Jian S. Dai

Bio: Jian S. Dai is an academic researcher from King's College London. The author has contributed to research in topics: Kinematics & Screw theory. The author has an hindex of 50, co-authored 499 publications receiving 9906 citations. Previous affiliations of Jian S. Dai include Chinese Ministry of Education & Purdue University.

Mobility in Metamorphic Mechanisms of Foldable/Erectable Kinds

Abstract: This paper looks at a class of mechanisms that change structure when erected or folded. The class includes a variety of artefacts and decorative gifts and boxes comprised of flat card creased to enable the folding or unfolding of a structure. Such a structure admits kinematic study in keeping with theory of mechanisms when the creases are treated as hinges joining card and paper panels treated as links. New horizons have been brought up in the use and mechanised manufacture of mechanisms of this kind. Here typical types are described in terms of their fundamental parts and their equivalent mechanisms. Screw sy.'item theory is brought into the analysis of mechanisms of these kinds, particularly those containing multiple loops. Different geometry and system combinations are used for the study of mobility and kinematics making use of the result from the equivalent screw systems. Introduction A mechanism is most commonly characterised by its function as part of a machine or mechanical arrangement that transforms an input motion or a force into another. If, alternatively, a mechanism has the ability to have its structure transformed from one kind to another then another class of mechanism emerges, one whose primary function may be just to change structure. Amongst these new developments is a group of devices or arrangements that can be described as mechanisms whose number, the total of all effective links, changes as they move from one configuration to another or a singular condition in geometry occurs that makes it behave differently. We refer to this group of mech­anisms as metamorphic. The mechanism may start as an open chain or in a folded (plicated) chain loop to be subsequently erected as a structure. New interest areas around such mechanisms are growing. For example the study of deployable mechanisms has applications in space technology that requires a highly collapsible and portable mechanism to be carried in a spacecraft and expandable for use either for large antenna structures (Costabile et al., 1996), for ramp assembly (Spence and Sword, 1996) or for the solar array paddle (Kuramasu et al., 1995). New deployable structure has been found in the study of truss structures (Takamatsu and Onoda, 1991). A so called smart fractal structure and mechanisms are recommended in robot manipulators (Shahnipoor, 1993), and sequential logic (Chew and Ho, 1996) was used for the analysis of the mechanisms. A recent study by Pellegrino (1996) focused on one combination of mechanisms and presented a potential application of this kind of mechanisms. Less obviously related to the above examples is another class typically found in artefacts and fancy gift packs. A list of this kind of application can readily be drawn, including, for example Chi­nese lanterns, paper folding in Christmas decorations, and card boxes for used in packaging a various of products. Some exotic and innovative forms of the latter represent a technological chal­lenge in producing them by machine. This sets up the need to describe the process in quantifiable kinematic terms. This would also open an avenue for mechanism study leading to innovation in the design of artefacts and packaging. We usually conceive of mechanisms to be made of ostensibly

Product Cost Estimation: Technique Classification and Methodology Review

Abstract: This paper provides a detailed review of the state of the art in product cost estimation covering various techniques and methodologies developed over the years. The overall work is categorized into qualitative and quantitative techniques. The qualitative techniques are further subdivided into intuitive and analogical techniques, and the quantitative ones into parametric and analytical techniques. Each of the techniques is then described and discussed, in detail, with further subdivisions. The paper also signifies the importance of cost estimation in the early phases of the design cycle and, as such, briefly discusses the current trends and future directions in the area. Research work carried out in the field with reference to specific applications is also reviewed. The paper provides a comprehensive literature review in the field and should be useful to researchers and practitioners interested in this field.

Mobility of Overconstrained Parallel Mechanisms

Abstract: The Kutzbach-Grubler mobility criterion calculates the degrees of freedom of a general mechanism. However, the criterion can break down for mechanisms with special geometries, and in particular, the class of so-called overconstrained parallel mechanisms. The problem is that the criterion treats all constraints as active, even redundant constraints, which do not affect the mechanism degrees of freedom. In this paper we reveal a number of screw systems of a parallel mechanism, explore their inter-relationship and develop an original theoretical framework to relate these screw systems to motion and constraints of a parallel mechanism to identify the platform constraints, mechanism constraints and redundant constraints. The screw system characteristics and relationships are investigated for physical properties and a new approach to mobility analysis is proposed based on decompositions of motion and constraint screw systems. New versions of the mobility criterion are thus presented to eliminate the redundant constraints and accurately predict the platform degrees of freedom. Several examples of overconstrained mechanisms from the literature illustrate the results.

Interlayer-Crosslinked Micelle with Partially Hydrated Core Showing Reduction and pH Dual Sensitivity for Pinpointed Intracellular Drug Release

Abstract: Although the utilization of polymeric micelles has demonstrated great potential in delivering anticancer drugs, this technique is facing tremendous challenges. In particular, polymeric micelles usually show a drug-release profile that is not in favor of achieving optimal drug availability inside tumor cells. That is, a “burst release” of up to 20–30 % of the encapsulated drug within several hours post micelle formation, followed by a slow diffusional drug release lasting for many days. The premature burst release leads to drug loss in micelle storage and blood circulation. Meanwhile, the secondstage slow drug release results in low intracellular drug availability insufficient for killing cancer cells. Therefore, development of delivery systems with better drug-release properties is still of great importance. One of the most promising strategies is to construct polymeric micelles that respond to specific stimulation, such as light exposure, enzymatic degradation, redox reaction, or change in pH or temperature. Acid-triggered rapid release of drugs can be achieved inside tumor tissue (pH below 6.8) or lysosomal compartments (pH about 5.0) of cancer cells by using micelles of copolymers bearing pH-sensitive blocks, such as poly(lhistidine) and poly(b-amino ester). Nevertheless, these pH-sensitive micelles were not designed to avoid the premature burst release of drugs. In addition, supramolecular nanoassemblies de-micellize when the polymer concentration drops below the critical micelle concentration (CMC), which is another underlying cause for the loss of drugs during blood circulation. Recently, covalent crosslinking of the core or shell of selfassembled polymeric micelles has emerged as a viable strategy to prevent de-micellization-associated drug loss. 11] Among various approaches, the utilization of disulfide-containing reversible crosslinkers is of particular importance, owing to the fact that the disulfide bond is reducible and therefore can be cleaved by glutathione (GSH), a thiol-containing oligopeptide predominantly found inside cells (up to the millimolar scale). Indeed, shell-crosslinked micelles (SCMs) obtained using disulfide-containing agents have demonstrated great potential for specifically releasing the loaded cargos inside cells. 13] In spite of their potential in reducing premature drug leakage, these SCMs cannot rapidly release drugs inside cells because drug release from their nonsensitive cores still follows a diffusion-controlled mechanism. Herein, we describe the first example of a highly packed interlayer-crosslinked micelle (HP-ICM) with reduction and pH dual sensitivity, which comprises a polyethylene glycol (PEG) corona to stabilize the particles, a highly compressed pH-sensitive partially hydrated core to load anticancer drugs, and a disulfide-crosslinked interlayer to tie up the core against expansion at neutral pH. The HP-ICM was stable and drug leakage free in a neutral pH environment without reducing agent. However, when the HP-ICM was internalized into cells and trapped inside lysosomes featuring low pH ( 5) and enriched reducing agent (GSH), the pH-sensitive core was unpacked and thus erupted to burst release the anticancer drug (Figure 1). The reductionand pH-sensitive interlayer-crosslinked micelle with partially hydrated core was prepared from a triblock copolymer of monomethoxy polyethylene glycol (mPEG), 2-mercaptoethylamine (MEA)-grafted poly(laspartic acid) (PAsp(MEA)), and 2-(diisopropylamino)ethylamine (DIP)-grafted poly(l-aspartic acid) (PAsp(DIP)). The copolymer was synthesized by ring-opening polymerization of b-benzyl l-aspartate N-carboxy-anhydride (BLA-NCA) in combination with click and aminolysis reactions (see the Supporting Information, Figure S1). So far, most reported shell-crosslinked nanoparticles have been based on polyacrylate or polyacrylamide. 14] We chose biodegradable polypeptide as the copolymer backbone in consideration of biocompatibility requirements in drug delivery. Poly(BLA) aminolysis with MEA and DIP introduced the crosslinkable thiol and pH-sensitive tertiary amino groups onto the middle and end blocks of the copolymer, respectively. NMR and FTIR analyses confirmed the chemical structures of the polymers (see the Supporting Information, Figures S3–S6). Gel permeation chromatography measurements also evidenced the successful synthesis of mPEG[*] Dr. J. Dai, S. Lin, Dr. D. Cheng, Prof. X. Shuai PCFM Lab of Ministry of Education, School of Chemistry and Chemical Engineering Sun Yat-sen University, Guangzhou 510275 (China) E-mail: shuaixt@mail.sysu.edu.cn

Stimuli-responsive nanocarriers for drug delivery

Abstract: Spurred by recent progress in materials chemistry and drug delivery, stimuli-responsive devices that deliver a drug in spatial-, temporal- and dosage-controlled fashions have become possible. Implementation of such devices requires the use of biocompatible materials that are susceptible to a specific physical incitement or that, in response to a specific stimulus, undergo a protonation, a hydrolytic cleavage or a (supra)molecular conformational change. In this Review, we discuss recent advances in the design of nanoscale stimuli-responsive systems that are able to control drug biodistribution in response to specific stimuli, either exogenous (variations in temperature, magnetic field, ultrasound intensity, light or electric pulses) or endogenous (changes in pH, enzyme concentration or redox gradients).

Functional block copolymer assemblies responsive to tumor and intracellular microenvironments for site-specific drug delivery and enhanced imaging performance

Abstract: Self-assembled nanostructures of amphiphilic and double hydrophilic block copolymers have been increasingly utilized as potent polymeric nanocarriers of therapeutic drugs, genes, bioactive molecules, and imaging/contrast agents due to improved water solubility, bioavailability, and extended blood circulation duration. Though passive and active targeted drug delivery strategies have long been proposed to promote desirable drug accumulation specifically at the disease sites, the introduction of stimuli-responsiveness into self-assembled block copolymer nanocarriers can additionally lead to controlled/triggered release of therapeutic/imaging agents into target pathological tissues and cells, with concomitant advantages of enhanced delivery efficiency and therapeutic efficacy. Appropriately designed stimuli-responsive block copolymer assemblies can exhibit chemical structure transformation, microstructural rearrangement and inversion, or even disassembly into unimers or smaller ones under external stimuli such as pH, temperature, ion strength, redox potential, light, electric, and magnetic fields, and specific bioactive molecules and metabolites. Compared to normal tissues, pathological sites such as tumor tissues typically exhibit vascular abnormalities, weak acidity (∼pH 6.8), abnormal temperatures, over-expressed proteins and enzymes, hypoxia, high levels of metabolites and reactive small molecule species, etc. Moreover, upon cellular uptake, drug-loaded polymeric nanocarriers will be subjected to intracellular pH gradients (pH 5.9–6.2 in early endosomes and pH 5.0–5.5 in late endosomes and lysosomes) and redox and H2O2 gradients within different cell organelles and the cytosol. Thus, block copolymer nanocarriers responsive to the above described bio-relevant stimuli or biochemical signals characteristic of pathologic tissues and cells will provide an alternative type of “active targeting” strategy, which can be utilized to further boost therapeutic efficacy and imaging sensitivity via disease site-specific delivery and controlled release. A variety of extracellular or intracellular stimuli innate to disease sites, such as mildly acidic pH, temperature, enzymes (matrix metalloproteinase, β-glucuronidase, and phosphatase), oxidative/reductive microenvironments, and abnormal levels of bioactive molecules or metabolites, have been utilized for this purpose. In this review, we summarize recent advances in stimuli-responsive block copolymer assemblies which are responsive to tumor and intracellular microenvironments and their applications in anticancer drug delivery and enhanced imaging sensitivity.

Biomedical applications of soft robotics

Abstract: Soft robotics enables the design of soft machines and devices at different scales. The compliance and mechanical properties of soft robots make them especially interesting for medical applications. Depending on the level of interaction with humans, different levels of biocompatibility and biomimicry are required for soft materials used in robots. In this Review, we investigate soft robots for biomedical applications, including soft tools for surgery, diagnosis and drug delivery, wearable and assistive devices, prostheses, artificial organs and tissue-mimicking active simulators for training and biomechanical studies. We highlight challenges regarding durability and reliability, and examine traditional and novel soft and active materials as well as different actuation strategies. Finally, we discuss future approaches and applications in the field. Soft robots have broad applications in medicine. In this Review, biomedical applications, including surgery, drug delivery, prostheses, wearable devices and artificial organs, are discussed in the context of materials, actuation strategies and challenges.