Journal of Biomimetics, Biomaterials and Tissue Engineering Vol. 6

Abstract: Polymer microspheres loaded with bioactive particles, biomolecules, proteins, and/or growth factors play important roles in tissue engineering, drug delivery, and cell therapy. The conventional double emulsion method and a new method of electrospraying into liquid nitrogen were used to prepare bovine serum albumin (BAS)-loaded poly(lactic-co-glycolic acid) (PLGA) porous microspheres. The particle size, the surface morphology and the internal porous structure of the microspheres were observed using scanning electron microscopy (SEM). The loading efficiency, the encapsulation efficiency, and the release profile of the BSA-loaded PLGA microspheres were measured and studied. It was shown that the microspheres from double emulsion had smaller particle sizes (3-50 m), a less porous structure, a poor loading efficiency (5.2 %), and a poor encapsulation efficiency (43.5%). However, the microspheres from the electrospraying into liquid nitrogen had larger particle sizes (400-600 m), a highly porous structure, a high loading efficiency (12.2%), and a high encapsulation efficiency (93.8%). Thus the combination of electrospraying with freezing in liquid nitrogen and subsequent freeze drying represented a suitable way to produce polymer microspheres for effective loading and sustained release of proteins.

Abstract: The functionality of tissue scaffolds in vivo plays a critical role in the treatment process. Due to the time dependent nature of the mechanical properties of the constituent phases of the scaffold, a wide range of mechanical property histories may be observed during the treatment process, possibly influencing outcomes. The critical nature of the mechanical properties in load bearing applications indicates a need for the simultaneous modelling of both scaffold degradation and tissue regeneration with time, and the resulting effective properties of the tissue engineering construct. To this end, a review of the literature is conducted to identify the various existing approaches to modelling scaffold degradation, tissue behavior, and the dependency of the two processes on one another.

Abstract: To investigate the influence of initial copolymer compositions of poly (lactic-co-glycolic acid) (PLGA) on mechanical properties, degradation behavior and biological properties of the scaffolds, porous PLGA scaffolds with different initial copolymer compositions (lactide/glycolide (PLA/PGA) molar ratio: 50:50, 70:30 and 80:20) were prepared by solvent casting/particulate leaching method. Mechanical properties were measured by testing the tensile strength and degradation rate was detected by soaking the scaffolds in phosphate buffered solution at 37 °C for various time points. Human dermal fibroblasts were seeded on PLGA scaffolds with different copolymer compositions. The morphology, adhesion efficiency, proliferation rate, and total collagen contents of cells on the scaffolds were analyzed. The results showed that the ratio of PLA/PGA is one important factor which influences the degradation of scaffolds. The mechanical strength of PLGA scaffolds with the ratio of 70:30 and 80:20, was higher than that of PLGA scaffolds with the ratio of 50:50.. Compared to 70:30 and 80:20 PLGA scaffolds, 50:50 PLGA had a quicker degradation. The three PLGA scaffolds had no obvious difference for cell response and all of them had excellent cytocompatibility, indicated by their high efficiency for human dermal fibroblast adhesion, fast proliferation rate and stretched cell morphology. A large amount of extracellular matrix was secreted and after 7 days of culture, and cell nearly covered the entire surface of the scaffolds. Overall, our results indicate that the copolymer compositions of PLGA have important effect on degradation and mechanical strength, but have no obvious effect on the biological properties of the scaffolds.

Abstract: This review paper presents a fail-safe approach in designing biomaterials against wear for application in an artificial total hip replacement in view of the recent advances in orthopedic bioengineering materials. It has been established that substantially different alloys should be used for minimizing wear in bearing surfaces. Frictional forces at these rubbing counter-faces must be minimized to prevent loosening of the femoral stem and acetabular socket assembly from their positions secured by the fixation agent. A comparative analysis of various wear-resistant biomaterials resulted in the lowest production of wear particles in a total hip where a ceramic socket articulates against the ceramic ball: it produces only 0.004 cubic millimeters of ceramic wear particles. Surface modification, through the application of coatings, offers the potential to reduce the wear rate without compromising the bulk mechanical behavior of the implant material. These hard coatings were found to include diamond-like carbon, amorphous diamond, and titanium nitride.

Abstract: This paper reviews the applications of advanced technology such as CT, reverse engineering (RE), computer aided design (CAD) and rapid prototyping (RP) in medicine. We described: 1) the use of RP and medical imaging in surgical planning; 2) the design process for the production of customized medical implants by rapid prototyping; and 3) the fabrication of three-dimensional scaffolds for tissue engineering of human liver. In order to examine the applicability and efficiency of the rapid prototyping technology, some case studies are presented, involving visualization and surgical planning; the design of custom implant for cranial reconstruction; and the use of RP in the production of tissue scaffold. From the results, it has been shown that RP can be applied with high level of accuracy in surgical planning, custom implant and tissue engineering.

Abstract: A nonapeptide, which is sensitive to enzymatic digestion by collagenase, was modified by the covalent attachment of an acrylamido group at the terminal positions. The functionalized peptide was used as a crosslinking agent during polymerization of 2-hydroxyethyl methacrylate (HEMA). Reversible addition-fragmentation chain transfer (RAFT) method was used to obtain a polymer (PHEMA) with an average theoretical molecular weight of 4000 Da, containing enzymatically labile peptide crosslinks. The functionalized peptide was analyzed in detail by 1H and 13C nuclear magnetic resonance (NMR) spectrometry. The polymerization reaction was monitored by near infrared spectrometry, while the resulting polymer was analyzed by size exclusion chromatography and solid NMR spectrometry. The peptide-crosslinked PHEMA was subjected to an in-vitro degradation assay in the presence of collagenase. At the highest concentration of enzyme used in the study, a weight loss of 35% was recorded after 60 days of incubation in the collagenolytic medium. This suggests that crosslinking with enzymatically degradable peptides is a valid method for inducing biodegradability in polymers that otherwise are not degradable.

Abstract: Strong and tough, macroporous alumina/zirconia composites are superior to alumina scaffolds but still biologically inert to bone tissue, leading to poor tissue ingrowth and osteointegration. One way to solve this problem is applying a bioactive coating onto the pore walls of the macroporous composites. In this study, macroporous alumina/zirconia (20vol%) composites (scaffolds) were prepared by a vacuum infiltration method involving the use of strained (10%) compacts of the expanded polystyrene (EPS) beads (typically 1-2.8 mm in diameter). A bioactive glass (58S33C) coating (~ 20 μm) was applied on the pore walls of the macroporous composites by slurry dip coating and sintering at 1200 oC for 1 hour. A top or outer bioactive glass (58S33C) thin layer (< 10 μm) was further applied by sol dip coating and sintering at a low temperature (< 800 °C). The bioactive glass-coated macroporous alumina/zirconia composites had well interconnected pores, relatively large pore sizes (1-2 mm), medium porosities (60-66%), high compressive strengths (7.52 – 5.42 MPa), and high bioactivity (with an apatite layer formed within 24 hours in the simulated body fluid). The combination of the strong and ultrafine (if not nano-structured) macroporous scaffolds with the multiple or graded bioactive coatings represented a new generation of bone substitutes or permanent scaffolds for bone tissue regeneration.