Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Reversible 4D-printing of shape memory polymers using heat and ethanol swelling

The advancements in smart materials have boosted additive manufacturing into a new form of printing known as 4D printing. 4D printing provides the means to create a dynamic structure for self-actuating devices fabricated by additive manufacturing techniques. Most existing 4D printing processes are only capable of one-way shape morphing using a single mechanism for stimulation. With increasing improvements in design and using multiple stimuli, reversible 4D printing has been proven to be feasible. This technology would eliminate the need for human interference, as the programming is driven by external stimuli, which allows 4D-printed parts to be actuated in multiple cycles. To combat the lack of reversibility in 4D-printing, this study introduces a new swelling, and the heat-driven reversible 4D-printing process developed to achieve contactless programming and recovery. The forward shape setting programming is realised by asymmetric swelling using ethanol and heating. The shape recovery is accomplished by drying and heating. The process was validated using a 4D-printed bilayer composite with a transition material (VeroWhitePlus) and an elastomer (TangoBlackPlus) that was printed with the PolyJet Connex500 printer. This et-swell (swelling by ethanol) and heat-driven process minimise the required materials to maintain the simplicity of the 4D-printed part. An analytical model has been developed to determine the shape after programming using different parameters to attain control over the shape morphing. The analytical model could be used to predict the curvatures with the given conditions. The values predicted by the analytical model was compared to the experimental results and yield an average error of 10.1%. The error of the model reduced to ~ 5% under conditions of low temperature, low transition material thickness and an elastomer thickness of 2 – 3 mm. To overcome these limits and to attain a better accuracy in the prediction of curvatures, a finite element analysis was conducted. It produced a lower error of ~ 4% in shape morphing accuracy and provided stress study to gain insight into the swell and heat-driven programming process. The study progressed to combine the stimuli to empower rapid response to the 4D-printing process. The entire shape morphing cycle could be completed within as short as 3 minutes. Twisting shape morphing motions were investigated to contribute more potential 3D-to-3D shape morphing during programming that are rarely achieved. The rapid response and twisting were incorporated into different designs such as flowers, butterfly and gripper to demonstrate potential applications for reversible 4D-printing of polymers in biomimetic and soft robotics.Doctor of Philosoph

Proteomic profiling of hair proteome and its potential antimicrobial activity

Antimicrobial proteins/peptides (AMPs) are a promising class of antimicrobial agents which play an important role in host defence systems. In addition, they aid in apoptosis, wound healing and immune modulation. Skin and hair form an impervious barrier to pathogens and act as the first line of defence. Maintenance of skin and hair microbiota leads to the establishment of effective antimicrobial defence and microflora containment as the vital part of the skin’s innate immune system. Previous studies reveal the presence of AMP’s from the skin, but no activity has been reported from hair till now. Hair proteomics studies have shown the presence of known AMP’s like histones, RNAse7 and psoriasin which indicates possible AMP activity in the hair. Hence, this project aims to (1) optimise hair protein extraction methods, (2) identify and fractionate hair proteins; (3) evaluate the antimicrobial properties of hair protein fractions. High-throughput mass spectrometry analyses and reverse phase high-performance liquid chromatography (RP-HPLC) were carried out to identify and fractionate AMP enriched fractions which were analysed for antimicrobial activity. Two different types of hair protein enrichment analyses were performed, extraction using urea and extractions using sodium dodecyl sulfate (SDS) which were known as KAP extraction and SDS extractions respectively. Mass spectrometry revealed the presence of 115 common proteins, 65 were unique to KAP, 124 to SDS I and 69 to SDS II extractions respectively. Several histone isomers were identified in each method, of which H1, H2A, H2B, H4 from KAP and H2B, H3, H4 from SDS extractions were validated by Western blotting. AMP activity against E.Coli was observed in 15-18 minute fractions of KAP extraction analysed on HPLC. Subsequently, dot blot analyses confirmed the presence of histones. Hence, it was concluded that hair proteome contained promising antimicrobial activity probably due to the presence of histones. Further studies should be carried out to purify and characterize histones by mass spectrometry, electrophoretic methods and analyse the mode of action of the observed antimicrobial activity.Bachelor of Engineering (Materials Engineering

Review on 4D printing of polymer and its reversibility

Developments in multi-material polymer printing have kickstarted the advancements in 4D printing of polymers. Currently, there are many different methods to produce shape memory polymers via 3D printing techniques. However, most of them are one-way shape memory, which means that they cannot be used reversibly. The new direction of development in 4D printing is achieving reversibility. This review will present the different 3D printing techniques used to produce one-way shape memory polymers (SMPs) and reversible SMPs.NRF (Natl Research Foundation, S’pore)Published versio

Two-way 4D printing : a review on the reversibility of 3D-printed shape memory materials

The rapid development of additive manufacturing and advances in shape memory materials have fueled the progress of four-dimensional (4D) printing. With the right external stimulus, the need for human interaction, sensors, and batteries will be eliminated, and by using additive manufacturing, more complex devices and parts can be produced. With the current understanding of shape memory mechanisms and with improved design for additive manufacturing, reversibility in 4D printing has recently been proven to be feasible. Conventional one-way 4D printing requires human interaction in the programming (or shape-setting) phase, but reversible 4D printing, or two-way 4D printing, will fully eliminate the need for human interference, as the programming stage is replaced with another stimulus. This allows reversible 4D printed parts to be fully dependent on external stimuli; parts can also be potentially reused after every recovery, or even used in continuous cycles—an aspect that carries industrial appeal. This paper presents a review on the mechanisms of shape memory materials that have led to 4D printing, current findings regarding 4D printing in alloys and polymers, and their respective limitations. The reversibility of shape memory materials and their feasibility to be fabricated using three-dimensional (3D) printing are summarized and critically analyzed. For reversible 4D printing, the methods of 3D printing, mechanisms used for actuation, and strategies to achieve reversibility are also highlighted. Finally, prospective future research directions in reversible 4D printing are suggested.NRF (Natl Research Foundation, S’pore)Published versio

Preliminary investigation of the reversible 4D printing of a dual-layer component

The rapid development of additive manufacturing and advances in shape memory materials have fueled the progress of four-dimensional (4D) printing. With increasing improvements in design, reversible 4D printing—or two-way 4D printing—has been proven to be feasible. This technology will fully eliminate the need for human interference, as the programming is completely driven by external stimuli, which allows 4D-printed parts to be actuated in multiple cycles. This study proposes a new reversible 4D printing actuation method. The swelling of an elastomer and heat are used in the programming stage, and heat is used in the recovery stage. The main focus of this study is on the self-actuated programming step. To attain control over the bending, a simple predictive model has been developed to study the degree of curvature. The parameters, temperature, and elastomer thickness have also been studied in order to gain a better understanding of how well the model predicts the curvature. This understanding of the curvature will provide a great degree of control over the reversible 4D-printed structure.NRF (Natl Research Foundation, S’pore)Published versio

Contactless reversible 4D-printing for 3D-to-3D shape morphing

4D printing provides a means to create dynamic structures for self-actuating devices fabricated by additive manufacturing techniques. Most existing 4D printing processes are only capable of one-way shape morphing using a single mechanism for stimulation. In the limited successful reversible 4D-printing studies, most only demonstrate 2D-to-3D shape morphing. This study introduces a contactless shape setting mechanism to empower reversible 4D printing using a combination of stimuli. The forward shape programming is realised by asymmetric swelling with heated ethanol, and the shape recovery is accomplished by dry heating. The shape morphing can be predicted using a simulation model. Several designs are 4D-printed to achieve different forms of morphing to obtain 3D-to-3D shape morphing. The entire shape morphing cycle could be completed within as short as 3 min. The capability of 3D-to-3D shape morphing and reversibility of our 4D-printing process promise great potential for different applications such as biomimetics and soft robotics

3D food printing of fresh vegetables using food hydrocolloids for dysphagic patients

Three-dimensional food printing (3DFP) leads to advances in digital gastronomy by targeting consumers’ specific requirements for nutrition customization and visual appeal. Dysphagia, or difficulty swallowing, is prevalent in elderly people and patients suffering from debilitating illnesses. Dysphagic diets require textural modifications to render them soft and safe to swallow. Diets must be visually pleasing to enable a greater food uptake to prevent malnutrition in patients. 3DFP so far has mainly utilized freeze-dried vegetable powders for shaping 3D designs. Our work focuses on fresh and frozen vegetables having better nutritional profile and low costs. Three different categories of vegetables are identified based on the number of hydrocolloids required to render them printable. Garden pea, carrot and bok choy are chosen as representatives in each category, which requires no HC, one type of HC and two types of HCs, respectively. Food inks are prepared by the addition of HCs i.e. xanthan gum (XG), kappa carrageenan (KC) and locust bean gum (LBG) for texture modification. Rheological, textural, microstructural and syneresis properties of the inks are examined. International dysphagia diet standardisation initiative (IDDSI) tests are done to assess the potential of the inks for dysphagic diets. Optimized ink formulations display excellent 3D printability, minimal water seepage, and dense microstructures with minimal amount of HCs. Using fresh vegetables instead of freeze-dried foods serves the purpose of preserving flavour and nutrition like real food. This in turn may bring 3DFP closer to the hospital and nursing home kitchens.National Research Foundation (NRF)Accepted versionThis work was supported by National Additive Manufacturing Innovation Cluster Project ID 2019048 569 and the National Research foundation Singapore under its Medium-Sized Centre funding scheme

Studies on the Proteome of Human Hair - Identification of Histones and Deamidated Keratins

Human hair is laminar-fibrous tissue and an evolutionarily old keratinization product of follicle trichocytes. Studies on the hair proteome can give new insights into hair function and lead to the development of novel biomarkers for hair in health and disease. Human hair proteins were extracted by detergent and detergent-free techniques. We adopted a shotgun proteomics approach, which demonstrated a large extractability and variety of hair proteins after detergent extraction. We found an enrichment of keratin, keratin-associated proteins (KAPs), and intermediate filament proteins, which were part of protein networks associated with response to stress, innate immunity, epidermis development, and the hair cycle. Our analysis also revealed a significant deamidation of keratin type I and II, and KAPs. The hair shafts were found to contain several types of histones, which are well known to exert antimicrobial activity. Analysis of the hair proteome, particularly its composition, protein abundances, deamidated hair proteins, and modification sites, may offer a novel approach to explore potential biomarkers of hair health quality, hair diseases, and aging