A study on the in vitro degradation properties of poly(l-lactic acid)/β-tricalcuim phosphate(PLLA/β-TCP) scaffold under dynamic loading

The Structural, Thermal and Morphological Characterization of Polylactic Acid/Β-Tricalcium Phosphate (PLA/Β-TCP) Composites upon Immersion in SBF: A Comprehensive Analysis

Biocomposite films based on PLA reinforced with different β-TCP contents (10%, 20%, and 25%wt.) were fabricated via solvent casting and immersed in SBF for 7, 14, and 21 days. The bioactivity, morphological, and thermal behavior of composites with immersion were studied using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) microanalysis, weight loss (WL), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). This broad analysis leads to a deeper understanding of the evolution of the polymer-filler interaction with the degradation of the biocomposites. The results showed that β-TCP gradually evolved into carbonated hydroxyapatite as the immersion time increased. This evolution affected the interaction of β-TCP with PLA. PLA and β-TCP interactions differed from PLA and carbonated hydroxyapatite interactions. It was observed that β-TCP inhibited PLA hydrolysis but accelerated the thermal degradation of the polymer. β-TCP retarded the cold crystallization of PLA and hindered its crystallinity. However, after immersion in SBF, particles accelerated the cold crystallization of PLA. Therefore, considering the evolution of β-TCP with immersion in SBF is crucial for an accurate analysis of the biocomposites' degradation. These findings enhance the comprehension of the degradation mechanism in PLA/β-TCP, which is valuable for predicting the degradation performance of PLA/β-TCP in medical applications.

Fused Deposition Modeling Printed PLA/Nano β-TCP Composite Bone Tissue Engineering Scaffolds for Promoting Osteogenic Induction Function

Purpose

Large bone defects caused by congenital defects, infections, degenerative diseases, trauma, and tumors often require personalized shapes and rapid reconstruction of the bone tissue. Three-dimensional (3D)-printed bone tissue engineering scaffolds exhibit promising application potential. Fused deposition modeling (FDM) technology can flexibly select and prepare printed biomaterials and design and fabricate bionic microstructures to promote personalized large bone defect repair. FDM-3D printing technology was used to prepare polylactic acid (PLA)/nano β-tricalcium phosphate (TCP) composite bone tissue engineering scaffolds in this study. The ability of the bone-tissue-engineered scaffold to repair bone defects was evaluated in vivo and in vitro.

Methods

PLA/nano-TCP composite bone tissue engineering scaffolds were prepared using FDM-3D printing technology. The characterization data of the scaffolds were obtained using relevant detection methods. The physical and chemical properties, biocompatibility, and in vitro osteogenic capacity of the scaffolds were investigated, and their bone repair capacity was evaluated using an in vivo animal model of rabbit femur bone defects.

Results

The FDM-printed PLA/nano β-TCP composite scaffolds exhibited good personalized porosity and shape, and their osteogenic ability, biocompatibility, and bone repair ability in vivo were superior to those of pure PLA. The merits of biodegradable PLA and bioactive nano β-TCP ceramics were combined to improve the overall biological performance of the composites.

Conclusion

The FDM-printed PLA/nano-β-TCP composite scaffold with a ratio of 7:3 exhibited good personalized porosity and shape, as well as good osteogenic ability, biocompatibility, and bone repair ability. This study provides a promising strategy for treating large bone defects.

Degradation behavior of 2D auxetic structure with biodegradable polymer under mechanical stress

Coronary heart disease is serious harm to human health. Vascular scaffold implantation is the main treatment. Biodegradable polymers are widely used in vascular scaffolds for good biodegradability and biocompatibility. However, whether the mechanical properties and radial expansion ability can successfully implant the scaffold without acute elastic retraction remains to be further studied. Because of the unique deformation mechanism, shear resistance, and resilience, auxetic structures can effectively avoid the restenosis of degraded vascular scaffolds. Firstly, the plane isotropic and plane anisotropic auxetic structural scaffolds were designed. The control structures (traditional structures) scaffolds were taken as the contrast. PCL was used to prepare the vascular auxetic by 3D printing. The printing parameters of fused deposition 3D printing, such as printing temperature, printing speed, and printing pressure, were studied to determine the optimal printing parameters of PCL. A self-assembled cyclic tensile stress loading device was used to investigate the degradation behavior of different scaffolds under different sizes of cyclic tensile stress, such as surface morphology, pH changes, mass loss rate, and mechanical properties. The increase of stress, surface roughness, and mass loss rate of the scaffolds all showed an increasing trend. pH gradually decreased from the fifth week, and the decrease was proportional to the stress. A large level of stress loading intensifies the decline of elastic modulus and the ultimate strength of the scaffold. In conclusion, the increase of periodic tensile stress will accelerate the degradation of scaffolds, and the degradation behavior of scaffolds with different configurations is different. The degradation rate of dilatant scaffolds was higher than that of control scaffolds, and the degradation rate of anisotropic auxetic scaffolds was higher than that of isotropic auxetic scaffolds, which provides a theoretical reference for the application of auxetic structure in the degradation of vascular scaffolds.

Medical-Grade Poly(Lactic Acid)/Hydroxyapatite Composite Films: Thermal and In Vitro Degradation Properties

Production of biocompatible composite scaffolds shifts towards additive manufacturing where thermoplastic biodegradable polymers such as poly(lactic acid) (PLA) are used as matrices. Differences between industrial- and medical-grade polymers are often overlooked although they may affect properties and degradation behaviour as significantly as the filler addition. In the present research, composite films based on medical-grade PLA and biogenic hydroxyapatite (HAp) with 0, 10, and 20 wt.% of HAp were prepared by solvent casting technique. The degradation of composites incubated in phosphate-buffered saline solution (PBS) at 37 °C after 10 weeks showed that the higher HAp content slowed down the hydrolytic PLA degradation and improved its thermal stability. Morphological nonuniformity after degradation was indicated by the different glass transition temperatures (T_g) throughout the film. The T_g of the inner part of the sample decreased significantly faster compared with the outer part. The decrease was observed prior to the weight loss of composite samples.

An overview of polyester/hydroxyapatite composites for bone tissue repairing

Objectives

The polyester/hydroxyapatite (polyester/HA) composites play an important role in bone tissue repairing, mostly because they mimic the composition and structure of naturally mineralized bone tissue. This review aimed to discuss commonly used geometries of polyester/HA composites, including microspheres, membranes, scaffolds and bulks, and their applications in bone tissue repairing and to discuss existed restrictions and developing trends of polyester/HA.

Methods

The current review was conducted by searching Web of Science, and Google Scholar for relevant studies published related with polyester/HA composites. Selected studies were analyzed with a focus on the fabrication techniques, properties (mechanical properties, biodegradable properties and biological properties) and applications of polyester/HA composites in bone repairing.

Results

A total of 111 articles were introduced to discuss the review. Different geometries of polyester/HA composites were discussed. In addition, properties and applications of polyester/HA composites were evaluated. The addition of HA into polyester can adjust the mechanical and biodegradability of composites. Besides, the addition of HA into polyester can improve its osteogenic abilities. The results showed that polyester/HA composites can ideal candidate for bone tissue repairing.

Conclusion

Polyester/HA composites have many remarkable properties, such as appropriate mechanical strength, biodegradability, favorable biological properties. Diverse geometries of polyester/HA composites have been used in bone repairing, drug delivery and implant fixation. Further work needs to be done to investigate existed restrictions, including the controlled degradation rate, controlled drug release performance, well-matched mechanical properties, and novel fabrication techniques.

The translational potential of this article

The present review reveals the current state of the polyester/HA composites used in bone tissue repairing, contributing to future trends of polyester/HA composites in the forthcoming future.

Bioactive glasses and glass-ceramics for hyperthermia treatment of cancer: state-of-art, challenges, and future perspectives

Bioactive glasses and glass-ceramics are well-proven potential biomaterials for bone-tissue engineering applications because of their compositional flexibility. Many research groups have been focused to explore the utility of bioactive glass-ceramics beyond bone engineering to hyperthermia treatment of cancer. Hyperthermia refers to raising the temperature of tumor close to 44°C at which malignant cells perish with negligible harm to normal cells. Hyperthermia can be employed by many means such as by ultrasonic waves, electromagnetic waves, infrared radiations, alternating magnetic fields, etc. Magnetic bioactive glass-ceramics are advantageous over other potential candidates for thermoseeds such as nanofluids, superparamagnetic nanoparticles because they can bond not only to the natural bone but also with soft tissues in few cases, which helps regenerating the affected part due to its bioactive nature. Strict restrictions on clinical settings ( H × f < 5 × 10 9 ) force the research activities to be more focused on material characteristics to raise the implant temperature to required ranges. Lots of efforts have been made in past years to tackle these challenges and design best-suited glass-ceramics for hyperthermia treatment. This review aims to provide essential information on the concept of hyperthermia treatment of cancer and recent developments in the field of bioactive glass-ceramics for cancer treatment. The advantages and disadvantages of magnetic glass-ceramics over other potential thermoseed materials are highlighted. In this field, the major challenges are to develop magnetic glasses, which have fast and bulk crystallization with optimized magnetic phases with lower Curie and Neel temperatures.

In Vitro Tests of FDM 3D-Printed Diclofenac Sodium-Containing Implants

One of the most promising emerging innovations in personalized medication is based on 3D printing technology. For use as authorized medications, 3D-printed products require different in vitro tests, including dissolution and biocompatibility investigations. Our objective was to manufacture implantable drug delivery systems using fused deposition modeling, and in vitro tests were performed for the assessment of these products. Polylactic acid, antibacterial polylactic acid, polyethylene terephthalate glycol, and poly(methyl methacrylate) filaments were selected, and samples with 16, 19, or 22 mm diameters and 0%, 5%, 10%, or 15% infill percentages were produced. The dissolution test was performed by a USP dissolution apparatus 1. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide dye (MTT)-based prolonged cytotoxicity test was performed on Caco-2 cells to certify the cytocompatibility properties. The implantable drug delivery systems were characterized by thermogravimetric and heatflow assay, contact angle measurement, scanning electron microscopy, microcomputed tomography, and Raman spectroscopy. Based on our results, it can be stated that the samples are considered nontoxic. The dissolution profiles are influenced by the material properties of the polymers, the diameter, and the infill percentage. Our results confirm the potential of fused deposition modeling (FDM) 3D printing for the manufacturing of different implantable drug delivery systems in personalized medicine and may be applied during surgical interventions.

3D Printing of Bone-Mimetic Scaffold Composed of Gelatin/β-Tri-Calcium Phosphate for Bone Tissue Engineering

3D printed scaffolds composed of gelatin and β-tri-calcium phosphate (β-TCP) as a biomimetic bone material are fabricated, thereby providing an environment appropriate for bone regeneration. The Ca²⁺ in β-TCP and COO^- in gelatin form a stable electrostatic interaction, and the composite scaffold shows suitable rheological properties for bioprinting. The gelatin/β-TCP scaffold is crosslinked with glutaraldehyde vapor and unreacted aldehyde groups which can cause toxicity to cells is removed by a glycine washing. The stable binding of the hydrogel is revealed as a result of FTIR and degradation rate. It is confirmed that the composite scaffold has compressive strength similar to that of cancellous bone and 60 wt% β-TCP groups containing 40 wt% gelatin have good cellular activity with preosteoblasts. Also, in the animal experiments, the gelatin/β-TCP scaffold confirms to induce bone formation without any inflammatory responses. This study suggests that these fabricated scaffolds can serve as a potential bone substitute for bone regeneration.

Additive manufacturing of PLA-based scaffolds intended for bone regeneration and strategies to improve their biological properties

Polylactic acid (PLA) is one of the most commonly used materials in the biomedical sector because of its processability, mechanical properties and biocompatibility. Among the different techniques that are feasible to process this biomaterial, additive manufacturing (AM) has gained attention recently, as it provides the possibility of tuning the design of the structures. This flexibility in the design stage allows the customization of the parts in order to optimize their use in the tissue engineering field. In the recent years, the application of PLA for the manufacture of bone scaffolds has been especially relevant, since numerous studies have proven the potential of this biomaterial for bone regeneration. This review contains a description of the specific requirements in the regeneration of bone and how the state of the art have tried to address them with different strategies to develop PLA-based scaffolds by AM techniques and with improved biofunctionality.

Micro and nanoscale characterization of poly(DL-lactic-co-glycolic acid) films subjected to the L929 cells and the cyclic mechanical load

In this paper, the effect of the presence of L929 fibroblast cells and a cyclic load application on the kinetics of the degradation of amorphous PLGA films was examined. Complex micro and nano morphological, mechanical and physico-chemical studies were performed to assess the degradation of the tested material. For this purpose, molecular weight, glass transition temperature, specimen morphology (SEM, μCT) and topography (AFM) as well as the stiffness of the material were measured. The study showed that the presence of living cells along with a mechanical load accelerates the PLGA degradation in comparison to the degradation occurring in acellular media: PBS and DMEM. The drop in molecular weight observed was accompanied by a distinct increase in the tensile modulus and surface roughness, especially in the case of the film degradation in the presence of cells. The suspected cause of the rise in stiffness during the degradation of PLGA films is a reduction in the molecular mobility of the distinctive superficial layer resulting from severe structural changes caused by the surface degradation. In conclusion, all the micro and nanoscale properties of amorphous PLGA considered in the study are sensitive to the presence of L929 cells, as well as to a cyclic load applied during the degradation process.

A novel akermanite/poly (lactic-co-glycolic acid) porous composite scaffold fabricated via a solvent casting-particulate leaching method improved by solvent self-proliferating process

Desirable scaffolds for tissue engineering should be biodegradable carriers to supply suitable microenvironments mimicked the extracellular matrices for desired cellular interactions and to provide supports for the formation of new tissues. In this work, a kind of slightly soluble bioactive ceramic akermanite (AKT) powders were aboratively selected and introduced in the PLGA matrix, a novel l-lactide modified AKT/poly (lactic-co-glycolic acid) (m-AKT/PLGA) composite scaffold was fabricated via a solvent casting-particulate leaching method improved by solvent self-proliferating process. The effects of m-AKT contents on properties of composite scaffolds and on MC3T3-E1 cellular behaviors in vitro have been primarily investigated. The fabricated scaffolds exhibited three-dimensional porous networks, in which homogenously distributed cavities in size of 300–400 μm were interconnected by some smaller holes in a size of 100–200 μm. Meanwhile, the mechanical structure of scaffolds was reinforced by the introduction of m-AKT. Moreover, alkaline ionic products released by m-AKT could neutralize the acidic degradation products of PLGA, and the apatite-mineralization ability of scaffolds could be largely improved. More valuably, significant promotions on adhesion, proliferation, and differentiation of MC3T3-E1 have been observed, which implied the calcium, magnesium and especially silidous ions released sustainably from composite scaffolds could regulate the behaviors of osteogenesis-related cells.

The effect of mechanical loads on the degradation of aliphatic biodegradable polyesters

Aliphatic biodegradable polyesters have been the most widely used synthetic polymers for developing biodegradable devices as alternatives for the currently used permanent medical devices. The performances during biodegradation process play crucial roles for final realization of their functions. Because physiological and biochemical environment in vivo significantly affects biodegradation process, large numbers of studies on effects of mechanical loads on the degradation of aliphatic biodegradable polyesters have been launched during last decades. In this review article, we discussed the mechanism of biodegradation and several different mechanical loads that have been reported to affect the biodegradation process. Other physiological and biochemical factors related to mechanical loads were also discussed. The mechanical load could change the conformational strain energy and morphology to weaken the stability of the polymer. Besides, the load and pattern could accelerate the loss of intrinsic mechanical properties of polymers. This indicated that investigations into effects of mechanical loads on the degradation should be indispensable. More combination condition of mechanical loads and multiple factors should be considered in order to keep the degradation rate controllable and evaluate the degradation process in vivo accurately. Only then can the degradable devise achieve the desired effects and further expand the special applications of aliphatic biodegradable polyesters.

Anti-infective efficacy, cytocompatibility and biocompatibility of a 3D-printed osteoconductive composite scaffold functionalized with quaternized chitosan

Contaminated or infected bone defects remain serious challenges in clinical trauma and orthopaedics, and a bone substitute with both osteoconductivity and antibacterial properties represents an improvement for treatment strategy. In this study, quaternized chitosan (hydroxypropyltrimethyl ammonium chloride chitosan, HACC) was grafted to 3D-printed scaffolds composed of polylactide-co-glycolide (PLGA) and hydroxyapatite (HA), in order to design bone engineering scaffolds endowed with antibacterial and osteoconductive properties. We found that both the PLGA/HA/HACC and PLGA/HACC composite scaffolds decreased bacterial adhesion and biofilm formation under in vitro and in vivo conditions. Additionally, ATP leakage assay indicated that immobilizing HACC on the scaffolds could effectively disrupt microbial membranes. Using human bone marrow-derived mesenchymal stem cells (hBMSCs), we demonstrated that HA incorporated scaffolds, including PLGA/HA and PLGA/HA/HACC, favoured cell attachment, proliferation, spreading and osteogenic differentiation compared to HA-free PLGA or PLGA/HACC scaffolds. Finally, an in vivo biocompatibility assay conducted on rats, showed that HA incorporated scaffolds (including PLGA/HA and PLGA/HA/HACC scaffolds) exhibited good neovascularization and tissue integration. Taken together, our findings support the approach for developing porous PLGA/HA/HACC composite scaffold with potential clinical application in the treatment of infected bone.

STATEMENT OF SIGNIFICANCE

Although plenty of conductive scaffold biomaterials have been exploited to improve bone regeneration under infection, potential tissue toxicity under high concentration and antibiotic-resistance are their main deficiencies. This study indicated that HACC-grafted PLGA/HA composite scaffold prepared using an innovative 3D-printing technique and covalent grafting strategy showed significantly enhanced antibacterial activities, especially against the antibiotic-resistant strains, together with good osteogenic activity and biocompatibility. Therefore, it provides an effective porous composite scaffold to combat the infected bone defect in clinic with decreased risks of bacterial resistance and open a feasible strategy for the modification of scaffold interfaces involved in the bone regeneration and anti-infection.

Degradation characteristics, cell viability and host tissue responses of PDLLA-based scaffold with PRGD and β-TCP nanoparticles incorporation

This study is aimed to evaluate the degradation characteristics, cell viability and host tissue responses of PDLLA/PRGD/β-TCP (PRT) composite nerve scaffold, which was fabricated by poly(d, l-lactic acid) (PDLLA), RGD peptide(Gly-Arg-Gly-Asp-Tyr, GRGDY, abbreviated as RGD) modified poly-{(lactic acid)-co-[(glycolic acid)-alt-(l-lysine)]}(PRGD) and β-tricalcium phosphate (β-TCP). The scaffolds’ in vitro degradation behaviors were investigated in detail by analysing changes in weight loss, pH and morphology. Then, the 3-(4,5-dimethyl-2-thiazolyl) -2,5-diphenyl-2 -H-tetrazolium bromide (MTT) assay and cell live/dead assay were carried out to assess their cell viability. Moreover, in vivo degradation patterns and host inflammation responses were monitored by subcutaneous implantation of PRT scaffold in rats. Our data showed that, among the tested scaffolds, the PRT scaffold had the best buffering capacity (pH = 6.1–6.3) and fastest degradation rate (12.4%, 8 weeks) during in vitro study, which was contributed by the incorporation of β-TCP nanoparticles. After in vitro and in vivo degradation, the high porosity structure of PRT could be observed using scanning electron microscopy. Meanwhile, the PRT scaffold could significantly promote cell survival. In the PRT scaffold implantation region, less inflammatory cells (especially for neutrophil and lymphocyte) could be detected. These results indicated that the PRT composite scaffold had a good biodegradable property; it could improve cells survival and reduced the adverse host tissue inflammation responses.

Characterization of Silk Fibroin/Chitosan 3D Porous Scaffold and In Vitro Cytology

Bone tissue engineering is a powerful tool to treat bone defects caused by trauma, infection, tumors and other factors. Both silk fibroin (SF) and chitosan (CS) are non-toxic and have good biocompatibility, but are poor biological scaffolds when used alone. In this study, the microscopic structure and related properties of SF/CS composite scaffolds with different component ratios were examined. The scaffold material most suitable for osteoblast growth was determined, and these results offer an experimental basis for the future reconstruction of bone defects. First, via freeze-drying and chemical crosslinking methods, SF/CS composites with different component ratios were prepared and their structure was characterized. Changes in the internal structure of the SF and CS mixture were observed, confirming that the mutual modification between the two components was complete and stable. The internal structure of the composite material was porous and three-dimensional with a porosity above 90%. We next studied the pore size, swelling ratio, water absorption ratio, degradation and in vitro cell proliferation. For the 40% SF-60% CS group, the pore size of the scaffold was suitable for the growth of osteoblasts, and the rate of degradation was steady. This favors the early adhesion, growth and proliferation of MG-63 cells. In addition to good biocompatibility and satisfactory cell affinity, this material promotes the secretion of extracellular matrix materials by osteoblasts. Thus, 40% SF-60% CS is a good material for bone tissue engineering.

Development and performance analysis of Si-CaP/fine particulate bone powder combined grafts for bone regeneration

Background

Although autogenous bone grafts as well as several bone graft substitute material have been used for some time, there is high demand for more efficient and less costly bone-substitute materials. Silicon-substituted calcium phosphates (Si-CaP) and fine particulate bone powder (FPBP) preparations have been previously shown to individually possess many of the required features of a bone graft substitute scaffold. However, when applied individually, these two materials fall short of an ideal substitute material. We investigated a new concept of combining Si-CaP with FPBP for improved performance in bone-repair.

Methods

We assessed Si-CaP/FPBP combined grafts in vitro, by measuring changes in pH, weight loss, water absorption and compressive strength over time.

Results

Si-CaP/FPBP combined grafts was found to produce conditions of alkaline pH levels compared to FPBP, and scaffold surface morphology conducive to bone cell adhesion, proliferation, differentiation, tissue growth and transport of nutrients, while maintaining elasticity and mechanical strength and degradation at a rate closer to osteogenesis.

Conclusion

Si-CaP/FPBP combined grafts was found to be superior to any of the two components individually.

Design, materials, and mechanobiology of biodegradable scaffolds for bone tissue engineering

A review about design, manufacture, and mechanobiology of biodegradable scaffolds for bone tissue engineering is given. First, fundamental aspects about bone tissue engineering and considerations related to scaffold design are established. Second, issues related to scaffold biomaterials and manufacturing processes are discussed. Finally, mechanobiology of bone tissue and computational models developed for simulating how bone healing occurs inside a scaffold are described.

A New Bioactive Polylactide-based Composite with High Mechanical Strength

A new bioresorbable polylactide/calcium phosphate composite with improved mechanical strengths and a more basic filler, tetracalcium phosphate (TTCP), was prepared by melt compounding. N-(2-aminoethyl)-3-aminoproplytrimethoxysilane (AEAPS) and pyromellitic dianhydride (PMDA) were used to improve the interfacial adhesion between TTCP and polylactide (PLA). While AEAPS improved the dispersion of TTCP in the matrix, PMDA might react with the terminal hydroxyl group of PLA and the amino group on the surface of AEAPS modified TTCP, which could further enhance the interfacial strength. The tensile strength was improved to 68.4 MPa for the PLA/TTCP-AEAPS composite from 51.5 MPa for the PLA/TTCP composite (20 wt% of TTCP). Dynamic mechanical analysis suggested that there was a 51 % improvement in storage modulus compared to that of PLA alone, when PMDA (0.2 wt% of PMDA) was incorporated into the PLA/TTCP-AEAPS composite (5 wt% of TTCP). Using this new bioresorbable PLA composite incorporated with a more basic filler for biomedical application, the inflammation and allergic effect resulted from the degraded acidic product are expected to be reduced.

The Effect of Static and Dynamic Loading on Degradation of PLLA Stent Fibers

Understanding how polymers such as PLLA degrade in vivo will enhance biodegradable stent design. This study examined the effect of static and dynamic loads on PLLA stent fibers in vitro. The stent fibers (generously provided by TissueGen, Inc.) were loaded axially with 0 N, 0.5 N, 1 N, or 0.125–0.25 N (dynamic group, 1 Hz) and degraded in PBS at 45 °C for an equivalent degradation time of 15 months. Degradation was quantified through changes in tensile mechanical properties. The mechanical behavior was characterized using the Knowles strain energy function and a degradation model. A nonsignificant increase in fiber stiffness was observed between 0 and 6 months followed by fiber softening thereafter. A marker of fiber softening, β, increased between 9 and 15 months in all groups. At 15 months, the β values in the dynamic group were significantly higher compared to the other groups. In addition, the model indicated that the degradation rate constant was smaller in the 1-N (0.257) and dynamic (0.283) groups compared to the 0.5-N (0.516) and 0-N (0.406) groups. While the shear modulus fluctuated throughout degradation, no significant differences were observed. Our results indicate that an increase in static load increased the degradation of mechanical properties and that the application of dynamic load further accelerated this degradation.

Tissue-engineered bone formation in vivo for artificial laminae of the vertebral arch using β-tricalcium phosphate bioceramics seeded with mesenchymal stem cells

STUDY DESIGN

A rabbit laminectomy model was used to evaluate the efficacy of artificial laminae of vertebral arch using bone marrow-derived mesenchymal stem cells (MSCs) transplanted in porous beta-calcium phosphates (β-TCP) bioceramics.

OBJECTIVE

The aim of this study was to establish artificial lamina of the vertebral arch for bone tissue engineering using β-TCP bioceramics seeded with MSCs in a rabbit model of decompressive laminectomy.

SUMMARY OF BACKGROUND DATA

Decompressive laminectomy may induce various degrees of scar tissue and adhesion formation in the epidural space, and thus is the most common cause of failed back surgery syndrome. However, there is no effective method of bone defect treatment to control and reduce the scar tissue formation.

METHODS

MSCs were harvested from New Zealand rabbits (2-week old) by femoral bone marrow extraction. These cells were seeded into porous β-TCP bioceramics and cultivated for up to 3 weeks in the presence of osteogenic supplements. Segmental defects (20 × 8 mm) were created in 48 adult New Zealand rabbits that underwent laminectomy at the L5 to L6 levels. The animals were transplanted with cell media (control), β-TCP bioceramics (group I), or MSC-loaded β-TCP bioceramics (group II). Bone formation was evaluated after operation using scanning electron microscopy, computed tomography, magnetic resonance imaging, histomorphometry, and immunohistochemistry.

RESULTS

Scanning electron microscopy showed that MSCs filled the pores and surfaces of bioceramics in MSC-loaded β-TCP. In addition, significant increases in bone formation were observed in group II compared with other groups. Computed tomography and magnetic resonance imaging at 16 weeks showed that the artificial lamina of the vertebral arch was successfully formed. Hematoxylin-eosin and Masson trichrome staining were used to show the artificial laminae of the vertebral arch and the degraded bioceramics. In addition, immunohistochemistry results showed that the expression of bone morphogenetic protein-2 increased significantly in group II compared with group I at 2,4, and 8 weeks after implantation (P < 0.05).

CONCLUSION

β-TCP bioceramics seeded with MSCs are a promising source of tissue-engineered bone for the artificial lamina of the vertebral arch.

Microstructure and chemistry affects apatite nucleation on calcium phosphate bone graft substitutes

The bioactivity of calcium phosphate bone grafts of varying chemistry and strut-porosity was compared by determining the rate of formation of hydroxycarbonate apatite crystals on the material surface after being soaked in simulated body fluid for up to 30 days. Three groups of silicate-substituted hydroxyapatite material were tested, with each group comprising a different quantity of strut-porosity (23, 32, and 46 % volume). A commercially available porous β-tricalcium phosphate bone graft substitute was tested for comparison. Results indicate that strut-porosity of a material affects the potential for formation of a precursor to bone-like apatite and further confirms previous findings that β-tricalcium phosphate is less bioactive than hydroxyapatite.

Degradation and osteogenic potential of a novel poly(lactic acid)/nano-sized β-tricalcium phosphate scaffold

The purpose of this study was to investigate the influence of nano-sized β-tricalcium phosphate (β-TCP) on the biological performance of poly (lactic acid) (PLA) composite scaffolds by using in vitro degradation and an in vivo model of heterotopic bone formation. Nano-sized β-TCP (nβ-TCP) was prepared with a wet grinding method from micro-sized β-TCP (mβ-TCP), and composite scaffolds containing 0, 10, 30, or 50 wt% nβ-TCP or 30 wt% mβ-TCP were generated using a freeze-drying method. Degradation was assessed by monitoring changes in microstructure, pH, weight, and compressive strength over a 26-week period of hydrolysis. Composite scaffolds were processed into blocks, and implanted into muscular pockets of rabbits after loading with recombinant human bone morphogenetic protein-2 (rhBMP-2). New bone formation was evaluated based on histological and immunohistochemical analysis 2, 4, and 8 weeks after implantation. The in vitro results indicated that the buffering effect of nβ-TCP was stronger than mβ-TCP, which was positively correlated with the content of nβ-TCP. The in vivo findings demonstrated that nβ-TCP enhanced the osteoconductivity of the scaffolds. Although composite scaffolds containing 30% nβ-TCP exhibited similar osteoconductivity to 50% nβ-TCP, they had better mechanical properties than the 50% nβ-TCP scaffolds. This study supports the potential application of a composite scaffold containing 30% nβ-TCP as a promising scaffold for bone regeneration.

Strut size and surface area effects on long-term in vivo degradation in computer designed poly(L-lactic acid) three-dimensional porous scaffolds

Current developments in computer-aided design (CAD) and solid free-form fabrication (SFF) techniques enable fabrication of scaffolds with precisely designed architectures and mechanical properties. The present study demonstrates the effect of precisely designed three-dimensional scaffold architectures on in vivo degradation. Specifically, three types of porous poly(L-lactic acid) (PLLA) scaffolds with variable pore sizes, strut sizes, porosities, and surface areas fabricated by indirect SFF. In addition, one experimental group of PLLA solid cylinders was fabricated. The scaffolds and cylinders were subcutaneously implanted into mice for 6, 12 and 21 weeks. The solid cylinders exhibited a faster percentage mass loss than all porous scaffolds. Among the porous scaffolds the group with the largest strut size lost percentage mass faster than the other two groups. Strong correlations between surface area and percentage mass loss were found at 12 (R(2)=0.681) and 21 (R(2)=0.671) weeks. Scaffold porosity, however, was not significantly correlated with degradation rate. Changes in molecular weight and crystallinity also resulted in changes in the chemical structures due to degradation, and the solid cylinders had faster crystallization due to more advanced degradation than the porous scaffolds. Scaffold compressive moduli decreased with degradation, but the resulting modulus was still within the lower range of human trabecular bone even after 21 weeks. The loss in compressive moduli, however, was a complex function of both degradation and the initial scaffold architecture. This study suggests that CAD and fabrication, within a given material, can significantly influence scaffold degradation profiles.

Effects of designed PLLA and 50:50 PLGA scaffold architectures on bone formation in vivo

Biodegradable porous scaffolds have been investigated as an alternative approach to current metal, ceramic, and polymer bone graft substitutes for lost or damaged bone tissues. Although there have been many studies investigating the effects of scaffold architecture on bone formation, many of these scaffolds were fabricated using conventional methods such as salt leaching and phase separation, and were constructed without designed architecture. To study the effects of both designed architecture and material on bone formation, this study designed and fabricated three types of porous scaffold architecture from two biodegradable materials, poly (L-lactic acid) (PLLA) and 50:50 Poly(lactic-co-glycolic acid) (PLGA), using image based design and indirect solid freeform fabrication techniques, seeded them with bone morphogenetic protein-7 transduced human gingival fibroblasts, and implanted them subcutaneously into mice for 4 and 8 weeks. Micro-computed tomography data confirmed that the fabricated porous scaffolds replicated the designed architectures. Histological analysis revealed that the 50:50 PLGA scaffolds degraded but did not maintain their architecture after 4 weeks implantation. However, PLLA scaffolds maintained their architecture at both time points and showed improved bone ingrowth, which followed the internal architecture of the scaffolds. Mechanical properties of both PLLA and 50:50 PLGA scaffolds decreased but PLLA scaffolds maintained greater mechanical properties than 50:50 PLGA after implantation. The increase of mineralized tissue helped support the mechanical properties of bone tissue and scaffold constructs between 4-8 weeks. The results indicate the importance of choice of scaffold materials and computationally designed scaffolds to control tissue formation and mechanical properties for desired bone tissue regeneration.

Degradation-induced changes of mechanical properties of an electro-spun polyester-urethane scaffold for soft tissue regeneration

The aim of this study was the in vitro investigation of the change in mechanical properties of a fast-degrading electro-spun polymeric scaffold for the use in soft tissue regenerative implants. Tubular scaffolds were electro-spun from a DegraPol® D30 polyesther-urethane solution (target outer diameter: 5.0 mm; scaffold wall thickness: 0.99 ± 0.18 mm). Scaffold samples were subjected to hydrolytic in vitro degradation for up to 34 days. The fiber network structure and fiber surfaces were inspected on scanning electron micrographs. Following vacuum drying and determination of mass, flat samples (9.69 ± 0.21 × 18.47 ± 2.62 mm, n = 5) underwent uni-axial tensile testing (5 load cycles, strain ε = 0 to 20%; final extension to failure) in circumferential scaffold direction after 5, 10, 14, 18, 22, 26, 30, and 34 days of degradation. Scaffold mass did not change with degradation. Maximum elastic modulus, maximum stress and associated strain were E(max) = 1.14 ± 0.23 MPa, σ(max) = 0.52 ± 0.12 MPa and ε(max) = 176.8 ± 21.9% before degradation and E(max) = 0.43 ± 0.26 MPa, σ(max) = 0.033 ± 0.028 MPa and ε(max) = 24.6 ± 3.0% after 34 days of degradation. The deterioration of mechanical properties was not reflected in the ultrastructural surface morphology of the fibers. The current exploratory study provides a basis for the development of constitutive computational models of biodegradable scaffolds with future extension of the investigation most importantly to capture mechanical effects of regenerating tissue. Future studies will include degradation in biological fluids and assessment of molecular weight for an advanced understanding of the material changes during degradation.