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Chapter 5: Conclusion, Interpretation and Discussion

Introduction.

The following chapter concludes this report. A summary of the research is presented, and findings of the study are discussed and interpreted. The significance of this research in the immediate context of El Gallo and in the field of low-income housing is examined. Recommendations for further research end the chapter.

The scope of the following conclusions is limited to the context and historical characteristics of El Gallo. Thus, applied to other situations, these conclusions may yield incorrect assumptions. Still, these conclusions are relevant to the process of dwelling evolution in progressive development projects.

5.1 Summary of Research

This study observed the process of dwelling evolution in progressive development projects. The literature review was concentrated on the process of progressive development occurring in planned sponsored projects. It was found that, based on observations of the informal settlement process, progressive development under different contextual conditions was not questioned, and its benefits were taken for granted. Studies in the area were reduced to the period of improvement up to the time when the dwelling was physically consolidated. Longer term evaluation of progressive development projects were not found.

Research was undertaken on a 27-year-old progressive development project in Venezuela. The intention was to observe the process of dwelling evolution and the kind of housing that was being produced under progressive urban development projects on a long-term basis. The case study showed dwellings built with different initial levels of user-participation. Dwelling evolution was observed in a survey sample using parameters relevant to the case study (i.e., area increase, dwelling spatial growth and plot occupation, and changes in the functional structure).

Survey dwellings followed identifiable patterns of evolution in size, spatial structure and use-layout. Patterns were affected by aspects of the surrounding context and by aspects inherent to characteristics of the initial dwelling. Consequently, different dwelling groups showed different processes of progressive development.

5.2 Discussion and Interpretation of Findings.

As progressive developments, dwellings at El Gallo were able to adopt new and diverse roles along their whole process of evolution. In this section, relevant issues of the process of dwelling evolution observed at El Gallo are discussed. The first concerns the role of the non-permanent structure in the context of El Gallo as a sponsored progressive development project. The second comments on the process of dwelling evolution that followed the construction of the permanent structure.

In principle, non-permanent structures at El Gallo were similar to ranchos built in informal settlements. Ranchos at El Gallo served as primary shelters while more basic household priorities were met (i.e., services and infrastructure were provided, sources of income were found and generated, and even a favourable social environment was developed among neighbours). However, the majority of tin shacks were neither considerably increased nor upgraded with better materials even when they were used for long periods of time. This fact, together with the sudden change in the pace of development caused by the construction of a very complete permanent dwelling and subsequent removal of the rancho, had no connection with the gradual process of shack replacement observed in invasion settlements of Ciudad Guayana during this study (Portela, M. 1992). Neither did this process have a relationship with the system of "piecemeal construction" described by several housing researchers as characteristic of low-income dwellers.

The shanties were... housing in process of improvement. In particular the piecemeal system of building afforded great advantages to those who, like most of the poor in developing societies, have great variations in income from month to month (Peattie L. 1982:132).

Under El Gallo conditions of land security, ranchos did not show consolidation, and revealed their transient character because they were eventually substituted by permanent structures. The non-permanent structure revealed the primary household's aspiration for a minimum satisfactory habitable area. However, besides basic shelter during the initial stage, ranchos served to the purposes of capital accumulation that eventually allowed households to buy a basic unit according to official standards, or building a bigger, more complete first permanent structure. The size of ranchos reflected households' aspirations for the permanent dwelling, that is,smaller ranchos were substituted by basic units of the housing programs. Instead larger ranchos were substituted by large self-produced dwellings.

It is difficult to ascertain why ranchos were removed when they could have been kept as part of the dwelling, as in fact did a minority of households (2 cases). Is a fact that the temporary materials of ranchos contributed to their deterioration that ended with the total removal of the rancho. However, an idea that may have contributed to the demolition of the rancho was the household's adoption of the planner's belief that ranchos were a bad but necessary step on the way to obtaining permanent housing. Thus, once the permanent dwelling was built, the price households paid to gain credibility (i.e., that this stage was reached) was the demolition of the rancho itself. This interpretation can be specially true for Ciudad Guayana, where dwellings of certain quality such as those of El Gallo were seen as "casas" or houses. Instead, structures of similar quality in the hills of cities such as Caracas were still considered ranchos. In the long run, informal settlements obtained the largest benefits from this process because they gained far more official tolerance and social credibility (i.e., that shacks were actually temporary means of residence towards good-quality housing).

Those who lived in smaller ranchos improved their spatial conditions by moving to the small basic dwellings. Those who occupied bigger ranchos built bigger dwellings by themselves. Still, some households built their dwellings without going through the rancho stage. Self-produced dwellings followed the formal models either to gain the government's credibility of user commitment to build "good" government-like housing, or because households believed so. Imitation of the formal models, however, varied according to the builder's interpretation. For instance, the pattern of the detached dwelling was adopted, but often one of the side yards was reduced to a physical separation between the dwelling and the plot separation wall. More effective interpretations involved enlarging the front porch or using the central circulation axis to allow easy extension in the future.

The building approach of the permanent structure influenced the process of evolution that followed. Basic units built by the housing agencies had a compact, complete layout with higher standards of construction; however, aspects of the design, such as internal dimensions, were inadequate for household criteria, and the layout was not well adapted. Dwellings built according to provided plans and specificationshad similar problems, but households enlarged spaces and modified layouts when they were building the units. The level of construction standards was also reduced since the lateral façades of some dwellings were unfinished. Dwellings built totally by self-help means were the largest permanent structures. Aspects of the design of the first permanent structure allowed easy extension of the dwelling towards open areas of the plot. More user participation was reflected in straight-forward processes of evolution without internal modifications, and fewer stages to reach the current houseform.

5.3 Significance of the Study

While this study acknowledges again the effectiveness of progressive development in the housing system, it shows how dwelling evolution in progressive development projects can have different characteristics produced by internal and external interventions. Usually, projects are designed and launched to reproduce certain desirable outcomes and meet specific expectations. However, conditions prevailing in these projects and sometimes strategies that are introduced to "improve," "speed up" or make more "efficient" the process of evolution can affect the outcome in many different ways. This study showed how contextual characteristics of El Gallo, as well as the design and level of user participation in the initial permanent dwelling, affected successive stages of progressive development. However, it is important to recognize that are other issues beyond the spatial aspects that are intrinsically related with the evolution of the dwellings and that were not included within the scope of these particular research (i.e., household's changes in income, size, and age or gender structure).

The findings at El Gallo add modestly to the body of knowledge of literature on progressive development. Progressive Urban Development Units, UMUPs , have been the main housing strategy in Ciudad Guayana these last years, and they are likely to keep being used. Simple facts such as knowing the characteristics of the additions and modifications that households make to their dwellings over time can be the basis for more assertive actions supporting or enforcing progressive development activities. Understanding the process of dwelling evolution in low-income developments would be an effective way to help the process that, in the case of Ciudad Guayana, zonings and bylaws have been unable to regulate.

5.4 Recommendations for Further Research

Long term assessments are particularly constrained by the availability and reliability of recorded data. The frequency, and often the methodology, in which censuses and surveys are made do not always suit the purposes of this kind of research. Household interviews are very important, but they may become troubled by informant's limited memories and the continuity of the household in the dwelling. Aerial documentation, if available, represents one of the most reliable sources to observe physical change. Nevertheless, a careful and detailed process of observation of aerial data becomes very time consuming. For similar studies, a first phase in which the housing diversity is identified in the aerial data according to the selected criteria, would allow to reduce the number of detailed survey samples needed, thus considerably reducing the time of data collection.

In the context of Ciudad Guayana, further studies of the non-permanent dwelling in recent UMUPs would reveal new insights into the function of these structures in progressive development projects. This would be essential especially if any kind of initial aid is to be provided. On the other hand, following the growth of progressive developments is necessary if services and infrastructure are, as they are now, the responsibility of the local government. Identifying the producers of physical evolution -- i.e., the drivers and catalysts of change -- would be an important step for further research. An interesting step within this trend could be to ascertain the extent in which other household processes -- family growth, income increase and economic stability, household aging, changes in the household composition (single- to multi- family), etc., affect the process of dwelling evolution.

In the context of low-income housing, the process of progressive development needs further understanding. As in Ciudad Guayana, progressive development is likely to be the main housing strategy for other developing countries in the near future. Local authorities would do well to follow the evolution of settlements and to identify real household needs, and the consequences of public and/or private interventions in low-income settlements. Perhaps the most important learning of this study is that the experience of El Gallo acknowledges again the dynamic participation of the low-income households under different conditions, and still leaves wide room for a positive participation for the many other actors in the evolving urban entity.

. Notes for Chapter V

1 Dodge reports that some settlers of Ciudad Guayana kept the rancho and rented it to poorer families (Dodge,C. 1968:220). This attitude has been more common in other progressive development projects. The Dandora site and services also encouraged the construction of temporary shacks while the permanent dwelling was built. However, non-permanent structures remained to be rented or used as storage areas even after the permanent dwelling was built (McCarney, P.L. 1987:90).

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Chapter 5 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

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Thesis Writing: What to Write in Chapter 5

Table of contents, introduction.

This article tells what a budding researcher must include in Chapter 5-the Summary. It also includes the tense of the verb and the semantic markers, which are predominantly used in writing the summary, conclusions, and recommendations.

For others, writing Chapter 5 is the easiest part of thesis writing, but there are groups of students who would like to know more about it. If you are one of them, this article on how to write chapter 5 of your thesis is purposely written for you.

What to Write in Chapter 5

1. write the summary.

Your summary in Chapter 5 may include:

• objectives of the study.
• statement of the problem.
• respondents.
• sampling procedures.
• method/s of research employed.
• statistical treatment/s applied, or hypotheses tested, if there is any; and

If you notice, all the parts mentioned above are already included in your Chapters 1- 4. So, the challenge is on how you are going to write and present it in Chapter 5 briefly.

First, you must go directly to the point of highlighting the main points. There is no need to explain the details thoroughly. You must avoid copying and pasting what you have written in the previous chapters. Just KISS (keep it short and simple)!

Then, write sentences in  simple past  and always use  passive voice  construction rather than the active voice. You must also be familiar with the different semantic markers.

When I was enrolled in Academic Writing in my master’s degree, I learned that there are semantic markers which can be used in order not to repeat the same words or phrases such as  additionally, also, further, in addition to, moreover, contrary to, with regard to, as regards, however, finally, during the past ___ years, from 1996 to 2006, after 10 years, as shown in, as presented in, consequently, nevertheless, in fact, on the other hand, subsequently and nonetheless.

Next, you may use the following guide questions to check that you have not missed anything in writing the summary:

• What is the objective of the study?;
• Who/what is the focus of the study?;
• Where and when was the investigation conducted?;
• What method of research was used?;
• How were the research data gathered?;
• How were the respondents chosen?;
• What were the statistical tools applied to treat the collected data?; and
• Based on the data presented and analyzed, what findings can you summarize?

Finally, organize the summary of the results of your study according to the way the questions are sequenced in the statement of the problem.

2. Write the Conclusion or Conclusions

Once you have written the summary in Chapter 5, draw out a conclusion from each finding or result. It can be done per question, or you may arrange the questions per topic or sub-topic if there is any. But if your research is quantitative, answer the research question directly and tell if the hypothesis is rejected or accepted based on the findings.

As to grammar, make sure that you use the  present tense of the verb  because it comprises a general statement of the theory or the principle newly derived from the present study. So, don’t be confused because, in your summary, you use past tense, while in conclusion; you use the present tense.

3. Write the Recommendations

The recommendations must contain practical suggestions that will improve the situation or solve the problem investigated in the study.

First, it must be logical, specific, attainable, and relevant. Second, it should be addressed to persons, organizations, or agencies directly concerned with the issues or to those who can immediately implement the recommended solutions. Third, present another topic which is very relevant to the present study that can be further investigated by future researchers.

But never recommend anything that is not part of your study or not being mentioned in your findings.

First, it must be logical, specific, attainable, and relevant. Second, it should be addressed to persons, organizations, or agencies directly concerned with the issues or to those who can immediately implement the recommended solutions. Third, present another topic that is very relevant to the present study that can be further investigated by future researchers.

Recommend nothing that is not part of your research or not being mentioned in your findings.

However, there are universities, especially in the Philippines, that require a specific thesis format to be followed by students. Thus, as a student, you must conform to the prescribed form of your college or university.

Nordquist, R. n.d. Imperative Mood. Retrieved July 29, 2014, from https://www.thoughtco.com/imperative-mood-grammar-1691151

© 2014 July 29 M. G. Alvior | Updated 2024 January 10

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About the author, mary g. alvior, phd.

Dr. Mary Gillesania Alvior has PhD in Curriculum Development from West Visayas State University. She earned her Master of Arts in Teaching English from De La Salle University, Manila as Commission on Higher Education (CHED) scholar. As academic advisor, she helps learners succeed in their academic careers by providing them the necessary skills and tips in order to survive in this wobbling financial environment. In 2014, she got involved in the establishment of a language institute in the Middle East, particularly in the use of Common European Framework of Reference for Languages (CEFR). Then she went to Thailand and became a lecturer in the international college and handled English and Graduate Education courses. From 2017 to 2021, she became the Focal Person for the Establishment of a Medical School, Director of Curriculum and Instructional Materials Development Office (CIMDO), Head of BAC Secretariat, Quality Management System (QMS) Leader, and TWG member of the Procurement for Medical Equipment. Currently, she is the coordinator of the Project Management Committee for the Establishment of the Medical School. In spite of numerous tasks, she is into data privacy, quality management system, and space industry.

100 Comments

can you please make a summary about “Centella Asiatica with virgin Coconut Oil as Ointment”?

I am still having problem in organizing my summary and conclusion (my topic is dress code in public schools. to be more specific, at the Voinjama Public School. Can you help me with a sample?

This is very helpful especially the grammar part. It really jumped start my writing effort… really want to finish my study with style.

I just pray you are okay. Thanks for responding to the questions, I have also learnt a lot.

Hello, Daryl. Thank you so much. About your request, I will find time to write about it. I got so busy the past months.

Precise and direct to the point ,, Thanks maam Mary.

Thanks very much for this all importing information on how to write chapter five in thesis writing. It gives me more insight as to how to develop the chapter five perfectly.

Hello maam my PhD research purely a qualitative study on community based organization of slum ..i used 3 tool case study , participant observation and FGDs to analyse role, impact, challenge and aspiration of CBOs . i used tabular form (matrix to analyse ) did not use any software..

PLEASE HELP/GUIDE ME WHAT SHOULD I WRITE in my Chapter 5 .. your help is very much crucial as i have to submit thesis this weekend KULDEEP

I’m so sorry, Kuldeep. I wish you are done with your doctorate research. It is been a year then. I got sick and had a lot of work to do. God bless!

Hello ma’am, can I ask about in what part the recommendation in chapter 1 reflect the recommendation in chapter5? Thanks.

Sorry, Aly. This is very late. Take your statement of the problem. the results for the statement of the problem will be the basis for your recommendation.

You are welcome, Prince. God bless to your research endeavor.

Thank you very much very insightful.

Eric, you are welcome. I wish you are able to finish your work.

how to write a recommendation, my title is common causes of financial problem. Hope you can help me…

Hello, Jolven. Your recommendation must be based on your findings. So, if that is your title, and you found that the common causes are the ——-, then write a recommendation based on the causes.

Thanks a lot, Mimimi.

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Conclusion: The Practice of Longitudinal Research

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Part of the book series: Perspectives on Children and Young People ((PCYP,volume 15))

In their germinal work on Researching Social Change McLeod and Thomson (Researching social change: Qualitative approaches. Sage, 2009) conceptualise the longitudinal researcher as a time traveller who works across multiple timescapes and with interwoven memories and hopes—both their own and those of their participants. While considering the practice of longitudinal research the three authors in this section have, in essence, reflected on their own experiences as time travellers, and the temporal work that they have performed alongside their research participants. The chapters in this section present perspectives on the history of longitudinal research in the field of youth studies, and how it has been shaped into the present-day field; the affordances that longitudinal research presents to researchers; and the way in which longitudinal research methods can be used to create meaning in both prospective and retrospective work. In considering these topics the authors highlight insights that are specific to the locale in which their studies were conducted, and yet have resonances that extend beyond these contexts to provide inspiration and instruction for other longitudinal youth researchers.

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Cook, J. (2024). Conclusion: The Practice of Longitudinal Research. In: Cook, J., Maire, Q., Wyn, J. (eds) Longitudinal Methods in Youth Research. Perspectives on Children and Young People, vol 15. Springer, Singapore. https://doi.org/10.1007/978-981-97-2332-4_5

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Home > Books > Nanocellulose - Sources, Preparations, and Applications

Bacterial Nanocellulose: Methods, Properties, and Biomedical Applications

Submitted: 13 August 2023 Reviewed: 22 January 2024 Published: 29 May 2024

DOI: 10.5772/intechopen.114223

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Unlike plant and wood-origin cellulose, bacterial nanocellulose (BNC) produced by bacteria exhibits the highest purity and natural nanofiber morphology, attracting increasing interest from many researchers and industrial sectors. It has numerous unique features including the biomimetic nanoscale three-dimensional (3D) network, high water holding capacity, and moldability in different shapes, accepted wet strength, outstanding gas permeability, and good biocompatibility, which makes the BNC show great potential in a wide variety of biomedical applications. Extensive research has verified the feasibility of application in wound dressing, bone/cartilage tissue regeneration, vascular tissue engineering, and so on. This chapter focuses on the production and properties of BNC, the fabrication of BNC-based biomaterials, and the biomedical applications of BNC.

• bacterial nanocellulose
• fabrication techniques
• biomaterials
• biomedical applications

Author Information

Haiyong ao *.

• School of Materials Science and Engineering, East China Jiaotong University, Nanchang, PR China

Xiaowei Xun

*Address all correspondence to: [email protected]

1. Introduction

Bacterial nanocellulose (BNC) as a type of extracellular polysaccharide polymer synthesized by bacteria has unique physical and chemical properties, including high purity (free from lignin and hemicellulose) and crystallinity (84–89%), high degree of polymerization, good mechanical properties, high water retention, and three-dimensional (3D) nanofibrous structure [ 1 , 2 ]. All these features make BNC attractive for material scientists and engineers.

Importantly, BNC is environment-friendly due to its nontoxic, nonimmunogenic, biocompatible, biodegradable, and renewable nature [ 3 ]. The nanofibrillar network of BNC is similar to the structure of collagen in the native extracellular matrix (ECM), and the 3D uniform and interconnected pores facilitate cell infiltration and nutrient and waste exchange [ 4 , 5 ]. As a promising natural biomaterial, BC has been extensively utilized in various biomedical fields for wound healing, bone, cartilage, and blood vessel engineering [ 6 , 7 ].

During the past two decades, many studies have been dedicated to developing various BC-based biomaterials. The 3D porous structure and easily modified surface (abundant OH groups) of BNC are beneficial for introducing into BC varieties of reinforcement substances including biomolecules, nanoparticles, and polymers to acquire new materials with highly desirable properties, which can lead to the formation of BC-based functional materials for biomedical applications [ 3 ]. Moreover, BC-based scaffolds have been specifically designed to mimic the 3D structures of native tissues to support and provide the microenvironments required for cell adhesion, proliferation, migration, and differentiation [ 8 ]. These extensive efforts have accelerated the development of BNC-based biomaterial.

In this chapter, we briefly introduced the biosynthesis and properties of BNC. Furthermore, the strategies for fabricating the BNC biomaterial and applications in various biomedical fields were summarized.

2. Biosynthesis and properties of BNC

2.1 biosynthesis and production of bnc.

The bacterial synthesis of cellulose was first reported by Brown as early as 1886 [ 9 ]. Brown found that a white gel-like thin layer was formed on the surface of the culture medium after incubating Bacterium xylinum’ in a static state. Chemical analysis determined that the main component of the white gel is cellulose and does not contain hemicellulose and lignin, and further research found that the diameter of this cellulose is at the nanoscale.

Gluconacetobacter genus , as one of the most efficient BNC producers, is widely used in the biosynthesis of BNC [ 10 , 11 ]. The general process to produce BNC is schematically described in Figure 1A . The biosynthesis process of BNC is mainly divided into four steps ( Figure 1B ): (1) glucose is converted into glucose-6-phosphate, (2) glucose-6-phosphate is converted into glucose-1-phosphate by phosphoglucomutase, (3) uridine diphosphate glucose (UDP-glucose) pyrophosphorylase converts glucose-1-phosphate to UDP-glucose, (4) the UDP-glucose is converted to cellulose by the action of cellulose synthase ( Figure 1C ) [ 13 , 14 ]. The self-assembly and crystallization of BNC nanofibrils are regulated by the cell itself [ 15 ]. The synthesized chains are sequentially gathered in the culture medium at a rate of up to 200,000 glucose molecules per second and form protofibrils or sub-elementary fibrils, which are 2–4 nm in diameter. Each sub-elementary protofibril is composed of 12–16 glucan chains, where the glucan chains are aligned and stacked into ordered nanostructures called the microfibrils. The micro- and macrofibrils and loose bundles finally form 30–100 nm ribbon-like structures. The ribbons are highly porous and have 3D fibrous network.

(A) A schematic illustration of BNC production. (B) Schematic illustration of biochemistry of cellulose synthesis in a bacterial cell and the extracellular transport of cellulose chains and the formation of highly ordered structures. (C) Chemical structure of BNC. (D) Schematic illustration of the aerosol-assisted biosynthesis of BNC [ 12 ].

For many years, many researches have been focused on BNC production. Various culture methods have been used by controlling the fermentation conditions to increase the yield of BNC or obtain BNC with different characteristics [ 16 ]. Under static culture conditions, bacteria need to float on the surface of the medium to obtain enough oxygen, and cellulose microfibrils are extruded from the bacteria and synthesize a tight BNC pellicle. The BNC formed under static conditions usually has high crystallinity and tensile strength. In contrast, a fluffy, spherical, or irregular lump BNC was obtained via the agitating culture method. Although the agitating culture has faster cell growth rate than static conditions because of more oxygen filling in the culture medium, the production of BNC decreased, which perhaps due to the uniform aeration of cultures induced cells to grow intensively instead of the polymer synthesis. Based on this, the bioreactors have been developed that can produce BNC pellicles at higher yields under static conditions ( Figure 1D ) [ 12 ].

2.2 Properties of BNC

Compared to vegetal cellulose, its unique chemical composition and physical structure endows BNC with numerous unparalleled physical, chemical, and biological properties ( Figure 2 ). BCN is an attractive candidate for widespread applications in various fields, especially in applications related to biomedical.

A schematic representation of properties of BNC.

2.2.1 Physical properties

BNC has natural 3D porous network structure, which is composed of nanofibers and exhibits enormous mechanical properties. The Young’s modulus of BNC sheets up to 15 GPa, which is much greater than plant cellulose and several synthetic fibers [ 17 ]. The excellent mechanical properties make BNC to be used for blood vessels and bone tissue engineering. The water holding capacity of BNC is about 100 times its dry weight, which is attributed to the high surface area and pore volume of BNC that can intercept more water [ 18 ]. In addition, the average diameter of BNC nanofibers is 1.5 nm, showing higher surface area and flexibility. These fascinating physical properties make BNC become desirable wound dressing material.

2.2.2 Chemical properties

BNC is composed of linear homopolysaccharides conjugated by β-D-glucose units linked by 1,4-β-glycosidic linkages and has considerably higher crystallinity (80–90%) and degree of polymerization (up to 8000), which means that pure BNC can be obtained with simple processing. The abundant hydroxyl groups and high-level hydrogen bonds on the surface of BNC nanofibers allow for manipulation in their loading of functional molecules. Although BNC exhibits significant intrinsic characteristics, it is still necessary to develop more modified properties of BNC to meet the requirements of the required biomedical applications.

2.2.3 Biological properties

BNC has wide applications in biomedical engineering because of its excellent biological properties. Héctor and coworkers confirmed the nontoxicity and extremely low bacterial endotoxin of BNC nanofibers by using in vitro and in vivo tests [ 19 ]. In addition, the good biocompatibility of BNC is due to its peculiar 3D nanofibrous network structure that supports cell penetration and proliferation. Helenius et al. subcutaneously implanted the BNC in rats to systematically evaluate the biocompatibility of BNC [ 20 ]. The results showed no inflammation around the implants and the fibroblasts infiltrated BNC, which indicates the good biocompatibility of BNC and has the potential to be used as a scaffold in tissue engineering.

3. Fabrication of BNC biomaterials

Although the above excellent inherent characteristics make BNC have broad application prospects in the field of biomedical, pure BC possesses certain restrictions that limit its application due to the lack of unique biological functions. In recent years, several approaches have been developed to improve the physicochemical properties and function of BNC, including producing BNC composites, surface medication, and changes in porosity. These efforts have significantly improved the surface properties and biological functions of BNC and tremendously expanded its application in various tissue engineering fields.

3.1 Surface modifications

3.1.1 physical modifications.

The BNC nanofibers were physical modifications by using bioactive materials, which not only preserves the unique properties but also enhances the biological functions to meet the requirements of biomedical applications. To improve the biocompatibility of BNC, Luo et al. selected a new type of coating, chondroitin sulfate (CS) modified with gelatin (Gel), to modify BNC scaffold [ 21 ]. The coating on the surface of the BNC nanofibers is linked by hydrogen bonding. The results of in vitro cell studies indicated that the CS/Gel coatings significantly promote cell proliferation, adhesion, differentiation, and ingrowth into scaffolds. Nanomaterials can also be used for surface modification of BNC. He et al. developed a Cu 2+ loaded phase-transited lysozyme (PTL) nanocoating for surface modification of BNC. The coating endowed the BNC with inhibiting bacterial growth and inflammation and simultaneously induced vascularization, collagen deposition, and reepithelialization of wounds promising dressings for healing infected wound, which was considered a promising dressing for treating infected wounds. In addition, polymer composite nanoparticles are also used for surface modification of fibers. Ma et al. developed a homogeneous AgNP-loaded polydopamine (PDA)/polyethyleneimine (PEI) coating on the surface of BNC nanofibers, which exhibited excellent antibacterial activities and cytocompatibility [ 22 ].

3.1.2 Chemical modifications

The only surface functional group on the surface of BNC nanofibers is the hydroxyl group, which is not suitable for cell proliferation [ 23 ]. Nevertheless, the hydroxyl groups on the surface of BNC nanofibers are beneficial for surface chemical modifications; they can be treated with various chemical reagents tomodify their chemical structure and incorporate additional functionalities. Therefore, the surface chemical modifications of BNC are required for biomedical applications. Oxidation is an important reaction for adding new functional groups to BNC, which creates infinite possibilities for the functionalization of BNC nanofibers. TEMPO (2,2,6,6-Tetramethylpiperidinyloxy or 2,2,6,6-Tetramethylpiperidine-1-oxyl radical)-mediated oxidization is a simple and effective chemical reaction, in which C 6 of a hydroglucose units selectively gain an anionic carboxyl group [ 24 ]. A new bone repair composite scaffold (CS/OBC/nHAP) was constructed by evenly dispersing the in situ crystalline nano-hydroxyapatite (nHAP) in oxidized bacterial cellulose (OBC) and chitosan (CS) scaffolds [ 7 ]. Shahriari-Khalaji et al. achieved high carboxylate content by optimizing the TEMPO-mediated oxidation of BNC and then covalently bonded the ε-poly-L-lysine (PLL) with oxidized BNC to develop an O-BNC-based functional wound dressing [ 25 ]. Furthermore, Xie et al. prepared biofunctional group-modified bacterial cellulose (DCBC) by carboxymethylation and selective oxidation to achieve the perfect compound of cellulose and chitosan [ 26 ]. The obtained BNC-based dressing can effectively inhibit bacterial proliferation in wounds and kill the bacteria.

3.2 BNC-based composites

3.2.1 bnc nanocomposites.

To improve the mechanical and biological properties of BNC biomaterials, various BNC-based nanocomposites were prepared by incorporating different kinds of nanomaterials, including carbon-based nanoparticles (NPs) [ 27 ], metal/metal oxide NPs [ 28 ], and other inorganic NPs [ 29 ]. The simplest and most convenient method for fabricated BNC nanocomposites is the mechanical mixing method. Yang et al. prepared the BNC/Ti3C2Tx nanocomposites using mechanical mixing. Although this strategy allows for sufficient mixing of nanomaterials with BNC nanofibers, it damages the intrinsically continuous 3D structure of BNC. To maintain the intrinsically continuous 3D structure of BC, Luo et al. developed a cost-effective, scalable, and efficient approach, membrane-liquid interface (MLI) culture, to prepare BNC-based nanocomposite [ 30 ]. The MLI culture technology is schematically illustrated in Figure 3A [ 31 ]. First, a layer of BNC film (around 3 mm in thickness) was grown as a substrate using a conventional static culture method. Then, a nanomaterials-dispersed medium was sprayed onto the BNC substrate followed by the culturing of BNC on the substrate–medium interface. After the sprayed medium was completely consumed off by the BNC growth, another layer of the medium was sprayed. This process was repeated until the designed thickness was achieved. It is noted that the thickness of nanocomposites prepared using the MLI method can be accurately controlled by the spray cycles of the medium. In addition, the sample shape and dimension can be facially designed by the geometry of the containers used for the preparation. This method has been widely used to prepare various nanocomposites ( Figure 3B ) [ 12 ].

(A) Schematic illustration of the preparation of BNC nanocomposites by using membrane-liquid interface culture technology [ 31 ]. (B) SEM and photographs of BC-based nanocomposites were prepared by using membrane-liquid interface culture technology [ 12 ].

3.2.2 BNC-based biocomposites

Compared with other natural biopolymers, pristine BNC lacks cytocompatibility and important biological functions. The abundant ∙OH groups on the surface of BNC provide binding stable sites for biopolymers in biocomposites. Therefore, various techniques including in situ addition, solution impregnation, and chemical cross-linking were used to combine various bioactive substances to obtain the BNC-based biocomposites with enhanced physicomechanical, antimicrobial, and biocompatible properties. In order to enhance the antibacterial properties and cytocompatibility of BNC, Zhou et al. composited the collagen I (Col-I) and the antibacterial agent hydroxypropyltrimethyl ammonium chloride chitosan (HACC) into the BNC 3D network structure by a novel membrane-liquid interface (MLI) culture ( Figure 4A and B ) [ 32 ]. The introduction of HACC and Col-I makes BNC have outstanding antibacterial properties and improved cytocompatibility to promote NIH3T3 cell and HUVEC proliferation and spread ( Figure 4C ). The BNC-(polypyrrole) Ppy composites were prepared to mimic the natural myocardial microenvironment by in situ polymerization [ 33 ]. The composites were flexible and still maintained 3D network structure and displayed electrical conductivities in the range of native cardiac tissue. Wan et al. reported extracellular matrix (ECM)-mimetic scaffolds by conjugating electrospun cellulose acetate (CA) submicrofibers with BNC nanofibers via a facile and scalable dispersion freeze-drying process [ 34 ]. It is found that the composites have a 3D porous network structure and improved cell behavior.

(A) Schematic illustration of the preparation of BNC-based biocomposites. (B) SEM images of BNC-based biocomposites. (C) The characteristice of BNC-based biocomposites [ 32 ].

3.3 3D porous BNC scaffold

As a promising biomaterial, BNC has some intrinsic disadvantages when applied in tissue engineering; its dense nanofibrous network (the pore sizes of pristine BNC are only approximately 0.02–10 μm) markedly limits cell migration and 3D tissue regeneration. To date, different methods have been reported for the fabrication of 3D porous BNC scaffolds. The paraffin microparticles, potato starch, agarose microparticles, and gelatin microspheres as porogens have also been used to fabricate 3D porous BNC scaffolds by using the in situ porogen technique [ 35 , 36 , 37 , 38 ]. Cui et al. described the utilization of gelatin microspheres in BNC production for porosity enhancement, and the observed porosity depended on the diameter of microspheres ( Figure 5A ) [ 36 ]. However, a nonuniform pore structure would be formed due to the bacteria moving to the air/medium interface during the culture process of the in situ porogen impregnation technique.

Different 3D porous BNC scaffolds were fabricated by using in situ porogen [ 34 ], laser patterning [ 39 ], freeze-drying and cross-linking [ 40 ], and 3D bioprinting [ 41 ].

Laser patterning as an efficient method is used to prepare 3D porous BNC scaffold. Laser treatment has universality, and the obtained scaffolds do not contain pollutants and chemical cross-linking agents, thereby having better biocompatibility. The pore structure prepared by laser is parallel microchannels. Yang et al. fabricated the nano-submicrofibrous cellulose scaffolds with microchannels by laser-aided punching ( Figure 5B ) [ 39 ]. The cell study found that the presence of microchannels favors cell proliferation and migration at an optimum microchannel size. However, laser-aided punching prepared microchannels can lead to cell leakage from the scaffold, making it difficult to achieve 3D culture.

Freeze-drying is the most common technique for preparing a 3D porous BNC scaffold, which can obtain the BNC sponges with higher porosity and specific surface. However, the pore size of freeze-dried BNC sheets is unable to precisely regulate, and the pore structure is instability. Therefore, improvements need to be made to address these issues. Xun et al. first reported an improved strategy to fabricating 3D macroporous BNC scaffolds with controllable pore size by freeze-drying and cross-linking the mechanically disintegrating shortcut BNC nanofiber suspensions ( Figure 5C ) [ 40 ]. The pore sizes of the MP-BNC scaffolds were controlled by adjusting the concentration of BNC in the suspensions. The fabrication process was facile, scalable, and effective in controlling the pore structure. The cross-linked BNC scaffolds exhibited excellent compression properties and shape recovery ability compared to the original BNC. Moreover, the results of in vitro and in vivo studies demonstrated that the scaffolds had excellent biocompatibility and were effective in regenerating cartilage tissue.

Additive manufacturing or 3D printing is an emerging technology to prepare 3D porous scaffolds through rapid prototyping. In recent years, it has been widely used in personalized customization of tissue engineering scaffolds. Li et al. used the gelatin methacrylate (GelMA)/BNC bioink formulations to develop heterogeneous tissue-engineered skin (HTS) containing layers of fibroblast networks with larger pores, basal layers with smaller pores, and multilayered keratinocytes ( Figure 5D ) [ 41 ]. The results revealed that the 10%GelMA/0.3%BNC bioink was better to bioprint dermis due to its high printability and cell-friendly sparse microenvironment. The approaches developed in the above-described studies and their findings suggest that BNC has great potential to be printed into 3D microstructures for the development of scaffolds and medical devices for various biomedical applications.

4. Biomedical applications of BNC

In the past two decades, BNC has aroused great attention to fundamental and scientific research for biomedical applications due to its unique properties [ 42 ]. Functionalized BNC and its composites have been applied in several medical applications, such as wound dressing, bone and cartilage tissue regeneration, and the development of artificial organs and blood vessels’ substitutes ( Figure 6 ) [ 23 , 43 ]. This section focuses on the research progress of the main biomedical applications of BNC in recent years.

A schematic representation of the potential biomedical applications of BNC biomaterials.

4.1 Wound healing

The skin is the main protective barrier of the human body and has many functions, such as controlling body temperature and maintaining a balance of electrolytes and water [ 44 ]. However, large-scale skin damage caused by trauma, ulcers, and burns is difficult to heal on its own and requires human intervention to promote wound healing [ 45 , 46 ]. Wound dressings have been developed to prevent infection and dehydration of wound, reduce inflammatory responses, and promote wound healing. BNC is one of the most promising wound dressings due to its ultrafine 3D network structure, excellent gas permeability, high water absorbency, and favorable biocompatibility [ 47 ]. Furthermore, BNC-based dressings can also prevent bacterial invasion, absorb excess exudates, and retain moisture in wounds to promote the growth of granulation.

In the healing process, it is important to prevent bacterial infection on the wound site. However, BNC does not have intrinsic bactericidal properties to eliminate the colonized bacteria. Therefore, the initial research focus was on antibacterial BNC-based dressings. Hence, various promising antibacterial agents are introduced into BNC, such as metals and their oxides, antimicrobial peptides, and biological and synthetic polymers (chitosan) [ 48 ]. Ao et al. fabricated the quaternized chitosan (HACC)/BNC antibacterial wound dressing by using in situ synthesis possessed, and the obtained dressing had favorable antibacterial properties [ 49 ]. To further improve the antibacterial properties of BNC dressings, silver nanoparticles (AgNPs) were introduced into the BNC structure [ 22 ]. The results of the standard plate count assay indicated that the antibacterial BNC dressing showed antibacterial rates of over 99.9% against Escherichia coli  and Staphylococcus aureus . The in vivo assay demonstrated that the antibacterial BNC dressing could inhibit infection and inflammation and accelerate wound healing within 12 days compared with BNC. To reduce the cytotoxicity of sliver-based dressing and promote wound healing, a novel multifunctional sliver nanowires (AgNWs)/collagen I (Col I)/BNC dressing was constructed via compositing AgNWs into BNC and adsorbing Col I [ 50 ]. The antibacterial assay demonstrated that the multifunctional AgNWs/Col I/BNC dressing could kill S. ausreus and E. coli colonizing on the surface of material due to the silver ions released. Importantly, this dressing had lower cytotoxicity and promoted collagen deposition, hair follicle growth, neovascularization, and wound healing. A novel copper ion (Cu 2+ )-loaded BNC-based antibacterial wound dressing was prepared via codeposition of polydopamine (PDA) and Cu 2+ [ 51 ]. The in vivo study revealed that the dressing can eliminate S. aureus infections and inflammatory response and promote collagen deposition, capillary angiogenesis, and wound healing.

In addition, BNC composites containing nanomaterials, biopolymers, antioxidants, antibiotics, and blood clotting agents have been fabricated to improve the wound healing of BNC-based dressings. Cai et al. fabricated a composite adhesive organo hydrogel by introducing BNC and platelet-rich plasma (PRP) into a poly-N-(tris[hydroxymethyl]methyl)acrylamide (THMA)/N-acryloyl aspartic acid (AASP) hybrid gel network infiltrated with glycerol/water binary solvent [ 52 ]. The PRP-loaded organo hydrogel has good tissue adhesion properties and releases a variety of growth factors to accelerate the wound healing process through collagen deposition and angiogenesis. Shen et al. developed an aggregation-induced emission (AIE) molecule BITT-composited BNC for wound healing [ 53 ]. The BNC-BITT composites retained the advantages of biocompatible of BNC and displayed photodynamic and photothermal synergistic antibacterial effects under irradiation of a 660 nm laser, which endowed the dressings with excellent wound healing performance in a mouse full-thickness skin wound model infected by multidrug-resistant bacteria. In response to hemostasis and repair of irregular and deep skin wounds, an injectable aldehyde BNC/polydopamine (DBNC/PDA) photothermal cryogel was prepared by oxidation polymerization method [ 6 ]. The PDA enhances the photothermal properties of DBNC/PDA cryogel to kill most bacteria and provides wound protection under near-infrared light. Otherwise, the DBNC/PDA low temperature gel has rapid hemostatic effect in the face of irregular and deep skin wounds. It is worth noting that the nanoenzyme with excellent peroxidase (POD) activity has been used to prepare BNC-based wound dressing. Zhang et al. introduced the metal-organic frameworks (MOF)-based nanocatalysts loaded with glucose oxidase (GOx) into the BNC-reinforced hydrogel for the treatment of diabetic foot ulcers [ 54 ]. The designed nanoenzyme could effectively catalyze the decomposition of glucose and in situ generate •OH for bacteria killing. In addition, this nanoenzyme-based hydrogel exhibited excellent hemostatic properties owing to the enhanced absorption capacity.

4.2 Bone/cartilage tissue regeneration

Another area of potential exciting application for BNC biomaterial is bone/cartilage tissue engineering due to its biomimetic ECM properties, excellent mechanical properties, and highly porous structure [ 7 , 55 , 56 ]. Biosynthetic BNC has some intrinsic disadvantages (the dense nanofibrous network) that markedly limit its applications in tissue engineering. However, the in situ biosynthetic BNC could serve as a surface coating for Ti implants to improve their biological function [ 57 , 58 ]. Liu et al. reported a metal ions-containing BNC coating for functional Ti implant by in situ biosynthesis on the surface of Ti with complex shapes [ 59 ]. The results of in vitro and in vivo experiments confirmed that the functional BNC coating on the Ti can integrate the operative crevices and promote osteogenesis. To optimize the pore structure of BNC to meet the requirements of bone and cartilage tissue, Xun et al. developed a 3D macroporous BNC scaffold by freeze-drying and cross-linking the BNC shortcut nanofibers [ 40 ]. After the 3D macroporous BNC scaffolds were implanted into nude mice subcutaneously for 8 weeks, the neocartilage tissue with native cartilage appearance and abundant cartilage-specific extracellular matrix deposition was successfully regenerated. To construct the BNC scaffolds with structurally and biochemically biomimetic cartilage tissue microenvironment, the 3D hierarchical porous BNC/decellularized cartilage extracellular matrix (DCECM) scaffold was fabricated by freeze-drying technique after EDC/NHS chemical crosslinking [ 60 ]. The in vitro and in vivo tests indicated that the BC/DCECM scaffolds achieved satisfactory neocartilage tissue regeneration with superior original shape fidelity, exterior natural cartilage-like appearance, and histologically cartilage-specific lacuna formation and ECM deposition. Ling et al. fabricated a hierarchically porous SF/BC/MXene (FSCM) scaffold with ~20.0 μm macropore and nanofibrillar wall, which has excellent bone defect repair ability [ 61 ]. In addition, the BNC can also be used for the osteochondral repair. Lou et al. designed a bilayer structure osteochondral scaffold with a dense γ-Polyglutamic acid/carboxymethyl chitosan/BNC (PGA/CMCS/BNC) hydrogel cartilage layer and a porous nano HA-containing PGA/CMCS/BNC hydrogel osteogenic layer [ 62 ]. The in vivo experiments indicated that the scaffold with bioactive ions had a much better effect on the repair of osteochondral defects.

4.3 Blood vessels

BNC is a possible material to use for artificial blood vessels for small- or large-sized vascular grafts due to its good mechanical strength (a burst pressure of up to 880 mmHg), blood biocompatibility, and moldability [ 63 ]. The bioreactor to produce tubular BNC was developed to prepared BNC-based vascular grafts with excellent cytocompatibility and hemocompatibility [ 64 , 65 ]. A tubular BNC graft with greater mechanical strength and thinner walls was obtained by mercerization; this technology made fewer platelets adhere to the luminal surface and promoted the proliferation of endothelial cells [ 63 ]. Mimicking the morphological structure of native blood vessels is critical for the development of vascular grafts. Vascular grafts with BNC nanofibers and submicrofibrous cellulose acetate (CA) were fabricated to mimic the morphological structure of native blood vessels. Regulating the content of BNC can reduce the thrombosis potential of stents and enhance endothelialization.

4.4 Other biomedical application

In addition to the above biomedical applications, BNC has been applied in other biomedical fields, such as nerve repair [ 66 , 67 ] and muscle [ 33 ], corneal [ 68 , 69 ], urethral [ 70 ], and intervertebral disc [ 71 ]. These researches will be sure of certain theoretical value and practical significance to the biomedical application of BNC.

5. Conclusion

In this chapter, we provide an overview of the fabrication and biomedical application of BNC-based biomaterials. First, the biosynthesis of BNC in biology, chemistry, and physics is introduced, and the properties of BNC are summarized. Furthermore, we introduce and discuss the various techniques to fabricate BNC-based composites and 3D porous BNC scaffolds to enhance the mechanical and biological properties. Due to the rapid development of the abovementioned technologies, BNC has a broad range of applications in biomedicine, including wound dressing, bone/cartilage tissue regeneration, vascular tissue engineering, and so on.

Acknowledgments

This work was supported by National Natural Science Foundation of China (grant nos. 82160355), the Science and Technology Research Project of Jiangxi Education Department (grant nos. GJJ2200657), and Natural Science Foundation of Jiangxi Province (grant nos. 20212ACB214002).

Conflict of interest

The authors declare no conflict of interest.

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