A synthetic aragonite-based bioceramic: influence of process parameters on porosity and compressive strength

Challenges on optimization of 3D-printed bone scaffolds

Advances in biomaterials and the need for patient-specific bone scaffolds require modern manufacturing approaches in addition to a design strategy. Hybrid materials such as those with functionally graded properties are highly needed in tissue replacement and repair. However, their constituents, proportions, sizes, configurations and their connection to each other are a challenge to manufacturing. On the other hand, various bone defect sizes and sites require a cost-effective readily adaptive manufacturing technique to provide components (scaffolds) matching with the anatomical shape of the bone defect. Additive manufacturing or three-dimensional (3D) printing is capable of fabricating functional physical components with or without porosity by depositing the materials layer-by-layer using 3D computer models. Therefore, it facilitates the production of advanced bone scaffolds with the feasibility of making changes to the model. This review paper first discusses the development of a computer-aided-design (CAD) approach for the manufacture of bone scaffolds, from the anatomical data acquisition to the final model. It also provides information on the optimization of scaffold's internal architecture, advanced materials, and process parameters to achieve the best biomimetic performance. Furthermore, the review paper describes the advantages and limitations of 3D printing technologies applied to the production of bone tissue scaffolds.

Mechanical improvement of calcium carbonate cements by in situ HEMA polymerization during hardening

The brittleness of calcium carbonate-based cements, which currently impedes their exploitation, can be overcome by a straightforward polymer-reinforcement strategy.

Lightweight Open-Cell Scaffolds from Sea Urchin Spines with Superior Material Properties for Bone Defect Repair

Sea urchin spines (Heterocentrotus mammillatus), with a hierarchical open-cell structure similar to that of human trabecular bone and superior mechanical property (compressive strength ∼43.4 MPa) suitable for machining to shape, were explored for potential applications of bone defect repair. Finite element analyses reveal that the compressive stress concentrates along the dense growth rings and dissipates through strut structures of the stereoms, indicating that the exquisite mesostructures play an important role in high strength-to-weight ratios. The fracture strength of magnesium-substituted tricalcium phosphate (β-TCMP) scaffolds produced by hydrothermal conversion of urchin spines is about 9.3 MPa, comparable to that of human trabecular bone. New bone forms along outer surfaces of β-TCMP scaffolds after implantation in rabbit femoral defects for one month and grows into the majority of the inner open-cell spaces postoperation in three months, showing tight interface between the scaffold and regenerative bone tissue. Fusion of beagle lumbar facet joints using a Ti-6Al-4V cage and β-TCMP scaffold can be completed within seven months with obvious biodegradation of the β-TCMP scaffold, which is nearly completely degraded and replaced by newly formed bone ten months after implantation. Thus, sea urchin spines suitable for machining to shape have advantages for production of biodegradable artificial grafts for bone defect repair.

3D artificial bones for bone repair prepared by computed tomography-guided fused deposition modeling for bone repair

The medical community has expressed significant interest in the development of new types of artificial bones that mimic natural bones. In this study, computed tomography (CT)-guided fused deposition modeling (FDM) was employed to fabricate polycaprolactone (PCL)/hydroxyapatite (HA) and PCL 3D artificial bones to mimic natural goat femurs. The in vitro mechanical properties, in vitro cell biocompatibility, and in vivo performance of the artificial bones in a long load-bearing goat femur bone segmental defect model were studied. All of the results indicate that CT-guided FDM is a simple, convenient, relatively low-cost method that is suitable for fabricating natural bonelike artificial bones. Moreover, PCL/HA 3D artificial bones prepared by CT-guided FDM have more close mechanics to natural bone, good in vitro cell biocompatibility, biodegradation ability, and appropriate in vivo new bone formation ability. Therefore, PCL/HA 3D artificial bones could be potentially be of use in the treatment of patients with clinical bone defects.

Effects of fibrinogen concentration on fibrin glue and bone powder scaffolds in bone regeneration

Fibrin polymers are widely used in the tissue engineering field as biomaterials. Although numerous researchers have studied the fabrication of scaffolds using fibrin glue (FG) and bone powder, the effects of varied fibrinogen content during the fabrication of scaffolds on human mesenchymal stem cells (hMSCs) and bone regeneration remain poorly understood. In this study, we formulated scaffolds using demineralized bone powder and various fibrinogen concentrations and analyzed the microstructure and mechanical properties. Cell proliferation, cell viability, and osteoblast differentiation assays were performed. The ability of the scaffold to enhance bone regeneration was evaluated using a rabbit calvarial defect model. Micro-computed tomography (micro-CT) showed that bone powders were uniformly distributed on the scaffolds, and scanning electron microscopy (SEM) showed that the fibrin networks and flattened fibrin layers connected adjacent bone powder particles. When an 80 mg/mL fibrinogen solution was used to formulate scaffolds, the porosity decreased 41.6 ± 3.6%, while the compressive strength increased 1.16 ± 0.02 Mpa, when compared with the values for the 10 mg/mL fibrinogen solution. Proliferation assays and SEM showed that the scaffolds prepared using higher fibrinogen concentrations supported and enhanced cell adhesion and proliferation. In addition, mRNA expression of alkaline phosphatase and osteocalcin in cells grown on the scaffolds increased with increasing fibrinogen concentration. Micro-CT and histological analysis revealed that newly formed bone was stimulated in the scaffold implantation group. Our results demonstrate that optimization of the fibrinogen content of fibrin glue/bone powder scaffolds will be beneficial for bone tissue engineering.

Evaluation of the zein/inorganics composite on biocompatibility and osteoblastic differentiation

We have previously studied the biocompatibility and mechanical properties of porous zein scaffolds. We based the study on the concept that composite scaffold materials, especially when combined with inorganic materials, are more suited to the mechanical and physiological demands of the host tissue than individual scaffold materials. We investigated the effect of zein/inorganic composite on the physical and biological properties of porous zein scaffolds, which were fabricated by salt-leaching. The composite was prepared by immersion in simulated body fluid. The hydroxyapatite (HA)-coated zein scaffold had the same porosity as the zein scaffold (over 75%). Using scanning electron microscopy, it was established that the morphology of pores located on the surface and within the porous scaffolds showed equally good pore interconnectivity with zein. However, the compressive Young's modulus decreased from 240.1+/-96.8 to 34.4+/-12.6MPa, and compressive strength decreased from 7.8+/-1.2 to 4.2+/-0.8MPa. From the in vitro test with human bone marrow stroma cells, the osteoblastic differentiation on the surface of the HA-coated zein scaffold was increased, as expressed by the alkaline phosphatase activity and reverse transcription-polymerase chain reaction analysis for marker genes. From both the mechanical and biological evaluations, the HA-coated zein scaffold was found to be the optimal biomaterial for bone tissue engineering.

Antibiotic cements in articular prostheses: current orthopaedic concepts

The possibilities and limits of antibiotic cements (ACs) have been assessed by many researchers. ACs are now approved by many drug agencies, including the US Food and Drug Administration (approval in 2003), with widespread use in prophylaxis and curative treatments. Laboratory experiments have achieved satisfactory antibiotic delivery without impairing the mechanical properties of ACs. Implantation in large animals (e.g. sheep) showed an antibiotic concentration in the bone cortex four times the minimal inhibitory concentration (MIC) 6 months after implantation. Human pharmacokinetics during total hip replacement (THR) show antibiotic concentrations 20 times the MIC in drainage fluids. No toxic concentrations have been detected in blood or urine, and no allergies, toxic effects, mechanical failures or selection of resistant microorganisms have been observed. Antibioprophylaxis has been assessed in prospective studies in over 1600 cases. In data from the Scandinavian arthroplasty registers, with an exhaustive follow-up of more than 240000 THRs, infection rate was reduced by ca. 50% (0.9% compared with 1.9%). In prostheses with severe infection, use of AC increases the infection control rate from 86% to 93% when using two-stage prosthetic exchanges. In moderate infection, a similar infection control rate (86%) was achieved either by two-stage exchange without local antibiotic or by one-stage exchange with AC; however, one-stage exchange achieved better functional results at lower cost and with reduced pain and hospital stay. Therefore, AC prophylaxis is widely used in countries with prostheses registers (Northern Europe), and use of ACs as treatment for infected prostheses is often considered as the gold standard in the EU and North America. However, AC is only an adjuvant treatment, and excision of infected and devascularized tissues as well as systemic antibiotic treatment managed by a multidisciplinary team remain the main factors of infection control.

Preparation, physical–chemical characterisation and cytocompatibility of calcium carbonate cements

The feasibility of calcium carbonate cements involving the recrystallisation of metastable calcium carbonate varieties has been demonstrated. Calcium carbonate cement compositions presented in this paper can be prepared straightforwardly by simply mixing water (liquid phase) with two calcium carbonate phases (solid phase) which can be easily obtained by precipitation. An original cement composition was obtained by mixing amorphous calcium carbonate and vaterite with an aqueous medium. The cement set and hardened within 2h at 37 degrees C in an atmosphere saturated with water and the final composition of the cement consisted mostly of aragonite. The hardened cement was microporous and showed poor mechanical properties. Cytotoxicity tests revealed excellent cytocompatibility of calcium carbonate cement compositions. Calcium carbonates with a higher solubility than the apatite formed for most of the marketed calcium phosphate cements might be of interest to increase biomedical cement resorption rates and to favour its replacement by bone tissue.

Gentamicin-loaded calcium carbonate materials: Comparison of two drug-loading modes

Synthetic aragonite-based porous materials were drug loaded with gentamicin sulphate, an antibiotic active on Staphylococcus aureus responsible for osteomyelitis. Drug loading was accomplished by two different ways: by integration of gentamicin in material during processing or by soaking material into gentamicin solutions. We first investigated the influence of drug loading on compressive strength of materials. Results indicate that soaked materials presented the same compressive strength than unloaded materials with the same porosity. By contrast, the integration of gentamicin during processing increased significantly the compressive strength of materials. The materials drug content before elution was a least 10 times higher when gentamicin was integrated during processing comparatively to soaked materials. The study of in vitro gentamicin release showed that for materials with gentamicin integrated during material processing, high concentrations of gentamicin were released up to 8 or 12 days, against 4 days for soaked materials. The transport coefficients calculation, for the first step of release, indicated that the rate of release was higher for materials with integrated gentamicin because of the higher gentamicin content. The porosity rate influenced the rate of release for materials positively with gentamicin integrated during processing contrary to soaked materials for which a higher porosity rate allowed a deeper penetration of gentamicin during drug loading and then a slightly slower release. Results indicate that aragonite-based material with gentamicin integrated during material processing may be used either as resorbable device for release of high concentrations of gentamicin or as biomaterial for combined therapy: bone substitution and prevention or treatment of osteomyelitis.