Potential use of plant fibres and their composites for biomedical applications

Namvar, F., Jawaid, M., Md Tahir, P., Mohamad, R., Azizi, S., Khodavandi, A., Rahman, H. S., and Nayeri, M. D. (2014). "Potential use of plant fibres and their composites for biomedical applications," BioRes. 9(3), 5688-5706.

Abstract

Plant-based fibers such as flax, jute, sisal, hemp, and kenaf have been frequently used in the manufacturing of biocomposites. Natural fibres possess a high strength to weight ratio, non-corrosive nature, high fracture toughness, renewability, and sustainability, which give them unique advantages over other materials. The development of biocomposites by reinforcing natural fibres has attracted attention of scientists and researchers due to environmental benefits and improved mechanical performance. Manufacturing of biocomposites from renewable sources is a challenging task, involving metals, polymers, and ceramics. Biocomposites are already utilized in biomedical applications such as drug/gene delivery, tissue engineering, orthopedics, and cosmetic orthodontics. The first essential requirement of materials to be used as biomaterial is its acceptability by the human body. A biomaterial should obtain some important common properties in order to be applied in the human body either for use alone or in combination. Biocomposites have potential to replace or serve as a framework allowing the regeneration of traumatized or degenerated tissues or organs, thus improving the patients’ quality of life. This review paper addresses the utilization of plant fibres and its composites in biomedical applications and considers potential future research directed at environment-friendly biodegradable composites for biomedical applications.

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Potential Use of Plant Fibres and their Composites for Biomedical Applications

Farideh Namvar,^a,b,* Mohammad Jawaid,^a,g Paridah Md Tahir,^a Rosfarizan Mohamad,^a,cSusan Azizi,^d Alireza Khodavandi,^eHeshu Sulaiman Rahman,^f and Majid Dehghan Nayeri ^a

Keywords: Fibres; Polymers; Biocomposites; Biomedical applications

Contact information: a: Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; b: Mashhad Branch, Islamic Azad University, Mashhad, Iran; c: Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Serdang, Malaysia; d: Faculty of Chemistry, Universiti Putra Malaysia, Serdang, Malaysia; e: Department of Paramedical Sciences, Gachsaran Branch, Islamic Azad University, Gachsaran, Iran; f: Department of Microbiology and Pathology, Faculty of Veterinary Medicine, Universiti Putra Malaysia, Serdang, Malaysia; g:Department of Chemical Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia;* Corresponding author: farideh.namvar@gmail.com

INTRODUCTION

Natural fibres are of interest to scientists due to advantageous traits such as low cost, high strength to weight ratio, low density per unit volume, non-corrosive property, and acceptable specific strength, in addition to their renewable and degradable characteristics (Joshi et al. 2004; Ticoalu 2010; Kalia et al.2009). Compared to synthetic fibres, natural fibres are often available at low cost and cause less health and environmental hazard problems for people producing the composites as compared to glass fibre based composites (Jawaid and Abdul Khalil 2011). Natural fibres can be used for development of highly thermally stable and acoustic insulator materials (Puglia et al. 2005a; Biagiotti et al. 2004). It is possible to produce highly durable consumer products from natural fibres that can be easily recyclable (Corbie 2001). However, natural fibres generally exhibit poor water resistance, low durability, and poor fibre/matrix interfacial bonding that leads to a loss in final properties of the composites and ultimately hinders their industrial usage (Milanese et al. 2011; Puglia et al. 2005b; Romanzini et al.2012). Fibre/matrix interfacial bonding in polymer composites can be improved by using coupling agents and/or surface modification techniques (Kalia et al. 2009). Abundant amounts of natural fibres are available in nature, and these can be applied as reinforcement or bio-fillers in the manufacturing of polymer composites (Yang et al. 2006). In the past few years, demand for natural fibres has shown a dramatic increase for making new types of environmentally–friendly composites (Cheung et al. 2009). Natural fibres have been used by people throughout historical times, but in recent years natural fibres application in polymer composites has increased due to their availability as renewable materials and increased concerns about the environment (Majeed et al. 2013). Polymer composites are those materials that can be developed by combination of either natural fibers/synthetic resin or natural fibers/bio-resin (Chandramohan and Marimuthu 2011). The properties of polymer composites can be altered by the constituent components and filler which significantly different from those of the individual constituents (Ramakrishna et al. 2001).

Biocomposites can be fabricated by combining biofibres such as oil palm, kenaf, industrial hemp, flax, jute, henequen, pineapple leaf fibre, sisal, wood, and various grasses with polymer matrices from either non-renewable (petroleum based) or renewable resources (Jawaid and Khalil 2011). Biocomposites can be employed in bioengineering or biomedical applications (Cheung et al. 2009) or alternatively as composites that contain at least one natural fibre/plant fibre component. Presently fibre-reinforced polymer composites are extensively used multiphase materials in orthopedics, and most of the today’s upper and lower limb prostheses are made from composites with an underlying polymer matrix (Chandramohan and Marimuthu 2011). The primary reason for the development of biocomposites from natural fibre is flexibility of type/distribution of the reinforcing phases in the composites and the possibility to obtain biocomposites having a wide range of mechanical and biological properties (Ramakrishna et al. 2001). Biobased materials such as natural fibers, biopolymers, and biocomposites integrate the principles of sustainability, industrial ecology, eco-efficiency, and green chemistry. They may be engineered into the development of the next generation of materials, products, and processes (Barthelat 2007; Zainudin and Sapuan 2009). Biodegradable and bio-based products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock (Mohanty et al. 2002). Most of the living tissues such as bone, cartilage, and skin are essentially composites (Meyers et al. 2008).

Natural Fibres

Natural fibres are those that are not synthetic or manmade (Garmendia et al. 2007). Natural fibres can be obtained from plant fibres such as sisal, hemp, bamboo, coir, flax, kenaf, jute, ramie, oil palm, pineapple, banana, cotton, etc., as well as from animal sources, e.g. wool, silk, and chicken feather fibres (Mukhopadhyay and Fangueiro 2009). Natural fibres can be divided into six main categories (Fig. 1) depending on the part of the plant from which they are extracted, bast or stem fibers (jute, flax, hemp, ramie, roselle, kenaf, etc.), leaf fibers (banana, sisal, manila hemp, agave, abaca, pineapple, etc.), seed fibers (coir, cotton, and kapok), fruit fibres (oil palm, coir), stalk (wheat, rice, rye, etc.), and grass/reed (bamboo, bagasse, corn, etc.) (Jawaid and Abdul Khalil 2011). Traditionally, natural fibers have been cultivated and used comprehensively for non-structural applications and have also been used for applications in housing as roof material and wall insulation. A large variation is found in the properties of natural fibers (Joshi et al. 2004). The type of fibers, moisture content, and form of fibers (yarn, woven, twine, chopped, felt, etc.) can affect the properties (Navarro et al. 2008). Moreover, the properties are also affected by the place where the fibers are grown, cultivation conditions, the part of the plant they are harvested from, the growing period, and any retting or extracting processes (Ticoalu 2010).

Fig. 1. Classification of natural and synthetic fibres (Jawaid and Khalil 2011 – With Permission)

Table 1 shows mechanical properties of different types of natural fibers for composite applications as compared with human tissue. Human tissue can be grouped into hard (bone and tooth) and soft tissues (skin, blood vessels, cartilage, and ligaments). Hard tissues are stiffer (with higher elastic modulus) and stronger (with higher tensile strength) than the soft tissues. Furthermore, they are essentially composite materials with anisotropic properties that depend on the roles and structural arrangements of various components (e.g. collagen, elastin, and hydroxyapatite) of the tissues (Ramakrishna et al. 2001). In general, natural fibres have comparable mechanical properties as well as biocompatibility to human tissues, such that often there is no adverse effect on host tissue, which is required for any materials to be used in biomedical applications (Cheung et al. 2009). Recent advances in natural fibres based polymer composites have enhanced their application in biomedical applications and offer significant opportunities for improved materials from renewable resources with enhanced support for global sustainability.

Table 1. Mechanical Properties of Natural Fibres for Composite Applications

Source: Cheung et al. 2009

Bio-binders

Bio-binders, commonly known as biopolymers, are compounds obtained from natural resources and consist of monomeric units that are covalently bonded to form larger structures (Asokan et al. 2012a). Bio-binders vary with respect to their melt flow indices, impact properties, hardness, vapor transmission characteristics, coefficient of friction, and decomposition (Flory and Requesens 2013). Bio-binders find many applications in a number of fields such as drug delivery system, wound healing, food containers and agricultural films, waste bags, soil retention sheeting, filtration, hygiene and protective clothing, and automobile industries (Wu and Wu 2006). There are many types of bio binders, of which the most common are shown in Fig. 2. From a search of the literature it is clear that fully resorbable biocomposite fracture fixation has been achieved based on the group of PLA (polylactic acid) polymers; PLAs possess two major characteristics that make them an extremely attractive bioabsorbable material: (1) they can degrade inside the body at a rate that can be controlled, e.g. by varying molecular weight, the share of their enantiomers L and D-lactide, or copolymerising it with PGA (polyglycolic acid) polymer, and (2) and, if crystallization of the PLA-polymer is prevented, their degradation products are nontoxic, biocompatible, and easily metabolized (Hutmacher et al. 2000).

Fig. 2. Different type of composites from bio-fibre and bio-binders

Biocomposites

Polymer composites have been fabricated mainly by using high strength synthetic fibres such as carbon, glass, and aramid and low strength polymeric matrix; such composites have dominated the aerospace, leisure, automotive, construction, sporting industries, and biomedical applications (Cheung et al. 2009). Due to the need for more environmental friendly materials, natural fiber composites have been regaining increased attention. Although synthetic fiber such as glass fibers, carbon fibers, and aramid-based composite materials are high performance materials, they are less biodegradable and sourced from non-renewable resources. Researchers and entrepreneurs are interested in the utilization of environmentally friendly and sustainable biocomposite materials for biomedical and industrial applications. Table 2 displays advantages and disadvantages of natural fibres products. Therefore, the use of natural fibers may bring environmental benefits as well as cost benefits.

Table 2. Advantages and Disadvantages of Natural Fibres Products

In polymer composites, natural fibres usually provide strength, while the matrix provides binding to the fibres (Verma et al. 2013). Natural fibres by themselves cannot be used to sustain the range of loads expected in many biomedical applications (Everitt et al. 2013). Therefore, a matrix material is used to bind and protect the natural fibres. Depending on the type of natural fibres, type of matrix, the proportion of fiber-matrix, and the type of manufacturing process, the properties of fiber composites can be tailored to achieve the desired end product (Ticoalu 2010). Both synthetic and bio-resin can be either in the form of thermoset or thermoplastic type of resin. The matrix (the bioresin/synthetic resin) supports the fibrous material (natural fibres) and transfers the stress to the fiber to carry the load in natural fibre-reinforced polymer composites. Biocomposites fabrication can be done by different methods, sometimes placing natural fibre in the desired direction to obtain polymer composites having specific mechanical properties. Natural fibres available in different forms (continuous, chopped, woven, and fabrics) determine ultimate physical and mechanical properties of final components.

Several factors that must be considered to achieve desirable mechanical properties in fibre-reinforced composites include the kind of natural fibres, compatible surface chemistry of the fibre and matrix phases, corresponding surface energies, and the quality of the interface (Cullen et al. 2013). The properties of natural fibres vary not only between species but also depend strongly on the cultivation, isolation, and processing methods (Zhu et al. 2013). In the case of pulp fibre-reinforced composites, incompatibilities often exist due to the hydrophilic nature of fibre surface and the generally hydrophobic nature of the polymer matrix types that are most widely used (Cullen et al. 2013). This leads to insufficient bonding adhesion at the interface, as well as poor fibre dispersion, in turn resulting in non-uniform material properties in the composites (Kabir and Wang 2011). The improvement of mechanical properties of these composites has been an important topic for many researchers (Sarasini et al. 2013). Many studies have been carried out to determine the impact of fibre type and processing methods on the tensile strength, modulus, and elongation at break of natural fibre composites (Mueller and Krobjilowski 2004; Mukhopadhyay and Fangueiro 2009; Bledzki and Jaszkiewicz 2010). The following table summarizes some of these results.

Table 3. Mechanical Properties of Different Natural Fibre Composites

Natural fiber composites can be used for biomedical applications for bone and tissues repair and reconstruction (Dhandayuthapani et al. 2011). The property (tensile strength) of natural fiber composites has been found to vary depending on the type of fibers (Table 3), and the type of resin and manufacturing process. Figure 3 illustrates fabrication of different types of bio-composites according to their reinforcement forms. It is clear from Fig. 3 that different kinds of reinforcements, i.e. short fibers, continuous fibers, and particulates (powders) can be used for fabrication of biocomposites. The main problem of those composites is the coordination of the degradation behavior of both phases and, especially, of the interphase between fibre and matrix.

Biomaterial

The National Institutes of Health Consensus Development Conference defined a biomaterial as “any material or mixture of materials manufactured or natural in base which can be used for any interval of time, as a complete item or as a part of a system which treats, enhances or replaces any tissue, organ, or function of the body” (Patel and Gohil 2012). Biomaterials can also be defined as “materials used in implants or medical devices and intent or compatible to interact with biological systems” (Ratner and Hoffman 2004). Human beings have been utilizing biomaterials from ancient times: Egyptian mummies, as well as artificial teeth, eyes, noses, and ears have been found. Indian and Chinese craftspeople have been utilizing glues, waxes, and tissues to repair or regenerate abnormal parts of the body as a traditional treatment of wounded or traumatized patients (Patel and Gohil 2012). Over the centuries, improvements in synthetic materials, surgical techniques, and sterilization methods have permitted the use of biomaterials in many ways. Ideally, these biomaterials must be nontoxic, non-carcinogenic, chemically inert, stable, and mechanically strong enough to withstand the repeated forces of a lifetime.

Selection of Biomaterials for Biomedical Applications

A biomaterial used for implant should possess some important properties in order to allow long-term usage in the body without rejection. There are several factors and issues required to be considered before choosing appropriate natural fibres composites for biomedical and engineering applications such as biodegradability, bioresorbability, biocompatibility, sterilizability, functionability, manufacturability, as well as mechanical and thermal properties (Ambrose and Clanton 2004; DiGregorio 2009; Hin 2004). In another study, researchers reported that several additional issues such as biological response, biocompatibility, and flexibility must be considered for designing biomedical composites and predicting their performance (Kutz et al. 2003). Biocompatibility is an important factor that can distinguish between the chemical, biological, and physical suitability of materials and its compatibility in terms of mechanical properties (stiffness, strength, optimum loading) at the implant/tissue interface (Ramakrishna et al. 2001). The design and selection of biomaterials depend on different properties that are summarized in Table 4. Moreover, it should be noted that success of biomaterials in the body depends on surgical techniques, health conditions, and way of life of patients (Ramakrishna et al. 2001). For example, the longitudinal mechanical properties of cortical bone are higher than the transverse direction properties. The anisotropy of the elastic properties of the biological tissues has to be considered as an essential design criterion for implants made from composite biomaterials.

Many materials can be used in biomedical applications and they may be grouped into (a) metals, (b) ceramics, (c) polymers, and (d) composites. These four classes are used singly and in combination to form most of the implantation devices available on the market (Table 5). Metals or ceramics seem to be more suitable for hard tissue applications from the mechanical point of view as compared to polymers for soft tissue applications. On the other hand, the elastic moduli of metals and ceramics are 10 to 20 times higher than those of the hard tissues. Thus, implants made from these materials tend to be much stiffer than the tissue to which they are attached. In orthopedic surgery, this mismatch of stiffness between the bone and the metallic or ceramic implants influences the load at the implant/tissue interface. Since the extent of stress carried by bone and metallic or ceramic implant is directly related to their stiffness; bone is insufficiently loaded compared to the implant. Wolffs law of stress related bone remodeling states that it will lead to lower bone density and altered bone architecture (Goldstein et al. 1991). In osteosynthesis, this may affect healing of the fractured bones and may increase the risk of refracture of the bone after removal of the osteosynthesis implant, e.g.bone plate.

Table 4. Key Factors for the Selection of Materials for Biomedical Applications

Source: Ramakrishna et al. 2001

In this respect, the use of low-modulus materials such as polymers appears interesting because low strength associated with a lower modulus usually impairs their potential use. Since fiber-reinforced polymers, i.e. polymer composite materials, offer both low elastic modulus and high strength, they have been proposed for several orthopedic applications (Table 1). Another merit of a fibre-reinforced polymer is that it is possible to obtain properties and design of an implant to suit the mechanical and physiological conditions of the host tissues by variation of volume fractions and arrangement of reinforcement phase. Therefore, composite materials offer a greater potential of structural biocompatibility than the homogenous monolithic materials. Biomedical devices fabricated from composite materials are anti-corrosive and have high fracture toughness and higher resistance against fatigue failure as compared to metal alloys and ceramics (Teoh 2000).

Table 5. Mechanical Properties of Different Biomedical Materials Classes

Source: Black and Hasting 1998; Cheung et al. 2009; Ramakrishna et al. 2001.

Applications

Commercial usage of biomaterials obtained from sustainable materials has been significantly rising due to increasing prices of petroleum products and the demand for environmental friendly and sustainable biomedical devices. Innovations in the composite material design and fabrication processes are raising the possibility of realizing implants with improved performance by using plant fibres based biocomposites. However, for successful application, surgeons must be convinced of the long term durability and reliability of composite biomaterials. Recently, ongoing work has explored the use of palm tree fibres for industrial and biomedical applications (Anon 2013). In the cited study, researchers planned to utilize the hybrid fibres of Egyptian and Qatari palm tree with starch, water, and glycerin to fabricate materials that cost little to manufacture but possess high strength for industrial and biomedical applications. A schematic diagram shows the potential use of biocomposites in the repair, reconstruction, and replacement of human hard tissues (Fig. 3).

Fig. 3. Various applications of different polymer composite biomaterials

(Source: Ramakrishna et al. 2001; With Permission)

Casting materials (composite materials made of woven cotton fabrics) have been used to form splints, casts, and braces to fix bone fragments (Ramakrishna et al. 2001). Other researchers also reported that traditional plant-originated cellulose and cellulose-based materials (woven cotton gauze dressings) have been used in medical applications for many years and are mainly utilized to stop bleeding (Czaja et al. 2007; Daunton and Kothari 2012). It is also known that plant cellulose can be used as a clinical application in wound-healing research as a factor which stimulates granulation tissue in the wound bed after damage (Morgan and Nigam 2013).

Cellulosic nanofibres obtained from plant fibres have unique mechanical, electrical, chemical, and optical properties that can be utilized for diverse applications. Pineapple leaf fibres (PALF) have been reported to be very versatile material with promise for a wide range of biomedical and biotechnology applications such as tissue engineering, drug delivery, wound dressing, and medical implants (Cherian et al. 2010). The same authors also reported development of nanocomposites from PALF nanofibres for a wide range of biomedical applications such as cardiovascular implants, scaffolds for tissue engineering, repair of articulate cartilage, vascular grafts, urethral catheters, mammary prostheses, penile prostheses, adhesion barriers, and artificial skin (Giri et al. 2013; Cherian et al. 2010). In another interesting work, researchers reported that thermal stable nanocellulose from banana, jute, and PALF fibres can be used for various advanced nanotechnological applications (Abraham et al. 2011). Researchers obtained cellulose nanofibers from flax bast fibers, hemp fibers, kraft pulp, and rutabaga and developed nanocomposites from cellulose nanofibres which can find application in the medical field such as blood bags, cardiac devices, and valves as reinforcing biomaterials (Bhatnagar 2005). Kalia et al. (2011) have reviewed the processing methods, properties, and biomedical applications of nanocellulose and cellulosic composites. Also Eichhorn et al. (2009) reviewed recent progress made in the area of cellulose nanoﬁbre-based nanocomposites and their application. Table 6 summarizes some patent regarding application of natural fibre for biomedical applications.

Biocompatibility

Biocompatibility is generally defined as the ability of a biomaterial to perform with an appropriate host response in a specific application. Several issues must be considered regarding the biological and host response to design biomedical biocomposites and predicting their performance (Hutmacher et al. 2000). As the number of constituent materials in composite increases, so can the variations in the host response. Different in vitro and in vivo tests are necessary to establish that the individual materials by themselves be biocompatible. Also, additional tests are required to ensure that their specific composition, arrangement, and interaction are biocompatible too.

Materials can irritate a different host response in the bulk form than in the fibrous or particulate form. For instance, an acetabular cup of a hip prosthesis, is generally biocompatible, whereas its fibrous form, as in a finely woven fabric, has been shown to produce a different, more adverse reaction (Patel and Gohil 2012). Moreover, in orthopedic or dental composites, friction in a moving part can scrape the matrix and expose the reinforcing material to the host and produce new challenges at the interface.

Table 6. Published Patents for Biomedical Applications of Natural Fibre

The interaction of materials at the interface is essential to composite performance, and this can be affected by the tissue response in various ways. As biomedical application of natural fibre and biocomposite is a new field, most of the research has focused on improving properties of natural fibre and also enhancement properties between the polymer matrices and natural ﬁllers in order to improve the physical and mechanical properties of the end products. Novel and innovative approaches in the in vitro and in vivo tissue compatibility of this biomaterial product must be developed to address these significant issues.

CLOSING STATEMENTS

Development of biocomposites by using natural fibres as an alternative to petroleum based materials would help to reduce dependence on imported oil, carbon dioxide emission, and help to generate more economical opportunities for the agricultural sector. Furthermore, biocomposites offer opportunities for environmental gains, reduced energy consumption, insulation, and sound absorption properties. Nowadays, the use of biocomposites in biomedical applications offers several advantageous characteristics such as being low cost, lightweight, environmentally friendly, bio-renewable, and more durable. However, they have some disadvantages as well, such as moisture absorption and photochemical degradation because of the UV radiations. In this regard, there is ongoing research to address these issues.

Human bone and tissue are essentially composite materials having anisotropic properties. The anisotropy of the elastic properties of the biological tissues has to be considered in the design criterion for implants made from composite biomaterials. The solution to this is a new porous resorbable ceramic-polymer biocomposite, with morphology and a mechanical resistance similar to those of natural cancellous bone. Moreover surgeons can easily cut the graft directly in the surgery room to adapt its shape to the defect. Since they offer both low elastic modulus and high strength, they have been proposed for several orthopedic applications. Also, by controlling the percentage of the reinforcing and continuous phase, the properties and design of the implant can be tailored to suit the mechanical and physiological conditions of the host tissues. Moreover, problems of corrosion and release of allergenic metal ions, such as nickel or chromium, are totally eliminated. The composite provides high fracture toughness and high resistance against fatigue failure. These biocomposites are highly compatible with modern diagnostic methods, such as computed tomography (CT) and magnetic resonance imaging (MRI) as they show very low X–Ray scattering and their magnetic susceptibility is very close to that of human tissue. Also, they are lightweight. For some applications as in dental implants, biopolymers offer a better aesthetic characteristic. The cost of production of these implants is generally low, but the production process may be highly sophisticated. Biocomposites are used for hard tissue applications, including prosthetic socket, dental post, external fixator, bone plate, orthodontic archwire, orthodontic bracket, total hip replacement, and composite screws and pins. An example of the use of biocomposites in clinical application is cages for spinal fusion. Benefits for patients are a faster bone healing, no risk of pathogen transfer compared to allograft, faster and cheaper surgery, and less pain compared to auto graft.

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Article submitted: January 24, 2014; Peer review completed: March 29, 2014; Revised version received: April 22, 2014; Accepted: May 4, 2014; Published: May 12, 2014.