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Article

Delivery Systems for Curcumin Derivatives Based on Calcium Carbonate Structures for Biomedical Applications

by
Alina Raditoiu
1,
Valentin Raditoiu
1,
Maria Grapin
1,2,
Radu Claudiu Fierascu
1,2,
Cristian Andi Nicolae
1 and
Monica Florentina Raduly
1,*
1
National Institute for Research & Development in Chemistry and Petrochemistry—ICECHIM, 202 Splaiul Independentei, 060021 Bucharest, Romania
2
Faculty of Chemical Engineering and Biotechnology, National University of Science and Technology Politehnica Bucharest, 1–7 Gh. Polizu Street, 011061 Bucharest, Romania
*
Author to whom correspondence should be addressed.
Crystals 2025, 15(6), 508; https://doi.org/10.3390/cryst15060508
Submission received: 30 April 2025 / Revised: 19 May 2025 / Accepted: 22 May 2025 / Published: 26 May 2025
(This article belongs to the Special Issue Multi-Component Hybrid and Composite Nanostructures for Healthcare Applications)
Browse Figures
Versions Notes

Abstract

One of the most researched minerals in terms of how to produce it and the range of uses for it is calcium carbonate. This work describes how to generate hybrid materials by co-precipitating calcium carbonate loaded with either bis-dehydroxycurcumin (CCOH) or the calcium complex of bis-dehydroxycurcumin (Ca(CCOH)2). Composite materials with various morphologies were produced when calcium carbonate and different amounts of curcumin derivatives were precipitated in alcoholic media. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used for structural and morphologic characterization of the materials, while thermal stability was verified by thermal-gravimetric analysis (TGA), and porosity analysis was performed to evaluate surfaces and pore sizes. The hybrid materials were embedded in a cosmetic matrix lacking a sun protective effect in order to assess the UV-shielding properties. The transmittance spectra were subsequently measured in the 290–400 nm region, and the sun protection factor (SPF) was calculated. Thus, the co-precipitation approach produced hybrid materials loaded with curcumin derivatives, which were further evaluated for possible applications in the medical field for the delivery of drugs or in skincare products.

1. Introduction

Abundantly present in nature and within reach of man, calcium carbonate (CaCO3) has found various uses in the modern paper and plastic industry, especially for the manufacture of packaging. It is used in paints, for construction materials, and in water treatment [1,2,3]. However, the most significant applications are found in the cosmetic and pharmaceutical industries. Here, the proven biocompatible properties have led to the development of a series of hybrid materials in which calcium carbonate acts as a host matrix [4]. Thus, various synthesis strategies have been developed by varying different reaction parameters or molar ratios of the reactants to obtain inorganic matrices with various shapes. Knowing the polymorphic properties of calcium carbonate, most often, the temperature and pH of the precipitation medium have been modified to obtain one or combinations of its three crystallization states: calcite–aragonite–vaterite [5,6,7,8,9,10]. In relation to the type of applications pursued, the particle size was also of particular importance, which for the medical field is between 1 and 500 nm, while for cosmetic products, particles with sizes larger than the order of microns are accepted [11,12,13]. Calcium carbonate is often found as a carrier matrix for bioactive compounds such as natural compounds, antioxidants, enzymes, or chemotherapeutic agents [14,15,16,17,18,19]. Together with other precursors such as hyaluronic acid, chitosan, alginate, and other synthetic polymers, calcium carbonate has been used to obtain the most efficient delivery systems. In this manner, composite materials with different sizes and designs, such as capsules, halo-capsules, stable emulsions, or hydrogels, have resulted [20,21,22,23]. Curcumin and its derivatives are natural compounds that, in recent years, have received special attention in the field of research and medical applications [24,25]. Due to their antioxidant, antitumor, antiviral, or antimicrobial properties, these compounds have found various applications. Among these, we can mention their use as adjuvant in cancer treatment, as marking agents due to their fluorescent properties, and in dermatocosmetic treatments [26,27,28,29]. The main obstacle to the use of these compounds is their hydrophobic properties and poor bioaffinity [30]. In order to overcome this inconvenience, two research directions were targeted. The first was the structural modification of the molecules [31,32,33], and the second aimed at obtaining delivery systems compatible with their structure to preserve their properties unaltered [34,35,36,37,38,39,40].
The second path was the focus of this work, which provided five distinct types of host-guest hybrid materials. In order to encapsulate the curcumin derivative, bis-dehydroxycurcumin (CCOH), or the calcium complex of bis-dehydroxycurcumin (Ca(CCOH))2 (Figure 1), inorganic calcium carbonate matrices were developed for the host matrix. The resulting composite materials were morphostructurally evaluated, and the outcomes showed that they have the best qualities for a range of cosmetic and medicinal uses.

2. Materials and Methods

2.1. Materials

The raw materials used to obtain the inorganic matrices were calcium chloride (CaCl2) and sodium bicarbonate (NaHCO3), while the curcumin derivatives were obtained according to a proprietary method mentioned in another work [41]. The calcium curcumin complex was synthesized according to the Altundag method [42]. All reagents used in this work were obtained from Aldrich, St. Louis, MO, USA, and were used without further purification. Tests were performed to evaluate the shielding effect against ultraviolet light by incorporating the hybrid materials into a cream that did not have a protective factor (Eveline, Zytnia, Poland).

2.2. Preparation of the Hybrid Materials AP1–AP5

Briefly, 0.04 g of curcumin derivatives (CCOH)/curcumin complex with calcium (Ca(CCOH)2) is dissolved in 60 mL of ethyl alcohol, to which is added, under stirring (200 rot/min), 60 mL of aqueous solution containing 0.02–0.1g CaCl2, followed by heating the reaction mass to 70–90 °C for 2 h. The solution is cooled to 40 °C, and a 4% NaHCO3 solution (corrected with the addition of sodium hydroxide 0.1 mol/L to pH 10–12, checked with basic pH control paper) is added until pH 7. The pH change was monitored by checking with neutral pH control paper after each 3–5 mL of NaHCO3 solution was added. The suspension obtained is poured over 50 g of ice under continuous stirring (400–700 rot/min) for 6 h, then filtered and dried at 110 °C in a convective oven. Curcumin derivatives incorporation efficiency was expressed both as active compound entrapment (%) and active compound content (% w/w), following Equations (1) and (2), respectively.
A c t i v e   c o m p o u n d   e n t r a p m e n t   ( % ) = C 0 − C 1 · 100 C 0
where C0 represents the initial mass of the curcumin derivative, and C1 representsthe final mass of the curcumin derivative after the evaporation of the residual solvent of the co-precipitation process.
A c t i v e   c o m p o u n d   c o n t e n t   ( % w / w ) = m a c · 100 m h m
where mac represents the mass of the curcumin derivative in the hybrid material, and mhm is the total weight of the hybrid material.
Therefore, the five types of host–guest hybrid materials AP1–AP5 presented in Table 1 were obtained.

2.3. Characterization

The obtained organic–inorganic hybrid materials were structurally characterized by a series of FTIR analyses recorded in the 400–4000 cm−1 range (with JASCO FT-IR 6300 instrument, Jasco Int. Co., Ltd., Tokyo, Japan) and XDR diffractograms recorded in the 2θ range 2–90° (9 kWRigaku SmartLab equipment, Rigaku Corporation, Tokyo, Japan), operated at 45 kV and 200 mA, CuKα radiation—1.54059 Å, in scanning mode 2θ/θ. All the XRD data interpretation and calculations were performed using the dedicated software PDXL (v. 2.7.2.0.) by comparison with the ICDD database. The shape of the crystals obtained after co-precipitation was captured using a scanning electron microscope operated at an accelerating voltage between 10 and 20 kV (SEM, model TM4000Plus from HITACHI in Tokyo, Japan) and an energy-dispersive X-ray spectrometer (EDS, model X-stream-2 from Oxford Instruments in Oxford, UK) in the SEM configuration enabling to analyze the elemental composition using AZtecOne 1.0 software from Oxford Instruments. The host matrices were morphologically evaluated with regard to surface porosity and generated pore size by the BET method following isothermal N2 adsorption–desorption processes at −196 °C (Nova 2200e Quantachrome, Quantachrome Instruments Corporate Drive, Boynton Beach, FL, USA).Their thermal stability was monitored by thermogravimetric analysis (TGA, Q5000IR instrument, and TA Instruments, New Castle, DE, USA) of 8–10 mg of each sample placed in platinum pans under the following conditions: heating ramp 10 °C/min up to 700 °C and Nitrogen 5.0 (99.999%)—used as purge gas at a 50 mL/min flow rate.
The fluorescence of the obtained materials was evaluated at room temperature by recording steady-state fluorescence spectra on a JASCO FP 6500 spectrofluorimeter (Jasco Int. Co., Ltd., Tokyo, Japan). The spectrophotometric properties of the composite materials were evaluated by recording diffuse reflectance spectra with a spectrophotometer (V570 UV-VIS-NIR, Jasco Int. Co., Ltd., Tokyo, Japan) equipped with a JASCO ILN-472 (150 mm) integrating sphere, using Spectralon as reference, in the range 290–780 nm. Total color differences in the CIELAB system, using a 10° standard observer and illuminant D65, were calculated. Each hybrid material sample (AP1–AP3) was embedded in an emulsion-type matrix without shielding properties, and three measurements were recorded for each sample. The evaluation of the UV shielding effect was carried out in accordance with the ISO-24444 standard [43] and under the following measurement conditions: bandwidth: 5.0 nm; scan speed: 100 nm/min; response: 0.96 s; data interval: 1 nm. The equation for calculating the equivalent SPF value was:
S P F   e q u i v a l e n t   v a l u e = ∑ λ = 290 λ = 400 E ( λ ) · R ( λ ) ∑ λ = 290 λ = 400 E λ · R ( λ ) · T ( λ )
where E(λ) is the radiation intensity of sunlight, R(λ) is the CIE reference erythema action spectrum and T(λ) is the diffuse transmittance spectrum (%) measured in the range 290–400 nm.

3. Results and Discussion

The aim of this work was to obtain hybrid host–guest materials, taking into account the multitude of biomedical applications of curcumin derivatives developed in recent times [44,45,46]. Since curcumin derivatives are sensitive to acidic and basic environments and have low hydrophilic qualities, it was suggested that they could be encapsulated in calcium carbonate crystalline networks. These delivery structures were obtained through a process of co-precipitation of calcium carbonate and curcumin derivatives from a mixture of solutes of different concentrations. For this purpose, solutions of 2.1 mmol/L CCOH and a solution of 1 mmol/L Ca(CCOH)2 were used to investigate if, during the co-precipitation process, the host molecules’ structure has a significant impact on the delivery matrix’s crystallization form. The experiments were repeated respecting the conditions of temperature, pH, and stirring speed, but the ratio between calcium chloride and the encapsulated active compound was varied. The results showed a very high loading efficiency of the active compound at low concentrations (Table 1), but it has the disadvantage of modifying the optical properties. In this case, it is AP5, whose fluorescence intensity is very weak and almost absent. Contrary to these, increasing the concentration of the active compound in AP1 leads to hybrid materials with dark orange shades. In such composites, the process of encapsulating the organic compound in the CaCO3 network is supplemented by adsorption processes that take place on the surface of the matrix due to the high concentration of the active compound. These types of superstructures behave differently by modifying the properties aimed at thermal stability or decreasing the fluorescent intensity.
As a result, the organic–inorganic hybrid materials AP1, AP2, and AP5 had progressively reduced CCOH concentrations, whereas AP3 and AP4 had variable Ca(CCOH)2 contents. In order to determine whether the kinds of chemical bonds formed as a result of this method varied, FTIR spectra of the resultant composite materials were recorded (Figure 2a). As can be seen in Figure 1a, the spectra of the hybrid materials AP3 and AP1 present very similar vibration bands. The main vibration band common to the three types of material analyzed is located around 1400 cm−1 and is characteristic of the asymmetric stretching vibration of carbonate bonds ( C O 3 2 − ) with higher absorption maximum shifts in the case of AP2. For AP3 containing Ca(CCOH)2, the absorption band is symmetrical, while for the composites AP1 and AP2, the FTIR spectra show asymmetric bands characteristic of the C O 3 2 − group. This asymmetry may be due to the vibration bonds established between the calcium ions and the oxygen atoms, as observed in Figure 2b, wherein the spectrum of Ca(CCOH)2 shows a similar vibration band with an absorption maximum at 1440 cm−1. The presence of organic compounds hosted in the delivery matrices is confirmed by the assignment of vibration bands at 1780–1795 cm−1 characteristic of carbonyl bonds, respectively 1280 cm−1, 1080 cm−1 attributed to C-O bond stretching vibrations, in agreement with the FTIR spectra of the hosted compounds (Figure 2b). The second important band present in the recorded spectra is situated at 875 cm−1, a symmetric bonding deformation of the C-O-C within the carbonate ion. An asymmetric vibration of the C-O-C group in the calcite occurs in the 745–713 cm−1 range. These two bands are present in minerals with a major content of calcium carbonate [47]. However, in the spectrum of AP2, an almost symmetrical doublet with the same intensity appears at 853 cm−1, characteristic of the polymorphic structure of calcium carbonate in the crystallized form of calcite and aragonite [48].
To confirm the structural differences of the calcium carbonate networks predicted by the FTIR spectra, X-ray diffractograms were recorded for all the hybrid materials (Figure 3). Considering the polymorphic nature of the composites, the identification of peaks corresponding to each type of crystalline structure was performed using ICDD-01-083-3085 for the aragonite crystallization form, ICDD-04-017-8634 for vaterite, and ICDD-01-085-1108 for the calcite crystalline form, respectively. For the curcumin phase, reference was made to the ICDD card no. 02-075-3596.
Comparing the diffractograms of the five types of synthesized materials, it can be observed that polymorphism is present in all of them. The calcite crystalline form is confirmed in absolutely all samples by the presence of characteristic peaks at 29.5°, 36.04°, 39.5° and the doublet in the range 47.21°–47.62°(2θ). In the case of matrices hosting the Ca(CCOH)2 complex (AP3 and AP4), the intensities are almost equal compared to the other cases in which the peak intensities differ. A similar case is present in the case of AP2 and AP5.However, the doublet is formed by peaks with comparable intensities, andthe characteristics of different crystalline forms, 27.02°, are attributed to the vaterite crystalline form and 27.23° for the aragonite structure, respectively. On the other hand, the presence of peaks at 36.12°, 37.29°, 37.90°, 38.43°, and 38.63°(2θ) confirms the presence of the aragonite crystalline phase predicted in the AP2 and AP5 composites by the FTIR spectra. However, the intensities of these peaks are different in the two diffractograms, which implies that the polymorphic structure of the two materials contains all of the three types of crystals: calcite, aragonite, and vaterite in different ratios. It is also worth noting that although the vaterite phase is the most unstable, it is present in all the analyzed samples and confirmed by the presence of peaks at 24.89°, 27.02°, 32.75°, 50.01°(2θ). In order to have a clearer image regarding the composition of the samples, the reference intensity ratio(RIR) method was used. Although the method does not necessarily provide high-accuracy analytical data [49], it can provide some important information on the sample’s composition. Using the method, it was determined that the vaterite content varied in the series AP1–AP3 (9%, 0.013%, respectively 22.1%), calcite (0.68%, 0.068%, 59.2%), while sample AP2 also showed the presence of aragonite (0.03%). Although the content level cannot be considered as “a real value” due to the very high variability of the curcumin content (90.4%, 99.95%, respectively 19%), which is most probably due to the different spatial arrangement of the curcumin (on the surface/in the pores) or to the different thickness of the curcumin layer, the vaterite content is higher in sample AP1, while the lowest content (by reference to the calcite content) is recorded for sample AP2. Under these conditions, we can say that by keeping the same temperature and pH parameters (Table 1), polymorphic structures were obtained preferentially and directed towards certain crystalline phases with the help of the molecular structures of the guests. Thus, AP1 contains a higher proportion of the vaterite phase, influenced by the steric modifications (cis–trans and keto–enol) of CCOH in the environment where the co-precipitation takes place. By comparison, the Ca(CCOH)2 complex with fewer degrees of freedom favors the organized growth of calcite crystals in AP3.
The structural differences can be seen even from the first phases of crystal formation, as shown in the SEM images of samples AP1–AP3one hour from the start of the crystallization process after adding the NaHCO3 solution (Figure 4a,c,e). In the case of composites AP1 and AP3, a homogeneous structure of vaterite-type crystals can be observed. For AP2, the image in Figure 4b highlights an inhomogeneous mixture of crystals of different shapes and sizes.
In contrast to AP2, which exhibits a mixture of crystal types attributed to cubic, vaterite, and aragonite phases that are consistent with the XRD diffraction patterns, cubic and vaterite are found in the case of AP1 and AP3during the crystallization process and after 24 h. Moreover, it can be observed that in the case of AP4andAP5 obtained at higher temperatures, the direction of crystal formation is preserved, but their size is reduced. According to SEM data, different morphologies of the hybrid materials were obtained, and they were correlated with the degree of loading of the active compound (Table 1) in the carrier matrix. Following these analyses, it is evident that the decrease in CCOH concentration in the co-precipitation medium favors more efficient loading in the host matrix AP1<AP2<AP5. However, the content of active compounds in the inorganic matrix is higher in AP1, which contains the vaterite crystalline phase in the highest percentage. From SEM images, AP3 and AP4, it is observed that the crystalline networks are more organized and are not drastically affected by the modification of the synthesis parameters. However, in comparison with the data in Table 1, an increase in the loading efficiency of the active compound was observed as its concentration and temperature increased. However, the content of Ca(CCOH)2 in the network is lower than AP3 and is attributed to the increase in the crystallization process in which the network develops rapidly to the detriment of the loading process with the organic compound. On the contrary, at lower temperatures, the loading efficiency of Ca(CCOH)2 decreases as expected, but the content of the compound in the inorganic matrix is the highest. This can be explained by an optimum achieved between the ratio of the initial concentrations and the synthesis parameters that create an equilibrium in the co-precipitation process without favoring the formation of additional CaCO3 crystals, as in the case of AP4.
By EDX analysis of the composite materials, it is observed that the composition of the materials differs by the percentage of carbon, which reflects the amount of curcumin derivatives loaded in the inorganic matrix (Table 2). As expected, AP1 and AP4 recorded a similar percentage of carbon having loaded comparative concentrations of CCOH, respectively Ca(CCOH)2. On the other hand, AP3 recorded the highest percentage of carbon, although the ratio CaCl2:Ca(CCOH)2 (5:1) targeted a lower concentration of Ca(CCOH)2 by increasing the amount of CaCl2 in the system. Comparing AP3 with AP2, wherein the initial concentration of curcumin derivatives was almost the same, it is observed that AP2 retained fewer organic compounds in the network under the same temperature and pH conditions. Thus, it can be concluded that the structure of the Ca(CCOH)2 complex favors a more efficient loading of the carbonate network, probably through the presence of calcium atoms in the organic compound that sterically restrict the organic molecules. This phenomenon is also reflected in the much more organized structure of the composite materials AP1, AP3, and AP4 in accordance with the images in Figure 4 and Figure 5. If we compare the materials AP3 and AP5, wherein the synthesis starts from the same amount of CaCl2, it is observed that the calcium content is significantly higher for AP5. This is probably due to the organic molecules of bis-dehydroxycurcumin, which, through the carbonyl groups in the structure, induce affinity for calcium ions, and the complexation process competes with the formation of the calcium carbonate network.
The hybrid materials were also characterized in terms of optical properties by color measurements (Table 3) in the CIELAB system using D65 as a light source and a 10° observatory. Comparing the standard color parameters, it is observed that the lowest luminosity value (L*) was recorded for AP1, which corresponds to a higher CCOH content in the inorganic matrix. Then follows the AP4 composite, whose low luminosity cannot be justified by the concentration of Ca(CCOH)2, but rather, taking into account the volume of the curcumin complex, it can be attributed to its placement in the carbonate network at the surface. As the concentration of the encapsulated organic compound decreases, the luminosity increases for AP2, AP5 compared to AP1, andAP3 compared to AP4. As the concentration of encapsulated curcumin complex increases, the values of the a* coordinate increase and show a shift towards red, and b* moves towards yellow. In the case of hybrid materials, although the concentration of CCOH content increases in the order AP5, AP2, and AP1, we cannot find the same concordance in the evolution of the values of the a* and b* coordinates, probably due to the different crystal structure. The same situation is found in the case of the K/S coefficient calculated (Table 3) with the Kubelka–Munk equation. It can be observed that AP3 shows a lower value of the K/S coefficient compared to AP4, which is more concentrated in Ca(CCOH)2. Increasing the concentration may also result in the presence of the chromophore on the surface of the matrix more than inside the pores through adsorption processes. These results highlight the importance of polymorphism in the optical properties of the obtained hybrid materials. On the other hand, the results of the fluorescence spectra illustrate different intensities between the two types of hybrid materials. Thus, it is observed that the AP3 and AP4 materials have higher fluorescence intensities compared to the materials containing CCOH. The decrease in the fluorescence intensity of AP1 and AP2 is attributed to the preferential aggregation processes of organic molecules during co-precipitation, to the detriment of host–guest interactions [50]. The formation of aggregates leads to fluorescence quenching phenomena, and these are avoided in the case of AP3 and AP4 by the initial formation of Ca(CCOH)2 complexes. In this way, the presence of calcium atoms in the complex favors the establishment of ionic interactions with the calcium carbonate matrix or covalent intermolecular bonds established between the hydroxyl and carbonate groups. In order to highlight these interactions between the host matrix and the guest in relation to the fluorescence quenching processes, further studies are needed in the future. For this purpose, we will repeat the experiments by varying other parameters, such as the solvent in which the curcumin derivative is dissolved or the pH.
As can be seen in Figure 6, the obtained hybrid materials have the same thermal decomposition rates as in the case of unmodified calcium carbonate. However, they present certain exceptions and have lower thermal stability than CaCO3. The characteristics of the calcium carbonate-based carrier matrix were evaluated in terms of thermal stability and correlated with the textural features obtained by measuring porosity (Table 4). According to the IUPAC classification, the obtained materials have a mesoporous structure with a pore size greater than 2nm. Thus, by comparing the results of the thermogravimetric analyses, it can be observed that AP1, which contains the largest amount of curcumin derivative, has a lower thermal stability, although the surface area (SBET) is comparable to that of AP3, which has the curcumin complex encapsulated. On the other hand, the increased porosity of AP1 (Vtot = 0.00408 cm3/g) further justifies the fragility of the inorganic matrix. Moreover, the amount of adsorbed water lost in the first heating stage up to 155 °C was higher compared to the other composite materials. The same phenomenon can be observed in the second heating stage, during which AP1 loses almost 19% of the mass represented by interstitial water and the encapsulated organic compound. At the same temperature, AP2 and AP3 had losses of approximately 3–4% of their weight. These hybrid materials are characterized by much more compact structures with a total pore volume of comparable dimensions but are characterized by pores with different sizes in correlation with the crystallization form identified by XRD analyses. In the range of 600–750 °C, all hybrid materials had a significant mass loss ranging between 34 and 42%. This is due to the thermal decomposition of calcium carbonate and the release of CO2, and at the end, a CaO [51] and carbon particle residue remains in a percentage of approximately 54–55% for AP2 and AP3, respectively 45% for AP1. However, AP2 has a smaller surface area than AP3, but it hasa larger pore size. Taking into account all these results, we can conclude that the structure and steric arrangement of the encapsulated organic compound plays an important role in the morphology of the host matrix.
For the hybrid materials AP1–AP3 that differ structurally by the crystallization mode (AP1 and AP2) or by the type of encapsulated active compound (AP2 and AP3), the UV light shielding properties were evaluated. The results were compared with a calcium carbonate matrix with a calcite crystal lattice. The samples containing 10% hybrid material were measured in the range of 290–400 nm, and the transmittance spectra are illustrated in Figure 7a. It can be observed that the samples containing hybrid material reported a lower transmittance percentage compared to the CaCO3 blank. This can be attributed to the crystallization type of the carbonate matrix, and we are able to affirm that the presence of the vaterite crystallization phase leads to a decrease in the transmittance percentage. At the same time, comparing the transmission spectra of AP1 with AP3, these having the same polymorphic phase, it is observed that AP1 (SPF 35 ± 4) with a higher content of active compound has the lowest percentage of transmittance. This will correspond to an increased efficiency of shielding UV light, as shown in Figure 7b, wherein the SPF values are calculated according to the ISO-24444 standard and applying Equation (3). For all that, AP2 shows a slight decrease in shielding efficiency (SPF 30 ± 5) with a decrease in active compounds encapsulated in the network, compared to AP1. However, we cannot attribute this decrease entirely to the decrease in CCOH content. The shielding efficiency also decreases in the case of AP3 (SPF 25 ± 7), which contains a concentration of Ca(CCOH)2 comparable to the CCOH in AP2. The SPF evaluation for each sample is the average resulting from three measurements of the transmittance spectrum at wavelengths between 290 and 400 nm. The results are limited by a series of factors, such as the compatibility between the hybrid materials and the emulsion in which they were embedded. Another factor that influences the final SPF values is the concentration of curcumin derivative adsorbed on the surface of the carrier matrix. During the embedding process, the curcumin derivative preferentially migrates into the emulsion phase through desorption processes from the matrix. Comparing these results, it can be concluded that the polymorphism of the inorganic matrix has an essential role in the efficiency of the shielding properties of composite materials, but they are complemented by the nature of the hosted compound and the degree of loading in the carrier matrix. At the same time, the concentration of the encapsulated active compound is limited in cosmetic products by the yellow-orange shades that the hybrid materials have. Anyhow, they can have applications in areas such as packaging and textiles where color shades do not bother, and the UV-light shielding effects are essential [52,53,54,55].
Considering the limitations of the current systems, several particularities should be noted.
In the case of curcumin derivatives, the UV-shielding effect is mainly based on the absorption of the UV radiation followed by excitation of the electrons and energy dissipation either by interactions with other molecules or by fluorescence emission. Usually, it is expected that the higher the amount of curcumin, the higher the UV-shielding effect will be. However, this type of hybrid material contains some of the curcumin derivatives embedded into the inorganic structure and another part at the surface of the particles.
Thermal and mechanical stability of the hybrid structures is enhanced by π–π stacking together with hydrogen-bonding interactions and the formation of calcium complexes of curcumin derivatives. All of these interactions exhibit controlled release of embedded curcumin derivatives. However, curcumin derivatives loading, as self-assembled nanoaggregates, is driven by π–π interactions and determines the maximum loading level in the inorganic matrix. However, interactions of this type also occur between curcumin molecules on the outer surface of the inorganic network. These dye aggregates on the surface of the hybrids determine the lower thermal and mechanical resistance of the hybrid material.
In conclusion, there is a maximum amount of dye that forms the hybrid material with optimal composition and maximum mechanical–thermal resistance. The addition of additional dye leads to the formation of dye aggregates that negatively modify the mechanical–thermal resistance of the materials.
Regarding the long-term stability and degradation behavior of hybrid materials under environmental conditions, a few observations need to be made.
The decrease in the aqueous medium pH leads to an increase in the solubility of calcium carbonate in water and the decomposition of the calcium complex of curcumin derivatives, while alkaline waters maintain low solubility, but the curcumin derivatives begin to transform into phenolate, accompanied by a bathochromic color change, an increase in water solubility and the beginning of their degradation at an accelerated rate. The increase in temperature and humidity favors all these processes listed above. The oxygen in the air will contribute to the oxidation of phenolates to quinones, and solar radiation will photochemically and rapidly decompose the new species generated in alkaline environments.
The stability of the hybrids is maintained under conditions of application to the skin whose pH is around 7. Washing with alkaline soaps or acting on acidic atmospheric humidity from industrially polluted regions will favor decomposition, according to the cases previously presented. Wetting in water with a pH different from neutral after applying this type of UV-shielding materials to the skin causes their degradation.

4. Conclusions

The host–guest hybrid materials containing CaCO3–curcumin derivative we obtained through the co-precipitation process represent a good solution from the perspective of curcumin delivery methods for medical applications. This study shows that in the co-precipitation process, the structure and concentration of the guest compound have decisive influences on the design of the carrier matrix. The mass ratio of the CaCl2/CCOH precursors (3:1) leads to hybrid materials with polymorphic structures, in which the CaCO3 network is formed as mixed crystals of vaterite, calcite, and aragonite. The 50% increase in the CCOH concentration led to the inhibition of crystal growth in certain directions, and the resulting matrices are found as a mixture of vaterite and calcite. Furthermore, it was observed that the reduction in the degrees of freedom to CCOH by complexation with calcium ions improves the stability of the vaterite form in the case of AP3, as shown by XRD phase analyses and illustratively from SEM images. The optimal loading conditions of Ca(CCOH)2 were achieved in the case of AP3, in which the loading rate of the active compound and its content in the inorganic network was the highest. The fluorescent properties of the curcumin derivatives were preserved even after loading in the host matrix. The hybrid materials obtained are thermally stable and have optical properties that recommend them for applications in the medical field in various treatments. The host matrix also favors applications of curcumin derivatives in hostile environments with different light, temperature, and pH parameters, such as sunscreen.

Author Contributions

Conceptualization, A.R. and M.F.R.; methodology, M.F.R.; validation, A.R. and V.R.; formal analysis, M.G., R.C.F. and C.A.N.; investigation, R.C.F.; writing—original draft preparation, M.F.R.; writing—review and editing, A.R.; visualization, M.F.R.; supervision, V.R.; project administration, V.R. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Romanian Ministry of Research, Innovation, and Digitization through INCDCP ICECHIM Bucharest Core Program—ChemNewDeal PN 23.06, within the National Plan for Research, Development, and Innovation 2022–2027, project no. PN 23.06.01.01(AQUAMAT). R.C.F also gratefully acknowledges the support of a grant from the Ministry of Research, Innovation, and Digitization (Ministry of Education and Research), CCCDI-UEFISCDI, project number PN-IV-P7-7.1-PTE-2024-0522, within PNCDI IV.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The SEM analysis was carried out on equipment acquired in the context of a grant from the Romanian Ministry of Research, Innovation and Digitization, MCI, NeXT-BExcel 15PFE/2021.

Conflicts of Interest

The authors declare no conflicts of interest.

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Crystals 15 00508 g001
Figure 1. Molecular structures of curcumin derivatives encapsulated in calcium carbonate matrices: bis-dehydroxycurcumin (a) and calcium complex of bis-dehydroxycurcumin(b).
Figure 1. Molecular structures of curcumin derivatives encapsulated in calcium carbonate matrices: bis-dehydroxycurcumin (a) and calcium complex of bis-dehydroxycurcumin(b).
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Figure 2. FTIR spectra of AP1 (green line), AP2 (blue line)and AP3 (red line) composite materials (a) and normalized spectra at 1440 cm−1 (red line) of curcumin-derived composites (b).
Figure 2. FTIR spectra of AP1 (green line), AP2 (blue line)and AP3 (red line) composite materials (a) and normalized spectra at 1440 cm−1 (red line) of curcumin-derived composites (b).
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Figure 3. XRD patterns of the hybrid material organic–inorganic AP1–AP5 (a,b).
Figure 3. XRD patterns of the hybrid material organic–inorganic AP1–AP5 (a,b).
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Figure 4. SEM images of composites in different stages of crystallization AP1 (after 1 h—(a), after 24 h—(b)), AP2 (after 1 h—(c), after 24 h—(d)), AP3 (after 1 h—(e), after 24 h—(f)), AP4 (after 24 h—(g)), AP5 (after 24 h—(h)).
Figure 4. SEM images of composites in different stages of crystallization AP1 (after 1 h—(a), after 24 h—(b)), AP2 (after 1 h—(c), after 24 h—(d)), AP3 (after 1 h—(e), after 24 h—(f)), AP4 (after 24 h—(g)), AP5 (after 24 h—(h)).
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Figure 5. Image of hybrid material (AP1) during EDX analysis.
Figure 5. Image of hybrid material (AP1) during EDX analysis.
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Figure 6. Thermogravimetric curves of hybrid materials (AP1–AP3) and CaCO3.
Figure 6. Thermogravimetric curves of hybrid materials (AP1–AP3) and CaCO3.
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Figure 7. The transmittance spectra in the range of 290–400 nm (a). Sun protective performances of calcium carbonate and AP1–AP3 (b).
Figure 7. The transmittance spectra in the range of 290–400 nm (a). Sun protective performances of calcium carbonate and AP1–AP3 (b).
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Table 1. Conditions for the process of obtaining hybrid materials AP1–AP5.
Table 1. Conditions for the process of obtaining hybrid materials AP1–AP5.
SampleCalcium Source for Host MatrixCurcumin Derivative—GuestMolar Ratio (CaCl2–CC)Temp. [°C]pHActive Compound Entrapment (%)Active Compound Content (% w/w)
AP1CaCl2CCOH1.5:17011–1220.814.1
AP2CaCl2CCOH3:1701020.111.8
AP3CaCl2Ca(CCOH)25:17011–1254.725.8
AP4CaCl2Ca(CCOH)22.5:1901075.319.3
AP5CaCl2CCOH5:1901097.211.5
Table 2. SEM-EDX results for hybrid materials AP1–AP5.
Table 2. SEM-EDX results for hybrid materials AP1–AP5.
ElementLine TypeAP1
Weight %		AP2
Weight %		AP3
Weight %		AP4
Weight %		AP5
Weight %
CK series42.9 ± 0.637.2 ± 0.745.8 ± 1.143.1 ± 0.732.6 ± 1.0
OK series41.8 ± 0.638.0 ± 0.738.2 ± 1.139.9 ± 0.625.0 ± 1.1
CaK series15.3 ± 0.224.1 ± 0.116.0 ± 0.715.9 ± 0.442.4 ± 1.0
Table 3. The optical properties of AP1–AP5.
Table 3. The optical properties of AP1–AP5.
SampleL*a*b*K/S
(λ = 420)		Fluoresc. Int. (a.u.)
λ = 420 nm
AP163.5322.9935.383.0641175
AP290.103.2420.890.2589185
AP397.460.271.850.0048305
AP477.254.6723.710.9316250
AP596.9323.2437.110.6448-
Table 4. Characteristics of AP1–AP3 subjected to thermogravimetric and textural analysis.
Table 4. Characteristics of AP1–AP3 subjected to thermogravimetric and textural analysis.
SampleRT-155 °C
Wt.Loss		155–600 °C
Wt.LossTmax		600–750 °C
Wt.LossTmax		Residue
at		SBETVtotDpor
(%)(%)(°C)(%)(°C)750 °C[m2/g][cm3/g]∙10−3[nm]
AP 12.0718.81360.034.13721.045.003.63 (±0.2)4.08 (±0.001)4.5 (±0.04)
AP 20.062.61370.742.04714.155.262.72 (±0.3)3.48 (±0.001)5.1 (±0.03)
AP 30.264.14373.241.26716.254.093.69 (±0.3)3.86 (±0.002)4.2 (±0.03)
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Raditoiu, A.; Raditoiu, V.; Grapin, M.; Fierascu, R.C.; Nicolae, C.A.; Raduly, M.F. Delivery Systems for Curcumin Derivatives Based on Calcium Carbonate Structures for Biomedical Applications. Crystals 2025, 15, 508. https://doi.org/10.3390/cryst15060508

AMA Style

Raditoiu A, Raditoiu V, Grapin M, Fierascu RC, Nicolae CA, Raduly MF. Delivery Systems for Curcumin Derivatives Based on Calcium Carbonate Structures for Biomedical Applications. Crystals. 2025; 15(6):508. https://doi.org/10.3390/cryst15060508

Chicago/Turabian Style

Raditoiu, Alina, Valentin Raditoiu, Maria Grapin, Radu Claudiu Fierascu, Cristian Andi Nicolae, and Monica Florentina Raduly. 2025. "Delivery Systems for Curcumin Derivatives Based on Calcium Carbonate Structures for Biomedical Applications" Crystals 15, no. 6: 508. https://doi.org/10.3390/cryst15060508

APA Style

Raditoiu, A., Raditoiu, V., Grapin, M., Fierascu, R. C., Nicolae, C. A., & Raduly, M. F. (2025). Delivery Systems for Curcumin Derivatives Based on Calcium Carbonate Structures for Biomedical Applications. Crystals, 15(6), 508. https://doi.org/10.3390/cryst15060508

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