suitable for cell seeding and proliferation than those without gelatin added.

A new type of composite bone cement was prepared and investigated by adding calcium silicate (CS) to calcium phosphate cement (CPC). Low-crystalline CS prepared by heat treatment at low temperature had excellent bioactivity and degradability. Adding CS to CPC did not affect the phase composition and chemical structure of CPC, and had a little effect on the setting time and compressive strength of the composite cement. CS could effectively improve the in vitro and in vivo bioactivity of CPC, and enhance the cell proliferation on the CPC material. The introduction of CS is an effective way to improve the bioactivity and degradability of CPC, which will provide a new strategy to modify CPC.

Calcium phosphate films were fabricated on titanium substrates heated up to 773 K using radiofrequency (RF) magnetron sputtering. The deposition rate, phase and preferred orientation of the calcium phosphate films were studied. Immersion tests for the films were conducted using Hanks' solution and PBS(−), and the surface reactions on the specimens coated with the calcium phosphate films were investigated. The bonding strength between the coating films and the titanium substrates before and after the immersion tests was evaluated; the bonding strength decreased after the immersion tests. The alkaline phosphatase (ALP) activity of SaOS-2 cells on a titanium plate coated with a calcium phosphate film was examined by conducting a culture test. Calcium phosphate coating increased the ALP activity of SaOS-2 cells cultured for 3 and 7 days. Titanium cylinders were coated with an amorphous calcium phosphate film and implanted into the mandibles of beagle dogs. An increase in the extent of bone-implant contact for the coated titanium cylinders was confirmed 8 to 12 weeks after implantation and compared with the case for uncoated titanium cylinders.

The frictional wear characteristics of Ti–29Nb–13Ta–4.6Zr alloy subjected to solution treatment (referred to as TNTZ_ST) and aged at 598, 673 and 723 K after solution treatment (referred to as TNTZ_598K, TNTZ_673K and TNTZ_723K, respectively) were investigated in air and a simulated body environment (Ringer's solution) as a function of the loading level. Ti–6Al–4V ELI alloy aged at 813 K after solution treatment (referred to as T64_STA) was employed as a reference material. Wear weight losses of TNTZ_ST, TNTZ_598K, TNTZ_673K, TNTZ_723K and Ti64_STA are lower in Ringer's solution than in air under both low and high loading conditions (1.96 and 29.4 N, respectively). It is considered that the frictional factor decreases because of the lubricating effect of Ringer's solution between the contact surface of the specimen and the zirconia ball—the mating material. Moreover, the wear weight losses of TNTZ_598K, TNTZ_673K and TNTZ_723K are lower than that of Ti64_STA in both air and Ringer's solution under the low loading condition, but are higher under the high loading condition. This result implies that the transition from severe wear to mild wear versus loading level depends on the type of material.

Fibroblast growth factor-2 (FGF-2) was immobilized on a hydroxyapatite (HAP) ceramic in supersaturated calcium phosphate solution prepared using solutions corresponding to clinically approved infusion fluids. To avoid the risk of FGF-2 denaturation, FGF-2 immobilization was carried out at 25 °C. FGF-2 was successfully immobilized on HAP ceramic surfaces by deposition with calcium phosphate to form a FGF-2 and calcium phosphate composite layer. A maximum of 2.72 ± 0.01 µg cm⁻² of FGF-2 was immobilized in the composite layer formed on the HAP ceramic under the optimum condition. A FGF-2-immobilized HAP ceramic is likely to have the ability to release a sufficient amount of FGF-2 to promote bone formation. FGF-2 released from a FGF-2-immobilized HAP ceramic maintained its biological activity, since the proliferation of fibroblastic NIH3T3 was promoted. Therefore, the FGF-2-immobilized HAP ceramic is expected to be a useful material for promoting new bone formation.

An ascorbate–apatite composite layer was successfully formed on NaOH- and heat-treated titanium by coprecipitating L-ascorbic acid phosphate and low-crystalline apatite in a supersaturated calcium phosphate solution at 37 °C for 48 h. The supersaturated calcium phosphate solutions used have chemical compositions attainable by mixing infusion fluids officially approved for clinical use. The amount of immobilized L-ascorbic acid phosphate ranged from 1.0 to 2.3 µg mm⁻², which is most likely to be sufficient for the in vitro osteogenic differentiation of mesenchymal stem cells on titanium. Since ascorbate is important for the collagen synthesis and subsequent osteogenesis of mesenchymal stem cells, titanium coated with the ascorbate–apatite composite layer would be useful as a scaffold in bone tissue engineering and as a bone substitute.

Fibre-based scaffolds have been widely used for tendon and ligament tissue engineering. Knitted scaffolds have been proved to favour collagenous matrix deposition which is crucial for tendon/ligament reconstruction. However, such scaffolds have the limitation of being dependent on a gel system for cell seeding, which is unstable in a dynamic environment such as the knee joint. This study developed three types of hybrid scaffolds, based on knitted biodegradable polyester scaffolds, aiming to improve mechanical properties and cell attachment and proliferation on the scaffolds. The hybrid scaffolds were created by coating the knitted scaffolds with a thin film of poly (ε-caprolactone) (group I), poly (D, L-lactide-co-glycolide) nanofibres (group II) and type 1 collagen (group III). Woven scaffolds were also fabricated and compared with the various hybrid scaffolds in terms of their mechanical properties during in vitro degradation and cell attachment and growth. This study demonstrated that the coating techniques could modulate the mechanical properties and facilitate cell attachment and proliferation in the hybrid scaffold, which could be applied with promise in tissue engineering of tendons/ligaments.

New biomaterials combined with osteogenic cells are now being developed as an alternative to autogeneous bone grafts when the skeletal defect reaches a critical size. Yet, the size issue appears to be a key obstacle in the development of bone tissue engineering. Bioreactors are needed to allow the in vitro expansion of cells inside large bulk materials under appropriate conditions. However, no bioreactor has yet been designed for large-scale 3D structures and custom-made scaffolds. In this study, we evaluate the efficiency of a new bioreactor for the in vitro development of large bone substitutes, ensuring the perfusion of large ceramic scaffolds by the nutritive medium. The survival and proliferation of cells inside the scaffolds after 7 and 28 days in this dynamic culture system and the impact of the direction of the flow circulation are evaluated. The follow-up of glucose consumption, DNA quantification and microscopic evaluation all confirmed cell survival and proliferation for a sample under dynamic culture conditions, whereas static culture leads to the death of cells inside the scaffolds. Two directions of flow perfusion were assayed; the convergent direction leads to enhanced results compared to divergent flow.

In the present contribution, electrospinning (e-spinning) was used to fabricate ultra-fine fibers of silk fibroin (SF) from cocoons of indigenous Thai silkworms (Nang-Lai) and Chinese/Japanese hybrid silkworms (DOAE-7). The effects of solution concentration (i.e., 10–40% (w/v) in 85% (v/v) formic acid) and applied electrostatic field strength (EFS; 10, 15 and 20 kV/10 cm) on morphology and size of the electrospun (e-spun) SF products were investigated by scanning electron microscopy. The average diameter of the resulting e-spun SF fibers was found to increase with an increase in both the solution concentration and the EFS value. Specifically, the average diameter of the e-spun SF fibers from Nang-Lai SF solutions ranged between 217 and 610 nm, while that of the fibers from DOAE-7 SF solutions ranged between 183 and 810 nm. The potential for use of the e-spun SF fiber mats as bone scaffolds was assessed with mouse osteoblast-like cells (MC3T3-E1) in which the cells appeared to adhere and proliferate well on their surface.

Fibres, scaffolds and membranes have shown in the past decade their tremendous applicability to the life sciences. Essentially, these constructs have recently spearheaded focused applications in and within approaches to assist in the development of biologically active tissues to effective mechanisms for targeted and controlled cellular/drug delivery. There are several routes for forming continuous fibres from which functionalized scaffolds to membranes are prepared. One such technique that has demonstrated its wide versatility is none other than electrospinning. This is an electrified threading process capable of generating micro- and nano-sized (<50 nm) threads, which have been explored with a wide range of material compositions in their many manifestations. Although this threading process is economical and flexible, the process has its downsides, namely the associated high voltage to the preclusion of threading highly conducting viscoelastic media. In the current work we unveil a three-needle pressure-assisted spinning (PAS) approach comparable to coaxial- or co-electrospinning, without the hazardous high voltage and possessing the ability to thread highly conducting viscoelastic media from which pre-designed to functionalized compound structural units could be generated. Previously in our hands we demonstrated this technique with a two-needle system, which was only able to process a single- or multi-phase suspension at any given time. In its present form, two single/multi-phase miscible or immiscible media could be processed simultaneously. Therefore, PAS would be most useful to the biomedical world because a majority of biological media containing biological matter such as living cells have within them unprecedented concentrations of ions, which are needed by the living organisms for maintaining the cells/organisms' intricate metabolisms. In our hands, pressure-assisted spinning will compete directly with electrospinning and have a revolutionary effect on the fibre, scaffold and membrane preparation arena as applied to the plethora of applications within the life sciences.

A porous hydroxyapatite (HA) coating on commercially pure titanium was prepared by micro-arc oxidation (MAO) in electrolytic solution containing calcium acetate and β-glycerol phosphate disodium salt pentahydrate (β-GP). The thickness, phase, composition morphology and biocompatibility of the oxide coating were characterized by x-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy (SEM) with an energy dispersive x-ray spectrometer (EDS) and cell culture. The thickness of the MAO film was about 20 µm, and the coating was porous and uneven without any apparent interface to the titanium substrates. The result of XRD showed that the porous coating was made up of HA film. The favorable osteoblast cell affinity gives HA film good biocompatibility. HA coatings are expected to have significant uses for medical applications such as dental implants and artificial bone joints.