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Effect of seed husk waste powder on the PLA medical thread properties fabricated via 3D printer

  • Sura S. Ahmed , Alaa A. Abdul-Hamead , Enass H. Flaieh EMAIL logo and Sarah A. Abdulhameed
Published/Copyright: May 23, 2024
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Curved and Layered Structures
From the journal Curved and Layered Structures Volume 11 Issue 1

Abstract

With the increasing use of medical equipment, threads are the catchy choice for medical personnel to solve wound closures. One raw material used in medical surgical threads is polylactic acid (PLA), which is appropriate for its environmentally friendly and biodegradable properties. However, the weakness of PLA is in mechanical properties. This work used extrusion-based three-dimensional (3D) printing (fused deposition modeling) to fabricate medical threads from PLA. The effect of adding seed husk waste powders (SHWPs) to PLA filament (1.75 mm) and its manufacture by the 3D printer was studied. Four types of SHWP waste plants were used: pistachio, coffee, chestnuts, and walnuts crushed and milled by ball-milling after chemical processing and drying. The structural, particle size, and physical properties of the prepared powders were studied. The results of SHWPs show that the particle size is near the nano-size range of NPs and of low density. Different SHWP weight mixing ratios (5–15 wt%) were coated to PLA threads (0.4–0.45 µm) by grafting to study the mechanical (surface hardness and roughness) properties. The result shows that 15 wt% was the best ratio that combined the mechanical properties. The coated layer thickness was less than 5 µm. This ratio was adopted to fabricate grafted PLA and SHWPs/PLA medical threads by 3D printing with a radius of 400 ± 5 µm. The structural and biological properties of the fabricated medical threads were investigated. The results of SHWP-coated PLA show a significant improvement in structural and physical properties besides the mechanical properties. The results adopted this percentage from thread SHWP-coated PLA for medical applications, creating a new benefit for agricultural SHW and accelerated healing.

Graphical Abstract

Keywords: polylactic acid; 3D printing; medical threads; coffee; chestnut; pistachio; walnut; coated by grafting

Nomenclature

M

mass of the specimen (g)

ρ

bulk density (g/cm3)

W r

weight ratio (wt%)

ZOI

inhibition zone (mm)

K

bactericidal rate (%)

MLR

mass loss ratio (%)

USP

United States Pharmacopeia

1 Introduction

One of our time's most pressing public health issues is healing and infection, which exacerbates various health risk factors. Medical treatment customs include surgical thread, splints, and adhesives. It is related to therapy's instantaneous response and surgical threads' use [1]. The thread material should possess excellent tensile strength, be biologically inert and stretchable, accommodate wound edema and recoil to the original length with wound contraction, be pliable, and have good antimicrobial properties and good knot security. Moreover, specific requirements such as biocompatibility, bio-degradable, and absorbable are inevitable. Threads are divided into absorbable and non-absorbable materials and contain monofilament or multifilament [2]. Polylactic acid (PLA) is a natural biopolymer and a thermoplastic with formula C3H4O2. PLA is heat-sensitive and molded into different shapes with heat, so it cannot resist heat or can be used in high-temperature applications like cellulose acetate [3]. Yet, PLA has good biocompatibility and is absorbable [2,4].

Three-dimensional (3D) printing is a vital technological pillar of the biomedical industry and is used in surgical threads, tissue engineering, human bone replacement, and scaffolding [1,5]. 3D printers based on fused deposition modeling (FDM) have been used. In recent years, polymers have been used to develop uniform PLA-based composite threads [6]. To meet the complete concept of sustainability, however, greener strategies still need to be implemented for preparing the PLA membranes [7]. Polymers for biomedical applications have many additions, including plasticizers and additives. Polymers include bio-based/non-biodegradable and biodegradable polymers such as PLA [8]. The utilization of PLA filaments is a challenge in extrusion-based 3D printing applications; PLA polymer and composite have some drawbacks regrettably, for example, low toughness, high brittleness (with less than 10% elongation at break), low melt strength, poor heat bending temperature, poor thermal stability, narrow processing window, and non-conductivity, which limit its use in many industrial applications. The PLA's mechanical strength is low compared to acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) polymers since PLA has a more linear molecular chain structure, preventing chain entanglement and imparting mechanical strength [9]. Moreover, the dimensional stability of PLA objects after printing is unsuitable due to the volume changes that occur and stress formation during 3D printing caused by the variation of PLA crystallinity. The adhesion between two fused PLA filaments during 3D printing occurs via a three-step process. When two separated PLA surfaces link, a neck grows between them, and after that, the prevalence of PLA linear chain molecules at the interphase region forms the solid surface meniscus. This weak interfacial adhesion between the fused chain is the primary source of the poor mechanical properties of the 3D-printed PLA objects. Rapid heat transfer during cooling in a room temperature environment and the presence of defects due to the non-adjacent nature of the main chain occurring in the interphase and surface have an essential role, and the presence of nanopowders may improve these properties [9,10]. Plant waste can be leaves, stems, roots, etc. Pistachio, coffee, chestnut, and walnuts are plants considered as Tracheophytes, Angiosperms with type Eudicots, and have residual husks [10,11]. Their husks are employed in many applications: pistachio waste (PW) can be beneficial in many nutraceuticals, including antioxidation, cytoprotection, anti-obesity, anti-diabetic, anti-melanogenesis, neuroprotection, anticancer, anti-mutagenesis, anti-inflammation, and antimicrobial [12], denture applications [13], and dental replacement [14]. Coffee seed husk powder has medical applications, such as bone cement [15]. Chestnut husk powder has many biomedical applications [16]. Walnut husk powder has biomedical applications [17,18]. It is possible to reach fine and nano-size powder using appropriate mechanical milling techniques. Nanopowders have characteristic dimensions in the 1–100 nm range. Due to their novel appearance and high surface area to volume ratio, these particles have a wide range of potential biological and mechanical applications. The nano-metric scale powder can be prepared using either top-down or bottom-up approaches. A top-down approach using mechanical milling and ball-to-powder ratios (BPRs) has a critical role, as the diameter of the balls, the materials, and the shape of the milling media, as well as milling speeds, milling environments, the milling atmosphere, and the temperature [19]. Nanopowder, mainly recycled, is given more attention due to its advantageous properties and applications [20,21]. Antioxidant activity and protective effects toward DNA damage with H2O2 activity must be handled. PLA is a promising drug candidate because of its multifaceted properties, such as anti-inflammatory, antioxidant, and anticancer [22].

The need to improve the surface and mechanical properties and close the cracks is still a challenge for those working in this field (such as medical threads joints between bones, extensive tendon repairs, thick fascial closures, and drain sutures, usually orthopedic surgery), which is the objective of our current study. Four types of seed husk waste nano-range powder of seed husk waste powders (SHWPs) were fabricated and added to PLA for preparing threads and to avail agricultural waste.

2 Experimental section

The experimental work contains five steps. First is the chemical treatment procedure for seed husks, the second step is to prepare SHWPs, and then the powder is subjected to a series of inspections to ensure it is appropriate for employment. The fourth step is to prepare PLA and SHWPs/PLA threads coated by grafting, and in the fifth step, an inspection of the prepared PLA threads is performed to infer appropriate information from SHWPs.

2.1 Chemical treatment for seed husks

At first, husks were manually broken, crushed into small pieces, and roughly shredded. The chemical treatment for seed husks (Pistachio P, Coffee C, Chestnut Ch, and Walnut W) was as follows:

  1. Rinse with running and deionized water.

  2. To 40 g of NaOH, add 100 ml of distilled water and agitate in a magnetic stirrer at 60°C for 15 min.

  3. After that, 5 g of seed husks were placed in the solution.

  4. The seed husks were kept in NaOH solution for 1 h; then, the husks were taken out and dried at 60°C for 4 h.

  5. Rinse and vigorously stir for 30 min with distilled water.

  6. Dried in an oven at 100°C for 4 h.

2.2 Preparation of SHWPs

Powders from seed husks were prepared using the top-down fabrication method. A planetary ball mill type (CAPCO, England) was used, with ten porcelain balls (BPR = 5:1), at a rotational speed of 400 rpm for 3 h with half fill to ensure uniformity during milling. Figure 1 shows the ball mill device and the prepared recycled powders during milling.

Figure 1 (a) The ball mill device and (b) the prepared SHWP powders.
Figure 1

(a) The ball mill device and (b) the prepared SHWP powders.

2.3 Characterization of SHWPs

The prepared powder was subjected to the following characterization and measurements:

  1. X-ray fluorescence (XRF): The specimen components were analyzed by XRF (PHILIPS, PW1410, The Netherlands). XRF is the emission of characteristic “secondary” (or fluorescence) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays.

  2. Particle size analysis (PSA): The inspection of particle size was conducted at the Nanotechnology and Advanced Research Center/University of Technology. The model of the device was Brookhaven Nano-Brook 90 Plus, USA. The measurement parameters were as follows: temperature, 25°C; liquid, water; viscosity, ∼0.890 cP; angle, 15°; and wavelength, 659 nm.

  3. Scanning electron microscopy (SEM): The SEM test was conducted via electron gun tungsten (Japan) with an accelerating voltage from 200 V to 30 kV.

  4. Bulk density test: Apparent or bulk density measures the weight of the material that can be contained in a given volume under specified conditions. A 20 ml pycnometer was filled to a specified volume with SHWPs that had been dried in an oven at 80°C for 24 h. The pycnometer was weighed. The bulk density ρ (g/cm3) was then calculated as [23]

(1) ρ = W d V T ,

where W d is the weight of dry material (g) and V T is the volume of packed dry SHWPs (cm3).

2.4 Preparation of PLA and coated SHWPs/PLA threads

The composite of PLA and a 5–15% weight ratio W r from four types of seed husk recycled powders (P, C, Ch, and W) were used to fabricate the specimens via a 3D printer. Table 1 shows some specific properties of the PLA. The used PLA filament was from Trowel company (TW-PLA175TR), with a diameter of 1.75 mm, a print temperature of 190–220°C, and a bed temperature of 25–60°C.

Table 1

Properties of PLA [24]

Properties Values
Density (g/cm3) 1.24
Glass transition temperature T g (°C) 53–64
Crystalline melting temperature T m (°C) 145–186, 150–155
Melt temperature (°C) >185–190
Tensile strength (MPa) 29.9–46.3
Ultimate tensile strength (MPa) 51.7–60.4
Tensile modulus (GPa) 1.2–3.0
Izod impact strength (J/m) 26.7–152.5
Hardness (Shore D) 48–87

The printing parameters are shown in Table 2. The specimens are printed on a CR-10S 3-D printer of Chinese origin, as shown in Figure 2. The filaments' printing parameters have been adopted to prepare FDM fused filament fabrication specimens. According to standards, 3D models are produced using CAD software and turned into stereolithography files for test specimens. Figure 3 shows the process description of the fabricated specimens, a process where the printing direction angle was 90°.

Table 2

Configurations of 3D printing parameters for the PLA material

Printing parameters Configurations
Layer height (mm) 0.1
Layer orientation Upright
Printing temperature (°C) 215
Bed temperature (°C) 60
Filament diameter (mm) 1.75
Nozzle diameter (mm) 0.8
Printing speed (mm/s) 50
Raster angle 90
Figure 2 The 3D printer device.
Figure 2

The 3D printer device.

Figure 3 Process description of the fabricated specimens.
Figure 3

Process description of the fabricated specimens.

PLA coating was done by grafting using four waste SHWP powders and three weight ratios (W r) for each, as shown in Table 3. Dichloromethane (DCM or methylene chloride) is an organochlorine compound. This colorless, unstable liquid with a caramel-like chloroform odor is widely used as a solvent [25]. A thin layer dissolution of the PLA filament surface was done using a DCM solvent, and four types of waste powders (P, C, Ch, and W) were taken in separate and sealed containers in 5–15% weight ratios W r from the PLA filament. The sealed containers were put at Kq-3200e 6L digital sonication for about 2 h at 50°C, as shown in Figure 4, where (a) the grafting steps are clarified, and (b) represents the dissolution of the PLA filament surface using DCM in an oven at 40°C for 15 min, and (c) is the digital sonication used. Several coated filaments were used to prepare the specimens for each test using an experimental design via a 3D printer.

Table 3

Weight mix proportion ratio (W r %) of PLA and SHWP powders

Material code PLA P C Ch W Total
P0 100 — — — — 100
PP1 95 5 — — —
PP2 90 10 — — —
PP3 85 15 — — —
PC1 95 — 5 — —
PC2 90 — 10 — —
PC3 85 — 15 — —
PCh1 95 — — 5 —
PCh2 90 — — 10 —
PCh3 85 — — 15 —
MW1 95 — — — 5
MW2 90 — — — 10
MW3 85 — — — 15
Figure 4 (a) SHWP PLA coating by grafting steps, (b) dissolution of the PLA filament in the oven, and (c) digital sonication.
Figure 4

(a) SHWP PLA coating by grafting steps, (b) dissolution of the PLA filament in the oven, and (c) digital sonication.

2.5 Characterization of the prepared PLA and coated SHWPs/PLA threads

The structural inspection was done by SEM, as mentioned in Section 2.3.3. The mechanical tests were repeated three times for each specimen to take the average, and all samples were fabricated via a 3D printer.

2.5.1 Hardness test

Figure 5 shows the prepared models for hardness test specimens. The hardness of the printed specimens was measured using a digital Shore D ASTM D2240 test method with a measuring range of 0–100 HD, a resolution of 0.5 HD, a depth of indenter of 0–2.5 mm, and a test pressure of 0–45.5 N. Test specimens were placed on a firm and fixed slab before starting the test. The indenter needle was pressed vertically onto the test specimen, and the displayed reading was noted within 1 s after the bottom of the pressure foot touched the specimen surface completely.

Figure 5 SHWPs/ PLA specimens prepared for hardness and surface roughness test.
Figure 5

SHWPs/ PLA specimens prepared for hardness and surface roughness test.

2.5.2 Surface roughness (AFM measurement)

Atomic force microscopy (AFM; AA3000 220V, USA) was performed by using digital tools. The specimens, as shown in Figure 5, were used in this test to find the surface roughness.

After completing the previous tests, the ratio for best properties was chosen to fabricate the medical threads by 3D printing. As mentioned in Table 1, the same parameters were adopted, and the subsequent inspections were done.

2.5.3 Anti-bacterial activities of SHWPs/PLA test

To determine the anti-bacterial and ZOI of PLA and PLA/SHWP threads towards Escherichia coli bacteria (E. coli negative) and Staphylococcus aureus bacteria (S. aureus positive), the disk diffusion method was used. The ZOI against bacteria was measured in (ml) in diameter units, and the formula to calculate the bactericidal rate is as follows [26]:

(2) K % = A − B A × 100 % ,

where K is the bactericidal rate, and A and B are the number of bacteria colonies surviving, corresponding to the control sample and mixed sample, respectively. To identify dominant colonies, a stereomicroscope was used, and the magnification used was 50×. The anti-bacterial activities and in vitro degradation of SHWPs/PLA threads were also determined.

2.5.4 In vitro degradation of SHWP/PLA thread tests

Hank's balanced salt solution that simulated the body fluid was created to investigate the degradation behavior of SHWPs/PLA threads in the human body fluid. Hank's solution was supplied by Sciencell Company, USA, with a standard chemical composition as shown in Table 4; the pH was 7 ± 1. The SHWPs/PLA threads were put into Hank’s fluid maintained at 37°C, which is the same as the inner body temperature. The Hank fluid was changed every 2 days, simulating the human circulatory system. At different time points in the degradation process, these sutures were taken out and rinsed with deionized water two times to remove the chemical residues, as shown in Figure 6. After that, these sutures were dried, and the MLR was calculated, as shown in the following equation [27]:

(3) MLR = W 0 − W f W 0 × 100 % ,

where W 0 is the mass of threads, and W f is the final mass in each measure of threads taken after 6 h.

Table 4

Composition of Hank's solution

Unit g/L
NaCl 8.0
C6H12O6 1.0
KCl 0.4
CaCl 0.14
MgCl2 0.1
MgSO4 0.06
KH2PO4 0.06
Na2HPO4 0.06
NaHCO3 0.35
Figure 6 In vitro degradation of SHWP/PLA thread test: (a) fabricated threads, (b) the oven, and (c) the thread in a Petri dish.
Figure 6

In vitro degradation of SHWP/PLA thread test: (a) fabricated threads, (b) the oven, and (c) the thread in a Petri dish.

3 Results and discussion

3.1 Characteristics of SHWPs

3.1.1 SEM results

Ball milling is a low-cost and green technology that offers mechanical actions (shear, friction, collision, and impact) to modify and reduce the seed husks' waste to nanoscale size. It is one of the physical modification techniques used to reduce the relative crystallinity and alter surface morphology [28]. The surface physical morphology of SHWPs was characterized after milling by SEM analysis. Figure 7(a–d) shows SEM images with a magnification of 3 KX for P, C, Ch, and W SHWPs, respectively. The SEM images in the figure confirmed that the obtained powders differed in size and shape. The most significant difference in appearance was observed between the ground coffee waste and the remaining powders; it does not have a fibrous nature [29] in Figure 7(a) showing the SEM image of the Pistachio mill powder, which has a continuous, uniform, and lamellar natural structure with apparent roughness without pores [30]. When we compare the nature of the pistachio seed husks before grinding, we find that grinding has changed it [31]. The SEM image of the coffee mill powder in Figure 7(b), which has a rough and amorphous surface (corrugated), agrees with that of Guevara-Bernal et al. [32].

Figure 7 SEM images of SHWPs: (a) P, (b) C, (c) Ch, and (d) W.
Figure 7

SEM images of SHWPs: (a) P, (b) C, (c) Ch, and (d) W.

Furthermore, it has a porous structure and apparent accumulation [33]. The general morphology of the chestnut husks before milling could be characterized as rough and folded [34]. After milling, Figure 7c shows that the chestnut husk turns into a fibrous tape form, with interlocking and superficial roughness along the fiber; chestnut fiber by ball milling after treatment is not found in the literature. The walnut husk has a non-porous, smooth structure [35]. After milling, some pores with different particle sizes were observed in the walnut husk powders; in addition to a more roughened aspect, irregular-shaped granules were predominant.

3.1.2 PSA results

Figure 8(a–d) shows the PSA results of SHWPs for pistachio, coffee, chestnut, and walnut, respectively. Table 5 also indicates the PSA results of SHWPs (effective diameter and polydispersity). It should be stressed that despite applying the same grinding parameters, different particle sizes of natural powder were obtained. The lowest particle size was observed for the pistachio seed husks (lower than that in the study of Barczewski et al. [36]), and the highest was in chestnut. The mean particle size of the chestnut seed husks was about three times as large as the pistachio, while the ground pistachio and walnut husk powders were concurrent in the nano-range. The walnut particle size was lower than that found using the ball mill technique, which makes it effective.

Figure 8 PSA results of SHWPs: (a) P, (b) C, (c) Ch, and (d) W.
Figure 8

PSA results of SHWPs: (a) P, (b) C, (c) Ch, and (d) W.

Table 5

PSA results of SHWPs by ball milling

P C Ch W
Effective diameter (nm) 49.0 115.8 162.7 91.0
Polydispersity 0.491 0.533 0.382 0.624

3.1.3 Bulk density results

Density is an essential parameter affecting the material's properties; Figure 9 shows the bulk density result of SHWPs. The obtained density values are close to those in previous studies [37,38,39,40,41]. This implies that there is no significant change in the density of PLA specimens due to the presence of SHWPs in the fine powder and the low bulk density of SHWPs compared with PLA density. An exception is the result of the high density of chestnut powder, which reached 1.48 g/cm3.

Figure 9 Bulk density results of SHWPs.
Figure 9

Bulk density results of SHWPs.

3.1.4 XRF results

DX-ray fluorescence is a widely used and nondestructive analytical technique capable of highly rapid qualitative and semi-quantitative analysis, and it can be used for the quantitative determination of major and trace elements. In the case of an SHWP analysis, a few grams of homogeneous specimens are required [39]. Figure 10(a–e) shows the XRF analysis of SHWPs for carbon, hydrogen, oxygen, sulfur, nitrogen, and sodium, respectively. As shown in Figure 10(a), the highest concentration percentage of carbon was in PCh, and the lowest was PC, while the highest concentration percentage of hydrogen was in PC and the lowest in PCh in Figure 10(b). Also, higher ratios of oxygen are similar to carbon levels (Figure 10(c)) where the highest percentage was found in PC, and the lowest rate of oxygen was in PCh. Figure 10(d–f) shows lower ratios than in (a) and (c); in Figure 10(d), the sulfur element appeared in PP and PC only. The rate of nitrogen and sodium was high in (e) and (f) only for PCh. These results are generally consistent with those of previous studies [42,43,44,45].

Figure 10 XRF analysis of SHWPs, (a) carbon, (b) hydrogen, (c) oxygen, (d) sulfur, (e) nitrogen, and (f) sodium.
Figure 10

XRF analysis of SHWPs, (a) carbon, (b) hydrogen, (c) oxygen, (d) sulfur, (e) nitrogen, and (f) sodium.

Moreover, the (O/C), (H/C), and (O + N)/C ratios were calculated and are listed in Table 6. These results represent the organic contents in SHWPs that contribute to the interaction of PLA threads with the living body (in vivo) [37].

Table 6

The concentration percentage ratios of SHWPs from XRF results

SHWPs O/C H/C (O + N)/C
PP 0.950 0.13 0.98
PC 1.005 0.15 1.01
PCh 0.37 0.09 0.57
W 0.91 0.1 0.923

3.2 Mechanical properties of SHWPs/ PLA results

3.2.1 Hardness results

According to Figure 11, it was noticed that the pure PLA, denoted by P0, has the lowest value of hardness within the tested groups. The addition of SHWPs to the PLA raw material improves the hardness properties. The coffee group had a minor effect on the hardness properties, where the increased ratio was 5% for coffee with a 15% weight ratio.

Figure 11 Hardness results of SHWP/PLA thread surface.
Figure 11

Hardness results of SHWP/PLA thread surface.

Chestnuts with a 5% weight ratio increased the hardness by 7%, pistachios with 5% increased by 7%, Pistachio with 5% increased hardness by about 9%, and chestnuts of 10% increased the value to 13%. A high increase was noticed in pistachios by 15%, which has a 28% increased ratio; chestnuts with 15% had a value of 25%, and walnuts with 5% increased the hardness by about 24%. The most significant value of increasing the ratio of the hardness value was for walnuts; 15% increased by 41%, and then walnuts 10% by 36%. It is known that the hardness properties correlate with material reliability and suitability. It is essential, especially in moving parts such as sutures in joints between bones, as increasing hardness increases wear resistance against cyclic or repeated motion [46]. This improvement in hardness and other PLA properties makes the SHWPs/PLA threads promising in different medical wound applications.

3.2.2 Surface roughness results

Medical threads may lead to inciting abnormal collagen deposition or abnormal wound healing with hypertrophic scar formation. Therefore, the evolution of thread material by coating is the key to the next generation of surgical threads. Figure 12 shows the AFM results of SHWPs/PLA thread surface in (a) P, (b) P1, (c) P2, (d) P3, (e) C1, (f) C2, (g) C3, (h) Ch1, (i) Ch2, (j) Ch3, (k) W1, (l) W2, and (m) W3. As shown in the figure, the coating formed on PLA affected the surface roughness. The group (b and c) caused a decrease in the surface roughness values (about 61%) and more clearly than the sample without coating (a) due to the fine particle size of 49 nm, which led to a smooth surface structure as observed in the SEM and PSA results. Meanwhile, the surface roughness level was maintained in the group (from e to g). In the models (from h to j), the surface roughness values increased significantly by about two and a half times. The last group (k to m) also caused a slight increase in the surface roughness values (about 76%). This increase in surface roughness enhances the mechanical properties of the PLA.

Figure 12 AFM results of SHWP/PLA thread surface: (a) P, (b) P1, (c) P2, (d) P3, (e) C1, (f) C2, (g) C3, (h) Ch1, (i) Ch2, ( j) Ch3, (k) W1, (l) W2, and (m) W3.
Figure 12

AFM results of SHWP/PLA thread surface: (a) P, (b) P1, (c) P2, (d) P3, (e) C1, (f) C2, (g) C3, (h) Ch1, (i) Ch2, ( j) Ch3, (k) W1, (l) W2, and (m) W3.

3.3 PLA and SHWP/PLA thread coat characteristics

3.3.1 SEM of SHWP/PLA thread results

Figure 13 shows the SEM images of the PLA thread cross-section and surface in (a, b), SHWP/PLA thread surface in (c) P, (d) C, (e) Ch, and (f) W, and the SEM of threads cross-section of coat in (e) P, (f) C, (g) Ch, and (h) W. In Figure 13(a), the PLA thread cross fabricated by a 3D printer shows a smooth and homogenous structure without defects or pores; in (b), it also has a smooth surface with a radius of 400 ± 5 µm. Figure 13(c–f) shows that SHWP particles were filled in voids and holes on the surface of PLA threads caused by the treatment with DCM solution, and the grafting process was adequate to get an outer layer of SHWP envelope PLA thread surface totally to give them their novel properties. Figure 13(c–f) represents the formation of nanopowders on the surface of PLA ranging from 18.91 nm in P to 57.3 nm in Ch, and these thin layers formed are continuous and contain only a few voids, homogeneous, and fully adhesive. In the same form and the cross-section of coat threads in (g) P, (h) C, (i) Ch, and (j) W were homogeneous with a coated layer thickness of about 50 ± 5 µm. It should be pointed out that the weight ratio higher than 15 wt% did not give us a homogenous and continuous grafted coat in (h) for the coffee SHWP. The PLA threads coated size was <0.5 µm, which represents (United States Pharmacopeia (USP) size 1 appropriate to orthopedic surgery [47].

Figure 13 SEM images of PLA threads cross section and surface in (a, b), respectively, SHWP/PLA thread surface coated in (c) with P powder, (d) with C powder, (e) with Ch powder, and (f) with W powder, and the SEM of threads cross-section of coat in (g) P, (h) C, (i) Ch, and (j) W.
Figure 13

SEM images of PLA threads cross section and surface in (a, b), respectively, SHWP/PLA thread surface coated in (c) with P powder, (d) with C powder, (e) with Ch powder, and (f) with W powder, and the SEM of threads cross-section of coat in (g) P, (h) C, (i) Ch, and (j) W.

3.3.2 Anti-bacterial effects of SHWP/PLA thread results

A global effort is focused on discovering novel therapeutics with anti-bacterial effects from plants or plant extracts as bioactive powder. The potential SHWPs to find a surgical thread that accelerates healing and reduces infection or bacteria effect is to be used alone or in combination with the existing drugs [48]. Figure 14 shows the bactericidal rate results of SHWPs in (a) positive (Staphylococcus) and (b) Gram-negative bacteria (E. coli), different concentrations (100–25)% were adopted after the 24-h bacteria culture. The data confirmed that chemical treatment did not reduce the activity compared to natural raw and roasted salted fractions [49]. Phenolics have different mechanisms of action, which explain their diversified activity, such as neuroprotective activity, cardioprotective activity, anti-inflammatory activity, anti-diabetic activity, anticancer activity, and anti-bacterial activity [50]. In anti-bacterial activity, phenolic inhibition of protein and DNA synthesis causes bacterial cell death. In general, the mechanisms of phenols' protective action against bacterial activity on three different roots modify the properties of secreted toxins, increase target cell resistance, and directly affect bacterial cell biology. The collected SHWPs contained varying proportions of phenolic compounds in the hull. For example, hull coffee has 36.74%, and so on [51,52,53,54,55]. On the other hand, the milling process increased bacterial resistance to these SHWPs due to the increment in the surface area ratio for the finest powders. P, C, Ch, and W also have biodegradation and antioxidation activities that differentiated them for our application.

Figure 14 The bactericidal rate results of SHWPs/ PLA in (a) Gram-positive and (b) Gram-negative bacteria at different concentrations (100–25)%.
Figure 14

The bactericidal rate results of SHWPs/ PLA in (a) Gram-positive and (b) Gram-negative bacteria at different concentrations (100–25)%.

Figure 15(a–d) shows agar diffusion pictures after 24-h culture results of SHWPs in (a) P, (b) C, (c) Ch, and (d) W for Staphylococcus and E. coli bacteria. Four microbe concentrations were adopted (100–25)%. A clear difference appears in the effect of SHWP powders on bacterial resistance and the ZOI, as shown in Table 6. P, C, Ch, and W were active against S. aureus and E. coli bacteria. The ZOI was not developed in pure PLA specimens compared with the SHWP composite.

Figure 15 Agar diffusion pictures after 24-h culture results of SHWP/PLA, in (a) P, (b) C, (c) Ch, (d) W, and (e) pure PLA for Staphylococcus and in (f) P, (g) C, (h) Ch, (i) W, and (j) pure PLA for E. coli bacteria.
Figure 15

Agar diffusion pictures after 24-h culture results of SHWP/PLA, in (a) P, (b) C, (c) Ch, (d) W, and (e) pure PLA for Staphylococcus and in (f) P, (g) C, (h) Ch, (i) W, and (j) pure PLA for E. coli bacteria.

Table 7 shows the inhibition zone of SHWPs/PLA-coated threads. Although all the tests were done with the same concentration of microbes, different values and effects of SHWPs on PLA appeared. The fabricated SHWP/PLA-coated thread specimens showed apparent resistance to both types of bacteria, Staphylococcus and E. coli. The powder structure and shape impact affected these values, as shown in Figure 7, SEM result; a rougher and irregularly shaped aspect hindered the bacteria growth.

Table 7

Inhibition zone ZOI of SHWPs/PLA-coated threads after 24-h culture

Material code Staphylococcus (mm) E. coli (mm)
PP3 16 20
PC3 12 13
PCh3 19 18
PW3 21 22
PLA pure 2 1
Standard Not inhibition halos [53,54,55]

Furthermore, particle size also affects this result; in P and W SHWPs, their particle size is in the nano-size range. That increased the inhibition zone and decreased bacteria growth due to the large surface area ratio. In addition to active ingredients and vitamins, it is crucial in minimizing bacteria development. ZOI increased five times in the PC3 to more than nine times in PW3 compared to PLA without coat [56,57,58].

3.3.3 In vitro degradation of SHWP/PLA thread results

Figure 16 shows the in vitro degradation of PLA and SHWP/PLA thread results. In the degradation process, the mass of the PLA-base thread decreased gradually until the thread broke. The figure shows that SHWP/PLA thread can be remnants in the human body or would continue to be degraded until absorbed totally by the body. The main issue is the time of thread residue persisting in the body; it may require a little time (2–6 weeks) as in appendicitis wounds or long periods as in the case of Osteorrhaphy (>40 weeks) [27]. The PLA thread ran out within 50 weeks, and SHWPs/PLA threads showed different values. All PP3, PCh3, and PW3/PLA thread specimens show an increment in time required to degrade about >20, 5, and >20 weeks, respectively. At the same time, the PC3/PLA thread sample has the opposite effect by reducing the time by about 5 weeks. Many parameters related to these results include mechanical properties, chemical composition, particle size, and surface texture [58,59]. As mentioned in Table 5, the PC3 has the highest ratio of (O/C), (H/C), and (O+N)/C compared with other SHWPs.

Figure 16 The degradation of SHWP/PLA thread results.
Figure 16

The degradation of SHWP/PLA thread results.

4 Conclusions

Plant waste is a global management problem with the highest waste ratios needed for practical solutions, and nuts SHW is one of the primary plant wastes due to its wide consumption as a component of healthy diets globally, in both raw and roasted forms. These nuts' husk waste may be extracted from beneficial nutrients or used directly after treatments. Bioactive compounds in SHWPs, such as phenolic compounds, did not lose their ability after treatment. Spatial interaction between the balls and husks in milling depends on their hardness and mass amount. The grafting process is effective and affordable for covering the surgical threads. It is possible to double the lifespan of PLA threads according to medical requirements. The mechanical properties after coating were satisfactory. Also, both anti-bacterial and in vitro degradation results were good. Ultimately, the fabricated SHWP/PLA threads have the criteria with size 0.5 µm < (USP size 1), are eco-friendly, and can be a large-scale production. The possible theoretical extension of the present work contribution in scaffolds for bone tissue engineering was coating with SHWPs, which fulfilled general and specific requirements, and PW3/PLA and PP3/PLA thread specimens show reliability to orthopedic surgery.

  1. Funding information: Authors state no funding is involved.

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results and approved the final version of the manuscript. SSA: Visualization, preparies the raw material, investigation mechanical properties. AAA-H: Fabrication of nano-natural powder, chemical processing, reviewing, and the scientific explanations. EHF: Writing - original draft preparation, methodology. SAA: Biological properties of fabricated medical threads.

  3. Conflict of interest: Authors state no conflict of interest.

  4. Data availability statement: Measurement data is available to anyone who wants it.

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Received: 2023-08-12
Revised: 2024-01-01
Accepted: 2024-02-09
Published Online: 2024-05-23

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/cls-2022-0222
Keywords for this article
polylactic acid; 3D printing; medical threads; coffee; chestnut; pistachio; walnut; coated by grafting
Creative Commons
BY 4.0

Articles in the same Issue

  1. Research Articles
  2. Flutter investigation and deep learning prediction of FG composite wing reinforced with carbon nanotube
  3. Experimental and numerical investigation of nanomaterial-based structural composite
  4. Optimisation of material composition in functionally graded plates for thermal stress relaxation using statistical design support system
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  7. Performances of the sandwich panel structures under fire accident due to hydrogen leaks: Consideration of structural design and environment factor using FE analysis
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  11. Strength assessment of fiberglass layer configurations in FRP ship materials from yard practices using a statistical approach
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