Li Dichen

Preparation of chitosan–gelatin hybrid scaffolds with well-organized microstructures for hepatic tissue engineering

The structural organization of natural liver is instrumental in the multifunctionality of hepatocytes, and mimicking these specific architectures in tissue-engineered scaffold plays an important role in the engineering of an implantable liver equivalent in vitro. To achieve this goal, we have developed a novel fabrication process to create chitosan-gelatin hybrid scaffolds with well-organized architectures and highly porous structures by combining rapid prototyping, microreplication and freeze-drying techniques. The scaffolds obtained not only have analogous configurations of portal vein, central vein, flow-channel network and hepatic chambers, but also have high (>90%) porosity, with the mean pore size of 100microm. Swelling and degradation studies showed that the scaffold has excellent properties of hydrophilicity and biodegradability. A hepatocyte culture experiment was conducted to evaluate the efficiency of the well-defined chitosan-gelatin scaffold in facilitating hepatocyte growth in the inner layer of the scaffold in vitro. Scanning electron microscopy and histological analysis showed that hepatocytes could form large colonies in the predefined hepatic chambers, and these cavities could the completely filled with hepatocytes during 7 day culture. Albumin secretion and urea synthesis further indicated that the well-organized scaffolds were more suitable for hepatocyte culture.

Fabrication of customised maxillo‐facial prosthesis using computer‐aided design and rapid prototyping techniques

Purpose – This paper describes computer‐aided design (CAD) and rapid prototyping (RP) systems for the fabrication of maxillofacial implant.Design/methodology/approach – Design methods for medical RP of custom‐fabricated are presented in this paper. Helical computed tomography (CT) data were used to create a three‐dimensional model of the patient skull. Based on these data, the individual shape of the implant was designed in CAD environment and fabricate by RP process. One patient with a large mandible defect underwent reconstruction with individual prefabricated implant resulting from initial surgical failure with hand contoured reconstruction plate.Findings – Results shows that the custom made implant fit well the defect. Overall, excellent mandible symmetry and stability were achieved with the custom made implants. The patient was able to eat. There was no saliva drooling after the reconstruction. The operating time was reduced.Research limitations/implications – The methods described above suffer from ...

Customized design and manufacturing of chin implant based on rapid prototyping

Purpose – To develop a computer‐assisted prefabricated implant design and manufacturing system to improve the esthetic outcome in chin surgery.Design/methodology/approach – Design methods for medical rapid prototyping (RP) of custom‐fabricated chin augmentation implant are presented in this paper. After a careful preoperative planning based on cephalometric tracing for esthetic assessment, helical computed tomography data were used to create a three‐dimensional model of the deficient mandible. Based on these data, the inner surface of the prosthesis was designed to fit the bone surface exactly. The outer geometry was generated from a dried human mandible to create anatomically correct shape prosthesis. The inner and outer surfaces were then connected, and a solid model resulted. A RP system was used for production of the physical models. The surgical planning was performed using the implants and skull models. The resulting SLA implant is used for the production of a mold, which is used to cast the titaniu...

Custom fabrication of composite tibial hemi-knee joint combining CAD/CAE/CAM techniques

Abstract A custom fabrication approach combining computer-aided design (CAD), computer-aided engineering (CAE), and computer-aided manufacturing (CAM) techniques for constructing a novel composite tibial hemi-knee joint is presented. Anatomical modelling was used to provide the computer model with specific geometry for individuals and the finite element method (FEM) was adopted to understand the loading distribution on each component of the composite substitute. Rapid prototyping (RP) was employed to build the negative patterns, based on which the titanium alloy tibial tray and the porous artificial bone were custom fabricated through quick casting and powder sintering techniques. The results show that the titanium alloy component bears most of the loading while the artificial bone shares little, which could prevent it from fracturing in vivo. The final porous artificial bone has controllable microchannels (600 μm) and random micropores (100-200 μm), which ensures full interconnectivity and is expected to address the biological consideration. Clinical application demonstrates that the composite tibial hemi-knee joint has enough mechanical strength and can fit with the upper hemi-knee joint. This novel approach provides a new way to repair large bone defects in the loading sites.

Nano‐TiO2‐modified photosensitive resin for RP

Purpose – The purpose of this paper is to improve the mechanical and thermal properties of photosensitive resin for rapid prototyping (RP) by modifying with nano‐TiO2.Design/methodology/approach – The silane coupling agent was selected to treat the surface of anatase nano‐TiO2 particles. The IR spectrum showed that the hydroxyl (−OH) group on the surface of nano‐TiO2 reacted with the coupling agent effectively. The effects of TiO2 content on the curing depth and viscosity of the photosensitive resin were studied by experiments. The mechanical properties including tensile strength, tensile modulus, flexural strength and hardness were tested according to ASTM standards. The thermal stability of modified photosensitive resin was tested by differential scanning calorimetry.Findings – The comprehensive performance of the modified photosensitive resin was good when TiO2 content was at 0.25 per cent, the tensile strength was increased by 89 per cent from 25.26  to 47.82 MPa, the tensile modulus increased by 18 p...

The customized mandible substitute based on rapid prototyping

Traditional standard bone substitutes cannot realize the individualized matching for the bones of different patients. In order to make a bone substitute match the shape of a patients bone easily, a technology based on reverse engineering (RE) and rapid prototyping (RP) is put forward to design and fabricate a customized bone substitute. By RE, the customized bone substitute is designed according to the CT sectional pictures, and the customized localizer is designed to locate the customized bone substitute in the patients body at the right position. A customized mandible substitute designed and fabricated by RE and RP has been put into clinical use and is discussed in detail. The results confirm that the advantage of RP in the field of bone restoration is that it can fabricate the customized bone substitute rapidly and accurately.

Using variable beam spot scanning to improve the efficiency of stereolithography process

Purpose – The purpose of this paper is to present a new stereolithograhy (SL) process which could substantially improve the efficiency of building process through controlling the beam spot size and optimizing the process parameters dynamically.Design/methodology/approach – In this process, the focus length of UV laser scanning head is changed by the dynamic focus mirror according to the building program. The beam spot in the resin surface varies with the focus length, and the laser power is adjusted accordingly to the changing spot in building process.Findings – The study finds that the efficiency of building process has a close relationship with the beam spot size. The experiments showed that the larger the laser spot diameter was, the less the depth and the larger the width of the cured lines would be. Then the building program would adjust the UV laser power to compensate for the decreased curing depth caused by the enlarged beam spot. At last, the spot compensation was optimized for the new method tha...

Mechanical Performance of Chitosan Fiber/Calcium Phosphate Cement Composite for Artificial Bone

Chitosan fiber(CF)as reinforcement to improve the mechanical properties of calcium phosphate cement(CPC)is presented,while CF/CPC composite artificial bone with concentric fiber structure that mimics the microstructure of natural bone is fabricated.Special resin precise moulds produced by rapid prototyping(RP)are used to prepare two types of cylindrical CF/CPC artificial bones(φ20mm×20 nun andφ10 mm×20mm),which are evaluated respectively by initial intensity and in vivo intensity experiment.The initial strength of the CF/CPC composite specimens is 11～26 MPa,significantly higher than CPCs 4～10 MPa.And the porous structure and the macropores,which are gradually achieved for bone growth with the dissolution of chitosan fibers during the canine condyle defect repairing,do not lower mechanical properties of the implanted CF/CPC composite artificial bone.In conclusion,the existence of chitosan fibers can achieve the needed initial strength for CFC while tissue regeneration is occurring,and create porous structure for bone growth to turn to strengthen the implant when the fiber is dissolved,and this alleviate s the conflict between artificial bones porous structure and its strength.

Micro-and nanoscale 3D printing

There are great demands for complicated three-dimensional (3D) micro/nanostructures in various areas and micro-components, such as MEMS, bio-medical engineering, tissue engineering, new materials, new energy, HD display, micro fluidics, micro- and nano-optical devices and systems, micro/nano sensors, micro/nano electronics, optoelectronic device, printed electronics, etc. However, existing micro/nano manufacturing technologies cannot well meet these requirements of cost-effective mass producing 3D micro/nanostructures. High volume manufacturing complex 3D micro/nanostructures with low cost and high throughput, particularly for producing 3D micro/nanostructures with high aspect ratios and multi-materials as well as from wide range of materials, currently has been considered as the most significant challenging issues. Micro-and nanoscale 3D printing (micro/nanostructure additive manufacturing) has showed high potentials and unique strengths in creating arbitrary 3D micro/nanostructures, true micro/nanostructures with high aspect ratios, and advanced materials with micro/nanostructures as well as composite materials. It can also be considered to enhance capability of micro/nanofabrication technology in true 3D microcomponents manufacturing area. This paper provides a comprehensive review on significant results, recent progress for a large variety of 3D micro-and nano scale 3D printing processes, and performs the comparison of each process. Furthermore, typical applications and various 3D printing materials available are presented. Finally, the prospects, challenges and future trends are discussed. The paper may provide a reference and direction for the further explorations and studies of micro/nanostructure additive manufacturing both in industry and academia.

The Research of Technique on Fabricating Hydrogel Scaffolds for Cartilage Tissue Engineering Based on Stereo-lithography

Based on stereo-lithography, the polyacrylamide hydrogel scaffolds with controlled accurate internal structures were fabricated. The structure accuracy of the scaffolds was evaluated by the size measurement compared with the CAD model. The mechanical property evaluation showed that the hydrogel compressive modulus of elasticity reached 4.54MPa, which was similar to that of the articular cartilage, therefore meeting the basic requirements of cartilage tissue engineering. The technique based on stereo-lithography showed promising in fabricating cartilage scaffolds.